Qinshan Nuclear Power Plant Outages And Site Consequence Analysis,

The Station Blackout (SBO) accident of PWR could lead to a severe accident with core melting. The accident might also lead to the containment failure by overpressure. This report describes the analytical studies of SBO accident and its consequence for QinShan Nuclear Power Plant (QSNPP). The results of this study might be used as a reference for the determination of severe accidents management measures or off-site emergency response actions.Analytical tool used in the study of station blackout accident was the MELCOR (version 1.8.1) code, and the tool for the off-site consequence analysis was MACCS.This report describes the analysis of early phase of the SBO accident sequences firstly. In SBO accident the reactor Coolant Pump (RCP) seal might be deteriorated due to loss of cooling. Moreover, an intentional Reactor Coolant System (RCS) depressurization, as suggested by foreign experts, might defer the progressing of the accident and mitigate the consequence during SBO. The above variations of SBO accident have been calculated. For the SBO accident without RCP seal failure or any operator action, the calculation predicts a vessel breach at 21676s, while the RCS pressure is kept at Safety Relief Valve (SRV) set point, causing a High Pressure Melt Ejection (HPME). The RCP seal leak during SBO might give different effects on accident sequence depending on the time of the accurrence of the seals failure. Early leak results in early core damage. Contrarily, the vessel breach is predicted to be delayed about 3000 s by later RCP seal leak. If the SRVs are latched open during SBO accident to depressurize the RCS, the vessel breach is predicted to delay over 8000 s. If the SRVs are latched open during SBO with RCP seal leak accident, the calculation results show that, compared with the SBO with RCP seal leak, the vessel breach could be delayed 2000s. Anyway, the HPME is avoided by the RCP seal failure or the RCS depressurization.The long term process of the accident till 10~6 s is analyzed to study the system responses, such as primary system thermo-hydraulics, core damage, cavity response, containment thermo-hydraulics, fission product behaviors, etc. The source term released into environment is calculated, which will be used for off-site consequence evaluation. The containment is predicted to low pressure leak at about 1.8 X 105 s after the accidentinitiation. Failure of containment by overpressure is predicted to occur at 8.76 X 105 s. When the calculation terminates at 106 s, nearly 100% of the gaseous radioactive fission products are released into the environment, and the released fractions into environment of volatile and non-volatile radioactive fission products are respectively 10"2~10"4 and 10"6~10"9.Off-site consequence of SBO accident for QSNPP is calculated by MACCS using the plant's site data and the calculated source term. There are some modifications in transforming the source term data calculated by MELCOR into the input data needed by MACCS, such as the advancing of release time, the shortening of the duration of release, etc. Sensitive studies have been performed to ensure that these corresponding corrections would make the calculated consequence more conservative. The other input data are also selected conservatively through sensitive studies.The results show that SBO accident of QSNPP would cause few off-site early health effects with very low possibility. On the other hand, off-site inhabitants' doses and potential risk are predicted to be biggish. Some protective measures are necessary. According to the calculation, the best measures are sheltering after the containment low pressure leak and quick evacuation after the containment failure by overpressure if the containment failure is unavoidable.Source term data must be drawn out from about 1G documents generated by MELCOR. Furthermore, the huge meteorological data containing 8760 hourly records including wind direction, velocity, stability, and rainfall etc. must be transformed to fit MACCS meteorological data file format. Two programs were developed to do these extremely tedious and easily mistakable works. This report also gives brief introduction to the two programs.