International Comparison of a Depletion Calculation Benchmark on Fuel Cycle Issues - Results from Phase 1 on UOx Fuels

Although there are many reactor system benchmarks in the literature, they mostly
concentrate on the reactor system in isolation with only a few considering the fuel cycle.
However, there is currently increased emphasis on the performance of reactor systems
linked to their associated fuel cycle (Generation-IV for example). The published
international benchmark studies which relate to burn-up depletion calculations are
restricted to specific aspects of the fuel cycle:
• Burn-up credit benchmark [working party on nuclear criticality safety (WPNCS)] [1]:
the nuclide density calculations focused mainly on the 15 most poisoning fission
products and only a short cooling time (5 years) was studied.
• Benchmark on decay heat calculation [2]: this benchmark focused on calculations of
decay heat due to 235U fissions.
The NEA/OECD Working Party on Scientific Issues of Reactors Systems (WPRS) has
defined a new benchmark investigating a broader range of isotopes, physical quantities and
fuel types [3]. The objective is to compare existing burn-up depletion calculations obtained
with various codes and data libraries, applied to fuel and back-end cycle configurations:
transport, reprocessing, interim storage and waste repository. The benchmark concentrates
on nuclide densities for the most important nuclides in the fuel cycle (actinides, fission
products and activation products) and the associated fuel cycle quantities (masses, neutron
emission rate and decay heat). Additional but optional calculations were also specified;
they relate to sensitivity calculations linked to the assumptions made on irradiation
parameters: the width of the half water gaps, the boron content, the fuel and moderatorcoolant
temperature and the irradiation history. The objective is that detected
discrepancies between participants’ results will enable us:
• to improve the calculation schemes (e.g. self-shielding, subdivisions in fuel or
moderator etc.);
• to improve the knowledge of burn-up chains used in depletion calculations (maybe
to recommend a chain for fuel cycle applications);
• to improve the knowledge of nuclear data (capture cross-sections, branching ratio,
fission yields and decay constants) involved in fuel cycle studies.
This report is devoted to the first phase of the benchmark. The aim of this phase is to
create a reference case for an UOx fuel. The benchmark uses experimental data from the
Japanese Post-Irradiation Experiment in the Takahama-3 PWR. This experiment has
already been used in French nuclear data studies [4]. The trends seen in this experiment
are consistent with the trends in spent fuel experiments performed in France [5]. This
experiment was also used by JAERI for the validation of the SWAT burn-up code system [6].
It is therefore possible to compare the calculational and experimental results for the major
actinides and verify how accurate the predictions of the models of the experiment are for
well-known isotopes (full details of these results and comparisons are included in
Appendix A). The list of available experimental results and associated uncertainties are
given at the end of Appendix C.
This report provides a description of the benchmark, summarises the international
participants, the codes that they used and finally presents a comparison of their results.