French regulator Autorité de Sûreté Nucléaire (ASN) has temporarily modified its prescriptions governing thermal discharges from several NPPs. ASN said that, “faced with the exceptional meteorological situation, and in response to the need to ensure the safety of the electrical network and to save the natural gas and water reserves of the hydroelectric dams”, it was “temporarily modifying its prescriptions governing thermal discharges from nuclear power plants at Blayais, Bugey, Golfech, Saint-Alban and Tricastin”.

The current exceptional episode of heat wave and drought is leading to the warming of certain rivers used to cool NPPs, it said, adding that temperature forecasts still remain high and continue to affect stream temperatures.

“In addition, the issues of public necessity associated on the one hand with the security of the electricity network required by RTE and on the other hand with the preservation of the natural gas and water reserves of the hydroelectric dams in view of the fall and next winter, lead the Government to wish to maintain as much as possible the electricity production of the nuclear power stations.”

ASN said that, after reviewing the issues related to environmental protection, it had adopted a decision setting temporary requirements relating to thermal discharges from the Blayais, Bugey, Golfech, Saint-Alban and Tricastin nuclear power plants until 11 September.

ASN explained that, for some power plants, based on experience feedback from the 2003 and 2006 heat waves, two levels of thermal discharge limits are permanently prescribed. The first level applies during normal climatic conditions. When these limits cannot be respected mainly due to the temperature of the water upstream of the plant, the power of the reactors is lowered to reduce the effect of thermal discharges on the natural environment. This can go as far as the complete shutdown of the reactor.

The second level of limit applies during periods of high temperature. This limit level can only be used if the electricity network operator (RTE) expresses the need to maintain a minimum power to ensure the security of the electricity network. It applies without a decision from ASN, which is however informed. It is associated with an enhanced environmental monitoring programme. This second limit level was used this summer by the Golfech NPP for a few days.

However, the exceptional meteorological and hydraulic situation encountered this summer led to an unusual rise in the temperature of certain rivers. “Due to this exceptional situation, the limit values in force (the first and second levels set out above) on the temperature of liquid discharges could not be respected, which would lead, preventively to any overrun, to the reduction of the power , or even the shutdown of the electricity production of the reactors concerned.” ASN noted. “When, at the same time, the need to maintain the operation of these reactors is a public necessity, the provisions… the environment code allow ASN, based on a request sent by EDF, to temporarily modify its requirements governing thermal discharges from the nuclear power plants concerned.”

RTE identifies the need to maintain until 21 August the NPPs of Blayais, Bugey, Golfech, Saint-Alban and Tricastin at a minimum level of electricity production to ensure the security of the electricity network. “In addition, the context of tension on the reserves of natural gas and water of the hydroelectric dams for the fall and winter of 2022/2023 has led the Government to save them now by optimising electricity production of nuclear origin. The Ministry of Energy Transition considers that it is a public necessity to favour the production of electricity of nuclear origin and therefore to maintain the production of these five power stations until 11 September despite the exceptional climatic conditions.”

In this context, EDF has submitted to ASN a request for temporary modification of the thermal discharge limits of the Blayais, Bugey, Golfech, Saint-Alban and Tricastin nuclear power plants until September 11, 2022.

Image: Tricastin nuclear power plant (photo courtesy of EDF)