There are reports that the International Atomic Energy Agency (IAEA) has lost contact with Chernobyl nuclear data systems and that the Chernobyl site is currently cut off from the power supply.
Malcolm Grimston, Hon. Senior Research Fellow at the Imperial Centre for Energy Policy and Technology, Imperial College London, said:
“The IAEA (referring back to Update 8 – IAEA Director General Statement on Situation in Ukraine | IAEA issued March 3) is making the point that the decay heat in the spent fuel is now very low – there are some 20,000 assemblies at the site, each generating an average of the order of 35 Watts of heat (according to a source at the Argonne Nuclear Laboratory in the US). If correct, this has two implications: first that, in the event of a complete and sustained loss of power, the water in the cooling pools would only reach around 60C (over several weeks) before heat loss at the surface was sufficient to reach equilibrium – though the water level would obviously have to be kept topped up – and second that even if all the water escaped the maximum temperature that the most active assemblies would reach would be of the order of 300C, well within the normal operating temperature when it was in the reactor and for which its zirconium cladding was designed (though of course this would create considerable difficulties in handling). Indeed I gather the Chernobyl operators were already in the process of moving some of the spent fuel to a dry fuel store as circulating air is now all that is needed to keep the temperature down in many cases.
“In all it is difficult to create a route whereby there would be more than very local contamination, or even that. There is no motive force to push any material into the atmosphere (unlike at the time of the accident), the vast bulk of the radioactivity has decayed away (including, many years ago, all of the iodine-131 associated with the threat of thyroid cancer, which only has a half-life of 8 days) and the fuel is still in the robust ceramic form it took when in the operating reactors. That being said, clearly a return of power to ensure that monitoring equipment is operating, restore communications, maintain proper ventilation, take some much unwanted stress off the shoulders of the operators and allow the ongoing long-term work on the site is important.”
Mr Tony Roulstone, Department of Engineering, University of Cambridge, said:
This comment was updated with a correction on 10/03/2022
“Cutting the power to Chernobyl required to cool the fuel possibly could lead to the overheating due to lack of power for cooling other than the stand-by generators. It is not as worrying as Fukushima because the Chernobyl reactors have already been shut down for a long time and the decay heat will be very much reduced. Nevertheless, it is an unhealthy situation for both for staff at the site and the surrounding area.
“Spent fuel is more of a long-term problem. Until cooling water in the pond has boiled off uncovering the fuel, which will take many weeks, the fuel should remain adequately cooled containing the radioactive fission products.
“The lack of ventilation and fire systems will become a problem if there were to be release from the fuel, or if there was a fire. The lack of these safety systems is therefore a conditional concern.”
Prof Tom Scott, Professor in Materials, University of Bristol, said:
“I would concur with the IAEA statement released this morning that the spent fuel in the storage ponds at Chernobyl does not present a substantial risk, even with the current power outage.
“The fuel in these pools is decades old, and hence has very little residual heat being generated. This low heat load added to the very large volume of water in the cooling pools means that the heat coming from the fuel can be dissipated safely even without power to circulate the water. Hence the risk of spent fuel overheating is relatively low but it is still very important that the situation at the plant (and other nuclear facilities in Ukraine) should still continue to be actively reported to the IAEA. Any break in communications needs to be quickly re-established.”
Prof Claire Corkhill, Chair in Nuclear Material Degradation at the University of Sheffield, said:
“With the electricity supply to the Chernobyl site unavailable, there are several areas of concern with regards to the safety of the nuclear material stored there.
“Spent nuclear fuel, originating from reactors 1 and 3, is stored in a cooling pond. This material produces heat through radioactive decay and requires constant cooling, which is achieved by pumping fresh cool water into the ponds. With no power supply, this water could slowly evaporate, potentially resulting in contamination of the building by low levels of radioactive isotopes.
“It is essential that radiation monitoring systems are able to constantly monitor the situation inside reactor 4 so that we can be aware of any potential reasons for concern about the exposed nuclear fuel that resides there.
“Another serious concern is the maintenance of the ventilation system in the New Safe Confinement structure. This prevents further degradation of Reactor number 4 and the hazardous exposed nuclear fuel within, and is essential to the future decommissioning of the site. If there is no power to this structure, we could see the complete failure of the 1.5 billion euro decommissioning programme to make the site safe once and for all.”
Dr Mark Foreman, Associate Professor of Nuclear Chemistry at Chalmers University of Technology, Sweden, said:
“Any nuclear or radioactivity site where either the radioactivity is not well sealed or where cooling is needed normally needs a supply of electric power to operate safety equipment such as ventilation and cooling plant which is needed to keep the materials in a safe state. By cutting off the power lines to Chernobyl the site will have to depend on their own generators, which will have a limited supply of diesel or gas.
“I think that the event is far less serious than the on-site power failure which caused the nuclear accident at Fukushima. While the fuel in the ponds needs to be kept cool, the last Chernobyl reactors were shut down years ago so the heat generation in the used fuel stored in their ponds will be far less than that of the fuel in the reactors at Fukushima which had been in operation very recently. I think that while it is important to avoid the cooling ponds drying out, the consequences of drying out the ponds will be far less than either the Chernobyl accident of 1987 or the more recent Fukushima accident.
“I think that drying out the ponds will generate a threat to workers rather than the general public. If the thickness of the water layer above the fuel becomes too small then the radiation levels in the fuel store and nearby will increase. If the fuel was allowed to stay dried out for a long time then it might be possible for some damage to occur to the cladding of the fuel. Depending on how clean the insides of the ponds are drying them out might mobilize some radioactivity.
“But I would not expect a large release of radioactivity on the scale of the 1987 accident which would have consequences outside the plant site. It is also important to note that drying out of the ponds will not cause a nuclear reaction or explosion to occur.
“I think that the loss of ventilation will reduce the ability of the site to manage radioactive dust and to protect workers, I strongly suspect that conditions for the workers will get worse. It may become much harder for workers to enter some parts of the site without full protective clothing, they may also have greater difficulty in changing in and out of their protective clothing. Some parts of the site might become off limits to the workers until the power is restored.
Prof Geraldine Thomas, Imperial College London and Director of the Chernobyl Tissue Bank, said:
“The Chernobyl Power Plant has been shut down since 2000, and therefore the spent fuel rods stored on the site have been cooled for 22 years. Therefore they will not be producing significant amounts of heat, making a release of radiation very unlikely. In the unlikely event of a release of any radiation, this would be only to the immediate local area, and therefore not pose any threat to Western Europe – there would be no radioactive cloud. The workforce in the plant are a group of highly skilled and dedicated individuals. The greatest threat is to their wellbeing from lack of food and rest, as a result of being prevented from leaving the plant, rather than from radiation.”
Dr Mark Wenman, Reader in Nuclear Materials at Nuclear Energy Futures, Imperial College London, said:
“Whilst this is a another concerning development the last reactor unit at Chernobyl was shut down over 20 years ago and units 1 and 2 were shut down between 1991 and 1996. This means the heat, produced by the fuel in the storage ponds will have substantially reduced (decayed) over the 20-30 year period. The fuel storage ponds are also very deep and would likely take weeks for the water to boil down even without cooling pumps active. This should hopefully allow enough time for the power to cooling systems to be restored.
“It is also concerning that communications with the IAEA to the plant are being lost so it will be far more difficult to get up to date live information on the ongoing situation.
“Fire is another risk to the plant in general but this is less concerning as the worst radioactivity is in the fuel, which is protected by being underwater.”