Archive for April, 2011

Fukushima Reactors (part 3)

April 26, 2011

Tales from the Nuclear Age

Copyright © 2011 by Charles Glassmire

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Apr. 26, 2011

Fukushima Reactors (part 3)

What about Plutonium found on the ground near the reactors?

          Plutonium is an element of concern, but it’s important to understand why that is. The principal Plutonium isotope made in power reactors (239Pu) has a half life of 24,000 years. So once created, it stays around for a very long time. When you run a Uranium fueled reactor, such as those BWR’s used at Fukushima, you manufacture Plutonium along with other fission products. So there are small amounts of Plutonium in the spent fuel rods stored in the rooms at the top of the reactors, and inside the reactor core containment. There are about 11,175 spent fuel rods stored for the six reactors on site. It seems that Japan does not have a geologically safe underground storage site for these used fuel rods. The United States has spent several Billion dollars building such a storage site in Nevada which is in a geologically stable salt formation under a mountain. The nuclear industry could look forward to shipping its spent fuel there for permanent safe storage. Sadly, President Obama has closed down the site and cancelled all future work as a payoff to Senator Harry Reid. Now all those fuel rods are sitting in the cooling pools at U.S. reactor sites with no where to go.

           Plutonium has a very odd history. This element is a metal not found in nature (except possibly from a few spontaneous fissions of Uranium in the Earth’s crust). It had to be created by man, specifically by Glenn Seaborg and his team at Berkeley during World War II. They bombarded a Uranium isotope (238) with a heavy Hydrogen nucleus. This created another new element called Neptunium which decayed within a few days to Plutonium 239. But they didn’t get very much. In fact the first amounts were invisible; only a few atoms. Indeed, they had to run the process for a whole year in a cyclotron to get a miniscule amount enough to even be weighed and measured! Then because of the secrecy of the atom bomb project, they couldn’t even publicize their discovery until after the War in 1946!

 Why go to all this trouble over Plutonium?

          The 239Pu isotope proved of great interest to the Manhattan Project. It turned out to be fissionable, releasing lots of usable energy when its nucleus split apart. When 239Pu fissions, it generates two new neutrons, and sometimes three. So you use one neutron to fission it and you get two new ones to go on and break up other nuclei. This multiplication factor means it’s a better candidate for a chain reaction weapon than even Uranium 235. So you need much less Plutonium to create a critical mass for a bomb. In fact, a softball sized sphere will do the trick. For this reason Plutonium is a great candidate for weapons mounted on Ballistic Missiles. Much less weight to carry, which means less rocket fuel etc.

          The Manhattan project immediately began two production facilities for Plutonium. One was located at Oak Ridge and another major one at Hanford in the north western U.S. They began design of a Plutonium bomb, which ultimately proved successful and was dropped at Nagasaki.

          The fuel rods in Fukushima number 3 are a special design using a mixture of Plutonium Oxide and Uranium Oxide. This mix is called MOX. So there are significant amounts of Plutonium in reactor 3, which carries over into the spent fuel rods stored in the number 3 fuel cooling pool. After the tsunami killed the pumps, these cooling pools were subjected to hundreds of tons of cooling water to keep the temperature down. This water filled tunnels under the site and drained into the ocean. It’s no surprise that small amounts of Plutonium are detected in the surrounding area.

          Oddly enough, Plutonium radiation is not a significant problem unless it’s inhaled or ingested. 239Pu radiates by releasing an alpha particle. This is a big low energy particle which can’t penetrate a sheet of paper, or even the skin thickness of a human being. If amounts are left on the skin for enough time however, a burn and skin lesions could occur. This may be prevented by simply washing with cold water and controlling the runoff water.

          However it is a serious problem in any quantity inside the body. The metal is a chemical poison if ingested or inhaled into the body. The symptoms which may occur in the event of ingestion or inhalation of Plutonium depends heavily on the amount taken in. In a heavy exposure the symptoms might include liver damage, increased risk of bone, liver or lung cancer, and increased risk of leukemia. Children and pregnant women would be especially susceptible to damage. 

