Deviation from Nucleate Boiling Ratio (DNBR) in Flow Decreasing Conditions in the “Cooling Part of VVER1000 Reactor Core”

Document Type : Original Article

Authors

دانشگاه امام حسین ع

Abstract

In a hypothetical accident in a reactor, the coolant mass flow decreases gradually. In such a condition, the deviation from nucleate boiling ratio decreases the heat transfer from the fuel and increases the heat flux. In this paper, firstly, by means of a transient analysis, core analysis thermohydraulic parameters of the VVER-1000 reactor core were determined by
COBRA-EN code in the conditions of reduced coolant current. Then the time-based DNBR variations and a number of thermohydraulic parameters of reactor cooling heart in a 120 seconds time span were evaluated, based on the reduction of temporal changes of reactor heart power and the cooling inlet flow, using the RELAP5 code to model the reactor heart in the “30% cooling flow reduction” transient mode, and the results were compared with COBRA-EN code.  Then, based on the outputs of COBRA-EN code under conditions of reactor core coolant reduction, for the hottest reactor core channel based on the reactor FSAR values, the departure of nucleate boiling (DNBR) parameter was evaluated and the safety analysis of the reactor core was performed. To analyze the sensitivity of the changes, we investigated three modes of flow reduction in the hot channel (30%, 60%, and 90%). The results showed that as the time goes on, the flow becomes biphasic and DNBR limitations are established, but the surface temperature of the clad and the fuel rod do not exceed the safety limit and the reactor is within the safety range.

Keywords

References

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History

  • Receive Date: 29 April 2019
  • Revise Date: 24 May 2021
  • Accept Date: 28 May 2021

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