Bleed & Feed with One Pressurizer PORV Investigation for Loss of All Feedwater Using MAAP5 at STP


Zhiping Li

STP Nuclear Operating Company
ping65203@hotmail.com1


For the beyond-design-basis event of loss of both main feedwater (MFW) and auxiliary feedwater (AFW), bleed & feed is used to remove core heat to prevent fuel damage. The bleed path for bleed & feed typically requires two pressurizer pilot-operated relief valves (PORVs) to be opened. WCAP-17208-P supports the development of realistic bleed & feed scenarios using best estimate methods for Probabilistic Risk Assessment (PRA) success criteria and human reliability analysis (HRA) model development. Thermal-hydraulic analyses documented in NUREG-2187 for Byron Unit 1 supported changing bleed & feed success criteria from two pressurizer (PZR) PORVs to one PZR PORV along with one centrifugal charging pump (CCP). The success criteria for bleed & feed at the South Texas Project (STP) originally required at least one operating high-head safety injection (HHSI) train and two PZR PORVs based on NUREG/CR-4550. These success criteria were subsequently changed to require one CCP and two operating HHSI trains (feed path) plus two PZR PORVs (bleed path), based on updated Westinghouse Emergency Response Guidelines and analyses documented in WCAP-16902-P. An STP site-specific thermal-hydraulic analysis was performed for bleed & feed using the Modular Accident Analysis Program (MAAP5). These results show that the success criteria for loss of all feedwater bleed & feed at STP can be changed from (one CCP, two HHSI and two PORVs) to (one CCP, two HHSI and one PORV). The study also assesses timing requirements for bleed & feed operator actions.

Keywords: Bleed & Feed, One PORV, MAAP5, Success Criteria, Loss of Feedwater
1Work presented in this paper was conducted while the author was employed at STP Nuclear Operating Company. The author is currently with X-energy.