Nuclear Operation Division Tel: Fax: EDF Site Cap Ampère 1 place Pleyel

Transcription

1 Ref.: CODEP-DCN For the attention of the Director Person in charge: Romain PIERRE Nuclear Operation Division Tel: Fax: EDF Site Cap Ampère 1 place Pleyel romain.pierre@asn.fr SAINT-DENIS CEDEX Montrouge, 20 th March 2015 Subject: Nuclear power reactors - EDF Summary of generic studies performed as part of the third ten-yearly outage safety reviews for the 1300 MWe reactors Ref.: See appendix 4 Dear Sir, As licensee of basic nuclear installations (BNIs) and in accordance with Article L of the Environment Code, Electricité de France (EDF) is required to conduct a safety review of each of its reactors every ten years. The purpose of this periodic review is to assess the condition of each reactor in the light of the applicable rules and to update the assessment of the risks or drawbacks that presents this reactor with regard to the interests mentioned in Article L of the Environment Code, more specifically taking account of the condition of the facility, the experience acquired during its operation, evolution of knowledge and the rules applying to similar facilities. It must also take account of international best practices. Taking advantage of the design similarities between the twenty reactors of the 1300 MWe plant series, EDF initiated an advance generic review of all the reactors in the series. The results of these generic studies will then be applied by EDF to each of the reactors of the 1300 MWe plant series during the course of their third tenyearly outage inspections (VD3) scheduled to run from April 2015 until about The purpose of this letter is to present ASN s conclusions regarding this generic phase of the VD periodic safety review. After this generic phase, in the months following each of the VD3 of the 1300 MWe reactors, EDF will submit a report to ASN and the Minister responsible for nuclear safety, in accordance with Article L of the Environment Code, presenting the conclusions of the periodic safety review of the concerned reactor and the modifications implemented or envisaged in order to correct the detected non-compliances and improve the level of safety. ASN will then complete its present generic position and send the Minister responsible for nuclear safety its analysis of the conclusions report for each reactor review and will if necessary issue new prescriptions determining the conditions to be met for continued operation of the facility concerned up until the following periodic safety review. * * * In 2010, or five years before the periodic safety review of the first reactor of the 1300 MWe, the Advisory Committee for nuclear reactors (GPR) was consulted by ASN concerning the orientations of the programme of work proposed by EDF for its VD generic safety review, in particular comprising a list of the studies to be carried out in order to reassess the safety of these reactors. Further to the opinion of the GPR, ASN issued a position statement on these orientations in the letter mentioned in reference [1]. The studies produced since then by EDF on the basis of this programme were the subject of numerous position statement letters and requests from ASN further to the reviews carried out with the technical support of IRSN and, for some of them, following consultation of the GPR.

2 To close this generic examination phase for the VD periodic safety review, ASN consulted the GPR on 15 th and 16 th October 2014, on the subject of the general conclusions of the studies and the modifications envisaged by EDF (reference [2]) to improve the safety of the 1300 MWe series reactors with respect to the orientations initially adopted. Following these two days of meetings, the GPR sent ASN its opinion in reference [3] and, in the letter in reference [4], EDF confirmed the commitments presented to the GPR session. * * * Monitoring the conformity and condition of the facilities ASN considers that the steps taken or planned by EDF to verify the conformity of the condition of its 1300 MWe reactors and ensure the satisfactory control of their ageing up until their fourth ten-yearly outage inspection (VD4) are acceptable. This generic assessment in no way anticipates any additional opinions ASN may express later following the forthcoming consultation of the Advisory Committee for nuclear pressure equipment (GP-ESPN) on the subject of the strength of the 1300 MWe nuclear reactor vessels beyond 30 years of operation. Reassessment of hazard-related risks ASN considers that the studies carried out by EDF to reassess the protection of its reactors against internal and external hazards is on the whole satisfactorily based on a review of the practices in use on similar facilities in other countries (for example the development of baseline requirements to take account of tornados and projectiles caused by strong winds) and on evolution of knowledge resulting from research programmes or test results (for example the effects of over-pressure in the event of a fire). ASN in particular underlines the scope of the studies carried out by EDF and the importance of their results, both in terms of improving the demonstration of the ability of its facilities to withstand hazards and in terms of the modifications envisaged by EDF to reinforce the protection of its facilities, more specifically with regard to hazards not considered in the initial design of the 1300 MWe series of reactors. ASN also notes that given the mobilisation of the engineering capacity of EDF for the stress tests conducted following the events at Fukushima, the initial review schedule for reassessing hazards in the generic phase of the VD periodic safety review was significantly disrupted and numerous answers to ASN requests, some of which are recent, are still being waited for, despite the imminence of the first ten-yearly outage inspections of the 1300 MWe reactors. ASN therefore considers it acceptable that some of the safety improvements it requests will be integrated by EDF in accordance with a schedule which, for certain reactors of the 1300 MWe series, goes beyond their VD3. Reassessment of the control of accident risks In order to update the safety demonstration of the 1300 MWe reactors, EDF went back over a large number of deterministic assessments of the design basis accidents, in certain cases using new methods including a more accurate representation of the phenomena involved. EDF also corrected anomalies in the studies identified before the periodic safety review. ASN considers these actions to be positive. ASN also has a positive opinion of the action plan initiated by EDF and aimed at mitigating the radiological consequences of a steam generator tube rupture (SGTR) and the resulting modifications, which will make a significant step towards mitigating radioactive releases into the environment. It does however recall that certain studies are to be supplemented, with these additions currently being prepared by EDF or undergoing technical review by IRSN. They could be the subject of subsequent requests by ASN. In addition to the deterministic demonstration, EDF also developed a number of level 1 1 probabilistic safety assessments (PSA) concerning events inside the Nuclear Steam Supply System (NSSS) and the spent fuel pool, as 1 The level 1 PSAs examine the scenarios leading to fuel melt and determine their frequency. These assessments are thus able to identify any weak points requiring design or operating modifications. 2 / 49

