Workshop on Risk informed decision making on nuclear power plant safety January 2011 SNRC, Kyiv, Ukraine Benefits and limitations of RIDM by Géza Macsuga Nuclear Safety Directorate Hungarian Atomic Energy Authority

Outline The complex character of PSA What do we need PSA for…? Role of PSA Whom? What benefits derive from IRIDM? January 2011Benefits and limitations of RIDM

The complex character of PSA (1) Plant operational states  POS –nominal power –low power and shut down states reduced power, reactor shut down cool down states refuelling  fuels in the Spent Fuel Storage heat up states reactor start up, power increase All postulated initiating events –operational  pipe line breaks, transients, feed-water loss –internal hazard  fire and flood –external hazard  earthquake, meteorology, external grid, fire, flood etc. –human induced  sabotage (internal), terror (external) January 2011Benefits and limitations of RIDM maintenance and tests

The complex character of PSA (2) All structures, systems and components –passive elements pipelines, vessels –active elements mechanical and I&C components Human failures –pre-accident (maintenance, test)  hidden failure –leading to initiating events  requiring safety system actuation –post-accident  during accident management Technical Specifications, operational manuals, procedures –indirectly in event trees, fault trees, common cause and human reliability models January 2011Benefits and limitations of RIDM

The complex character of PSA (3) Deterministic Safety Analyses on –accident sequences coolant boiling fuel cladding failure core damage RPV failure containment processes –success criteria January 2011Benefits and limitations of RIDM medium LOCA RP-1 early HP ECCS closure of damaged loop HP ECCS LP ECCS secondary heat sink primary B&F end state event identifier no ECCS heat-exchanger tube rapture

The complex character of PSA (4) Levels of PSA –level 1 with consideration of all possible factors the core damage risk is characterised with one number –Core Damage Probability – CDP –Core Damage Frequency – CDF 6 typical CDF values NPP of 2 nd generation: CDF ~ ÷ y -1 NPP of 3 rd generation : CDF ~ ÷ y January 2011Benefits and limitations of RIDM

The complex character of PSA (5) Levels of PSA –level 2 the entire process of fuel damage –in- and ex-vessel phenomena –containment phenomena and modelling of building failures risk of radioactive discharges is characterised with one (or several) number(s) –Large Early Release Probability – LERP –Large Early Release Frequency – LERF 7 Typical LERF values NPP of 2 nd generation: LERF ~ 10-6 ÷ 10-5 y -1 NPP of 3 rd generation : LERF ~ 10-7 ÷ 10-6 y January 2011Benefits and limitations of RIDM

The complex character of PSA (6) Uncertainties –data plant specific, plant type specific, generic –models (common cause, human failure) –calculation-algorithm Sensitivity –specific components –group of components, e.g. component type like human failure –systems January 2011Benefits and limitations of RIDM

What do we need PSA for…? Understanding changes in hardware  processes  modifications  failures, hazards  component ageing  maintenance operation  organisation  individuals  regulation  staff ageing  safety culture surroundings  hazards  environment  population hardware of installation operation of installation surrounding environment January 20119Benefits and limitations of RIDM

Role of PSA methodology and tool January 2011Benefits and limitations of RIDM hardware  processes  modifications  failures, hazards  component ageing ?  maintenance operation  organisation ?  individuals ?  regulation ?  staff ageing ?  safety culture ? surroundings  hazards  environment ?  population ? in evaluation of safety significance

Whom…? Regulatory body –Risk-informed Regulation  if in all areas of activities IRIDM is applied licensing, inspection, evaluation, enforcement, etc. Operator –Risk-informed Performance Management  if in all areas of activities IRIDM is applied operation, maintenance, engineering, etc.

What benefits derive from IRIDM? Strengthens safety through extending understanding of processes and better focus of resources Provides that decisions and underlying activities are more consistent and better targeted Increases public confidence through extending transparency of decisions Reduces undue burden allowing flexibility and enforcing ownership by the performance based regulatory approach

Summary Complexity of PSA is a unique character It helps to understand/consider safety related aspects Applicable for both –utility –RB Benefits of IRIDM January 2011Benefits and limitations of RIDM

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