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Fukushima Q & A (update 7/11/11)
(The following questions have been submitted by readers of this website. The issues in question are either not answerable in the "Fukushima Accident" page, or the numerous other pages of this website. All questions sent through the "contact" button of the site menu will be answered, either personally or on this page.)
Q - When you mention seawater contamination levels, you never say anything about Cesium. Why?
A - Cesium is not considered to be nearly the health hazard of Iodine in sea water, unless the concentrations are extremely high...100 (for Cs-137) to 1000 (Cs-134) times greater than the I-131 health standard. No one drinks sea water, of course, but it is something to consider with respect to the sea's food fishes. Cesium is only mildly soluble what little is ingested in fish passes through their bodies very rapidly...no longer than a day or two. Very little actually gets into the meat of the fish. On the other hand, Iodine is much more soluble in water and has a much longer retention time in the fish of up to 80 days (the effective radioactive lifetime of I-131). Regardless, the Cesium levels found in the seas have not approached the health standards since April, 2011.
Q - Has anyone written to you saying anything negative about how you are depicting the events at Fukushima?
A - Out of more than 100 Emails, only one has been negative! All other Emailers have been quite appreciative of the rationality involved and our devotion to presenting the facts in a fashion devoid of fearful terminology. That so few have said anything negative is frankly astonishing to the writer. Back in the 1980s, a local newspaper editor told me that opponents to nuclear energy seldom confront those who support the peaceful uses of the atom. They avoid confrontation for two reasons. First, they don't want to take a chance on challenging their personal foundation of "objectivity"; they don't want to find out they might be basing their opinions on misconceptions and misunderstandings. Second, the groups who oppose nuclear energy don't want their membership exposed to the "other side", and run the risk of losing supporters. I'm assuming it's just as true today as it was nearly three decades ago.
Q – Zirconium alloy is used in reactors, and it will make hydrogen gas if over-heated. Why would the super-smart people designing reactors do something as bad as this?
A – One of the necessities in designing a reactor that will produce a fission chain reaction, and an efficient one, is building the core out of materials that do not absorb neutrons. (With the exception of the control rods, of course.) Zirconium is a highly non-corrosive metal (another necessity) that is transparent to neutrons. It should be noted that the water in the reactor is also relatively transparent to neutrons. But not totally. The hydrogen atoms on the water molecules slow down the very fast-moving, freshly-released high-energy neutrons (necessary step for a reactor chain reaction). Plus, the U-238 (95% - 99% of the fuel) is quite transparent to both the fast and slow neutrons. Regardless, Zirconium is, to date, the best neutron-transparent material for the tubes that hold the uranium fuel, which also meets the strict, demanding non-corrosive criteria required for reactor fuel cells. Without a doubt, if a better material is ever discovered or synthesized, it will be used and replace the zirconium.
Q - The Nuclear Regulatory Commission and International Atomic Energy Agency both continue to say Zirconium-based spent fuel pool fires are possible, but you say it's impossible.
A - If the spent fuel in ever reached ~4,000 degrees centigrade, the Zirconium would certainly burn. The problem with the Zirconium fire scenario is getting to such an incredibly high temperature inside a spent fuel pool. Let's assume the spent fuel pool goes dry due to rapid evaporation caused by on-going decay heat production. (This would take at least ten days, in a worst case situation.) Instead of the heat being removed by water, it would now be lost to the air surrounding the fuel and effectively dispersed into the huge air volume inside the pool's enclosed building. There is no way on God's Green Earth for the dry fuel to reach the extraordinary temperature that would result in a Zirconium fire. The NRC and the IAEA say it is highly improbable, largely in the interest of politically-correct conservatism. We say "impossible".
The Zirconium fire myth has been reported by most western press and a few Japanese papers citing the western press reports. The source of this myth is nuclear nay-sayer authors who refer to the low grade Zirconium powder that used to be used to make the popping flash in old-time camera flash bulbs. Modern Zirconium alloys are very high grade, and the metal is not in powdered form in nuclear fuel cells. There is, and never has been any realistic connection between the two.
Q - As I understand it, the nuclear reaction cannot happen without water to slow the neutrons. So what's the point of putting the used fuel into to a water pool?
A - The spent fuel cells at Fukushima are stored in vertical racks, and boric acid is added to the pool's water to absorb stray neutrons. This prevents any neutron moderation that occurs within a fuel cell from propagating into a chain reaction. There is some industry information that says the aluminum alloy used in storage racks also absorbs neutrons and makes a chain reaction even more unlikely, but we have not been able to confirm.
Q - Can you better explain the process by which hydrogen is produced in a nuclear reactor? Did the very visible Fukushima explosions---reported as “hydrogen” based---actually mean the reactor core was somewhat exposed and meltdown had occurred?
