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“Results from a screening sample taken March 25 from Spokane, Wash. detected 0.8 pCi/L of iodine-131, which is more than 5,000 times lower than the Derived Intervention Level set by the U.S. Food and Drug Administration. These types of findings are to be expected in the coming days and are far below levels of public health concern, including for infants and children. Iodine-131 has a very short half-life of approximately eight days, and the level detected in milk and milk products is therefore expected to drop relatively quickly.”
Here is the thing though. How can it not be considered that this has been going on steady for over 2 weeks now. Logically, wouldn’t it be common sense that the thyroid is absorbing it a little at a time, will build up? And it just keeps coming.
Thanks for your question. The DIL limits take into account not only consuming milk a single time, but continuous consumption, at a high rate, for a long period of time, by the most vulnerable members of the population (usually children). We aim to make a post in the next few days on how these limits are set, and what they mean to consumers.
Iodine-131 can’t really “build up”. Your body can’t tell the difference between regular iodine and iodine-131, so it has no preference for either. Iodine is fairly common, an essential nutrient, and your body is constant processing and excreting it. So at best (or worst), all that will happen is an equilibrium – the ratio of iodine-131 to regular iodine in your body will match the ratio of the two in the environment.
This is not a situation like with arsenic or mercury. Those elements are relatively rare, can be picked up by your body if you’re exposed to higher quantities, and serve no biological function so your body can’t do much with them nor dispose of them easily. Consequently, exposure to them leads to them “building up” in your body. (And if you’ll excuse me for getting a bit political – I would worry far more about the mercury released continuously by our coal plants via their normal operations than this release of iodine-131 in a one-time accident.)
Latest articles on CNN seem to indicate that there has been significant leak of contaminated water into the Pacific Ocean, but your post from yesterday makes me think that the contaminated seawater has been contained inside the trenches surrounding the reactors. Have you seen confirmed reports of significant contamination beyond the reactor trenches? I truly do appreciate the work you guys are doing in fact-finding/reporting. I’m updating my students on the facts as best I can and I find your information to be far more direct than most of the mainline media.
Thanks again to mitnse, and also to all the other informed posters.
My question on the Boron/neutron absorbtion was based on wondering if Boron waffers might not produce an electron, like a silicon waffer does from solar radiation. In my nonscientific ignorance, I had already “invented” spent fuel batteries. LOL
I find it very sad that so many people are still being hit with scare tactics. That ‘media’ sources are allowed to spread fear and panic without being accountable is a poor reflection on our world. I (admitedly non expert), very much doubt that there has been any melt through of the reactors. My reason for thinking that is; If there was so much heat available, all the injected water would evaporate immediatly. I have seen no signs of gysers of steam. jmo??
You referred in your latest post to past nuclear weapons testing near the site of the Fukushima plant. When did this testing take place?
Atmospheric testing of nuclear weapons occurred in China as late as 1980.
Currently the news focus is on the amount of contaminated water on the site and the low-tech, apparently desperate, efforts of sandbagging to try to keep it from entering the sea. It seems they are running out of storage for the water and the only ideas I have seen thus far are to dig a large hole on site,or to pump to a tanker ship off shore. Is it not feasible to set up a waste water filtration plant on site that would clean this water so it could be returned to the ocean? Could you provide some information on the treatment processes for radioactive waste water,i.e. nature of filters, throughput, and effectiveness of removal of the main isotopes of concern (which seem to be of iodine, cesium and plutonium)? Are there portable units generally available in the industry or via the military to perform this job? If there are such units available or practically constructible, would it not have been prudent to get one,or more, on-site in anticipation of this problem? Many thanks for your informative website.
From Denman Island, British Columbia.
We could do with some informed commentary:
• what you think is actually happening in the reactors and storage ponds
• what steps might be taken to gain control – of reactors, storage ponds, leaking radioactivity
• how control can be achieved with a dwindling workforce exposed to 2.5x their annual radiation limit
• how to control radioactive water
I hope you are not being muzzled by the powers that be.
can you comment on this ?
Like Dr. Dalnoki-Veress, we’ve been unable to find any confirmation of Kyodo’s statements regarding observation of “neutron beams”, even within TEPCO’s own press releases.
Do you have any comment on the report that the core has melted through one of the reactor vessels?
We are working on getting more information about this hypothesis. Based on the information currently available to us, we have no way of differentiating whether the high radiation levels in the water surrounding Unit 2 come as a result of something more serious than leakage of water which has been in contact with the damaged core inside the vessel.
I don’t want to be alarming, but I thought I just heard on Pacifica Radio that unit 2 had melted and was in danger of breaching the containment vessel, they said of melting through the bottom. I have not been able to find a corroborating source – no mention I can find on TEPCO site or any MSM. I hope I heard them wrong. Do you have status of any critical core at Daichi? And again, I don’t mean to misinform or be alarmist, but just want to check status of what, if true, would be a serious development.
Thanks for lending you technical leadership to this issue.
What if you created an energy “crash rating” system that normalized the relative global safety status of various energy formats, i.e. gas, coal, electricity, and wood that encourages rational comparison?
You’d think that would be relatively straightforward, but it quickly becomes a highly political process. The only formal report I’ve seen on it looked at severe accidents.
There are informal attempts to normalize safety as well.
The following site has a very neutral and thorough handling of all the different power technologies (not too much on safety though).
If you’re curious how I got these links, I helped research and evaluate renewable energy technologies for a large hotel undergoing renovation. They wanted to know the viability of different ideas, like installing PV panels or putting up a wind turbine, in terms of cost, maintenance/longevity, and safety. I’ve got lots more links on the relative costs of the different technologies. The best bang for the buck actually turned out to be conservation rather than generation – geothermal heat pumps.
The one thing which nearly everyone agrees upon though is that coal is really, really bad compared to the alternatives. I’m not so much pro-nuclear as I am anti-coal.
Thanks for the latest update. Not to start an argument, but “widely available information” perhaps, but detailed, spot on, pragmatic info is only found here. Keep on blogging!
I live in Tokyo and it crossed my mind that there were tremendous releases of radioactivity from South Pacific and Asian hydrogen bomb tests from around 1950 to the first nuclear test ban agreements in the ’60s (I believe). In those days, such horrific tests were more or less taken for granted by most people. I wonder what are the qualitative and quantitative differences between those repeated tests by the U.S., France, Britain, China and the U.S.S.R. and what is happening or might happen at Fukushima, in terms of effects on the oceans and the atmosphere. Did those tests, singly or cumulatively, dwarf the current disaster, or were they essentially different in their effects? And what is the difference between a (Chinese) H-bomb test on land and, say, Chernobyl?
I hope you will reconsider and post more frequent updates. There are many news articles,but often they seem to be wildly wrong or contradictory. It was very helpful to have a reliable source of information.
It was stated that there are now other sources of reliable information available. Could someone point me in the direction of these? Thank you.
