Fukushima power outage to spent nuclear fuel storage ponds partially restored


Publish date: March 19, 2013

Written by: Charles Digges

Four fuel storage ponds at Japan's tsunami-damaged Fukushima Daiichi nuclear plant were deprived of fresh cooling water for more than 20 hours due to a power outage, the plant's operator said today, raising concerns about the fragility of a facility that still runs on makeshift equipment.

The plants owner said power has “partially” been restored at one of the cooling ponds, and that the others were expected to be back on line by later today and tomorrow.

The outage had hit ponds at reactors 1, 3 and 4, the statement said, but cooling to the reactors themselves was not affected. Fukushima Daiichi’s common storage pool was also affected by the outage, Japan’s NHK reported.

Power has been partially restored to the No 1 the cooling pond at about 2:20 p.m. Tokyo time, the plant’s owner, Tokyo Electric Power Co, or Tepco, said in a statement. The primary system of Unit 4 spent fuel pond alternative cooling system was started at 1:20 PM. The secondary system is planned to be restarted at 8:00 PM today.

The statement went on to say that power the No 3 spent fuel pond was scheduled to come back online by 8:00 p.m. today, and that the common pond’s cooling purification system is planned to be restarted at 8:00 AM tomorrow.

Tepco’s earlier announcement today about the power outage said it had hit at 6:57 Japan time on Monday. The nearly day long delay in reporting the incident has done nothing to settle the nerves of the Japanese public.

Tepco had been racing against a deadline of four days before the ponds heat up beyond safety limits, said the company.

The temperature in the hottest fuel pond, at Unit 4, was 30.5 degrees Celsius on Tuesday morning, Tepco said, well below the safety limit of 65 degrees. However Tepco did say that temperatures at the ponds had risen slightly.

“This is an unstable situation that will continue to be so for several years until fuel is removed from the plant to safe storage,” said Bellona’s nuclear physicist and General Manager Nils Bøhmer, who, with other Bellona staff, returned from Fukushima on Friday.

The ponds store spent fuel from the nuclear reactors. They cool the fuel – which generates intense heat – and provide shielding from radiation. The spent fuel remains in the ponds for a year or more.

Lack of fresh water could lead to boil off and radiation

There is no apparent immediate threat of a radiation release. But if fresh cooling water is not restored to all the ponds within deadlines, there is a possibility that the water in the ponds could start to boil, which would lead to a loss of water and eventually to the exposure of the fuel rods to air.

If that happened, said Bøhmer, it would be a very serious situation and could lead to a release of radiation.

Pond No 4’s special circumstances

The “highest priority” was being placed on restoring the cooling system to the spent fuel pool at reactor 4, Kyodo news agency quoted Tokyo Electric Power Company (Tepco) spokesperson Masayuki Ono as saying.

The hottest of the ponds, its temperature stood at 30.5 degrees Celsius on Tuesday morning, Tepco said, well below the safety limit of 65 degrees

Despite Tepco’s assurances, the announcement is alarming, given that experts interviewed last week by Bellona in Japan said that the cooling pond at reactor No 4 is by far the most vulnerable to enormous leaks of radiation.

Hideyuki Ban, co-director of the Citizens’ Nuclear Information Center, said in an interview in Tokyo last week that the No 4 pond must be emptied over the course of the next year to assure against chain reactions in the fuel stored there.

A report issued last year found that a collapse of the No 4 pool, which sits atop a reactor building that is in rickety shape from the three hydrogen blasts the plant experienced during the height of the crisis, could outweigh the initial disaster.

Tepco scrambling to find out what happened

Tepco workers meanwhile are still trying to find the cause and repair the problems.

Workers were fixing the last of the three switchboards that they suspect as a possible cause of the problem and the utility was preparing a backup system in case the repairs didn’t fix the issue, Masayuki Ono, another Tepco spokesman Masayuki Ono told the Associated Press.

“If worse comes to worst, we have a backup water injection system,” said Ono.

Japan’s earthquake and tsunami on March 11, 2011 destroyed the plant’s power and cooling systems, causing three reactor cores to melt and fuel storage ponds to overheat.

Tepco could be pushing too hard with makeshift equipment

Ono acknowledged to reporters that the plant was vulnerable and that decommission efforts were strained.

“Fukushima Dai-ichi still runs on makeshift equipment, and we are trying to switch to something more permanent and dependable, which is more desirable,” he told Japanese media. “Considering the equipment situation, we may be pushing a little too hard.”

Ono said the utility did not immediately try to switch to a backup cooling system because doing so without finding and fixing the cause could lead to a repeat of the problem. There is a backup cooling system but no backup outside power.

Japan’s Nuclear Regulatory Agency in interviews with Bellona last week raised concerns about the makeshift equipment and is urging the plant to switch them to more permanent arrangement.

The operator still has to remove melted, fatally radioactive fuel from reactors before fully decommissioning the plant, which officials say could take 40 years.

The plant’s command center at the plant suffered a brief power outage before 7 pm on Monday evening. Electricity was quickly restored to the command center but not to equipment pumping water into the fuel pools.

Engineers have worked to stabilize the plant, but years of work lie ahead to fully contain the disaster and tackle its effects. Japan’s Nuclear Regulatory Agency has set a target of 40 years for decommissioning the plant.

Meanwhile, tens of thousands of evacuees remain unable to return home.