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Treatment of Dependency and Correlation in Multiunit PSA Considering Seismic as External Event

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Abstract

In the wake of Fukushima accident, throughout the world there is a concern about the safety of the nuclear reactor sites from external events such as seismic, flood, tsunami etc. Nuclear reactor sites around the world are mostly twin units or multi units. Hence, these days the concept of Reactor Park is also widely discussed, which brings out the requirement for proper site safety goals. As per International Atomic Energy Agency (IAEA) safety guide lines, the safety goals for single unit Nuclear Power Plants (NPPs) are very well established, but when it comes to multiunit sites the concept of site safety goals is not matured enough, hence, it is very much needed to establish these goals at the site level.Unlike the single unit Probabilistic Safety Assessment (PSA), the procedure for performing the PSA for multi-unit sites is not yet established. However, efforts are being made to standardise the procedure considering the various plants and their releases in a given site under consideration. In the multi unit PSA, special attention should be given while modeling the multi-unit initiating events, multi-unit PSA model, shared resources, inter-unit correlations, Common Cause Failure (CCF), modeling of Human Reliability Analysis (HRA) in the multi-unit parlance and risk aggregation. Among these issues, in the present paper focus is given for treatment of dependency and correlation as seismic core damage frequency is highly dependent on the modelling of dependency among the components. Conservative approach of considering fully dependence will give highly conservative results which may not be realistic. Hence, the main objective of the present study is treatment of dependency and correlation among various components considering the internal and external events possible in the site. The site under consideration is Tarapur site (Maharashtra, India) having two hypothetical advanced reactors. Scope of the analysis includes full power, external event (Seismic), Level 1 PSA considering reactor core as radioactivity source.

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Abbreviations

IAEA:

International atomic energy agency

NPP:

Nuclear power plant

PSA:

Probabilistic safety assessment

HRA:

Human reliability analysis

CCF:

Common cause failure

SPSA:

Seismic probabilistic safety assessment

SSMRP:

Seismic safety margins research program

MVN:

Multivariate normal

NRNFs:

Non reactor nuclear facilities

RB:

Reactor building

IE:

Initiating event

MUPSA:

Multi unit PSA

SWS:

Service water system

MSLBOB:

Main steam line break outside reactor building

LOOP:

Loss of offsite power

CD:

Core damage

CDF:

Core damage frequency

R1:

Reactor 1

R2:

Reactor 2

S-IE-MUPSA-P:

Seismic IE of primary event tree of MUPSA

S-R1-STRUCT:

Seismic induced structural failure of reactor 1

S-R2-STRUCT:

Seismic induced structural failure of reactor 2

S-R1R2-PUMP-HOUSE:

Seismic induced structural failure of pump house

S-R1R2-TURB-BLDG:

Seismic induced structural failure of turbine building of reactor 1&2

S-LOOP:

Seismic induced loss of off-site power

S-R1-IES:

Seismic induced IEs of reactor 1

S-R2-IES:

Seismic induced IEs of reactor 2

S-IE- HZ18:

Seismic IE hazard category 18

H18:

Hazard category 18

S-GRID:

Seismic induced grid failure

PPIS:

Passive poisson injection system

SDS1:

Shutdown system 1

SDS2:

Shutdown system 2

APWS:

Active process water system

APWS-P:

APWS pump failure

PPIS-GBPV-F:

Gas balancing passive valve failure of PPIS

PPIS-PIPV-F:

Passive injection passive valve failure of PPIS

SDS1-SR-F:

Shutoff rod guide tube failure of SDS1

SDS2-I-T-F:

Poison injection tank failure of SDS2

SDS2-HE-T-F:

Helium tank failure of SDS2

SDS2-IN-P-F:

Poison injection loop piping failure of SDS2

SDS2-H-PI-F:

Helium tank loop piping failure of SDS2

PGA:

Peak ground acceleration

SSC:

Structures, systems and components

CoV:

Covariance

FORM:

First order reliability method

SORM:

Second order reliability method

MCS:

Minimal cut set

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Authors and Affiliations

  1. Bhabha Atomic Research Centre, Trombay, Mumbai, India

    Gopika Vinod & M. Hari Prasad

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  1. Gopika Vinod
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  2. M. Hari Prasad
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Correspondence to M. Hari Prasad.

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Vinod, G., Prasad, M.H. Treatment of Dependency and Correlation in Multiunit PSA Considering Seismic as External Event. Trans Indian Natl. Acad. Eng. 8, 435–447 (2023). https://doi.org/10.1007/s41403-023-00409-8

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