Well there is no difference in practice, as the reactors are closed anyway. But they are not closed because the physics don’t work, or because they are function

Well there is no difference in practice, as the reactors are closed anyway. But they are not closed because the physics don’t work, or because they are functionally unable to work in the current situation (the “nuclear cannot work when it’s hot” line you see in some newspapers). Nobody has done a serious assessment when the limits were decided, more based on guesswork than anything else. The reactors are at ~300°C. It does not matter one bit if the input water is at 40°C or 20°C. As for the output, if temperatures keep increasing it just means they will have to build pools to let the water cool down some more before going back to the river or recycled through the external cooling loops. If the water level is the problem, the quantities involved are negligible compared to the throughput of a large river or what we spray on maize fields.