2016/3/30 Learnings from Fukushima Dai-ichi Accident: - Defense-in-Depth, Human and Organizational aspects, Safety approaches- Akira OMOTO, Professor, Tokyo Institute of Technology (omoto@nr.titech.ac.jp) Ou Outline Weakness in the application of Defense in Depth ü concept Human and organizational aspect Implications to approaches/methodologies for safety 2 A. Omoto, Titech 1
2016/3/30 Ø Fukushima Dai-ichi accident: failure of risk governance in a country prone to natural disasters Ø This failure was: not because (as often mentioned) “Japan did not apply level 4 & 5 of Defense-in-Depth” “Nuclear safety principle failed” but because of “Weakness in the application of concept of Defense in Depth” Ø Weakness may be linked with underlying assumptions and traits of the organizations Ø What were the weakness and strength? A. Omoto, Titech 3 A. Omoto, Titech 4 2
2016/3/30 De Defense-in in-de dept pth: h: Hierarchical deployment of different levels of equipment and procedures to maintain the effectiveness of physical barriers between radioactive materials and environment What is it for? To compensate for uncertainty and incompleteness in our knowledge of accident initiation and progression” (Sorensen et al. 1999) Relevant to Fukushima Accident Level 5: How to limit offsite consequences by Emergency Plan? Level 4: How to stop progress of accident beyond design basis and limit its consequences? Level 1: What is the appropriate setting of design basis External Events? A. Omoto, Titech 5 3.11 Earthquake: Ø A combination of “Plate boundary earthquake” & “Tsunami earthquake”, initiated from B, extended to A and South Ø Multi-segment failures in 200 x 500km zone, Magnitude 9.0 Ø Superimposed Tsunami waves hit Fukushima site 6 A. Omoto, Titech 3
2016/3/30 Earthquake & Tsunami by plate techtonics 7 A. Omoto, Titech ３．２ 再現計算結果：広域再現モデル High Tsunami along the “rias coastline” (originated from Spanish “ria”) Run-up height Inundation height Onagawa Deeply indented coastline magnifies Tsunami height NPS [SOURCE] Attachment to the report http://www.bousai.go.jp/jishin/chubou/higashinihon/R eport.pdf Fukushima NPS Local differences of Tsunami height due to depth of sea bed Fukushima- Fukushima- Daiichi NPP Daiini NPP [SOURCE] Reconstruction of Tsunami height map (TEPCo) 8 A. Omoto, Titech 4
2016/3/30 Level 1 Defense in Depth Prevention of abnormal operation and failures History of re-evaluation of Tsunami height by TEPCO TEPCO studies: Tsunami deposit, Tall Tsunami wall TEPCO organized experts panel for review Hypothetical analysis: 10m by assuming Tsunami Earthquake* off Fukushima coast, max. 15.7m by further parametric study (2008) 15.7m (inundation) * shallow epicenter with large slip causing high tsunami even though magnitude is low Probabilistic T sunami hazard study (2006): 10(-5)/year for 10m Re-evaluation of Design basis Tsunami using JSCE guide(2002) 5.7m with limited assessment of impact to NPP in case of 10m 3m Design basis (1966) 9 A. Omoto, Titech ü IAEA SSG-9 (Seismic hazard evaluation) “Comparisons with similar structures for which historical data are available should be used in this determination. “ • M9.5 [Chile, 1960] or M9.2 [Alaska, 1964] or M9.1 [Aleutian, 1957] ü Comparative subductology: “Magnitude depends on local characteristics of lower plate” (convergence rate and age) • Sumatra earthquake [2004] was a challenge to this “theory” • Discussion on why failed among seismologists can be found in such documents as http://www.jsnds.org/contents/shizen_saigai_back_number/ssk_31_1_3.pdf ü Documents related to Headquarter of Earthquake Research (HER) • Report from long-term projection WG, 2002 • NISA projection of earthquake at NPP greater than scale 6 based on HER A. Omoto, Titech 10 5
2016/3/30 Map of world’s major subduction zones [SOURCE] R. McCaffrey, Geological Society of America, 2009 11 A. Omoto, Titech Comparative subductology Relationship of seismicity to the two variables (convergence rate and age) [SOURCE] L. Ruff and H. Kanamori, “Seismicity and the subduction process” , Physics of the Earth and Planetary Interiors, v23, p240-252, 1980 12 A. Omoto, Titech 6
2016/3/30 Assessment of external hazards and their Design Basis Ø An important part of Owner’s engineering Ø Needs periodic reassessment ü it is not a one-time work outsourced from Owner to a consulting company ü Epistemic uncertainties needing a group of experts to discuss 13 A. Omoto, Titech Storegga slide Ø Amongst the largest known landslide Ø Study of deposited sediment Ø 8,000 years ago Ø Around 10% of Tsunami by landslide? Storegga tsunami deposits, Scotland 14 A. Omoto, Titech 7
