Abstract
Nuclear power plant radiation protection design features are based on radionuclide source terms derived from conservative assumptions that envelope expected operating experience. Two parameters that significantly affect the radionuclide concentrations in the source term are failed fuel fraction and effective fission product appearance rate coefficients. Failed fuel fraction may be a regulatory based assumption such as in the U.S. Appearance rate coefficients are not specified in regulatory requirements, but have been referenced to experimental data that is over 50 years old. No doubt the source terms are conservative as demonstrated by operating experience that has included failed fuel, but it may be too conservative leading to over-designed shielding for normal operations as an example. Design basis source term methodologies for normal operations had not advanced until EPRI published in 2015 an updated ANSI/ANS 18.1 source term basis document. Our paper revisits the fission product appearance rate coefficients as applied in the derivation source terms following the original U.S. NRC NUREG-0017 methodology. New coefficients have been calculated based on recent EPRI results which demonstrate the conservatism in nuclear power plant shielding design.
Highlights
Nuclear power plant (NPP) occupational doses are maintained ALARA by both design and operating practices
NPPs are designed with radiation protection requirements that reflect the ICRP three fundamental principles of radiation protection [1]: x Justification, x Optimization of Protection, and x Application of Dose Limits Optimization is an important part in establishing design requirements for NPP radiation protection features
Reactor coolant system (RCS) source terms used for shielding calculations are derived by applying a failed fuel fraction and effective appearance rate coefficients
Summary
Nuclear power plant (NPP) occupational doses are maintained ALARA by both design and operating practices. Two variables that are important are failed fuel fraction and fission product appearance rate coefficients. These two input variables significantly affect the radionuclide concentrations in the source term. It should be pointed out that failed fuel fraction assumption and fission product appearance rate coefficients are applied in calculating initial source term for radiological consequences from design basis accidents. Another application is in the design of radioactive effluent processing systems. Other design applications may benefit from an updated appearance rate coefficients
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