Abstract
Nuclear power plant risk has to be quantified in full power and in other modes of operation. This latter situation corresponds to low power and shutdown modes of operation in which the residual heat removal (RHR) system is required to extract the heat generated in the core. These accidental sequences are great contributors to the total plant risk. Thus, it is important to analyze the plant behavior to establish the accident mitigation measures required. In this way, PKL facility experimental series were undertaken to analyze the plant behavior in other modes of operation when the RHR is lost. In these experiments, the plant configurations were changed to analyze the influence of steam generators secondary side configurations, the temperature inside the pressurizer, and the inventory level on the plant behavior. Moreover, different accident management measures were proposed in each experiment to reach the conditions to restart the RHR. To understand the physical phenomena that takes place inside the reactor, the experiments are simulated with thermal-hydraulic codes, and this makes it possible to analyze the code capabilities to predict the plant behavior. This work presents the simulation results of four experiments included in PKL experimental series obtained using RELAP5/Mod3.3.
Highlights
When a pressurized water reactor is in other modes of operation (OM), the reactor coolant system (RCS) water level can be reduced to a height lower than the top of the hot leg pipe, for example, to perform U-tubes or reactor coolant pump maintenance activities
The experimental series E3.1, F2.1, and F2.2 conducted at PKL facility consist of the loss of the residual heat removal (RHR) system when the plant is in OM conditions, with the reactor coolant system closed and filled up to 3/4 of the loop and considering different steam generators secondary side configurations
This study focuses on determining whether the level in the loop improves or not the heat transfer from steam generators primary to secondary side when the RHR is lost
Summary
When a pressurized water reactor is in other modes of operation (OM), the reactor coolant system (RCS) water level can be reduced to a height lower than the top of the hot leg pipe, for example, to perform U-tubes or reactor coolant pump maintenance activities Under these conditions, the residual heat removal (RHR) system is used to extract the decay power heat generated in the reactor core. To better understand the thermal-hydraulic processes following the loss of the RHR in OM, transients of this kind have been simulated using best-estimate codes such as RELAP5 [4] or CATHARE Such codes have initially been developed to simulate full power operation conditions, which are different physical conditions from the ones faced in midloop operation mode. The physical phenomena to investigate in all the experiments are the mechanisms of heat removal in presence of nitrogen, the deboration in critical parts of the primary system, the influence of steam generator secondary side configurations to act as final heat sink, and how to return to a safe condition to restart the RHR through different injections
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