Milestone Report: Grain growth and fission gas behaviour in doped UO2 M2MS-18LA0201034
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Univ. of Florida, Gainesville, FL (United States)
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Here, the microstructure of UO2 can be modified during nuclear fuel fabrication by using additives. Several dopants (e.g. Cr, Ti, V, Mg, Nb) are used to enhance grain growth and densification during sintering. In previous work, we used atomic scale simulation techniques to identify a common interstitial solution mechanism for a range of dopants that form positively charged de- fects at sintering temperatures. As a result, negatively/positively charged defect concentrations were enhanced/supressed relative to undoped fuel under the same conditions (temperature and oxygen partial pressure). Importantly U and fission gas migration is vacancy mediated, such that the increase in the concentration uranium vacancies (which have negative charge), due to doping, causes an increase in U and fission gas di ff usivity. This is important because U di ff usivity is the rate limiting step in mass transport during sintering and bulk fission gas dif- fusivity is the underlying property that governs fission gas release. In this work, we implement analytical expressions for uranium vacancy concentrations in doped fuel (based on atomic scale results) into mesoscale and engineering scale simulations of sintering and fission gas release. It is shown that densification is dramatically enhanced at 1850 K and 1950 K due to dopant solution and that Mn-doping has a greater e ff ect than the more widely used Cr-doping. The ef- fect of both dopants is strongly temperature dependent and is negligible below approximately 1800 K. The e ff ect of enlarged grain size and enhanced fission gas di ff usivity has been included in BISON. Fuel temperatures under normal operating conditions are not su ffi cient to activate the enhanced fission gas di ff usivity mechanism predicted by atomic scale calculations. There- fore, the benefits of enlarged grains for reduced fission gas release should not undermined by enhanced fission gas di ff usivity for doped UO2.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE Office of Nuclear Energy (NE)
- DOE Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1477619
- Report Number(s):
- LA-UR-18-29629
- Country of Publication:
- United States
- Language:
- English
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