PWR heat, materials, and feedback

01 / Choose one

Why is the primary water in a PWR kept at high pressure?

1. To make all primary water turn into steam
2. To keep the bulk coolant liquid at a higher temperature
3. To keep the primary and secondary water at the same pressure

B. Pressure raises the boiling temperature. The primary water transfers heat across steam-generator tubes to a separate secondary system.

02 / Choose one

Which statement correctly separates nucleate boiling from departure from nucleate boiling?

1. Every bubble means cooling has already failed
2. Steam conductivity alone determines all boiling heat transfer
3. Nucleate boiling can improve heat transfer; departure from it can sharply degrade surface cooling

C. A boiling regime matters. Latent heat and bubble motion can assist heat transfer; a vapor-covered surface can transfer heat much less effectively.

03 / Calculate · kW

An ideal solid path has k = 400 W/(m·K), A = 1 m², L = 1 m, and ΔT = 100 K. What heat rate does Q̇ = kAΔT/L predict, in kW?

400 × 1 × 100 ÷ 1 = 40,000 W = 40 kW.

04 / Calculate · m²

Keep k = 400 W/(m·K), L = 1 m, and ΔT = 100 K. What cross-section would the ideal conduction model require to carry 100 MW?

100 MW = 100,000 kW. Area = 100,000 ÷ 40 = 2,500 m². This is an ideal arithmetic comparison, not a reactor design.

05 / Choose one

The pellet model runs cooler when conductivity increases. What does that establish about the Doppler coefficient of a different fuel?

1. Nothing by itself: the model has no neutronics calculation
2. It proves that all negative feedback disappears
3. It proves that conductivity alone determines the coefficient

A. It calculates a temperature profile under fixed assumptions. A different fuel’s reactivity response requires neutron-physics and material information, not conductivity alone.

06 / Choose one

Two generated power fields have the same whole-volume mean. What can still differ?

1. Nothing; equal averages require identical local values
2. Their local peaks and where those peaks occur
3. Their total power must differ if either has a peak

B. Redistribution can change local peaks while preserving the total. The teaching model deliberately holds its whole-volume mean at 1.

07 / Choose one

A component operates at nearly steady temperature. Which conclusion follows?

1. Irradiation embrittlement cannot accumulate
2. Every component has the same lifetime limit
3. Some thermal cycling is reduced, but irradiation damage and other stresses can still matter

C. Steady temperature does not stop neutron exposure, remove every gradient, or describe every transient. A specific component and history are needed.

08 / Reflection

Someone proposes replacing water with a more conductive coolant. What would you ask before calling it an improvement?

Compare heat transport at stated conditions, neutron moderation and absorption, chemical compatibility, pressure and circulation needs, freezing or boiling behavior, material aging, shutdown heat removal, and the complete heat sink.

• Distinguishes conductivity from convective or phase-change heat transport
• Considers moderation and neutron absorption
• Names chemical or materials compatibility
• Includes operating conditions and an eventual heat sink
• Identifies information still needed rather than declaring a universal winner