The TerraPower Natrium Reactor – a Quick Review

TerraPower, a company funded by billionaire Bill Gates, has teamed up with several partners to build a demonstration nuclear power station in Wyoming by the end of the decade. Several sites are under consideration. The plan is to re-use the grid connection of a former thermal coal power plant, of which Wyoming has many.

The Natrium reactor developed by TerraPower in cooperation with GE Hitachi Nuclear Energy is quite a departure from the design of the light water reactors (LWRs) that produce the bulk of nuclear power worldwide today. For one, its output is highly variable because it incorporates gigawatthour (GWh) energy storage using tanks of molten salt. The design is quite innovative, which creates both upsides and challenges.

After reviewing the company’s website and watching a webinar, I am quite impressed but also concerned. The reactor will still run on uranium and will produce radioactive fission products that will need to be contained and stored safely for thousands of years. This is still a largely unsolved problem. Countries that have been generating power from nuclear fuels are today sitting on thousands of tons of waste kept in intermediate storage, still without a proven long term storage solution. Eight decades since the start of the “atomic age” with the Manhattan Project that gave us nuclear reactors and atomic bombs we are only now seeing the first permanent storage site being used in Finland. Some consider this the Achilles heel of the nuclear industry. Proponents of nuclear power will argue that, given we already have existing waste, this is a problem we will need to address anyway and that the volume of highly active nuclear waste will remain relatively compact. Nevertheless, there is a lot that can go wrong there, especially if the volume keeps increasing.

What most excited me about the reactor concept was its incorporation of the heat store using molten salt tanks, which it borrowed from concentrated solar power (CSP). Everything from the molten salt tank to the grid connection is basically the same as in this type of solar power plant. The major difference is that the heat source is not solar power focused onto a tower by thousands of mirrors but an underground nuclear reactor. This means the designers could use existing technology developed to maturity over the last 2-3 decades for use in solar projects in Nevada, Australia, Morocco and other locations.

This part of the plant is conventional technology that will not be subject to the same regulatory oversight as the nuclear portion, making it easier and cheaper to build. At the same time, the nuclear portion of the plant is much smaller and simpler, requiring a lot less concrete and steel than in a LWR per MW of output capacity.

By incorporating the heat storage, the electrical output of the power station can be varied considerably – the TerraPower presentation showed a range of about 240 to 500 MWe, with 345 MWe available continually without charging or discharging the heat store. Output that varies by 100 percent roughly covers the demand swing between day and night in many power markets. If combined with solar and wind, the stored heat can be used to smooth out fluctuations in power output from those natural energy sources. Heat from the power station may also have applications for desalination, industrial processes and residential heating.

Conventional nuclear power stations such as PWRs or BWRs can not vary their output very much. They basically can only run at 100 percent load or be switched off. Once shut down, bringing them back up again takes a very long time. That makes them suitable only for base load but not for demand peaks such as in the afternoon or evening. For that they would have to be combined with energy storage such as pumped hydro, opportunities for which are limited by geography. Due to the literally built-in output flexibility of the salt storage system, a zero carbon grid could theoretically incorporate a lot more Natrium output capacity than would be possible with existing LWRs. From an economic point, it means the operators in a competitive electricity market with bidding for supplies can sell more power at lucrative peak prices instead of having to try to find buyers at night when demand and prices are low.

So what’s the catch? The nuclear reactor itself is a sodium-cooled fast reactor (SFR), basically a Fast Breeder Reactor (FBR) without the breeding: Except for the absence of a breeding blanket made of depleted uranium that slowly turns into plutonium, the technology is very similar. Perhaps you remember the Monju reactor in Fukui, Japan that was shut down after a major accident in 1995. The operators attempted to hide the extent of a coolant leak and fire, which led to a 15-year shutdown. After a second accident in 2010 the reactor was eventually decommissioned. In 1966 the prototype Fermi 1 FBR in Monroe, Michigan suffered a partial meltdown. It was permanently shut down in 1972. Several other sodium-cooled fast reactors have been built around the world, such as the French Superphénix, the Prototype Fast Reactor in Dounreay, Scotland and the SNR-300 in Kalkar, Germany. All of the above have since been shut down due to high costs or troubles or, like the one in Kalkar, were never even started up.

