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Fission product yield evaluation

Mills, Robert William (1995)
Ph.D. thesis, University of Birmingham.

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A new evaluation has been made of the independent and cumulative yields of fission products for a selection of fissioning systems, including fission of nuclides important for reactor design and operation, and for fuel and waste management. The evaluation, which has been given the reference name UKFY3, used a new database of measurements and is considered complete up to early 1993. This database considerably extends and updates the database used for the previous UKFY2 evaluation.

The measurement database was analysed to produce a “best estimate” set of fission product yields. Careful study has been made of experimental uncertainties and discrepancies in the data. As some discrepancies could not be resolved the normalised residual technique was used to down-weight discrepant values. Relative and ratio-of-ratio measurements were included in the analysis by an iterative procedure. The measured data, results of the analysis and discrepancies in the data are shown in extensive tables included as appendices to this thesis.

The “best estimates” of fission product yields generated by the analysis were then studied to improve the understanding of the systematics of the yield distribution in mass, charge and isomeric state. Models describing these distributions were investigated and fitted. The effects of the fissioning nucleus mass and charge were examined, as well as the effect of neutron energy on the distributions from neutron-induced fission.

The results of these studies were then combined with the “best estimates” to generate complete independent and cumulative yields sets for a list of fissioning systems considered important for applications. This set consists of the neutron-induced fission of 232Th, 233,234,235,236,238U, 237,238Np, 238,239,240,241,242Pu, 241,242m,243Am, and 243,244,245Cm, plus the spontaneous fission of 242,244Cm and 252Cf. These complete yield sets were subsequently adjusted to fit the physical constraints of the fissioning process. The new adjusted library produced by the analysis of the UKFY3 database, provisionally called UKFY3.0 has been produced as a computer file in the ENDF-6 format.

The new UKFY3.0 file and the UKFY2 file, which has been revised for use in JEF2.2 during this work, were then tested against integral experimental results for delayed neutron and decay heat production respectively.

Finally, results of this work are summarized, remaining problems discussed and areas for future work high-lighted.

Type of Work:Ph.D. thesis.
School/Faculty:Faculties (to 1997) > Faculty of Science
Department:School of Physics and Space Research
Subjects:Q Science (General)
QC Physics
Institution:University of Birmingham
ID Code:4353
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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