New Practice for Standard Practice for Destructive Analysis Sample Preparation of TRISO Particles Using Crush/Burn/Leach
1. Scope
1.1 This practice covers the preparation of uranium-bearing TRISO fuel particles samples for the determination of total uranium content. The procedure describes the controlled burn-back of pyrocarbon coating layers, mechanical comminition of the residual silicon carbide (SiC)-coated particles, oxidation of uranium to U3O8, and nitric acid dissolution of the uranium oxide residue.
1.2 The resulting nitric acid leachate is suitable for uranium assay by the Davies and Gray titration method or by Isotope Dilution Mass Spectrometry (IDMS).
1.3 This practice includes an activity-based verification measurement to confirm that at least 99.9% of the uranium contained in the original particle sample has been recovered and dissolved.
1.4 This practice has been validated for TRISO particle sample masses ranging from 1 gram to 3 grams.
1.5 This practice may be used to support compliance with nuclear fuel specifications for TRISO-coated particle fuel by providing a reproducible method for quantitative uranium recovery and assay sample preparation.
1.6 This practice can be used to determine the average uranium loading of fuel particles given that the mean average weight per particle is known.
Keywords
kernel; particle fuel
Rationale
This practice can be used to prepare TRISO particle samples prior to uranium assay analysis by Davies and Gray titration or Isotope Dilution Mass Spectrometry. The accuracy of the uranium assay analysis is dependent on the recovery and dissolution of the uranium contained in the residue of the burned-back and milled particles. The practice described herein ensures that a minimum of 99.9% of the uranium contained in the fuel particles is recovered by checking that the activity of the remaining residue is less than that measured for a sample of particles in the same geometry, where the number of particles is approximately 0.1% of the total number of particles analyzed.