While sodium has a high temperature range between melting and boiling point and is a good heat conductor, it also reacts violently with water and oxygen. Naturally, you can not put out a sodium fire with water. Normally the top of the reactor vessel is filled with an inert gas such as argon to prevent sodium fires but it needs to be opened for loading and unloading fuel, during which time the sodium has to remain heated above its melting point. You do not want to start a fire then.

If an LWR overheats, steam bubbles will form that reduce the criticality, interrupting the chain reaction. By contrast, control of the chain reaction in SFRs depends 100 percent on positioning of the control rods.

While the cooling pipes will not have to withstand high steam pressures as in a BWR, they will be subject to thermal stress: The coolant temperature in an SFR is much higher, around 550 deg C (1020 F) which is basically red-hot and hot enough to melt some aluminium alloys (and of course salt, for the heat storage). When SolarReserve decided to build a molten salt CSP solar power station in Nevada, it turned to Rocketdyne to make some of the metal parts, because of their metallurgical expertise in rocket engine nozzles that are also exposed to high temperatures.

There are other viable solutions for base load in a zero carbon grid, such as geothermal power, utility scale battery storage, thermal storage using rock heated electrically with surplus wind and solar or green hydrogen powering fuel cells or gas turbines. Costs for wind, solar and battery storage have been falling rapidly for years. Once renewables are cheap enough, you can partially address issues of intermittent output by overbuilding capacity and simply idling some of it when not needed. Or you can use spare output when supply exceeds demand to produce hydrogen, for making ammonia and for use by the steel industry.

Some of these solutions depend more on geography than the Natrium reactor, which can be installed on any continent and provide power at time of day and in any season. However, it would definitely need to be safe and reliable. Ultimately, this new technology will first have to prove itself.

Releasing Tritium-tainted Water from Fukushima 1

The Japanese government has approved a plan by Tepco to release more than a million tons of water stored in tanks at the site of the Fukushima 1 nuclear power station. The water is supposed to be gradually released into the ocean starting two years from now.

Currently about 1.2 million t of contaminated water are stored on site, an amount that is increasing by about 170 t per day. Tepco is expected to run out of space at the end of 2022. Water is being injected into severely damaged reactors on the site to cool the remains of nuclear fuel left inside. It leaks back out, mingles with ground water that seeps in and is then purified through a filtration system called ALPS. This removes most of the radioactive contamination, but leaves tritium, a radioactive isotope of hydrogen which can not be chemically removed from water. So it ends up in the storage tanks.

Proponents of the release argue that tritium poses little hazard in small quantities. Radiation from tritium is so weak, it only travels for a couple of mm through air and it is stopped by the dead cells on the outside of human skin. Even if ingested it does not accumulate in the human body.

The water released will be diluted to levels so low it would meet drinking water standards in Japan and in other countries. Opponents fear an economic backlash against local fisheries or argue in principle that Japan has no right to contaminate the Pacific ocean, which is not just their territorial waters but shared by many other countries.

Proponents call such criticism hypocritical, given that many other countries, including the Republic of Korea, routinely release tritium into the ocean from their own nuclear facilities.

The issue is complicated. First of all, whether the danger from the water release is real or exaggerated, fishermen will suffer economically because consumers will end up avoiding fish from Fukushima more than they already do, even if it was safe to eat. If the release is unavoidable, the fishermen should receive compensation for their economic losses. That is only fair.

The truth about the water is not black or white. The 1.2 million t of water that has accumulated over the past decade was treated in different ways at different times. Some may indeed contain only those low levels of tritium as a contaminant, but other tanks will hold water that still has significant amounts of caesium, strontium and other dangerous isotopes that unlike tritium can accumulate in organisms and pose long term hazards. More purification and testing will definitely be needed before a release can take place. As Motoko Rich and Makiko Inoue reported for the New York Times in 2019:

Until last year, Tepco indicated that with the vast majority of the water, all but one type of radioactive material — tritium, an isotope of hydrogen that experts say poses a relatively low risk to human health — had been removed to levels deemed safe for discharge under Japanese government standards.

