June 2011 Shigeo Ebata Nuclear Energy System Safety Division

1. Japan Nuclear Energy Safety Organization Review Guide forClassification of Importance of Safety Functions of NPP- Comparison with IAEA Guide - June 2011 ShigeoEbata Nuclear Energy System Safety Division Japan Nuclear Energy Safety Organization (JNES)

2. Contents • “Japanese Guide” and “IAEA Guide” 2. Japanese Guide --- How it was established? • Comparison of two Guides • Summary • Comments on “Draft Circular”

3. Japanese Guide 1. “Japanese Guide” and “IAEA Guide” Review Guide for Classification of Importance of Safety Functions of LWR Facilities, 1990 (rev.2009) Objective - Define the relative importance of “safety functions” and provide adequate requirements on design of SSCs. Position and scope - Application basis of safety functions for “Design Guide” : Purview - Example of classification for SSCs of PWR/BWR : Attached Table - More specific and detailed explanation : JEAG 4612-2010, JEAG 4611-2009 Application - Each stage of NPP design, construction and operation - Especially, in determining the measures and requirements for maintenance and operations with related SSCs (Risk informed ISI) (rev.2009) SSCs: Structures, Systemsand Components Design Guide: Review Guide for Safety Design of NPP

4. IAEA DS367 IAEA SAFETY GUIDE DS367 : Safety Classification of Structures, Systems and Components in Nuclear Power Plants, Draft 6.2 (Feb. 2011) Background • Originally issued as Safety Series No.50-SG-D1 in 1979 butwithdrawn in 2000 because the recommendations were considered not to comply with IAEA Safety Requirements (Safety of Nuclear Power Plants: Design, Safety Standard Series No.NS-R-1) • In 2006, new plan for the classification was approved by NUSCC (The Nuclear Safety Standard Committee), thereafter proceeded (Latest version: Draft 6.2) • Japanese Guide was referred in this drafting stage Position and Objective • Provide recommendation and guidance for identification and categorization of safety functions and for classification of related SSCs to ensure safety by meeting associated quality and reliability requirements • Classification of SSCs which are designed, manufactured, constructed, installed, commissioned, quality assured, maintained, tested and inspected • Applicable to all SSCs at NPP, any type of nuclear facility • Technology neutral (not depend on reactor type) • Describes the steps of safety classification (method) • Not necessary invalidate classifications of SSCs achieved using other methods or the national requirements of the individual Member States

5. Japanese Guide 2. Japanese Guide --- How it was established? History of Establishment • Before TMI-2 accident (1979), classification of two class (Safety and Non-safety) was applied in the United States. In Japan, this approach was also followed in the previous “Safety Design Guide”. • After TMI-2, it was pointed out that some SSCs, classified as non-safety, performed important role in the accident. • Therefore, in Japan, it was decided to hold the sub-committee in NSC to re-classify the then importance classification. (1984) • After extensive discussion how “Nuclear Safety” be achieved, it was concluded the importance of the appropriate protection of the public, plant personnel and environment from the radiation threatens. • As for discussion on what is important from the safety classification viewpoint, conclusion was that it should be appropriate to based on the “Safety Functions” , not on the “SSCs” themselves. （参考資料）「発電用軽水型原子炉施設の安全機能の重要度分類に関する審査指針」の策定経緯と検討の背景,　　　　　　 平成20年12月10日,原子力安全委員会事務局 審査指針課

6. Japanese Guide • 3 classes each for Preventing and Mitigating safety functions were applied as PS-1,2,3 and MS-1,2,3. And principles for “subjected system”, “relating system”, “separation and isolation” and “connection of different classes” were defined. And examples of classification for PWR and BWR were described in the Attached Table. • For the consistency of three guides, i.e., “Importance Classification Guide”, “Design Guide” and “Evaluation Guide”, these guides were revised together in 1990. Afterwards… • The Commentary of this guide describes; “Although this Guide is to be applied in carrying out the safety review regarding the application for the light water reactor establishment permit, it can be a useful reference in deciding the requirements for the subsequent design phase and the requirements for each phase after the design phase.” • About 20 years passed after this establishment, recently it was agreed that the review of this guide from the viewpoint of its specific application to operation management stage would be necessary based on the operation experience and utilization of risk information until now.

7. 3. Comparison of two Guides IAEA DS367 Japanese Guide

8. IAEA DS367 Japanese Guide Cont’d

9. IAEA DS367 Japanese Guide Cont’d

10. IAEA DS367 Japanese Guide 4. Summary Comparison of “IAEA DS367” and “Japanese Guide”: - Different classification method- Basically no conflict in classification of “Safety Functions” “Japanese Guide” : - More straightforward classification- Supported by example (in Attached Table) and JEAG 4612/4611 “Severe Accident”: major issue for “Japanese Guide”

11. 5. Comments on “Draft Circular” • Draft Circular aims: Classification of “Safety Function” or “SSCs” ? • Definition and categorization of “Safety Function” (not SSCs) be “starting point” • Clarify the basis of high/low class(Based on DiD level, dose, event frequency …?) • Include example of SSCs classification of specific NPP (e.g. VVER, PWR, BWR …) • Include “Severe Accident” description

12. Appendix： Safety Classification in US Features - “SSCs of safety importance” are defined at each stage, in each rule - Basically two-level classification of SSCs (10CFR50.2) “Safety-related” and “Non-safety” For design/construction stage*… 10CFR50.2 “Safety-related structures, systems and components means those structures, systems and components that are relied upon to remain functional during and following design basis events to assure: (1) The integrity of the reactor coolant pressure boundary (2) The capability to shut down the reactor and maintain it in a safe shutdown condition; or (3) The capability to prevent or mitigate the consequences of accidents which could result in potential offsite exposures comparable to the applicable guideline exposures set forth in § 50.34(a)(1) or § 100.11 of this chapter, as applicable.” General Design Criteria (10CFR50 Appendix A) “Criterion 1--Quality standards and records. Structures, systems, and components important to safety shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be performed.” Regulatory Guide 1.26 “… the NRC staff developed a quality classification system to provide licensees with guidance for satisfying General Design Criterion 1. The system consists of four quality groups, A through D; methods for assigning components to those quality groups; and specific quality standards applied to each quality group.” Standard Review Plan 3.2.2 (NUREG-800) …..<Basic concept of NRC for Importance to safety and functions of SSCs> ASME Boiler & Pressure Vessel Code Sec. III ….. <Voluntary Consensus Standards> * Other codes and standards for “Operation management stage”