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

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
  • Definition of design basis
  • BWR mitigating systems and system dependencies
  • Earthquake
  • Niigata Chuetsu-oki, Japan, magnitude 6.8,16 July
  • 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
  • Recent external event challenges to U.S. NPPs
  • Missouri River flooding, July August 2011
  • Northern VA earthquake, magnitude 5.8, 23 August
  • Hurricanes
  • Conclusions

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
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
  • Accomplish reactor shutdown (GDC 20, 29)
  • Maintain primary system integrity (GDC 14, 15,
  • 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)

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
  • 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
    (HCLPF) level.

Source 10CFR50 Appendix A, General Design
Criterion 2
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
  • 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,
  • Utilities may choose to improve NPP operating
  • Longer operating cycles between refueling
  • Power increase

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
  • 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
  • Coping duration 4 16 hours
  • Non-electric driven pumps (steam, diesel) provide
    important capabilities for operating cooling and
    makeup systems during SBO.

BWR mitigating systems and system dependencies
Key mitigating systems available at the
Fukushima Daiichi units
BWR Mark-I containment steel shell
BWR Mark-I containment arrangement within the
reactor building
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

BWR Mark-I containment refueling floor arrangement
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
  • 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
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
  • Automatic pump suction realignment on CST low
  • Pump room cooling by service water
  • No cooling for the pump itself.

Source NRC BWR Concepts Manual
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
  • Automatic pump suction realignment on CST low
  • Pump room cooling by service water
  • No cooling for the pump itself.

Source NRC BWR Concepts Manual
Low-Pressure ECCS and Residual Heat Removal (RHR)
  • System Dependencies
  • Automatic pump actuation on reactor vessel low
    water level or drywell high pressure, or
  • 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
Niigata Chuetsu-Oki Earthquake (NCOE), Japan,
magnitude 6.8, 16 July 2007
Niigata Chuetsu-Oki Earthquake (NCOE), Japan,
magnitude 6.8, 16 July 2007
Source TEPCO
Source EQECAT Inc
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.

Kashiwazaki-Kariwa NPP
Source TEPCO
NCOE observed seismic data
  • The observed seismic accelerations largely
    exceeded the design basis values.

Source TEPCO
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
  • Reactor cooldown and depressurization
  • Reactor coolant at all units cooled to below
  • Reactor pressure in each unit reduced to
    atmospheric pressure
  • Stable cold shutdown condition achieved by 17
  • 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.

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
  • Many containers of LLW overturned, some lids came
  • 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

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
  • Differences between the Unit 1-4 and Unit 5-7
    sites, which are 1 km apart.

Source TEPCO
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
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.

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

Great East Japan Earthquake, magnitude 9.0, 11
March 2011
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

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)

FukushimaDaiichi SiteArrangement
Source INPO
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.

Tsunami following theGreat East Japan
Earthquake, 11 March 2011
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
  • 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.

Tsunami wave arrives at Fukushima Daiichi
Tsunami wave arrives at Fukushima Daiichi
Site inundation
Site inundation
Site inundation
Tsunami effects on storage tank
Fukushima Daiichi site inundation
Source IAEA
Fukushima Daiichi Units 1 4 inundation
Source INPO
  • Flooding resulted in common cause failure and
    loss of the ability to perform key safety
  • 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.

Fukushima Daiichi plant responses to the 11
March 2011 earthquake tsunami
Decay heat reactor units 1, 2, 3
Source MIT
Decay heat spent fuel pools
Fuel response to severe accident progression
Unit 1 sequence of events
Adapted from INPO
Unit 1 sequence of events (continued)
Adapted from INPO
Unit 1 Hydrogen Explosion, 12 March 2011
Loss if lighting in the control room
Source TEPCO
Unit 2 sequence of events
Adapted from INPO
Unit 2 sequence of events (continued)
Adapted from INPO
Unit 3 sequence of events
Adapted from INPO
Unit 3 sequence of events (continued)
Adapted from INPO
Unit 3 Hydrogen Explosion, 14 March 2011
Unit 4 sequence of events
Adapted from INPO
Unit 4 after hydrogen explosion
Possible hydrogen leak path to Unit 4
Source INPO
Units 1-4 before the tsunami explosion
Units 1-4 after the explosion
Unit 5 6 sequence of events
Source SECY-11-0093
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
  • 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,
  • Ground-level radiation releases

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

Protective actions
Source SECY-11-0093
Cleanup and Decommissioning Plan
  • December 2011 TEPCO released its 40-year plan
    to decommission the plan
  • Phase 1 Post cold shutdown stabilization and
  • 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
  • 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)

International Response to theFukushima Daiichi
  • 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,
  • Ability to monitor the condition of spent fuel
  • Sep 2011 NRC issues, Recommendations for
    Enhancing Reactor Safety in the 21st Century,
    with 12 recommendations, including
  • Balance defense in depth and risk
  • As needed, upgrade design basis seismic and flood
  • Strengthen prolonged station blackout mitigation
  • Study adequacy of hydrogen control
  • Enhance spent fuel makeup capability and
  • Strengthen on-site emergency response accident

  • 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.

