Why is nuclear+short term storage not an option

Because cold winter days exist. Yes you can only build nuclear capacities for the average day and then short-term storage to match the demand pattern. But you would need to do so for the day(s) of the year with the highest energy demand, a cold winter day. What do you do with those capacities the remaining year as throttling nuclear down is not really saving much costs (most lie in construction and deconstruction)?