3 well as certain external hazards. These studies revealed the need to modify the facility in order to reduce the risks associated with fire and events affecting the spent fuel pool. EDF also carried out the first level 2 2 PSAs for the 1300 MWe reactors, considering in turn the status prior to the VD3 and the status after incorporation of the VD3 modifications. A comparison between the results of these two studies showed a significant reduction in the frequency of large-scale releases, especially in the case of total loss of electrical power. ASN does however consider that these PSAs need to be modified in order to realistically reflect the condition of the facilities, their operation and the risk of releases in the event of an accident. The studies carried out by EDF on the prevention and mitigation of severe accidents mainly concerned the increased prevention of the severe accident risk, in particular with regard to scenarios involving an early loss of containment. These studies, supplemented by the level 2 PSAs, led EDF to propose about ten equipment modifications and update its severe accident baseline safety requirements. Generally speaking, ASN considers that the modifications proposed by EDF to improve the containment and reduce the risks of early, large-scale releases, are pertinent. Additional work is expected of EDF in response to its commitments and the requests already submitted by ASN. Concerning fuel storage in the spent fuel pool, ASN considers that the measures EDF intends to take, as a result of the periodic safety review and the stress tests, in order to avoid uncovering of the fuel stored or being handled in the pool, will constitute a significant safety improvement. Additional studies will however be required, focusing mainly on the vulnerability of these additional measures to hazards. In general, ASN considers that all these measures, leading to a more realistic appreciation of the risks and to the identification of modifications capable of reducing certain risks, are real advances in the safety approach. Reassessment of the control of detrimental effects 3 Article L of the Environment Code requires that the periodic safety review be able to update not only the assessment of the risks of accident, but also the detrimental effects of the facility as a result of its normal or degraded operation. The subject of satisfactory control of the detrimental effects has not however been fully integrated by EDF into its examination of the VD periodic safety review nor, more generally, into its examination of the other periodic safety reviews of its reactors. As mentioned in the letter in reference [6], the approach adopted by EDF to take account of these detrimental effects in the periodic safety reviews of its reactors will be gradually reinforced in accordance with the schedule for entry into force of the general regulations applicable as of 1 st July * * * Further to the risk control reassessment studies, in the summary note in reference [2], EDF presented an extensive list of modifications to be performed on the 1300 MWe reactors, which will in particular allow: reinforcement of protection against hazards, in particular through modifications concerning: o the protection of equipment that is important for safety against projectiles caused by strong winds; o increased capacity of the air-conditioning systems (ventilation, chillers), so that in the event of a heat wave, a temperature can be maintained in the premises that is compatible with the working of the equipment important for safety; 2 The level 2 PSAs examine the nature, importance and frequency of releases outside the containment. 3 Article 4.1 of the order of 7 th February modified in reference [5] defines a detrimental effect as being on the one hand, the health and environmental impact of the facility owing to water intake and discharges and, on the other, the nuisances that this can cause. 3 / 49

4 o the prevention of explosion risks in the event of an earthquake, by reinforcing the strength of the hydrogen-carrying circuits in the nuclear island and by ensuring automatic shutdown of the electrochlorination installations in the event of an earthquake. a reduction in the releases of radioactive substances in the case of an accident with or without core melt, more specifically by means of: o the modification designed, in the event of a steam generator tube rupture (SGTR) accident, to prevent the risk of the water in the affected steam generator from overflowing, thus significantly helping to reduce the risks of releases associated with this accident; o installing baskets of sodium tetraborate which would dissolve in the water recovered from the reactor building sumps following a primary loss of coolant accident, thus enabling a basic ph to be maintained, thereby limiting releases of radioactive iodine; o the modification designed to increase the performance of the pump on the system reinjecting into the reactor building any leaks collected from the safeguard systems which, in an accident situation, carry highly contaminated fluid from the reactor building, thus enabling this function to be used in a severe accident even when the pressure in the containment is high. reinforcement of the prevention of the risk of uncovering of the fuel assemblies stored in the fuel pool or being handled, more specifically the modification designed to automatically isolate the pool cooling in-line suction if a very low water level is detected in the pool. ASN considers that all the modifications thus identified by EDF following the generic phase of the periodic safety review of the 1300 MWe plant series reactors will contribute to making a significant improvement in the safety of these facilities. However, compliance with the requests made by ASN on various topics of the periodic safety review and with EDF s commitments made during the reviews are liable to require additional modifications, depending on the results of the corresponding studies. At this stage, ASN has identified nothing to compromise the ability of EDF to control the safety of the 1300 MWe reactors up until the periodic safety review associated with their fourth ten-yearly outage inspection. However, ASN would recall that, in accordance with Article L of the Environment Code, its position concerning continued operation will be given for each reactor after an analysis of the conclusions report of its periodic safety review, transmitted by EDF further to its third ten-yearly outage inspection 4. As and when necessary, ASN may issue new prescriptions concerning the operation of the reactor in question. * * * Appendix 1 gives details of ASN s position statements on each of the topics of the VD periodic safety review, examined as part of the generic phase. Appendix 2 gives all the additional requests or the requests that ASN considers should be maintained following analysis of your answers and Appendix 3 gives the requests concerning the content of the safety report. Sincerely yours, ASN Chairman, Pierre-Franck CHEVET 4 In accordance with letter ASN DEP-PRES of 1 st July 2009, these reports will be transmitted by EDF no later than 6 months after the end of the ten-yearly outage inspection of the reactor concerned. 4 / 49

