Workshop on Risk informed decision making on nuclear power plant safety 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 A good list of IRIDM applications for regulatory use IRIDM application examples –Hungary –others Summary January 2011Practical examples of RIDM application in the regulatory activity

A good list of IRIDM applications for regulatory use (by VVER Forum PSA WG) January 20113Practical examples of RIDM application in the regulatory activity 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 reviewIndependent 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 PSATech 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.

Use of PSA by the HAEA (1) Development of models and tools Application of tools Operational cases Preparation of special studies January 20114Practical examples of RIDM application in the regulatory activity

Use of PSA by the HAEA (2) Available PSA environment –Risk Spectrum framework software PSA 2.10 –3 users Risk Watcher 1.20 –2 users –the same what the Paks NPP uses –for the legal use of PSA models and tools No PSA development activities at the HAEA –only use and follow up January 20115Practical examples of RIDM application in the regulatory activity

Use of PSA by the HAEA (3) Available models at the RB –FPSA-1 full-power operation mode unit specific models –for all 4 units including internal fire and flood hazards concept of living PSA –updated every year after refuelling outage January 20116Practical examples of RIDM application in the regulatory activity Unit-1 FPSA internal IEs

Use of PSA by the HAEA (4) Available models at the RB –SPSA-1 for internal initiators  comprehensive update in 2010 the unit-2 model is representative for all units including internal fire and flood hazards January 20117Practical examples of RIDM application in the regulatory activity Year CDP 19971,4· /y 19993,5· /y 20022,8· /y 20105,1· /y

Use of PSA by the HAEA (5) Available models at the RB January 20118Practical examples of RIDM application in the regulatory activity Level 1 PSA models for Paks NPP internal initiating eventsexternal initiating events operational IEsfloodfireseismicothers nominal powerunits 1 – 4unit 3X low power & shut down statesunits 1 – 4unit 3X CDP T for Unit-1 Fire at nominal power 22 % Flood at nominal power 25 % Shut down, internal IEs 27 % Internal IEs at nominal power 26 %

Use of PSA by the HAEA (6) Available models at the RB –PSA-2 by the end 2003 unit 1 covers SPSA-1 for internal initiators no internal fire and flood hazards –revision was started in 2010 in connection with the lifetime extension January 20119Practical examples of RIDM application in the regulatory activity Level 2 PSA model for Paks NPP internal initiating eventsexternal initiating events operational eventsfloodingfireseismicothers nominal powerunit 1, includes sources others then reactor coreX low power & shut down statesXXXX

Use of PSA by the HAEA (7) Available PSA tools –Risk Supervisor a kind of risk monitor for evaluation of safety performance by the RB –Precursor Analyser for evaluation of risk significance of operational events –Core Damage Prediction System 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 Risk Supervisor Precursor Event Analyser –results used during the comprehensive evaluation of the Paks NPP safety performance January Practical examples of RIDM application in the regulatory activity

Risk superviser A simplified Risk monitor –for the nominal power failures repairs/maintenance changes in configuration –manual input of changes off-line mode Objective –present the actual value of CDF –follow up of risk profile January 2011Practical examples of RIDM application in the regulatory activity

Risk Supervisor results for 2002 Annual outage: 29 June - 3 Aug 2002 Annual outage: 18 Aug - 20 Sep 2002 Annual outage: 15 Mar – 29 Apr 2002 Annual outage: 27 Apr - 23 June January Practical examples of RIDM application in the regulatory activity

Precursor Event Analyser Determination of safety significance of operational events –extending for shut down states Initiating event type events –safety system actuation –conditional core damage probability  CCDP failure type events –affecting safety system operations –increment of core damage probability  ΔCDP US NRC  Precursor Event Assessment Program –CCDP –ΔCDP direct regulatory attention  type of event investigation (A, B, C) January 2011Practical examples of RIDM application in the regulatory activity

The Core Damage Index for Paks NPP January 2011Practical examples of RIDM application in the regulatory activity

Precursor results for January Practical examples of RIDM application in the regulatory activity

Use of PSA by the HAEA (8) Safety comparison of different POSs of Unit 2 Paks NPP –objective: to select the POS with less risk F  cold shut down, but closed reactor –T < 70 °C; atmospheric < p < 20 bar; hermetic zone is open; forced cooling 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 F  CDF = 1,39·10-6 y -1 andPCBF = 9,67·10-7 y -1 G  CDF = 9,67·10-7 y -1 andPCBF = 5,64·10-6 y -1 –decision POS F + actions to reduce risk of cold overpressure January 2011Practical examples of RIDM application in the regulatory activity

Use of PSA by the HAEA (9) Flexibility in timing of test cycles –Paks NPP TechSpecs  every 6 weeks operating manual  6 weeks ±10 days for implementation –Paks NPP model FPSA-1 generic PSA model  static ideal: Risk Monitor  for handling of time dependences –results the average annual CDF may increase even by 9 % –decision more proper regulation of test intervals –fixing the centre time of test –reducing the duration of time for implementing tests 17

The test cycles test cycle 6 week T ’ t1 T ’ t2 T ’ t3 T0T0 T t1 ±10 dT t2 +10 d ±10 dT t3 +20 d ±10 d refuellingtest cycle 6 week start of operational cycle T t1 T t2 T t3 T0T0 T t1 ±10 dT t2 ±10 dT t3 ±10 d

Use of PSA by the HAEA (9) Preparation of special studies –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) January Practical examples of RIDM application in the regulatory activity

The role of TSO NUBIKI  the former VEIKI Electric Power Research Institute –special role  serves for both the utility and RB January Practical examples of RIDM application in the regulatory activity Regulatory Body Paks NPP

Database of risk informed decisions (1) The international COOPRA initiatives ( ) –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 MW e 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 January 2011Practical examples of RIDM application in the regulatory activity

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 January 2011Practical examples of RIDM application in the regulatory activity

Summary Extensive PSA modelling program Living PSA program Use of PSA –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 January Practical examples of RIDM application in the regulatory activity

Questions Thank you for your attention! January Practical examples of RIDM application in the regulatory activity