Japan may raise nuke accident severity level to highest 7 from 5
TOKYO [April 12, Kyodo News]
The Nuclear Safety Commission of Japan released a preliminary calculation Monday saying that the crippled Fukushima Daiichi nuclear plant had been releasing up to 10,000 terabecquerels of radioactive materials per hour at some point after a massive quake and tsunami hit northeastern Japan on March 11.
The disclosure prompted the government to consider raising the accident’s severity level to 7, the worst on an international scale, from the current 5, government sources said. The level 7 on the International Nuclear Event Scale has only been applied to the 1986 Chernobyl catastrophe.
The current provisional evaluation of 5 is at the same level as the Three Mile Island accident in the United States in 1979.
According to an evaluation by the INES, level 7 accidents correspond with a release into the external environment radioactive materials equal to more than tens of thousands terabecquerels of radioactive iodine 131. One terabecquerel equals 1 trillion becquerels.
Haruki Madarame, chairman of the commission, which is a government panel, said it has estimated that the release of 10,000 terabecquerels of radioactive materials per hour continued for several hours.
The commission says the release has since come down to under 1 terabecquerel per hour and said that it is still examining the total amount of radioactive materials released.
M 7.0 quake hits northeastern Japan
A strong earthquake struck north-eastern Japan at 5:16 PM, local time, on Monday, April 11. The earthquake’s magnitude was 7.0, and that its focus was in Fukushima Prefecture at a depth of 10 kilometers. Intensities of 6 minus on the Japanese scale of 0 to 7 were registered in some areas of Fukushima and Ibaraki prefectures, including Furudono Town, Nakajima Village and Hokota City. An intensity of 5 plus was registered in many areas in the southern Tohoku and northern Kanto regions.
Several minor quakes occurred following the major quake at 5:16. The agency is also warning of possible aftershocks with intensities of 6 plus or 6 minus. The operator of the crippled Fukushima Daiichi nuclear power plant, Tokyo Electric Power Company, says radiation figures at monitoring posts around the plant remain unchanged. The utility firm also says outdoor workers had been ordered to temporarily evacuate.
[Japan Atomic Industrial Forum Monday, April 11, 2011 18:46 +0900 (JST)
Expanded evacuation considered
The Japanese government is considering expanding its current 20-kilometer evacuation radius around the Fukushima Daiichi nuclear power plant, taking into account the risks of long-term accumulated radiation exposure. Chief Cabinet Secretary Yukio Edano said on Monday that the government may advise residents in areas between 20 and 30 kilometers from the plant to evacuate, based on accumulated radiation exposure levels. Currently such residents have been advised to remain indoors. Edano also said the government is considering advising residents to evacuate even from areas outside the zone where cumulative radiation exposure risks are higher. He said the possibility that the situation at the plant will worsen cannot be ruled out. Iitate Village
Water injection resumed at Fukushima Daiichi plant
The operator of Fukushima Daiichi nuclear power plant says water injection into the crippled reactors was briefly suspended after outside power lines were shut down by a magnitude 7.0 earthquake on Monday evening. Tokyo Electric Power Company said that outside power was restored for reactors No.1, 2 and 3. Water injection was resumed for these reactors after a suspension of about 50 minutes.
Monday, April 11, 2011 18:34 +0900 (JST)
Radiation dose higher than 1000 mSv was measured at the surface of water accumulated on the basement of Unit 2 turbine building and in the tunnel for laying piping outside the building on Mar. 27th.
Plutonium was detected from the soil sampled at Fukushima Dai-ichi NPS site on Mar. 21st, 22nd, 25th and 28th. The amount is so small that the Pu is not harmful to human body.
Radioactive materials exceeding the regulatory limit have been detected from seawater sample collected in the sea surrounding the Fukushima Dai-ichi NPS since Mar. 21st. On Apr. 5th, 7.5 million times the legal limit of radioactive iodine, I-131, was detected from the seawater, which had been sampled near the water intake of Unit 2 on Apr 2nd.
It was found on Apr. 2nd that there was highly radioactive (more than 1000mSv/hr) water in the concrete pit housing electrical cables and this water was leaking into the sea through cracks on the concrete wall. It was confirmed on Apr. 6th that the leakage of water stopped after injecting a hardening agent into holes drilled around the pit.
Release of some 10,000 tons of low level radioactive wastewater into the sea began on Apr. 4th, in order to make room for the highly radioactive water mentioned above.
