The Amount of Hydrogen Generation andRadionuclides Release during SevereAccidents of a Pressurized Water Reactor

摘要

The need for a methodology to assess thedegree of core damage was part of the U.S. NuclearRegulatory Commission's change in licensing andoperation requirements after the Three Mile Islandaccident. Core damage assessment is used by theemergency response organization to determine theappropriate Emergency Action Levels (EALs), toselect the source term for estimation the offsite dose,to predict the radiation protection actions that shouldbe considered for long term recovery activities. In theCore Damage Assessment Guidance (CDAG)documented in WCAP-14696 report, WestinghouseOwners Group suggested that the containmentradiation level and hydrogen concentration in thecontainment together with some other existinginstrumentation, e.g. core exit thermocouples, reactorwater level, can be used to determine the degree ofcore damage.It is well known that the amount radionuclidesreleased from the fuel, retained in the reactor coolantsystem (RCS), and its distribution amongcontainment compartments depend on the accidentsequence. The amount of hydrogen generation andthe containment hydrogen concentration are alsosequences dependent. In the present analysis, asystematic MAAP calculation is performed toinvestigate the impact of accident scenarios on theamount of radionuclides and hydrogen concentrationin the containment. The purpose of the study is tosupport the developed of the plant specific CADG.Eleven sequences are analyzed in the presentstudy. The sequences analyzed included loss coolant accidents (several breach sizes and locations) andstation blackout sequence. Various mitigation actionsare considered in the calculations to study the impactof these actions on the containment radiation leveland hydrogen concentration. The major resultsdiscussed in the paper include: fractional release ofradionuclides from the fuel pellets, retention factor ofradionuclides within RCS, oxidation fraction ofcladding, retention factor of hydrogen within RCS,possibility of hydrogen combustion.