NHK reports that Tepco is using remote-controlled bulldozers and power shovels for clearing rubble around the wrecked reactor. While it’s good news that Tepco finally can perform some cleanup work without putting workers at risk, the bad news is how necessary such equipment may be. The New York Times reported on April 5 about a confidential document prepared by the US Nuclear Regulatory Commission:
The document also suggests that fragments or particles of nuclear fuel from spent fuel pools above the reactors were blown “up to one mile from the units,” and that pieces of highly radioactive material fell between two units and had to be “bulldozed over,” presumably to protect workers at the site. The ejection of nuclear material, which may have occurred during one of the earlier hydrogen explosions, may indicate more extensive damage to the extremely radioactive pools than previously disclosed.
There was more nuclear fuel in the spent fuel pools of units 1-4 than there is in the reactor cores of these units.
Today I read the article “What Caused the High Cl-38 Radioactivity in the Fukushima Daiichi Reactor #1?” by F. Dalnoki-Veress, which discusses the possibility that a chain reaction could have happened in Fukushima 1 unit 1 even after the reactor had been shut down, based on the presence of chlorine isotope Cl-38.
Another quake knocks out pumps at Fukushima 1
Today at 17:16 JST a magnitude 7.1 quake with its epicenter close to the Fukushima reactor sites caused another loss of grid power, like during 9.0 quake one month earlier. Since the backup diesel generators had been destroyed by the tsunami on 2011-03-11 the electric pumps used for water injection for core cooling in the wrecked reactors stopped immediately this time. They didn’t start up again until 50 minutes later, during which time no water was being pumped into the reactor.
This raises the question of what would have happened if the reactor had stayed off the grid for days. After the big quake it took about two weeks before electric pumps could be used for cooling agin. Are there no mobile diesel generators available on site yet or if there are, is there no way to connect them to the temporary electric pumps used for water injection?
Tsunami was 15 meter high at Fukushima 1
More information on the tsunami on 2011-03-11: According to Tepco the devastating wave that hit the power plant was 15 meter high, flooding the surroundings of the reactors including outside the turbine halls up to a height of 5 meters.
Diesel problems at Higashidori nuclear power plant
After the 7.1 quake on 2011-04-07 at 23:23 JST that knocked out the grid supply to a shut down reactor at Higashidori, one of the emergency diesels was stopped due to an oil leak at 2011-04-08 at 14:06 JST. By that time only one of the three grid connections had been restored (at 03:30 JST). The other two connections came back online at 14:59 JST. The emergency diesel was repaired by the following morning, 07:00 JST.
What’s the recovery plan?
Currently 6000 liters of fresh water per hour are being injected into unit 1. Units 2 and 3 which contain more fuel elements are receiving 7000 liters per hour. There is no working cooling cycle. All this water must either be released somewhere as steam or leaking as liquid or building up inside the containment. If it escapes as steam or leaks out through cracks in the containment or from pipes it will contain highly radioactive fission products from the damaged fuel rods. While you can read about how much water is being injected, nobody seems to want to talk about where and how this water is coming out again and in what quantities.
As mentioned before in this blog, Sankei Shimbun has reported about a plan to build new cooling circuits for units 1, 2 and 3 using new pumps and heat exchanges located far enough away from the reactor blocks and their spent fuel pools to not expose operators to high levels of radiation. Tepco expects this work to take about a month, but it probably hinges on first clearing highly radioactive water from the basement of the turbine hall and associated tunnels. Considering the ongoing major afterquakes and the high levels of radioactivity in the reactor core to be cooled, this project is going to be extremely challenging.
There has been talk about covering the reactors in sheets with filters for emissions, which could happen around June. One would expect radioactivity levels under those sheets to be very high, considering that it will probably trap steam from the spent fuel pools, some of which hold damaged spent fuel rods. Basically, most of the radioactivity now being carried out over the Pacific by winds (or spread across Northeast Japan or the Kanto area, depending on the direction of the winds) should then stay behind, right outside the building. I suspect the sheets or tents won’t be put up until there is some kind of closed circuit cooling system in place, to minimize water vapor trapped under the sheets.
Toshiba has submitted a plan for decommissioning and cleaning up the reactors. The likely price tab will run into billions of dollars, considering experience from Three Mile Island, Chernobyl and the Vermont Yankee reactor.
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