Can anyone clarify to me why when I use UO2 highest fuel enrichment of 4.88% that gets keff of 1.35 but I have to use the highest fuel enrichment of triso fuel which packing fraction at 0.4 and has U3Si2 as kernel (in FCM form) is 20.5 for reach keff of 1.30? This made me beyond the limit of nonproliferation.
The keff of fuel assembly is highly dependent on moderation, the UO2 with water moderation can get better keff then without water.
This is why light water reactor can use low-enriched UO2, but fast reactor (have no water in core) usually use 20% w/o UO2 or even higher.
usually you can trust the keff result from monte-carlo code.
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