The Fukushima earthquake + tsunami and other recent external events that have challenged the design basis for commercial nuclear power plants

1
The Fukushima earthquake tsunami and other
recent external events that have challenged the
design basis for commercial nuclear power plants
Peter Lobner 18 January 2012
2
Agenda

• Definition of design basis
• BWR mitigating systems and system dependencies
• Earthquake
• Niigata Chuetsu-oki, Japan, magnitude 6.8,16 July
  2007
• Great East Japan, magnitude 9.0, 11 March 2011
• Tsunami
• Fukushima Daiichi, 11 March 2011
• Fukushima Daiichi plant responses to the 11 March
  2011 earthquake tsunami
• International Response to the events at Fukushima
  Daiichi
• Recent external event challenges to U.S. NPPs
• Missouri River flooding, July August 2011
• Northern VA earthquake, magnitude 5.8, 23 August
  2011
• Hurricanes
• Conclusions

3
Definition of design basis

• Design bases that information which identifies
  the specific functions to be performed by a
  structure, system, or component (SSC) of a
  facility, and the specific values or ranges of
  values chosen for controlling parameters as
  reference bounds for design.
• These values may be
• (1) restraints derived from generally accepted
  "state of the art" practices for achieving
  functional goals, or
• (2) requirements derived from analysis (based on
  calculation and/or experiments) of the effects of
  a postulated accident for which an SSC must meet
  its functional goals.

Source 10CFR50.2
4
Safety design basis and safety functions

• Safety design basis focuses on assuring that
  nuclear power plant (NPP) safety functions
  defined in 10CFR50 Appendix A, General Design
  Criteria, can be accomplished when required to
  protect the integrity of multiple fission product
  barriers
• Accomplish reactor shutdown (GDC 20, 29)
• Maintain primary system integrity (GDC 14, 15,
  31)
• Maintain reactor core cooling (GDC 33 37)
• Maintain containment integrity (GDC 16, 38-43,
  50, 51, 52-57)
• Maintain the cooling water heat transport path to
  the ultimate heat sink (GDC 44-46)
• Prevent an uncontrolled release of radioactive
  material to the environment from fuel and waste
  systems (GDC 60-64)

5
Safety design basis for protection against severe
natural phenomena

• GDC 2, Design bases for protection against
  natural phenomena.
• SSCs important to safety shall be designed to
  withstand the effects of natural phenomena such
  as earthquakes, tornadoes, hurricanes, floods,
  tsunami, and seiches without loss of capability
  to perform their safety functions.
• The design bases for these SSCs shall reflect
• Most severe historically reported for the site
  and surrounding area, with sufficient margin
• Combinations of the effects of normal and
  accident conditions with the effects of the
  natural phenomena, and
• The importance of the safety functions to be
  performed.
• Generic Letter 88-20, Supplement 4, Individual
  Plant Evaluation of External Events (IPEEE) for
  Severe Accident Vulnerabilities
• Licensees requested to perform analyses to
  determine vulnerabilities to beyond-design-basis
  external events and determine if any improvements
  are needed.
• SSCs were examined to estimate their
  high-confidence-of-low-probability-of-failure
  (HCLPF) level.

Source 10CFR50 Appendix A, General Design
Criterion 2
6
The design basis is not static

• 10CFR50.54,Conditions of License, paragraph (f)
• The licensee shall at any time before expiration
  of the license, upon request of the Commission,
  submit, as specified in 50.4, written
  statements, signed under oath or affirmation, to
  enable the Commission to determine whether or not
  the license should be modified, suspended, or
  revoked.
• Except for information sought to verify licensee
  compliance with the current licensing basis for
  that facility, the NRC must prepare the reason or
  reasons for each information request prior to
  issuance to ensure that the burden to be imposed
  on respondents is justified in view of the
  potential safety significance of the issue to be
  addressed in the requested information.
• Value / impact ratio used for prioritizing safety
  issue resolution is determined using the
  conversion factor of 2,000/person-rem, which was
  approved by the Commission in September 1995.
• Resolving generic safety issues may require
  utilities to implement changes. For example
• Station blackout rule (SBO) (10CFR50.63, 1988)
• Mark I containment hard vents (Generic Ltr 89-16,
  1989)
• Utilities may choose to improve NPP operating
  capability.
• Longer operating cycles between refueling
• Power increase

7
Station blackout rule (SBO)

• 10CFR50.63 Loss of all alternating current
  power, requires that each NPP be able to cope
  with and recover from an SBO event of specified
  duration
• Cope means that the core is cooled and
  appropriate containment integrity is maintained
  in the event of a station blackout for the
  specified duration.
• Implemented by Regulatory Guide 1.155 and
  industry document NUMARC 87-00.
• 44 U.S. NPP implemented AC-independent solutions
• Batteries only
• Maximum coping duration 4 hours
• 60 U.S. NPPs implemented alternate AC power
  sources. For example
• Emergency diesel generator from an adjacent unit
• Gas turbine or other diesel generators, hydro
  generator.
• Coping duration 4 16 hours
• Non-electric driven pumps (steam, diesel) provide
  important capabilities for operating cooling and
  makeup systems during SBO.

