Fukushima watch 2011-04-13

Since yesterday evening Tepco (or its subcontractors or sub-subcontractors) has been pumping highly radioactive water from the pipe and cable ducts under the turbine hall of unit 2 to the condenser storage tank. The presence of this water has been a major obstacle to reactivating cooling pumps or installing a new cooling system. The water has been in contact with damaged fuel rods and is loaded with fission products, with radiation levels exceeding 1000 mSv/hour.

A crack in a concrete wall near the cooling water intake building for unit 2 is being blocked with a steel sheet to stop radioactive water from leaking into the sea.

Yesterday a water sample was taken from the spent fuel pool of unit 4, which will be quantitatively analyzed for various radioactive isotopes to gain information about the state of the more than 1300 fuel rod assemblies in that pool. The spent fuel pool of unit 4 holds the biggest amount of long lived radioactive isotopes such as caesium 137 of all reactor cores and spent fuel pools at Fukushima 1. It has gaping holes in its walls and its roof was blown off in a hydrogen blast early in the nuclear disaster. When the cooling system failed due to a lack of external power after the March 11 quake, the fuel rods overheated and caught fire (it was that fire that prompted me and my family to head out of Japan the week after the quake…).

The last of five Putzmeister concrete pumps took off from Stuttgart/Germany for Japan in a Russian transport plane on Tuesday night. The remote controlled pumps have highly mobile arms 58 to 70 meters in length in 5 or 6 segments that are typically used for pouring concrete in dam or bridge construction, but can also be used for fire fighting. Between May and November 1986, 11 of the pump trucks were used to entomb the stricken unit 4 reactor in Chernobyl.

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Fukushima rated same level as Chernobyl

NISA, the Japanese Nuclear and Industrial Safety Agency has finally raised the Fukushima accident to level 7 (the highest) on the INES scale. Previously, the Chernobyl accident was the only one worldwide ever rated at that level. At the same time NISA stated that the amount of radioactivity released so far was about 10% of the amount released in Chernobyl. Most of the leaked radioactivity is assumed to have come from unit 2, which leaked highly radioactive water into its basement and from there into the sea.

The rating probably does not indicate a recent surge of danger to the public, but reflects a more realistic assessment of the existing data than the previous rating of 5, which would have put it on a level with the Three Mile Island accident in 1979: Only one reactor block suffered a melt down in TMI and the containment remained intact, versus 3 damaged reactor blocks and 4 overheating spent fuel pools in Fukushima and a damaged pressure vessel and containment in at least one unit. According to Gesellschaft für Anlage- und Reaktorsicherheit the revised rating primarily reflects the fact that a lot more than 10,000 terabecquerel (TBq) of Iodine-131 have been released into the atmosphere so far. The release of Iodine-131 and Cesium-137 lies somewhere between 370,000 TBq and 630,000 TBq.

US NRC assessment of Fukushima 1

The March 26 NRC assessment of the situation in the six units at Fukushima one makes for interesting reading. It suggests that water flow inside the base of the reactor pressure vessels is severely restricted by melted fuel and salt buildup. Water injected into unit 1 apparently does not contain any boron to guard against criticality. The seals in the recirculation pumps of units 1, 2 and 3 are assumed to have failed, effectively preventing the reactor cores from being filled high enough to cover all fuel, even if sufficient water could get past the melted fuel and salt crust: If the water rises any higher, it will simply leak out of the pumps. The primary containments of units 2 and 3 are assumed to be damaged. Spent fuel may have been ejected “up to 1 mile” from the spent fuel pools of unit 4 or unit 3 in a hydrogen explosion

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Fukushima watch 2011-04-11

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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Magnitude 7.1 quake, more power trouble

Today a magnitude 7.1 quake that registered an upper 6 on the Japanese scale near the epicentre in Miyagi prefecture exposed how vulnerable nuclear sites other than the wrecked plant Fukushima 1 still are.

The nuclear reprocessing plant and high level waste storage site in Rokkasho village, Aomori prefecture was without external power – again. Luckily its diesel backup generators are providing emergency power, as they already did after the site lost grid power on March 11.

Two of the three grid connections at Onagawa nuclear power station north of Fukushima are down. Backup diesels are working.

The Higashidori nuclear power station is also running on diesel power right now.

Luckily none of these sites got hit by tsunamis this time, but after the core damage and massive radiation release at Fukushima 1 following a loss of grid power and failed backup generators, any incident in which nuclear sites are only one or two failed diesel engines away from disaster will make a lot of people very nervous, especially as Fukushima 1 is still not secured almost four weeks later.

