A Comparison and Abstraction of the Commercial Spent Fuel Corrosion Experiments in the U.S.
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A Comparison and Abstraction of the Commercial Spent Fuel Corrosion Experiments in the U.S. Eric R. Siegmann Framatome ANP, 1180 Town Center Drive, Las Vegas, NV 89144, U.S. ABSTRACT This paper compares the results of three different fuel corrosion experiments by taking the existing corrosion data reported for various temperatures and recalculating corrosion rates at a single temperature of 25oC using a temperature dependent model developed elsewhere. Three types of light water reactor fuel corrosion tests (sometimes called dissolution or alteration tests) were performed in support of Yucca Mountain Project. The tests used three water contact modes and various fuel burnups. All measurements were adjusted for temperature differences and then compared. Five different isotopes (cesium, technetium, iodine, strontium, and, in the flowthrough tests, uranium) were considered as a measure of corrosion. The data used represent over ten years of experiments with about nine different fuel types. Most experiments were with repository type fluids, containing dissolved constituents such as carbonate, calcium and silicon. The results show that all of the experiments predict similar fuel corrosion rates. Small differences in the isotope release rates are observed and incorporated in the abstracted uncertainty. Water contact mode (flow-through, batch, or drip) does not seem to be very important although the drip tests introduced larger variations. In developing a corrosion abstraction, all of the isotope measurements were considered equally. The distribution of release rates was used directly to develop the uncertainty. The mean corrosion rate was 1.8 x 10-4 fraction/year at 25oC (5%-95% range = 5.7 x 10-5 to 1.7 x 10-3). Using the derived corrosion rate for 25oC, and considering rapid axial splitting of the cladding, the CSNF fuel rod is expected to corrode in less than 2,000 years. The abstraction uses all the available experiments performed with water containing carbonates, silicon, or calcium and irradiated fuel to produce a corrosion rate distribution. Sensitivity studies using this corrosion rate abstraction in the TSPA-SR analysis show very small changes in dose (3%) in response to changes in the UO2 corrosion abstraction. INTRODUCTION A licensing requirement for the Yucca Mountain Project (YMP) is to estimate the performance of the repository. The Total System Performance Assessment (TSPA) predicts the dose rate to a critical group 20 km from the repository. A part of this assessment is modeling how the commercial spent nuclear fuel (CSNF) alters when exposed to water. Earlier models [1] were based solely on one type of experiment, the flow-through tests [2]. This paper compares the results of three different types of experiments and looks at the effect of water contact mode, fuel burnup and marker isotopes. Three types of light water reactor fuel corrosion tests were performed in support of the Yucca Mountain Project. Each test used irradiated UO2 fuel particles or cracked pellets and a different water contact mode
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