This one has a nifty summary chart of each reactor’s situation.
The following has the radiation readings for cities near Fukushima for March 19. It probably has readings for other days too, but the site is in Japanese so I haven’t been able to find them. But perhaps someone who can read Japanese can.
Personally I would have thought the link marked ENGLISH would have been a bit of a giveaway. (:>)
Damn, there goes one of my primary sources of non-ideological matter-of-fact information on the Fukushima issue and its possible ramifications…you MITNSE people really should think that over and get back to posting regular updates…the world’s thinking people need you!
Otherwise we might just as well go with the mass media and prepare for our own funerals in lead-lined coffins right now…
I have been looking at the reports from WHO and the UN on Chernobyl, deaths caused by radiation are minimum to the amount of people exposed to it. Have found other reports from GreenPeace and IPPNW an organization that does not agree with WHO or UN reports, this organizations use a different statistical method.
It seems that there are less deaths than feared.
But does it mean that the quality of life of those exposed is not altered or jeopardized? It seems that the only number that makes an impact is if one dies, not if you get another form of cancer or sickness that is not thyroid cancer.
Can you comment on this assumption?
I also wanted to ask about the myth or truth of genetic mutation by exposure to radioactivity, is it just an old tale or what kind of exposure would produce this outcome?
I understand you are not health professionals and what is talked about here mostly is more technical.
Much of the literature on Chernobyl does in fact include discussions of cancer incidence rates as compared to those of the general population. Many papers on the topic also discuss impacts on quality of life brought about by the effects of mental stress on cardiovascular health, and on pregnant women.
DNA can be damaged by radiation, with the result often being either functional death of the damaged cell, reproductive death (in which the cell is unable to produce a replacement before its death), or production of new cells with mutations. It’s important to keep in mind that mutation is a natural process that’s ongoing all the time, and that therefore it’s hard to determine whether a mutation is the result of natural occurrences or exposure to radiation. All we can tell is whether some deviation from a population average has occurred.
The problem with genetic effects is that they are “stochastic” which means statistically we know the probability but there is no “safe” limit of ionizing radiation which causes no damage.
“Stochastic” refers to the fact that we can not determine causation of a health effect (i.e., whether it is natural or induced by radiation): we can only observe that the effect occurs with some probability at certain doses, and extrapolate to find the effects at other doses.
Your comment on “no safe limit” refers to a specific extrapolation method, the linear non-threshhold model. Other models exist, in which there is some “safe” level of radiation, or in which small amounts of radiation even produce positive health effects, or hormesis.
The word stochastic, by itself, does not imply that there is no safe limit of ionizing radiation.
Re stochastic genetic effects. A large dose of radiation may not necessarily cause cancer in an individual. A relatively small dose of radiation may still be the cause of cancer in an individual. The effect is statistically measurable bur not predictable for the individual. A single photon damaging a single piece of DNA may be the cause.
First, thank you for further educating me on nuclear issues and technologies.
My question regards the heightened visibility of thorium reactor technology. Since nuclear tech is such a hot (pun intended) topic these days, I would like to get some less biased information on the pros and cons of the thorium tech (aside from the cool name).
I am begging you. I am in California and he is right, the EPA and DOE are being evasive and most people are doubting their competence.
From the start they were not honest @ when they had detected the Iodide 131 or Cesium 137. They had it the 16th and told the public the 18th. There has been no effort to be transparent or any effort to give us peace of mind. We need someone to present this to us in simple, straightforward terms.
Most of all, we need to know that we have competent people reading the incoming data and doing the appropriate tests for the situation. Never has there been an event with these elements. We have been getting low level radiation now for 2 weeks! And on top of that we had buckets of rain delivered straight from Japan. With more to come.
I am starting to think I should have given my grandson the potassium iodide and now it’s too late to make a difference. He is 4yrs old (I am a young grandma haha) Please check the readings to be sure its being handled correctly and please take in to consideration the duration of this event, the rain. And the fact that we are still getting it with no end in sight.
Thank you for your time, either way. Take care,
Thanks for your comment. We understand your concern, and would like to point out that the EPA has attempted to make the radiation measurement process transparent by publishing the data collected by the RadNet air monitoring stations at points around the country: http://www.epa.gov/japan2011/rert/radnet-data-map.html#westcoast .
This data consists of graphs, updated daily, with information on radiation levels both before and since the events at Fukushima. You’ll notice that there are no obvious differences between the “background” radiation levels (brought about by sunlight, and by radioactive decay of the elements all around us each day) and those present since Fukushima. We know that there are tiny, tiny, quantities of radioactive materials reaching the West Coast from Japan, because the RadNet stations have extremely sensitive equipment. However, these quantities are far too low to affect anyone’s health.
Another good reference is http://www.nuc.berkeley.edu/UCBAirSampling.
Just wanted to say “thank you”.
Another big-picture question that you might consider tackling was raised at BraveNewClimate by commenter Douglas Wise, here. It concerns the fate of a reactor core if cooling water is not supplied. “China Syndrome”, mostly-contained radioactive slag, or something in between?
The cores of reactors 1, 2, amd 3 are now somewhat stable in temperature and pressure, while fuel assemblies are still producing substantial heat from decay of fission products, on the order of a few megawatts, I believe. The March 28 IAEA briefing gives core temperature at the feed water nozzle of Unit 1’s RPV as 274 °C.
(1) How are the operators removing heat from the cores, at present? The strategy used at first was “bleed and feed,” whereby water (salt or fresh) was injected, and a similar mass of steam was vented in a controlled fashion into the atmosphere. Is this still being done? That IAEA briefing notes
the pumping of fresh water into the reactor pressure vessel of Unit 1 is to switch from the use of fire trucks to temporary electrical pumps running on offsite power on 29 March. At Unit 2, this switch was carried out on 27 March, with a diesel generator as backup in case offsite power is interrupted. Fresh water is also being injected continuously into the reactor pressure vessel of Unit 3, albeit currently pumped by fire trucks. The switch to temporary electrical pumps for this unit is planned for today.
If water is being pumped in, water must be coming out. If not as steam, then as hot liquid. Is it being sent into the ocean? Through purpose-built pipes? Via storm sewers? Is an appreciable fraction leaking into the containment building’s basement, or seeping into the ground?
(2) What is the next step for the engineers on-site? Is there a thought of setting up hot-water circuits that run through heat exchangers, so that more radioactivity is contained in the core? Will one of the low-pressure emergency core cooling circuits be re-started?
It would be awesome if you guys could help add sources and/or revise the Wikipedia article on molten salt reactors.
We see lots of fission products in the list of contents in the spilled water. Why is it we do not find any uranium or plutonium that are main components of the nuclear fuel? Is it just a matter of solubility?
Any word on the following stuff floating around in the news? (1) China detains Japanese travelers with “high” levels of radiation, (2) “Japanese officials began encouraging people to evacuate a larger swath of territory around the Fukushima Daiichi nuclear plant on Friday as new signs emerged that parts of the crippled facility are so damaged and contaminated that it will be hard to bring the plant under control soon.” (this was the New York Times).
