Nuclear Regulatory Strength for Protection against Natural Hazards in Taiwan

1. Nuclear Regulatory Strength for Protection against Natural Hazards in Taiwan Maanshan NPS Ting Chow Convener, Nuclear Regulatory Technology Support Center Institute of Nuclear Energy Research Atomic Energy Council, Taiwan Sep 26, 2013

2. Contents • NPPs in Taiwan • Seismic Design Overview of Taiwan’s NPPs • Implementation of Lessons Learned from Past Domestic and Foreign Earthquake Experiences --Advanced Seismic Monitoring System (including ASTS) --US NRC NTTF Requirement as well as EU Stress Test Requirement • 10 year Periodic Safety Review Requirement --take seismic as an example • Other Natural Hazards • Remarks

3. General Background • US NRC App.A of 10 CFR 50 GDC 2 ““Design Bases for Protection Against Natural Phenomena,” requires that structures important to safety be designed to withstand the effects of expected natural phenomena when combined with the effects of normal accident conditions without loss of capability to perform their safety function. • 2 stage review process to assure the plant safety operation, following USNRC NUREG 0800 Standard Review Plan --CP issued, after having reviewed and approved of Preliminary Safety Analysis Report t (PSAR), to allow site to pour the first concrete on the first rebar --OL issued, after having reviewed and approved of Final Safety Analysis Report (FSAR), to allow plant to commercial operation • Plant operator to submit Periodic Safety Review (PSR) 6 months before plant to operate for next 10 years. • First full scope level 2 PRA on KSNPP was performed in 1982 by AEC, and since then living PRAs have been updated continuously until now.

4. NPPs in Taiwan

5. Design Basis Earthquake Determination • The BDE (SSE and OBE) was determined following US 10 CFR 100 App. A “Seismic and Geologic Siting Criteria for NPPs” --deterministic method --tectonic province approach: The vibratory ground motion at the site should be determined by assuming that the epicenters or locations of highest intensity of the earthquakes are situated at the point on the tectonic structures or tectonic provinces nearest to the site. --OBE is usually ½ of SSE

6. Definition of OBE and SSE • SSE: Safe Shutdown Earthquake --The NPP shall be designed so that, if the SSE occurs, those SSCs will remain functional to assure (i) the integrity of the reactor coolant pressure boundary, (ii) the capability to shut down the reactor and maintain it in a safe condition, or (iii) the capability to prevent or mitigate the consequences of accidents which could result in potential offsite exposures • OBE: Operating Basis earthquake --If vibratory ground motion exceeding that of the OBE occurs, shutdown of the NPP will be required.

7. Site Seismic Design Response Spectrum (defined at free surface at foundation level) RG 1.60 Plant specific

8. Locations for DBE free ground surface Up to 30 meters foundation level competent soil hypothetical outcrop Up to several hundred meters rock few to hundreds KM

9. DBE comparison (LM ABWR vs KK ABWR)

10. Chin Shan NPP Kuo Sheng NPP Maanshan NPP

11. Tectonic Plates C.P. Chang(2000), after Angelier(1986)

12. Seismicity of Taiwan (ML>4.0 in last 40 years)

13. Island wide seismic network

14. Major Earthquakes Experienced at Taiwan’s NPPs • 199909/21 Great Chi-Chi Earthquake (M=7.3) --the most devastating earthquake in 100 years. -- Due to the more than 170km distance away from the epicenter and good geological conditions, the recorded PGAs at NPPs were less than 0.02g, which is far less than 1/10 of DBE. • 200612/26 Maanshan NPP (M=7.0) --the severest earthquake intensity ever experienced at Taiwan’s NPPs (a little bit less than OBE level) (two consecutive strong quakes strikes in 8 minutes) --RCP motor and turbine high vibration alarms --unit 2 shutdown by operator’s decision --the first (and the only) reactor shutdown case in Taiwan due to earthquake

15. 2006 Earthquake Response Spectrum (at containment base floor in Maanshan NPP)

16. Implementation of Lessons Learned from Past Earthquake Experiences (1/2) • 1999 Chi-Chi Earthquake --installation of Automatic Seismic Trip System; • 2006 Heng-Chun Earthquake --regular cleanup of ventilation system at main control room (in 2010-27); --handrail installed in MCR benchboards; --potential movable equipment fixed at MCR and other safety related rooms

