Reuters is reporting that a Ukrainian attack hit the reactor dome of reactor #6 at Zaporizhzhia Nuclear Power Plant (ZNPP). The article is very clear that radiation levels at the plant are stable.
This is exactly what I would expect of any attack short of a bunker-buster style bomb. The containment structure is engineered to withstand external impacts, as well as contain the results of any reactor accident. There is also the fact that all the reactors at the facility have been shutdown for 18 months, so decay heat is very low.
Containment is 1 of 3 fission product barriers. These are just what they sound like: things that keep the dangerous fission products contained away from any people.
The first, and most important fission product barrier is the fuel itself. Nuclear fuel rods are essentially pipes with small pellets of ceramic UO2 fuel inside of them. The fuel pellets themselves are very robust and will generally not melt until around 5000F centerline temperature. The pipe that surrounds the fuel pellets is called the cladding. It is made of an alloy of zirconium. As long as cladding temperatures stay below ~2000F, the cladding should not fail either.
The safety systems at nuclear plants are designed to ensure that, even in the event of a severe accident, the fuel is prevented from reaching these limits. The emergency core cooling systems for US reactors must comply with 10CFR50.46. These acceptance criteria ensure that the results of any accident are acceptable. ZNPP has a similar system, with high pressure and high flow pumps to keep the core covered in the event of an accident.
A lot more goes into how nuclear plants are designed to protect the fuel, but this is almost irrelevant at ZNPP. The reactors have been shutdown for so long that decay heat is very low. The fuel can still melt, but it would be a slow process with plenty of time for the crews to take action to prevent it.
The second barrier is the reactor coolant system itself. This includes the reactor vessel and all associated piping. This system is designed to operate at high temperatures (600F) and pressure (2500 psig), and to contain any fission products that do leak out of damaged fuel inside of it.
All of the the reactor coolant system is located inside the containment structure, so any leakage from the RCS is isolated. The containment at ZNPP is a 3.6 foot thick pre-tensioned concrete dome and is lined with .33 inches of steel. This is thicker than the walls of most military bunkers. It is designed to contain the consequences of an accident occurring from full power operations with minimal leakage.
In order for their to be a significant release of radiation from ZNPP, all three of these barriers must be overcome. A small bomb, such as the possible drone strike being reported, would hardly damage the containment structure at all. US containment structures are similar in design and can withstand the impact of a large passenger jet with minimal damage. To test this, the government rammed a Phantom fighter jet into a similar wall. The jet lost.
https://youtu.be/xESkLydLt3Y?si=0e8ZMKG6t4rFPySs
All the reactors are the plant are shutdown and cold, except reactor #4. Reactor #4 is hot (but still shutdown), but the fuel is not at high temperatures. The heat they are using to make steam actually comes from the huge reactor coolant pumps, not the nuclear fuel. This reactor is hot and at high pressure, but the massive amount of energy contained in hot fuel when an accident happens at 100% power is just not there.
Even if a bomb or missile did manage to breach the containment structure, I still don’t think a significant release is likely. None of the units at the plant have been critical since September of 2022. The decay heat and fission product inventory has fallen drastically since then.
IMO, the only way for the ZNPP to cause a large scale disaster at this point would be intentional sabotage. Any external attack large enough to destroy the containment and reactor building would almost certainly be nuclear itself.
The biggest risk for any kind of nuclear event at the ZNPP remains an extended loss of electrical power to the site and a failure of the dozen or so emergency diesel generators. This would remove power from the systems cooling the cores. They would slowly heat up, and if nothing was done to cool them, eventually begin to melt. This would take a few days and the only way I see the crews being unable to get some cooling in place in that time frame is the Russians preventing it.
As always, open source. Here are some links.
https://finance.yahoo.com/news/2-russia-says-ukraine-strikes-131122287.html
https://www.nrc.gov/reading-rm/doc-collections/cfr/part050/part050-0046.html
https://www.oecd-nea.org/jcms/pl_66130/ukraine-current-status-of-nuclear-power-installations
Sleepy Neutron's Nuclear Knowledge 
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