<p>The precise knowledge of the Fast Fission Ratio is of considerable importance in Reactor Physics due to its effect on the overall reactivity of a nuclear reactor. Calculations obtained with the codes WIMS and LATREP disagreed by as much as 3% with experiments performed in the Zed-II critical facility of the Chalk River Nuclear Laboratories. It was felt that this variation might be due to the coarsity of the energy mesh since the energy range where Uranium (238) fission occurs (.8 to 10 MeV) was covered by only a few energy groups.</p> <p>Two multigroup cross-section libraries having respectively 100 and 46 groups were therefore generated with SUPERTOG. Values for the Fast Fission Ratio were then calculated using first the one dimensional transport code ANISN and the Monte Carlo code MORSE. The 28 element fuel bundle geometry was used and the thermal fission was inputted to the codes as a fix source leaving to the codes the calculation of the activities in the upper groups of the multigroup structure (above 500 KeV). The cross-section data was obtained from the ENDF/B-IV library produced by the Brookhaven National Laboratory, U.S.A.</p> <p>It was found that the WIMS energy structure with six groups above 500 KeV offered a sufficiently small energy mesh. In ANISN both the order of the angular quadrature (SN) and of the Legendre approximation to the scattering cross-sections (PN) were investigated. It was found that as SN increases the Fast Fission Ratio distribution across the fuel bundle flattens, approaching the distribution measured experimentally in Zed-II, while as PN increases the overall value of the Fast Fission Ratio increases leaving the distribution relatively unaffected.</p> <p>Cases where the coolant has been received and replaced by air have also been investigated. This simulates what would be happening to the Fast Fission Ratio in the event of a total loss of coolant accident (LOCA). It was found that the Fast Fission Ratio would increase by about 15%. This represents a substantial positive contribution to the reactivity of the reactor.</p> <p>Geometry effects were also investigated using the code MORSE. In this code the full two-dimensional pin distribution of the fuel bundle could be represented as opposed to the one dimensional smeared annuli model which had to be used in ANISN. However, it was found that this did not improve the results since a 3% decrease was observed in the absolute value of the Fast Fission Ratio while its distribution became slightly steeper than what was measured experimentally.</p> <p>Two lattice pitches were also investigated, namely 24 and 28 em. It was found that the tighter pitch led to an increase in the Fast Fission Ratio of the order of 5% without significant effect on the distribution.</p> <p>The results obtained for the estimation of the Fast Fission Ratio with these Reactor Physics codes do not agree to better than 5% with the values determined experimentally. However, if one considers the experimental errors and the fact that the cross-sections are not known to better accuracies than a few percent, especially for Uranium (238) inelastic scattering, the results obtained are quite justifiable.</p> / Master of Engineering (ME)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/13244 |
| Date | 08 1900 |
| Creators | Archer, Paul Henri |
| Contributors | Garvey, Peter M., Engineering Physics |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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