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Basis for criticality incident detection coverage for a typical MTR-type fuel elements fabrication plant

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  • arn argentina
  • deteccion
  • incidentes
  • elementos combustibles







ARN (Argentina)


Cruzate, J.A


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The bases for the design, and nuclear criticality evaluation, of a typical facility for the

manufacturing of fuel elements for material testing reactor (MTR) are given. A general-purpose process is presented, which starts with metallic uranium hexafluoride, and ends with the assembling of the final fuel element. Well-known international guides were used for establishing the main process parameters, including some important geometric dimensions. The feasible design basis accidents were identified by analysing the defined representative process. The more probable accidents were found to happen during the chemical stage of the process. The criticality of the accidents were analysed, and the total number of fissions for these accidents were estimated using a simplified formula based on an improved heat energy method. As the assumed accidents take place in moderated media, the radiation spectra for neutrons and photons arising from thermal fission of 235U were estimated in order to assess the doses received by workers. The whole facility was simulated, with the estimated primary radiation source placed at assumed accidents locations, and a dose mapping was made covering the entire facility. All the calculations were made by using the MCNP6.1 Monte Carlo code, adopting cross sections from the ENDF/B-VII.1 nuclear data. The obtained dose mapping was used to define the composition and dimensions of walls and doors within the facility. On the other hand, according to ISO 7753 International Standard, a criticality accident alarm system (CAAS) is not required in areas where the maximum foreseeable accidental dose in free air will not exceed 0.12 Gy. Then, the obtained mapping may be used as an aid for determining the zones of the facility to be covered by CAAS, for stating the evacuation zone boundary and the evacuation routes, and to design the emergency plan. Moreover, this methodology may be adapted for deciding the feasible locations for criticality alarms. International Conference on Nuclear Criticality Safety ICNC2015. Charlotte, EE. UU., 13 al 17 de setiembre de 2015