Question 17.5: Suppose that a thermal water reactor is fueled with U-235. A......

Introduction to Nuclear Reactor Physics [1368692]

Suppose that a thermal water reactor is fueled with U-235. Assuming the neutron energy spectrum is Maxwellian, how much do you expect the reactivity to decrease when the average temperature of the fuel is raised from 1000°C to 1200°C? What is the expected reactivity change in this reactor in dollars and cents?

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According to our previous discussion, the temperature coefficient for U-235 is $α_T(η) = −3.0 × 10^{−5}$ per °K. Therefore, raising the fuel temperature by 200°C lowers the reactivity by 200 × −3.0 × $10^{−5}$ = −0.006 = −600 pcm. In dollars and cents, this is a reactivity change of Δρ = −0.006/β = −0.006/0.0065 ≈ −92 cents.

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