March 17, 2011

Fukushima Daiichi - possible crack in wall of the No. 4 reactor pool and progress on restoring power


LA Times - U.S. government nuclear experts believe a spent fuel pool at Japan's crippled Fukushima reactor complex has a breach in the wall or floor, a situation that creates a major obstacle to refilling the pool with cooling water and keeping dangerous levels of radiation from escaping.

That assessment by U.S. Nuclear Regulatory Commission officials is based on the sequence of events since the earthquake and information provided by key American contractors who were in the plant at the time, said government officials familiar with the evaluation. It was compelling evidence, they said, that the wall of the No. 4 reactor pool has a significant hole or crack.


Tokyo Electric Power Co. said it hopes to activate the cooling system for Fukushima Daiichi reactor 2 “as early as Friday night” (Japan time). The company said it could restore power from the electric grid to reactor 2 by Thursday night (U.S. time).

The International Atomic Energy Agency reported that TEPCO completed connecting electrical cable from a makeshift transformer to reactor 2 at 4:30 A.M. EDT. Engineers were waiting to complete spraying sea water into the reactor 3 fuel pool before they restore power through the cable to the reactor 2 cooling system.

TEPCO says that if it can provide power supply to the other reactors, it could begin restoring some cooling functions. The company said that after fire trucks injected water into reactor 3’s fuel pool, radiation levels at the plant’s west gate dropped from 31 millirem per hour to 29 millirem per hour at 10:00 A.M. EDT.

IAEA UPdate - Japan Earthquake Update (18 March 2011, 06:10 UTC)

Temperature of Spent Fuel Pools at Fukushima Daiichi Nuclear Power Plant - UPDATED

Spent fuel removed from a nuclear reactor is highly radioactive and generates intense heat. Nuclear plant operators typically store this material in pools of water that cool the fuel and shield the radioactivity. Water in a spent fuel pool is continuously cooled to remove heat produced by spent fuel assemblies. According to IAEA experts, a typical spent fuel pool temperature is kept below 25 °C under normal operating conditions. The temperature of a spent fuel pool is maintained by constant cooling, which requires a constant power source.

Given the intense heat and radiation that spent fuel assemblies can generate, spent fuel pools must be constantly checked for water level and temperature. If fuel is no longer covered by water or temperatures reach a boiling point, fuel can become exposed and create a risk of radioactive release. The concern about the spent fuel pools at Fukushima Daiichi is that sources of power to cool the pools have been compromised.

Japan's Nuclear and Industrial Safety Agency has reported increasing temperatures in the spent fuel ponds at Units 5 and 6 since 14 March. An emergency diesel generator at Unit 6 is now powering water injection into the ponds at those Units, according to NISA.

The IAEA can confirm the following new information regarding the temperatures of the spent nuclear fuel pools at Units 4, 5 and 6 at Fukushima Daiichi nuclear power plant:

Unit 4
13 March, 19:08 UTC: 84 °C

Unit 5
17 March, 03:00 UTC: 64.2 °C
17 March, 18:00 UTC: 65.5 °C

Unit 6
17 March, 03:00 UTC: 62.5 °C
17 March, 18:00 UTC: 62.0 °C

The IAEA is continuing to seek further information about the water levels, temperature and condition of all spent fuel pool facilities at the Fukushima Daiichi nuclear power plant.

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