News Brief, 4/11/11
The region surrounding the troubled nuclear power station has suffered two aftershocks in recent days. The first, a magnitude 7.1 on the Richter scale, took place on 4/7/11. This aftershock injured thousands, and killed four, but no issues in maintaining supply of cooling water were experienced at Fukushima Dai-ichi.
The second aftershock, rated a 6.6 on the Richter scale, occurred at 08:16 UTC this morning. As a result of the aftershock, workers at Fukushima Dai-ichi were temporarily evacuated to the facility’s earthquake shelter. The event caused loss of offsite power to the water injection pumps for Units 1, 2 and 3. Power to these pumps was restored approximately 50 minutes later. No change in radiation readings was observed as a result of either aftershock.
Ongoing Mitigation Efforts
Management of contaminated water is still ongoing. Water from turbine buildings and trenches is being pumped into the condensers of the units, into the plant’s wastewater treatment facility, and into temporary storage tanks being brought in for this purpose. In order to make way for this highly contaminated water to be stored, low-level radioactive water was discharged from the wastewater treatment facility and from the “sub-drain” pits of units 5 and 6. This operation was completed on April 10.
Nitrogen is being pumped into the containment vessel of Unit 1. This is being done in order to displace oxygen, which could allow ignition of any hydrogen that has built up or builds up in the future. We have no information on the current level of concern about hydrogen buildup.
In order to prevent the spread of radioactive materials which have been deposited on the ground at the reactor site, workers have sprayed an anti-scattering agent. This agent prevents the material from being swept up from the ground as dust, and carried away from the site.
Monitoring is ongoing by a variety of organizations: TEPCO, IAEA, and MEXT, among many others. Radiation levels in most prefectures continue to hover at or slightly above background. However, radiation dose rates in a few isolated areas are higher. Yukio Edano named these locations: Katsuo, Kawamata, Namie, Iitate, and Minami Soma, most of which are inside the zone already ordered to evacuate or take shelter. The dose rates reported by the IAEA in these areas have a maximum of 1.6 microsieverts per hour. For comparison, the average background rate is 0.05-0.1 microsieverts per hour.
Monitoring of food and water from the region is ongoing. In a few prefectures, iodine and cesium isotopes have been detected in quantities below regulatory limits. An advisory against giving water to infants is in place in just one village in Fukushima prefecture. Food samples have for the most part shown either no detectable contamination, or levels below regulatory limits. Of 157 samples of foods, one sample of seafood (sand lance) and three samples of shiitake mushrooms, all originating from Fukushima prefecture, exceeded regulatory limits on I-131.