Behavior of high-burnup BWR UO₂ fuel with additives under reactivity-initiated accident conditions

ABSTRACT

Fuels with additives are expected to provide enhanced fuel performance in fission gas retention owing to their large grain size, which elongates fission gas migration path. To investigate behavior of the fuels during a reactivity-initiated accident (RIA), RIA-simulated experiments OS-1 and LS-4 were performed on ADOPT (chromia- and alumina-doped UO₂) fuel of 64 GWd/t and chromia-doped UO₂ fuel of 48 GWd/t, respectively. The OS-1 rod failed at a fuel enthalpy increase of 160 J/g due to pellet–cladding mechanical interaction failure, which was the lowest failure limit among the test results ever obtained at the NSRR on high-burnup fuels from 40 to 65 GWd/tU. Comparison of the hydride morphologies in the cladding metallic layer between the rods subjected to the past NSRR tests suggests the contribution of radially oriented hydrides during base irradiation to the low failure limit. The LS-4 rod survived for a peak fuel enthalpy increase of 549 J/g, which resulted in cladding deformation of ~2.4% in the residual hoop strain and FGR of 1.4–6.1%. Whereas the low fission gas release exhibits the effect of additives, the cladding deformation is within the range explained by the deformation mechanism essentially identical to those recognized for high-burnup undoped fuels.

Graphical Abtsract

KEYWORDS:

• RIA
• high-burnup fuel
• NSRR
• BWR
• additive
• PCMI
• fuel failure
• hydrides
• cladding deformation
• fission gas release

Acknowledgments

The OS-1 and LS-4 experiments in this research were performed under the research entrusted by the Nuclear Regulation Authority, Japan. The OS-1 tested fuel rod and the information on fuel fabrication and irradiation at the Oskarshamn nuclear power station were provided under cooperative research agreements between OKG Aktiebolag, Studsvik Nuclear AB, Vattenfall Nuclear Fuel AB, Westinghouse Electric Sweden AB, and JAEA. The LS-4 tested fuel rod and the information on fuel fabrication and irradiation at the Leibstadt nuclear power station were provided under cooperative research agreements between Kernkraftwerk Leibstadt, the Paul Scherrer Institute, Framatome, and JAEA. The LS-1 tested fuel rod was provided under cooperative research agreements between Kernkraftwerk Leibstadt, the Paul Scherrer Institute, Westinghouse Electric Sweden AB, and JAEA. The FK series tested fuel rods were provided under cooperative research agreements between Tokyo Electric Power Company Holdings, Inc. and JAEA. The authors would like to acknowledge and express their appreciation for the time and effort devoted by the engineers and technicians in the Fuel Safety Research Group, NSRR Operation Section, Fuel Examination Section, JAEA.

Disclosure statement

No potential conflict of interest was reported by the authors.