analysis codes, boron, computer analysis codes, dangers of nuclear, Japan, major hazard management, MOX, MOX fuel, neutron poison, nuclear accident, nuclear energy, nuclear excursion, nuclear re-start, nuclear reactors, risk assessment, risk probability
Some recent comments, about the proposed re-opening of a Japanese nuclear reactor, are more broadly applicable: the dangers of MOX fuel, as well as the possibility of the nuclear industry manipulating computer analysis codes to get the answer which they want.
We have been suspicious of the possibility of the nuclear industry manipulating computer analyses, simply because we have never read of an analysis being used to see if continued operation of a nuclear reactor is safe. Rather, we always read about how computer analysis will be used to prove that they are safe, or some similar language. The wording suggests that they are setting out to prove that the nuclear reactors are safe. And, they could quickly and easily use the computer programs to play with the numbers, until they get what they want “proven”: that the nuclear reactors are safe. When thinking of this, I always think of two computer programmers who, long ago, tried to write computer codes to game the lottery.
However, it seems that the manipulation could be even more basic – faulty assumptions by either design, or by ignorance.
As we have discussed elsewhere, there are too many variables, some of which are, or may be, unknown. This includes the randomness of the radiation impact on materials, as well as unknowns in the material fabrication process.
From the CNIC (Citizens’ Nuclear Information Center) Japan response to the call for public comments (December 18, 2014 to January 16, 2015) regarding KEPCO’s draft report on reopening Takahama Nuclear Reactors:
Issue 2: The problem of MOX fuel
KEPCO has applied for the new regulatory requirements compliance screening on the premise that the Takahama NPP Units 3 and 4 will be loaded with MOX fuel. The draft report states that the critical boron concentration* will be set at 1,850 ppm, somewhat higher than the roughly 1,700 ppm for general uranium reactor cores. This is because MOX fuel is more reactive than uranium fuel.
According to the severe accident scenarios in the application document to NRA from KEPCO, the boron concentration in the primary coolant is usually set at 2,800 ppm at Takahama NPP. If, due to some accident, an inflow of pure water causes a reduction in the boron concentration, a mere one minute is all the time that will be available to stop the concentration reduction before it reaches the critical boron concentration. When some kind of trouble arises, will it be possible to deal with the situation with only this thin margin of safety?
Furthermore, it has been claimed that all spent fuel will be reprocessed in Japan, but even the Rokkasho reprocessing plant, intended for the reprocessing of spent uranium fuel, has had to postpone the start of operations 22 times and is effectively inoperable. There is no likelihood of a MOX fuel reprocessing plant being constructed in this situation. Thus the MOX fuel used at Takahama NPP has nowhere to go and will simply continue to accumulate at the NPP site. Since spent MOX fuel has a higher heat release value than spent uranium fuel, it will be necessary to store it in a spent fuel pool for a longer period.
NRA maintains that the behavior and characteristics of MOX fuel differ very little from uranium fuel, and that therefore no special safety standards are necessary. However, the nuclear reactions are extremely fast, difficult to control, and can very rapidly get out of hand once the means of control have been overwhelmed by the reactions. The reaction is accelerated and difficult to control in the case of MOX fuel. Moreover, the storage of MOX fuel at NPP sites is a huge cause for concern and anxiety among local residents. It is unacceptable that MOX fuel should be used without special safety standards.
Issue 3: The arbitrary use of analysis codes and the whittling away of accident likelihoods
KEPCO claims that the analysis codes it uses in countermeasure scenarios against severe accidents are appropriate, and the NRA has approved this procedure.
For instance, in the scenarios submitted by KEPCO, up until the time when the reactor vessel is damaged, 75% of all the zirconium in the reactor core reacts with water. The hydrogen then produced by the molten core concrete interaction (MCCI) is said, according to the analysis code MAAP (an analysis code which gives the extremely safe result that once the MCCI reaction begins all other reactions will cease), to be 6% of the amount of the zirconium, resulting in the hydrogen concentration being at or lower than 13% by volume. This 13% by volume is the judgement criterion for a detonation stipulated in the regulatory requirements. In other words, use of the result of the MAAP analysis will lead to highly dangerous design conditions.
However, despite the fact that the NRA acting chairman Fuketa has recognized that the analysis code for MCCI has not yet reached the level of practical application (September 24, 2014 regular press conference), the NRA has approved this analysis result and claims that assuming 75% of the zirconium reacts is, in itself, sufficiently conservative and that there is therefore no problem.
What this means is that KEPCO has carried out an arbitrary analysis in order to clear the numerical hurdles required by the regulatory requirements, and by saying that the regulatory requirements have been set conservatively, the NRA has then approved the analysis. There are far too many of these arbitrary usages of analysis codes to mention, and this procedure of using codes to whittle away the likelihood of the occurrence of accidents is an extremely serious problem.
NAIIC report here http://warp.da.ndl.go.jp/info:ndljp/pid/3856371/naiic.go.jp/en/report/
*In pressurized water reactors, the output of the reactor is adjusted by the absorption of neutrons by boron dissolved in the primary coolant. The concentration of boron at criticality is known as the critical boron concentration.
(Hajime Matsukubo, CNIC)” Entire comment at link: http://www.cnic.jp/english/newsletter/nit164/nit164articles/04_Takahama.html (Emphasis our own).
Note that the CNIC has long researched MOX: “During 1995-97, the center spearheaded an independent study on mixed uranium-plutonium oxide (MOX) fuel with a number of prominent researchers from Europe, the U.S.A., and Japan.” http://www.cnic.jp/english/cnic/index.html (Read more at the link)
THE IMPLICATION IS THAT IF THERE IS NOT ENOUGH BORON AND IF NO WORKER IS ABLE TO REACT ALMOST INSTANTLY, THE NUCLEAR REACTION WILL GET OF CONTROL IN AN “EXCURSION” AND IT IS HIGHLY PROBABLE THAT THERE WOULD BE A NUCLEAR DISASTER.
“Soluble poisons, also called chemical shim, produce a spatially uniform neutron absorption when dissolved in the water coolant. The most common soluble poison in commercial pressurized water reactors (PWR) is boric acid, which is often referred to as soluble boron. The boric acid in the coolant decreases the thermal utilization factor, causing a decrease in reactivity. By varying the concentration of boric acid in the coolant, a process referred to as boration and dilution, the reactivity of the core can be easily varied. If the boron concentration is increased, the coolant/moderator absorbs more neutrons, adding negative reactivity. If the boron concentration is reduced (dilution), positive reactivity is added. The changing of boron concentration in a PWR is a slow process and is used primarily to compensate for fuel burnout or poison buildup.” http://en.wikipedia.org/wiki/Neutron_poison
“Lies, damned lies, and statistics” http://en.wikipedia.org/wiki/Lies,_damned_lies,_and_statistics
Photo Credit: “Revolving lottery machine,kaitenshiki-cyusenki(回転式抽選機),japan”, 23 December 2007, by katorisi, CC-BY-3.0 via Wikipedia” http://en.wikipedia.org/wiki/Lottery_machine
Were the two computer programmers, in question, successful in gaming the lottery? Nope. They failed, probably largely because they went about it the wrong way. Their assumptions were wrong. They weren’t that bright. Maybe they were too honest. In fact, I think they were only approaching it according to how many tickets they would have to buy to have a good statistical chance of winning and they found it too costly. Others have developed ways and means to outwit the system, which you can read about online. Lotteries apparently have sometimes even been used for money-laundering.