Are we not talking about two different kinds of intermittency here? Both types require a level of redundant capacity within the system to make good any production loss at any given windfarm/nuclear site.

However wind-farm outage occurs regularly during calm periods whereas nuclear shut-downs are exceptional events. The capital costs of providing redundant capacity to provide cover for the loss of a GW of wind or nuclear capacity will be similar.  However the ongoing production cost of replacing 1 GW of wind energy on a regular basis will be a lot more than the occasional loss of 1 GW of nuclear energy.

It is a valid point, however, to point our that no production system is without its downtime (planned, unplanned, predictable or not) and that they thus all require a level of overcapacity within the system to guarantee 100% supply/demand balancing at all times.

Intermittancy is not limited to windfarms, and their generally more diffuse connections to the grid may make that easier to provide for than losing one giant nuclear plant at one point in the grid.

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