I’m sorry to bother you guys with a really basic question (and I have tried to figure this out myself first) but exactly how much is a ton of water? For example, on the IAEA website, they say:
“Workers conducted an operation to spray 40 tonnes of seawater to the spent fuel pool on 20 March, and they added another 18 tonnes on 22 March.”
What measurement are we talking about here when we say tons (tonnes)? What would the measurements be of a container that holds a ton of water? How long does it take to spray a ton of water? (I guess that depends on the kind of pump and hose.)
I’ve found this on wikipedia: 1,000 kg (2,204.62 lb) or approximately the mass of one cubic metre of water. I assume that’s what we’re talking about, but I would love clarification. If that’s so, then 40 tonnes of seawater doesn’t seem like that much to me – is that the size of a typical home in-ground swimming pool, example?
Thanks for your help.
A”tonne” is the same as a metric ton, ie. 2,205 lbs.
Fresh water = 8.32 lb/gal
Seawater varies with location but averages = 8.6 lb/gal
So 40 tonnes of seawater would be 2,205 * 40 = 88,200lbs / 8.6 = 10,256 gal
So it would be about 1-1/2 times more than a typical large round above ground pool in the US (7,000gal) 18ft ID x 52″ deep.
excellent blog, but you have misspelled Cesium.137 as Caesium-137 twice in the latest article in the third section. Just thought you might want to fix that.
Both spellings are correct. The name for the element comes from the Latin caesius, sky-blue.
These days more problems seem to be caused by the spent-fuel pools than by the reactor cores themselves. Would you say the placement of these pools is a flaw of the reactor design? Do you expect nuclear regulators around the world to recommend/enforce a change in this respect (maybe store the spent fuel off-site etc)?
The pools are in the correct place, even the newest designs have them there.
It is the only way to transfer hot (thermally and radiologically) fuel to and from from the reactor, eg. the cells are never exposed to air. Once they are cool enough to withstand some air exposure the spent fuel is transferred via wet cask to the long term pool located outside the reactor building, until such time as it cools enough to be stored in a dry cask, in preparation to transport to the re-processing plant, or in the case of the US (Stupid) to be buried somewhere.
When the top of the reactor primary containment and reactor vessel dome is removed it forms a continuous water barrier from the new fuel pool to the spent fuel pool with the reactor in between.
Just want to say a big THANK YOU to Solandri for the answer. Well worth the wait here in Surreal Tokyo. Awesome job you guys are doing….
In this evening’s New York Times, and article entitled “New Problems at Japanese Plant Subdue Optimism” states this about salt buildup in the reactors: “If the crusts are thick enough, they can block water from circulating between the fuel rods. As the rods heat up, their zirconium cladding can rupture, which releases gaseous radioactive iodine inside, and may even cause the uranium to melt and release much more radioactive material.”
It seems unlikely to me that salt buildup would lead to uranium meltdown — sodium chloride melts at 800 C; uranium melts at 1100 C, and uranium oxide at 2800 C. Long before the uranium melted, the salt deposits would melt, and while that might lead to more releases of radioactive steam, it wouldn’t lead to a meltdown. I’m not as sure about the other scenario. Is it plausible that the zircaloy would rupture before the salt deposits on the outside of the tubes melted? Can you comment on this? Thank you!
Since the proposed salt accumulations would be taking place in pretty much a pure steam environment (No Air), they will not condense onto any surfaces, sodium chloride, potassium chloride and calcium chloride (the predominant salts in seawater) will remain in a brine state with the un-evaporated water in the reactor shell and suppression pool (torus). And at 100C (temp they are attempting to maintain) the salts and other minerals in the seawater will stay in solution, until which time and if the water is all boiled away. (If this happens salt will be the least of their problems). Note: It has been 2 weeks since the reactors were scrammed, the odds of them generating 1200C are probably slim to none as long as the control rods remain in place.
The zircalloy tubes have a plastic failure point of 2200F (1200C)
On another note:
According to TEPCO and NEI they have completed wiring up all of the reactors to the grid, the crews are presently checking and repairing/replacing flood damaged pump motors and switch gear and the control rooms are being powered up. They anticipate return to semi-normal cooling operations tomorrow or Saturday.
They have also switched to borated freshwater to put into the spent fuel pools and are putting it in as it becomes available for all of the places where they are currently using seawater.
At this point in the game after using seawater, the reactors where they have done so are now junk, they will in all probability be scrapped and replaced with new MK3 systems.
Sorry to take your time with a simple question.
Could you describe, to a layperson what happens when a neutron strikes a boron atom?
Boron has a high probability of absorbing neutrons. When a neutron is absorbed in boron, a helium nucleus (alpha particle) is ejected and a lithium-7 atom remains. This is important in nuclear reactors because boron will steal some neutrons that would otherwise cause more fission reactions.
From what I read, 20% of boron is boron-10 which can absorb a neutron to become boron-11. After boron-11
undergoes fission, lithium-7 will react with water to make lithium hydroxide and hydrogen gas. All these reactions will create heat. Lithium hydroxide is apparently used as anticorrosive in nuclear plants.
Boron-10 undergoes an (n, alpha) reaction when struck by a neutron. Boron-11 is a stable isotope that does not fission.
I don’t understand the furor over increased radiation levels in seawater close to the discharge. I would have thought it self evident that with increased water flooding and spraying, that water would absorb any dust and precipitant particles on it’s way to the drain system.
The figures for radioactive fallout (I-131 and Cs 137) are found at: http://i.yimg.jp/images/evt/eq/110321/110321fallout_1900.pdf (a Ministry of Education, Culture, Sports, Science and Technology source)
They are measured in MBq/km2.
The readings for levels of I-131 and Cs 137 for the affected cities are as follows:
Iwate 7,800 | 690
Yamagata: 58,000 | 4,300
Ibaraki (Hitachi city) 93,000 | 13,000
Tochigi 5,300 | 250
Saitama 7,200 | 90
Chiba 160 | 16
Tokyo (Shinjuku) 2,900 | 560
Could you give us a primer on what these Becquerel or MBq (MicroBecquerel??) figures mean? Figures like these are frightening for the layperson and it would be appreciated if you could explain what this means? All we have been able to find is the following (which isn’t too helpful):
Apart from the normal measures of mass and volume, the amount of radioactive material is given in becquerel (Bq), a measure which enables us to compare the typical radioactivity of some natural and other materials. A becquerel is one atomic decay per second. (A former unit of (radio)activity is the Curie – 1 Bq is 27 x 10-12 curies.)
