Category Archives: nuclear power

Tepco drowning in radioactive water

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A recent leak of 300 tons of highly radioactive water at Fukushima No. 1 has highlighted the long term problems that Tokyo Electric Power Co. (Tepco) is facing in its struggle to manage the crisis at the wrecked nuclear power station (see Japan Times, 2013-08-21). One massive steel tank had been leaking as much as 10 tons of water a day for a month before the leak was noticed. The water level in the tank dropped by 3 m before anyone noticed. It is not clear yet how the water is escaping.

The water in the tank has been used for cooling the melted reactor cores. Consequently it is highly radioactive from strontium, cesium and tritium. At a distance of 50 cm, as much as 100 millisieverts per hour (mSv/h) were measured. That means a nuclear worker there would absorb as much radiation in one hour as is legally permitted over a total of 5 years.

You might think that with a witches’ brew like that on its hands, Tepco would take every possible precaution to prevent leaks and to monitor fluid levels. Tepco uses both welded steel tanks and temporary tanks for storing contaminated water at Fukushima No. 1. Welded tanks are supposed to be stronger and more leak proof, whereas temporary tanks can be bolted together quickly from sheet metal and plastic. About one third of the over 1000 tanks at Fukushima No. 1 are temporary tanks, including the one that recently leaked. Tanks of this type have been used at the site since December 2011 and they are supposed to last five years before needing repair or replacement. So far 4 of these tanks have leaked, yet Tepco is planning to install even more temporary tanks for storing water. I guess they must be cheaper.

I am curious why the leaks were not detected sooner. Are there no monitoring devices installed that can automatically report water levels?

Tepco is planning to treat the water in the tanks with its ALPS filtering system, which can remove radioactive cesium and strontium from the water, but not tritium. It was meant to start operating this month, but after problems it is now expected to not resume operation until December.

Even after treatment, Tepco will have a water problem. Any water pumped from the turbine halls that has been in contact with the reactor basements has elevated levels of radioactive tritium. No chemical removal system exists for tritium, as it’s an isotope of hydrogen, one of the two elements that make up water. Tepco can not simply evaporate water from those tanks to reduce volume and concentrate contaminants into a smaller volume, as the tritium would be released with water vapour and come down as rain again elsewhere. So what is it going to do? Release it into the atmosphere slowly? Dilute it with sea water? Or store hundreds of thousands of tons of water for hundreds of years? Neither alternative seems very appealing.

Japan without nuclear power

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Since last weekend, Japan is without a single nuclear power station feeding power into the grid, the first time in 42 years. All 50 nuclear power stations are currently off-line (this count does not include the 4 wrecked reactors in Fukushima I, which are no longer officially counted — it used to be 54 nuclear power stations).

Some of these power stations were shut down because of problems after the March 11, 2011 earthquake and tsunami. Others were taken offline one by one for routine inspections and maintenance but have not been started up again, which would only happen with the consent of nearby local governments. That consent has not been forthcoming.

Electrical utilities and the government are raising concerns about a power shortage when the summer heat sets in, which usually results in peak usage for air conditioners. Critics of nuclear power see an opportunity for a quick exit from nuclear power. Others are concerned that if the government rushes to bring power stations back online before the summer without safety upgrades and a change in the regulatory regime, a unique chance to prevent the next nuclear disaster will be squandered. If upgrades and reforms don’t happen when the memory of Fukushima is still relatively fresh, what’s the chance of it happening a few years down the road?

The utility companies are facing high costs from buying more fossil fuels for gas and oil fired thermal power stations to cover the demand; restarting the nuclear power stations would keep those costs in check. But that is only part of the reason they are keen on a restart. The sooner they can return to the pre-Fukushima state of power generation, the less leverage governments and the public have for making them accept new rules, such as retrofitting filters for emergency venting systems or a permanent shutdown of the oldest and seismically most vulnerable stations. Because of this it’s in the interest of the utilities to paint as bleak a picture of the situation as possible. Japan would be smart to proceed cautiously and not miss a unique chance to fix the problems that are the root cause of the Fukushima disaster and of disasters still waiting to happen.

Fukushima “cold shutdown” announcement up to 25 years too soon

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The Japanese government has announced that the wrecked Fukushima Daiichi power station has reached a “cold shutdown”. The BBC quotes Prime Minister Noda:

“The nuclear reactors have reached a state of cold shutdown and therefore we can now confirm that we have come to the end of the accident phase of the actual reactors.”

