The gas-cooled fast reactor (GFR) has great advantages of finance and sustainability which combines the features of high temperature gas-cooled reactor and fast reactor. However, safety issue has become the main challenge in the development of GFR due to the high temperature and high neutron flux in the GFR core. Coated particle fuel (CPF) has been widely used in high temperature reactor (HTR) due to the excellent high temperature tolerance.

In order to strengthen the safety property in GFR, this paper puts forward a block-type fuel assembly (FA) model based on CPF. Based on the FA model, neutronics analysis and thermal hydraulics validation is carried out to verify the rationality of the design.

Monte Carlo method is used in the calculation. Physical parameters including plutonium fraction in the U-Pu mixture fuel, diameter of fuel pins/coolant channels, the number of coolant channels, pitch-to-diameter ratio, thickness of cladding and thickness of assembly wrapper were selected and sensitivity analysis were conducted on the FA property to these parameters.

Analysis results show that among the above six parameters, plutonium fraction and pitch-to-diameter ration have the most obvious effect on the neutronic property and the number of the coolant channels mainly influences the power distribution of the GFR FA. Finally, temperature distribution of the FA is calculated using single channel model under a low coolant fraction and requirements in terms of thermal-hydraulic property are put forward for the FA parameters.

The block-type FA model put forward in this paper meets the design requirements well. The research conclusion of this paper provides reference for the future study on GFR nuclear design.