Decommissioning plans must wait for stable reactor conditions
The world’s biggest nuclear energy firms are lining up with proposals to clean up a historically huge radioactive mess at the Fukushima, Japan, reactor site. There six reactors in various degrees of damaged condition are presenting new engineering challenges on a daily basis punctuated by earthquake aftershocks and the continuing threat of new tsunamis.
At the same time, the Japanese and U.S. news media are publishing stories about the early stages of the crisis which may partially explain why NRC Chairman Gregory Jaczko issued a call for Americans to evacuate to a distance of 50 miles from the site.
Control of Fukushima reactor Units 1-3 is key with the most urgent priority the need to keep the reactor fuel assemblies covered with water. The reactor pressure vessel for Unit 1 is being filled with nitrogen, an inert gas, that drives out any oxygen which could sustain combustion of free hydrogen. It isn't known if there are plans to do the same with Units 2 & 3.
At the spent fuel pool on top of the badly damaged secondary containment building for Unit 4, a stationary pump truck is pouring 100-200 tons of water a day on the pool. Even at that rate, rapid evaporation is taking place that threatens to uncover the spent fuel assemblies in the pool. Some are quite hot having only recently been removed from the reactor.
The radioactive water from the Unit 4 spent fuel pool spills down to the ground where TEPCO is now setting up measures to try to contain it. The emergency pumping of fresh water to all four reactors will likely continue through June according to utility officials. This process of pumping in cool water and venting radioactive steam is called “feed and bleed.”
Decommissioning rivals may join forces
Two giant nuclear consortium are forming to manage the cleanup of the Fukushima site, remove of all reactor fuel, and eventually make it a much less dangerous place. The first consortium is composed of General Electric and Hitachi with support from Exelon and Bechtel. The second group is led by Toshiba which is partnered with the U.S. branch of Areva, the French state-owned nuclear giant. Babcock & Wilcox and The Shaw Group are part of the Toshiba team.
The cost of decommissioning the six reactors could be as much as $12 billion and take more than a decade to complete. Industry experts agree this won’t be an ordinary job to tearing down a safe and cold reactor. For instance, to remove the spent fuel from Unit 4, a giant superstructure will have to be built around the devastated secondary containment structure to safely load the hot fuel assemblies underwater into special transportation casks.
The job is so big that the two consortium are reported to be having exploratory talks to combine forces. So far TEPCO, the utility that owns the site, hasn't said how it plans to pay for the cleanup. The Japanese government is said to be considering a form of receivership for the Fukushima site which would allow taxpayer funds to cover cleanup costs and pay compensation to people forced to evacuate their homes within the 13 km government defined danger zone around the plants.
The government is expanding the evacuation area working with people in so-called "hot spots" where radioactive cesium ejected from the reactors has been found at levels above the danger limits. The C-137 has a half life of 30 years which may present long term management problems for these hot spots.
Does TEPCO have a plan?
While the longer term plans to clean up the site are forming, it isn’t clear that TEPCO is able to do much more that try to keep the reactors stable on a day-to-day basis. The utility has moved the emergency diesel generators from their original location to one that is 30 meters higher than the sea. The tsunami that swept over the plant site is now said to have been 15 meters high or more than two times the height of the sea wall meant to stop them.
Temperatures inside some of the reactor pressure vessels are still a cause for concern. On April 14 TEPCO reported that Unit 1 had temperatures of over 200 Celsius and that it was believed that 1.65 meters of the 4 meter long fuel assemblies were not covered by water. TEPCO reports little progress in raising the water level there despite 20 days of pumping water into the damaged reactor.
What did the NRC know and when?
U.S. NRC Chairman Gregory Jazcko called the situation at Fukushima “static,” but not “stable.” In testimony April 12 to the Senate Committee on Environment and Public Works. Jaczko said “significant additional problems” could still occur at Fukushima with the first four reactors. Units 5 & 6 are in cold shutdown.
However, the NRC has had to back off from other statements it’s officials have made about conditions at Fukushima. The New York Times reported April 14 that Jaczko said explosions in the secondary containment structures might have been caused by hydrogen from spent fuel pools rather than from exposed fuel assemblies and oxidation of zirconium cladding from inside reactor pressure vessels.
Second, the newspaper reported that Jaczko had said the NRC believed, based on an agency risk assessment, that there was a plausible scenario in which the core in one or more of the reactors had melted through the pressure vessel and made its way into the dry well of the primary containment. It is now thought that is not the case based on the kinds of radioactive releases that are being measured outside the reactor building.
