Influences of fabrication tolerance on thermal hydraulic performance of HTGR helical tube once through steam generator

Abstract High temperature is one of the key advantages of High Temperature Gas-cooled Reactors (HTGRs). This also brings challenges to the design of its heat transfer equipment. Adequate temperature uniformity in the heat transfer equipment should be guaranteed. This helps to lower the maximum material working temperature and also keeps the equipment working in good condition. The temperature non-uniformity in the HTGR helical tube once through steam generator (OTSG) is composed of inter-unit difference and in-unit difference. Fabrication tolerance of the helical tube bundle will influence both the inter-unit and in-unit differences. The factors causing temperature non-uniformity in the HTGR OTSG were discussed. Then the influences of fabrication tolerances on the flow and heat transfer uniformity in a 5-layer helical tube bundle were numerically investigated using the 2D URANS methods. The results show that a fabrication tolerance of 0.5 mm in helical diameter will result in 1.4% pressure resistance variation and 0.7% flow rate variation among the 19 units. The influences of fabrication tolerance on the outlet steam temperature uniformity among the 5 layers of tubes were also numerically studied using the 2D tube and shell side coupled method. The fabrication tolerance of 0.5 mm in helical diameter will induce about 5℃ steam temperature variation among the 5 layers of tubes. The temperature non-uniformities induced by this fabrication tolerance for both inter-unit and in-unit differences are acceptable.