Coupled Neutronic/Thermal-Hydraulic Hot Channel Analysis of High Power Density Civil Marine SMR Cores


Core average power density of standard small modular reactors (SMR) are generally limited to 60-65 MW/m3, which is 40% lower than for a standard civil PWR in order to accommodate better thermal margins. While designing a SMR core for civil marine propulsion systems, it is required to increase its power density to make more attractive for future deployment. However, there are obvious thermal-hydraulic (TH) concerns regarding a high power density (HPD) core, which needs to be satisfied in order to ensure safe operation through accurate prediction of the TH parameters. This paper presents a coupled neutronic/thermal-hydraulic (TH) hot channel analysis of a HPD 375 MWth soluble-boron-free PWR core using 19.25% 235U enriched micro—heterogeneous ThO2-UO2 duplex fuel and 16% 235U enriched homogeneously mixed all-UO2 fuel with a 15 effective full-power-years (EFPY) core life. To perform this analysis the hybrid Monte Carlo reactor physics code MONK is coupled 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 82 and 111 MW/m3, three cases were chosen by optimizing the fuel pin diameter, pin pitch and pitch-to-diameter ratio. These cases have been studied to determine whether TH safety limits are satisfied by evaluating key parameters, such as minimum departure from nucleate boiling ratio, surface heat flux, critical heat flux, cladding inner surface and fuel centreline temperatures, and pressure drop. The results show that it is possible to achieve a core power density of 100 MW/m3 for both the candidate fuels, a ∼50% improvement on the reference design (63 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 substantially and the economic competitiveness of the proposed civil marine PWR reactor core significantly improved.


Nuclear Engineering and Radiation Science

Keywords and Phrases

Fuels; Heat flux; Heat pump systems; Monte Carlo methods; Ship propulsion; Small nuclear reactors; Thoria; Uranium dioxide; High power density; Hybrid Monte Carlo; Neutronics; Small modular reactors; Soluble-boron-free operation; Subchannel analysis; Pressurized water reactors; Civil marine propulsion; High power density SMR; Micro-heterogeneous thorium-based duplex fuel; Neutronic/thermal-hydraulic coupling; Small modular reactor; Soluble-boron-free operation; Sub-channel analysis

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Article - Journal

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© 2019 Elsevier, All rights reserved.

Publication Date

01 May 2019