Pressure Controlled Heat Pipe Based Heat Exchanger for Dynamic Process Heat Extraction Control for Nuclear Power Plants

Nuclear power plants (NPP) are clean energy sources typically designed for baseload power operations but usually incapable of dynamic operations. One method to improve the NPP flexibility is dynamically extracting process heat. Conventional heat exchangers for heat extraction may be less suitable due to potential for tritium migration into the process stream. This study discusses a novel heat exchanger (HX) based on Pressure Controlled Heat Pipe (PCHPs) that ensures faster responses to varying heat load and mitigates challenges typical to conventional heat exchangers. Thermosiphons were used here as a PCHP. To demonstrate this technology, a prototype PCHP-HX was fabricated with stainless steel 304. The main stream heat from the NPP and the process heat were divided into two shells and connected by a bundle of PCHP tubes. The dynamic response to heat load switching was achieved by introducing Non-Condensable Gas (NCG) into the thermosiphons. Within the given operating conditions, the PCHP-HX demonstrated up to 6.5 kW of heat transfer. When NCG was added, system shutdown, was achieved within 7 minutes. When NCG was evacuated, complete system start-up was achieved within 4 minutes with 100% heat delivery.