Here is a brief update of recent nuclear reactor news from Japan, some of it on the lighter side including a look at naturally occurring radiation from bananas and Brazil nuts, and a humorous video of “Nuclear Boy” used to explain radiation to kids in Japan.

Japan Churns Through ‘Heroic’ Workers Hitting Radiation Limits

Bloomberg reports Japan Churns Through ‘Heroic’ Workers Hitting Radiation Limits

More workers were drafted for the frontline of Japan’s biggest nuclear disaster as radiation limits forced Tokyo Electric Power Co. to replace members of its original team trying to avert a nuclear meltdown.

The utility increased its workforce at the Fukushima Dai- Ichi plant to 322 yesterday from 180 on March 16 as it tried to douse water over exposed nuclear fuel rods to prevent melting and leaking lethal radiation. Levels beside the exposed rods would deliver a fatal dose in 16 seconds, said David Lochbaum, a nuclear physicist for the Union of Concerned Scientists and a former U.S. Nuclear Regulatory Commission safety instructor.

An hour’s exposure in some areas equates to half the annual maximum level, said John Price, a Melbourne-based consultant on industrial accidents and former safety policy staffer at the U.K.’s National Nuclear Corp.

“They have an access time of 10 to 25 hours at the most,” Price, 60, said in a telephone interview yesterday. “At that rate, you are going to go through workers very fast.”

Radiation exposure levels are measured in millisieverts. Exposure totaling 100 millisieverts over a year is the lowest level at which any increase in cancer is evident, according to the World Nuclear Association in London. The cumulative maximum level for nuclear workers was increased to 250 millisieverts from 100 millisieverts by Japan’s health ministry on March 15.

“Once they have reached that limit, they can’t go in the plant anymore,” Price said. “You shouldn’t be doing that sort of work ever again.”

“What we are seeing now is, really, heroics,” said Seth Grae, chief executive officer of Lightbridge Corp., a nuclear consultancy in McLean, Virginia.

The on-site team is likely foregoing sleep and food, and working with minimal light as levels of radiation rise, according to Gennady Pshakin, a former International Atomic Energy Agency official.

“They are like the Spartans, standing up against all that’s thrown against them,” said Pshakin, who has worked in the nuclear industry for 40 years, referring to the people of ancient Greece who fended off military attacks for centuries. “They are probably working on thin air,” he said by phone from Obninsk, the site of the world’s first nuclear power plant.

High Radiation Severely Hinders Emergency Work to Cool Japanese Plant

The New York Times reports High Radiation Severely Hinders Emergency Work to Cool Japanese Plant

Amid widening alarm in the United States and elsewhere about Japan’s nuclear crisis, military fire trucks began spraying cooling water on spent fuel rods at the country’s stricken nuclear power station late Thursday after earlier efforts to cool the rods failed, Japanese officials said.

The Japanese efforts focused on a different part of the Fukushima Daiichi Nuclear Power Station, 140 miles northeast of here, from the reactor — No. 4 — depicted in Washington on Wednesday as presenting a far bleaker threat than the Japanese government had offered.

The decision to focus on the No. 3 reactor appeared to suggest that Japanese officials believe it is a greater threat, since it is the only one at the site loaded with a mixed fuel known as mox, for mixed oxide, which includes reclaimed plutonium.

Western nuclear engineers have said that the release of mox into the atmosphere would produce a more dangerous radioactive plume than the dispersal of uranium fuel rods at the site. The Japanese authorities also expressed concern on Wednesday that the pressure in the No. 3 reactor had plunged and that either gauges were malfunctioning or a rupture had already occurred.

After the military’s effort to cool the spent fuel atop the reactor with fire trucks, Hidehiko Nishiyama, deputy director-general of the Nuclear and Industrial Safety Agency, said it was too early to assess the success of the attempt.

Mr. Nishiyama also said that radiation of about 250 millisievert an hour had been detected 100 feet above the plant. In the United States the limit for police officers, firefighters and other emergency workers engaged in life-saving activity as a once-in-a-lifetime exposure is equal to being exposed to 250 millisieverts for a full hour. The radiation figures provided by the Japanese Self-Defense Force may provide an indication of why a helicopter turned back on Wednesday from an attempt to dump cold water on a storage pool at the plant.