Radioactivity of some natural and other materials:
1 adult human (100 Bq/kg) 7000 Bq
1 kg of coffee 1000 Bq
1 kg superphosphate fertiliser 5000 Bq
The air in a 100 sq metre Australian home (radon) 3000 Bq
The air in many 100 sq metre European homes (radon) up to 30 000 Bq
1 household smoke detector (with americium) 30 000 Bq
Radioisotope for medical diagnosis 70 million Bq
Radioisotope source for medical therapy 100 000 000 million Bq (100 TBq)
1 kg 50-year old vitrified high-level nuclear waste 10 000 000 million Bq (10 TBq)
1 luminous Exit sign (1970s) 1 000 000 million Bq (1 TBq)
1 kg uranium 25 million Bq
1 kg uranium ore (Canadian, 15%) 25 million Bq
1 kg uranium ore (Australian, 0.3% 500 000 Bq
1 kg low level radioactive waste 1 million Bq
1 kg of coal ash 2000 Bq
1 kg of granite 1000 Bq
I did stumble on another safety feature of the MK1 ABWR.
There is a poison pill you can feed it, but it requires power to do so.
It injects high pressure boron water into the reactor, they may not have used it because they assumed they would want to start the reactors up again.
If this device is engaged it would require a complete refuel and clean out of the entire steam and reactor vessel and piping.
“The standby liquid control system injects a neutron poison (boron) into the reactor vessel to shutdown the chain reaction, independent of the control rods, and maintains the reactor shutdown as the plant iscooled to maintenance temperatures.
The standby liquid control system consists of a heated storage tank, two positive displacement pumps, two explosive valves, and the piping necessary to inject the neutron absorbing solution into the reactor vessel. The standby liquid control system is manually initiated and provides the operator with a relatively slow method of achieving reactor shutdown conditions.”
I have two questions:
One, I’ve read that carbon filtration is not effective in removing cesium from water. Is there anything the population at large can do to filter out the radioactive elements at least in from drinking water?
Two, I’ve also read “An accident at the Mayak Plutonium Facility in the South Ural Mountains of Russia is considered by some to have been worse than Chernobyl. Cooling equipment at the Mayak Facility broke down and failed to cool nuclear waste. The overheated nuclear waste exploded. Approximately 270,000 people and 14,000 square miles were exposed to radiation. Five hundred square miles were exposed to extremely high levels of radiation. Prior to the 1957 accident the Mayak Facility had a history of contaminating the environment with radioactive material through dumping in nearby water sources and several accidents. The accident in 1957 was the most severe of the incidents with the power plant. Today, radiation levels in the area are among the highest in the world, with natural water sources in the area are still contaminated with radioactive waste. Source: http://www.brighthub.com/environment/science-environmental/articles/13602.aspx#ixzz1HIIXbdfM
How different is this situation from the Mayak Russian incident, given that all the focus is now on cooling the reactor units? Is there a potential for Fukushima to develop into a Mayak like incident or worse? The “14,000 square miles were exposed to radiation. Five hundred square miles were exposed to extremely high levels of radiation. ” bit sounds horrendous – but nobody has yet mentioned the Mayak incident.
It is not a good idea to compare events in the old USSR and Russia, with events in Japan. The equipment, infrastructure and the people are vastly different.
To date there has been no damaging fallout in the affected area in Fukushima, this is according to several sources. They have pulled milk and spinach and one other broad leaf plant from the market as a precaution, these food items are particularly susceptible to accumulating radiation, tobacco plants do the the same. Water from sealed containers will not be affected. To date the civic water supplies have yet to be repaired from quake and tsunami damage, so you would not want to drink the tap water anyway, even if it was flowing.
It will take many weeks for the utility companies to get the water systems restored, there are millions of broken lines and seawater has contaminated and damaged treatment / pumping facilities. Until then best be prepared to drink lots of bottled water, and using porta-johns for your other needs. Even if they get the system online soon, I would invest in a reverse osmosis filter, which will filter out pretty much anything in the water.
I can not confirm this, but I heard a rumor that the US military is going to send in some portable water treatment units and bathing facilities, but as said this is yet to be confirmed. I am not up enough on the state of the Japanese SDF to know if they have this type of equipment, or if they have it in sufficient quantities.
Reverse osmosis is pretty effective at removing most molecular contaminants. RO-filtered water is so pure that it has to have minerals added back to it to improve its taste and reduce damage to pipes (the water is so pure the pipe material starts leeching into it). The figures I found online say it should be 80%-84% effective at removing Cesium, and 90+% effective at removing other contaminants.
Aside from water sold as “spring water” or “mineral water”, pretty much all bottled water is RO-filtered, as are waters used to make soft drinks and beers. The two most popular brands, Dasani (Coca Cola) and Aquafina (PepsiCo), are RO-filtered tap water that they otherwise use to make their soft drinks. Water that comes from desalination plants is also typically RO-filtered, although another paper I found said an RO filter’s effectiveness at removing Cesium degrades in the presence of salt. So bottled water or a home reverse osmosis filter is probably your best bet.
For lack of a better place, I will mention it here. Newly conceived blastocysts and embryos are much more susceptible to damage from radiation. Approximately 9 months after the Chernobyl accident, there were a large number of stillbirths and deformed babies born to women who were within the evacuation zone. So if you are in Japan and pregnant, think you may be pregnant, or planning to become pregnant soon, please take the warnings about radiation in food and water very seriously. I haven’t seen the media mention this, and they really should be. Children and infants are somewhat more vulnerable than adults, but the real danger is to newly pregnant women.
100 degrees C in all 6 reactors………Stable????
The Tempco press releases have stated this as a fact for the past few days and it is reported worldwide. How can 100C be considered stable?
100C is the boiling point of water (seawater) Any additional heat/energy does not cause the water to heat further, rather, the energy is used in the process of changing water to steam. From my understanding and from Tempco’s statements holes have made to allow for pressure to be released constantly instead of allowing the pressure to build causing yet another explosion. (Water expands into steam 1-1000, plenty dangerous)
My question, do you at MIT consider 100 C to be a stable temperature for water inside a nuclear reactor/fuel pond?
99 C and holding is stable………. 100 is a problem.
The boiling point of water increases with pressure. At 2 atmospheres, the boiling point is about 120 C. Since they’re maintaining a mix of water + steam under pressure inside the core, 100 C would be under the boiling point and thus stable.
If a valve blew out and released the pressure, then it might not be stable anymore. Depends on how much energy content is in the water and what the initial pressure was. The depressurization could be enough to lower the water temperature below 100 C (think of how a can of compressed air gets colder as you release the pressure), and thus it could remain stable.
The drilled holes you’re reading about are in the superstructure of the building, not the containment vessel. They’re to allow hydrogen to bleed into the atmosphere instead of remaining trapped within the building and blowing up as we saw in units #1 and #3.
Thank you for your excellent information. I live in Tokyo, and read the following from a blog post on SFGate.com, generally not exactly a reliable source. However, the post raised what he called the fallacy of comparing radioactive isotopes of, eg., plutonium, with X-rays or the sun. Here is his whole post. Can you please comment? Thank you!
