PassivesystemreliabilityanalysisusingtheAPSRAmethodologyOriginalResearchArticle

Inthispaper,wepresentamethodologyknownasAPSRA(AssessmentofPassiveSystemReliAbility)forevaluationofreliabilityofpassivesystems.ThemethodologyhasbeenappliedtotheboilingnaturalcirculationsystemintheMainHeatTransportSystemoftheIndianAHWRconcept.IntheAPSRAmethodology,thepassivesystemreliabilityisevaluatedfromtheevaluationofthefailureprobabilityofthesystemtocarryoutthedesiredfunction.Themethodologyfirstdeterminestheoperationalcharacteristicsofthesystemandthefailureconditionsbyassigningapredeterminedfailurecriteria.Thefailuresurfaceispredictedusingabestestimatecodeconsideringdeviationsoftheoperatingparametersfromtheirnominalstates,whichaffectthenaturalcirculationperformance.Sinceapplicabilityofthebestestimatecodestopassivesystemsareneitherprovennorunderstoodenough,APSRAreliesmoreonexperimentaldataforvariousaspectsofnaturalcirculationsuchassteady-statenaturalcirculation,flowinstabilities,CHFunderoscillatorycondition,etc.APSRAproposestocomparethecodepredictionswiththetestdatatogeneratetheuncertaintiesonthefailureparameterprediction,whichislaterconsideredinthecodeforaccuratepredictionoffailuresurfaceofthesystem.Oncethefailuresurfaceofthesystemispredicted,thecauseoffailureisexaminedthroughrootdiagnosis,whichoccursmainlyduetofailureofmechanicalcomponents.ThefailureprobabilityofthesecomponentsareevaluatedthroughaclassicalPSAtreatmentusingthegenericdata.Reliabilityofthenaturalcirculationsystemisevaluatedfromtheprobabilityofavailabilityofthecomponentsforthesuccessofnaturalcirculationinthesystem.