Fuels and Materials Fast-Reactor Dosimetry Data Development and Testing

The development, design, and operation of nuclear reactors require the accurate prediction of (a) fission rates and burnup for fuels and (b) neutron exposure for neutron-induced property changes for fuels and materials. Goal accuracies of as low as 1% (1σ) have been set for the determination of fission rates, burnup, and neutron fluences for the fast-reactor development program. Based on the discussion of the status of fuels and materials fast-reactor dosimetry data development and testing, attainable goal accuracies presently appear to be in the range of 2 to 5%. Significant progress has been made in achieving high-accuracy measurements through a coordinated interlaboratory effort of integral measurements in low- and high-intensity neutron fields. A few of the major accomplishments of this interlaboratory work are as follows.

1. identification and selection of a number of standard or reference neutron fields for study and/or intercomparison
2. demonstrated absolute fission and nonfission reaction-rate measurements with an accuracy of ±1 to ± 7% (1σ), depending on the reaction and environment
3. initial data testing to establish the similarity of the high-energy (>2-MeV) shape of two of the neutron fields [the Coupled Fast Reactivity Measurements Facility (CFRMF) and the Mol- ∑∑ secondary standard facility (∑∑)] to that of the ²³⁵U thermal-fission spectrum, and the observation of serious discrepancies between measured and calculated spectra
4. initial data testing of ENDF/B-IV and other evaluated dosimetry cross sections and key fission product fast-fission yield values using newly developed CFRMF and ∑∑ integral data.

Comparisons are made of CFRMF and ∑∑ results with those reported previously for GODIVA and the ²³⁵U fission spectrum. Fission yield results are considered, based on measurements in the high-intensity environment of EBR-II. These results are coupled with those from CFRMF, ∑∑, and other neutron fields to more clearly define and document existing uncertainties associated with reaction-rate, fuel burnup, and flux-spectral-fluence determinations in fast reactors.