It is meaningless to still use the term “cold shutdown” for a reactor in which the fuel rods and containment vessel have lost their integrity. It’s like saying the bleeding has been stopped in an injured patient who had actually bled to death.

The normal definition of “cold shutdown” is when, after the chain reaction has been stopped, decay heat inside the fuel rods has been reduced enough that the cooling water temperature finally drops below 100 C. This means the cooling water no longer boils at atmospheric pressure, making it possible to open the pressure vessel cap and remove the fuel rods from the reactor core into the spent fuel pool. After that the reactor core no longer needs to be cooled.

Only units 4, 5 and 6 have reached a genuine cold shutdown. Unit 4 had been shut down for repairs in 2010 and did not contain any fuel at the time of the accident. In units 5 and 6 a single emergency diesel survived the tsunami and prevented a meltdown there.

In units 1, 2 and 3 of Fukushima Daiichi the fuel melted, dropped to the bottom of the reactor pressure vessel and penetrated it. The melted rods then dripped down onto the concrete floor of the containment vessel and are assumed to have partly melted into the concrete up to an unknown depth.

While in a regular cold shutdown fuel can be unloaded within weeks, the Japanese government estimates it may take as much as 25 years before all fuel will have been removed. The technology to remove fuel in the state it’s in now does not even exist yet and will have to be developed from scratch. Even the most optimistic schedule puts it at 5 years, during which time the reactors will have to be cooled 24 hours a day, with no new earthquakes damaging them or knocking out cooling again, no major corrosion problems, no clogged water pipes, etc.

In my opinion, the announcement of a “cold shutdown” at Fukushima Daiichi is greatly exaggerated and was made mainly for political purposes. More than anything, it is meant to provide political cover for restarting other idled nuclear power stations during the coming year.

Radiation maps for Eastern Japan

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The Japanese government has released updated radiation maps for Eastern Japan from its helicopter survey. The maps now cover prefectures as far west as Gifu and as far north as Iwate and Akita. Previously there was map data only for Tokohoku (excluding Aomori) and the Kanto area. The PDF can be downloaded here.

The previous set of maps documented caesium contamination and background radiation levels in Fukushima, Tochigi, Miyagi, Ibaraki, Chiba, Saitama, Tokyo and Kanagawa. The latest set adds maps for Iwate, Shizuoka, Nagano, Yamanashi, Gifu and Toyama. Akita, Yamagata and Niigata have also been surveyed and are shown on the overview map.

The most heavily contaminated areas are in the eastern half of Fukushima prefecture, within about 80 km of the wrecked nuclear power stations. The southern part of Miyagi to the north and the northern part of Ibaraki to the south also took a hit.

A major radioactive plume moved south-west from Fukushima, polluting the northern half of Tochigi and the northern and western part of Gunma. A separate plume reached the southern part of Ibaraki, the north-west of Chiba and the eastern part of Tokyo.

There is also some caesium in the mountainous far west of Tokyo and Saitama that extended from Tochigi, but most of Saitama, Tokyo and Kanagawa seem relatively OK, as are Shizuoka, Yamanashi, Nagano, Gifu, Tokyama, Niigata, Yamagata and Akita. There is some fallout in a strip from southern Iwate to northern Miyagi, while central Miyagi and the rest of Iwate look clean. There is no published data for Aomori and Hokkaido yet, but based on the distance and the absence of significant pollution in Akita and adjacent parts of Iwate they will probably be fine.

The maps only give the overall picture, as there may be local hotspots in areas that are relatively clean overall, based on rainfall and wind patterns as well as soil and vegetation that can retain more or less fallout.

Update 2011-12-06:
The ministry has also published radiation maps for Aichi, Aomori, Ishikawa and Fukui prefecture.

How (not) to decontaminate Japan

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An article in Japan Times (2011-11-09, “Scrub homes, denude trees to wash cesium fears away”) provided advice on how to decontaminate areas affected by nuclear fallout, such as in Fukushima, Tochigi and northern Chiba prefecture. Most of the advice is sound, but some is downright alarming:

As for trees, it’s best to remove all their leaves because of the likelyhood they contain large amounts of cesium, Higaki [of University of Tokyo] said.
(…)
What should you do with the soil and leaves?
(…)
Leaves and weeds can be disposed of as burnable garbage, a Fukushima official said.

