ASN Report 2018

1.7  ̶  Other systems important for safety The other main systems or circuits important for safety and required for reactor operation are: ∙ ∙ the Component Cooling System (RRI) which cools a certain number of nuclear equipment items. This system functions in a closed loop between the auxiliary and safeguard systems on the one hand and the systems carrying water from the river or sea (heatsink) on the other; ∙ ∙ the Essential Service Water System (SEC) which cools the RRI system with water from the river or sea (heatsink). This is a backup system comprising two redundant lines. In certain situations, each of its lines is capable of removing heat from the reactor to the heatsink; ∙ ∙ the Reactor Cavity and Spent Fuel Pool Cooling and Treatment System (PTR), used notably to remove residual heat from fuel elements stored in the fuel building pool; ∙ ∙ the ventilation systems, which confine radioactive materials by depressurising the premises and filtering all discharges; ∙ ∙ the fire protection water systems; ∙ ∙ the instrumentation and control system, which processes the information received from all the sensors in the NPP. It uses transmission networks and sends orders to the actuators from the control room, through the programmable logic controllers or operator actions. Its main role with regard to reactor safety is to monitor reactivity, control the removal of residual heat to the heatsink and take part in the containment of radioactive substances; ∙ ∙ the electrical systems, which comprise sources and electricity distribution. The French nuclear power reactors have two external electrical sources: the step-down transformer and the auxiliary transformer. These two external sources are supplemented by two internal electrical sources: the backup diesel generators. Finally, in the event of total loss of these external and internal sources, each reactor has another electricity generating set comprising a turbine generator and each NPP has an ultimate backup source, the nature of which varies according to the plant in question. Over the next few years, these latter resources will be supplemented by an “ultimate back-up” diesel generator set for each reactor. 2 —  Monitoring of nuclear safety 2.1  ̶  Fuel 2.1.1  –  Changes to fuel and fuel management in the reactor In order to enhance the availability and performance of the reactors in operation, EDF, together with the nuclear fuel manufacturers, is developing improvements to fuels and their use in the reactor. EDF has standardised its fuel management methods. ASN ensures that each change in fuel management is the subject of a specific safety case for the reactors concerned. Any change in the fuel or its management must first be examined by ASN and may not be implemented without its consent. When these changes are significant, their implementation requires an ASN resolution. Fuel behaviour is an essential element in core safety in normal operation or accident conditions, and its reliability is therefore of prime importance. The leaktightness of the fuel rods, of which there are several tens of thousands in each core and which constitute the first containment barrier, are therefore the subject of particular attention. In normal operation, leaktightness is monitored by EDF through permanent measurement of the activity of the radionuclides contained in the primary system. Any increase in this activity beyond predetermined thresholds indicates a loss of leaktightness in the fuel assemblies. During each shutdown, EDF must look for and identify the assemblies containing leaking rods, which may not then be reloaded. If this activity in the primary system becomes too high, the General Operating Rules require reactor shutdown before the end of its normal cycle. ASN ensures that EDF looks for and analyses the causes of the observed leaktightness losses, in particular by examining the leaking rods in order to determine the origin of the failures and prevent them from reoccurring. Preventive and remedial actions may therefore affect the design of rods or assemblies, their manufacture, or the reactor operating conditions. Furthermore, the conditions of assembly handling, of core loading and unloading, and the measures taken to exclude foreign material from the systems and pools are also the subject of operating requirements, some of which contribute to the safety case and for which EDF’s compliance is verified by ASN spot-checks during inspections. ASN also carries out inspections to check the nature of EDF’s monitoring of its fuel suppliers. Finally, ASN periodically consults the Advisory Committee for Nuclear Reactors (GPR) concerning the lessons learned from fuel operating experience feedback. 2.1.2  –  Evaluation of the condition of the fuel and its management in the reactor In 2018, the state of the first containment barrier was on the whole satisfactory in all the NPPs, with the exception of Nogent-sur-Seine. On this site, ASN found recurring shortcomings in compliance with the provisions designed to prevent the entry of foreign material into the reactor coolant system and the reloading of a leaking fuel assembly. ASN notes that the progress observed in 2017 continued in 2018 with regard to the risk of entry of foreign material into the reactor coolant system. For example, several sites set up training programmes for outside contractor personnel, without which they are not authorised to work. However, despite this progress, ASN once again repeatedly found the presence of foreign material in the reactor coolant systems and will thus maintain close attention on this subject in 2019. In 2018, the number of significant events linked to fuel handling remained low, as was the case in 2017. The recurring blockages encountered during control rod operation or dropping in 2017 and 2018 on certain 1,300 MWe reactors, owing to wear of the reactor vessel closure head thermal sleeves, led EDF to initiate an inspection programme on all the reactors and replace the most heavily worn thermal sleeves (see box). Until such time as these inspections are carried out during the reactor outages, operating restrictions are in place at the request of ASN. 280  ASN report on the state of nuclear safety and radiation protection in France in 2018 10 – EDF NUCLEAR POWER PLANTS