Annie  Kammerer  Bechtel  Corporation  Pacific  Earthquake  Engineering  Center,  UC  Berkeley  

Nuclear  Energy:  Resources,  Geological  Hazards,  and  Waste  Management  Energy  from  the  Earth  Series  March  2014  

  The  US  Nuclear  Regulatory  Commission  (NRC)  uses  a  risk-­‐informed  regulatory  framework  

  Assessing  seismic  risk  requires:    Understanding  and  quantifying  seismic  hazards    Understanding  and  quantifying  plant  seismic  capacity  

  Earth  science  data  has  a  direct  impact  on  nuclear  safety  by  allowing  the  nuclear  industry  and  the  NRC  to  better  quantify  the  natural  hazards  that  plants  must  be  able  to  withstand  (and  their  associated  uncertainties)  

Risk  

Seismic  Load   Capacity  

Seismic  Motion  Parameter  

Prob

ability  of  E

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Seismic  Motion  Parameter  

Cond

ition

al  Proba

bility  of  Failure  

  In  1971  the  NRC  established  General  Design  Criteria  2,  which  required  that  plants  be  designed  to  withstand  natural  phenomena  with  a  consideration  of  data  uncertainty  (Appendix  A  to  10  CFR  Part  50).    

  In  1973,  “Seismic  and  Geologic  Siting  Criteria  for  NPPs”  provided  detailed  criteria  to  evaluate  the  suitability  of  proposed  sites  and  the  suitability  of  the  plant  seismic  design  basis.  (Appendix  A  to  10  CFR  Part  100)    

Appropriate  data  collection  and  field  investigation  efforts  to  meet  10  CFR  100.23  requirements  

Site  (>1km)  

Site  Area  (>8  km)  

Site  Vicinity  (>40  km)  

Site  Region  (>320  km)  

Increasing  level  of  effort  close  to  site.      

However,  any  seismic  sources  that  may  impact  hazard  should  be  appropriately  assessed.  

  In  1996,  the  NRC  issued  an  update/reorganiztion  to  complete  the  current  legal  basis  for  seismic  design  (10  CFR  Part  50  Appendix  S):  

  Defined  “Safe-­‐shutdown  earthquake”  (SSE)  ground  motion  

  Specified  that  “The  nuclear  power  plant  must  be  designed  so  that,  if  the  Safe  Shutdown  Earthquake  Ground  Motion  occurs,  certain  structures,  systems,  and  components  will  remain  functional  and  within  applicable  stress,  strain,  and  deformation  limits.”  

  Added  the  explicit  requirement  to  consider  uncertainty  

  In  1997,  the  commission  issued  a  directive  to  move  towards  “risk  informed”  policies.  

  2007  NRC  issued  Regulatory  Guide  1.208,  which  describes  the  current  hazard  assessment  approach  works  with  risk-­‐based  engineering  guidance  (ASCE  43-­‐05)    Uses  10,000  to  100,000  year  ground  motions  (10-­‐4    to  10-­‐5  annual  probability)  for  design  ground  motions.    

  VERY  rare  ground  motions  used  for  design.  Significant  earth  science  needs  to  quantify  these  rare  events  appropriately.  

  Risk  targets:  Frequency  of  damage  of  individual  safety-­‐related  elements  (individual),  core  damage  frequency  (systems),  and  large  early  release  frequency  (containment)  

  The  current  US  risk-­‐informed  regulatory  approach  to  seismic  safety  provides  a  rational  framework  for  decision  making  that  is  targeted  on  risk  factors  that  matter.  

  The  assessment  of  seismic  risk  relies  directly  on  quantification  of  seismic  hazard;  which  itself  relies  directly  on  sufficient  and  robust  earth  science  information  from  the  broader  technical  community.  

Probabilistic  Seismic  Hazard  Analysis  •  Objective  to  determine  the  best  estimate  (and  

uncertainty  estimate)  of  ground  motion  levels  at  a  particular  location  over  time  periods  of  interest.    

•  PSHA  considers  ground  motions  from  all  possible  earthquakes  from  all  seismic  sources  that  may  impact  a  site,  and  accounts  for  the  likelihood  of  any  particular  earthquake.  

•  (Approach  can  be  used  for  any  natural  hazard)  

The PSHA mode is developed through a well defined process that incorporates evaluation and integration of all of the available data, models & methods

NUREG/CR-6372 NUREG 2117 (1989) (2012)

“aleatory” randomness is

integrated

“epistemic” uncertainty from

alternative models is addressed through a

logic tree

Seismic  Source  Characterization  

Ground  Motion  Characterization  

Base  figure  from  Reiter  (1990)  

Earthquake  Recurrence  

Source  Geometry  

Seismic  Hazard  Model  

Seismicity  

Geology  

Tectonics  

Magnetics  

Gravity   Paleo-­‐seismic  

Geodetics  (GPS)  

Crustal  stress  

Crustal  geophysics  

Site  Characteristics  

12  

Seismic  Source  Characterization  

PUBLISHED    January  2012  

Ground  Motion  Characterization  IN  PROGRESS  expected  2015  

15 Courtesy  of  TEPCO  

Fukushima  Lessons  Learned  Report  with  Significant  Recommendations  for  changing  NRC  regulations  and  practices  

NRC  ML111861807  

17  

Early

Near  term  

Long  term  

2.3  

2.1  

2.2  

Walkdowns  

Hazard  evaluation  

Risk evaluation

Regulatory  Actions  

10  year  update  

Walkdowns  to  assure  plants  are  meeting  licensing  basis  and  to  look  for  potential  seismic  issues.  Reports  due  November  2012.  Some  equipment  

delayed  until  outage.  

Hazard  evaluation  due  in  18  months  for  plants  within  the  new  CEUS  SSC  (NUREG  2115)  model  area.  3  years  for  western  US  NPPs  performing  

plant-­‐specific  studies.    

Risk  results  due  3  years  after  hazard  using  seismic  probabilistic  risk  assessments  (SPRA)  

After  receiving  the  information  from  the  SPRA,  the  NRC  will  determine  what  regulatory  action  is  

appropriate.  

Rulemaking  to  require  a  reevaluation  every  10  years.  

11/2012  (+outages)  

Spring  2014  (CEUS)  3/2015  (WUS)  

3  years  after  hazard  

Depends  on  findings  

Rulemaking  timeline  

•  Operating reactors designed using scenario earthquake (deterministic) approach •  No assessment of likelihood of scenario earthquake or resulting

ground motions •  Coupled with very conservative “margins” engineering •  New assessments provide apples to orange comparisons with old

values

Seismic  Motion  Parameter  

Prob

ability  of  E

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Thank  You