UPDATE 2011-04-08:

Grid power was restored at Higashidori at 03:30 JST on Friday, 2011-04-08. Grid power was restored at Onagawa the same morning.

Due to the loss of grid power the spent fuel pool cooling system failed for 20-80 minutes at Onagawa and Higashidori, which was not long enough for temperature to rise significantly.

Fukushima watch 2011-04-06

Tepco is now discussing installing a new cooling system in units 1, 2 and 3 of wrecked nuclear power station Fukushima 1 (Fukushima Daiichi), according to a report in Sankei Shimbun. Fresh water will be circulated around the reactor core using new electric pumps running on grid power and cooled in a new heat exchanger using sea water. Two of the five pipes leading into the reactor will be used for that purpose. The heat exchanger and pumps will be located further from the reactor building, exposing technicians to less radioactivity then inside the existing turbine hall. The company expects to be able to get this system working within about one month.

If the plan is successfully implemented, it would be a big step towards regaining control over the ruined reactors. Reestablishing some working cooling circuit is necessary to avoid having to entomb the reactor buildings in concrete, which would forever prevent a removal of the highly radioactive core from the tsunami-exposed site at the Northeast Japanese coast line.

Water leak plugged

The company also reports to have stopped the highly radiaocative water leaks at unit 2 using water glass (a watery solution of sodium silicate). Two previous efforts involving concrete and a water absorbent polymer had failed.

Meanwhile a “megafloat” previously used as a floating island for anglers is being converted at a shipyard in Yokohama for use as a water storage tank and will be towed to Fukushima around April 16. The 146 m long and 46 m wide vessel will be able to hold up to 10,000,000 liters of contaminated water from the reactor site.

Fear of hydrogen explosions

Tepco is currently injecting nitrogen gas into the unit 1 reactor building to dilute a potential buildup of hydrogen gas from overheated fuel elements. It is also considering nitrogen injections into units 2 and 3.

As it is suspected that hydrogen gas is accumulated inside reactor containment vessel, we are considering injection of nitrogen gas inside the vessel.
(Tepco press release)

Hydrogen explosions were responsible for severe damage to units 1, 3 and 4 in the first days after the cooling systems failed. The explosions occurred when gas had to be vented from inside the containment after pressure increased to twice the design limit of the containment vessel. Other Boiling Water Reactors (BWRs) based on GE designs had been retrofitted during the 1980s with hydrogen burners that ignite leaked hydrogen before it has time to accumulate and mix with air in large quantities, but Tepco reportedly considered this retrofit an unnecessary expense.

Fukushima killed “oru denka”

Tepco announced halting its commercial push for “oru denka” (Japanese: オール電化, “all electric power”) households. Sales of “orudenka” goods such as heat pumps will be suspended. Until right before the earthquake and loss of 10,000 Megawatts of electric generation capacity in Fukushima and elsewhere, the company had been luring consumers away from using natural gas or propane for heating, cooking and hot water production and instead relying on Tepco’s now overloaded grid for all domestic power needs. The “eco cute” heat pumps previously sold by Tepco now compete for scarce power while Tepco has to struggle to bring replacement capacity online as quickly as possible to end rolling blackouts that are badly hitting the economy and are set to continue until the end of April. Depending on how quickly alternative power sources can be brought online, more severe power cuts are possible in the summer, the usual peak time for power load when most of Japan switches on air conditioners to escape near tropical humid heat. This summer may be the first in decades without widespread availability of air conditioning in Japan.

Sales of “orudenka” equipment is continuing at Kansai Electric Power Company and Chubu Electric Power Company, two companies not affected by the quake, but the latter has suspended TV advertising for the products.

Tepco has a near monopoly for electricity in Eastern Japan. It can import a maximum of 600 MW through an undersea cable from Hokkaido and a maximum of 1000 MW from Western Japan via DC couplings (Western Japan uses 60 Hz AC vs 50 Hz in Eastern Japan, so it takes more than simple lines and transformers to exchange power between those two grids). Until now this limited exchange of power had worked to Tepco’s advantage, as it kept out competition from suppliers in Western Japan, but Tepco’s customers are now paying the price for it, quite literally, as Tepco is raising their prices to encourage power savings.

Tepco will urgently have to import and start up gas turbines to replace lost capacity. GE in the US has announced it will ship gas turbines to Japan. So far restrictions on power usage are expected to last until summer 2012 in the world’s third biggest economy.