Parametric neutronics analyses of lattice geometry and coolant candidates for a soluble-boron-free civil marine SMR core using micro-heterogeneous duplex fuel

Abstract

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 limitations on the use of soluble boron. One way to achieve higher burnup/longer 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 two-dimensional lattice geometry of a 333 MWth soluble-boron-free marine PWR for 18% 235 U enriched micro-heterogeneous ThO 2 -UO 2 duplex fuel and 15% 235 U enriched homogeneously mixed all-UO 2 fuel. We consider two types of coolant: H 2 O and mixed 80% D 2 O + 20% H 2 O. We aim to observe in which spectrum discharge burnup is maximized in order to improve uranium utilization, while satisfying the constraint on moderator temperature coefficient. It is 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. The thorium-rich duplex fuel exhibits higher discharge burnup potential than the all-UO 2 fuel for all moderation regimes for both coolants. The candidate fuels exhibit higher initial reactivity and discharge burnup with the mixed D 2 O-H 2 O coolant than with the H 2 O coolant in the under-moderated regime, whereas these values are lower for the D 2 O-H 2 O coolant in the over-moderated regime.

Neutronic investigation of alternative & composite burnable poisons for the soluble-boron-free and long life civil marine small modular reactor cores

“…In this study, we have used deterministic reactor physics code WIMS 10 20,21 for the lattice-level calculation while considering JEF 2.2 nuclear data library and 6 energy group structure 9–12,17,22–24 . WIMS performs deterministic neutron transport calculations for every pin in a fuel assembly using an established calculation route through sequence of separate modules 19,20,22,25,26 .…”

“…For the analyses of alternative burnable poison, this study considers 15% U-235 enriched homogeneously mixed UO 2 fuel enriched in in a 13 × 13 assembly while assuming 7.5% neutron leakage and discharge burnup limit of 100 GWd/tonne in the WIMS model 22 . The detailed computational and design methods are reported in our previous studies 9–12,17,22,30 . Table 1 shows the 2D lattice-level (WIMS) and 3D whole-core (PANTHER) system parameter values 12,19,30–38 .…”

“…The detailed computational and design methods are reported in our previous studies 9–12,17,22,30 . Table 1 shows the 2D lattice-level (WIMS) and 3D whole-core (PANTHER) system parameter values 12,19,30–38 . It is also important addressing that the results of this article have been introduced in the PhD thesis 19 of the corresponding author and also in a conference paper 34 .…”

“…Our previous studies 9–12,18,19 demonstrated that using localized, self-shielded gadolinia is an effective means of moderate, long-term reactivity control. However, it has a number of drawbacks.…”

“…This study, therefore, focuses on the design of 333 MWth 9,10 SBF and long life civil marine SMR core while utilizing LEU. We set a target operational life of at least 15 years under high irradiation of around 100 GWd/tonne and constrain uranium enrichment at 20%– in line with proliferation resistance related limits on low-enriched uranium (LEU) 9–12 . It is noteworthy to mention that reactor cores for the purpose of civil marine applications cannot be conceivably as highly enriched as the reactor cores used in military vessels 9,10,17 .…”