So let me get this right: you should collect all those leaves because they contain so much radioactive cesium (cesium 134 has a half life of 2 years and cesium 137 of 29 years). And then, when you have all that cesium in plastic garbage bags, you have it sent to the local garbage incinerator, so the carefully collected cesium gets spread over the whole neighbourhood again via the incinerator smokestack. That makes no sense at all.

My Terra-P dosimeter (MKS-05) by Ecotest

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Yesterday my geiger counter arrived here in Japan. It is a Terra-P dosimeter made by Ecotest, a company based in L’viv/Ukraine, about 300 km west of Chernobyl.

I bought the device on eBay from a supplier in Australia for US$399 including shipping. It arrived within 9 days and seems to work well. Although the buttons on my Terra-P are labelled in Cyrillic (either Russian or Ukrainian) and so is the manual, English manuals for it are easy to find online, so that’s not really a problem.

The Terra-P is a consumer grade dosimeter, so it’s not quite as versatile or as precise as professional devices costing $1000 or more, but it covers the basics very well. Its power source are two AAA-batteries, accessible via a lid at the back of the unit, which are easy to replace. It measures gamma rays and is suitable for checking for caesium contamination.

The user interface consists of an LCD, two buttons and speaker. One push of the right hand button (“режим” = mode) switches the dosimeter on and puts it into the measuring mode. The display switches to a microsievert per hour (µSv/h) readout. For the first 70 seconds the resulting number blinks, as it averages the dose over that period and the number gradually becomes more meaningful. After the initial sampling period, the number displayed will always be the average of the last 70 seconds, so you can move it from location to location and will get a decent result provided you wait for about a minute.

After several minutes the device enters power save mode, in which it continues counting radioactive decays, but the LCD is off and less power is used. To turn it off completely when it’s active, push the mode button once more and then push and hold it for four seconds, until the LCD blanks.

The Terra-P also has a user-settable alarm threshold (default: 0.30 µSv/h) and a clock mode. The built-in speaker usually makes one click for every gamma photon detected and sounds an alarm if the radiation exceeds the alarm threshold.

Checking my home after unpacking the device, I found the radiation level was a little higher than the 0.055 µSv/h reported for Tokyo by the local government, but still somewhat lower than the 0.10 µSv/h in my home town in Germany. On the other hand, I was relieved to see the wooden deck outside our living room was no more radioactive than inside the house. As expected, the gutters at the edge of the road, where rain water drains into the sewers, was more radioactive, with about 0.20 µSv/h, which is still far from alarming.

See also:

Radiation map of Japan

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The Japanese government has published online map data about radiation levels in Eastern Japan. You can zoom in and out, scroll around and select data from:

  • Background radiation in microsievert per hour
  • Contamination by caesium 134 and 137 combined (Cs-134+Cs-137) in becquerel per square metre
  • Contamination by caesium 134 (Cs-134) in becquerel per square metre
  • Contamination by caesium 137 (Cs-137) in becquerel per square metre

The data was collected via helicopter flights carrying instruments that detect gamma radiation of different energy spectrums, allowing a breakdown by isotopes causing it.

There are the following data sets:

  • April 29
  • May 26
  • July 2
  • Miyagi prefecture, July 2
  • Tochigi prefecture, July 16
  • Ibaraki prefecture, August 2
  • Chiba and Saitama prefecture, September 12
  • Tokyo and Kanagawa prefecture, September 18

Click on this link:

either the online maps or download PDF files of the maps and click on “同意する” (“I do agree”, the left button) to get access.

The government is planning to extend the radiation survey to the whole of Japan, not just within about 250 km of the wrecked reactors as is currently the case.

See also:

Tepco’s unfiltered vent path

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On August 13, 2011 I wrote about TEPCO not adding filters to their reactors even decades after Sweden did. Since the, on August 16, 2011, Tepco defended not having any kind of filters in the so-called “hardended vent” path between the containment and the exhaust stack:

Corrections and Clarification of a news report program, “ETV Special” by NHK, broadcasted on August 14

August 16, 2011
Tokyo Electric Power Company
NHK TV program regarding Fukushima Daiichi Nuclear Power Station reported contents that are incorrect and could cause misunderstandings. We hereby provide facts below.
(…)
3. Claim on the PCV ventilation has no filtration
In the program, it was mentioned several times that there were no filters in the primary containment vessel ventilation line. However, boiling water reactors that we operate use “wetwell vent”, which has scrubbing effect to mitigate emission of radioactive materials at the comparative level to the filters. That is to say, in principle, our venting procedure uses the water in the suppression chamber as filteration and we have prepared and added the necessary equipment and procedures for accident management measures.

