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maltatoday | SUNDAY • 21 AUGUST 2022 12 OPINION Shelling of Europe's biggest nuclear power plant exposes multiple risks SHELLING has recently inten- sified at the Russian-controlled Zaporizhzhia nuclear pow- er plant, raising international safety concerns. Ukrainian staff continue to operate the massive plant under strict control and stressful conditions. Both Russia and Ukraine are blaming one another for the continued attacks, and damage. Disinformation and fake news have played a major role in this conflict, and so the exact nature of the situation is unclear. It seems unlikely that either side would want to seriously damage Europe's biggest nucle- ar plant, in the near-frontline city of Enerhodar, and cause a release of radiation. Ukrain- ian plant workers claim that Russia is deliberately targeting non-critical equipment. A de- liberate attack against a nucle- ar facility would break inter- national norms, and concerns over the potentially dangerous consequences are well justified. This plant is not like Cherno- byl, the site of the world's big- gest nuclear disaster. Chernobyl was an older reactor type, with several questionable design choices. Like Zaporizhzhia, it was cooled by water, but it al- so contained large quantities of graphite to perform a function known as neutron moderation, which is necessary for the reac- tor to operate. When the Cher- nobyl reactor overheated, the water boiled away and became less effective at cooling. How- ever, the graphite continued to moderate the neutrons, allow- ing the reactor power and thus temperature to build uncon- trollably. The shutdown system at Chernobyl was also poorly designed and contributed to the accident. At Zaporizhzhia, as with the majority of reactors globally, if the reactor overheats, both cooling and moderation are re- duced, and so the reactor power also reduces. Nuclear engineers see this as fundamental to safe reactor design. But a breach of a fuelled and operating reactor could still be disastrous if attacks damage nu- clear materials or safety-critical equipment. This could release large quantities of hazardous nuclear material into the air, potentially contaminating vast areas of land and water supplies. The reactors are surrounded by high strength containment buildings. These are designed to both contain explosions from within, and to withstand a cer- tain amount of force from out- side. However, while modern plants are designed to withstand aircraft strikes, it is debatable whether they could withstand deliberate bombardment. They are made of many metres of concrete, with steel liners, but a concerted effort with appropri- ate weapons would eventually be able to penetrate them. Of perhaps greater concern are the outdoor spent fuel cooling pools, where highly radioactive spent nuclear fuel is stored un- derwater. A direct attack on any of these could lead to a major release of radioactive material into the atmosphere, as the fuel is relatively unprotected against strikes from the air. Safety-critical equipment, such as pumps and pipes, re- mains important even after the nuclear power plant has been shut down. Three of Zapor- izhzhia's six reactor units are currently in a shutdown state. Fuel within the reactor, as well as used fuel, remains very hot for several years after shutdown and removal from the reactor. At plants such as Zaporizhzhia, unless the fuel is constantly cooled, it can overheat, gener- ating explosive gases, melting, or catching fire. This would also lead to a radiation release. The fuel at Zaporizhzhia re- quires a constant flow of cool- ing water over it to take away excess heat. Should this water be lost through damage to pip- ing, pools or reactors, or should pumps become inoperative, there would only be a limited time to intervene before dan- gerous consequences might be felt. Claimed attacks thus far have largely hit power lines, ra- diation monitoring equipment, and non-nuclear buildings such as training facilities. The attacks on power lines are particular- ly worrying, as reliable access to offsite power is required for cooling water pumping. The plant can generate its own pow- er during operation, and has a range of back-up diesel gener- ators in case access to offsite power fails, but the loss of any safety system is a concern. Should there be a release of Ross Peel Ross Peel is Research and Knowledge Transfer Manager, King's College London A serviceman with a Russian flag on his uniform stands guard near the Zaporizhzhia Nuclear Power Plant in the course of Ukraine-Russia conflict outside the Russian-controlled city of Enerhodar in the Zaporizhzhia region