But last summer, the power company acknowledged that only about a fifth of the stored water had been effectively treated.

Last month, the Ministry of Economy, Trade and Industry briefed reporters and diplomats about the water stored in Fukushima. More than three-quarters of it, the ministry said, still contains radioactive material other than tritium — and at higher levels than the government considers safe for human health.

The authorities say that in the early years of processing the deluge of water flowing through the reactors, Tepco did not change filters in the decontamination system frequently enough. The company said it would re-treat the water to filter out the bulk of the nuclear particles, making it safe to release into the ocean.
(New York Times, 2019-12-23)

Long term there is no real alternative to releasing the water. Once its radioactivity has been reduced to only tritium, dilution and disposal at sea should pose little risk.

The challenge however is that Tepco and the government have a public trust problem, at home and abroad. How do we know the water released will be as clean as claimed?

Any release process needs to be transparent and independently verified to make sure there are no shortcuts or other shenanigans.

See also:

Germany Reaches Renewable Energy Milestone

The drop in demand for electric power due to the Covid-19 pandemic helped Germany reach an environmental milestone in 2020: For the first time more electricity from renewable sources was fed into the German grid than from fossil fuels and nuclear combined.

50.5 percent of the net electricity production came from wind, solar, hydro and biomass vs. 49.5 percent from fossil or nuclear. Wind power alone accounted for 27 percent of all electricity, more than brown coal and hard coal combined (24.1 percent).

2020 numbers for Japan are not yet available, but in 2017 renewables excluding hydro power accounted for only 8.1 percent of the Japanese electricity production, with hydro providing another 7.9 percent. 39.5 percent came from LNG, 32.7 percent from coal 8.7 percent from oil and 3.1 percent from nuclear.

Japan’s power generation plan for FY2030 foresees only 1.7 percent for wind power, 7 percent for solar and an overall share for renewables (including hydro power) of 22-24 percent of the total. That is less than half the share that Germany achieved in 2020, a whole decade before Japan.

Olympic Hydrogen Hype

Today’s Japan Times reports that the Organizing Committee of the 2020 Tokyo Olympics is considering the use of hydrogen torches to light the Olympic flame (“Olympic panel mulls high-tech hydrogen torch, pares soccer venues” — JT, 2017-02-27):

“An important theme of the Olympics is how to promote environmental sustainability. We will talk to experts and see how realistic it is in terms of technological development,” a committee member said.

One official said there are still safety and cost concerns, and asserted that there also was a need for a lightweight torch that can be easily carried.

In March 2016, the Tokyo Metropolitan Government announced a project to have the 6,000-unit athletes’ village for the games run entirely on hydrogen power.

The Japanese government is one of the most active promoters worldwide of a so called “hydrogen economy”. It sees the 2020 Olympics as an opportunity to showcase Japan’s lead on hydrogen. Other projects are the construction of a nationwide network of hydrogen filling stations for hydrogen fuel cell vehicles (HFCV) such as the Toyota Mirai, research into shipping liquefied hydrogen from overseas using special tankers and production of hydrogen from lignite (brown coal) in Australia for export to Japan.

Let’s start with the most obvious problem in the article, the hydrogen fueled torch: The usual Olympic torches use LPG (propane/butane) as a fuel, a gas mixture that can be stored as a liquid under moderate pressure at normal outdoor temperatures. This makes it easy to carry a significant amount of fuel in a light weight container. Hydrogen by contrast does not liquefy unless chilled to about -252 C. Hydrogen powered vehicles run on compressed hydrogen instead, at pressures of up to 700 bar, equivalent to half the weight of a car on each cm2 of tank surface. As you can imagine that kind of pressure calls for some fairly sturdy containers. An even bigger problem is that pure hydrogen flames are invisible because they radiate energy not as light but as UV. You could feel the heat, but you couldn’t directly see if the flame is burning or not, which makes it quite hazardous. Talk about playing with fire…

The comment about running the Olympic village on “hydrogen power” is quite misleading. It’s like saying they would run the Olympic village on battery power, without explaining where the energy to charge those batteries came from. Like batteries, hydrogen is not a primary energy source, it’s an energy carrier. Since elementary hydrogen does not exist in significant quantities on earth, it has to be produced using another energy source such as natural gas or electricity generated using coal, nuclear, wind or solar.