8
BWR mitigating systems and system dependencies
9
Key mitigating systems available at the
Fukushima Daiichi units
10
BWR Mark-I containment steel shell
11
BWR Mark-I containment arrangement within the
reactor building
12
BWR Mark I containment performance improvement
(CPI) program

• Resolution of Generic Safety Issue 157,
  Containment Performance, resulted in significant
  modifications to BWR Mark 1 containments.
• All affected BWRs had in place emergency
  procedures directing the operator to vent via the
  non-pressure bearing Standby Gas Treatment System
  (SGTS) ducting under certain circumstances
  (primarily to avoid exceeding the primary
  containment pressure limit).
• A hard pipe vent path bypassing the SGTS and
  capable of withstanding the anticipated severe
  accident pressure loadings would eliminate the
  problems with venting the containment wetwell
  during a severe accident.
• The vent isolation valves should be remotely
  operable from the control room and should be
  provided with a power supply independent of
  normal or emergency AC power (i.e., operable
  during SBO).
• In Generic Letter 89-16 (1989), NRC requested
  each licensee to provide cost estimates for
  implementation of a hardened vent.
• GE reports that US operators installed hardened
  vents in their Mark I BWRs.
• In 1992, Japan's Nuclear Safety Commission
  rejected establishing a regulatory requirement
  for a hardened wetwell vent for Mark 1 BWR
  containments, leaving it to the NPP operators to
  decide to install a hardened vent.
• GE reports that Japanese operators, including
  TEPCO, installed hardened vents in their Mark I
  BWRs.

13
BWR Mark-I containment refueling floor arrangement
14
Isolation Condenser (IC) System

• System Dependencies
• Automatic start on reactor vessel high pressure
  or low water level, or remote manual,
• DC power to open the normally closed valve in the
  condensate return line
• AC power to operate normally open valves in the
  steam supply and condensate return lines
• Steam supply from main steam line to isolation
  condenser
• Periodic water supply to the secondary-side of
  the isolation condenser to make up for
  evaporation to the environment
• Periodic makeup to the primary system to make up
  for coolant shrinkage during cooldown

Source NUREG/CR-5640
15
Reactor Core Isolation Cooling (RCIC) System

• System Dependencies
• Automatic start on reactor vessel low water
  level, or remote manual,
• DC power to open RCIC turbine steam supply
  valves, injection valve, wetwell suction valves
  (when needed)
• Steam from main steam line
• Turbine exhaust path to wetwell and wetwell
  pressure lt turbine backpressure trip setpoint.
• Water supply from condensate storage tank or
  wetwell.
• Automatic pump suction realignment on CST low
  level
• Pump room cooling by service water
• No cooling for the pump itself.

Source NRC BWR Concepts Manual
16
High-Pressure Coolant Injection (HPCI) System

• System Dependencies
• Automatic actuation on reactor vessel low water
  level or drywell high pressure, or remote-manual
• DC power to open HPCI turbine steam supply
  valves, injection valve, wetwell suction valves
  (when needed) and operate the aux lube oil pump
  during startup
• Steam from main steam line
• Turbine exhaust path to wetwell and wetwell
  pressure lt turbine backpressure trip setpoint.
• Water supply from condensate storage tank or
  wetwell.
• Automatic pump suction realignment on CST low
  level
• Pump room cooling by service water
• No cooling for the pump itself.

Source NRC BWR Concepts Manual
17
Low-Pressure ECCS and Residual Heat Removal (RHR)

• System Dependencies
• Automatic pump actuation on reactor vessel low
  water level or drywell high pressure, or
  remote-manual
• Automatic Depressurization System (ADS) actuation
  on low vessel level high drywell level LP
  ECCS pump running
• AC power for LPCS and LPCI (RHR) pumps valves
• DC power to open ADS valves
• Water supply from wetwell.
• Pump room cooling by service water
• RHR pump cooling by service water

Source NRC BWR Concepts Manual
18
Niigata Chuetsu-Oki Earthquake (NCOE), Japan,
magnitude 6.8, 16 July 2007
19
Niigata Chuetsu-Oki Earthquake (NCOE), Japan,
magnitude 6.8, 16 July 2007
Source TEPCO
Source EQECAT Inc
20
Kashiwazaki-Kariwa NPP

• Worlds largest nuclear power facility 7,965
  MWe net from 7 BWR units.
• U1 5 BWR, 1067 MWe
• U6 7 ABWR, 1315 MWe
• During NCOE
• 3 operating at rated power (U3, U4 U7)
• 1 starting up (U2)
• 3 shutdown for periodic inspection (U1, 5 U6)
• 16 km from NCOE epicenter.
• No tsunami.

