Mechanical design of a sodium cooled fast reactor fuel assembly in Korea: Normal operation condition.

Highlights • The design criteria and stress limits for the mechanical design of a PGSFR fuel assembly are newly developed. • The structural integrity of the PGSFR fuel assembly during the period of normal operation is ascertained. • The brittle fracture concerning the DBTT will not take place for the PGSFR fuel assembly through the conventional non-destructive examination during refueling period. Abstract The mechanical design of the fuel assembly of a sodium cooled fast reactor is presented in this paper. This is one of the design works of a prototype generation IV sodium cooled fast reactor (PGSFR), which is planned to be built in Korea. Among the design tasks of the fuel assembly, the normal operation conditions is primarily considered here. One of the main issues is the lack of an applicable design code because the currently available worldwide codes such as the ASME Section III Division 5 and RCC-MRx do not incorporate the material (HT-9, the ferriticmartensitic steel) of the fuel assembly's structural components. To resolve this, the formulae of the yield and ultimate strengths of HT-9 are used here, which have been verified through comparing with the existing data in the references other than the codes. From this, we conservatively set up new design criteria and stress limits. Two fuel assemblies of different locations in the reactor core are chosen for the analysis. The results show that the stresses are far below the stress limits. In addition, a brittle fracture of the components is concerned considering the low temperature below the ductile-brittle transition temperature of the HT-9 during handling a fuel assembly in the reactor. It is found that the crack sizes that can cause a fracture failure are much larger than what can be detected using a normal non-destructive test method. Thus, it is soundly concluded that the presently designed PGSFR fuel assembly has sufficient structural integrity during normal operation and refuelling outage. [ABSTRACT FROM AUTHOR]