Tepco’s reactors have a “Standby Gas Treatment System” for filtering gases released into the atmosphere. This system is claimed to be at least 97% effective in unit 1 and at lest 99.9% effective in units 2 and 3. However, it can’t be used for venting high pressure gas from the drywell or wetwell (the containment) in emergencies. In the above press release Tepco defends its decision by claiming that the water pool in the suppression chamber (wetwell) is as effective as some other kind of filter system that it could have had installed when adding the hardended vent path in 1999-2001.

This claim is disingenuous. The FILTRA system installed at the Swedish Barsebäck nuclear power station was in addition to any filtration provided by the wetwell pool, not in place of it. Barsebäck had boiling water reactors like in Fukushima (the plant has since been decommissioned).

Furthermore, it’s not clear how effective the filter effect of the wetwell on its own really is. A US report from 1988 entitled “Filtered venting considerations in the United States” writes:

Within the United States, the only commercial reactors approved to vent during severe accidents are boiling water reactors having water suppression pools. The pool serves to scrub and retain radionuclides. The degree of effectiveness has generated some debate within the technical comnunity. The decontaminatlon factor (DF) associated with suppression pool scrubbing can range anywhere from one (no scrubbing) to well over 1000 (99.9 % effective). This wide band is a function of the accident scenario and composition of the fission products, the pathway to the pool (through spargers, downcomers, etc.), and the conditions in the pool itself. Conservative DF values of five for scrubbing in MARK I suppression pools, and 10 for MARK II and MARK III suppression pools have recently been proposed for licensing review purposes. These factors, of course, exclude considerations of noble gases, which would not be retained in the pool.

The decontamination factor of 5 for the Mark I containment (as used in units 1 through 5 of Fukushima Daiichi) means that 80% of the radioactive substances (excluding noble gases) is retained, while 20% is released. The FILTRA system installed at 10 Swedish nuclear power plants and one in Switzerland is designed to ensure that in a severe accident 99.9% of core inventory is retained in the containment or the filters. The difference between releasing up to 20% versus 0.1% is huge, it means up to 200 times more radioactivity is released in the system defended by Tepco versus the enhanced system used in Europe and commercially available worldwide.

Fukushima: Keep out indefinitely

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The government of Japanese prime minister Kan is finally telling evacuees from within the 20 km exclusion zone around the wrecked Fukushima-I nuclear power plant that they won’t be able to return any time soon.

For months the official line had been that residents could not return until the reactors had achieved “cold shutdown”, which normally means that the chain reaction had stopped and the decay heat in the core had subsided enough for the coolant to be below 100 degrees C (below boiling point). This line ignores the fact that three of the reactors no longer have a cooling system in the usual sense and more importantly, that the area around the power station was severely contaminated by radioactive fallout from the broken reactors.

That reality has finally been accepted, explains the New York Times:

The government was apparently forced to alter its plans after the survey by the Ministry of Science and Education, released over the weekend, which showed even higher than expected radiation levels within the 12-mile evacuation zone around the plant. The most heavily contaminated spot was in the town of Okuma about two miles southwest of the plant, where someone living for a year would be exposed to 508.1 millisieverts of radiation — far above the level of 20 millisieverts per year that the government considers safe.

The survey found radiation above the safe level at three dozen spots up to 12 miles from the plant. That has called into question how many residents will actually be able to return to their homes even after the plant is stabilized.

Many of the evacuees had been led to believe that most of them might be able to return to their homes some time after the turn of the year, based on Tepco’s promises of establishing some sort of a cooling system and generally stabilizing the situation at the plant. Probably over 100,000 people will have to rebuild their lives from scratch elsewhere now, with no prospect of returning for decades, just like in the exclusion zone in Ukraine and Belarus near the Chernobyl plant, that has been off-limits for over a quarter of a century already. Besides a semicircle of 20 km radius around Fukushima-I there is also a strip of land to the North West, towards Fukushima City, that includes the village of Iitate mura, which is just as badly contaminated as the vicinity of the reactor itself.

