Study on supercritical fluids in an intermediate heat exchanger for an SCWR hydrogen cogeneration system

Abstract

SuperCritical Water-cooled Reactors (SCWRs) are one of six Generation-IV nuclear reactor concepts under development worldwide. SCWRs benefit from an increase in thermal efficiency due to the reactor coolant operating above the critical point of water. They are currently being designed to work at pressures of 25 MPa with outlet temperatures up to 625°C. These operating conditions make them a suitable candidate for thermochemical hydrogen cogeneration. This work investigates the use of SCWR process heat for the thermochemical production of hydrogen. A thermochemical cycle currently being studied for this purpose is the 4-step Copper-Chlorine (Cu-Cl) cycle. This is due to its relatively low temperature requirements when compared to other existing thermochemical cycles. To achieve this, an intermediate Heat eXchanger (HX) linking a SuperCritical Water (SCW) Nuclear Power Plant (NPP) and a hydrogen production facility is considered. The objective of this work is to assess the performance of supercritical fluids in an intermediate HX to be used for the cogeneration of hydrogen. The thermal energy requirement for the 4-step Cu-Cl cycle is identified and a numerical model is developed in MATLAB. Reference cases for an SCW-to-SCW HX and an SCW- to-supercritical CO₂ HX are developed. A heat transfer analysis is conducted on each of these reference cases as well as on subsequent test cases. In these test cases, various sensitivity analyses are performed to determine the effect that mass flux, pressure and piping dimensions will have on the overall system. Ultimately, this will give an indication as to what combination of parameters should be used to optimize the design of the HX in terms of overall heat transfer surface area.