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Nuclear and particle physics

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Question 6

In a nuclear reactor, the fission of a plutonium-239 nucleus (94239Pu^{239}_{94}\text{Pu}94239​Pu) can be triggered by a slow-moving neutron.

a.

Explain the role of a moderator in sustaining a chain reaction in a thermal nuclear reactor, and describe how control rods are used to regulate the power output.

[4]
b.

The energy released in each fission reaction of plutonium-239 is equivalent to a decrease in mass of 0.23 u0.23\text{ u}0.23 u. A fuel pellet in a MOX (mixed oxide) fuel assembly contains 5.6%5.6\%5.6% of plutonium-239 by mass.

Estimate the total energy produced from the fission of all the plutonium-239 in a 0.85 kg0.85\text{ kg}0.85 kg fuel pellet.

Give your answer to an appropriate number of significant figures.

Data:

  • molar mass of plutonium-239 = 0.239 kg mol−10.239\text{ kg mol}^{-1}0.239 kg mol−1
  • 1 u=1.66×10−27 kg1\text{ u} = 1.66 \times 10^{-27}\text{ kg}1 u=1.66×10−27 kg
  • Avogadro constant NA=6.02×1023 mol−1N_A = 6.02 \times 10^{23}\text{ mol}^{-1}NA​=6.02×1023 mol−1
  • speed of light in vacuum c=3.00×108 m s−1c = 3.00 \times 10^8\text{ m s}^{-1}c=3.00×108 m s−1
[7]

Nuclear and particle physics Questions

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