Studies And Design Of The Fast Zone Assembly In SCWR Mixed Core

The supercritical water-cooled reactor (SCWR) system has been regarded as an innovative reactor and was selected as one of six candidates of the Generation-IV program. Extensive R&D activities have been launched covering various aspects of the SCWR development around the world.. Compared to state-of-the-art light water reactors, SCWR has many unique advantages: higher thermal efficiency, more compact plant, simpler systems.Most of the concepts are based on thermal spectrum. Efforts were also made to design SCWR reactor cores with fast neutron spectrum In spite of the merits mentioned above, both thermal and fast design show some shortages from the long-term development point of view. In order to solve those problems, a supercritical water cooled mixed core combined the merits of some thermal spectrum SCWR cores and fast SCWR cores have been proposed.The SCWR mixed core is composed of two zones with different neutron spectrum, but this paper only focuses on studies of the fast fuel assembly in SCWR mixed core. Both neutron-physical and thermal-hydraulic performance of fast fuel assembly are investigated using the MCNP code and the sub-channel analysis code STAFAS, respectively. The arrangement and parameters of fuel assembly have been optimized to enhance the inherent safety behavior and to achieve a high breeding ratio. Therefore, the analysis work is mainly divided into two stages: single-layer fuel assembly research and multi-layer fuel assembly research.In the first stage, the effect of design parameters and fuel pins arrangement on neutron-physical and thermal-hydraulic behavior in single-layer fuel assembly has been studied. The results showed that compared with triangle arrangement of fuel pins, single-layer assembly with square arrangement of fuel pins achieved a better neutron-physical and thermal-hydraulic behavior. However, it could not achieve a negative void reactivity coefficient and realized fissile nuclide breeding by adjusting configuration parameters and fuel rod arrangement.In order to improve the performance of fast fuel assembly, a multi-layer fuel assembly have been proposed in the second stage, based on the investigation of reduced-moderation water reactors some supercritical water cooled fast reactor. The pre-research results showed that with the proposed multi-layer structure the fast fuel of the mixed core has breeding capability. At the same time, a negative void reactivity coefficient can be achieved. The design parameters including wall material and fissile Pu enrichment are investigated to optimize the characters of fast fuel assembly. All the research work in this paper will offer reference model and theory supporting for further design and research work of fast fuel assembly in SCWR mixed core.