Though it’s possible to produce hydrogen from carbon-free energy sources such as solar electricity (splitting water through electrolysis) and then produce electricity from hydrogen again, this process is far less efficient than either consuming renewable electricity directly or via batteries. When you convert electric energy to chemical energy in hydrogen and back to electricity, about 3/4 of the energy is lost in the process. This is incredibly wasteful and far from green.

With its sponsorship of hydrogen, the Japanese government is trying to create business opportunities for industrial companies such as Kawasaki Heavy Industries, a Japanese shipbuilder (see “Kawasaki Heavy fighting for place in ‘hydrogen economy'” — Nikkei Asian Review, 2015-09-03) and for its oil and gas importers, as almost all hydrogen is currently made from imported liquefied natural gas (LNG). In the longer term, the government still has a vision of nuclear power (fission or fusion) producing the electricity needed to make hydrogen without carbon emissions. Thus the ‘hydrogen economy’ is meant to keep oil companies and electricity monopolies like TEPCO in business. The “hydrogen economy” is coal, oil and nuclear hidden under a coat of green paint.

These plans completely disregard the rapid progress being made in battery technologies which have already enabled electric cars with ranges of hundreds of km at lower costs than HFCVs and without the need for expensive new infrastructure.

Hydrogen, especially when it’s produced with carbon-intensive coal or dangerous nuclear, is not the future. Japan would be much better served by investing into a mix of wind, solar, geothermal and wave power, combined with battery storage and other technologies for matching up variable supply and demand.

See also:
Hydrogen Fuel Cell Cars Are Not The Future (2016-12-05)

Hydrogen Fuel Cell Cars Are Not The Future

On my bicycle ride last Saturday I passed a service station near Hachioji in western Tokyo that is being set up as a hydrogen station for fuel cell cars. Japan is in the process of setting up such infrastructure to support a small fleet fuel cell vehicles such as the Toyota Mirai (its name means “future” in Japanese).

For decades, hydrogen has been touted as an alternative fuel for transport once we move beyond fossil fuels. The idea was that it can be made in essentially unlimited amounts from water using electricity from solar, wind or nuclear power (from either fission or fusion reactors). The only tailpipe emission would be water, which goes back into nature.

Unlike electric cars, which have limited range compared to fossil fuel cars, hydrogen cars can be refilled fairly quickly, like conventional cars, giving them a longer operating range. Car manufacturers have experimented with both internal combustion engines (ICE) running on hydrogen and fuel cell stacks that produce electricity to drive a traction motor. Both liquefied and compressed hydrogen has been tested for storage.

Here is a Honda fuel cell car I photographed on Yakushima in 2009:

It’s been a long road for hydrogen cars so far. Hydrogen fuel cells were already providing electricity for spacecrafts in the Apollo missions in the 1960s and 70s. With the launch of production cars and hydrogen fuel stations opening now in Japan, the US and Europe it seems the technology is finally getting ready for prime time. However, the reality is quite different.

Arguably the biggest challenge for hydrogen cars now is not the difficulty of bringing down the cost of fuel cells or improving their longevity or getting refueling infrastructure set up, but the spread of hybrid and electric cars. Thanks to laptops and mobile devices there has been a huge market for new battery technology, which attracted investment into research and development and scaled up manufacturing. Eventually reduced costs allowed this technology to cross over into the automotive industry. The battery packs of the Tesla Roadster were assembled from the same industry standard “18650” Li-ion cells that are the building blocks of laptop batteries.

Li-ion batteries have been rapidly falling in price year after year, allowing bigger battery packs to be built that improved range. A car like the Nissan Leaf that is rated for a range of 135 to 172 km (depending on the model) would cover the daily distances of most people on most days without recharging during daytime. Not only are prices falling and range is increasing, the cars can also harness the existing electricity grid for infrastructure. A charging station is a fraction of the price of a hydrogen filling station.