21
Kashiwazaki-Kariwa NPP
Source TEPCO
22
NCOE observed seismic data

• The observed seismic accelerations largely
  exceeded the design basis values.

Source TEPCO
23
NPP response to NCOE (1/2)

• Units operating (Units 3, 4 7) and being
  started up (Unit 2) automatically scrammed on
  detection of large seismic acceleration.
• Off-site power remained available during and
  after NCOE.
• Reactor vessel water level maintained in all
  units.
• Reactor cooldown and depressurization
  accomplished.
• Reactor coolant at all units cooled to below
  100ºC.
• Reactor pressure in each unit reduced to
  atmospheric pressure
• Stable cold shutdown condition achieved by 17
  July.
• In spite of significantly exceeding the original
  seismic design basis, the safety-related
  structures, systems and components at all seven
  units demonstrated good performance and
  accomplished their intended safety functions.

24
NPP response to NCOE (2/2)

• No change in fission product concentration in
  reactor coolant and spent fuel water, indicating
  that fuel in all units was sound.
• Minor releases of radioactive material
• Some water sloshed out of the Unit 6 spent fuel
  pool.
• Many containers of LLW overturned, some lids came
  off.
• Minor release via main stack detected on 17 July
  at Unit 7.
• Relatively minor physical damage, mainly to
  non-safety-related items.
• Mechanical anchorages, ducting to main stacks,
  various water, oil air leaks
• Structural wall embankment cracking
• Ground deformations, with potential to damage
  underground tunnels pipeways and surface roads
  drainage paths.
• Transformer fire

25
Improved understanding of site seismicity

• The NCOE seismic intensity exceeded the original
  seismic design basis for all NPP units.
• The NCOE seismic intensity also exceeded the
  seismic intensity estimated from an empirical
  evaluation of a magnitude 6.8 earthquake.
• Japans newer (2006) seismic design guidelines
  redefine active faults and the process for
  defining a Standard Seismic Ground Motion (SSGM)
  to be used in design.
• Post-NCOE seismic study findings
• New and extended fault lines.
• Geologic structure amplifies seismic motion from
  sea-side.
• Differences between the Unit 1-4 and Unit 5-7
  sites, which are 1 km apart.

Source TEPCO
26
Standard seismic ground motion (SSGM) defined for
Kashiwazaki-Kariwa NPPs.

• Post-NCOE seismic hazard studies yielded the
  largest values for ground motion ever considered
  for a nuclear power plant site.

Source TEPCO
27
Post-NCOE safety actions

• Install seismic reinforcements to tolerate
  seismic motion of 1000 Gal (1.5 times NCOE max)
• Add more pipe snubbers pipe supports
• Reinforce reactor building roof truss structure
• Reinforce reactor building overhead crane,
  including derailment prevention
• Reinforce refueling machinery, including
  derailment prevention
• Add vibration control device for stacks
• Perform facility integrity evaluation
• Confirm NCOE loads on each equipment was within
  applicable elastic limits.
• Perform equipment, system plant-level
  functional inspections tests
• EPRI supporting evaluation of hidden damage
• Improve the spent fuel storage pool structure to
  prevent radioactive water overflow (from
  seismic-induced sloshing) by Sep 2012.

28
Re-start status

• May 2009 Unit 7 re-started (22 mos)
• August 2009 Unit 6 re-started (25 mos)
• May 2010 Unit 1 re-started (34 mos)
• November 2010 Unit 5 restarted (40 mos)
• Units 2 4 investigations, modifications
  tests in-progress. Unit 3 likely to be next unit
  restarted.

29
Great East Japan Earthquake, magnitude 9.0, 11
March 2011
30
Great East Japan Earthquake, magnitude 9.0, 11
March 2011, 1446 JST
Source USGS
Source EQECAT Inc

• An earthquake of this magnitude is
  unprecedented in this region.
• Megathrust rupture on the Japan Trench
  subduction zone
• Earthquake lasted about 2 -2.3 minutes
• 11 aftershocks on 11 March, ranging from 6.0 to
  7.4.

