Hot channel analysis of a 333 MWth high power density civil marine core using 3D neutronic/thermal-hydraulic coupling of hybrid Monte Carlo monk with sub-channel analysis COBRA-EN code

This paper presents a coupled neutronic/thermalhydraulic (TH) hot channel (HC) analysis of a high power density (HPD) 333 MWth soluble-boron-free PWR core using 18% U-235 enriched micro-heterogeneous ThO₂-UO₂ duplex fuel and 15% U-235 enriched homogeneously mixed all-UO₂ fuel with a 15 effective full-power-years (EFPY) core life. This work utilizes the coupling of MONK as a hybrid Monte Carlo (MC) reactor physics code with sub-channel analysis TH code COBRA-EN. This approach is used to investigate the feasibility of different HPD marine PWR concepts and to identify the main TH challenges characterising these designs. To design HPD cores of between 90 and 250 MW/m³, five cases were chosen by optimizing the fuel pin diameter (D), pin pitch (P) and pitch-to-diameter ratio (P/D). These cases have been studied to evaluate key TH parameters, such as MDNBR, surface heat flux, critical heat flux, cladding inner surface and fuel centreline temperatures, and pressure drop to determine whether TH safety limits are satisfied. The results show that it is possible to achieve a core power density of 120 MW/m³ for both the candidate fuels, a ∼90% improvement on the reference design and ∼18% greater than that of the Sizewell B PWR (101.6 MW/m³), while meeting the target core lifetime of 15 EFPY and remaining within TH limits. The size of the pressure vessel can therefore be reduced dramatically and the economic competitiveness of the proposed civil marine PWR reactor core significantly improved. (author)