Nuclear Fuel Cycle

Review Questions

Q1. Approximately how many different isotopes are formed as fission products?

(a) 20 (b) 50 (c) 200 (d) 1000

Answer: (c) — Approximately 200 isotopes of some 40 elements are produced by fission.

Q2. The bimodal fission yield curve has peaks at approximately which mass number ranges?

(a) 50—70 and 150—170 (b) 85—105 and 130—150 (c) 100—120 and 120—140 (d) 60—80 and 160—180

Answer: (b) — The bimodal yield curve has a light peak (~85—105) and a heavy peak (~130—150).

Q3. Which approximation should be used to calculate the activity of $^{131}$I ($T_{1/2}$ = 8 days) in a reactor that has been running for 6 months?

(a) Long-lived (linear) approximation (b) Full general equation with computer codes (c) Short-lived (equilibrium) approximation (d) None; $^{131}$I cannot be calculated by simple methods

Answer: (c) — 8 days is much less than 6 months, so equilibrium has been reached: $A = FY$.

Q4. What is the approximate number of fissions per second per watt of thermal power?

(a) $3.1 \times 10^{5}$ (b) $3.1 \times 10^{10}$ (c) $3.1 \times 10^{15}$ (d) $3.1 \times 10^{20}$

Answer: (b) — Each fission releases ~200 MeV; 1 W = $6.24 \times 10^{12}$ MeV/s.

Q5. A minimum depth of water above the fuel in a cooling pond is:

(a) 0.5 m (b) 1.0 m (c) 2.5 m (d) 10 m

Answer: (c) — At least 2.5 m of water above the fuel is needed for adequate shielding.

Q6. What voting logic is typically used for gamma monitors at a cooling pond?

(a) 1 out of 1 (b) 1 out of 2 (c) 2 out of 3 (d) 3 out of 5

Answer: (c) — 2/3 voting logic reduces spurious (false) alarms while maintaining safety.

Q7. At what dose rate should an evacuation alarm sound at a cooling pond?

(a) 1 mSv/h (b) 10 mSv/h (c) 100 mSv/h (d) 1 Sv/h

Answer: (c) — Local alarm at ~100 mGy/h; evacuation alarm at ~100 mSv/h.

Q8. A typical Magnox fuel flask has steel walls approximately how thick?

(a) 36 mm (b) 100 mm (c) 360 mm (d) 1000 mm

Answer: (c) — Magnox flask walls are 360 mm thick steel, providing shielding and structural integrity.

Q9. In the IAEA Type B(M) test, the flask must survive a fire at what temperature and for how long?

(a) 500 degrees C for 15 minutes (b) 800 degrees C for 30 minutes (c) 1000 degrees C for 60 minutes (d) 1200 degrees C for 10 minutes

Answer: (b) — IAEA Type B(M) fire test requirement.

Q10. Which of the following isotopes has an activity that increases after the reactor is shut down?

(a) $^{131}$I (b) $^{95}$Zr (c) $^{241}$Am (d) $^{137}$Cs

Answer: (c) — $^{241}$Am increases after shutdown because it is produced by the beta decay of $^{241}$Pu ($T_{1/2}$ = 14.3 y).