First, what’s being called “radiation” in the press should really be called “ionizing radiation” – that is, radiation of high enough energy to strip an electron off a molecule. This leads to chemical reactions.
Now, if that chemical reaction takes place in a DNA molecule, it can cause a mutation. A mutation in a gene that controls the cell cycle can lead to a cancer cell. That can lead to early death. This happened to many, many Chernobyl responders.
The more ionizing radiation you’re exposed to, the more damage. Cells stop functioning. Wound healing slows. The immune system is damaged.
There are four kinds of ionizing radiation – gamma (penetrating), beta (penetrating), neutrons (penetrating), and alpha (close-range). A solid block of gamma or beta-emitting material is unsafe if you’re near it. A solid block of alpha-emitting material is fairly safe – UNLESS IT IS BURNED!
If you inhale this stuff in particle form – smoke, steam, dust – if you eat it in your food – a lot gets incorporated into your body. Some of the fission products pass right through – some, like iodine, cesium, strontium, plutonium, etc. are incorporated into your bone and muscle tissue, where the alpha radiation does close-range damage along with the beta and gamma. It does this damage for YEARS!
This is why you can still find radioactive strontium in the bones and teeth of skeletons of people who lived in Europe during Chernobyl in the 1980s. You can also find it in everyone who was alive during the atmospheric nuclear testing era.
So, this is why comparisons to chest X-rays and solar UV are NONSENSE! You don’t get radioactive strontium or iodine or plutonium from a trip to the dentist. You do get it from inhaling or eating nuclear fallout products.
SO: When the EPA and the DOE and the nuclear lobbyists and ‘crisis management’ bloggers make such comparisons, they are deliberately misleading the public!
They need to start reporting the actual concentration of iodine, plutonium, etc. per cubic meter of air, per liter of rainwater, etc. Why aren’t those numbers being reported?
Read more: http://www.sfgate.com/cgi-bin/article.cgi?f=/n/a/2011/03/20/international/i025005D28.DTL#ixzz1HCSna6IC
There are two units of measure which the press is frequently mis-reporting. Both are covered extensively in the Technical section of this site.
One is a dose of radiation. This is what you get from an x-ray, or from working at the Fukushima plant for an 8 hour shift. It’s usually given in microsieverts.
The other is a dose rate. This is the rate at which you are receiving a dose. It’s usually given in microsieverts per hour. A lot of reporters have been misunderstanding this and reporting it as just microsieverts.
The article you quoted is correct that a dose rate, like continuously standing at the Fukushima plant gate, is not comparable to a dose like getting an x-ray. However, it is wrong in saying that the two can’t be compared. To properly compare the two, you simply multiply the dose rate by the duration of exposure. e.g. If an x-ray gives you 20 microsieverts, and a town near Fukushima is reading 0.5 microsieverts/hr, then staying in that town for 40 hours will give you a dose of (40*0.5) = 20 microsieverts. The same as the x-ray. (Doses over time are actually a little less harmful than a one-shot dose like an x-ray, since it gives your body time to repair some of the damage.)
The article is also correct that ingestion or inhalation of these radioactive particles is very dangerous because it leads to direct and prolonged exposure. However, I should point out that your body is not some pure fortress completely devoid of radioactivity. A relatively common natural isotope of potassium (K-40) is radioactive. Potassium is necessary for your body’s nerves and cells to function, and thus K-40 is unavoidable. It accounts for your body receiving about 390 microsieverts each year. Potassium is found in all sorts of food, but occurs most in bananas and chocolate (yes, I cried a bit when I learned that too :D ).
So while ingesting or inhaling a certain amount of iodine-131 or cesium-137 can significantly increase your health risk, at smaller amounts the risk is small or insignificant compared to the naturally occurring radioactivity within your body. It is these levels of risk which the government is using as the basis for whether or not to ban certain foods with radioactivity found on them.
Various news reports have been using a lot of different units to describe the radiation. I’ve seen rem, rad, roentgen, bequerel, curie, sievert, and gray, with various prefix and per-time-period permutations. Can you explain what these are, and how they’re related?
The units you mentioned measure three different things, each having two units.
First is a measure of radioactive decay rate. The Becquerel (Bq) is one decay per second; the Curie (Ci) is 3.7e10 decays per second. These measure the frequency at which a mass of radioactive material emits a particle.
Second is a measure of absorbed dose. These measure the amount of radiation received by something, most often a person in the news right now. The rad is the historical unit, and the Gray (Gy) is the metric unit. One Gray is equal to 100 rad.
Finally, there is a measure of equivalent dose. Not all particles emitted by radioactive materials cause the same amount of damage to tissue. Because, of this, radiation scientists weight the dose received by an individual by the type. This is the most important number when considering health effects. The historical unit is the rem, and the metric unit is the Sievert (Sv). One Sievert is equal to 100 rem.
Hi. MIT Course 13 grad here (Ocean Engineering, sadly no longer a separate department). As you can guess, I deal a lot with machinery and systems in the ocean.
Your charts say each of the reactors should be producing 5-10 MW of heat at this time. If I did my math right, ignoring pressure changes, cooling this much power requires roughly 1.9-3.8 kg of 20 C water converted into steam every second.
The first concern I had when they started using seawater to cool the reactors was salt buildup. When you boil seawater, the steam is pretty much pure water. So the water gets vented off, but the salt remains. Each kg (liter) of seawater contains about 35 grams of salt. At 5 MW for 1 day, this would result in a buildup of:
[ (4.187 kJ/kgK specific heat)*(80 C) + (2270 kJ/kg heat of vaporization) ]
* (1/1000 MJ/kJ) = 2.6 MJ/kg of water converted to steam
(5 MJ/sec) / (2.6 MJ/kg) = 1.92 kg/sec
(1.92 kg water/sec) * (0.035 kg salt/kg water) * (3600 sec/hr)*(24 hr/day)*(1 days)
= 5804 kg salt
So nearly 6 tons of salt building up within the reactor’s containment vessel each day for the smaller reactor. More for the two bigger ones, and even more over the last week when the heat generation was higher.
Can the reactor continue to operate with this rate of salt buildup? Do they have a way to flush out the salt (or high-salinity water)? Wouldn’t the salt/salt water be contaminated with other radioactive decay products like strontium-90, which normally can’t be emitted via venting?
They finally seem to be getting a handle on things, and I would hate to see it go out of control again because nobody thought of this. I had thought using seawater to cool was just a temporary measure until they could truck more fresh water to the site. But they say they are still using seawater, which worries me.
What you’re proposing would be correct, IF they were venting off the steam continuously, they are not, they only vent when it becomes absolutely necessary to do so in order to lower the vessels internal pressure.
Reason one is if they lower the pressure in the reactor vessel it increases steam production, which in turn lowers the liquid water level, causing them to add more seawater in order to keep the fuel covered.
Reason two, venting steam also releases a large quantity of bad radio isotopes, which is what they are trying to prevent in the first place.
