BEST-ESTIMATE APPROACH FOR IGNALINA NPP LICENSING PROCESS

摘要

According the international practice the best-estimate approach is used mainly for Loss of Coolant Accident (LOCA) in reactor cooling circuit type accidents. In Lithuania the best estimate approach is successfully applied not only for LOCA but also for reactor transients and accident confinement system response analyses. This paper presents the three examples of best-estimate accident analysis developed for Ignalina NPP licensing: break of Main Circulation Pump (MCP) pressure header; blocking of coolant flow rate in Group Distribution Header (GDH); break of fuel channels inside Reactor Cavity (RC). The first case with its consequences covers all LOCA type accidents, while the second - transients. The response of specific reactor cavity venting system, which prevents the radioactivity release into atmosphere is analyzed in the last case. Thermal hydraulic analyses were performed by employing best estimate thermal-hydraulic codes RELAP5 Mod3.2 (for analysis of reactor cooling circuit response) and CONTAIN (for analysis of reactor cavity response). For the uncertainty analysis the code SUSA 3.2 was employed.