Thread by @ManagingtheAtom

Incoming 🧵 by Matthew Bunn, the James R. Schlesinger Professor of the Practice of Energy, National Security, and Foreign Policy at the Harvard Kennedy School (and PI of Managing the Atom): (1/x)

It appears that Russian forces are shelling the Zaporizhzhia nuclear power plant. At least one building at the site is on fire. Live cam: Zhaporizhzhia (2/x)

This is shockingly reckless, and a violation of multiple agreements. (3/x)

The member states of the IAEA unanimously agreed years ago that attacking a nuclear power plant “constitutes a violation of the principles of the United Nations Charter, international law and the Statute of the Agency,” as IAEA DG @Rafael Grossi has pointed out. (4/x)

This shelling COULD cause a major radioactive release, but it’s too soon to tell whether (a) that will happen, (b) that’s what Russian forces intended, or (c) if it does happen, how big the release will be. (5/x)

The most crucial thing for maintaining safety of a nuclear plant is keeping the core cooled. In the core of a nuclear reactor, and even in its spent fuel pool, there’s a LOT of heat... (6/x)

...even if the reactor has been shut down (it comes from radioactive decay of the fission products). If it’s not kept continuously cooled, bad things happen, as we saw at Fukushima. (7/x)

That cooling requires off-site electricity to run the relevant pumps and so on. Because sometimes electricity goes down, all nuclear reactors have on-site diesel generators as a backup (and typically batteries that can last for a few hours). (8/x)

Shelling could cause what’s called “station blackout” – if the off-site power goes down, and either the diesel generators don’t work or they run out of fuel. (9/x)

Then the reactor’s cooling would fail and the reactor would melt down, and a radioactive release would be quite likely (though the specifics depend on how well the building holds in the steam pressure... (10/x)

...and whether hydrogen released from the reaction of the zirconium fuel cladding with high-temperature steam detonates and causes an explosion that shatters the building, as happened at Fukushima, etc.) (11/x)

Shelling could also cause damage to critical cooling systems – pumps, pipes, etc. – but in general the building surrounding the reactor is heavily reinforced concrete, so those systems MAY be adequately protected. (12/x)

The spent fuel pool, outside the heavily protected reactor building, is also an issue. (13/x)

If IT loses electricity, the water will eventually boil/evaporate away, the fuel would melt and make a nasty mess in the pool, which might NOT lead to a radioactive release, depending on the design of the fuel building. (14/x)

If the fuel building was shattered by shelling, then any fission products released from the melted fuel could get out into the surrounding countryside. Shelling could also cause a water leak that could lead to fuel melting, even if the electricity stayed on. (15/x)

IF the fuel pool is really overstuffed with spent fuel , AND the hot fuel assemblies recently discharged from the reactor are stored next to each other (rather than interspersed throughout the pool)... (16/x)

...the fuel can get so hot it catches fire – that, plus a shattering of the building, is really the worst-case scenario. That could release a quantity of radioactivity even worse than Chernobyl, potentially. (17/x)

Exactly under what circumstances fire would occur is hotly debated, as there is very little real data on the subject. (18/x)

If anyone has good data on the quantity of spent fuel in the pools at Zhaporizhzhia, and the arrangements for preventing fire, I’d [Matthew Bunn] want to see it, as should others. (19/x)

Staff are likely to be unable to continue at the plant. Responsible staff will likely have shut down the reactors at the site by now, but even so, the heat from radioactive decay is is still getting generated, (20/x)

the cooling still has to happen – you need knowledgeable operators on-site to keep things safe. None of these plants are “walk-away safe.” Nevertheless, the main hazard to Ukrainians today is bullets, shells, and bombs, not radiation. (21/21)