Thesis (Ph. D.)--University of New South Wales, 2000. / "Submitted as part of the requirement for the degree of Doctor of Philosophy, School of Safety Science, University of New South Wales, March 2000." Includes bibliographical references. Also available online.

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Reproduction de : Thèse de doctorat : Physique Nucléaire : Lyon 1 : 2002. / Titre provenant de l'écran titre. 81 réf. bibliogr.

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Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 247-251).

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Simultaneous measurements of the angular distribution, mass distribution and average total kinetic energy of fission fragments produced by the neutron-induced fission of 235U and 232Th have been made using a gridded ionisation chamber. The neutron energy range used was thermal to 1.9 MeV for 235U and 1.4 to 1.7 MeV for 232Th. The following topics were investigated: the interdependence of the fission fragment angular and mass distribution; the anomalous behaviour of fragment anisotropy for 235U(n,f) at neutron energies En below 150 keV; the possible existence of a third symmetric mass peak for 232Th(n,f); the mass fine structure in 235U(n,f) and 232Th(n,f); and the dependence of the fission fragment average total kinetic energy on the excitation energy of the fissioning nucleus. For this study, mono-energetic neutrons were produced by the and reactions. Four signals produced by the fission chamber were fed into a data acquisition system and processed by a specially modified comprehensive computer program. The results indicate that there is no interdependence between the angular and mass distributions of fragments for 235U(n,f) and for 232Th(n,f). The angular distribution of 235U fission fragments showed an anisotropy of less than one for En below 150 keV. For 232Th, the expected minimum in the anisotropy near En = 1.6 MeV was confirmed. No evidence for a third peak in the mass symmetry region of 232Th(n,f) was observed, within the yield sensitivity limitation of the chamber. Fine structure was observed in the mass yield distributions for 235U(n,f) and 232Th(n,f) at mass locations predicted by theory. The fission fragment average total kinetic energy for 235U(n,f) and 232Th(n,f) showed no significant dependence on the excitation energy of the fissioning nucleus. Possible reasons for some of these results are advanced.

This dissertation entails the calculation of the release of gaseous fission products and iodine from the Pebble Bed modular reactor (PBMR) 400MW core under a Depressurised Loss of Forced Coolant (DLOFC), where the temperature history of fuel sphere is taken into account. The release is calculated by developing a computer code (REALESE) based on a simple coated particle failure and a gas diffusion model. The computer code calculates failure fraction, kernel release fraction, layer release, Iodine decay correction, core release fraction and other parameters pertaining to a PBMR. This source code is developed in the FORTRAN 77 programming language on a Compaq Virtual FORTRAN Development Platform. Verification of the results is done in Mathcad and the Getter code. RELEASE calculations compare very well with the MathCAD calculations with deviation from 0-5%. The effects of a number of parameters on fission product release are investigated by means of sensitivity analysis involving parameters like temperature, failure fraction and diffusion coefficient. Sensitivity analysis showed that the variation of failure fraction has the greatest effect on release fission products in a PMBR. The RELEASE results are compared with GETTER calculations in addition to the MathCAD verification. RELEASE calculations showed an expected value of 2.00x10 12 Bq whereas GETTER calculations produced an expected value of 2.13x10 12 Bq, representing a percentage deviation of 6%. / Thesis (MSc. ARST) North-West University, Mafikeng campus, 2003