          But we live in a radioactive world. In fact, those of us living in the United States all have trace amounts of Pu in our bodies left over from the atomic testing which went on in Nevada in the 50’s and 60’s. On the average, this probably gives us less exposure than we get from the Cosmic Rays which continually bombard the Earth on a daily basis, or the Radon gas collecting in our cellars…

  (to be continued …)

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More on the Fukushima Reactors

April 8, 2011

Tales from the Nuclear Age

Copyright © 2011 by Charles Glassmire

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Apr. 7, 2011

More on the Fukushima Reactors

Why is this situation taking so long to control?

          The situation is complicated. Working in a radioactive contaminated site requires caution and constant supervision. In the United States, all worker activity in a radiation zone is regulated by the Nuclear Regulatory Commission (NRC).

(Note: For an account of high radiation work see my earlier blog post in June of 2010, on the Army’s SL-1 reactor incident. Several workers lost their lives in the initial excursion there but this was not a “commercial power” incident since the experimental reactor was operated by the U.S. Army.)

          The NRC has established specific exposure limits for U.S. commercial power radiation workers which must not be exceeded on a yearly basis. If a worker receives a short term dose above the weekly limit, Federal law requires that worker to be removed from all radiation work and placed elsewhere until his exposed time limit passes. The law requires the company to keep detailed exposure records for each worker on a daily basis, and these are periodically inspected. Health Physicists are put in charge of the repair work and specifically limit the amount of exposure each day to keep each worker under his limit for that day.

          Each U.S. worker is required to wear a pocket instrument called a “dosimeter” which is the size of a fountain pen and measures the accumulated exposure to the workers body while in the radiation zone. When he emerges from the zone, the amount of exposure is recorded on his chart. The Health Physicist has legal control of the workers and determines who works, how long they work and who is put on temporary leave to allow the body to recover. New personnel are rotated into the work if too many workers are removed for exposure limits. So the entire work force is maintained below the annual limits which are set at a safe level to show no body harm.

 What about Personnel at Fukushima?

          So to Fukushima: I do not know the relevant Japanese legal requirements on the reactor operator TEPCO, but if the situation reported by the media is accurate, TEPCO seems to be operating under a much less stringent set of rules. In Japan, workers are not necessarily provided with a personal dosimeter. In the weeks before this post, CNN reported that all workers had been evacuated from the site except for a volunteer crew of 50, who remained on the site to do all the work. Its reported their work conditions were sparse, sleeping on metal floors, receiving very little food etc. Some reporters even hinted at a “suicide” group who has chosen to die to save their country. This seems more than a bit exaggerated.

How did the contaminated workers happen?

          What we do know is that only three have encountered serious radiation damage after mistakenly wading through highly radioactive water. These were hospitalized and, while their legs have received damage, there are no reports of their imminent death. In fact, a few days ago the three were released from the hospital. (At this dose level there is also the possibility of cancer onset later in life, but their whole body dose has not been published.) This is the reported extent of endangered human life to date. Three persons injured.

          This incident should not have happened, and seems to be a serious misjudgment by management at the site. These men should not have entered unknown (5 inch deep) water without a prior Geiger Counter check, and should have been equipped with dosimeters – which they were apparently not given.

 What’s the situation now?

          The government and TEPCO are not releasing much information to the press. Reactors 1 thru 4 have probably been ruined by salt corrosion from the sea water. They cannot be restarted safely. The spent fuel cooling pools have been exposed to the air from the Hydrogen explosions and then hundreds of tons of water poured in to cool the rods. The result is that draining water and steam are moving isotopes from these spent fuel rods out through the open roofs into the surrounding area, and down into the underground maintenance tunnels underneath the reactor buildings. This is most likely the source of the amounts of radiation being found on the grounds. No levels are given except for statements like “1000 times background”.       This is not meaningful since background levels of radiation vary considerably around the world. The media, in ominous terms, treats each new announcement of local ground contamination as “… a possible meltdown…”. In reality much of this probably originates from the spent fuel storage rooms since the roofs are blown off, and not from a containment breach. Ultimately reactors 1 thru 4 will have to be buried in borated cement. The land area will be declared a contaminated zone for many years.

