Holooly Plus Logo
Holooly Plus Logo

Question 17.8: A thermal water reactor fueled with pure U-235 has an effect......

A thermal water reactor fueled with pure U-235 has an effective multiplication factor of 1.0 when the fuel temperature reaches 300°C. When is the effective multiplication factor of the core when the average fuel temperature reaches 1000°C?

Step-by-Step
The 'Blue Check Mark' means that this solution was answered by an expert.
Learn more on how do we answer questions.
Report Answer

Since the effective multiplication factor of the core is given by K = νΣ_f ϕ ∕ Σ_aϕ, we can estimate how the effective multiplication factor changes with temperature by considering how the value of G_{f/a} (see Equation 17.66) changes with temperature. At a temperature of 300°C, the value of G_{f/a} is 0.9920, and at a temperature of 1000°C, the value of G_{f/a} is 0.9822. If the effective multiplication factor is 1.0 at a temperature of 300°C, and the thermal flux is Maxwellian, the value of K when the fuel reaches a temperature of 1000°C is 1.0 × (0.9822/0.9920) = 0.99

Δρ = α_FΔT                (17.66)

Related Answered Questions

Question: 17.9

In the previous example, how much additional reactivity has to be added to the core by withdrawing the control rods to keep the core critical when the average fuel temperature rises from 300°C to 1000°C? What is the value of this additional reactivity in pcm and in dollars and cents? ...

Verified Answer:

In Example Problem 17.8, the initial reactivity of...
Question: 17.4

If the value of αF at a temperature of T is known to be −2.0 × 10^−5 per °K, what is the value of αF at a temperature of 4T? ...

Verified Answer:

Since α_{\mathrm{F}}=\frac{{C}}{\sqrt{T}\ln...
Question: 17.7

The average temperature of the fuel in a TRIGA reactor immediately increases by 300°C after a control rod is withdrawn from the core. If the reactor is exactly critical at the time the rod is withdrawn (ρ = 0), how much negative reactivity is introduced into the core through the process of ...

Verified Answer:

Earlier in the chapter, we mentioned that the fuel...
Question: 17.6

If the average values for αM(T), αF(T), and αS(T) (where “s” refers to the structure) are −0.5 × 10^–5 per °C, −3.0 × 10^−5 per °C, and −0.1 × 10^−5 per °C, for a reactor that is just starting up, what is the total temperature coefficient for the core? Assume the core is 25% fuel, 25% structure, ...

Verified Answer:

We need to apply the relationship Δρ = α_TΔ...
Question: 17.5

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 ...

Verified Answer:

According to our previous discussion, the temperat...
Question: 17.3

Suppose that a thermal water reactor has a fuel temperature coefficient of –1 cent/°C, a moderator temperature coefficient of −0.5 cents/°C, and a leakage temperature coefficient of −0.1 cents/°C. If the temperature of all three materials is suddenly increased by 100°C, how much does the reactivity ...

Verified Answer:

The total change in the reactivity is given by [la...
Question: 17.2

Suppose that a thermal water reactor is fueled with Plutonium-239 instead of Uranium-235, that the thermal utilization of the fuel is 0.90, and that the average neutron flux is 3 × 10^14 neutrons/cm²/s. If one-third of the neutrons in the reactor are thermal neutrons, how much of the Pu-239 will be ...

Verified Answer:

From Appendix C, we know that the thermal fission ...
Question: 17.1

Suppose that a fuel assembly in a thermal water reactor contains 50 lb (18.7 kg) of Uranium-235 when it is first started up and that the enrichment of the fuel at start-up is 4%. If the remaining fuel is Uranium-238, and the reactor operates at an average flux of 2 × 10¹³ neutrons/cm²/s for 400 ...

Verified Answer:

Since the fuel contains 50 lb of Uranium-235, it m...