Practical examples of RIDM application in the regulatory activity

Workshop on
Risk informed decision making on nuclear power plant safety
27 - 28 January 2011
SNRC, Kyiv, Ukraine
Practical examples of RIDM application in
the regulatory activity
by
Géza Macsuga
Nuclear Safety Directorate
Hungarian Atomic Energy Authority
Outline
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A good list of IRIDM applications for regulatory use
IRIDM application examples
– Hungary
– others
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Summary
Practical examples of RIDM application in the regulatory activity
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A good list of IRIDM applications
for regulatory use (by VVER Forum PSA WG)
Scope of existing PSA
models
Level 1, full power
Level 1, shutdown and low power
Level 2, full power
Level 2, shutdown and low power
PSA review
Independent internal review of existing models and tools by the
licensee
International review of existing models and tools
Independent regulatory review of existing models and tools
Regulatory use of PSA
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Tech Specs exemptions
PSA based event analysis
Risk monitor
Licensing of plant modifications
Risk informed regulatory inspection activities
Emergency preparedness planning and emergency response
Training of RB staff, etc.
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Use of PSA by the HAEA (1)
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Development of models and tools
Application of tools
Operational cases
Preparation of special studies
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Use of PSA by the HAEA (2)
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Available PSA environment
– Risk Spectrum framework software
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PSA 2.10
– 3 users
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Risk Watcher 1.20
– 2 users
– the same what the Paks NPP uses
– for the legal use of PSA models and tools
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No PSA development activities at the HAEA
– only use and follow up
Practical examples of RIDM application in the regulatory activity
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Use of PSA by the HAEA (3)
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Available models at the RB
– FPSA-1
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full-power operation mode
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unit specific models
– for all 4 units
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including internal fire and flood hazards
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concept of living PSA
– updated every year after refuelling outage
Unit-1 FPSA internal IEs
Practical examples of RIDM application in the regulatory activity
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Use of PSA by the HAEA (4)
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Available models at the RB
– SPSA-1 for internal initiators  comprehensive update in 2010
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the unit-2 model is representative for all units
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including internal fire and flood hazards
Year
1997
1999
2002
2010
CDP
1,4·10-4 1/y
3,5·10-5 1/y
2,8·10-5 1/y
5,1·10-6 1/y
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Use of PSA by the HAEA (5)
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Available models at the RB
Level 1 PSA models
for Paks NPP
internal initiating events
operational IEs
flood
external initiating events
fire
seismic
others
nominal power
units 1 – 4
unit 3
X
low power & shut down states
units 1 – 4
unit 3
X
Flood at nominal power
25 %
Shut down, internal IEs
27 %
Fire at nominal power
22 %
Internal IEs at nominal power
26 %
CDPT for Unit-1
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Use of PSA by the HAEA (6)
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Available models at the RB
– PSA-2
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by the end 2003
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unit 1
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covers SPSA-1 for internal initiators
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no internal fire and flood hazards
– revision was started in 2010 in connection with the lifetime extension
Level 2 PSA model for
Paks NPP
nominal power
internal initiating events
external initiating events
operational events flooding fire
seismic
others
unit 1, includes sources others then reactor core
X
X
X
low power & shut down states
Practical examples of RIDM application in the regulatory activity
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27-28 January 2011
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Use of PSA by the HAEA (7)
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Available PSA tools
– Risk Supervisor
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a kind of risk monitor for evaluation of safety performance by the RB
– Precursor Analyser
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for evaluation of risk significance of operational events
– Core Damage Prediction System
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for quick estimation of potential consequences in emergency
Application of tools
– since 1999 all reported events are analysed systematically by the TSO for the RB
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Risk Supervisor
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Precursor Event Analyser
– results used during the comprehensive evaluation of the Paks NPP safety
performance
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Risk superviser
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A simplified Risk monitor
– for the nominal power
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failures
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repairs/maintenance
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changes in configuration
– manual input of changes
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off-line mode
Objective
– present the actual value of CDF
– follow up of risk profile