5 DISTRIBUTION LIST External distribution of paper version: EDF: o DPN/UNIE o DIN o DIN/CIPN o DIN/SEPTEN IRSN: 1 copy External distribution of electronic version: EDF: S. Walter IRSN: P. Lejuste Internal distribution (electronic version) DCN: all DCN staff DEP All regional divisions in charge of regulating 1300 MWe PWR nuclear safety DCN archival: DCN: Starting point 5 / 49

6 TABLE OF CONTENTS OF APPENDICES TO LETTER CODEP-DCN APPENDIX 1 TO LETTER CODEP-DCN DETAILS OF ASN POSITION STATEMENTS ON THE GENERIC STUDIES OF THE VD PERIODIC SAFETY REVIEW A. CONFORMITY AND CONDITION OF 1300 MWE REACTORS... 8 A.1. PROGRAMME OF THE CONFORMITY CHECK (ECOT)... 8 A.1. VERIFICATION OF THE DESIGN OF THE CIVIL ENGINEERING STRUCTURES... 8 A.2. TEN-YEARLY TEST PROGRAMME... 8 A.3. SUPPLEMENTARY INVESTIGATIONS PROGRAMME (PIC)... 9 A.4. SATISFACTORY CONTROL OF REACTOR AGEING... 9 B. REASSESSMENT OF HAZARD-RELATED RISKS B.1. RISKS ASSOCIATED WITH EARTHQUAKES B.1.1. Reassessment of ground response spectra B.1.2. Reassessment of the seismic behaviour of the civil engineering structures B.1.3. Reassessment of the seismic strength of the equipment B.1.4. Study of earthquake-induced internal flooding B.1.5. Experience feedback from the Kashiwazaki-Kariwa earthquake B.2. RISKS ASSOCIATED WITH HIGH AIR AND WATER TEMPERATURE CONDITIONS B.3. RISKS ASSOCIATED WITH THE FRAZIL ICE PHENOMENON B.4. RISKS ASSOCIATED WITH STRONG WINDS B.5. RISKS ASSOCIATED WITH TORNADOS B.6. RISKS ASSOCIATED WITH HEATSINK LOWEST SAFE WATER LEVEL SITUATIONS B.7. RISKS ASSOCIATED WITH EXTERNAL FLOODING B.8. PUMPING STATION HAZARD RISK FROM A DRIFTING HYDROCARBON SLICK B.9. SITE S ABILITY TO WITHSTAND COMMON MODE HAZARDS B.10. RISKS ASSOCIATED WITH INTERNAL FIRES IN THE FACILITIES B.11. RISKS ASSOCIATED WITH EXPLOSIONS OF INTERNAL ORIGIN B.12. RISKS ASSOCIATED WITH THE INDUSTRIAL ENVIRONMENT AND COMMUNICATION ROUTES B.13. RISKS ASSOCIATED WITH AIR TRANSPORT B.14. RISKS ASSOCIATED WITH THE ON-SITE TRANSPORT OF HAZARDOUS GOODS B.15. RISKS ASSOCIATED WITH ON-SITE FLOODING AND HIGH-ENERGY LINE BREAKS B.16. RISKS ASSOCIATED WITH ELECTRICAL DISTURBANCES OF ON-SITE OR OFF-SITE ORIGIN C. STUDIES OF OPERATING CONDITIONS OF 1300 MWE REACTORS AND THEIR RADIOLOGICAL CONSEQUENCES C.1. REVIEW OF THE STUDIES OF OPERATING CONDITIONS AND THEIR RADIOLOGICAL CONSEQUENCES C.1.1. Rules, methods and accident studies in the safety report C.1.2. Boron dilution risks C.1.3. Sensitivity analysis for passive failure of the safety injection system C.1.4. Impact of the behaviour of the secondary system valves on the coverage of design-basis transients C.1.5. Prevention and mitigation of severe accidents C.1.6. Baseline requirements associated with the fuel criticality risk in spent fuel pools and the reactor building when the reactor vessel is open C.1.7. Elimination of reactor coolant system cold overpressure situations C.1.8. Assessment of the radiological consequences of accidents other than severe accidents C.2. FUEL BUILDING SAFETY REVIEW C.2.1. Risks associated with the spent fuel pools (FB pools) C.2.2. Handling of fuel transport packagings C.3. SAFETY REVIEW OF EFFLUENT PACKAGING AND TREATMENT AUXILIARY BUILDINGS (BAC/BTE) D. PROBABILISTIC SAFETY ASSESSMENTS (PSA) D.1. LEVEL 1 PSA D.2. LEVEL 2 PSA E. DESIGN OF SYSTEMS AND CIVIL ENGINEERING STRUCTURES E.1. SAFETY CLASSIFICATION OF EIP-S E.2. EQUIPMENT QUALIFICATION FOR ACCIDENT CONDITIONS E.2.1. Equipment qualification / 49

