The final working reactor on the Zaporizhzhia Nuclear Energy Plant, reactor No. 6, has been safely shut down. Xinhua Information Company by way of Getty Photographs
Energoatom, operator of the Zaporizhzhia Nuclear Energy Plant within the Ukrainian metropolis of Enerhodar, introduced on Sept. 11, 2022, that it was shutting down the final working reactor of the plant’s six reactors, reactor No. 6. The operators have put the reactor in chilly shutdown to reduce the danger of a radiation leak from fight within the space across the nuclear energy plant.
The Dialog requested Najmedin Meshkati, a professor and nuclear security professional on the College of Southern California, to elucidate chilly shutdown, what it means for the security of the nuclear energy plant, and the continued dangers to the plant’s spent gasoline, which is uranium that has been largely however not utterly depleted by the fission response that drives nuclear energy crops.
What does it imply to have a nuclear reactor in chilly shutdown?
The fission response that generates warmth in a nuclear energy plant is produced by positioning a variety of uranium gasoline rods in shut proximity. Shutting down a nuclear reactor entails inserting management rods between the gasoline rods to cease the fission response.
The reactor is then in cooldown mode because the temperature decreases. In line with the U.S. Nuclear Regulatory Fee, as soon as the temperature is under 200 levels Fahrenheit (93 Celsius) and the reactor coolant system is at atmospheric strain, the reactor is in chilly shutdown.
When the reactor is working, it requires cooling to soak up the warmth and hold the gasoline rods from melting collectively, which might set off a catastrophic chain response. When a reactor is in chilly shutdown, it not wants the identical stage of circulation.
The Zaporizhzhia Nuclear Energy Plant makes use of pressurized water reactors.
How does being in chilly shutdown enhance the plant’s security?
The shutdown has eliminated an enormous ingredient of danger. The Zaporizhzhia Nuclear Energy Plant is a pressurized water reactor. These reactors want fixed cooling, and the cooling pumps are gigantic, highly effective, electricity-guzzling machines.
Chilly shutdown is the state by which you do not want to continuously run the first cooling pumps on the similar stage to flow into the cooling water within the main cooling loop. The Worldwide Atomic Power Company (IAEA) has reported that reactor No. 6 is now in a chilly shutdown state like the ability’s 5 different reactors, and would require much less energy for cooling. Now, at the very least if the plant loses offsite energy, the operators gained’t have to fret about cooling an working reactor with cranky diesel mills.
And by shutting down reactor No. 6, the plant operators may be relieved of a substantial quantity of their workload monitoring the reactors amid the continued uncertainties across the website. This considerably diminished the potential for human error.
The operators’ jobs are prone to be a lot much less demanding and nerve-racking now than earlier than. Nevertheless, they nonetheless have to continuously monitor the standing of the shutdown reactors and the spent gasoline swimming pools.
What are the dangers from the spent gasoline on the plant?
The plant nonetheless wants a dependable supply of electrical energy to chill the six large spent gasoline swimming pools which might be contained in the containment buildings and to take away residual warmth from the shutdown reactors. The cooling pumps for the spent gasoline swimming pools want a lot much less electrical energy than the cooling pumps on the reactor’s main and secondary loops, and the spent gasoline cooling system might tolerate a short electrical energy outage.
Another vital issue is that the spent gasoline storage racks within the spent gasoline swimming pools on the Zaporizhzhia Nuclear Energy Plant had been compacted to extend capability, in keeping with a 2017 Ukrainian authorities report back to the IAEA. The higher quantity and extra compacted the saved spent gasoline rods, the extra warmth they generate and so extra energy is required to chill them.
These huge concrete cylinders retailer spent nuclear gasoline rods. The Zaporizhzhia Nuclear Energy Plant shops a lot of its spent gasoline open air in casks like these.
U.S. Nuclear Regulatory Fee
There may be additionally a dry spent gasoline storage facility on the plant. Dry spent gasoline storage entails packing spent gasoline rods into huge cylinders, or casks, which require no water or different coolants. The casks are designed to maintain the gasoline rods contained for at the very least 50 years. Nevertheless, the casks usually are not underneath the containment buildings on the plant, and, although they had been designed to face up to being crashed into by an airliner, it’s not clear whether or not artillery shelling and aerial bombardment, notably repeated assaults, might crack open the casks and launch radiation into the grounds of the plant.
The closest analogy to this state of affairs might be a terrorist assault that, in keeping with a seminal examine by the Nationwide Analysis Council, might breach a dry cask and doubtlessly outcome within the launch of radioactive materials from the spent gasoline. This might occur via the dispersion of gasoline particles or fragments or the dispersion of radioactive aerosols. This could be much like the detonation of a “soiled bomb,” which, relying on wind course and dispersion radius, might lead to radioactive contamination. This in flip might trigger severe issues for entry to and work within the plant.
Subsequent steps from the IAEA and UN
The IAEA has referred to as on Russia and Ukraine to arrange a “security and safety safety zone” across the plant. Nevertheless, the IAEA is a science and engineering inspectorate and technical help company. Negotiating and establishing a safety zone at a nuclear energy plant in a warfare zone is solely unprecedented and completely totally different from all previous IAEA efforts.
Establishing a safety zone requires negotiations and approvals on the highest political and army ranges in Kyiv and Moscow. It might be achieved via backchannel, Observe II-type diplomacy, particularly nuclear safety-focused engineering diplomacy. Within the meantime, the IAEA wants robust help from the United Nations Safety Council within the type of a decision, mandate or the creation of a particular fee.
Najmedin Meshkati acquired analysis funding from the U.S. Nuclear Regulatory Fee within the mid-Nineties.