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
  • 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
  • These reports are publically available on the
    ENSREG web site
  • http//

  • 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
  • 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.

  • 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

  • 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
  • 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.

  • 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
  • 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.

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
  • Finland
  • October 2011 First in Europe to approve a new
    green-field NPP site since the Fukushima Daiichi
  • Poland
  • Still moving ahead to select NPP supplier in
    2013, with initial operation of Polands first
    NPP in 2020.

  • 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
  • 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
  • Only 6 NPPs operating in Japan at the end of
  • July 2011 Japanese Prime Minister states the
    country must eliminate dependence on nuclear

  • 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

  • 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

  • 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.

Northern VA earthquakemagnitude 5.823 August
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.

Northern VA earthquakemagnitude 5.8, 23 August
  • Very short duration peak acceleration (1 3
  • No fault associated with the earthquake
  • epicenter and aftershocks.
  • No surface ruptures during the earthquake.
  • NRC classifies as blind reverse fault.

Northern VA earthquakemagnitude 5.8, 23 August
  • 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
  • USGS estimated the earthquake produced a peak
    ground acceleration of 0.26g at the North Anna
  • First time that an earthquake has exceeded the
    design basis for a U.S. NPP.

North Anna NPP
  • 2 unit Westinghouse PWRs
  • Net 1,806 MWe
  • Both operating at 100 power when earthquake
  • Site includes an independent spent fuel storage
  • 11 miles from epicenter
  • Seismic design basis
  • DBE, structures on rock 0.12g horiz, 0.08 g
  • DBE, structures on soil 0.18g horiz, 0.12g
  • OBE ½ DBE

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
  • 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

Reactor power during earthquake, before scram
Scram ?
North Anna earthquake timeline
Date Time Events at North Anna NPP
23 Aug 2011 1351 5.8 magnituide earthquake
23 Aug 2011 1351 Automatic reactor trip
23 Aug 2011 1351 Loss of offsite power and automatic main turbine trip
23 Aug 2011 1351 Automatic actuation of auxiliary feedwater system, charging system, emergency diesel generators, and service water system
23 Aug 2011 1403 Alert declared. Operators focus on stabilizing each unit and restoring offsite power.
23 Aug 2011 2055 NPP connection to offsite power restored
24 Aug   Unit 1 cooldown to cold shutdown started. Unit 2 cooldown started after Unit 1 cooldown completed
26 Aug   Review of seismic data determined that seismic acceleration potentially exceeded the Design Basis Earthquake at frequencies above 5 Hz.
Aug - Oct   Plant walkdowns, inspections, tests and analysis do not reveal any significant physical or functional damage to safety-related structures, systems or components, and only limited damage to non-safety, non-seismic SSC.
1 Nov   Public meeting with NRC to address readiness to re-start
11 Nov   NRC approves re-start
18 Nov   Unit 1 back at 100 power
21 Nov   Unit 2 back at 100 power
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
  • NRC, EPRI and industry agree on a CAV threshold
  • If CAV calculation gt 0.16 g-sec, then OBE
  • 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)

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
  • By December 2012 Improve seismic monitoring
  • 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
Basis for post-earthquake integrity of North Anna
structures, systems components
0.16 g-sec -------
Source Dominion 1 Nov 11 presentation to NRC
Missouri River FloodingFort Calhoun NPPJune
August 2011
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)

Fort Calhoun NPP site
Source ORNL-NSIC-55, V1
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

Missouri River floods Fort Calhoun NPP site
AquaDam temporary barrier
OPPD refers to the water-filled AquaDam as a
supplemental flood protection measure that
provides protection up to 1014 MSL.
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

Fort Calhoun flood timeline
Date Events at Fort Calhoun NPP
9 Apr 2011 NPP in cold shutdown for routing refueling
6 Jun Notice of Unusual Event (NOUE) due to high river level
8 Jun Fire in switchgear temporarily disables spent fuel pool cooling
17 Jun NRC implements 24 hr/day augmented coverage
26 Jun Worker punctures AquaDam with bobcat. Plant temporarily disconnected from offsite power to protect switchyard equipment that might become flooded. NPP loads supplied from the diesel generators.
29 Jun Missouri river crests at Blair
11 Jul Re-installation of AquaDam complete, water within the confines of the dam perimeter removed.
23 Jul Second Missouri river crest at Blair
29-30 Jul NOUE rescinded, NRC suspends 24 hr/day augmented coverage.
10 Aug OPPD issues post-flood recovery plan. Updated 30 Aug.
6 Oct NRC issues finding of inadequate flood protection strategies.
14 Dec NRC delays plans to restart Fort Calhoun at least to 2012 Q2.
17 Dec OPPD issues LER for inadequate flood protection for intake structure and auxiliary building due to unsealed wall and ceiling/floor penetrations and other reasons.
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

Hurricane Andrew - 1992
Hurricane Irene - 2011
  • Category 3 Hurricane Irene 2011
  • Only two NPPs in the hurricanes track were shut
  • 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.

Hurricane Irene - 2011
  • 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.
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