7 E.2.2. Calculation of doses integrated by the equipment in the event of an accident with or without core melt E.3. DESIGN OF THE REACTOR DIGITAL INTEGRATED PROTECTION SYSTEM (SPIN) E.4. MODERNISATION OF THE CONTROL ROOM INTEGRATION OF ORGANISATIONAL AND HUMAN FACTORS E.5. CONDITION OF AND IMPROVEMENTS TO REACTOR CONTAINMENT E.5.1 Monitoring the condition and behaviour of the containments E.5.2. Improving the containment safety function F. MODIFICATIONS TO THE FACILITIES AND THEIR OPERATING PROCEDURES APPENDIX 2 TO LETTER CODEP-DCN ASN REQUESTS A. MONITORING OF EDF COMMITMENTS B. REASSESSMENT OF HAZARD-RELATED RISKS B.1. INTERNAL SEISMIC-INDUCED FLOODING B.2. RISKS ASSOCIATED WITH HIGH AIR AND WATER TEMPERATURE CONDITIONS B.3. CLASSIFICATION AND REQUIREMENTS APPLICABLE TO THE MEANS NECESSARY FOR ENSURING SECONDARY WATER INDEPENDENCE FOR RIVERSIDE SITES B.4. INTERNAL FIRE C. STUDIES OF OPERATING CONDITIONS AND THEIR RADIOLOGICAL CONSEQUENCES C.1. BASELINE REQUIREMENTS ASSOCIATED WITH THE FUEL CRITICALITY RISK C.2. HANDLING OF FUEL PACKAGINGS D. LEVEL 2 PROBABILISTIC SAFETY ASSESSMENTS E. CONTINUOUS MONITORING OF THE LEAK RATE FROM THE INNER CONTAINMENT AND ITS PENETRATIONS F. REASSESSMENT OF THE CONTROL OF DRAWBACKS INHÉRENT TO THE INSTALLATION APPENDIX 3 TO LETTER CODEP-DCN ASN REQUESTS CONCERNING THE CONTENT OF THE VD3 EDITION OF THE SAFETY REPORT FOR THE 1300 MWE SERIES REACTORS A. DEMONSTRATION OF SATISFACTORY CONTROL OF THE RISKS OF AN ACCIDENT WITHIN THE WASTE PACKAGING AND RADIOACTIVE EFFLUENT PROCESSING BUILDINGS (BAC/BTE) B. DEMONSTRATION OF THE SATISFACTORY CONTROL OF THE ACCIDENT RISKS RESULTING FROM POSSIBLE MALICIOUS ACTS THAT CANNOT BE RULED OUT C. PRESENTATION OF THE EIP AND THEIR DEFINED REQUIREMENTS D. REFERENCING OF EIP EQUIPMENT SYSTEM ID NUMBERS E. ADDITIONAL ACCIDENT STUDIES E.1. STUDY CONCERNING THE INCORRECT POSITIONING OF A FUEL ASSEMBLY E.2. STUDY CONCERNING A STEAM LINE RUPTURE E.3. STUDY CONCERNING CONTROL ROD CLUSTER EJECTION APPENDIX 4 TO LETTER CODEP-DCN REFERENCES 7 / 49

8 APPENDIX 1 TO LETTER CODEP-DCN Details of ASN position statements on the generic studies of the VD periodic safety review A. Conformity and condition of 1300 MWe reactors A.1. Programme of the conformity check (ECOT) For the purposes of the periodic safety reviews, EDF carries out a check on the design and construction of its facilities, known as the unit conformity check (ECOT), in order to run a targeted check on the conformity of the reactors with their applicable baseline safety requirements, to detect any latent non-compliances and, as applicable, correct them. The VD ECOT program presented by EDF follows on from and supplements the ECOT programmes run during the previous periodic safety reviews. It also draws on the orientations adopted for the VD3-900 ECOT and on experience feedback from its application. The orientations of the VD ECOT programme were the subject of an initial ASN position statement letter in 2011 [7] to which EDF responded by transmitting a new version of the programme, incorporating six additional topics. Following the detailed examination of this new ECOT programme by IRSN at the request of ASN, EDF made commitments in the letter in reference [8] in order to complete certain aspects of this programme and clarify the implementation procedures. ASN considers that the ECOT programme adopted by EDF, plus the subsequent commitments made, is acceptable subject the last requests concerning its implementation procedures ASN formulated in the letter in reference [9] are taken into account. ASN would also recall that in January 2015, it published ASN guide 21 [10] which explains its recommendations regarding the application of the regulations concerning the procedures and deadlines for processing the conformity deviations detected on a reactor. A.2. Verification of the design of the civil engineering structures EDF verified the conformity of the design of the civil engineering structures with their safety requirements. In the letter in reference [11], ASN considered the following to be satisfactory: - the selection method and the resulting list of civil engineering structures selected by EDF for the conformity verification; - the verification studies carried out on the structures thus selected, except for justification of the ability of the main steam valve bunker 5 in the P4 series to withstand an external explosion. ASN therefore asked EDF to complete its verification studies on the design of the main steam valve bunker concerning this point and will examine EDF s answers. A.3. Ten-yearly test programme In addition to the surveillance testing of equipment as stipulated by the general operating rules and the functional post-maintenance or post-modification qualification tests, EDF is examining the need for and benefits to be gained from performing certain specific tests on the occasion of a ten-yearly inspection. By means of overall tests or tests which can only be performed in particular facility configurations, these ten-yearly tests aim more particularly to check that the required performance of certain systems has not been compromised by the 5 This structure, mainly consisting of a metal framework, houses the water-steam piping running along the outer wall of the Reactor Building (RB). 8 / 49

