Analysis of the NESDIP2 and NESDIP3 Radial Shield and Cavity Experiments.

摘要

Discrete ordinates calculations were made of a series of measurements performed using the NESTOR reactor at AEE Winfrith. These measurements are part of the NESDIP experimental program designed to benchmark methods and data commonly used in interpreting pressure vessel surveillance dosimetry placed at either in-vessel or ex-vessel locations. Results obtained using the LEPRICON procedures and updated ELXSIR cross sections indicate agreement to within about 10 percent with measured threshold dosimeter activities behind various components of a radial shield containing up to 25 cm of water and 24 cm of steel. Significant discrepancies in the energy range between 0.1 and 2 MeV were found to exist with measurements made on the centerline of a 29-cm-wide cavity and at vertical locations considerably above the centerline of a 21-cm-wide cavity, however. A logical explanation of the latter discrepancy is the failure of two independent two-dimensional calculations to properly treat the three-dimensional effects of vertical cavity streaming. No satisfactory explanation has yet surfaced for the first discrepancy, however, which is the more important of the two in possible affecting the interpretation of ex-vessel, low threshold dosimetry.