I received this from an expert on nuclear power and nuclear weapons
I think there are two targets in Russia that, if hit by NATO long-range missiles, could trigger a massive response from Russia. Those would be Moscow and the nuclear power plant in Kursk.
The Storm Shadow and Taurus cruise missiles do not have sufficient range to hit Moscow (the US has an extended-range JASSM missile that could hit targets in Moscow but there is no evidence that they have been transferred to Ukraine).
I think the greatest danger is a concerted attack on the two RMBK Chernobyl-type nuclear reactors at Kursk, which lack the protective concrete and steel dome (the reactor containment vessel that typically has steel-lined concrete walls that are 3 feet thick) that are found on more modern reactors. The spent fuel pools, which are next to the reactors, are equally vulnerable; these pools hold several complete sets of used (“spent”) fuel rods that hold 5 to 10 times more long-lived radiation (in particular, Cesium 137) than the reactor cores.
These reactors and spent fuel pools are in range of the Storm Shadow, Scalp, Taurus, and standard JASSM cruise missiles; they would be destroyed by a direct hit from these missiles, which are armed with 900 to 1000-pound high-explosive warheads.
The destruction of these reactors and spent fuel pools would release far more radiation than was released by the destruction of the Chernobyl reactor.
The subject of nuclear reactors and spent fuel pools becoming targets in war has been studiously avoided by MSM and proponents of nuclear power.