PRAMEA Probabilistic risk assessment method development and - PowerPoint PPT Presentation

PRAMEA – Probabilistic risk assessment method development and applications Presentation at the SAFIR2018 research programme final seminar, Hanasaari 21.3.2019 1 25.3.2019 VTT – beyond the obvious

HRA and advanced control rooms § Accepted review manuscript about the effect of digitalization of NPP control rooms, in RESS (Reliability Engineering and System Safety) • Digital systems provide operator with more information but also with secondary tasks, compared with analogue systems • With digital UI, operator is not self-evidently aware of activities of other operators • Digital systems are more often updated, causing pressure to plant design and training § User study among Finnish hybrid main control room operators about possible human errors in an emergency; comparison of errors • Operator interviews related to PRISE procedures in a hybrid control room (analogue for controlling, digital for monitoring the system) about possible errors • In practice, less possible errors in digital UI (user interface) • In principle, in most cases the same error could take place in both types of UIs § The cause behind digitally originating/analogue originating error may be different � may affect error probability BUT the mere digitality/analogueness does not does not dictate the amount or level of human errors 2 25.3.2019 VTT – beyond the obvious

Site risk analysis • Current PRAs are unit-specific • Inter-unit dependencies taken into account in a limited manner • Operational experience world-wide shows that multi-unit disturbances are not uncommon • No international consensus yet with regard to • Applicable risk criteria for a site • Method 3

Site PRA developments and findings: NKS project SITRON, report NKS-419 • Site risk analysis has two purposes • Complement single-unit PSAs • Provide multi-unit risk metrics • Safety goals are still connected to units, not at site level • SITRON method provides a practical and cost-effective way of performing a site risk analysis based on unit-specific PRAs • Multi-unit initiating events can be limited to external hazards • Loss-of-offsite power, Loss-of-ultimate heat sink 4

FinPSA level 2 § Tool based on dynamic containment event trees (CETs) developed further § Risk integrator combines results of different CETs and calculates total results § Tight integration of PRA levels 1 and 2 implemented • Contributions of basic events and initiating events in level 2 results • Level 1 results can be utilised in level 2 modelling 5 25.3.2019 VTT – beyond the obvious

Level 2 PRA modelling § A simplified BWR plant PRA model has been developed • Five containment event trees • Levels 1 and 2 tightly integrated • Model can be utilised in further research, demonstrations, trainings and FinPSA testing § Uncertainty analysis • Problems and good practises identified and demonstrated • In dynamic modelling, proper handling of epistemic and aleatoric uncertainties is important 6 25.3.2019 VTT – beyond the obvious

Time-dependent analysis in FinPSA § Can be used for maintenance planning, risk follow-up and analysis of seasonal variations § Time-dependent task file • User specifies events to a time line • e.g. maintenance activities, tests, parameter changes, configuration changes • FinPSA calculates time-dependent risk curve, using existing PRA results 7 25.3.2019 VTT – beyond the obvious

Level 3 PRA 8,00E+02 Population dose (M anSv) Improvements to an analysis method 6,00E+02 • Developed earlier by VTT 4,00E+02 • Systematic analysis of scenarios with event trees 2,00E+02 • Improvements: no discretization of continuous factors (e.g. wind speed) needed, source term 0,00E+00 0 10 20 30 40 uncertainty taken into account Rain intensity (mm/ hour) Nordic guidance document on level 3 PRA 1,00E+00 exceed the cancer The probability to • Uses, benefits, regulations, analysis steps etc. 1,00E-01 deaths 1,00E-02 Seasonal and contextual factors in level 3 1,00E-03 1,00E-04 • Groundwork for systematic incorporation in 1,00E-05 analyses 1,00E-06 0 50 100 150 200 The number of cancer deaths 8 25.3.2019 VTT – beyond the obvious

Portfolio optimization in PRAMEA § Pipe inspections (c.f. RI-ISI) • Problem : Which pipes should be inspected based on incomplete information about failure probabilities and failure impacts? • Large-scale optimization of inspections of the sewerage network in Espoo § Defence-in-depth • Problem : Which combinations of safety measures are cost-efficient in a system with event dependencies and multi-state failures? • Optimization of safety measures for the airlock system of a CANDU Nuclear Power Plant 9 25.3.2019 VTT – beyond the obvious

Portfolio optimization in PRAMEA § Dynamic systems • Problem : Which combinations of safety measures are cost-efficient in preventing time-dependent accident scenarios? • Real case study on the vapour cloud ignition of an industrial system § Cybersecurity • Problem : Which mitigation strategies minimize the risks of cyber threats to cyber physical systems? • Case study on the Advanced Metering Infrastructure (AMI) of an electric power system § Four papers in leading international journals (2 published in RESS, 1 revised for RESS, 1 submitted) 10 25.3.2019 VTT – beyond the obvious