9 cumulative effect of successive modifications. The definition and then the performance of this test programme thus participate in checking the facility s conformity with its baseline safety requirements. ASN has no particular comments regarding the methodology used by EDF on the occasion of the VD3 [12] to draw up this test programme. A.4. Supplementary investigations programme (PIC) The supplementary investigations programme (PIC) consists in running spot-checks on the condition of passive equipment for which no inspection is provided for in the EDF basic preventive maintenance programme (PBMP), nor in the regulation checks (for pressure equipment). As part of the periodic safety reviews, the PIC is thus able to complete the overall summary of the condition of the facility, verify the adequacy of the PBMP and improve them if necessary. ASN has no particular comments concerning the PIC presented by EDF for the VD periodic safety review [13]. A.5. Reactor ageing management As from the VD3, the PIC is supplemented by inspections to ensure the satisfactory reactor ageing management. EDF has established a methodology for controlling the ageing of its reactors after 30 years of operation, the aim of which is to demonstrate their ability to continue to function until their VD4 in satisfactory conditions of safety, on the one hand in the light of the condition of the facilities during their VD3 and, on the other, given the knowledge and control of the mechanisms and kinetics of deterioration linked to ageing. The method implemented by EDF for the VD3 for the 900 MWe series reactors was reused for the 1300 MWe series reactors. This first of all consists in drawing up ageing analysis sheets (FAV) for the structures, systems and components (SSC), the failure of which can have an impact on safety and which are liable to be affected by an ageing mechanism, and in verifying whether the applicable maintenance and operational measures are appropriate for the identified ageing mechanism. For each SSC susceptible to ageing, in other words for which at least one FAV highlights that the ageing management has not in principle been demonstrated by the normal maintenance and operating provisions, EDF conducts an in-depth assessment of the ageing management for the coming ten-year period and presents the results and conclusions in a general continued operation aptitude file for the SSC concerned (Equipment DAPE). Subsequently, on the occasion of the VD3 of each reactor and on the basis of a summary of the generic equipment DAPE files and after integration of the specific aspects of the reactor concerned, EDF produces a continued operation aptitude file for the reactor (reactor DAPE). ASN has no particular comments concerning this ageing management approach for the reactors of the 1300 MWe plant series on the occasion of their VD3. After review of the FAV and the Equipment DAPE for the reactors of the 1300 MWe plant series, ASN considers that the control of ageing of these reactors up until their VD4 is satisfactory with respect to all generic aspects. This generic position in no way anticipates the final individual position statement that ASN will subsequently be required to issue concerning each of the reactors after the review of its reactor DAPE. ASN however considers that EDF can further improve its generic approach and it submitted requests and observations accordingly in its letter in reference [14]. These requests aim to improve the way certain ageing mechanisms are taken into account, through the creation of additional generic FAV or Equipment DAPE, through the revision of certain FAV and through the changes to certain inspections and maintenance procedures. ASN will also subsequently issue a position statement on the strength of the 1300 MWe nuclear reactor vessels after 30 years of operation, following the forthcoming consultation of the Advisory Committee for nuclear pressure equipment (GP-ESPN), scheduled for September / 49

10 B. Reassessment of hazard-related risks B.1. Risks associated with earthquakes B.1.1. Reassessment of ground response spectra EDF reassessed the seismic motion of the 1300 MWe sites in accordance with the RFS in reference [15] and with ASN s requests already submitted in 2011 in the letter in reference [16]. Given the current state of scientific knowledge 6, ASN considers that the ground response spectra that EDF intends to apply for the VD periodic safety review are acceptable, with the exception of the spectrum for Saint-Alban which is too weak and does not adequately cover the uncertainties associated with the data used by EDF. For this site, ASN will examine the answers to the requests it made in the letter in reference [17] concerning: - the reassessment of the ground response spectrum to take account of uncertainties; - the definition of a programme of work to verify the seismic resistance of the equipment and civil engineering structures; - the completion of any modifications and seismic reinforcements, no later than 5 years after submission of the periodic safety review conclusions reports (RCRS) as stipulated in Article L of the Environment Code. * When the ground response spectrum for the safe shutdown earthquake (SSE) thus reassessed is higher than that of the design basis earthquake (DBE) of the facility or than that of the SSE considered during the previous periodic safety review, if this latter was already greater than the DBE, the compliance of the equipment and civil engineering structures with the seismic strength requirements must be verified. B.1.2. Reassessment of the seismic behaviour of the civil engineering structures ASN considers that the results of the new floor spectra for the auxiliary safeguard buildings (BAS) and electrical buildings (BL) for the 1300 MWe plant series are acceptable for the reassessment of the seismic strength of the equipment in these buildings. ASN also considers that EDF s general methodology for verifying the seismic strength of the civil engineering structures on the 1300 MWe plant series sites is on the whole satisfactory, with the exception of the possible direct use of structure damping ratios that are higher than the values recommended in ASN guide ASN 2/01 in reference [18]. ASN will review EDF s answers to the requests it made in the letter in reference [19] concerning on the one hand the changes in EDF methodology on this subject of the damping ratios and, on the other, concerning the repetition re-running of the studies to reassess the seismic strength requirements for the turbine hall 7 (SDM) on the 1300 MWe sites carried out with a damping ratio higher than the value recommended for this type of structure in the guide in reference [18]. EDF also implemented the seismic interaction approach applied to civil engineering structures which themselves constitute hazards. In the letter in reference [11], ASN considered the initial studies 8 transmitted by EDF to be satisfactory, except for the justification of the absence of seismic collapse of the H2 9 building on the Paluel site. ASN therefore asked EDF to complete its seismic behaviour verification study for the H2 building 6 ASN points out that the probabilistic assessmetns of the seismic hazards transmitted by EDF have proven to be an important tool for ruling on the acceptability of the spectra determined using application of the RFS basic safety rule, given current knowledge. 7 The turbine halls in Nuclear Power Plants (NPPs) are covered by a seismic stability requirement to prevent the risk of their collapse constituting a hazard for the adjacent safety classified buildings. 8 As the seismic interaction approach requires that the specificities of each site be taken into account (non generic structures, plot plans that differ from one site to another, etc.), the corresponding studies initiated by EDF have not yet been finalised and will continue for several years to come, ahead of the VD3 on each of the sites. 9 Building housing numerous areas for tertiary and industrial uses, including the laundry and the demineralisation station. The non-collapse of this building in the event of an earthquake is designed to prevent constituting a hazard for the essential service water system (ESWS) galleries running below it. 10 / 49