31
Fukushima Daiichi NPP

• One of Japans larger nuclear power facilities
  4,696 MWe net from 6 BWR units.
• U1 BWR 3
• U2 5 BWR 4
• U6 BWR 5
• During earthquake
• 3 operating at rated power (U1, 2 3)
• 3 shutdown for periodic inspection (U4, 5 6)
• 112 miles from epicenter.
• Design basis tsunami 18.8 (5.7m)

32
FukushimaDaiichi SiteArrangement
Source INPO
33
Observed seismic data at Fukushima Daiichi

• Design Basis Earthquake maximum acceleration
  exceeded at Units 2, 3 and 5.
• The power lines connecting the site to the
  off-site transmission grid were damaged
• during the earthquake, resulting in a loss of
  all off-site power.
• All reactor safety functions were successfully
  performed after the
• earthquake and all units were in a safe state
  prior to the arrival of the tsunami.

34
Tsunami following theGreat East Japan
Earthquake, 11 March 2011
35
Tsunami timeline at Fukushima Daiichi

• 1527 First of seven tsunami waves arrived.
  Height about 13 (4 m) was less than the design
  basis tsunami and was mitigated by the
  breakwater.
• 1535 Second tsunami wave arrived. Height
  unknown. Tidal gauge failed.
• Five more tsunami waves. At least one of the
  waves measured 46 49 (14 15 m) high based
  on water level indications on the buildings.
• Unit 1 4 site area inundated to a depth of 13
  16 (4 5 m) above grade.
• Grade level at the Unit 5 6 site area is 3 m
  higher, so inundation there was less.

36
Tsunami wave arrives at Fukushima Daiichi
37
Tsunami wave arrives at Fukushima Daiichi
38
Site inundation
39
Site inundation
40
Site inundation
41
Tsunami effects on storage tank
42
Fukushima Daiichi site inundation
Source IAEA
43
Fukushima Daiichi Units 1 4 inundation
Source INPO

• Flooding resulted in common cause failure and
  loss of the ability to perform key safety
  functions
• Intake structure, pumps, and flow paths to the
  ultimate heat sink (the ocean) at Units 1 - 6.
• Most main and safety-related AC and DC electric
  power sources and distribution rooms / areas
  needed to support active safety systems at Units
  1 - 5. DC in Units 3, 5 6 survived.

44
Fukushima Daiichi plant responses to the 11
March 2011 earthquake tsunami
45
Decay heat reactor units 1, 2, 3
Source MIT
46
Decay heat spent fuel pools
47
Fuel response to severe accident progression
48
Unit 1 sequence of events
Adapted from INPO
49
Unit 1 sequence of events (continued)
Adapted from INPO
50
Unit 1 Hydrogen Explosion, 12 March 2011
51
Loss if lighting in the control room
Source TEPCO
52
Unit 2 sequence of events
Adapted from INPO
53
Unit 2 sequence of events (continued)
Adapted from INPO
54
Unit 3 sequence of events
Adapted from INPO
55
Unit 3 sequence of events (continued)
Adapted from INPO
56
Unit 3 Hydrogen Explosion, 14 March 2011
57
Unit 4 sequence of events
Adapted from INPO
58
Unit 4 after hydrogen explosion
59
Possible hydrogen leak path to Unit 4
Source INPO
60
Units 1-4 before the tsunami explosion
61
Units 1-4 after the explosion
62
Unit 5 6 sequence of events
Source SECY-11-0093
63
Severe accident response issues

• TEPCO confirmed that adverse conditions in the
  drywell may have resulted in boiling of the
  reference legs of the reactor vessel water level
  instruments, causing indicated water level to be
  higher than actual level.
• TEPCO severe accident procedures provided
  guidance for venting containment
• If core damage has not occurred, vent at
  containment maximum operating pressure 62.4
  psig for U1, 55.1 psig for U2 U5
• If core damage has occurred, delay venting until
  pressure approaches twice the maximum operating
  pressure.
• In Units 1, 2, and 3, the extended duration of
  high temperature and pressure conditions inside
  containment may have damaged the drywell head
  seals, contributing to
• Hydrogen leaks into the upper level of the
  reactor building and the subsequent explosions,
  and
• Ground-level radiation releases

64
Severe accident response issues

• Was there a re-criticality at Unit 2?
• While examining gases taken from the reactor,
  short-lived fission product Xe-133 was detected
  on 2 November 2011
• Boric acid water injected
• TEPCO general manager "Given the signs, it's
  certain that fission is occurring."
• The next day, TEPCO spokesman "Analysis suggests
  that it was not a criticality

