Abstract
The objective of this study was to evaluate accident-tolerant fuel (ATF) concepts being considered for CANDU reactors. Several concepts, including uranium dioxide/silicon carbide (UO2-SiC) composite fuel, dense fuels, microencapsulated fuels, and ATF cladding, were modelled in Serpent 2 to obtain reactor physics parameters, including important feedback parameters such as coolant void reactivity and fuel temperature coefficient. In addition, fuel heat transfer was modelled, and a simple accident model was tested on several ATF cases to compare with UO2. Overall, several concepts would require enrichment of uranium to avoid significant burnup penalties, particularly uranium-molybdenum (U-Mo) and fully ceramic microencapsulated (FCM) fuels. In addition, none of the fuel types have a significant advantage over UO2 in terms of overall accident response or coping time, though U-9Mo fuel melts significantly sooner due to its low melting point. Instead, the different ATF concepts appear to have more modest advantages, such as reduced fission product release upon cladding failure, or reduced hydrogen generation, though a proper risk assessment would be required to determine the magnitude of these advantages to weigh against economic disadvantages. The use of uranium nitride (UN) enriched in N15 would increase exit burnup for natural uranium, providing a possible economic advantage depending on fuel manufacturing costs.
Highlights
While there are many studies evaluating the performance of accident-tolerant fuels (ATF) in light water reactors (LWRs), there are comparatively few studies which look at the use of ATF in CANDU reactors
While thermal hydraulics were not modelled for this study, heat transfer from the fuel is a key consideration for accidenttolerant fuel and has a significant effect on the reactor physics; simple heat transfer models were constructed in order to calculate fuel temperatures for each case
The fuels evaluated in this study were as follows: (i) UO2/SiC composite fuel (ii) Uranium nitride fuel (iii) uranium nitride (UN)/U3Si2 composite fuel (iv) UN fuel mixed with zirconium nitride (as (U, Zr)N
Summary
While there are many studies evaluating the performance of accident-tolerant fuels (ATF) in light water reactors (LWRs), there are comparatively few studies which look at the use of ATF in CANDU reactors. As there are significant differences between LWRs and CANDU reactors in terms of reactor and fuel design, ATF should be evaluated for CANDU reactors in order to determine their viability for future use in CANDU reactors. This study in particular focused primarily on reactor physics, using Serpent 2 to evaluate the CANDU fuel lattice behaviour for different ATF loadings. While thermal hydraulics were not modelled for this study, heat transfer from the fuel is a key consideration for accidenttolerant fuel and has a significant effect on the reactor physics; simple heat transfer models were constructed in order to calculate fuel temperatures for each case.
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