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Risk Supervisor results for 2002
Annual outage:
15 Mar – 29 Apr 2002
Annual outage:
29 June - 3 Aug 2002
Annual outage:
27 Apr - 23 June 2002
Annual outage:
18 Aug - 20 Sep 2002
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27-28 January 2011
Practical examples of RIDM application in the regulatory activity
Precursor Event Analyser
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Determination of safety significance of operational events
– extending for shut down states
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Initiating event type events
– safety system actuation
– conditional core damage probability  CCDP
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failure type events
– affecting safety system operations
– increment of core damage probability  ΔCDP
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US NRC  Precursor Event Assessment Program
– CCDP
– ΔCDP
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direct regulatory attention  type of event investigation (A, B, C)
Practical examples of RIDM application in the regulatory activity
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The Core Damage Index for Paks NPP
2001-2009
Practical examples of RIDM application in the regulatory activity
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Precursor results for 2002
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Use of PSA by the HAEA (8)
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Safety comparison of different POSs of Unit 2 Paks NPP
– objective: to select the POS with less risk
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F  cold shut down, but closed reactor
– T < 70 °C; atmospheric < p < 20 bar; hermetic zone is open; forced cooling
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G  cold shut down, but open reactor
– T < 70 °C; p = atmospheric; hermetic zone is open; natural cooling
– POSs in TechSpecs  A, B, C, D, E, F and G (M and K POSs)
– SPSA  1 ÷ 24 POSs
– results
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F
CDF = 1,39·10-6 y-1 and
PCBF = 9,67·10-7 y-1
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G
CDF = 9,67·10-7 y-1 and
PCBF = 5,64·10-6 y-1
– decision
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POS F + actions to reduce risk of cold overpressure
Practical examples of RIDM application in the regulatory activity
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Use of PSA by the HAEA (9)
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Flexibility in timing of test cycles
– Paks NPP TechSpecs
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 every 6 weeks
operating manual 6 weeks ±10 days for implementation
– Paks NPP model FPSA-1
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generic PSA model
 static
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ideal: Risk Monitor
 for handling of time dependences
– results
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the average annual CDF may increase even by 9 %
– decision
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more proper regulation of test intervals
– fixing the centre time of test
– reducing the duration of time for implementing tests
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The test cycles
refuelling
T0
test cycle 6 week
start of operational
cycle
T0
test cycle 6 week
Tt1
Tt2
test cycle 6 week
Tt1±10 d
T’t1
Tt1±10 d
test cycle 6 week
Tt2±10 d
test cycle 6 week
Tt3
Tt3±10 d
T’t2
Tt2+10 d ±10 d
test cycle 6 week
T’t3
Tt3+20 d ±10 d
Use of PSA by the HAEA (9)
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Preparation of special studies
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Reliability study for specific functions of CERTA (1998)
Risk-informed classification of NPP SSCs (1999, 2003, 2009)
Risk aspects for evaluation of in-service and outage maintenance (1999, 2001)
Regulatory criteria for severe accidents (2000)
Probabilistic safety goals (2000)
Potential areas of PSA applications during the regulatory activities (2000, 2007)
Role of PSA in lifetime extension (2006)
Role of PSA in licensing of new units (2010)
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The role of TSO
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NUBIKI  the former VEIKI Electric Power Research Institute
– special role  serves for both the utility and RB
Regulatory Body
Practical examples of RIDM application in the regulatory activity
Paks NPP
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Database of risk informed decisions (1)
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The international COOPRA initiatives (2001-2006)
– WG on RIDM with several tasks
– one of the tasks was to establish a database for risk informed decisions of MSs
1. French data base
1.1Total loss of redundant system
1.2Loss of residual heat removal system at mid-loop operation
1.3Heterogeneous boron dilution
1.4Periodic safety review of 900 MWe series
2. Hungarian database
2.1Safety comparison of different plant operation states for Paks NPP Unit 2
2.2Deviation from the surveillance test schedule
3. Japanese database
3.1Accident management
Practical examples of RIDM application in the regulatory activity
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Database of risk informed decisions (2)
4. Korean data base
4.1Primary depressurization capability
4.2Aggressive cool down
4.3Reinforcement of building structure
5. US data base
5.1Indian Point 2 steam generator tube rupture
5.2Grand Gulf Unit 1 – issuance of TS amendment to permit extension of allowed outage time
for DGs
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Summary
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Extensive PSA modelling program
Living PSA program
Use of PSA
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defining plant vulnerabilities
general design safety evaluation
extensive R&D support
systematic efforts to risk-inform RB activities
no systematic consideration in decision making (yet!)
Generation of domestic and international experiences
Practical examples of RIDM application in the regulatory activity
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Questions
Thank you for your
attention!
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