3/9/22 Power Outage at Chernobyl
So this was posted a few hours ago and once again the world is freaking out over nothing.
This is concerning, but mostly for on-site personnel, it’s cold in Ukraine today! The problem is they followed it up with this:
As a nuclear engineer this immediately set off my BS alarms. Let's dig in.
Background
So there is only 1 place at Chernobyl where spent nuclear fuel (SNF) is stored in pools. That facility is ISF-1 and only contains fuel from the decommissioned Chernobyl units 1, 2, and 3. There is another, newer facility at Chernobyl, ISF-2, where SNF is stored in Dry Casks. Some of the SNF at ISF-2 in dry cask storage is from Chernobyl, some from other plants in Ukraine. Typically SNF is cool enough to remove from pool storage and place in dry storage after about 2-5 years. The Chernobyl fuel is at least 20y old as that is when the last reactor ceased operations.
So why has RBMK fuel sat in pools for 20 years? Well there is a little problem of geometry. You see, the fuel assemblies for RBMKs are far too long to fit in licensed dry casks, so they have to be cut in half. Assemblies are removed from the pools at ISF-1, placed in a special transport container on a special rail car, and transported to ISF-2. At ISF-2 the assemblies are removed from the transport container, cut in half, and placed in dry casks outside. A nice animation of this is here:
Risk of Fuel Melt?
Zero, absolutely zero. These assemblies have been cooling for 20 years and have extremely low hear output, about 50W per assembly.
The IAEA did a stress test about 10y ago to determine how long the water would last, what the max fuel temp would be when it’s all dry, and how long after the pool dried up it would take to reach that temp. They determined, under 45C environmental temperatures, that it would take about 2 months to evaporate all the water in the pool, and another 57 days to reach a final temperature of 300C. Note the current decay heat is about 30% less than what it was for that calc.
The Final Authority
The IAEA has stated exactly what I explained here, there is no critical safety concern, and the heat load is low enough that pumps aren't needed.
Additionally, we don’t even need to worry about any of this as Ukrenergo has announced that backup generators with 48hrs of fuel are on site and available should the need arise.
I did this as a rapid writeup on my phone. Please forgive spelling and grammatical errors.