65
Protective actions
Source SECY-11-0093
66
Cleanup and Decommissioning Plan

• December 2011 TEPCO released its 40-year plan
  to decommission the plan
• Phase 1 Post cold shutdown stabilization and
  planning
• Maintain stable reactor site conditions
• Conduct RD for later phases
• Complete within 2 years (by end of 2013)
• Phase 2 Removal of fuel from the spent fuel
  pools
• Remove fuel from spent fuel pools in all units
• Process accumulated water
• Conduct RD for later phase
• Complete within 10 years (by end of 2021)
• Phase 3 Removal of fuel debris through final
  decommissioning cleanup
• Fuel debris removal in U1, 2 and 3
• Decommissioning and site cleanup
• Complete in 30-40 years (by 2041 2051)

67
International Response to theFukushima Daiichi
Accident
68
USA

• Aug 2011 NRC released the results of its 90-day
  review of Fukushima lessons learned
• No "imminent threat, but some issues require
  immediate action
• Ability to withstand prolonged loss of AC power
• Ability to respond to earthquakes and flooding,
  and
• Ability to monitor the condition of spent fuel
  pools.
• Sep 2011 NRC issues, Recommendations for
  Enhancing Reactor Safety in the 21st Century,
  with 12 recommendations, including
• Balance defense in depth and risk
  considerations
• As needed, upgrade design basis seismic and flood
  protection
• Strengthen prolonged station blackout mitigation
• Study adequacy of hydrogen control
• Enhance spent fuel makeup capability and
  instrumentation
• Strengthen on-site emergency response accident
  management

69
USA

• Nov 2011 Proposed ballot initiative in
  California calls for immediate shutdown of PGEs
  Diablo Canyon and SCEs San Onofre NPPs, which
  generate 16 of California's power.
• Dec 2011 NRC approved the Westinghouse AP1000
  standard plant design
• 13 Jan 2012 Industry NRC meeting to recommend
  an approach for post-Fukushima improvements
• Diverse and flexible coping strategy (FLEX) for
  preventing fuel damage.
• FLEX differs from Severe Accident Management
  Guidelines (SAMGs), which come into play after
  core damage.
• FLEX is designed to expand the margin of safety
  at nuclear energy facilities and ensure they can
  cope with extended loss of power using pre-staged
  backup equipment and suppliessuch as fresh water
  and diesel fuel that are available
  on-sitesupplemented by off-site resources
  established for this purpose.
• Approach builds on concepts used to provide
  additional contingency at U.S. nuclear facilities
  after the 9/11 attacks.

70
European Union (EU) stress test

• The European Council of 24-25 March 2011
  requested that the safety of all EU NPPs be
  reviewed on the basis of a stress test.
• A reassessment of NPP safety margins in the light
  of the events that occurred at Fukushima
• Extreme natural events challenging the plant
  safety functions and leading to a severe
  accident.
• A deterministic sequential loss of lines of
  defense is assumed, irrespective of the
  probability of the loss.
• The final country-specific reports were due to be
  submitted to the European Nuclear Safety
  Regulators Group (ENSREG) by December 31, 2011.  
• The next stage is a peer review of the
  country-specific reports, to be completed by
  April 30, 2012
• A consolidated EU report will be issued in June
  2012.
• These reports are publically available on the
  ENSREG web site
• http//www.ensreg.eu/

71
France

• Current fleet of 58 NPPs has a generating
  capacity of 63,130 MWe and produce gt75 of
  Frances electricity.
• One new 1600 MWe EPR unit is under construction
  and one more committed in Nov 2011.
• Nov 2011 Green and Socialist parties call for
  shutting down 24 NPPs across France by 2024.
• President Sarkozy said the proposal would cost
  French consumers 5 B (6.63 B) a year.
• Dec 2011 First phase of EU stress test
  completed.
• Jan 2012 French Nuclear Safety Authority (ASN)
  stated that current NPPs have a sufficient
  safety level, but called for significant safety
  investment from EDF on the order of 10 B (about
  13.5 B) over 10 years. Identified safety
  improvements include
• Flood-proof diesel generators, and
• Bunkered remote back-up control rooms
• Nuclear Fast Response Force available to support
  an NPP site within 24 hours
• EDF is planning to operate its fleet of PWRs for
  60 years.

72
Germany

• Current fleet of 17 NPPs has a generating
  capacity of 20,429 MWe and produce about 23 of
  Germanys electricity.
• 30 June 2011 the country's parliament voted to
  phase out Germany's nuclear fleet
• The 8 oldest reactors (gt 8,000 MWe) already have
  been disconnected from the grid
• The remaining 9 reactors will be retired by 2022
• Sep 2011 International Energy Agency warns
  German government of risky phase-out strategy

73
Switzerland

• Current fleet of 5 NPPs has a generating capacity
  of 3,220 MWe and produce about 38 of
  Switzerlands electricity
• Parliament approved nuclear phase-out in 2011.
• Preliminary phase-out plan
• Beznau I in 2019 (365 MWe)
• Beznau II and Muehleberg in 2022 (720 MWe
  combined),
• Goesgen in 2029 (970 MWe)
• Leibstadt in 2034 (1165 MWe)
• Sources of replacement power
• Development of hydro-electric plants and other
  renewable energy
• Possibly importing electricity.
• If necessary the country could also fall back on
  electricity produced by fossil fuels.
• It has been estimated that the cost of reshaping
  the country's energy resources, offset by
  measures to cut consumption, would cost the
  country between 0.4 - 0.7 of gross domestic
  product per year.
• 2010 GDP was 524 B, so phase-out costs 2.1
  3.7 B / year
• Swiss nuclear safety authority ENSI requires EU
  stress tests applied to Swiss NPPs.