11 on the Paluel site. The additional data provided by EDF in the letter in reference [20] are currently being reviewed by IRSN and ASN. B.1.3. Reassessment of the seismic strength of the equipment ASN underlines the importance of the work done by EDF to establish an operational approach for reassessing the seismic strength of the equipment, collating the characteristics, general design principles, lessons learned from post-seismic feedback and the seismic behaviour diagnostic methods for the equipment most frequently encountered. ASN does however consider that the several points of the seismic reassessment approach proposed by EDF must be modified before it is applied and it sent EDF the corresponding requests in the letter in reference [21]. It will then review the replies. The complete implementation of the equipment reassessment approach thus modified could be incompatible with the scheduled date of the VD3 for the first 1300 MWe reactors. ASN therefore also asked EDF to send it a programme of work for performance of the studies and integration of any modifications and seismic reinforcements for which the deadlines will need to be adapted to the potential consequences and will not exceed 5 years following submission of the RCRS. B.1.4. Study of earthquake-induced internal flooding In addition to reassessing the direct effects of the earthquake on the civil engineering structures and the equipment for which there is a seismic resistance requirement, EDF supplemented its analysis of the ability of its facilities to withstand internal flooding in the buildings caused by the simultaneous failure of tanks not designed to withstand an earthquake. After reviewing these studies, ASN considers that EDF s demonstration of containment within the buildings of the contaminated water released by the tanks that are not designed to withstand an earthquake is satisfactory. With regard to the study of common mode failures caused by the internal flooding of the redundant equipment necessary for reaching and maintaining a safe state for the reactors and fuel storage pools, ASN asked EDF in the letter in reference [22] to provide additional justifications. ASN considers that the answers sent by EDF in the letters in references [23] and [24] are satisfactory and indicates that there is no need to modify the facilities to deal with the risk of internal earthquake-induced flooding. However, the acceptability of the consequences of earthquake-induced internal flooding, whether with regard to the containment of contaminated water or the absence of common failure modes, depends in particular on the confirmation of the retention capacity of certain tanks and the non-degradation of this capacity by the direct or indirect (falling loads) effects of the earthquake. EDF however considers that these seismic-induced flooding studies are not a part of the demonstration of the safety. This position means that EDF does not identify these retention basins as elements important for protection (EIP) and does not consider that their retention capacity as used in the studies and their integrity in the event of an earthquake constitute safety requirements. ASN disagrees with this EDF position and for its part considers that the demonstration of the safety for a nuclear facility with respect to earthquakes is not limited to an assessment of the loadings induced by the seismic waves but must also take account of hazards resulting from the failure of elements not designed to withstand an earthquake (falling loads, internal flooding). ASN therefore considers that the elements of the facility needed to justify the acceptability of the consequences of seismic-induced internal flooding are EIPs and it thus formulated request 2 in Appendix 2 to this letter. B.1.5. Experience feedback from the Kashiwazaki-Kariwa earthquake Following the earthquake in Japan on 16 th July 2007 close to the Kashiwazaki-Kariwa NPP, ASN asked EDF to identify the lessons to be learned for the French reactors concerning the anomalies which occurred in the Japanese NPP. The studies conducted by EDF on this point concerned: 11 / 49

12 - the consequences of a large-scale fire in an electrical transformer following an earthquake; - the effect of water movements in the Reactor Building (RB) and Spent Fuel Building (FB) pools, induced by the earthquake, on the gates and cofferdams in the pools as well as on the components of the fuel loading machine; - assessment of the internal flooding associated with overflowing of the FB pool under the effect of the wave induced by the earthquake. After a review of the studies transmitted by EDF, with the support of IRSN, ASN considers that: - the design of the gates and cofferdams in the FB and RB pools, and of the fuel loading machines in the RB and FB, satisfactorily cover the loadings resulting from the water movements induced by an earthquake; - the overflow volume of the FB pool that could result from a wave induced by an earthquake remains slight when compared with the other causes of internal flooding already examined in the demonstration of the safety. The study transmitted by EDF concerning the potential safety consequences of a large-scale transformer fire in the event of an earthquake, is under review and will be the subject of a subsequent position statement by ASN. B.2. Risks associated with high air and water temperature conditions Following the heatwave episodes of 2003 and 2006, EDF drew up extreme heat baseline safety requirements for each plant series, establishing an approach for a reassessment of the design of the reactors to deal with periods of probable high summer heat, and their ability to deal with a rarer heatwave episode. The reassessment of the probable high summer heat conditions constitutes the input data for the part of the extreme heat baseline safety requirements concerning the facilities re-design approach. This approach aims to ensure that the design of the air-conditioning systems means that in a high summer heat situation, they are able to maintain temperature conditions in the buildings which do not compromise the availability of the equipment required to deal with category 1 to 4 operating conditions of the safety report. In the letter in reference [25] ASN gave its position on the extreme heat baseline safety requirements for the CPY plant series and asked EDF to transpose its requests concerning this plant series to the baseline safety requirements applicable to the 1300 MWe plant series, whenever pertinent. EDF replied to ASN s requests in the letter in reference [26] and in early 2014 presented an update of the extreme heat baseline safety requirements for the 1300 MWe plant series [27]. ASN considers that the modifications envisaged by EDF through application of its extreme heat baseline safety requirements will contribute to achieving a significant improvement in the design of the 1300 MWe reactors and their ability to withstand the reassessed high air and water temperature conditions. Nonetheless, some of EDF s answers are not satisfactory and additional answers liable to have an impact on the extreme heat baseline safety requirements for the 1300 MWe plant series are still awaited. In particular, in addition to the modifications planned by EDF and for which deployment must not be delayed, ASN considers that it is essential that EDF demonstrate its ability to keep a reactor in a safe state in the long-term post-accident phase of an accident occurring at the same time as a period of high summer heat. On this point, ASN therefore formulated request N 3 in Appendix 2 to this letter. B.3. Risks associated with the frazil ice phenomenon Based on available meteorological data, EDF initially assessed the susceptibility of the 1300 MWe plant series sites to a risk of obstruction of the heatsink water intake by the appearance of frazil ice 10 and then studied the ability of the NPPs concerned to deal with such a hazard. 10 This complex phenomenon, which appears in the presence of particular meteorological and hydraulic conditions, leads to the formation of ice crystals which can either aggregate to form sheets of surface ice (passive frazil) or adhere to submerged items such as pre-filtration grilles and thus lead to icing-up of these items (active frazil). 12 / 49

