Gas releases and rod internal pressure of BN-added UO₂fuel

Abstract

Gadolinium (Gd), in the form of gadolinia (Gd 2 O 3 ), has been used as integral burnable absorber to UO 2 fuel by different companies. Recently, alternative burnable absorber materials are under investigation. In this paper, the results of the study on the use of boron mixed in UO 2 as an integral burnable absorber are presented. Boron nitride was selected as the form of B to be added to UO 2 fuel based on the stability of B during sintering. Fuel performance analysis code FRAPCON-UNI, which is based on FRAPCON code and has the modifications for boron and helium generation and gasses release models, was used for the calculation of fuel performance. Helium generation was calculated using a model and the result was verified against ORIGEN calculation results. Gas release calculation was based on Forsberg Massih model and different characteristics of the gasses were considered. Power histories of maximum burnup rods (B rod, no B rod, and Gd rod) were selected from reactor physics data. The results indicated significant increases in rod internal pressure by 500 ppm boron addition at the end of life with minimum influence of a grain boundary boron fraction due to high diffusivity of helium and nitrogen.

Fission Gas Behaviors and Relevant Phenomena in Different Nuclear Fuels: A Review of Models and Experiments

“…The release of fission gas increases with the amount of gas in the cavity on the basis of the original amount of gas (Hales et al, 2016). Jeong et al (2015) studied the UO 2 fuel mixed with boron, considering the boron's stability when fuel sinters and being able to be used as an integral burnable absorber, using fuel performance code FRAPCON-UNI. The result shows that increased gap pressure makes the GB gas release difficult by lifting the saturated limitation, and the gas release is retarded (Notley et al, 1980;Paraschiv et al, 1997;Karahan et al, 2009;Miao et al, 2018).…”

“…Due to their high diffusivities, the helium and nitrogen releases are merely affected by the various resolution parameters. The rod internal pressure with burnup at the end of life is summarized in Supplementary Table S5 (Jeong et al, 2015).…”