17. Implementation of Lessons Learned from past earthquake experiences (2/2) • 2007 K-K NCO Earthquake (6.8) --reroute underground fire water pipes to above ground; --protective metal wall installed surrounding SFP to prevent water spillage during earthquake --differential soil settlement check • 2009 Hamaoka Suruga Bay Earthquake (6.5) --installation of seismic instrumentation in every units and --additional seismic sensors in other locations for all NPPs (in progress); • 2011 Fukushima Accident --conduct EU stress test --take US NTTF recommendations (SPRA, SMA, seismic and flood walkdown/walkby)

18. Seismic Instrumentation at NPP • Seismic monitoring system --accelerometers deployed according to US NRC RG 1.12 requirement, e.g., free field, basemat slab, floors --annunciators and response spectrum analyzer console in main control room --to inform the operator the earthquake intensity and to assist to determine plant shutdown necessity • Automatic Seismic Trip System, ASTS --follow the good practice from Japan --automatically trip the reactor immediately when the earthquake intensity reach OBE --trip logic is the same as plant RPS trip logic

19. ●ASTS ●Seismic monitoring for OBE/SSE ∙ ∙ ∙ ∙ ∙ ∙ ∙ Seismic instrumentation at Chinshan NPP(instrumentation for system ID is not on this plot)

20. Seismic instrumentation at Maanshan(instrumentation for system ID is not on this plot) Seismic monitoring system ASTS

21. ASTS System Function Block NPP MCR ALARM WINDOW BAND PASS FILTER B/U V/I I / V SETPOINT COMPARE TIMER FBA-23 Sensor RPS OUTPUT RELAY Signal Conditioner Sensor Box Foxboro SPEC-200 Controller cabinet

22. ASTS Deployment at NPPs

23. Development of ASTS

24. Introduction to Taiwan’s 10 year PSR • Mandatory requirement in Taiwan Nuclear Reactor Facilities Regulation Act • Utility should submit the PSR report 6 months before running to another 10 years. • The first Commercial date is 1978/12, 1981/12, and 1984/07 for CS, KS and MS respectively. • Standard format, Chapter 1~8 • Seismic related is in Chapter 6, usually are over 600 pages • Focus on --new findings/evidences --new regulatory requirement reflected by new technological advancement and operation experiences

25. 3rd PSR contents in MSNPP • Chapter 1: operation evaluation in past 10 years • Chapter 2: radiation safety evaluation in past 10 years • Chapter 3: radwaste safety evaluation in past 10 years • Chapter 4: improvement and betterment work to be done in next 10 years • Chapter 5: integrated plant assessment on aging management • Chapter 6: seismic safety re-evaluation • Chapter 7: betterment from major events experience feedback • Chapter 8: Implementation learned from foreign operation experiences or research results • Chapter 9: plant major changes made during past 10 years • Chapter 10: safety enhancement in light of Fukushima accident --especially the BDBE countermeasures • Chapter 11: conclusion

26. Seismic Contents in MSNPP 3rd PSR (year 2012) • 6.1 Abstract • 6.2 Regional geology and fault/volcano activities --Henchun fault was defined suspicious fault before, until 2009 • 6.3 Reexamination of appropriateness of attenuation equations and design response spectrum • 6.4 Seismic hazard re-evaluation • 6.5 Structure system identification --seismic sensors installed in 2010.11 • 6.6 Seismic monitoring system (seismic records in 10 years) --old digital system deployed in 1991 was updated in 2008 --29 earthquakes were recorded from 1995.4~2011.8, the biggest is 2006/12/26 M=7.0, PGA is 0.17g, the biggest PGA is 0.17g during that earthquake, the second highest is 0.03g in 1995/4/9 M5.3 earthquake -- ASTS introduced • 6.7 Seismic re-analyses for seismic category II -- back-fit analysis to comply with the updated 2005 building code • 6.8 Structures and equipment damage examination during 2006/12/26 double M7.0 earthquakes • 6.9 Tsunami effect evaluation (in light of 2011 Fukushima accident) --result of new numerical simulation analysis • 6.10 Summary • 6.11 Reference • Appendix --strong motion procedure including post earthquake walkdown SSC checklist and strong earthquake inspection procedure (procedure 582 and 582.1)

