Lattice Design and Coolant Selection for a 333 MWth PWR Civil Marine Propulsion Core using Thorium-Based Checkerboard Micro-Heterogeneous Fuel


Civilian marine reactors face a unique set of design challenges in addition to the usual irradiation and thermal-hydraulic limits affecting all reactors. These include requirements for a small core size, long core lifetime, a 20% cap on fissile loading, and lim itations on using soluble boron. One way to achieve higher burnup/long core life is to alter the neutron spectrum by changing the hydrogen-to-heavy-metal ratio, thus increasing the conversion of fertile isotopes in the fuel. In this reactor physics study, we optimize the lattice geometry of a 333 MWth soluble-boron- free marine PWR for 15% U-235 enriched UO2 and 18% enriched micro-heterogeneous ThO2-UO2 duplex fuel arranged in a simple checkerboard configuration. Comparisons are made between the homogeneously mixed 15% U-235 enriched all-UO2 case and the checkerboard configuration. We have considered two types of coolant: H2O and mixed 80% D2O + 20% H2O. The main objective of this study is to observe in which spectrum maximum discharge burnup is obtained in order to improve uranium utilization while satisfying the moderator temperature coeficient constraint. Considering the entire range of moderation options, it was observed that higher discharge burnup for the candidate fuels is achievable by using either a wetter lattice or a much drier lattice than normal while epithermal lattices are distinctly inferior performers. Checkerboard fuel exhibits higher discharge burnup potential than the all-UO2 fuel for all moderation regimes for both coolants. Candidate fuels exhibit higher initial reactivity and discharge burnup with the mixed D2O-H2O coolant than the H2O coolant in the under-moderated regime, whereas these values are lower for the D2O-H2O coolant in the over-moderated regime.

Meeting Name

2016 International Congress on Advances in Nuclear Power Plants, ICAPP 2016 (2016: Apr. 17-20, San Francisco, CA)


Mining and Nuclear Engineering

Keywords and Phrases

Boron; Fuels; Heavy metals; Nuclear energy; Nuclear power plants; Pressurized water reactors; Ship propulsion; Discharge burn-up; Lattice design; Lattice geometry; Marine reactors; Micro-heterogeneous; Neutron spectra; Reactor physics; Thermal hydraulics; Coolants

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Document Type

Article - Conference proceedings

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© 2016 American Nuclear Society (ANS), All rights reserved.

Publication Date

01 Apr 2016