74
Belgium

• Current fleet of 7 NPPs has a generating capacity
  of 5,885 MWe, which represents 92 of domestic
  energy generation and 22 of domestic energy
  consumption. Belgium imports most of its energy.
• In October 2011, the Belgian government committed
  to implementing the nuclear exit law of 2003.
• The plan calls for the following shutdown
  schedule
• The three oldest NPPs by 2015 (1787 MWe)
• The remaining four NPPs by 2025 (4098 MWe)
• This plan is conditional on finding enough energy
  from alternative sources to prevent electric
  supply shortages and significant change in the
  price of electricity.

75
Elsewhere in Europe

• Italy
• Italy has no NPPs
• In a 12-13 June 2011 referendum, voters rejected
  government plans to build new nuclear plants.
• Lithuania
• July 2011 GE-Hitachi was selected to build a
  new BWR NPP to replace the Ignalina NPP, which is
  being decommissioned
• Will reduce Baltic states energy dependence on
  Russia.
• Finland
• October 2011 First in Europe to approve a new
  green-field NPP site since the Fukushima Daiichi
  accident.
• Poland
• Still moving ahead to select NPP supplier in
  2013, with initial operation of Polands first
  NPP in 2020.

76
Japan

• In 2010, the Japanese government approved a plan
  to build 14 new NPPs and increase reliance on
  nuclear energy.
• Current fleet of 48 NPPs (excluding 6 units at
  Fukushima Daiichi) has a generating capacity of
  42,300 MWe and produce about 25 of Japans
  electricity.
• Since the Fukushima Daiichi accident, all
  reactors that have been shut for regular
  maintenance have been kept offline as part of
  efforts to assuage public concerns about nuclear
  safety.
• Only 6 NPPs operating in Japan at the end of
  2011.
• July 2011 Japanese Prime Minister states the
  country must eliminate dependence on nuclear
  power.

77
Japan

• Tepco proposed to install a system of tide
  barriers with watertight doors at Kashiwazaki
  Kariwa units 1 to 4.
• In addition, TEPCO has installed facilities on
  the upland part of the site to provide backup
  power and water injection to the reactors and
  spent fuel pools, and taken measures to ensure
  cooling functions in the event of tsunamis
  flooding the reactor buildings

78
Japan

• Oct 2011
• Nuclear Safety Commission will mandate that
  Japans utilities install reinforced sources of
  electric power at all NPPs
• Kansai Electric submit the results of the stress
  test for Ohi Unit 3 to the Nuclear and
  Industrial Safety Agency (NISA).
• First stress test to be reported to NISA for
  consideration on restarting a shutdown reactor.
• Dec 2011
• New nuclear safety agency is being formed under
  the Environment Ministry from the merger of the
  Nuclear and Industrial Safety Agency of the
  Ministry of Economy Trade and Industry and the
  Nuclear Safety Commission of Japan
• Parliament appoints an independent panel formed
  to investigate the Fukushima Daiichi incident
• Jan 2012
• Japanese Prime vowed to revive the region
  surrounding the Fukushima Daiichi nuclear plant
• Amendment proposed to Japans Nuclear Plant
  Operations Law to limit NPP operating life to 40
  years

79
China

• Japan's Fukushima nuclear disaster in March led
  China to delay all nuclear project approvals.
• Dec 2011 China has approved a five-year nuclear
  safety plan, which is a prelude to their nuclear
  development plan that is expected to reduce the
  2020 nuclear capacity target by about 10.

80
Northern VA earthquakemagnitude 5.823 August
2011
81
U.S seismic design basis

• Licensing bases for existing NPPs considers
  historical data at each site.
• Data are used to determine design basis loads
  from the areas maximum credible earthquake, with
  an additional margin included.
• In Generic Letter 88-20, the NRC required
  existing NPPs to assess their potential
  vulnerability to earthquake events, including
  those that might exceed the design basis.
• Following the events of September 11, 2001, NRC
  required all nuclear plant licensees to take
  additional steps to protect public health and
  safety in the event of a large fire or explosion.
  If needed, these additional steps could also be
  used to mitigate severe natural phenomena.
• The NRC examined new Central Eastern US (CEUS)
  earthquake hazard information under Generic
  Issues GI-199 and completed a limited scope
  screening analysis for the seismic issue in
  December 2007.
• New CEUS seismic data were compared with earlier
  seismic evaluations.
• This analysis confirmed that operating nuclear
  power plants remain safe with no need for
  immediate action.