27. Seismic Contents in KSNPP 3rd PSR (year 2011) • 6.1 Abstract • 6.2 Regional geology and fault activities (include Volcano, Tsunamic) • 6.3 Reexamination of appropriateness of attenuation equations and design response spectrum • 6.4 Seismic hazard re-evaluation (Sanchiao Fault) • 6.5 Structure system identification 6.6 Seismic monitoring system (seismic records in 10 years and ASTS introduction) --(update of the digital system in 2005) --24 earthquakes were recorded from 2001~2010.6, the biggest is 2004/10/15 M=7.1, PGA is 0.01g, the biggest PGA is 0.02g during 2004/7/6 M5.2 earthquake • 6.7 Seismic re-analyses for seismic category II (the back-fit analysis to the 2005 updated building code) --push-over analysis • 6.8 Structures and equipment support degradation examination (base line inspection) • 6.9 Volcano activities/effect evaluation (Tatun volcano) • 6.10 Tsunami design re-assessment (in light of 2011 Fukushima accident) • 6.11 Conclusion • 6.12 Reference • Appendix --Earthquake emergency procedure --Post earthquake plant inspection procedure (checklist and damage state)

28. Seismic Contents in CSNPP 3rd PSR(year 2008) • 6.1 Abstract • 6.2 Special Report: 1999 Chi-Chi 921 M7.3 earthquake safety evaluation 6.2.1 Abstract 6.2.2 Regional geology and seismic activities (including volcano) --CGS in 2007 declared that the length of Class II Sanchiao fault could be possibly extended 6.2.3 Reexamination of appropriateness of attenuation equations and design response spectrum 6.2.4 Seismic hazard re-evaluation --no special treatment to model Sanchiao fault 6.2.5 Structure system identification 6.2.6 Seismic monitoring system -- 20 earthquakes were recorded from 1995~2007.9, the biggest is 1999/9/21 M=7.3, PGA is 0.03g in foundation mat, the biggest PGA is 0.03g during 1999/9/21 earthquake -- updated the old 1995 digital system to new Kinemetrics Condor system in 2005 6.2.7 Reference • 6.3 Seismic re-analyses for seismic category II (the back-fit analysis to the 2005 updated building code) • 6.4 Structures and equipment support degradation examination (base line inspection) • 6.5 Conclusion

29. New threat • A possibly longer length active fault lies between CSNPP and KSNPP • A suspicious fault which was not well-defined but is very close to MSNPP was declared as active in 2009

30. The new recognized active fault between Chinshan NPP and Kuosheng NPP and some major historical earthquakes(8 kilometers and 40 kilometers radius)

31. The new recognized active fault near Maanshan NPP and some major historical earthquakes(8 kilometers and 40 kilometers radius)

32. SMASeismic Margin Assessment • To assure the plant safety should the new near faults moves --Decide of RLE which is Max of 1.67SSE and new seismic value by DSHA, should the new faults moves --Plant HCLPF shall larger than RLE

33. SPRASeismic Probabilistic Risk Assessment • Perform the SPRA to find and improve the plant vulnerabilities so the plant risk in terms of SCDF/LERF is acceptable low

34. Fragility Derivation • Fragility evaluation is to estimate the capacity of a given component in terms of a ground motion parameter such as PGA. • Using information on the plant design basis and responses calculated at the design stage. • Extract the safety factors from design analysis/qualification reports • By characterizing the component fragility through a family of fragility curves, the analyst has expressed all his knowledge about the seismic capacity of the component along with the uncertainties. • The lognormal model for fragility --Material strength data follow a lognormal distribution. --The lognormal model is mathematically easy to use and can be partly justified by the Central Limit Theorem. • The fragility of a structure/component is expressed by the median ground acceleration capacity Am, and its variability estimates βR and βU (logarithmic standard deviation for aleatory randomness and epistemic uncertainty of a median value 1.0).

