Session: 07-02: Experiments and Analyses - I

Paper Number: 134892

134892 - Design and Performance Verification of Passive Core Cooling System Strainer in Nuclear Power Plants 

Abstract: 

After a LOCA accident occurs in the containment, various materials such as insulation and coating will be damaged by high-energy jet, and the ECCS strainer is used to filter the debris to avoid clogging of downstream equipment. A new nuclear power plant in China uses a Passive Core Cooling system (PSI), which relies on the natural circulation driven by the water head difference between sump and core to achieve long-term core cooling after a LOCA. In addition, in the case of a LOCA accident combined with PCS system failure, the Residual Heat Removal system (RHR) pump takes water through the ECCS filter to provide containment spray. The configuration of these safety systems poses new challenges for the design and performance verification of ECCS filters.

Some pipe break (e.g., RCS cold leg or DVI pipes) locate under the sump flood-up elevation, resulting in most of the debris entering the core directly from the break instead of being filtered through the strainer. The amount of debris must be strictly minimized to avoid clogging the fuel assembly flow path, such as the use of metal reflective insulation instead of glasswool, the restriction of t bare aluminum in containment, the protection of non-metallic materials from LOCA jet, sampling and analysis of potential debris, etc.. After upstream analysis, the LOCA debris amount includes 3kg of fiber, 400kg of particles and 16.1kg of chemical precipitate.

According to the layout of the nuclear power plant, the following improvements are considered in the design of the ECCS strainer: 1) W-shaped bending filter screen is used to twice the screen area than ordinary flat screen. 2) The screen is 600mm higher than the ground, which lead to potential debris sedimentation and decreasing screen load.3) The screen area can be flexibly adjusted by module trial design. The semi-theoretical formula of NUREG/CR-6224 is difficult to accurately calculate the screen head loss due to the fiber layer is less than the typical thin bed thickness (3.18mm). In addition, the influence mechanism of chemical precipitate on screen head loss is complex, and there is no mature calculation method right now. Therefore, it is necessary to evaluate the appropriate screen area through tests to achieve a balance between functionality and economy.

A strainer module was used as the test prototype, and the relation between screen area and head loss was evaluated in test A by increasing the flow rate and the amount of debris inputted, which means gradually increasing the test ratio. According to the results test A, when the screen area gradually decreases from 480m² to 120m², there will be an inflection point where the head increases, then 120m² is selected as the suitable screen area. Fibers, particles and chemical precipitates were put in sequence in test B, compared with fibers and particles, and the chemical precipitate would cause a sharp increase of screen head loss compared to the fibers and granular debris，so the aluminum exposed to the recirculate coolant should be strictly controlled in the containment. The ECCS filter has been verified to meet the head loss limits of PSI and RHR systems, and will not lead to the failure of long-term core cooling and containment spraying.

Presenting Author: Ruolin Huang China Nuclear Power Engineering Co., Ltd

Presenting Author Biography: Nuclear engineer，Master's degree, engaged in process equipment design for nuclear power plants

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