IP-EUROTRANS Meeting WP 1.5 Progress in safety approach development

1. IP-EUROTRANS Meeting WP 1.5Progress in safety approach development Sophie EHSTER TEE, March 17 2006

2. CONTENTS • Progress in the development of a safety approach for Eurotrans concepts • First assessment of MYRRHA/XT-ADS analyses results and impact on the design

3. Progress in activities associated with task 1.5.1 • Task 1.5.1: Safety approach • Coordination: FANP (AREVA NP) • Participants: FZK, CEA, EA, SCK, KTH • Budgets (first period): to be confirmed by KTH • Total: 180 keuros • FANP (100)/FZK (10)/CEA (10)/EA (10)/SCK (20)/KTH (30) • Deliverables: • D1.20: Report on the approach and acceptance criteria for safety design of XT-ADS • To be issued by the end of March 2006 • First draft expected by the end of April 2006 • D1.21: Report on the approach and acceptance criteria for safety design of EFIT • To be issued by the end of September 2006 • Participation to the safety studies (definition, assessment of results)

4. Development of a general safety approach for XT-ADS - 1 • D1.20: Report on the approach and acceptance criteria for safety design of XT-ADS • The safety approach is based on the one developed for PDS-XADS concepts • Application of defense in depth principle: prevention and mitigation of severe core damage • Elimination of the necessity of off site emergency response (Generation IV objective) • Probabilistic design targets: • 10-5 per reactor year for cumulative severe core damage frequency is a minimum objective (lack of experience feedback): 2 strong LOD as a minimum for each sequence with an objective of 2 strong LOD + 1 medium LOD • Severe core damage is studied as a Design Extension Condition (mitigation provisions: 1 medium LOD) • Enhancement of prevention assessed with ALARP • For severe core damage situations which cannot be mitigated, they must result from a limited number of sequences for which a higher level of prevention is required. Their exclusion is justified by at least 2 strong LOD + 1 medium LOD for each sequence

5. Development of a general safety approach for XT-ADS - 2 • Categories of events considered for the safety demonstration: • Determination of the list of "excluded situations" (i.e. their consequences are not considered in the design) and guidance for the provisions used for an adequate justification of their exclusion • Determination of the "dealt with" initiating faults list and associated sequences: assessment of PDS-XADS results and consideration of new XT-ADS design features • Determination of practical analysis rules and adapted to the risks (e.g. corrosion consideration) • Consideration of XT-ADS specific features: increase of the core power density, consideration of core partly loaded with minor actinides, risk of water/steam ingress, risk of freezing • Radiological consequences: use of national method (i.e. Belgium) Action: SCK • Determination of barriers (e.g. fuel, cladding, structures) criteria: to be preliminary defined and confirmed by R&D about the knowledge of material behaviour for higher temperatures Action: CEA?, KTH?, FZK?

6. Development of a general safety approach for XT-ADS - 3 • Implementation of the approach for new concepts: • Necessity of a prior assessment of the potential consequences of initiators without consideration of safeguard measures. This allows to determine: • The list of "excluded" and "dealt with" situations • What the means necessary to mitigate the consequences should be • How many and diverse are the means required in regard to the safety objectives by means of use of Line Of Defence/ PRA methods should be • What the performances expected for these safety related means (grace period, capability…) in regard to the criteria should be

7. Development of a general safety approach for XT-ADS - 4 • Specific safety issues have to be dealt with: • Sub-critical core: • Definition of the sub-criticality level: • No criticality any DBC and DEC (except severe core damage) • Risk of criticality during severe core damage has to be assessed • Consideration of events likely to occur during shutdown conditions (modification of the core, specific accidents): control of the sub-criticality level and implementation of a dedicated shutdown system Action: SCK?, CEA? • Confinement function: • Coupling of the reactor, spallation target and the accelerator needs to be assessed • Generation of polonium 210 due to the activation of bismuth under irradiation Action: EA? • Demonstration of exclusion of core support structures (internals, reactor vessel) failure: • ISIR of in-vessel structures under a metal coolant • Consideration of oxide formation (design, monitoring, mitigation provisions) Action: FANP

8. First assessment of MYRRHA/XT-ADS analyses results and impact on the design - 1 • A quick assessment of the available analyses results for MYRRHA indicates that a first feedback is already needed on the design: • Risk of freezing in the Emergency Heat Exchanger (e.g. case of partial PLOFC, partial PLOH, overcooling) , leading to the complete unavailability of the DHR function shall be excluded • Impact of EHX design: core by-pass, inversion of flowrate between power conditions and natural convection, impact on the procedure for reactor shutdown • Reliability (e.g. number of systems, redundancy, diversity, duty of the cavity walls cooling system) of the DHR means has to assessed • Adequate design and temperature in operating conditions of the water cooling circuit • SA blockage consequences • … • An early check and review of the available results and their impact on the design is requested in parallel to the analysis of XT-ADS transients Action: FANP, SCK, FZK (End of May)

9. First assessment of MYRRHA/XT-ADS analyses results and impact on the design - 2 • Safety input is necessary to implement the XT-ADS reference design • Selection of Reference Design: before summer • The general architecture (MYRRHA and its variants for XT-ADS such as fuel handling from the top) needs to be assessed in regard to safety • Use of check and review of analyses based on MYRRHA Draft 2 file • Use of available results of XT-ADS transient analyses • Working group: FANP, SCK, FZK, others? • Dedicated meeting (synthesis of the assessments) early in June?