2016/3/30 Strength 1. Continuous reassessment of design basis (Vigilance) 2. Study on what if design basis is exceeded (in 2002) 3. (In Tohoku) Margin in keeping dry site policy Weakness 1. Insufficient questioning attitude [To assumptions in the use of professional society’s guide, To “comparative subductology” theory] 2. Insufficient attention to alternative views (Tsunami, earthquake) 3. Insufficient margin assessment - What if design basis is exceeded? - Where is cliff edge to degraded core condition? - What is possible to increase distance to cliff edge? 4. Regulation 15 A. Omoto, Titech Level 4 Defense in Depth Control of accident beyond Design Basis Simplified response of unit 2 & 3 3.11 PM Earthquake and Tsunami left the plant under Complete SBO (AC/DC) + Isolation from Heat Sink automatic response Short term Ø Core cooling by AC-independent systems: use of decay heat as driving force Accident Management Long term Ø Depressurize reactor system Ø Activate Low Pressure water injection systems Failure of AC-independent systems à Core melt, hydrogen generation and explosion outside of CV 16 A. Omoto, Titech 8
2016/3/30 SBO Ø comply with US 1988 SBO rule Ø “30 minutes rule” in Japan: Not a 20 200 Depressurization decisive factor RPV water level 150 15 BWR operation in SBO+LUHS Rate (kg/s) Level (m) Fuel uncovered 10 100 ü 0-24hrs into the accident: Core water time period is short. TAF Water (less than 1 hour) Flow makeup by use of stored energy (RCIC/HPCI)) BAF RPV Loss of water inventory 50 ü 24 hrs: Depressurize RCS (Reactor Coolant RCIC Flow 5 equivalent to Decay Heat System) and Low-Pressure injection FP Flow ü 32 hrs: Heat dissipation to the alternative heat 0 0 0 10 20 30 40 50 60 70 80 sink (atmosphere) by containment venting Time (h) 1000 10 300 Depressurization Venting Depressurization 853kPa[gage ] Temperature (℃) 250 800 Pressure (MPa[gage]) Pressure (kPa[gage]) 8 2Pd 200 600 6 Wetwell Temperature 150 427kPa[gage] 400 Drywell Containment 4 Temperature Pd 100 Drywell Pressure RPV Containment 200 2 50 Rx Pressure Wetwell Pressure 0 0 0 0 10 20 30 40 50 60 70 80 0 10 20 30 40 50 60 70 80 17 A. Omoto, Titech Time (h) 17 Time (h) Ø Accident Management (AM) was prepared after Chernobyl, but - not assuming extended SBO + loss of UHS - not assuming extensive damages by external events Ø Limited available on-site resources on devastated Fukushima site Fire Engines Batteries taken from cars Mobile small Generators Mobile Engine-driven Air Compressors Mobile pumps/motors Ø Recovery actions hampered by Tsunami debris and hydrogen explosions 18 A. Omoto, Titech 9
2016/3/30 Decision-making, command and implementation in a complex environment Multi-hazard (Damage by Earthquake Crippled monitoring and Tusnami and communication Onsite Command system Multi-unit system accident Headquarter PM Plant condition Also, it just happened; - HE in Unit 3 damaged water injection to Unit 2 when it was ready - Large release from Unit 2 (March 15) happened to cause significant deposit in NW by occasional wind and precipitation. 19 A. Omoto, Titech Strength 1. Diversity by Air-cooled EDG against LUHS 2. Resilience (case of adaptationto loss of DC) 3. Self-sacrifice 4. Team work under the leadership of sinorities with professional experiences (oldest site) Weakness 1. Not prepared to very long-term SBO + Loss of UHS 2. Lack of robustness of AM provisions against external event 3. Insufficient External Event PRA and what-if study: v What if debris cooling outside of RPV failed v What if H2 leaked from CV was accumulated on top of R/B 20 A. Omoto, Titech 10
2016/3/30 Level 5 Defense in Depth Emergency Preparedness and Response (EPR) Ø Overall EPR (evacuation and food control) helped reduce health risks Ø Identified problems are; ü Offsite center’s function was lost ü Confusion in implementation of EPR ü Fatalities of hospital patients during evacuation ü Delineation of responsibility including PM, communication among decision-makers ü Dependence on computer-based prediction system and more……… Identified problems and recommendations by Japan Health Physics Society http://www.jhps.or.jp/jhp/wp-content/uploads/2015/10/Fukushima- recommendation2.pdf 21 A. Omoto, Titech Strength - Resident’s decision by collecting available information - Food control (learning from Chernobyl) Weakness ü Planning lacked serious consideration of what can happen ü No “Realistic drill” ü Inappropriatedesign of offsite center ü Inappropriate zoning ü Coordination scheme ü Delineation of responsibility, command line…. 22 A. Omoto, Titech 11
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