TEPCO has released radiation figures for the 2700 t of water in the basement of unit 1 of the Fukushima 1 nuclear power plant:

Tokyo Electric Power Co. <9501> said Monday that the amounts of radioactive materials in water at a reactor building of the Fukushima No. 1 nuclear power plant were about 10,000 times the normal levels for water inside a nuclear reactor.
The water, recently found in the basement of the No. 1 reactor building of the nuclear power plant, contained 30,000 becquerels of iodine-131 per cubic centimeter, 2.5 million becquerels of cesium-134 and 2.9 million becquerels of cesium-137.

(Jiji Press, 2011-05-30)

A total of 2700 t of water are estimated to be in the basement. That works out as 6.75E15 Bq = 6.75 PBq of Cs-134 and 7.83 PBq of Cs-137. For comparison, the total radioactive release from Chernobyl is estimated at 48 PBq of Cs-134 and 89 PBq of Cs-137. That means the water in the basement of unit 1 alone contains about one tenth of all the radioactivity released into the environment by the Chernobyl disaster. When the accident started, we were told that “Fukushima is no Chernobyl” because unlike the Soviet reactor its reactors had containments. Unfortunately, they didn’t work. All that radioactivity mentioned above is already outside of the containment, in a place that was never designed to be flooded with thousands of tons of radioactive water.

Units 2 and 3 are assumed to be in equally bad shape as unit 1, as both suffered a meltdown and neither of those units’ containments still hold any pressure. All three units have flooded basements. Water in a trench near unit 2 was measured at 2 million becquerels of cesium-137 per cubic centimeters on March 30, quite similar in contamination to the unit 1 basement.

When people first entered unit 1 again on May 13, the water level in the basement of unit was reported to be 4.2 m. Two weeks later it is 4.6 m and the storage tanks at the reactor site are almost full. Very soon something needs to happen about that water. To complicate things even more, June is the rainy season in Japan, when typhoons can dump huge amounts of water onto Japan.

The water treatment plant built by Areva is expected to start operating around the middle of this month. TEPCO quoted the cost of decontaminating water with this system at 210,000 yen per ton (about US$2600). It intends to decontaminate 250,000 tons of water by the middle of January 2012, for a total cost of 53.1 billion yen (about US$650 million).

Currently 5 cubic meters per hour (m3/h) are being pumped into unit 1 for cooling, 4.9 m3/h into unit 2 and 12.5 m3/h into unit 3 (which is still overheating). That’s about 550 tons of water per day, which is assumed to leak into the basements of the three reactors, loaded with dissolved radioactive waste from damaged fuel rods. If cooling water feeds continue at current rates, there will be another 8,000 tons of highly radioactive water to be taken care of by the time AREVA’s treatment plant starts up — that is, if all goes according to plan…

A “mega-float” that has been towed to the site for storing and transporting radioactive water can probably only be used for decontaminated water (i.e. with 99.9% of the radioactivity removed), otherwise radiation would be too high to handle. Contaminated water being pumped from the basement of the turbine buildings to storage tanks gives off so much radiation that the piping is covered up with lead wool wherever people have to walk over it and is cordoned off with security tape everywhere else.

If a water pump fails and it has to be replaced, someone will have to disconnect and reconnect pipes to pumps that carry billions of becquerels of radioactivity per liter of water. There will be leaks and puddles and spills. This is not how things would be done if there was any choice.

Fukushima 1 may not make the headlines of the world media much any more, but the situation there is still nightmarish. It’s not the TEPCO managers who are paying for their company’s gross negligence, but unnamed workers of hired subcontractors who are risking their lives and health.

The cleanup and compensation for thousands who lost their homes and incomes through the fallout far exceeds TEPCO’s ability to pay, so tax payers will be forced to pay the bill, yet the government chose not to force TEPCO into bankruptcy. Its share price may have fallen, but its stock did not become worthless as say General Motors in the US car industry bail-out, or perhaps the crops grown by farmers nearby or the now deserted homes owned by families around the plant. TEPCO’s well-connected shareholders were effectively bailed out by the government at our expense.

See also:

• Backroom deal saves Tepco from meltdow (BusinessDay, 2011-05-23)

A failure of a sea water pump at unit 5 of the Fukushima 1 Nuclear Power Plant demonstrated the still volatile situation at the reactors. It allowed water temperatures inside the reactor (which had officially been in “cold shutdown” since March 20) to climb as high as 93 degrees C again before a replacement pump restored the water flow and allowed temperatures to drop again. Unlike the heavily damaged units 1 through 3, units 5 and 6 (along with unit 4) had been shut down for maintenance when the quake and tsunami hit. Due to their slightly higher elevation they escaped the worst of the tsunami. A single backup diesel generator for units 5 and 6 survived. So far TEPCO has not announced any plans yet to permanently decommissioning the two units, although the government of Prime Minister Kan pushed for that.