82
Northern VA earthquakemagnitude 5.8, 23 August
2011

• Very short duration peak acceleration (1 3
  sec).
• No fault associated with the earthquake
• epicenter and aftershocks.
• No surface ruptures during the earthquake.
• NRC classifies as blind reverse fault.

83
Northern VA earthquakemagnitude 5.8, 23 August
2011

• Although the U.S. east of the Rockies has fewer
  and generally smaller earthquakes than the West,
  due to geologic differences, eastern earthquakes
  affect areas 10 time than western ones of the
  same magnitude. (ref NJ Geologic Survey)
• Hard ground and fewer faults
• Effective in conducting seismic waves over long
  distances.
• USGS estimated the earthquake produced a peak
  ground acceleration of 0.26g at the North Anna
  NPP
• First time that an earthquake has exceeded the
  design basis for a U.S. NPP.

84
North Anna NPP

• 2 unit Westinghouse PWRs
• Net 1,806 MWe
• Both operating at 100 power when earthquake
  occurred
• Site includes an independent spent fuel storage
  installation
• 11 miles from epicenter

• Seismic design basis
• DBE, structures on rock 0.12g horiz, 0.08 g
  vert
• DBE, structures on soil 0.18g horiz, 0.12g
  vert
• OBE ½ DBE

85
Plant response to the earthquake

• Reactor tripped automatically
• Reactor trip system does not include an automatic
  seismic scram.
• Direct cause for both Units 1 2 reactor trip
  was detection of high rate of change of neutron
  flux (decreasing) in the power range nuclear
  instruments (gt5 change in 2.5 seconds).
• Root cause is believed to be a synergistic
  combination of seismically-induced conditions
• Core barrel, core detector movement.
• Momentary change in thermal boundary layer
  conditions along the fuel rods.
• Momentarily under-moderated core with oscillatory
  but overall decreasing flux.
• Turbine tripped automatically and offsite power
  lost
• Main turbines tripped because of main transformer
  lockout, which interrupted the connection to
  the off-site grid.
• The earthquake caused multiple transformers to
  lockout due to activation of sudden pressure
  relays, which operated as designed due to
  earthquake-induced pressure pulses within the
  transformer, not due to an electrical fault.
• NPP connection to offsite power restored about 7
  hours later.
• Mitigating systems started automatically

86
Reactor power during earthquake, before scram
Scram ?
87
North Anna earthquake timeline
88
U.S. restart requirements and guidance

• Appendix A to 10CFR100Paragraph V(a)(2)
• If vibratory ground motion exceeding that of the
  Operating Basis Earthquake occurs, shutdown of
  the nuclear power plant will be required.
• Prior to resuming operations, the licensee will
  be required to demonstrate to the Commission that
  no functional damage occurred to those features
  necessary for continued operation without undue
  risk to the health and safety of the public.
• Regulatory Guide 1.166, Pre-earthquake planning
  and immediate NPP Operator Post-earthquake
  Actions (1997)
• Cumulative Absolute Velocity (CAV) is a measure
  of the damage potential of earthquake ground
  motion
• NRC, EPRI and industry agree on a CAV threshold
• If CAV calculation gt 0.16 g-sec, then OBE
  exceeded
• Regulatory Guide 1.167, Restart of Nuclear Power
  Plant Shut Down by a Seismic Event (1997)
• EPRI NP-6695, Guidelines for Nuclear Power Plant
  Response to an Earthquake (1990)

89
Dominion report of readiness to re-start

• Acceleration criteria were briefly exceeded in
  certain directions and frequencies by a strong,
  but very short duration earthquake
• Previous IPEEE evaluations establish that safe
  shutdown systems, structures and components can
  handle peak accelerations above design basis
• No safety-related systems, structures or
  components required repair due to the earthquake
• No significant damage was found or should have
  been expected and results of expanded tests and
  inspections have confirmed expectations
• Commitments
• By February 2012 With Westinghouse, develop a
  plan for additional evaluations or inspections to
  assure long-term reliability of reactor
  internals.
• By December 2012 Improve seismic monitoring
  equipment.
• By March 2013 Reevaluate equipment identified
  in the Individual Plant Evaluation of External
  Events (IPEEE) with a high-confidence-of-low-proba
  bility-of-failure (HCLPF) capacity of lt0.3g and
  recommend potential improvements

