| Summary: | This work contributes to the Hydride Fuels Project, a collaborative effort between UC Berkeley and MIT
aimed at investigating the potential benefits of hydride fuel use in light water reactors (LWRs). Core
design is accomplished for both hydride and oxide-fueled cores over a range of geometries via steadystate
and transient thermal hydraulic analyses, which yield the maximum power, and fuel performance
and neutronics studies, which provide the achievable discharge burnup. The final optimization integrates
the outputs from these separate studies into an economics model to identify geometries offering the
lowest cost of electricity, and provide a fair basis for comparing the performance of hydride and oxide
fuels.
This work focuses on the steady-state and transient thermal hydraulic as well as economic analyses for
PWR cores utilizing wire wraps in a hexagonal array with UZrH[subscript 1.6] and UO[subscript 2]. It was previously verified
that square and hexagonal arrays with matching rod diameters and H/HM ratio have the same thermal
hydraulic performance. In this work, this equivalence is extended to hexagonal wire wrap arrays, and
verified by comparing the thermal hydraulic performance of a single hexagonal wire wrap core with its
equivalent square array core with grid spacers. A separate neutronics equivalence is developed, based on
the assumption that arrays with matching rod diameters and H/HM ratios will have identical neutronic
performance.
Steady-state design limits were separated into hard limits, which must be satisfied, or soft limits, which
serve to keep the design reasonable. Design limits were placed on the pressure drop, critical heat flux
(CHF), vibrations, and fuel and cladding temperature. Vibrations limits on the wire wrap assemblies were
imposed for flow induced vibrations (FIV) and thermal hydraulic vibrations (THV). An analysis of the
fretting wear of wire wraps indicated that wire wraps outperformed the analogous fretting wear analysis
for grid spacers. A CHF study found wire wraps to outperform grid spacers. LOCA and overpower
transient analyses were performed for wire wraps. The overpower transient was analyzed over a range of
geometries, and found to be more limiting than the steady-state analysis. The LOCA was analyzed for
various powers at the reference geometry and another geometry of interest. Through all of these analyses,
it was determined that the thermal hydraulic performance of UZrH1.6 and UO2 are very similar. The
optimal wire wrap designs were found to have significantly higher maximum powers than the reference
core, allowing for uprates up to ~54%. This is due to improved vibrations, pressure drop, and CHF.
The steady-state and transient analyses were combined with fuel performance and neutronic studies into
an economics model that determines the optimal geometries for incorporation into existing PWR’s. The
model also provides a basis for comparing the performance of UZrH[subscript 1.6] to UO[subscript 2] for a range of core
geometries. Results presented herein show cost savings for oxide fuel with wire wraps over grid spacers
of at least 0.8 mils/kWe-hr, or 4%, due to power increases predicted by the thermal hydraulic analyses.
Wire wrap UZrH[subscript 1.6] has a COE savings over UO[subscript 2] of 0.7 mils/kWe-hr, or 4%. Due to the large power
uprates possible, cost savings of up to 10.9 mils/kWe-hr, or 40%, can be achieved, with a UZrH[subscript 1.6] wire
wrap uprate instead of building a new core.
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