Practice and Consideration of Design Basis Extension

Transcription

1 Practice and Consideration of Design Basis Extension Jinquan YAN Shanghai Nuclear Engineering R&D institute ASME Workshop, Washington D.C Dec.3-5, 2012

2 1. Practice in Safety Design 2. Design Basis Extension 3. Issues Concerned

3 1. Practice in Safety Design Chinese National Nuclear Safety Administration (NNSA) established safety codes (HAFs) and regulations based on IAEA safety requirements (e.g. NS-R-1: Safety Requirements of NPP: Design). NPP design shall comply with national requirements, with reference to (adoption of) international codes and standards, e.g. 10CFR, ASME, ANS, IEC, IEEE, RCCs., etc. DesignBasisisalmostsameasworldwidepractices, particularly similar to current practice in US, SRP has been used in licensing safety review. Beyond Design Basis Accidents (BDBA) are required to be considered in NPP design as per HAF/NS-R-1. 3

4 1. Practice in Safety Design(cont.) BDBA consideration in design is based on deterministic approach, and supplemented by probabilistic and engineering judgment. PSA/PRA has been used as a design tool to identify risk important sequences, to examine the plant safety goal, and reviewed by NNSA during licensing. Measures designed to cope with selected BDBAs (resulted from internal events) including, Provision of Additional AC power (AAC) to cope with SBO. Installation of ATWS Mitigation System Actuation Circuit (AMSAC). RCS depressurization device to cope with High Pressure Melt Ejection(HPME). Passive Autocatalytic Recombiners (PARs) for H2 Control. 4

5 1. Practice in Safety Design(cont.) Measures designed to cope with BDBAs (cont.), Ex-vessel Cooling/In-vessel Retention(some NPPs). Filtered venting (some NPPs). Procedures, such as EOP and SAMG, are required to guide the intervention actions of the operator. For operating NPPs, however, PRA analysis and SAMG implementation are required but still in progress. 5

6 2. Design Basis Extension-Undertaking 6 Selected BDBAs (accident sequences) have been considered in existing designs. After Fukushima, safety assessment (stress test) were performed by plant operators/supporting institutes, followed by safety inspection by NNSA for all operating and constructing NPPs. Based on safety assessments and inspections, safety enhancements were required by NNSA, focusing on increase in plant capabilities or safety margins to deal with BDBAs caused by unlikely external events. E.g., for external flooding, NPP shall be protected against Design Basis Flooding (DBF) in combination with precipitation of one-thousand-year return period at site.

7 2. Design Basis Extension-Undertaking 7 Immediate or near-term safety enhancement requirements were set for all operating and constructing NPPs, including, Site re-evaluation and margin increase to cope with beyond design basis flooding. Provision of long term mobile power supply. Provision of long term water injection to RCS/SGs. H2 control(for NPPs not yet PARs installed). Enhancement of emergency control facility. Enhancement of monitoring and cooling capability of spent fuel pool. Enhancement of environmental radiation monitoring. SAMGs, etc.

8 2. Design Basis Extension-Considering Mid-long term safety requirements and/or design considerations for new NPPs are under investigation, and may include but not limited to following, New design and construction of NPPs shall be GEN III or above, with reduced CDF and LRF, and comprehensive prevention and mitigation of BDBAs. Implementing Post-Fukushima action items, taking into consider world-wide engineering practices. Mitigative measures will be more emphasized while preventive ones enhanced. Containment filtered venting may be required for NPP w/o redundant heat removal systems. 8

9 2. Design Basis Extension-Considering All risks, internal and external, shall be indentified and evaluated in deterministic and probabilistic approaches. Design consideration of long-term safety requirements may probably include, Practically elimination of large release to minimize environmental, socio-political impact. Consideration of malevolent aircraft impact. However, how to specify the requirement of practically elimination of large release is still in discussion. 9

10 3. Issues Concerned Followings are some of concerns or questions for further going beyond design basis, Since ZERO RISK is not technically practicable, what is the acceptable risk for NPPs? Current safety goal is adequate? Equipment survivability/qualification for BDBAs, method and criteria? For accident mitigation and containment integrity concern, what is acceptable conditional containment failure probability, 10-1,10-2? Filtered venting for large dry PWR? Considering all risks, how to practically eliminate severe accident by design? 10

11 3. Issues Concerned As for all risk approach of NNSC, the following items are concerned and should be defined and/or investigated: The quality of PRA. The frequency of the exterior hazards. All risk is not zero risk, then what is the acceptableresidual risk. How to define the rare yet credibleevents as BDBA. 11

12 Question?