It is my understanding that when they vent it is from the water in the torus section “Suppression Pool” and being that that is a low point in the system that is where the concentrated brine would be. Venting liquid water would give them room to add more cool water without increasing steam production or raising the pressure in the reactor.
You may refer to the NRCs newest release on the incident, it has a good description of how the “torus” performs its job.
Seawater was a last-resort measure to be decided on. If I’ve read correctly, it means two things:
- A messy clean-up afterwards (probably due to the salt picking up radiation), and
- The discontinuation in using those reactors flooded with seawater, as the salt has more or less eroded away the strength of the containment. But this shouldn’t be a problem at all, due to these reactors having run the course of their 40-year expected life time anyway.
Unless you meant “continue to operate towards the goal of getting things under control” (by “continue to operate”), then I agree this is a concern indeed.
I’m by no means knowledgeable in this matter. I just thought I’d share what I’d read.
That doesn’t really make sense. The energy from that 5 MW has to go somewhere. If all other cooling systems except venting have failed, then the energy has to go into raising the temperature of the water and vaporizing it into steam. Since the final thermodynamic state of the steam is 1 atm, pressure changes within the reactor are irrelevant to the heat balance – the inputs (water) and outputs (steam) are both at 1 atm regardless of what happens inside the reactor. So the same amount of steam per hour has to be released on average, whether you’re releasing it continuously or in brief bursts.
The suppression pool should provide a large heat sink, but even it has a finite thermal capacity. Eventually the heat energy it absorbs will raise its temperature to 100 C, at which point it would become ineffective as a heat sink. I assume this point was hit early on, otherwise there would have been no need for them to vent steam into the atmosphere.
So my question remains. Is there an alternate form of cooling going on here? And if not, what is happening to all the salt building up within the reactor? I saw something called a demineralizer in one of the diagrams, but it looked like it needed functioning pumps to operate.
From what I can gather, they are holding close to operating pressure on the reactors, that would be 70-75 atm. not 1atm. At 75 atm the boiling point is 285C not 100C.
So as long as they keep the core covered with liquid water they will make no steam as the temperature drops. If the pressure rises they have to vent, simply to make room for more water. The majority of the heat is being convected from the reactor shell and torus to the air around the vessel, which in turn convects out of the containment via the ductwork provided for that.
In order for core damage to take place the core must reach at least 2200F which is the point at which the Zircalloy fuel tubes will begin to decompose.
According to design this temperature can never be reached as long as the control rods are in place.
The biggest danger in injecting seawater is not the salt, it is the corrosion and hydrogen and chloride attack on the hardware. Reactor and their associated components are constructed of 316NG and 316L stainless steel, which does not get along very well with high temp. seawater, the chlorides make it brittle and subject to cracks forming, excess hydrogen has the same effect. Seawater also contains large quantities of cobalt, iron and copper all of which become highly radioactive and deposit themselves in every nook & cranny in the system, and makes it very hazardous to work on afterwords.
I have a question regarding what constitutes adequate nuclear crisis management measures. As you all know, there has been a slew of criticisms being leveled from abroad and foreign media – including local clamor of course – and I suppose there will a massive POST-MORTEM of the disaster when the dust has cleared and we know all the facts.
In speaking of disaster response times and whether adequate steps have been taken, it seems to me that much depends on the differing local site conditions – here there is tsunami and quake wreckage conditions slowing disaster response even at the reactor that people are forgetting to factor in. Yesterday’s video footage showed concrete rubble everywhere around the reactor buildings. It is becoming increasingly apparent that disaster crisis management measures have to do with whether there onsite fact-finding work is possible, operable control information systems, access to facilities (impeded by rubble and debris from quake, dangerous radiation levels, surrounding power fuel supply access, weather/wind conditions and so forth). Journalists never address these differences in local conditions when they hurl their accusations of mismanagement or slowness to act at TEPCO and government authorities. I should be interested to know if anybody is tackling a comparative study on the disaster crisis management measures and response times – I should be interested to know how the factual differences in working environment factor upon the crisis containment steps taken – comparing Three Mile Island – Chernobyl and the current Fukushima Daiichi crisis. Although it had seemed excruciating slow at first, it would seem to me that the disaster response time is beginning to look pretty good under the terrible working circumstances now. Would you be able to comment on this?
I have been trying to determine the probability of a zircaloy fire in the unit 4 SFSP. Odds of propagation appear to be low. The fuel rods from the unit 4 reactor though, are at very different times of their fuel life. Chance of oxidation vary based on fuel life cycle. Could you provide some data on the subject?
This blogg is very informative, thanks.
Question: Are there any alarm systems for monitoring H2 levels inside the reactor? If yes what was failing prior to the explosion of reactor nr3?
Thank you so much for your informative and clear posts regarding Fukushima.
I have a couple of questions that if answered would ease my mind.
We live in Ueda Nagano which is about 3o0km away from the Fukushima reactors. We have decided to stay here and help in anyway we can. We have two young children and I cannot help but be worried. I picture the feather at the start of Forest Gump but replace it with a radiation particle invisible to the eye falling from the sky and landing on my kids .
Should I be concerned?
Also are these normal readings for Geiger Counters?
Thank you so much you all have been a blessing supply all this great info,
Riel, I live in Tokyo which – as you may know – has seen a mass exodus of foreigners in recent days. I have written the below commentary in reaction to that. You may find it helpful. If you do, please feel free to forward to anyone else who may benefit from it. From all I can see, you have nothing to worry about. Well, maybe not nothing, but certainly not from the plants in Fukushima.
I have heard online discussion the use of borated concrete as a sort of cure-all measure to a reactor crisis. (I assume this is based on the methods used on Chernobyl) Furthermore, these comments generally claimed that not dropping borated concrete on the reactor was reckless and putting the public at risk.
This sounds simplistic to me – I’m assuming that TEPCO hasn’t used it for a good reason – the reactors are total writeoffs after the fuel damage and pumping seawater into them, after all. I’d like your professional opinion on this method.
Although I am not with MIT, I am an engineer.
There is a LOT of very silly things floating around on the net as regards this situation. The borated concrete is one of them.
All of these reactors are intact at both primary and secondary containment’s.
Dumping concrete on them would be an exercise in futility, and would just make cleanup that much harder to do.
Secondly you would have to figure out how to get the top of the secondary containment open so you could dump anything into the area where the reactor vessel is.
At Chernobyl the reactor core was exposed and visibly burning, borated high temperature concrete was the only option they had, short of just letting it burn itself out.
Thank you very much for this service.
Right now, the biggest fear I’m hearing about is the spread of radiation. How does radiation spread during an event like this?
My second question is, many of the sensors checking people for radioactivity that we see on the news have a plastic bag over them. What’s the purpose of the plastic bag, and could it give false readings?
I live in Hokkaido, hundreds of miles from the accident, and I’m not really worried about it coming up here. But a lot of people are.