13 Following its review, with the technical support of IRSN, ASN considered that the studies and protective measures for the frazil ice phenomenon presented by EDF represent a significant step forward in safety, given that they now take account of a meteorological hazard which was not originally considered in the design of the NPPs of this series. ASN considered that the consideration given by EDF to a combination - during an episode of extreme cold - of a frazil ice situation with a loss of offsite power (LOOP) was in particular satisfactory. However, in its letter in reference [28], ASN asked EDF to supplement the susceptibility assessments of the Cattenom, Flamanville, Penly and Paluel sites concerning the frazil ice phenomenon and to provide additional justifications and improvements concerning the protection of the heatsink of certain sites. In response to ASN s requests, EDF (references [29] and [30]): - conducted a frazil ice susceptibility study on Mirgenbach Lake, concluding that the Cattenom site was not susceptible to the frazil ice phenomenon; - plans to conduct additional investigations to determine the susceptibility to the frazil ice risk on the Flamanville site and also plans to set up annual monitoring of water temperatures, in order to determine whether or not the climate watch needs to be reinforced for the Paluel and Penly sites. EDF also transmitted additional data concerning water temperature monitoring criteria triggering the deployment of frazil ice protective measures and additional data concerning the effectiveness of these measures on the Belleville site (winter recirculation 11 ). ASN considers that these points are satisfactory. EDF also intends to verify the effectiveness of the countermeasures envisaged for the Saint-Alban site (shutdown of production pumps 12 ); ASN will examine EDF s conclusions. With regard to the safety classification adopted for the frazil ice protection measures, EDF intends to apply the approach presented in the letter in reference [31], aiming to define a classification and associated requirements for equipment taking part in protection of the cooling safety function in the event of frazil ice. Without in any way anticipating the results of the application of this approach, ASN already considers that the provisions mentioned in request 8 of the letter in reference [28] should be classified in this way. B.4. Risks associated with strong winds Even if the direct effects of strong winds were incorporated into the design of the buildings, through the application of the snow and wind rules, the effects of strong winds on other elements of the facilities had not been considered. EDF therefore studied the ability of the NPPs of the 1300 MWe plant series to withstand the effects of strong winds over and above the simple resistance of the buildings and more particularly examined the risks of hazards resulting from projectiles induced by the strong winds. The strong wind speeds used by EDF are higher than those of the extreme wind conditions of the last 2009 edition of the snow and wind rules used for construction purposes. ASN considers that in the light of current knowledge and the state of the art in force on this subject, this approach is a satisfactory means of characterising the conditions associated with a meteorological hazard. With regard to the nature and characteristics of the projectiles caused by strong winds adopted by EDF, ASN considers them to be satisfactory when taken in conjunction with the consideration of other projectiles, such as steel balls and tubes, included in the baseline safety requirements for protection against tornados (see section B.5 below). Finally, ASN considers that the modifications planned by EDF on the basis of its studies will contribute to achieving a significant reinforcement of the protection of its facilities against the effects of strong winds but that EDF will need to provide additional data and it therefore formulated requests in the letter in reference [32], the answers to which will be reviewed by ASN. 11 This system consists of injecting hot water from plant releases onto the grilles, to prevent frazil ice from forming on them. 12 EDF considers that shutting down pumps not classified as being important for safety (IPS) helps slow down the formation of frazil ice and prevents complete clogging of the pumping station. 13 / 49

