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Question 4.11: A reactor designer decides to replace uranium with UO2 fuel ......

A reactor designer decides to replace uranium with UO_2 fuel in a water cooled reactor, keeping the enrichment, fuel diameter and water to fuel volume ratios the same.

a. Will p increase, decrease or remain unchanged? Why?
b Will ƒ increase, decrease or remain unchanged? Why?
c. Will η_T increase, decrease or remain unchanged? Why?

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Part a; As indicated by Table 4.3 the resonance integral increases when replacing U with UO_2. This effect is magnified by the lower density of UO_2.

Part b. The thermal utilization may decrease slightly as a result of the lower density of UO_2. The thermal absorption cross section of oxygen is so small that it has little effect.

Part c. Since the thermal absorption cross section of oxygen is so small it causes only a very slight decrease in η_T. The decrease in density cancels out of the definition of η_T.

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