The failed temporary pump provides cool sea water to the heat exchanger of the Residual Heat Removal System (RHRS). TEPCO reports:

At 9:14 pm on May 28th, we found that one temporary residual heat removal system seawater pump of Unit 5 stopped. At 8:12 am on May 29th, replacement work to the spare pump started. After finishing the replacement work, we started the pump at 12:31 pm, and restarted cooling from 12:49 pm.

The RHRS is a cooling system that is used whenever the reactor does not drive a steam turbine, where heat is removed via the attached condenser unit. It is also used to cool the water in the spent fuel pools. Both a loaded reactor core and fuel elements in the pool produce decay heat that needs to be removed for months and years after a shutdown. Both the condenser and the RHRS require a steady flow of seawater to carry away heat.

According to a diagram at the NISA website Units 5 and 6 had been using a temporary pump near their regular cooling water intake channels, which suggests that the normal pumps of the RHRS had been damaged in the tsunami. TEPCO has now set up a new pump (as well as a spare next to it) halfway between the cooling water intake channel and the RHRS and cooling water circulation pumps. For the last two months there had been no spare in place.

Unit 1 dry well radiation levels

There have been some online discussions about spiking radiation level figures in the dry well (primary containment) of unit 1. Here is a graph from atmc.jp:

The original data for this graph are figures published by TEPCO/NISA of the CAMS radiation monitor readings for the three units. Until May 25 this data was available in daily updates on the NISA website under “Seismic Damage Information（the nnnth Release）(As of hh:mm May dd, 2011″, document “Fukushima Dai-ichi Nuclear Power Station Major Parameters of the Plant (As of h:mm, May dd)”. Since then NISA no longer seems to publish those figures. It can still be found vi the “Status of Fukushima Daiichi and Fukushima Daini Nuclear Power Stations after Great East Japan Earthquake” page on the TEPCO website though: Look for “The parameters related to the plants in Fukushima Daiichi Nuclear Power Station”, which has a link to the latest document and a ling to an archive page with previous daily data sets. “CAMS radiation monitor” has entries for D/W A and B, S/C aA and B. The D/W B sensor is the one in the above chart. Strangely, the numbers on the atmc.jp do not always match the data on the NISA/TEPCO sites:

5/18: NISA: 25.4 Sv/h / atmc.jp: 45.4
5/19: NISA: 36.3 Sv/h / atmc.jp: 36.3
5/20: NISA: 46.5 Sv/h / atmc.jp: 46.5
5/21: NISA: 36.2 Sv/h / atmc.jp: 36.2
5/22: NISA: 196 Sv/h / atmc.jp: 196
5/23: NISA: 33.1 Sv/h / atmc.jp: 201
5/24: NISA: 30.5 Sv/h / atmc.jp: 192
5/25: NISA: 204 Sv/h / atmc.jp: 215
5/26: TEPCO: 39.3 Sv/h / atmc.jp: 43.7
5/27: TEPCO: 53.5 Sv/h / atmc.jp: 63.8
5/28: TEPCO: 215 Sv/h / atmc.jp: 215
5/29: TEPCO: 225 Sv/h / atmc.jp: 225
5/30: TEPCO: 41.8 Sv/h / atmc.jp: n/a

The source of the discrepancy between the two sources is unclear as ultimately TEPCO must be the only source of data on the reactor.

Some people have speculated that the sudden increase in the graph indicates that a large amount of fuel melted through the pressure vessel and leaked onto the floor of the dry well. However, that would not explain why the values significantly dropped again and then shot back up again.

TEPCO states that they think the radiation sensors are malfunctioning. I suspect their explanation is the correct one, but how reassuring is that?

Trying to manage a badly damaged nuclear reactor (actually, 3 of them!) and the 4 loaded spent fuel pools next to them with broken instruments whose readings can not be trusted any more is a bit like trying to drive a car without a speedometer and with a shattered windscreen that prevents you from seeing the road, going only by the directions of your passenger who sticks his head out of the window to keep you on the road.

The New York Times reports that the reactors at the Fukushima 1 nuclear power plant were equipped with an improved system for venting steam in an emergency, but it failed to work. Originally it had been reported that TEPCO did not retrofit the units that had been online since 1970s with the new designs introduced in the US in the 1980s. However, it appears to have done so between 1998 and 2001.

