Analysis of mass transfer processes in a reactor during a loss-of-coolant accident

Aleksey Kulikov,Vitaly Polunichev,Andrey Lepyokhin

doi:10.3897/nucet.4.30777

Abstract

The purpose of the work was to optimize the parameters of the spillage system equipped with a gas pressure hydroaccumulator for a ship pressurized water reactor in a loss-of-coolant accident. The water-gas ratio in the hydroaccumulator and the hydraulic resistance of the path between the hydroaccumulator and the reactor were optimized at the designed hydroaccumulator geometric volume. The main dynamic processes were described using a mathematical model and a computational analysis. A series of numerical calculations were realized to simulate the behavior dynamics of the coolant level in the reactor during the accident – by varying the optimized parameters. Estimates of the minimum and maximum values of the coolant level were obtained: depending on the initial water-gas ratio in the hydroaccumulator at different diameters of the flow restrictor on the path between the hydroaccumulator and the reactor. These results were obtained subject to the restrictive conditions that, during spillage, the coolant level should remain above the core and below the blowdown nozzle. The first condition implies that the core is in safe state, the second excludes the coolant water blowdown. The optimization goal was to achieve the maximum time interval in which these conditions would be satisfied simultaneously. The authors propose methods for selecting the optimal spillage system parameters; these methods provide the maximum time for the core to be in a safe state during a loss-of-coolant accident at the designed hydroaccumulator volume. Using these methods, it is also possible to make assessments from the early stages of designing reactor plants.

Highlights

The purpose of the work was to optimize the parameters of the spillage system equipped with a gas pressure hydroaccumulator for a ship pressurized water reactor in a loss-of-coolant accident
– the time, during which one the coolant level is above the blowdown nozzle, should be reduced to a minimum and further the coolant level should be maintained below the blowdown nozzle
The characteristic behavior of the coolant level when water is supplied from the hydraulic accumulators (HA) to the reactor is generally as follows: initially, the level is relatively quickly reduced to the minimum value corresponding to the moment of the first equalization of the blowdown and spillage flows; it increases due to the fact that the spillage flow rate exceeds the blowdown flow rate, reaching the maximum value corresponding to the moment of the second equalization of the blowdown and spillage flows; and further, the level decreases monotonically after the accumulator is drained

Summary

Introduction

The purpose of the work was to optimize the parameters of the spillage system equipped with a gas pressure hydroaccumulator for a ship pressurized water reactor in a loss-of-coolant accident. The authors propose methods for selecting the optimal spillage system parameters; these methods provide the maximum time for the core to be in a safe state during a loss-of-coolant accident at the designed hydroaccumulator volume Using these methods, it is possible to make assessments from the early stages of designing reactor plants. Kulikov AV et al.: Analysis of mass transfer processes in a reactor during a loss-of-coolant accident rience of analyzing such accidents (Kuul and et al 1992, Vorobyova and et al 2008, Lepyokhin and et al 2009, Vorobyova and et al 2016, Lepyokhin and et al 2017) allows us to clearly imagine the course of processes and the characteristic behavior of the main reactor thermohydraulic parameters (see Fig. 1 and 2) These parameters are given in relative units, reduced to the initial values at the time of depressurization. The process is accompanied by a rapid (with typical times of the order of tens of seconds) decrease in the pressure and temperature of the primary coolant; the blowdown rate falls

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Conclusion