People from the area should have been told much sooner, but presumably the prospect of having to pay compensation played a part in holding off giving people the facts. If somebody other than Kan was prime minister, they may well have waited for another 6 months. Kan will probably step down shortly and frankly I don’t hold much hope for how his successor, whoever he may be, will deal with the situation.

Kan famously took on ministerial bureaucracies and vested interests as health minister before and he tried his best in this situation. Many others would try to avoid confrontation with the nuclear industry, following the path of least resistance instead. Kan’s support ratings are extremely low now, but perhaps his efforts, however imperfect they were, may not be fully appreciated until we have his successors to compare with…

Tepco and the dirty secret of the radioactive stack

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On July 31, 2011 Tepco detected a radioactive hotspot at the base of an exhaust stack serving units 1 and 2 of Fukushima Daiichi. The following day, a measurement showed the activity to be more than 10 Sv/h (10,000 mSv/h), the highest measured in any accessible part of the wrecked nuclear power station so far (see “The worst hot spot in Fukushima“).

The high activity is assumed to date from attempts at venting the containment of unit 1 on March 12, after it had suffered core damage the previous evening. The venting, necessary to prevent the containment from bursting from excessive pressure, used a so called “hardened vent path” installed by Tepco between 1999 and 2001, following similar upgrades in the US after the Three Mile Island accident.

The reactors have filter system known as the “Standby Gas Treatment System” (SGTS), located on the second floor of the reactor building right next to the turbine hall, but the SGTS doesn’t work without electricity, i.e. the condition that triggered core damage in Fukushima Daiichi. Also, gas from the containment is released at high pressure, which would overwhelm the SGTS.

Therefore the gas is released untreated. Via a strong steel pipe it flows directly into the base of an over 100 m tall exhaust stack. High altitude winds carry it away from the plant. The only filtering that has taken place before than is by water in the pressure suppression pool at the bottom of the containment, through which any gas releases from the reactor pressure vessel are forced to bubble. As the high radioactivity level around the stack demonstrates some 5 months later, there is still plenty of activity left in the gas after that “wet scrubbing”.

It didn’t have to be that way. First of all, if Tepco had built the reactors at a higher location or surrounded them with a sea wall to protect them from a 14 meter high tsunami, there probably would not have been a total station blackout and hence a failure of the residual heat removal system (RHR). The cores wouldn’t have melted. It has long been known that the relatively small Mark 1 containment of these Boiler Water Reactors (BWRs) have problems dealing with vast volumes of hydrogen gas produced when core damage occurs. There was no way to make the containment bigger, short of decommissioning the old reactors and building new ones, which would have cost a lot of money. But that wasn’t the only option.

In 1981, Sweden came up with the FILTRA system for their Barsebäck nuclear power station, which consisted of two BWRs similar in size and functionality to the units in Fukushima. Construction of Barsebäck had started in 1969, only two years after the first unit in Fukushima. It was located about 500 km south of the Swedish capital of Stockholm, but only 20 km from the Danish capital of Copenhagen. The Copenhagen metropolitan region is home to about 1.9 million people in Denmark and South Sweden is also one of the most densely populated parts of the country.

The FILTRA system consists of concrete pipes or rock tunnels filled with gravel, through which the released gas must flow. It gives off heat to some 10,000 m3 of rock, which condenses steam and radioactive fission products, which collect at the bottom of the gravel chambers. After the gas has cooled it is sent through sand or water for further filtration. Only then is it released in the stack. The system is simple and robust enough to cope with high pressure and temperatures. Since it doesn’t use any high technology it was relatively cheap to build.

There was plenty of space available at Fukushima. The Swedish system was no secret. Here is the 30 year old report that discussed its details. Why did Tepco not build a filter system like that, to be shared among its 6 units at Fukushima Daichi? By building the hardened vent path, it already admitted to the possibility of a core meltdown, so why not make sure the venting could be cleaned up? Perhaps Tepco didn’t want to spend more money on safety than it absolutely had to. Perhaps it was also because the Swedish reactors were designed by Asea-Atom AB, whereas the Fukushima design was by GE. Whatever the reason, the technology to protect the people of Japan in a nuclear accident has been available for three decades and Tepco chose not to use it.