Normal residual heat removal exchanger (RNS HX) is used to remove reactor residual heat during the second stage of reactor shutdown. A hypothetical over-pressurized accident, during which RNS HX would suffer the normal operating pressure and operating temperature of RCS should be considered during the design of RNS HX.
This paper introduces Bolt-Flange-Gasket seal structures for RNS HX, considering the leakage-proof during over pressurized situation and some other operating-related aspects. At tube side, Metal-to-metal contact (MMC), with which a mass energy could be stored in metals during bolt preloading and could release when inner pressure increases, is used, so that the energy stored in metals could resist high pressure to prevent the joint disjoin. Another feather of tube side joint is that a slight angle is designed at the periphery of tubesheet.
At shell side, a segmental gasket, which is divided into two or more pieces rather than a whole circle, is used to seal the joint. As the gasket pieces are installed from the side of tube bundle, the shell does not need to be removed away completely from the bundle in order to install a circle gasket, which could facilitate gasket changing process and save the operating space.