I’m not from MIT, nor am I an engineer, but I can try and answer your first question base don the reading I’ve been doing.
Radiation itself is a form of energy. There’s multiple types, but what we’re concerned with is called ionizing radiation – this comes in four different types, which are each somewhat different. However, the radiation itself doesn’t tend to travel all that far from its source; it gets blocked and absorbed by buildings, trees, and general obstacles. Dentists often cover patients with a lead apron when they are getting an x-ray to prevent the radiation from the x-ray from hitting other parts of the body – this is because lead blocks some types of radiation energy. I believe boron also does this, as well as helping to prevent the fission process from occurring, which is why France (and possibly other countries?) shipped boron to the Fukushima plant.
The problem is when the radioactive materials, which emit this radiation energy, are themselves traveling. When the things that are emitting radiation escape confinement, then they can travel via wind or water, and they continue emitting radiation as they go. The major concern is if the radioactive material is inhaled, ingested, or otherwise enters the human body. Then, it can get stuck in the body in one way or another and continue to emit radiation from there.
Iodine tablets, for example, work by preventing the body from absorbing one type of radioactive material – they don’t provide protection against the radiation energy itself, they just keep it from getting stuck in your body and continuing to emit radiation there.
This is also why you hear the term ‘confinement’ tossed around a lot. Nuclear plants are designed to keep the radioactive material inside, as well as having shields in place to prevent the radiation itself from getting too far outside the plant. Protecting the public from the radiation that escapes the plant due to structural damage isn’t too difficult; evacuating the immediate area would take care of that. The wider evacuations are due to the possibility of radioactive material escaping the plant and continuing to emit radiation farther from the plant.
Regardless, if you live hundreds of miles away, you probably don’t need to worry about radiation reaching you in significant amounts – however as always, do follow what the local authorities tell you.
I don’t know much about the bags on sensors, but if I had to guess, it’d be to try and prevent radioactive material from sticking to the sensor itself and throwing off the readings…? I’m afraid I can’t help you much there.
By the way, if anyone in Japan missed this (and if you did, you should check on your embassy site — the US embassy site had it up a week or so ago), the Ministry of Education has sites in each of the prefectures, and some really lovely charts up. Compare your own prefecture to one of the “hotter” spots (like, say, Chiba) for a little dose of reality. Unfortunately, the Fukushima monitors are on a different system, so you’ll have to translate those numbers to the chart of your own prefecture.
It seems that efforts to cool the the spent fuel pools via water dumping and hosing has had almost zero effect including efforts this morning (JST, March 19th). Why wouldn’t TEPCO or the government fill the spent fuel pools with a mixture of concrete and boron in order to lower the radiation levels on site and be able to allow workers an opportunity to restore power to the cooling system of the reactors? (which NHK is now reporting will take time to actually implement due to conditions on the site)
thanks for all of your information! It’s been a great aid to help calm my family and myself who live in Tokyo.
I just want to say that if the cooling attempts had literally zero effects, it would mean a LOWER water level in the spent fuel ponds. No change actually means a positive situation being maintained.
I also heard of an effort to directly put a water hose into the reactor building for more effective pumping. I hope it succeeds.
An Update, via NEI:
TEPCO has brought in some extending arm concrete pumps, they are going to use these to more accurately place water directly into the spent fuel pools, as opposed to spraying with water cannon.
They have one in place and have already put water into the pool at Unit4 (no quantity mentioned), and 18 MT of (seawater?) into the Unit2 pool.
There has been mention of a fire in one of the units this morning, which is issuing black smoke, they have evacuated workers from that area.
Black smoke is not a spent fuel pool fire. It is in all likelihood a chemical fire which has ignited roofing material (asphalt) which has fallen into the buildings as a result of the earlier H2 explosions. Most plants I have been in have several pallets and drums of water treatment chemicals stored next to the spent fuel pools, they use these chemicals to adjust the chemistry of the water in the pools, there are bags of borax, caustic soda, barrels of muratic acid, and others. It would be my summation that some of this stuff has gotten wet and is having an exothermic reaction, caustic will do this for sure, and I think borax will as well.
I was curious, aside from potassium iodide, are the any substances you know of that the power plant workers in Japan could take to limit the damage from radiation. Also does the damage happen from damage only to the nucleotides in the DNA or is part of it from free radical damage as well.
The reason why I ask is because I found this website searching with Google
And it seems to me they could create some sort smoothie or ant-radiation drink to ingest periodically before they get near the reactor to protect them. I was curious on how much you think it might help them.
This was an area of intensive research early in the nuclear era. Potassium Iodide is probably the most well known agent, and it is designed specifically to block I-131 uptake. Other agents usually required doses near or exceeding toxic levels to protect against radiation. Organosulfur compounds provided a significant but very small improvement in survival, but only at doses very close to the toxic level. The other agents are actual poisons.
While I’m gathering taking an uncontaminated multi-vitamin preparation wouldn’t hurt, I don’t believe there is actual clinical evidence.
If things went right (best short-term scenario) with the water cannons and helicopters:
- spent fuel pools would be refilled
- reactors would be cooled down
- radiation would cease being released
But given that fission products take years to cool down, for how long would they have to use cannons and helicopters? Given that AFAIK 4 reactor buildings exploded already it’s likely that the pumps and piping that would otherwise work with generator or power lines are now disabled.
So the question is, if the best case scenario is confirmed is it likely that plumbing works can be done to restore the cooling systems? From the ruins we’ve seen in aerial footage this is far from evident. What is the permanent solution for the forthcoming years of cooling down?
According to schematics available to the public, the pipework and control systems for the reactor are not in the secondary containment building, about the only thing in the building above ground are fire suppression systems (sprinklers), instrumentation, ventilation ducts, lighting and gear for handling fuel bundles. There is no exposed reactor or containment pool piping in that building.
The cooling pumps themselves are located in a separate building away from the reactor buildings, and their pipework is below ground in a tunnel. (this is for obvious reasons that if the reactor build became too contaminated to work in, the cooling pumps can still be operated and serviced in a safe zone).
But the spent fuel pool seems to be part of the containment so its pipework must be inside and I doubt it is not damaged.
What was destroyed from the H2 explosion was the sheet metal and frame upper structure, it is only there to protect the top of the secondary containment structure proper and the fuel handling gear from the elements. What was exposed to the explosion was only the surface of the spent fuel pools, all of its piping is below that area.
The top of the secondary containment is the floor of this metal building, and is about 6ft thick reinforced concrete. The pool itself is a 2″ thick borated alloy stainless steel tank cast into the secondary containment structure, for it to leak, the steel liner and 6ft of reinforced concrete wall would have to be punctured.
The explosion although visibly impressive, could not have generated enough pressure to do much more than rattle the piping below in the secondary containment. I doubt if the whole steel building when intact, would take much more than 2 atmospheres to blow the sheet metal panels off.
