Theoretical Model for Volume Fraction of UC, 235U Enrichment, and Effective Density of Final U 10Mo Alloy

Abstract

The purpose of this document is to provide a theoretical framework for (1) estimating uranium carbide (UC) volume fraction in a final alloy of uranium with 10 weight percent molybdenum (U-10Mo) as a function of final alloy carbon concentration, (2) estimating effective 235 U enrichment in the U-10Mo matrix after accounting for loss of 235 U in forming UC and (3) calculating effective density of as-cast U-10Mo alloy with varying enrichment. Therefore, this report will serve as the baseline for quality control of final alloy carbon content and 235 U enrichment. v Acronyms and Abbreviations C carbon FA final alloy HEU highly enriched uranium LEU low-enriched uranium Mo molybdenum PNNL Pacific Northwest National Laboratory SEM scanning electron microscopy U uranium U-10Mo uranium alloyed with 10 weight percent molybdenum UC uranium carbide UMo body-centered cubic γ-UMo 235 U Enrichment

Effect of Silicon in U-10Mo Alloy

“…Volume, mass, and density were calculated using Equations 11-13, below: The two densities calculated for Case 1 and Case 2 are 13.44 g/cm 3 and 13.60 g/cm 3 , respectively. The density of 235 UC was estimated to be 13.4394 g/cm 3 in Devaraj et al (2016a), which is consistent with calculations reported here.…”

“…UMo matrix density varies with Si concentration from 17.283 to 17.288 g/cm 3 for Case 1, and 17.275to 17.284 g/cm 3 for Case 2. It is noted here that the effective density of the γ-UMo matrix with 19.75 wt% 235 U was previously calculated to be 17.33 g/cm 3 (constant) as is detailed in Devaraj et al (2016a). The UMo matrix density calculated in this report is generally in agreement with that which was previously calculated; however, in this work, we account for variation of the matrix density with 235 U enrichment, which is the reason for the small variation in calculated density values between the 2016 report and this work.…”

“…As previously reported in Devaraj et al (2016a), the fuel specification nominally requires a 19.75 wt% enrichment of 235 U in the FA, the bulk of which comes from the HEU feedstock. The UC and U2Si2MoC phases may be present in the HEU feedstock, or they could be formed during the melting and casting stages in the UMo alloy preparation.…”

“…The UMo matrix density varies with 235 U enrichment; thus, because of Assumption 6, the matrix density varies as a function of Si concentration. UMo matrix density is not assumed to be constant, as was previously assumed in Devaraj et al (2016a).…”

“…Prior work presented in Devaraj et al (2016a) determined the effect of carbon concentration on the density of the final formed fuel. In this 2016 report, it was hypothesized that 235 U could either remain in the γ-UMo matrix or form UC, thereby affecting final fuel microstructure, properties, and performance.…”