ASN Report 2020

cooling systems for equipment required for the nuclear safety case will in particular be improved. EDF has also initiated a climatic monitoring programme to anticipate climate changes which could compromise the temperature hypotheses adopted in its baseline requirements. ASN asked EDF to take account of the operating experience feedback from the heatwaves of 2015, 2016 and 2019, and their effects on the facilities. Other hazards The safety case for the EDF NPPs also takes account of other hazards such as high winds, snow, tornados, lightning, cold air temperatures, man-made hazards (transport of dangerous goods, industrial facilities, airplane crashes, etc.), and hazards affecting the heatsink. 2.4.6 Assessment of the risk prevention measures relating to hazards The Fukushima Daiichi NPP accident led EDF to reinforce its organisation for the management of risks relating to extreme hazards. More specifically, networks of coordinators were set up for all the NPPs to oversee the implementation of the actions defined to deal with these hazards. Annual reviews are also held to improve this organisation. Fire risks ASN observes that management of the fire risk needs to be improved, with a number of outbreaks of fire recorded in 2020 comparable to that observed in 2018, whereas it had been lower in 2019. The findings made in previous years are still relevant with regard to some of the sites inspected: ∙ deviations in management of equipment stores, which have high calorific potentials; ∙ deviations in the use of fire permits and management of the compensatory measures defined in the fire risk assessments that could be improved; ∙ deviations linked to the management of fire detection inhibitions; ∙ premises sectorisation anomalies management that could be improved in order to prevent the spread of a fire; ∙ firefighting equipment availability not guaranteed. In 2020, ASN carried out inspections on the topic of fire management on all the NPPs, despite the constraints arising from the health situation and asked for corrective measures to be taken to remedy the findings made. ASN observes the efforts made by certain sites to take the corrective measures needed, with the deployment of tools and Operation of nuclear reactors during heat waves The temperatures considered in the nuclear reactors safety case are regularly reassessed, notably during the periodic safety reviews. These reassessments take account of climate change. A heat wave has three main consequences for the operation of nuclear reactors. 1. The operation of safety systems during a heat wave: • In a heat wave, ventilation and air-conditioning systems are needed to guarantee the operation of the safety systems of the nuclear reactors. • Since the heat waves of 2003 and 2006, EDF has reinforced the ventilation and air-conditioning capacity of the premises containing the safety systems. These systems undergo preventive servicing, monitoring and maintenance and the general operating rules for the reactors make provision for steps to be taken in the event of failure of this equipment. This entails taking special measures, or even shutting down the reactor, as necessary. • In addition, EDF sets out special operating rules which, between April and October of each year, adapt the level of deployment of the internal organisations on the basis of the weather forecasts. 2. Reactor cooling and effluent management in the event of drought or low water levels: • Nuclear reactors must be permanently cooled in order to remain safe. Water is thus taken for this purpose from a watercourse or from the sea. • A period of drought can lead to a drop in the level and discharge of a watercourse. The licensee must permanently ensure that these remain sufficient to cool the safety systems. These parameters are specific to each nuclear reactor. • The discharge of the watercourse also affects the dispersal of liquid effluents from the nuclear reactors. For each Nuclear Power Plant (NPP), ASN sets a minimum watercourse discharge value at which effluent discharges are possible. Below this discharge rate (low water situation), effluent discharges are prohibited and the licensee has to store the effluents produced. 3. Controlling thermal discharges: • The water intake from watercourses or the sea to cool the reactor is generally speaking discharged at a higher temperature, either directly, or after cooling in the cooling towers, enabling some of the heat to be dissipated into the atmosphere. • In the case of NPPs using a watercourse, ASN has for each site defined the conditions for discharge of the water used for cooling. In order to protect the environment, the ecosystem in particular, limit values are set for the heating of the watercourse as a result of operation of the NPP, as well as for the temperature of the water downstream of the plant. If these limit values are exceeded, the licensee shall reduce the power of the reactor or shut it down. Since 2006, ASN has incorporated measures into the regulations covering NPP discharges, to define the operations of NPPs in exceptional climatic conditions leading to significant warming of the watercourse. These provisions are however only applicable if the security of the electricity grid is at stake. Temporary relaxation of the limit values for the thermal discharges may also be authorised by ASN, on the basis of a justified request from EDF, if there is a risk to the security of the electricity grid, as was the case during the heat waves of 2003 and 2006. In this case, environmental monitoring is reinforced. • During the heat waves of 2019, EDF had to shut down several reactors and reduce the power of some others. ASN Report on the state of nuclear safety and radiation protection in France in 2020 299 10 – THE EDF NUCLEAR POWER PLANTS 10