SCWR Concept in China

To avoid the mechanical and safety problems in both thermal and fast SCWR design, and in the other hand to achieve a high temperature at the reactor exit, a mixed core design with multi-layer fuel assembly has been proposed by the Shanghai Jiao Tong University. The core consists of two zones with different neutron spectra, one with thermal and the other with fast spectrum. In the thermal zone, a co-current downward flow is applied with an exit temperature over the pseudo-critical point. The downward flow in the thermal fuel assembly will provide an effective cooling of the fuel rods. As a result, the cladding temperature will be kept at a low value. In the forthcoming fast zone a high exit temperature is achieved. Due to the high coolant inlet temperature over the pseudo-critical point, the heat transfer deterioration phenomenon will be eliminated in this upward flowing area. The low density in the fast zone can provide a hard neutron spectrum with a wide lattice structure, which can mitigate the non-uniformity of the circumferential heat transfer at the cladding surface and ensure a big inventory of water in the core. Consequently, with a hard neutron spectrum and the multi-layer fuel assembly, a conversion ratio close to 1.0 can be achieved