Heat-transfer analysis of SCW to SCW double-pipe heat exchanger for indirect-cycle SCW NPPS

This paper presents the heat transfer analysis of an intermediate Heat eXchanger (HX) design for indirect-cycle concepts of Pressure-Tube (PT) and Pressure-Vessel (PV) SuperCritical Water-cooled Reactors (SCWRs). Thermodynamic configurations with an intermediate HX give a possibility to have a single-reheat option for PT and PV SCWRs without introducing steam-reheat channels into a reactor. Similar to the current CANDU and Pressurized Water Reactor (PWR) Nuclear Power Plants (NPPs), steam generators separate the primary loop from the secondary loop. In this way, the primary loop can be completely enclosed in a reactor containment building. This paper analyzes the heat transfer from a SuperCritical Water (SCW) reactor loop to SCW turbine loop using double-pipe intermediate HX. The numerical model is developed with MATLAB and NIST REFPROP software. Pipes wall thickness of the HX are sized for the design pressure with a safety factor of +25% on operating pressure and divided into several nodes for the analysis. Water from the primary (reactor) loop flows throw the inner pipe, and water from the secondary (turbine) loop flows through the annulus in counter direction of the double-pipe HX. The analysis on the double-pipe HX shows temperature and thermophysical properties profiles along the heated length of the HX. It was found that the pseudocritical region has a significant effect on the temperature profiles and heat-transfer area of the HX. An analysis shows the effect of variation in pressure, pipe size, and temperatures on pseudocritical region and heat-transfer area of the HX. The results from the numerical model can be used to optimize the heat-transfer area of the HX. The higher pressure difference on the hot side and higher temperature difference between the hot and cold sides reduces the pseudocritical-region duration. This decreases the heat-transfer surface area of the HX. (author)