Fission Product Yield Data for the Transmutation of Minor Actinide ...

FOREWORD
A report issued by an international study group for the transmutation of nuclear waste using accelerator
driven systems has highlighted the need for specific sets of nuclear data. These authoritative requirements
include fission product yields at an intermediate incident neutron energy of up to 150 MeV.
Before the start of the present CRP on fission product yield data for the transmutation of nuclear waste,
only four types of evaluated fission yield data sets existed, namely for spontaneous fission, and for fission
induced by thermal, fast (or fission) spectrum, and by ‘high energy’ (14–15 MeV) neutrons. A new type of
evaluation for energy dependent neutron induced fission yields was required for this project. In view of the
scarcity of experimental data, such an evaluation has to be based on systematics and theoretical model calculations.
Unlike fission cross-sections, where nuclear models are being used successfully for the calculation of
unmeasured cross-section ranges, such models or theories existed only for low energy fission yields. Hence the
CRP participants entered a completely new field of research for which the progress and outcome were unpredictable.
Clearly the ultimate goal of such an effort, namely an evaluation of energy dependent fission yields,
could not be realized within the perceived lifetime of a CRP.
The main emphasis of the CRP was on the development of adequate systematics and models for the
calculation of energy dependent fission yields up to 150 MeV incident neutron energy. Several problems had to
be solved, such as the correct choice of model parameters and multiplicity distributions of emitted neutrons, and
the effect of multi-chance fission. Models and systematics have been tested for lower energy yields, but they
failed to reproduce recent experimental data, particularly at higher energies, and the parameters had to be
modified. Other models have been developed from the analysis of experimental data in order to derive
systematic dependences and they were adapted in the course of the CRP to predict fission product yields. The
valuable role of the CRP in such work became evident during the meetings, at which the discussions formed a
fruitful basis for improvements to the models. The benchmark exercise revealed the true worth and predictive
capabilities of the systematics and theoretical models developed during the course of the CRP. Necessary
improvements and the direction of future studies were also revealed. These models have the potential to give
reliable predictions after implementation of the improvements suggested in this report.
A brief introduction and the various studies undertaken by individual participants are given at the
beginning of this publication, followed by a detailed description of the resulting overall achievements,
conclusions and recommendations of the CRP and a summary of the benchmark exercise and results. Additional
material is included on the enclosed CD-ROM, including compilations of the fission product yields, unedited
papers and all details of the benchmark exercise.
The IAEA wishes to thank all CRP participants for their contributions to the project. The IAEA
responsible officers were M. Lammer and A.L. Nichols of the Division of Physical and Chemical Sciences.