Gravity-Injection Core Cooling After a Loss-of-SDC Event n the YGN Units 3 & 4

  • Published : 1999.10.01

Abstract

In order to evaluate the gravity-injection capability to maintain core cooling after a loss-of-shutdown-cooling event during shutdown operation, the plant conditions of the Yong Gwang Units 3&4 were reviewed. The six cases of possible gravity-injection paths from the refueling water tank (RWT) were identified and the thermal-hydraulic analyses were performed using the RELAP5/MOD3.2 code. The core cooling capability was significantly dependent on the gravity-injection path, the RCS opening, and the injection rate. In the cases with the pressurizer manway opening higher than the RWT water level, the coolant was held up in the pressurizer and the system pressure continued increasing after gravity-injection. The gravity injection eventually stopped due to the high system pressure and the core was uncovered. In the cases with the injection path and opening on the same leg side, the core cooling was dependent on whether the water injected from the RWT passed the core region or not. However, in the cases with the injection path and opening on the different leg side, the system was well depressurized after gravity-injection and the core boiling was successfully prevented for a long-term transient. In addition, from the sensitivity study on the gravity-injection flow rate, it was found that about 54 kg/s of injection rate was required to maintain the core cooling and the core cooling could be provided for about 10.6 hours after event with that injection rate from the RWT. Those analysis results would provide useful information to operators coping with the event.

References

  1. NUREG-1449 Shutdown and Low Power Operation at Commercial Nuclear Power in the United States U.S. NRC
  2. NUREG-1269 Loss of Residual Heat Removal System-Diablo Canyon, Unit 2, April 10, 1987 U.S. NRC
  3. NUREG-1410 Loss of Vital AC Power and the Residual Heat Removal System During Midloop Operations at Vogtle Unit 1 on March 20, 1990 U.S. NRC
  4. KINS/GR-060 Safety Evaluation on Shutdown Operation of Nuclear Power Plants H.J.Kim(et al.)
  5. NUREG/CR-5855, EGG-2671 Thermal-Hydraulic Processes During Reduced Inventory Operation with Loss of Residual Heat Removal S.A.Naff(et al.)
  6. Journal of Korean Nuclear Society v.31 no.1 Containment Closure Time Following the Loss of Shutdown Cooling Event of YGN Units 3&4 K.W.Seul(et al.)
  7. Final Safety Analysis Report: YGN Unit 3 and 4 KEPCO
  8. NUREG/CR-5535 v.1-5 RELAP5/MOD3 Code Manual: User's Guide and Input Requirements K.E.Larson(et al.)
  9. Nuclear Technology v.126 no.3 Plant Behavior Following a Loss of Residual Heat Removal Event under Shutdown Condition K.W.Seul(et al.)
  10. International Conference on New Trends in Nuclear System Thermodynamics PWR Thermal-hydraulic Phenomena Following Loss of Residual Heat Removal During Mid-loop Operation H.Nakamura;Y.Kukita