The problem was, the improved system relied on the same sources of electricity to operate valves as the cooling system, so when the cooling system stopped working as diesel generators failed and dangerous levels of steam pressures built up, the venting system designed to protect the containment wasn’t working properly either. Instead of one system protecting the public if the other system failed, both had a single point of failure, their dependence on diesel generators in the flooded turbine hall basements.

The executives did not give the order to begin venting until Saturday — more than 17 hours after the tsunami struck and six hours after the government order to vent.

As workers scrambled to comply with their new directive, they faced a cascading series of complications.

The venting system is designed to be operated from the control room, but operators’ attempts to turn it on failed, most likely because the power to open a critical valve was out. The valves are designed so they can also be opened manually, but by that time, workers found radiation levels near the venting system at Reactor No. 1 were already too high to approach, according to Tokyo Electric’s records from the accident’s early days.

At Reactor No. 2, workers tried to manually open the safety valves, but pressure did not fall inside the reactor, making it unclear whether venting was successful, the records show. At Reactor No. 3, workers tried seven times to manually open the valve, but it kept closing, the records say.

The results of the failed venting were disastrous.

Reactor No. 1 exploded first, on Saturday, the day after the earthquake. Reactor No. 3 came next, on Monday. And No. 2 exploded early Tuesday morning.

The venting system could also have been damaged by the earthquake.

According to the NYT, the new venting system bypasses filters that hold back much of the radioactivity.

When TEPCO was talking about venting the reactors, before the spectacular hydrogen explosions, they reassured the public that the release of gas would be “filtered”. Either they were misleading the public, or they were talking about the old venting system, which was suspected of not being able to cope with the pressure of an emergency release, which is the very reason the new system had been introduced.

See also:

• Reactor Vents That Failed in Japan Are Used in U.S. (New York Times, 2011-05-17)

Data released by TEPCO on May 16 shows that apparently the isolation condenser, a cooling system that is supposed to protect the reactor after a shutdown, was manually shut down in unit 1 within 10 minutes of the earthquake.

When the quake hit at 14:46 on 2011-03-11, the power station lost its grid connection. Diesel generators sprang into life to provide backup power for the Residual Heat Removal System (RHR). Around 15:00 someone manually shut down the isolation condensor. About half an hour later tsunami hit the station. Within minutes the diesel generators failed and the RHR stopped. At that point the battery-operated pumps for the isolation condenser were the only system still able to remove heat from the reactor core, but the valve for this system had been closed by operators. From that point onwards the reactor core was entirely without cooling. Records show that at 18:10 the valve was open again. At 18:25 it was closed again and 21:30 it was open again. The isolation condenser finally failed at 01:48 on 2011-03-12, perhaps because its batteries ran out.

According to the AREVA presentation from 2011-04-07, the isolation condenser in unit 1 stopped at 16:36 on 2011-03-11, but perhaps that was based on incomplete or bad data from TEPCO.

See also:

• Worker error may have led to meltdown (Japan Times, 2011-05-17)

After pumping increased amounts of water into the reactor core of Fukushima 1 unit 1 with the aim of bringing it to a “cold shutdown”, TEPCO had to conclude that the water level in both the reactor core and the containment is much lower than expected and their plan appears not to be succeeding.

Previously it was believed that the lower half of the fuel rods in the reactor pressure vessel (RPV) was covered in water. Now it appears that part of the RPV is dry and the fuel rods (or what’s left of them) are fully exposed. However, due to the damage to the rods much of the uranium pellets inside may already have spilled into the bottom portion of the RPV and may thus receive some cooling after all. TEPCO had only recently revised its estimate of core damage for unit 1 down from 70% to 55%.

The plan to provide ouside cooling to the RPV by flooding the dry well of the containment surrounding it with enough water to raise the water level to above the top of the fuel rods has not worked yet. Even after pumping more than 10,000 m3 of water, the water level in the 7,400 m3 containment is still below half, not even reaching the bottom of the RPV, let alone its top.

If the water level doesn’t rise further because of leaks then it seems quite unlikely that it will be possible to repair those leaks using manual labour, especially at dose levels of 10 millisievert and more per hour. Even when it looked like the plan might work for unit 1, it was questionable if the same procedure could then be applied to unit 2 or 3, which were already assumed to have a leaky containment.

TEPCO has not yet discussed any alternative plan if flooding the containment won’t work for some or all of the units.

See also:

• Tepco: Leak Suggests Severe Damage (WSJ, 2011-05-12)