Open Access

ARTICLE

Verification of Mitigation Capability for Total Loss of Feedwater Accident and Sensitivity Study on Feed-and-Bleed Cooling in a CPR1000 Nuclear Power Plant

Bo Zhang, Zhenhua Zhang^*

Nuclear and Radiation Safety Center, MEE, Beijing, China

* Corresponding Author: Zhenhua Zhang. Email:

Energy Engineering 2026, 123(9), 24 https://doi.org/10.32604/ee.2026.087110

Received 10 June 2026; Accepted 10 July 2026; Issue published 06 August 2026

Abstract

Total loss of feedwater accident is a typical transient among the design extension conditions for pressurized water reactor nuclear power plants, directly related to the loss of core cooling capability. Chinese nuclear safety regulations require in-depth analysis of such conditions, while most of the Generation II and modified Generation II units currently in operation were designed prior to the issuance of these regulatory requirements, and their mitigation capability remains to be verified. To evaluate the mitigation capability of CPR1000 nuclear power units in operation in China for this accident, an accident sequence involving main feedwater pump trip combined with complete failure of the auxiliary feedwater system under full power condition was simulated based on a high-fidelity simulation platform. By strictly following the emergency operating procedures for operator interventions, the transient responses of key safety parameters including primary coolant system pressure, coolant inventory, core outlet temperature, fuel temperature, and containment pressure were analyzed. The results show that, under the synergistic effect of automatic system actions and procedure guidance, the operator manually opened all three sets of pressurizer safety valves at about 60 min, establishing the feed-and-bleed cooling mode. The minimum reactor pressure vessel water level was 67.7%, the core remained uncovered, and both the peak fuel cladding temperature and core outlet temperature remained below the limits. At about 98 min, the residual heat removal system entry conditions were satisfied, and the core was successfully brought to a safe state. A sensitivity study on the influence of the number of opened safety valve sets was performed. The results indicate that when only two sets of safety valves were successfully opened, all acceptance criteria were still satisfied; when only one set was opened, the heat removal capacity of the safety valves was insufficient, with the pressure exhibiting saw-tooth fluctuations in the range of 2.3–3.7 MPa(a), and the residual heat removal system entry conditions could not be satisfied, thus making a smooth transition to a safe state difficult. These results provide an engineering reference for similar units in coping with total loss of feedwater accidents and for optimizing the feed-and-bleed cooling operational strategy.

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