A - Boiling Water Reactors are not cooled with hydrogen, and there is not enough radiolysis inside a nuclear reactor to be worthy of mention. The Hydrogen production at Fukushima was probably due to the water level inside the three stricken reactors dipping below the tops of the fuel cells, if not a lot lower. Once "uncovered" the zirconium tubes (cladding) which holds the uranium pellets rapidly heat up in the steam environment above the water level. The interaction of overheated zirconium and steam generates the free hydrogen, and the more of the fuel cell that gets uncovered the more hydrogen that gets produced. Inside the reactor, this hydrogen is in no danger of ignition because there is no "spark" for ignition and the steam/water atmosphere is incorrect for ignition. The explosive danger occurs outside the reactor if and when pressure relief valves open to the suppression pool (torus) and the hydrogen becomes free in the building atmosphere. The buildup in the upper refueling deck areas of the three stricken power plants at Fukushima must have been terrific, judging by the video of Unit No. 1 blowing its top off.
Has there been fuel damage in these three reactors which produced the hydrogen? Unquestionably. Meltage of the fuel matrix? Absolutely. The degree of meltage is considerable, and surely greater than what happened at Three Mile island for all three fukushima fuel cells. There have been some media "experts" and Japanese academics who say there has been "melt-throughs" where all the melted fuel ate its way through the bottom of the Reactor Pressure Vessels (RPV) and literally plopped into molten heaps onto the stell-reinforced concrete basemats beneath. On-going temperature indications on the three RPVs demonstrate that all, or nearly all of the melted fuel (corium) remains inside and did not melt through. It is likely that a very small fraction of the corium dripped through instrument penetrations and around some of the control rod drive housings that go through the RPV bottom heads, but nothing like the melt-through scenarios reported.
Regardless, the fuel damage caused the hydrogen explosions at Fukushima. The hydrogen explosions did not cause the fuel cells to melt. In fact, it seems the fuel in each reactor began to melt several hours before each building's hydrogen blast. Plus, there is no doubt of unit #2 melting its fuel, but the building itself was not demolished by a hydrogen explosion.
Q- You mentioned 1 sievert being an LD-1. I gather this is from acute radiation poisoning. This may be viewed as underestimating the impact, as oncogenic (cancer causing) doses are likely far lower. You might want to address that.
A - The 1 sievert threshold statement is based on acute (short term) exposure using the Linear, No Threshold model (LNT). Chronic (over a long period of time) exposure actually raises the threshold to 2 sieverts or more, using the somatic radiation hormesis model. However, the conservatism used in establishing either the LNT or Hormesis threshold results an overestimation of risk. I'm sure many will challenge this point, but it doesn't change the reality of it.
As far as “oncogenic” dose vs. radiation risk modeling, there is considerable difference in the radiation-induced cancer risk threshold between the LNT model and radiation hormesis. Please keep in mind that LNT-based cancer risks are predicated on the “Cancer, Single Cell Theory”, which assumes that once a single cancerous cell emerges in someone's body, there is a risk of it propagating into a full-blown cancer disease. This is the foundation of "oncogenic" radiation risk. The single cell theory gives no credit to the body's natural cellular repair and removal properties, nor does it credit the recently discovered DNA repair mechanisms that occur through activation of a small portion of what used to be called “junk DNA”. The hormesis model takes bodily and repair mechanisms based on actual human population medical records.
We are not challenging the cancer single cell notion in general. It has been a paradigm of medical research and cancer treatment for more than 4 decades with considerable success, but there is no actual human population data to support applying it to low level radiation exposure. On the contrary, recent high background dose research with human populations strongly suggests applying the single cell theory to radiation exposure is incorrect. In fact, it seems populations that experience elevated exposures over long time periods develop an elevated level of immunity to high radiological exposures.
Q - You make Fukushima sound as if it is nothing to be worried about. Everything is rosy, right?
A - We are not sure this Emailer has actually been reading the updates. First, we have been taking the Japanese government and Nuclear and Industrial Safety Agency to task for not taking stronger tsunami protective measures, similar to those taken in the United States over the past two decades. It is probable that the accident could have been avoided if these more stringent safety standards had been met. Second, we have literally castigated the Health Physics program of the Tokyo Electric Power Company for poor emergency worker exposure control, lax worker anti-contamination control, and tardy internal exposure monitoring for emergency workers. Third, as more and more information becomes available, we admonished the Japanese "officials" for absolutely horrible public informational flow. These are but three examples of our not saying "everything" is rosy with respect to Fukushima Daiichi.
Q - Why do you mostly use Japanese news media? Isn't the Japanese news media controlled by their government?
A - Let's answer the second question first. There is nothing to support the belief that the Japanese government controls their country's news media. In fact, the Japanese Press has been lambasting the government in Tokyo for months, alledging withholding of information, inadequate nuclear safety regulations, and confounding public protection measures.
We don't often mention western news reports because they are almost always "spin-doctored" in as negative a fashion as possible. The west often speculates and exaggerates to amplify the fearful tone of their reporting. We agree with the general feelings of the Japanese Press that western news media disrespects their readers and viewers by trying to make the news sound more fearful than it actually might be. And, it's not only nuclear news that gets a bogey-man twist. They seem to do it to all major news topics.
On the other hand, the Japanese Press merely reports the news and leaves the "spin-doctoring" out of it. It's the same news we get in the west, without the irresponsible gloom and doom.