ASN Report 2017

348 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants Heat wave and drought risks During the heat waves in recent decades, some of the rivers used to cool NPPs experienced a reduction in their flow rate and significant warming. Significant temperature rises were also observed in certain NPP facilities housing heat- sensitive equipment. EDF took account of this experience feedback and initiated reassessments of the operation of its facilities in air and water temperature conditions more extreme than those initially included in the design. In parallel with development of these “extreme heat” baseline safety requirements, EDF initiated the deployment of priority modifications (such as an increase in the capacity of certain heat exchangers) and adopted operating practices optimising the cooling capacity of the equipment and improving the resistance of equipment susceptible to high temperatures. For the periodic safety review of the 1,300 MWe reactors, EDF has initiated a modifications programme on its facilities designed to provide protection against the effects of a heat wave situation. The capacity of certain cooling systems for equipment required for the nuclear safety case will in particular be improved. EDF has also initiated a climatic monitoring programme in order to anticipate climate changes, which could compromise the temperature hypotheses adopted in its baseline safety standards. With regard to the 900 MWe reactors, ASN gave its consent in 2012 to the implementation of the baseline safety requirements and integration of the resulting modifications. ASN also asked EDF to take account of the comments it made during this examination process with a view to drafting and implementing baseline requirements applicable to other types of reactors. In 2016, ASN asked EDF to take account of the lessons learned from the heat wave events of  2015 and  2016, along with their effects on the facilities, in the studies planned for the fourth periodic safety reviews of the 900 MWe reactors. The conclusions of these studies could, as applicable, be taken into account in the revision of the studies concerning other types of reactors. The impact on thermal discharges from the NPPs NPPs discharge hot effluents into rivers or the sea, either directly, from those NPPs operating with direct or “once- through” cooling, or after cooling of these effluents in cooling towers, enabling some of the heat to be dissipated to the atmosphere. Thermal discharges from NPPs lead to a temperature rise between the points upstream and downstream of the discharge which, depending on the reactors, can range from a few tenths of a degree to several degrees. These thermal discharges are regulated by ASN resolutions. Since 2006, provisions have been incorporated into these resolutions in order to define in advance the operating modes of NPPs in exceptional climatic conditions that would lead to significant warming of the watercourse. These special provisions are however only applicable if the security of the electricity grid is at stake. Lightning risks The measures taken to address the lightning risk for the NPPs is currently primarily based on the steps specified by the regulations applicable to installations classified for protection of the environment. These regulations require the performance of a lightning risk assessment to identify whether or not it is necessary to protect the various buildings, along with a technical study to determine the nature of the protection systems to be installed (mainly lightning arresters and lightning conductors), where they are installed and how they are checked and maintained. During the fourth periodic review of the 900 MWe reactors, ASN indicated that it considered that the application of this order would not enable a sufficient level of safety to be attained on the NPPs and asked EDF to transmit a new methodology more particularly taking account of plausible combinations with other hazards and the secondary effects of lightning (fires, loss of off-site electrical power supplies). This methodology is currently being reviewed by ASN. Other hazards The safety case for the EDF NPPs also takes account of other hazards such as high winds, tornados, cold air temperature, man-made hazards (transport of dangerous goods, industrial facilities, airplane crashes, etc.), and hazards affecting the heatsink. 2.4.6 Evaluation of the risk prevention measures relating to hazards The Fukushima Daiichi accident led EDF to reinforce its organisation for the management of risks relating to hazards. Networks of coordinators were in particular appointed on all the NPP sites to oversee the organisation related to these risks. Annual reviews are also held to improve this organisation. On the basis of its inspections, with regard to the fire risk, ASN observes that the integration of operating experience feedback is on the whole satisfactory and that the refurbishment of the fire detection system is continuing on the nuclear reactors. However, the number of outbreaks of fire recorded for 2017 is slightly higher than that for 2016. An outbreak of fire on 19th June 2017 in the Bugey NPP led to activation of the PUI. Moreover, the findings made in previous years are still valid with regard to some of the sites inspected: ཛྷ ཛྷ management of zoning anomalies in the premises could be improved in order to prevent the spread of fire; ཛྷ ཛྷ deviations linked to the management of fire detection inhibitions; ཛྷ ཛྷ deviations in the management of stores of equipment representing significant heat potential, in particular during reactor outage phases; ཛྷ ཛྷ deviations in the use of fire permits; ཛྷ ཛྷ problems with the accessibility of fire-fighting equipment. ASN notes the efforts made by certain sites to reduce these deviations through the deployment of tools and action plans, but considers that if they are to be effective, the personnel must receive more comprehensive assistance with their implementation. In addition the time taken to remedy certain