Regarding the influence of the low level radioactive waste release, TEPCO evaluated that eating fish and seaweed caught near the plant every day for a year would add some 25% of the dose that the general pubic receive from the environment for a year.
TEPCO and MEXT has expanded the monitoring for the surrounding sea area since Apr. 4th.
Radioactive materials were detected from underground water sampled near the turbine buildings on Mar. 30th.
Containment of radioactive material:
It is presumed that radioactive material inside the reactor vessel may leaked outside at Unit 1, 2 and Unit 3, based on radioactive material found outside.
NISA announced that the reactor pressure vessel of Unit 2 and 3 may have lost air tightness because of low pressure inside the pressure vessel.
NISA told that it is unlikely that these are cracks or holes in the reactor pressure vessels on the same occasion.
TEPCO started to inject nitrogen gas into the Unit 1 containment vessel to reduce the possibility of hydrogen explosion on Apr. 6th. The same measure will be taken for Unit 2 and 3.
Steam like substance has been observed rising intermittently from the reactor building at Unit 1, 2, 3 and 4. Injecting and/or spraying water to the spent fuel pool has been conducted.
Progress of the work to recover injection function:
Water injection to the reactor pressure vessel by temporary pumps were switched from seawater to freshwater at Unit 1, 2 and 3.
High radiation circumstance hampering the work to restore originally installed pumps for injection.
Discharging radioactive water in the basement of the buildings of Unit 1through 3 continue to improve this situation.
Water transfer work is being made to secure a place for the water to go.
Lighting in the turbine buildings became partly available at Unit 1 through 4.
Radioactive material was detected from milk and agricultural products from Fukushima and neighboring prefectures. The government issued order to limit shipment (21st-) and intake (23rd-) for some products.
Radioactive iodine, exceeding the provisional legal limit, was detected from tap water sampled in some prefectures from Mar. 21st to 27th.
Small fish caught in waters off the coast of Ibaraki on Apr. 4 have been found to contain radioactive cesium above the legal limit on Apr. 5th.
It was decided on Apr. 5th that as a legal limit of radioactive iodine, the same amount for vegetables should be applied to fishery products for the time being.
[ from Japan Atomic Industrial Forum.]
UPDATE (Apr 7) -TEPCO Completes Nitrogen Injection At Unit 1
An operation to reduce the risk of a hydrogen explosion at the crisis-hit Fukushima Daiichi atomic power station’s No. 1 reactor by injecting it with nitrogen has gone smoothly, the plant’s operator Tokyo Electric Power Co. said Thursday. Pressure in the reactor’s containment vessel has risen as expected, indicating the success of the operation.
In its operation to prevent a hydrogen explosion at the No. 1 reactor, TEPCO plans to insert nearly 6,000 cubic meters of nitrogen, an inert gas, into the reactor over six days and estimates that about 200 cubic meters were injected between 1:30 a.m. and 9:50 a.m. Thursday.
The firm and the government’s Nuclear and Industrial Safety Agency said they believe chances are slim that another hydrogen explosion will occur immediately or that high volumes of radioactive substances will be emitted following the nitrogen injection operation. – Kyodo News (April 7)
UPDATE – Nuclear and Industrial Safety Agency – Seismic Damage Information (the 74th Release)
The Nuclear and Industrial Safety Agency stated that at Units 1 through 4 at Fukushima Daiichi NPS , “White smoke was confirmed to generate continuously.” Reported on April 6.
TEPCO Press Release (Apr 6) – Measures Taken To Prevent Explosion
Injection of Nitrogen to Reactor Containment Vessel of Fukushima Daiichi Nuclear Power Station Unit 1
“Regarding Fukushima Daiichi Nuclear Power Station Unit 1, taking into account the possibility of hydrogen accumulating inside, we have been considering encapsulation of hydrogen by injecting nitrogen to the reactor containment vessel.
Today, we received an order from minister of economy, trade and industry to report on matter such as necessity of encapsulating nitrogen, method for implementation, and impact assessment of safety.
Accordingly, we have compiled related matters and reported to minister of economy, trade and industry today. The report was approved after the deliberation in the Ministry of Economy, Trade and Industry.
Based on the report, we will begin injecting nitrogen to the reactor containment vessel of Unit 1 today, around 10:30pm”. END
Update [Apr.9] - TEPCO announced 0n 4_9 that they would perform an additional operation to inject nitrogen gas into the containment vessel of the Number 1 reactor to prevent a possible hydrogen explosion, TEPCO plans to increase the purity of nitrogen gas from 98 percent to 99.98 percent.