Danger of Spent Fuel Outweighs Reactor Threat

The New York Times reports Danger of Spent Fuel Outweighs Reactor Threat

Years of procrastination in deciding on long-term disposal of highly radioactive fuel rods from nuclear reactors is now coming back to haunt Japanese authorities as they try to control fires and explosions at the stricken Fukushima Daiichi Nuclear Power Station.

Some countries have tried to limit the number of spent fuel rods that accumulate at nuclear power plants — Germany stores them in costly casks, for example, while Chinese nuclear reactors send them to a desert storage compound in western China’s Gansu province. But Japan, like the United States, has kept ever larger numbers of spent fuel rods in temporary storage pools at the power plants, where they can be guarded with the same security provided for the power plant.

Figures provided by Tokyo Electric Power on Thursday show that most of the dangerous uranium at the power plant is actually in the spent fuel rods, not the reactor cores themselves. The electric utility said that a total of 11,195 spent fuel rod assemblies were stored at the site.

That is in addition to 400 to 600 fuel rod assemblies that had been in active service in each of the three troubled reactors. In other words, the vast majority of the fuel assemblies at the troubled reactors are in the storage pools, not the reactors.

Now those temporary pools are proving the power plant’s Achilles heel, as the water in the pools either boils away or leaks out of their containments, and efforts to add more water have gone awry. While spent fuel rods generate significantly less heat than newer ones, there are strong indications that the fuel rods have begun to melt and release extremely high levels of radiation. Japanese authorities struggled Thursday to add more water to the storage pool at reactor No. 3.

Four helicopters dropped water, only to have it scattered by strong breezes. Water cannons mounted on police trucks — equipment designed to disperse rioters — were deployed in an effort to spray water on the pools. It is unclear if they managed to achieve that.

Nuclear engineers around the world have been expressing surprise this week that the storage pools have become such a problem. “I’m amazed that they couldn’t keep the water in the pools,” said Robert Albrecht, a longtime nuclear engineer who worked as a consultant to the Japanese nuclear reactor manufacturing industry in the 1980s and visited the Fukushima Daiichi reactor then.

Very high levels of radiation above the storage pools suggest that the water has drained in the 39-foot-deep pools to the point that the 13-foot-high fuel rod assemblies have been exposed to air for hours and are starting to melt, he said. Spent fuel rod assemblies emit less heat than fresh fuel rod assemblies inside reactor cores, but the spent assemblies still emit enough heat and radioactivity that they must still be kept covered with 26 feet of water that is circulated to prevent it from growing too warm.

Gregory Jaczko, the chairman of the United States Nuclear Regulatory Commission, made the startling assertion on Wednesday that there was little or no water left in the storage pool located on top of reactor No. 4, and expressed grave concern about the radioactivity that would be released as a result. The spent fuel rod assemblies there include 548 assemblies that were only removed from the reactor in November and December to prepare the reactor for maintenance, and may be emitting more heat than the older assemblies in other storage pools.

Even without recirculating water, it should take many days for the water in a storage pool to evaporate, nuclear engineers said. So the rapid evaporation and even boiling of water in the storage pools now is a mystery, raising the question of whether the pools may also be leaking.

Michael Friedlander, a former senior nuclear power plant operator who worked 13 years at three American reactors, said that storage pools typically have a liner of stainless steel that is three-eighths of an inch thick, and they rest on reinforced concrete bases. So even if the liner ruptures, “unless the concrete was torn apart, there’s no place for the water to go,” he said. …

I cannot assess the accuracy of any of the claims made by Gregory Jaczko. However Tokyo Electric disputes claims by Jaczko. Moreover, Japanese officials are particularly upset with the evacuation area set by US officials at 50 miles while theirs are set at 12 miles, a radius Japan considers more than sufficient.

