Nuclear
Wednesday, 03 August 2011 10:12

Update on Fukushima

The world’s greatest disaster, which was caused by the tsunami in Japan in March, has brought the economy to a standstill, with power plants, oil refineries and many industrial concerns generally either seriously damaged or ruined forever.

Add to this the ongoing disaster at the Fukushima nuclear power station, which is far from over, and one is left marvelling at the resolute attitudes of the nation in their loss and their dogged determination to do whatever is needed to put the country and its people back on their feet.

Overall, the situation at the Fukushima Dai-ichi nuclear power plant remains very serious, but there are signs of recovery in some functions, such as electrical power and instrumentation.

At a press conference held on 21 April, the chief Japanese cabinet secretary, Yukio Edano, announced the establishment of a no-entry zone around the Fukushima Dai-ichi nuclear power plant, as well as basic policies concerning temporary re-entry. At midnight (Japan local time) on 22 April 2011, the area within 20 kilometres of the nuclear power plant was announced as a no-entry zone.

Edano also announced a re-designation of the evacuation zone around the Fukushima Daini nuclear power plant. He said the size of the evacuation zone around the station would be reduced from ten kilometres to eight kilometres, and that the order to evacuate based on the incident at the Fukushima Daini nuclear power station would be lifted from areas further than eight kilometres from the station.

Regarding the changes to the status of the Fukushima Dai-ichi nuclear power plant, the IAEA receives information from a variety of official Japanese sources through the national competent authority, the Nuclear & Industrial Safety Agency. Additional detail is provided in the IAEA Incident & Emergency Centre (IEC) status summary with information received by 07:00 UTC on 21 April 2011.

Management of on-site contaminated water
An injection of approximately 17 000 litres of coagulant (liquid glass) to the power cable trench of Unit 2 was carried out on 18 April and an injection of approximately 7 000 litres of liquid glass was done on 19 April. The transfer of stagnant water from the Unit 2 turbine building to radioactive waste treatment facilities commenced on 19 April.

The stagnant water (about 100 m3) in the basement of the turbine building of Unit 6 was transferred to the condenser on 19 April.

Plant status
Work to strengthen the electrical power system between Units 1-2 and Units 3-4 by establishing multiple power lines was completed on 19 April. White “smoke” continues to be emitted from Units 2, 3 and 4.

In Unit 1 fresh water is being continuously injected into the reactor pressure vessel through the feedwater line at an indicated flow rate of 6 m3/h, using a temporary electric pump with off-site power.

In Unit 2 and Unit 3 fresh water is being continuously injected into the reactor pressure vessel through the fire extinguisher line at an indicated rate of 7 m3/h, using temporary electric pumps with off-site power. In Unit 4 tonnes of fresh water were sprayed over the spent-fuel pool on 19 April, using a concrete pump truck.

Nitrogen gas is being injected into the containment vessel in Unit 1 to reduce the possibility of hydrogen combustion in the containment vessel. The pressure in the containment vessel has stabilised. The pressure in the reactor pressure vessel is increasing.

The reactor pressure vessel temperatures in Unit 1 remain above cold shutdown conditions. The indicated temperature at the feedwater nozzle of the reactor pressure vessel is 154°C and at the bottom of the reactor pressure vessel it is 113°C.

The reactor pressure vessel temperatures in Unit 2 remain above cold shutdown conditions. The indicated temperature at the feedwater nozzle of the reactor pressure vessel is 135°C. The reactor pressure vessel and the dry well remain at atmospheric pressure. Freshwater injection (approximately 47 tonnes) to the spent-fuel pool via the spent-fuel pool cooling line was carried out on 19 April.

The temperature at the bottom of the reactor pressure vessel in Unit 3 remains above cold shutdown conditions. The indicated temperature at the feedwater nozzle of the reactor pressure vessel is 100°C and at the bottom of the reactor pressure vessel it is 108°C. The reactor pressure vessel and the dry well remain at atmospheric pressure. There has been no change in the status in Unit 6 or in the common spent-fuel storage facility.

The Tokyo Electric Power Co. (TEPCO) has released a roadmap to bring the Fukushima Dai-ichi nuclear plant to a stable condition. Priorities continue to be on cooling the reactors and spent-fuel pools, draining water from the turbine buildings and concrete structures that house piping to reduce radiation levels, and containing the spread of radioactive materials.

Overall, the utility says, site radiation dose rates are stabilising. The most recent radiation readings reported at the plant-site gates ranged from 5.7 millirem per hour to 2.6 millirem per hour.

Radiation monitoring
On 20 April, deposition of I-131 was detected in eight prefectures, ranging from 2.4 to 80 Bq/m². Deposition of Cs-137 was detected in seven prefectures, the values reported ranging from 2.6 to 87 Bq/m².

Gamma dose rates are measured daily in all 47 prefectures. For Fukushima a gamma dose rate of 1.9µSv/h was reported on 20 April, and for the Ibaraki prefecture a gamma dose rate of 0.12µSv/h was reported. In all other prefectures, reported gamma dose rates were below 0.1µSv/h.

Dose rates are also reported specifically for the eastern part of the Fukushima prefecture for distances beyond 30 kilometres from Fukushima Dai-ichi. On 19 April the values in this area ranged from 0.1 to 22µSv/h.

In cooperation with local universities, the Japanese Ministry of Education, Culture, Sports, Science & Technology has set up an additional monitoring programme. On 20 April, measurements of gamma dose rates were reported for 54 cities in 40 prefectures. In Fukushima City a value of 0.42µSv/h was reported.

In nine cities, gamma dose rates between 0.13 and 0.17µSv/h were reported. In all the other cities the reported gamma dose rates were below 0.1µSv/h.

Japan’s government has expanded evacuation to selected areas outside the original 12.5-mile zone. Authorities are also barring entry into nine municipalities near the plant.

It must be remembered that this situation is changing almost daily, but the information contained in this issue was correct at the time of going to press.

For more information, visit www.iaea.org/newscenter and nei.cachefly.net, to which full acknowledgement and thanks are given.