Nuclear power plants are based on the principle of layered safety mechanisms. The risk of failure of any safety system is low — and therefore, the risk of multiple systems collapsing like dominoes is extremely low. However, according to James Acton, director of the Nuclear Policy Program at the Carnegie Endowment for Peace, an active war zone would affect that system.
On Twitter, Acton noted the increased risk of “common mode” failures, where both the primary and backup systems fail simultaneously. In one scenario, a Russian attack on Ukraine’s power system disconnects the nuclear plant from the power grid, and then a safety incident, such as a fire, occurs. Normally, if power goes out and reactors need to be powered up, there are backup systems in place to keep the power plant cool – the IAEA recommends 72 hours of fuel use, Acton noted in an email. to WIRED. In times of peace, that should be enough time for the grid to return, or the arrival of the fire brigade, or at least to resupply diesel to run the emergency generator. In wartime, the arrival of such things is not guaranteed. The risk of such an incident is still very low, Acton wrotebut in war, “the unthinkable becomes completely imaginable.”
The Chernobyl plant, known as a “first generation” reactor, used graphite as a “modulator”, to slow down neutrons and facilitate fission chain reactions. But graphite burns, and when the graphite begins to melt, it helps release radioactive material into the air. After the disaster, that design was dropped worldwide. Currently, in Ukraine and elsewhere, most nuclear plants have “pressurized water reactors,” which use water, not graphite. But while newer water reactors are safer, the risk remains if plant operators cannot keep the cooling system running, as the water heated by the fuel rods needs to be replaced. with cool water.
“If the cooling system isn’t working, that’s the prescription for it,” said Bob Rosner, a physicist at the University of Chicago and former Bulletin chair of the Council for Science and Security of Atomic Scientists. disaster. He recalls the 2011 Fukushima Daiichi disaster in Japan, when the reactors there were cut off from the power grid by a 9.0-magnitude earthquake offshore. Then the ensuing tsunami knocked out the emergency diesel generators. Some spare battery power remains, but eventually runs out. With reactors no longer able to run their cooling pumps, much of the uncapped nuclear fuel would then melt.
Rosner says that Ukraine’s nuclear plants are aging to no avail. Most were built in the 1980s, dating back to the Soviet era; the only reactors the country has shut down are Chernobyl’s. In particular, the Rivne reactors northwest of Kyiv are near or have passed 40 years old limit. (In the US, plant operators can usually get their licenses extended for an additional 20 years, after necessary inspections and maintenance.) fuel. It is usually made of steel, but after years of bombardment by neutrons, the steel becomes brittle and can crack. Rosner said older reactors, like most in Ukraine, need constant monitoring for that reason.