Here in Japan I find many charging stations in convenience store parking lots, at restaurants, in malls and at car dealerships – just about anywhere but at gasoline stations, which is where the few hydrogen stations are being installed.

After the tsunami and nuclear meltdown hit Japan in March 2011, some people here viewed electric cars and their claimed ecological benefits with suspicion: The Nissan Leaf may not have a tail pipe, but didn’t its electricity come from nuclear power stations? This criticism is not entirely justified, because electricity can be produced in many different ways, including wind, sun and geothermal. Car batteries of parked cars are actually quite a good match for the somewhat intermittent output of wind and solar, because they could act as a buffer to absorb excess generating capacity while feeding power back into the grid when demand peaks. If cars were charged mostly when load is low (for example, at night) then no new power stations or transmission lines would have to be built to accommodate them within the existing distribution network.

The dark secret of hydrogen is that, if produced from water and electricity through electrolysis, it is actually a very inefficient energy carrier. To produce the hydrogen needed to power a fuel cell car for 100 km consumes about three times as much electricity as it takes to charge the batteries of an electric car to cover the same distance. That’s mostly because there are far greater energy losses in both electrolysis and in fuel cells than there are in charging and discharging a battery. A fuel cell car actually has all of the above losses, because even fuel cells still costing about $100,000 are not powerful enough to handle peak loads, therefore a battery is still required. Think of a hydrogen fuel cell car as a regular electric car with an added fuel cell stack to recharge the battery while the car is running. This means a fuel cell car suffers the relative small charge/discharge losses of a battery-electric car on top of the much bigger losses in electrolysis and fuel cells that only a hydrogen car has.

What this 3x difference in energy efficiency means is that if we were to replace fossil-fueled cars with hydrogen-fueled cars running on renewable energy, we would have to install three times more solar panels and build three times as many wind turbines as it would take to charge the same number of electric cars. Who would pay for that and why?

Even if the power source was nuclear, we would be producing three times as much nuclear waste to refill hydrogen cars than to recharge battery-electric cars — waste that will be around for thousands of years. That makes no sense at all.

So why are hydrogen fuel cell car still being promoted then? Maybe 20-30 years ago research into hydrogen cars made sense, as insurance in case other alternatives to petroleum didn’t work out, but today the facts are clear: The hydrogen economy is nothing but a boondoggle. It is being pursued for political reasons.

Electrolysis of water is not how industrial hydrogen is being produced. The number one source for it is a process called steam reformation of natural gas (which in Japan is mostly imported as LNG). Steam reformation releases carbon dioxide and contributes to man-made global warming. By opting for hydrogen fuel cell cars over electric cars, we’re helping to keep the oil industry in business. That you find hydrogen on the forecourt of gas stations that are mostly selling gasoline and diesel now is not a coincidence. Hydrogen is not the “fuel of the future”, it’s a fossil fuel in new clothes.

Due to the inefficiency of the hydrogen production it would actually make more sense from both a cost and environmental point of view to burn the natural gas in highly efficient combined cycle power stations (gas turbines coupled with a steam turbine) feeding electricity into the grid to charge electric cars instead of producing hydrogen for fuel cell cars from natural gas.

Even if electrolysis is terribly inefficient, by maximizing demand for electricity it can provide a political fig leaf for restarting and expanding nuclear power in Japan. Both the “nuclear fuel cycle” involving Fast Breeder Reactors and the promise of nuclear fusion that is always another 30-50 years away were sold partly as a power source for a future “hydrogen economy”.

While I’m sorry that my tax money is being used to subsidize hydrogen cars, I don’t think hydrogen as a transport fuel will ever take off in the market. Electric cars came up from behind and overtook fuel cell cars. The price of batteries keeps falling rapidly year after year, driven by massive investment in research and development by three independent powerful industries: IT/mobile, automotive and the power companies.

The hydrogen dream won’t die overnight. I expect the fuel cell car project will drag on through inertia, perhaps until battery electric cars will outnumber fossil fueled cars in Japan and only then will finally be cancelled.

Tepco drowning in radioactive water

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

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

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

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

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.