Nuclear power plants cannot be controlled and attempting to do so is dangerous

Nuclear power plants, although often used at full power, can perform "load following" as in France, without compromising their safety if it is done in accordance with rules. However, this modulation can accelerate the wear of some parts.

It is sometimes said that nuclear power plants are uncontrollable and are therefore intrinsically incompatible with intermittent renewable production. Some even go so far as to say that attempting modulation with a nuclear reactor threatens its safety.

A rare practice on a global scale but common in France

While we observe that most nuclear power plants are constantly operating at full power ("baseload"), this is not the case for all of them. The French nuclear fleet is the perfect counter-example: because of the very large share of nuclear power in the French electricity mix, French power plants perform what is called "load following" to adapt their production to residual consumption (= consumption – non-controllable production) [1], using control rods specially designed for this operating mode. When the use of the reactor in load following is carried out in accordance with the various safety rules, reactor safety is not threatened in any way.

Premature wear of some parts: a topic of controversy

It is generally recognized that the power modulation of a nuclear reactor can accelerate the wear of certain parts and therefore increase the need for maintenance, in particular at the level of the secondary circuit. However, the extent of this phenomenon remains subject to debate [2] [3]. 

It is therefore necessary for the operator to carry out an economic optimization between the possible loss in the event of sale at too low a price [3] and the additional maintenance cost induced by load following. Today, starting from design, EPR reactors account for the possibility of load following operation, which makes it possible to further improve the flexibility of reactors [4].