Flux and Fluence Determination Using the Material Scrapings Approach

The conventional approach to flux determination is to use high-purity dosimeters to characterize the neutron field. An alternative approach referred to as the material scrapings method is presented. Steel scrapings are cut from an in-service component and this material is used to measure the specific activity for various reactions. This approach enables the determination of the neutron flux and fluence incident on any component for which small chips of material can be safely obtained. The scrapings methodology was benchmarked by comparison with the results obtained using conventional dosimetry data from the San Onofre Nuclear Generation Station Unit 2. Pseudo fast fluxes (E 1.0 and 0.1 MeV) are cal culated by combining the surveillance capsule dosimetry measured activities with the corresponding effective cross sections. The effective cross sections for the reactions of interest are calculated using the analytically determined neutron spectrum at the surveillance capsule position. After the evaluation and testing of the surveillance capsule were completed, scrapings were taken from a broken Charpy specimen. The pseudo fluxes for the ⁵⁴Fe(n,p)⁵⁴Mn and ⁵⁸Ni(n,p)⁵⁸Co reactions were calculated using the same cross sections as those used for the capsule dosimetry analysis. The pseudo fluxes determined using the scrapings dosimetry are within 5% of the corresponding surveillance capsule pseudo fluxes.