Certification Report: Preparation and Certification of Large-Size Dried (LSD) Spike: IRMM-1027u

Abstract

Large-Sized Dried (LSD) spikes are used as a fundamental part of the fissile material control of irradiated nuclear fuel and have been provided on a regular basis to safeguards authorities and industry for more than 15 years. This report describes the preparation and certification of a new batch of LSD spikes. IRMM-1027u is a dried nitrate material in cellulose acetate butyrate with dioctyl phtalate (CAB/DOP) or carboxymethyl cellulose (CMC), certified for the mass of uranium and plutonium and the uranium and plutonium isotope amount ratios per unit. The material was produced in compliance with ISO/IEC 17034:2016 [ ] and certified in accordance with ISO Guide 35:2017. The certified reference materials uranium metal EC NRM 101, enriched uranium metal NBL PO CRM 116-A and plutonium metal CETAMA MP2 were used as starting materials to prepare the mother solution. This solution was dispensed into individual vials by means of an automated robot system and it was dried. A solution of an organic substance either cellulose acetate butyrate with dioctyl phtalate (CAB/DOP) or carboxymethyl cellulose (CMC) was added to the spike material and then the solution was evaporated. The organic matrix serves as a stabiliser to retain the dried nuclear material at the bottom of the vial. In total, 1003 units were produced. Between-unit homogeneity was quantified and stability during dispatch and storage were assessed in accordance with ISO Guide 35:2017. The certified values were obtained from the gravimetric preparation of the mother solution, taking into account the mass, purity and isotopic composition of the starting materials, the mass of the mother solution, and the mass of an aliquot in each individual unit. The certified values were confirmed by isotope dilution mass spectrometry (IDMS) and thermal ionisation mass spectrometry (TIMS) as independent methods on randomly selected units of IRMM-1027u. Uncertainties of the certified values were estimated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM) [ ] and include uncertainties related to possible inhomogeneity and to characterisation. The main purpose of this material is for use as a spike isotopic reference material to measure the plutonium and uranium amount content of spent nuclear fuel solutions using IDMS. Each unit contains about 55 mg of uranium with a relative mass fraction m(235U)/m(U) of 18.9 % and 1.8 mg of plutonium with a relative mass fraction m(239Pu)/m(Pu) of 97.8 % as dried nitrates in CAB/DOP or CMC. The whole amount of sample per unit has to be used for analysis.