Without accounting for any nuclear payloads being detonated intentionally, this weapon's propulsion at most risks a radiation leak if it crashes unintentionally. This is the terrifying part. Given what the purpose is for, this isn't something like nuclear submarines on patrol around the world, the scale of fuel and contamination being much greater if accidents happen. I doubt the Russians would loiter more of these cruise missiles than there are nuclear subs on patrol by all SSN and SSBN operators. And personally do not think they would be launching them in any significant numbers unless it is nuclear war, in which case, any faults are the least of humanity's worries.
Calling this a flying Chernobyl is rather jingoistic and what we can expect to hear from mouth foaming mindless western journalists. The genuine extra risk would be the fact that the missile flies around and would naturally be dealing with hazards that a nuclear submarine is far more engineered to overcome in corresponding hazards when operating underwater. I doubt you have the space and weight to engineer extra "protections" and redundancies for this cruise missile than nuke boat engineers have for their vehicles. Nevertheless the scale of operation and the type of weapon means it is seldom used, if ever. Overall the risks are no greater than having about 70 nuclear boats in total constantly operating around the worlds oceans. Unless of course the Russians intend for these missiles to operate in the same manner in which case yes it will pose a greater threat but the chances of that being the intention is slim to none.
They will insist on working this project out and that unfortunately for everyone else including Russia, is dangerous. That's a matter for states to discuss and if there are accidents during testing and development that involve another nation, then that's a bilateral matter first and then an international matter if the scale is serious and the outcomes uncertain. It's a type of weapon Russia considers useful I suppose. The reactor technology and propulsion is definitely interesting but the weapon itself is of course scary to have flying around. Gee I suppose that would mean some belligerent nations should stop being so belligerent and constantly attacking others? Maybe then people and countries won't even feel a need to risk these things
But of course it's always our faults and never theirs right. But Russia attacked Ukraine and so on... well look further back and see the bigger picture.