The Danger at Zaporizhzhia Nuclear Power Plant

Ukrainian warnings are becoming more urgent that the Russians plan an incident at the Zaporizhzhia Nuclear Power Plant. The warnings have been coming for about a week. The latest is that explosives have been rigged on top of two of the reactor buildings to simulate Ukrainian shelling of the plant. Other accusations are that the plant or the pond that holds the cooling water for the plant are mined.

The Russians are countering with accusations of their own.

Rafael Mariano Grossi, the Director General of the IAEA, has visited the plant recently, and two IAEA staff have been stationed at the plant. He says that the parts of the plant he has seen are not mined, but he has not seen everything he wants to see. He plans to go back in the near future.

Washington Post and the New York Times have both had articles about these warnings and accusations. The Times story is mostly human interest about people living near the plant. The Post story has a number of inaccuracies.

1. Iodine tablets are not a general protection against radiation. They protect against radioiodine damage to the thyroid gland. Radioiodine has a relatively short half-life, and the reactors have been shut down for some time, so radioiodine will not be a large component of any release. The tablets should be taken only when exposure is imminent.
2. The Post cites Ukrainian officials, who have consistently exaggerated dangers to the reactors. This may be part of their propaganda offensive, for which nobody can blame them, but their claims cannot be taken at face value.

The six reactors at ZNPP are not at all like the Chernobyl reactor and cannot, CAN NOT, have the same kind of accident. Chernobyl had a graphite moderator, and the building it was in was not the heavily reinforced concrete of the reactors at ZNPP. The ZNPP reactors have hard oxide fuel encased in metal, and are inside a stainless steel vessel. Chernobyl had no such vessel.

This is the top of a reactor of the Chernobyl type. This one is at the Ignalina Nuclear Power Plant, Lithuania – the upper biological shield lies several meters below the floor of the reactor hall. There are no channel covers on the fuel channels of the reactor; the control rod drives are below the colored covers.

Here is a vessel for a ZNPP type reactor in transport, before the reactor is placed into it. The vessel will hold the equivalent of all those channels you can see the top of in the other picture. [CORRECTION: This photo replaces an earlier one, which was incorrect.]

The Post mentions the possibliity of a Fukushima-type accident. The reactors at Fukushima operated right up until the earthquake. The ZNPP reactors have been mostly shut down for months. That means that the Fukushima reactors were much hotter, both thermally and radiologically, than the ZNPP reactors are now. Additionally, all control was lost at Fukushima. There are measures the ZNPP operators can take to mitigate such an accident.

I think – but am not positive – that the outer buildings at Fukushima were not as sturdy as those at ZNPP, which would make containment more likely at ZNPP.

The current understanding is that the Fukushima release was less dangerous than was believed at the time. The evacuation turned out to be more dangerous.

Any or all of the ZNPP reactors could be damaged so that they would need extensive repairs or could become useless without a radiation release. There is a spent fuel pond which is less protected, but it would take expert explosive rigging to disperse the fuel rods, and they would likely disperse in chunks in the immediate vicinity of the plant, not in a cloud. It’s harder to pulverize things with explosives than might appear from movies.

The danger to the plant is wholly Russia’s responsibility for starting the war and occupying the plant.

Cross-posted to Nuclear Diner