Source Dominion 31 Oct 2011 letter to NRC and 1
Nov 11 presentation
90
Basis for post-earthquake integrity of North Anna
structures, systems components
0.16 g-sec -------
Source Dominion 1 Nov 11 presentation to NRC
91
Missouri River FloodingFort Calhoun NPPJune
August 2011
92
U.S. design basis flood and flood protection

• A design-basis flood is a flood caused by one or
  an appropriate combination of several
  hydrometeorological, geoseimic, or
  structural-failure phenomena, which results in
  the most severe hazards to structures, systems,
  and components (SSCs) important to the safety of
  a nuclear power plant (NUREG/CR-7046).
• Sources of requirements guidance
• USNRC Regulatory Guide 1.59, Design Basis Floods
  for NPPs (1977)
• USNRC Regulatory Guide 1.102 (R1), Flood
  Protection for NPPs (1976)
• Standard Review Plan 3.4.1, R2, Flood
  Protection (1981)
• NUREG/CR-7046, Design-Basis Flood Estimation for
  Site Characterization at Nuclear Power Plants in
  the United States of America (Nov 2011)
• Temporary flood barriers, such as sandbags,
  plastic sheeting, portable panels, etc., which
  must be installed prior to the advent of the
  DBFL, are not acceptable for issuance of a
  construction permit.
• However, unusual circumstances could arise after
  construction that would warrant consideration of
  such barriers.
• One example of unusual circumstances that might
  justify use of temporary barriers is a
  post-construction change in the flood-producing
  characteristics of the drainage area.. In such
  circumstances, and with strong justification, the
  staff may accept temporary barriers (RG 1.102)

93
Fort Calhoun NPP site
Source ORNL-NSIC-55, V1
94
Missouri River floods Fort Calhoun NPP site

• Site grade elevation 1004 MSL, includes an
  independent spent fuel storage
• installation
• Alert level 1006 MSL
• Auxiliary building ground floor level 1007 MSL
• Tech Spec reactor shutdown level1009 MSL
• Current design basis flood level 1014 MSL with
  NPP main buildings
• switchyard protected by temporary barrier
  (AquaDam)

95
Missouri River floods Fort Calhoun NPP site
96
AquaDam temporary barrier
OPPD refers to the water-filled AquaDam as a
supplemental flood protection measure that
provides protection up to 1014 MSL.
97
Equipment at or below grade in the auxiliary
building that must be protected from flooding

• 1007 level
• Both divisions of AC and DC power
• Diesel generators
• Batteries
• 4160 VAC, 480 VAC and 125 VDC electric panels
• Alternate shutdown panel
• New fuel storage
• 989 level
• Emergency feedwater pumps
• 480 v Class 1E panels
• 971 level
• High pressure safety injection (ECCS) pumps
• Low pressure safety injection / shutdown cooling
  pumps

98
Fort Calhoun flood timeline
99
Hurricanes
100
Hurricane Andrew - 1992

• Category 4 Hurricane Andrew 1993
• First time a hurricane significantly affected a
  U.S. NPP
• Hurricane passed over 2-unit Turkey Point NPP,
  which was shut down 4 hours prior to the onset of
  hurricane strength winds
• 145 mph winds, gusts to 175 mph
• The onsite damage included loss of all offsite
  power for more than 5 days, complete loss of
  communication systems, closing of the access
  road, and damage to the fire protection and
  security systems and warehouse facilities.
• No damage to the safety-related systems except
  for minor water intrusion.
• There was no radioactive release to the
  environment.

101
Hurricane Andrew - 1992
102
Hurricane Irene - 2011

• Category 3 Hurricane Irene 2011
• Only two NPPs in the hurricanes track were shut
  down
• In Maryland, one reactor at the Calvert Cliffs
  plant automatically went off-line when wind blew
  a piece of aluminum siding into the units main
  transformer in the switchyard. The second unit
  remained online
• In New Jersey, the Oyster Creek NPP was taken
  offline as a precaution ahead of expected high
  winds and storm surge.
• All others remained on-line throughout the storm.

103
Hurricane Irene - 2011
104
Conclusions

• NPPs have demonstrated their robustness and
  ability to withstand some beyond design basis
  severe natural events and then be able to return
  to operation.
• The magnitude of some beyond design basis severe
  natural events were much greater than expected
  based on pre-event knowledge of historical events
  and site characteristics.
• The common cause failure potential for some
  beyond design basis severe natural events has
  been grossly underestimated.
• It is time to redefine the nuclear regulatory
  process and develop a more effective approach for
  assuring that nuclear safety functions can be
  accomplished when required so nuclear power
  plants can cope with events and combinations of
  events that exceed the traditional design basis.