Application of the LEPRICON Unfolding Procedure to the Arkansas Nuclear One-Unit 1 Reactor

The development and demonstration of a new unfolding procedure involving pressure vessel surveillance dosimetry in pressurized water reactors are described. The complete methodology is contained in the LEPRICON code system, and provides techniques for calculating pressure vessel fluences and then adjusting them, with reduced uncertainties, on the basis of surveillance dosimetry measurements and a benchmark data base. An application of these techniques to an existing on-line commercial reactor is presented. Results indicate that the best estimate of the pressure vessel lifetime based on a limiting fluence above 1 MeV of 2 × 10¹⁹ n/cm² is ∼129 ± 11 effective full-power years, whereas the unadjusted estimate has an uncertainty twice as large.