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According to reports, Ukraine has claimed “explosive devices” were placed on the roof of the plant’s third and fourth reactors on Tuesday.
Comment supplied by Fatti per Capire, an SMC-like organisation providing the views of scientists on controversial topics in Italy:
Dr Alessandro Dodaro, Director of Nuclear Fusion and Nuclear Security Technologies Department, National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Italy, said:
“The risk with the Zaporizhzhia nuclear plant is extremely low, and limited to possible consequences only and exclusively in the adjacent area. Even if a huge load of explosives were to be triggered, and if – in the very unlikely case – this would have damaged the core of the reactor causing leakage of material, the latter would not have the energy to expand into the rest of the world. The material would be instead ejected from the roof and would fall back not far from the nuclear plant. However, this is an extremely unlikely event. The walls of the reactor are made of very thick pre-stressed reinforced concrete and are designed to withstand even aircraft and missile impacts. Even more important is the fact that the core’s container, named vessel, is made of very thick steel. Even in the case the building collapses, the vessel may not be destroyed. The metaphor is that of the pressure cooker: if a building collapses with the pressure cooker inside, it is not definite that this will break, because of its resistance characteristics.
“The radioactive material, as mentioned, could not be spread very far. What would happen would be in fact an implosion, a collapse of the reactor building, in which the core would not explode outwards as happened in Chernobyl. In that case the material had been ejected outwards and there had been a widespread fire, due to the fact that the one of Chernobyl was not a water-cooled reactor and the reactor had exploded because of the enormous heat inside. In a water reactor like the one in Zaporizhzhia, fire is not contemplated. The probability of the spread of a radioactive cloud in Europe that replicates what happened in Chernobyl is close to absolute zero, even if a missile would hit Zaporizhzhia.
“Even a power outage would cause very little damage, because the reactors at Zaporizhzhia have been shut down since quite a long time and have already cooled down enough. The spent fuel, to be disposed as radioactive waste, is stored in buildings that have the same characteristics as the building containing the reactor itself: in any case there would be no significant release into the environment.
“In the case of Zaporizhzhia the possible most dangerous radioactive element is iodine-131, which in any case by now, given the long inactivity of the plant, has completely decayed and therefore does not involve any risk. To be more specific, iodine-131 decays by half every eight days. It means that, out of a thousand nuclei, after eight days 500 remain, after sixteen 250, and after eighty it has almost disappeared. Luckly, Zaporizhzhia’s reactors have been shut down for enough months to have allowed the radioactive iodine, to decay down to such little quantities as to be of little concern.
“In conclusion, any fear of a hypothetical radioactive cloud that could spread on Europe has no scientific basis. The risks are, in my opinion, very small, limited to the area surrounding the nuclear plant.
“It is clear that if somebody really wanted to cause a catastrophic accident there is a way, but with an enormous technical and organizational effort – it would be equivalent to dropping an atomic bomb on the plant. No one could pass it off as an accident of war.”
Prof Andrew Whittaker, State University of New York, Buffalo and Chair, ASCE Nuclear Standards Committee, said:
“Nuclear power plants are robust, hardened structures that are designed to resist the effects of extreme natural and man-made hazards. However, like other industrial infrastructure, nuclear power plants were not meant to operate within a warzone. It is a violation of international law and norms for a military to target a civil nuclear power plant or to use it as a military base or a launching pad for military operations.
“Breaching the steel-reinforced, concrete walls of a ZNPP containment building would be extremely difficult without expert technical knowledge. Containment buildings are designed to keep radioactive materials trapped inside in the event of an accident. If a ZNPP containment structure was somehow breached, there would be no significant release of radioactivity unless other barriers were also compromised. The use of multiple, independent barriers to prevent release of radionuclides, termed defence in depth in the nuclear industry in North America, the UK, Europe, and Asia, has been practiced for decades.
“Zaporizhzhia’s six reactors have been shut down for over ten months and are no longer making enough heat to cause a radiological release that could affect the public. The cooling needs for the shutdown reactors are relatively low and can be supplied with on-site equipment.”
Dr Mark Foreman, Associate Professor of Nuclear Chemistry / Industrial Materials Recycling, Chalmers University of Technology, Sweden, said:
“It is impossible for me to know exactly how the nuclear power plant has been sabotaged or prepared for an act of sabotage. For public safety reasons I refuse to discuss how someone might sabotage the reactor site. I have no idea how much people who might want to do this know about nuclear technology, and I am not going to give them an education on how to commit dangerous acts of vandalism. I am sure that other professionals in the nuclear sector will have a similar point of view.
“After the Chernobyl accident and after some of the hydrogen bomb tests (such as Ivy Mike and Castle Bravo) in the South Pacific the largest set of health effects in the general public were thyroid cancer. The reason why these events caused thyroid cancer is that the general public (children in particular) were exposed to short-lived radioactive iodine. There has been epidemiology work done in Sweden which indicates that moderate exposure to the longer lived iodines is not carcinogenic. The shorter lived iodines have half lives of less than a week. As none of the reactors have been used for months to generate electric power for exporting from the plant into the Ukrainian grid then the shorter lived iodines will have decayed away. I have seen reports that one of the reactors has been used to generate electric power for the needs of the site.
“But I suspect that the reactor will have been operated at a far lower power level than normal, if a reactor is operated for a long time (months) at a constant power then the amount of the shortlived radioisotopes in the reactor will reach an equilibrium level which is proportional to the power output of the core. So if the core is rated to make 3000 MW of heat then if it was operated for months at 30 MW then the reactor would contain 100 times less of the shortlived radioisotopes than if it had been operated at 3000 MW. This power history of the plants over the last year will tend to reduce the amount of the these shortlived radioisotopes.
