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AbstractEvaluating atmospheric dispersion and radiological doses in the vicinity of buildings is required for small modular reactors (SMRs) because of the reduced size of their exclusion area boundary. The current Canadian nuclear industry tool for these calculations implements the methodology defined in CSA Standard N288.2-M91, which was written to support large Canada Deuterium Uranium (CANDU) nuclear reactors as opposed to SMRs. The ORCA (On/offsite Radiological Consequences of Accidents) code has been developed to address this technical concern in addition to evaluating atmospheric dispersion and doses in the far field. The code calculates worker and public doses following an airborne release of radioactive material into the atmosphere under postulated accident conditions at a nuclear facility. The current paper presents the key assumptions and methods utilized in ORCA and discusses qualification of the software to the requirements of CSA Standard N286.7-16. The new model is applicable to SMRs and existing reactor designs and reduces conservatisms in the near field (i.e., <1 km from the source) relative to the methods in CSA N288.2-M91. [ABSTRACT FROM AUTHOR]

In an effort to help policy makers and manufacturers understand the impact of parameter uncertainties on UV reactor performance, a numerical bioassay model was developed by integrating a UV reactor model based on computational fluid dynamics with a Monte Carlo model developed to account for parameter uncertainty. For the model implemented, it was determined that reactor performance uncertainty was less than 6%. The integrated model was used to evaluate several checkpoint bioassay criteria including one currently used by the California Department of Public Health. The model showed that these criteria failed to take into account the fact that in an ideal case, a full scale reactor will pass a single checkpoint test 50% of the time. In reality, differences in equipment measurement errors between the system validation and checkpoint bioassay, and limitations of the power law form of the dose monitoring equation in accurately representing system validation data will result in poorer than expected performance. It was suggested that such checkpoint criteria be modified by crediting the inherent over-sizing of full scale reactors. [ABSTRACT FROM AUTHOR]