Objective: Investigate performance of modern high burnup fuel (lower corrosion / hydrogen pickup than some previous RIA tests) in RIA transients at representative pulse widths

Facilities: TREAT reactor and hot cells (USA) and NSRR reactor (Japan)

Core Group: DOE, NRC, Westinghouse (USA), JAEA (Japan), IRSN (France)

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HERA is dedicated to the understanding of LWR fuel performance at high burn-up under reactivity-initiated accidents (RIA). In-pile RIA experiments have been performed on high burn-up fuels in excess of 60 GWd/t in the CABRI reactor in France, and the Nuclear Safety Research Reactor (NSRR) in Japan. However, the majority of these experiments were conducted on vintage cladding materials and tested at conditions that are slightly different than those expected in today’s light water reactors (LWRs). Modern cladding materials are expected to perform better under prototypic reactor conditions however the operation of UO₂ fuel to higher burnups also presents new unknowns. The HERA tests will provide an opportunity to identify available cladding failure margin in modern claddings and identify any safety impacts from operation of extending the burnup of UO₂ fuels.

In HERA, pre-hydrided and irradiated fuel rod segments will be subjected to conditions similar to RIA conditions. Measurements made during the tests, detailed post-test examination and comparisons to historic RIA tests will make it possible to:

• quantify the impact of pulse width on fuel performance, offering new insight into the applicability of existing data;
• generate new data on high burn-up fuel under pulse conditions prototypic of LWRs;
• quantify the additional margin provided by modern cladding alloys to PCMI failure limits, and
• offer improved data for modellers using specially designed tests that eliminate key uncertainties in high-burn-up fuel tests.

HERA experimenters are collaborating closely with modelers to learn even more. A modeling exercise is being conducted alongside the HERA experiments, beginning with blind tests of the planned experiments. The results will help experiment designers finalise the details of the experiment. The exercise will also help modelers see where their models are good at predicting the complicated behavior of fuel during an RIA and reveal where the models need improvement. The NEA will publish updates on how this modeling activity is helping “close the loop” between modelers and experimenters to benefit both.

Image: Test device used in HERA experiments, Idaho National Laboratory