No one has been able to look inside any of the reactors since the earthquake March 11 which leaves these issues open to conjecture.
Third, Jaczko had said the NRC believed that the spent fuel pool for Unit 4 was dry, but there is less evidence now that might have happened and the NRC is reportedly less certain that it was ever the case. This early assessment was said to be the basis for the NRC Chairman’s call to evacuate Americans to a 50 mile radius from the plant. There may, it turns out, be other reasons.
Early delays in U.S. Japan cooperation
Despite the second guessing, Jaczko might have had good reason to assume a worst case scenario for radioactive releases at Fukushima in the first days following the earthquake. According to an April 11 report in the Japanese newspaper Daily Yomiuri, the Japanese government and TEPCO rebuffed early offers of help from the U.S. government even as the reactor crisis became more difficult. And they weren’t sharing information with American counterparts in Japan despite an obvious worsening of conditions based on news media reports.
According to the newspaper, U.S. Assistant Secretary of State Kurt Campbell became alarmed by what the paper calls the “on idle” mode of the Japanese prime minister’s office to unfolding events. Campbell, in a remarkably undiplomatic message, said at the time that if the Japanese government didn’t do more to get the reactors under control, that the U.S. government would call for the mandatory evacuation of all Americans from Japan.
This input from the State Department may have been shared with the White House and NRC’s Jazcko prior to his initial appearance before Congress where he called for the 50 mile evacuation zone for Americans.
Another view is that it may have been a political maneuver to signal to the Japanese that telling U.S. nuclear experts in Japan that "there was no room for them" in the Prime Ministers emergency command center was an unacceptable answer.
We probably won't know the real reasons for some time, but in any case this kind of locking the barn after the horse is gone won't do much to stabilize the reactors.
Status of reactors and control of radioactive water
(NucNet) April 15, 2011 - Water being used to cool the Unit 2 reactor at the Fukushima nuclear plant might be leaking into the trench between the reactor and turbine building, Japan's Nuclear and Industrial Safety Agency (NISA) has said.
The plant's operator, Tokyo Electric Power Company (TEPCO), transferred about 660 tonnes of highly contaminated wastewater from the Unit 2 turbine building installation trench to a turbine condenser on 13 April 2011. The contaminated water needs to be moved because there is a risk it might continue to leak outside the unit's controlled zone and from there flow into the sea.
Contaminated water has also been found in the turbine hall basements of Units 1 and 3, although its level of radioactivity is much lower than the water at Unit 2.
The total amount of water to be removed is estimated at more than 60,000 tonnes, the International Atomic Energy Agency said.
TEPCO plans to transfer contaminated water to the plant's waste processing facility, but the facility has not yet been made leak-proof. The utility says it does not know when it can start removing water from reactors other than Unit 2.
NISA reported that an earthquake that hit Fukushima prefecture on April 13 had an epicenter 75 km from the Fukushima nuclear power plant and 67 km from Fukushima, but no unusual events have been reported at either facility.
Meanwhile, interim analysis of water from the spent fuel pool of Unit 4 at Fukushima-Daiichi shows higher than normal levels of radiation, which suggests some of the fuel assemblies stored there might be damaged.
TEPCO said analysis of samples collected from the pool on 12 April 2011 showed 220 kilobecquerels per litre (kBq/L) of iodine-131, 88 kBq/L of cesium-134 and 93 kBq/L of cesium-137.
The utility also said the water temperature in the unit 4 SFP had risen to about 90 degrees Celsius, significantly higher than the normal temperature range of 20 to 40 degrees Celsius.
To cool the fuel, workers sprayed almost 200 tonnes of water on the SFP for six hours on Wednesday morning.
The condition of spent fuel in the SFPs at Units 1 and 2 is not known, while at unit 3 TEPCO says it suspects there might be some damage.
Update Saturday April 16, 2011
The Japan Times reported fragments of damaged nuclear fuel assemblies have sunk to the bottoms of three reactors at Fukushima. A scenario exists where they could melt through the pressure vessels if emergency water-pumping operations are seriously disrupted, the Atomic Energy Society of Japan said April 15th.
"It will take at least two or three months ... until the situation of fuel rods is stabilized" said Takashi Sawada, vice chairman of the nuclear group.
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