          Reactors 5 and 6 seem to have been shut down and suffered few problems from the tsunami. These might be capable of restart sometime in the future, but not until safeguards have been increased, this accident thoroughly analyzed, and power sources protected against tsunami and catastrophic earthquake. 

 Has there been a “Meltdown” as the press keeps suggesting?

          First lets determine what we mean by the term. It has been often misused by the media. The classic description of a meltdown has probably come from the motion picture “The China Syndrome” which was ironically released about the time of the Three Mile Island accident. This movie “explained” that the fuel in a reactor could melt into a puddle and then burn its way through the bottom of the reactor containment and continue melting through the ground until it got to China! An emotionally scary concept which made a lucrative movie! This, even in the absolute worst case could not happen since the core of the planet is already molten with red heat and would absorb such a silly idea. Three Mile Island did have partial fuel melting but did not breach its containment vessel  – i.e. no meltdown.

          In theory it is possible for a mass of fuel to melt its way through the bottom of the (3 inch thick) steel containment, then out of the reactor room (3 feet of concrete) and into the ground below. This is precisely the accident that reactors are designed to prohibit.

          Every new discovery of radiation outside of the reactor is decried as evidence of a “meltdown”. There likely has been partial melting of the fuel rods inside the containment vessels, due to the high temperatures created inside. However I have heard no evidence that there has been a breach of containment in any of the BWR’s 1 to 4. Yes there is radiation being spread from the open fuel storage rooms above the reactors and from controlled venting of the pressure inside the containment vessels. This is of course a very serious situation; but it is just not a complete meltdown.

 Where is the seawater contamination coming from?

          On April 2nd, it was announced that a 9 inch crack has been discovered in a maintenance pool for reactor number 2 which was draining high level water into the sea. The following day this was described as a “5 inch crack”? The opening was located in a 20 foot long pipe in a flooded underground tunnel below the reactor containment. This was probably damage caused by the earth tremor. Workers recently entered the underground tunnel, and working in darkness, have located the crack and filled it with liquid glass and hardener. Latest news says this crack has now been successfully plugged and no further release into the sea is occurring.

          Seawater radiation levels were quoted as “millions of times higher than the legal limit…” .  The next day it became “ten’s of thousands of times…”? This very high radiation reading was most likely from Iodine 131, one of the most radioactive products of fission; it is a major isotope component of reactor fission products (about 3% by weight.) This radiation level will dissipate quickly as 131 I  has a half life of only 8 days i.e. every eight days half the amount present changes into inert Xenon. In the next 8 days half of the remaining again disappears et cetera. So we should expect these levels in the sea to dissipate quickly. In addition, the hugh volume of the sea is diluting the remaining effluent and mixing it into the vast areas of the ocean, which will also reduce its intensity ultimately to background level.

          Sea life can accumulate the Iodine it swallows from the sea and can become a health hazard to the thyroid if eaten. Here Potassium Iodide pills (the “Iodine pills” you hear about) could be taken by persons to safeguard against uptake*. It should be noted that radioactive 131I is often administered medically for treatment of thyroid adenomas, and Graves disease. Hopefully regulations will prohibit fishing in the local area for quite some time. Fish markets should check their products for traces before sale…  

(to be continued …)

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* In an emergency, don’t expect the government to give you these pills. There just ain’t enough to go around. Potassium Iodide pills (Thyrosafe) can be purchased at low cost in the U.S. from a website:   

              http://www.KI4U.com