“Recriticality” the New Buzzword

Tokyo Electric said this week that there was a chance of “recriticality” in the storage ponds – that is to say, the uranium in the fuel rods could become critical in nuclear terms and resume the fission that previously took place inside the reactor, spewing out radioactive byproducts.

Mr. Albrecht said this was very unlikely, but could happen if the stacks of pellets slumped over and became jumbled together on the floor of the storage pool. Tokyo Electric has reconfigured the storage racks in its pools in recent years so as to pack more fuel rod assemblies together in limited space.

If recriticality occurs, pouring on pure water could actually cause fission to take place even faster. The authorities would need to add water with lots of boron, as they have been trying to do, because the boron absorbs neutrons and interrupts nuclear chain reactions.

If recriticality takes place, the uranium starts to warm. If a lot of fission occurs, which may only happen in an extreme case, the uranium would melt through anything underneath it. If it encounters water as it descends, a steam explosion may then scatter the molten uranium.

In short, if the water in the storage ponds is gone, no one seems to be able to explain it. There are conflicting reports as to whether the water is gone and how much, as well as conflicting reports as to whether or not water itself without boron may in some cases do more harm than good.

I am certainly not qualified to sort this out, I can only present the various opinions as I see them, ignoring the ones that are obviously hype, as best I can.

How Japan Explains Radiation to Kids

On the lighter side of the news, Japan uses videos of “Nuclear Reactor Boy” and “poop” to explain radioactive toxicity. I picked this video up from Mike in Tokyo Rogers. Those not speaking Japanese will have to follow the captions.

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Inquiring minds may also wish to consider Radiation in Tokyo Same as Eating 1.5 Bananas.

Wikipedia explains the Banana Equivalent Dose

A banana equivalent dose (BED) is a concept to place in scale the dangers of radiation by comparing exposures to the radiation generated by a common banana.

Radioactivity is measured in disintegrations per second (dps), in Curie (Ci), or in Becquerel (Bq). Radiation dose equivalent is measured in Roentgen equivalent man (rem) or in Sievert (Sv).

Many foods are naturally radioactive, and bananas are particularly so, due to the radioactive potassium-40, or 40K they contain. Bananas are radioactive enough to regularly cause false alarms on radiation sensors used to detect possible illegal smuggling of nuclear material at U.S. ports.

A medium sized banana contains about 450 mg of potassium. 0.0117%, or about 53 μg of this being 40K. 53 μg of 40K produces 14 radioactive decays per second (dps), or 0.00037 μCi of radiation. If the banana is eaten, the dose equivalent is about 0.01 mrem. 0.01 mrem is equivalent to 0.1 μSv.

A radiation dose equivalent of 100 μSv (10 mrem, or 1,000 BED) increases an average adult human’s risk of death by about one micromort – the same risk as eating 40 tablespoons of peanut butter, or of smoking 1.4 cigarettes.

Comparison to Three Mile Island and Chernobyl

After the Three Mile Island nuclear accident, the NRC detected radioactive iodine in local milk at levels of 0.74 Bq/l (20 pCi/l), much less than an equivalent quantity of normal banana. Thus a 12 fl oz glass of the slightly radioactive milk would have about 1/75th BED. However, radioactive iodine is exceptionally dangerous to children as it concentrates in the thyroid.

Following the Chernobyl disaster, levels of caesium-137 increased by more than tenfold throughout Europe, and wild mushrooms in the area contained radiation with up to an effective dose of 20 μSv/kg[8]. Thus, eating 1 kg of these mushrooms would have given the same dose as about 200 bananas.

Other foods

Nearly all foods are slightly radioactive. All food sources combined expose a person to around 0.4 mSv (40 mrem or 4,000 BED) per year on average, or more than 10% of the total dose from all natural and man-made sources.

Some other foods that have above-average levels are potatoes, kidney beans, nuts, and sunflower seeds. Among the most naturally radioactive foods known are Brazil nuts, with activity levels that can exceed 444 Bq/kg (12,000 pCi/kg).

Fears of radiation hitting the US are way overblown.

Mike “Mish” Shedlock
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