Had the crew thought about it or been instructed to do so, they should have removed a few of the panels just below roof line, before they vented steam from the reactor. That would have allowed accumulated hydrogen to escape the building and would not have allowed it to get to explosive levels.
The water in these pools is in all probability not leaking out but is evaporating.
They are designed to not be able to drain by gravity, they must be pumped out intentionally.
The pumps required to circulate the water in the pools are not running due to lack of power. So they will get hot enough to cause rapid evaporation, and sans a method of adding more water and circulating it to the coolers, the water must be put in manually, as they are doing presently with water cannon, and allowed to evaporate to cool the spent fuel.
Here is a proper drawing of a Mk-1 Reactor and containment.
Perhaps you can answer a question about the design of the reactors for me
If I understand correctly, the problems started because the tsunami knocked off the diesel generators that were supposed to generate electricity for the pumps that keep the cooling water flowing.
So my question is this: why do they need diesel generators in the first place? Why can’t the reactor generate its own electricity, even after being switched off?
After all, the reactor’s job is generating electricity through heat, and there’s plenty of heat left (too much of it in fact), so why not put that heat to good use?
This would make it a self-regulating system (as long as there’s heat, there’s electricity to keep the heat under control)
Are there technical/safety reasons why reactors weren’t designed like this? Or were they and this failed as well?
Such a system was in place apparently, but failed.
It’s discussed during this briefing by MIT NSE faculty: http://techtv.mit.edu/videos/11363-mit-department-of-nuclear-science-and-engineering-briefing-on-the-japan-nuclear-crisis
The biggest problem in doing that is turndown ratio. ie the reactor can not turndown enough to run a turbine that is only supplying power to cool itself off.
Like any other large power plant these have a maximum and minimum operating envelope.
In the case of the Daiichi reactors, they scrammed the moment the quake reached a predetermined motion amplitude (No one has said what that was .. yet) and slammed the control rods all the way in, and blew down the boiler drums of steam.
Like a conventional plant if the power sink (electric consumers) are suddenly cut off, the generators have to be immediately disconnected from their steam turbines or they will destroy themselves from over revving and excess heat buildup (the juice they are producing has to go somewhere).
And the steam to the turbines has to stop or they will over rev and destroy themselves. You could compare it to throwing your car in neutral when running down the highway at a 100mph, and not letting off the accelerator pedal, (your engine would probably blow-up).
That’s a very clear explanation, thanks. But still, couldn’t just a fraction of the steam drive the turbine after scram? The reason I’m asking is that I saw in the BWR document (posted under the Technical section) that something like this is used for RCIC (a fraction of the steam drives the RCIC pump).
Although I am not a nuke guy, I do know a bit about it, I do know a whole lot about the steam side.
That said it still applies that a reactor has a given range of operation.
In order to generate steam a reactor has to be coaxed to criticality to get hot enough to make steam, the problem with turndown on a nuke reactor or a large conventional boiler is the amount of heat that must be generated to induce nucleate boiling at a given pressure. The larger the boiler the more heat that must be input to do this.
With a nuke reactor is at its critical point where it’s a self sustaining fission reaction, it is generating more steam than can be used in a small turbine. The excess would have to run through knockout drums and through the entire condensing, recirculating and water conditioning system just as it would during normal plant operation. This would negate the purpose of shutting it down in the first instance, as all of the equipment involved in full operating mode would have to be used.
And in addition there is a lower limit that a nuclear reaction can be initiated, and maintained there has to be enough quantity of active fuel to reach criticality, from what I can gather that is dependent on the type of fuel as well as quantity, Naval reactors are comparatively small so they use a more potent fuel mix. ie the more potent the fuel the smaller the critical mass is.
If I understand you correctly, you’re suggesting that a reactor after shutdown can’t generate [enough] steam. But wasn’t it steam that they vented off on a few occasions because pressure was building up? And couldn’t part of that steam drive a turbine – perhaps a dedicated turbine that would drive the pumps directly?
There would be insufficient steam to drive a generator or for direct drive pumps.
The steam volumes and pressures required to drive a turbine that would run pumps of the sized and volume output required for cool down are beyond a cooling down reactors capacity due to the size of the system.
It is simply not hot enough to do the job. The core must still heat the same volume/weight of water that it heats during normal operation, as the inside of the reactor has to hold enough water to cover the fuel. It takes up to 60 high pressure high volume pumps to supply the circulating water during normal operation, and these are not small pumps they are on the order of 300-150hp high voltage motors each, depending on what duty they are doing.
Depending on the arrangement of the reactor cooling system it still takes a phenomenal amount of water during cool down, although at lower pressure.
Also you would get to a catch 22 situation where you are cooling the reactor below what heat you need to drive the turbine, even if you could get one running to start with.
I did some research on the RCIC (reactor core isolation cooling) which is what you are referring to, with a steam turbine powered pump.
It is designed to run for 15 minutes only, and it feeds water from the boiler make up water tank.
Although GE is not clear on this, I would make the assumption that this is a buffer between a scram and the time it takes to get the emergency power switched over and up to speed.
Here is some info on it from the NRC
on page #8
Just a note for curiosity: the testing of such a system – due to a conspiration of several other factors – was the base of the Chernobyl incident.
http://handle.dtic.mil/100.2/ADA335076 (from page 11)
In this case a temporary power supply based on the inertia of the turbine would drive the pumps until the diesel generators (which were slow to startup) were fully operating. The complexity of this design is scary by itself. The more complex things are, the more scenarios and factor conspirations we are likely to forget.
Thank you very much for this site and blog. There have been very few sources, which are both professional/knowlegable and unbiased.
I have a question about the water in the spent fuel pool…
in the blog what is criticality you mentioned water is use to slow the neutrons, and slower neutrons cause the majority of fission reactions.
Thats great to keep the reaction going in the fuel rod I suppose, but now we also have problem in the reactor 4 spent fuel pool that they were running hot and dont have enough water to cover up the fuel rod, and that caused the high radiation measurement. So when we dump more water back into the fuel rod…. we are cooling it while we are increasing the fission reactions which create more heat??
isnt that a loop until somehow the system can get itself into the subcritical state? which from all the information I gathered… seems like more baron or boric acid instead of pouring water or sea water?
Water slows down neutrons which cause the majority of fission reactions. However, this is only the case in a near-critical or supercritical system. In a significantly subcritical system with almost no neutron population, such as a spent fuel pool, there are no neutrons to slow down, and therefore there are no fissions. The heat production in the spent fuel comes from radioactive decay of the fission products, which is not affected by the presence of water.
Boric acid is added to the water in the spent fuel pool, which helps ensure its subcriticality.
It’s important to recall that there’s already a great deal of boron present in the pool, left behind from when borated water cooled the pool. As a result, the addition of water should allow some slowing of any neutrons present, but these would be absorbed by the boron. The moderation by water and the absorption by boron are two competing effects, and the boron should win.
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