Evaluation of the French Haut Taux de Combustion (HTC) Critical Experiment Data

In the 1980s, a series of critical experiments referred to as the Haut Taux de Combustion (HTC)
experiments was conducted by the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) at the
experimental criticality facility in Valduc, France. The plutonium-to- uranium ratio and the isotopic
compositions of both the uranium and plutonium used in the simulated fuel rods were designed to be
similar to what would be found in a typical pressurized-water reactor fuel assembly that initially had an
enrichment of 4.5 wt % 235U and was burned to 37,500 MWd/MTU. The fuel material also includes
241Am, which is present due to the decay of 241Pu. The HTC experiments include configurations designed
to simulate fuel handling activities, pool storage, and transport in casks constructed of thick lead or steel.
Rights of use for the HTC experiment data were purchased under an agreement that limits release of the
information. Consequently, a detailed and complete description of the experiments is not presented in
this report. This report discusses evaluation of the four HTC data reports, modeling of the experiments,
sensitivity and uncertainty analysis, and upper subcritical limit (USL) calculation. The report also
presents some conclusions and recommendations concerning use of the HTC experiment data for burnup
credit applications.
The similarity of the HTC experiments with PWR spent nuclear fuel has been quantified using
sensitivity/uncertainty analysis, confirming that the HTC experiments are significantly more applicable to
the validation of burnup credit calculations than other available mixed-oxide (MOX) experiments. The
HTC experiments were designed and executed with a high level of rigor, resulting in experimental
uncertainties that are lower than many of the earlier MOX experiments. The HTC data reports, together
with information provided in this report, provide sufficient data to allow for either detailed or simplified
computational models to be developed. The HTC experiments substantially strengthen the technical basis
for validation by adding to the previously small number of applicable experiments against which to
compare burnup credit applications. Existing MOX experiments found to be applicable are also identified
in this report.