35. Structure Fragility Example

36. Fragility Curve Meaning

37. Tsunami • Historical data is very short • Design tsunami source written in FSAR for CS, KS, and LM NPP were all based on one offshore volcano eruption event which occurred in 1867. • Design tsunami source written in FSAR for MSNPP was based on a hypothetical offshore earthquake of Magnitude 8 • Tsunami runup height was calculated by empirical formula • The design tsunami height is the combination of the tsunami runup height with high wave level and storm surge height plus some safety margin • So far, no plant has experience tsunami since the plant operation • The advanced numerical simulation of tsunami caused by 22 offshore trenches performed by NSC showed the current plant elevation is still OK, but the maximum potential magnitude of the sources for design purpose are yet to be confirmed. • Systematic paleotsunami study was started very lately, and the reliable paleotsunami evidences/data are yet to come-up

38. Design Tsunami Re-evaluation and Countermeasures • Tsunami hazard re-evaluation following US NUREG/CR6966 new guideline --in tsunami source, to study and locate paleotsunami evidence if any --in tsunami mechanism, to consider not only earthquake induced, but also submarine volcano eruption and landslide --Runup/drawdown and inundation numerical simulations • New sea walls constructions --add 6 meter margin to the revised design basis tsunami height based on latest 2007 USNRC SRP to account for the uncertainties

39. T1, Mw=8.1 花蓮外海 T2, Mw=8.2 馬尼拉海溝1 T3, Mw=8.4 馬尼拉海溝2 T8,Mw=8.7 亞普海溝 NSC Earthquake Tsunami Sources(18 trenches, 4 faults)

40. Volcano issues • If there is any potential hazard due to volcano, it should be described in Safety Analysis Report based on the Standard Review Plan (SRP), section 2.2 “the identification of potential hazards in site vicinity”. • 5 historical submarine eruptions in the offshore have been reported, only the one occurred in 1867 has caused damage to the Keelung harbor due to accompanied tsunami. • The offshore Gueshan Island is 20 km away from LM NPP, last eruption is about 7000 years ago, has been raised a concern to LMNPP, a 2001 research concluded it will not affect the plant safety. • The last eruption of the northern inland Tatun volcano was about 0.8Ma after 1.7Ma of silence since the first eruption. TPC concluded the volcano should not be a design basis event following IAEA SSG-21 volcanic hazard assessment methodology. • Still, AEC require TPC to perform probabilistic volcano hazard analysis

41. Strong Wind • The design wind is governed by typhoon with return period of 100 years plus substantial margin • Typhoon arrival time could be predicted, so plant have plenty of time for preparedness • As all safety related SSCs are enclosed in Rugged reinforced concrete, and typhoon load will not govern the design • Wind missiles is considered in the design

42. External Flood • Drainage system design was based on Probable Maximum Precipitation PMP of 10,000 year return period. For example, in MSNPP, PMP is 228mm/hr, and the total drainage capacity is 20 CMS (cubic meter per second) which is equivalent to 325mm/hr precipitation • The only flood experience was in KSNPP during 1987 typhoon because the improper penetration seal and flood discharge channel clogged

43. Remarkson Earthquake Threat • It was very fortunate in Taiwan that all operating NPPs have never suffered from earthquake strikes (i.e., no earthquake intensity greater than OBE has been experienced) • On the contrast, during last several years, there have been many OBE exceedance experiences in Japan, and 3 beyond SSE experiences (2 in Japan and 1 in USA) • in light of past earthquake experienced in foreign NPPs, we have done some seismic countermeasures • Besides, the regular 10-year PSR re-examined the plant safety, especially (1)the concerns caused by new finding as well as the new technology advancement, (2)feedback from lesson learned • Dealing BDBE, following AEC request, TPC has performed/updated SMA/SPRA, a logical and quantitative risk assessment method, to decide whether the plant should shutdown if the SMA result showed the plant has no enough margin against the RLE, or it can operate and perform plant SSC improvement in parallel when the SPRA result showed the SCDF is less than target safety goal value.

44. Remarkson Other Potential External Hazards • Flood --DBF is based on 10,000 year return period and the DBF calculation has been updated as more data become available --Several heavy rains by typhoon have tested the adequacy of the drainage system and modified the related procedure • Tsunami --Plant Elevations are all above the design tsunami runup height --in light of the Fukushima accident, new sea wall of extra 6 meters are to be built in every NPPs --further study including paleotsunami and hazard re-evaluation according to new guideline are required • Strong Wind --Plant SSCs were designed against this DBE, and shall not be a threat to the plant safety as the strong reinforced concrete building structures house almost all the safety related systems and components • Volcano --excluded from further consideration in FSAR --early warning system has been installed in Tatun volcano area --North and Northeastern offshore submarine volcanoes investigation are required • Earthquake/Flooding induced landslide/mudslide --Plant topography and environmental geology support the CGS’ conclusion of the plants are not with these potential risk --US NRC NTTF 2.3 on flood walkdown is required by requlatory

45. Thanks for your attention