“Radiation biology has a lot of uncertainties regarding low doses of radiation, much of what we know is from events where people had doses delivered to them in less than a minute. The majority of the dose delivered during the nuclear air attacks on Hiroshima and Nagasaki would have been delivered in less than a second by the bomb detonations. The people who survived the initial effects of the bombs were followed through life to try to find out how carcinogenic is radiation. The data from these studies is not good as the number of people who survived the bombs initial effects and had large doses was a small.
“What happened with radiation biology is that the limited data that we have in humans for high doses was combined with data from animal studies (such as with dogs) and the data for cells, then this was extrapolated back towards a zero dose. This has created a thing called the LNT model. Linear No Threshold model, the LNT model is one where the chance of developing a cancer is proportional to the radiation dose and there is no lower dose required to induce a cancer. I hold the view that the LNT model might be wrong, but of all the models which exist it is the least bad model. There are some people who claim that low doses of radiation are more dangerous than the LNT model claims but these are fringe opinions. I have had dealings with one very vocal advocate of another model which suggests that low doses are far more dangerous than the LNT model suggests but the evidence which this person cites is not convincing.
“Experience with the cohort of people whose mothers worked at Mayak while pregnant and adsorbed very large fetus doses by modern standards suggests that prebirth occupational exposure is not carcinogenic. This occupational exposure would have been chronic exposure delivered over many days / weeks. The classic work which indicates that prebirth irradiation with X-rays is carcinogenic was the work of Alice Stewart who looked at the health effects of diagnostic X-rays on the health of children. The radiation doses in Alice Stewart’s work would have been delivered in less than a minute. This reduces the chance of cells to self repair.
“The LNT model gives no credit for self repair which occurs if the dose is delivered over a long time rather than in a short time. The LNT model is a conservative model which is designed to err on the side of being overprotective rather than on the other side.
“For the acute effects of radiation which the public normally calls “radiation sickness” there are clear threshold doses required to cause the health effects. By lowering the radiation dose to people by lowering the amount of radioactivity which is available to release from the site the potential for a release of radioactivity from the site to cause “radiation sickness” in workers or the general public is greatly reduced. In some ways we know a lot more about acute effects of high doses of radiation than we know about the long term effects of small doses. Also for the short terms effects of radiation we know from animal experiments, studies of cells made during research on radiotherapy and on the few people who have been in radiation accidents that the longer the time that the radiation dose is spread over the smaller its ability to kill and maim.
“Thus if you have the choice between having a 10 Gy dose of gamma rays delivered to you in one minute and a having the same 10 Gy delivered to you over ten days, you are far better off having the protracted radiation dose. It will be less likely to kill the cells in vital organs. So a reduction in the radiation dose per day will reduce the ability of the radiation to kill people.
“If the bombs are on the roof then it will be possible to damage the building, but it will be hard for a bomb outside the building to destroy the reactors.
“There have been some nuclear reactors in which explosions have occurred. These are the SL1 reactor in the USA, a reactor during the BORAX trials and also Chernobyl. In terms of long term effects the Chernobyl accident was the worst of the three which come to mind. I do not think that the off site consequences of the SL1 and BORAX accidents were severe. What happened in the BORAX trial was that a series of nuclear safety trials were done in which greater and greater efforts were made to make a nuclear reactor explode. In the final test the size of the power surge was a bit bigger than was expected thus it does count as a reactor accident. But the effects of the BORAX accident were very limited when compared with the Chernobyl accident.
“Both BORAX and SL1 were much smaller than the reactors at the Zaporizhzhia site, but the key things which increased the release from Chernobyl were
“I think that if someone sets off a bomb on the roof then it might be possible to damage the containment building, but even a cracked or damaged containment can provide some protection.”
Dr Mark Wenman, Reader in Nuclear Materials, Imperial College London, said:
“Whilst we cannot be sure if there are any explosives, or where they are, the reactor containment buildings are very robust, made from 1.2 m thick heavily reinforced concrete, and able to withstand earthquakes and aircraft impact strikes. The reactors are themselves all now shut down and have been for many months meaning they are not generating a lot of heat anymore. The spent fuel, in the so-called fuel ponds, is within this robust concrete containment structure, which did not exist at Chernobyl. Any cold fuel, which is stored in concrete and steel containers outside on site is too cold to heat itself and cause a radioactive release.
“It would take a very concerted effort to damage the containment building and cause any form of radioactive release from within. Even then the most notable isotope of concern to humans, iodine-131, has all gone due to the time elapsed since the reactors were operational. Overall the risks are still very small.”
Declared interests
Dr Alessandro Dodaro: “No conflicts of interest to declare.”
Dr Mark Foreman: “I have worked for years on advanced nuclear reprocessing, normally funded by the European Union. I have also worked on reactor / radiation safety funded by the Swedish Radiation Protection authority (SSM) and APRI (A body funded by utility companies). I have also worked on nuclear waste chemistry funded by both SSM and the Swedish Nuclear Waste disposal company (SKB). I have had some training from a nuclear power using utility company, I have had the training needed to work in reactor buildings in a safe manner and I know how to work with radioactivity in a lab setting.”
Dr Mark Wenman: “No conflicts.”
For all other experts, no reply to our request for DOIs was received.