14 B.5. Risks associated with tornados The protection of reactors against tornados, not considered in the design of these facilities, is one of the subjects adopted at the request of ASN during the orientation phase of the VD periodic safety review. Following the technical review of the baseline safety requirements developed by EDF concerning the methodology for taking account of the tornado hazard, ASN considers that the characteristics of the reference tornado adopted by EDF, the associated projectiles and the safety objectives for reactor protection against the direct or indirect effects are satisfactory, subject the requests it formulated in the letter in reference [33] are taken into account. In accordance with Article L of the Environment Code, which requires that the periodic safety review allow the risk assessment to be updated, in particular taking account of the evolution of knowledge, ASN asked EDF in its letter in reference [33] to ensure that the reactors of the 1300 MWe plant series are protected against the tornado risk by implementing its baseline safety requirements on these reactors, without waiting for the next periodic safety review and it will analyse the deployment schedule envisaged by EDF. B.6. Risks associated with heatsink lowest safe water level situations The lowest safe water level (PBES) situations correspond to minimum heatsink water level or flow rate conditions at the pumping station so as to the operation of the ESWS is insured. EDF has defined a methodology for characterising PBES situations and checked that, in these situations, the heatsink characteristics did not compromise the availability of the ESWS for the reactors. The methodology for characterising PBES situations was covered in an initial ASN position statement letter in 2011 (reference [34]), in which ASN asked EDF to modify several points of its approach. The update of the PBES characterisation method transmitted in return by EDF in 2013 does not address all the requests made by ASN. Furthermore, the studies to justify the availability of the ESWS in a PBES situation transmitted by EDF were carried out on the basis of the approach not yet updated. ASN therefore asked EDF in the letter in reference [35]: - to revise its PBES characterisation methodology in accordance with the requests made in 2011, - to transmit an inventory of the protection of the 1300 MWe reactors, with application of the revised methodology. The first replies to this letter transmitted by EDF are currently being reviewed. B.7. Risks associated with external flooding When determining the generic phase of the VD periodic safety review, the baseline requirements adopted for protection of the 1300 MWe sites against external flooding were based on the "Le Blayais experience feedback" methodology developed following the partial flooding at Le Blayais NPP in 1999 and the additional requests formulated by ASN in the letter in reference [36]. In 2013, ASN published a guide based on new knowledge to ensure that the external flooding risk is taken into account more exhaustively and more robustly. By comparison with the baseline safety requirements initially adopted for definition of the VD periodic safety review, significant changes in the state of the art were introduced into this guide and the application of all of these recommendations requires that EDF carries out extensive studies which, for certain reactors, may imply integration time-frames that are incompatible with the VD3 dates. Consequently and in accordance with Article L of the Environment Code, which requires that the periodic safety review allows a ten-yearly update of the risk assessment, more specifically taking account of new knowledge available, ASN asked EDF, in the letter in reference [37], to reassess the protection of these reactors against flooding, for a 10-year period ( ), on the basis of the provisions of the guide and to propose an implementation schedule, giving priority to either the VD periodic safety review for each of these reactors or, with regard to an overall hazard affecting a site, the VD periodic safety review of the last reactor on the site. 14 / 49

15 In the letter in reference [38], EDF sent ASN a schedule with a time-frame conforming to its request. B.8. Pumping station hazard risk from a drifting hydrocarbon slick ASN urged EDF to examine the robustness of the NPPs to a drifting hydrocarbon slick as this hazard liable to affect the pumping stations on the sites was not included in the NPP design. After a technical review, ASN underlines the fact that the studies and tests performed by EDF led to a clearer understanding of the impact of hydrocarbons on the heatsink equipment and considers that the measures associated with the approach presented by EDF offer appropriate protection. ASN in particular considers that the additional protective measures planned by EDF on certain sites will improve the safety of the sites concerned. ASN will nonetheless examine EDF s replies to its requests formulated in the letter in reference [39] concerning the justification of the effectiveness of the cleaning systems and the time needed by the operators to deploy the mobile protective barriers. ASN also asked EDF to assign hazard resistance and maintenance requirements to the physical protections of the heatsink against a hydrocarbon slick and it will verify that these requirements have been taken into account. B.9. Site s ability to withstand common mode hazards EDF studied the ability of the NPPs, following an external hazard, to manage the consequences of a loss of heatsink (situation H1), a loss of offsite power (LOOP), or a combination of the two, simultaneously affecting all the reactors on the same site. Following its review, with the support of IRSN, ASN considered that the site independence studies presented by EDF represent a significant improvement in the way common mode external hazard risks are taken into account for a site. However, additional data was still required and ASN sent EDF a number of requests in the letter in reference [40], to which EDF replied with the letters in reference [41] to [43]. ASN considers that all of the responses provided by EDF are satisfactory, with the exception of the answers concerning the classification approach and the requirements associated with the measures included in the site H1 studies. This point is the subject of requests N 4 and 5 in Appendix 2 to this letter. ASN had also requested that these studies be revised, taking account of the study rules applicable to accidents of the design extension conditions. EDF intends to modify these studies for deployment of the hardened safety core. ASN has no objection to reviewing the corresponding modifications within this framework. B.10. Risks associated with internal fires in the facilities EDF carried out studies to reassess the demonstration that the risks of internal hazards associated with fire are satisfactorily controlled, with regard to: - the effects of smoke on the operation of the equipment; - the impact of fire-induced pressure effects on the fire sectorisation; - the fire-design of fire sectorisation elements. ASN underlines the progress made in understanding the impacts linked to pressure effects. EDF is nonetheless required to continue its efforts on certain points and ASN formulated requests in the letter in reference [44] to which EDF provided the first answers in the letters in reference [45] to [49]. These answers require detailed analysis and further exchanges are already planned. With regard to the impact of smoke on the operation of equipment, EDF does not envisage reviewing certain fire sectorisation justifications based on an analysis of the harmlessness of the propagation of smoke and simply proposes continuing its research work. ASN considers that EDF s reply is not satisfactory and reiterates its request in Appendix 2 of this letter (see request N 6 in Appendix 2 to this letter). 15 / 49