Low Pressure Injection System Crossconnect Modification

Abstract

How would you fix all of the Low Pressure Injection (LPI) system technical problems listed below with a single nuclear plant modification? • Large LPI Flow indication uncertainty; • Non-Safety power to important cross connect valves; • LPI Pump run-out / NPSH operator burden; • Unbalanced LPI cooling due to electrical single failure; • Unconventional response to valve single failure. A southeastern nuclear generation facility responded by contracting Framatome ANP to design a new passive single cross connect modification for each of their generating units. This new cross connect, consisting of approximately 130’ of 10” stainless steel piping, new gate valves, new check valves, and two new flow restrictors, was installed downstream of the LPI coolers and inside containment on each unit to tie the two injection trains together. The two flow restrictors (stemless globe valves with precision engineered disc stacks) were the centerpiece of the design. Though system resistance is increased, the flow restrictors eliminate all of the technical issues that the utility faced in the LPI system. The passive nature of this design eliminated the time-critical operator burden, the need for safety grade power on existing cross connect valves, the threat of pump run-out and marginal NSPHa, and the unusual single failure licensing basis to manually open LPI isolation valves in the event that they failed closed. The design also improved flow indication uncertainty with a change out of the existing flow measuring orifices. Framatome ANP faced many challenges during the design process. In addition to the problems to be solved, other constraints of the modification were significant, including: an unusually tight upper limit on pump strength, a narrow band of acceptable system resistance with an unknown baseline, first-of-a-kind accuracy requirements for the flow restrictor, and High Pressure Injection (HPI) system minimum flow limits challenged by modification operational changes. The NRC has approved the flow restrictor and the overall design for use in this facility. The passive cross connect modification has been installed in all units. All equipment has passed installation and post modification testing requirements.