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Nuclear Fission

Q11.

(a)

(i) Complete the equation below which represents the induced fission of a nucleus of uranium-235.

+ + +

Proton number balance: 92 + 0 = 38 + 54

Nucleon number balance: 235 + 1 = 98 + 135 + N

N = 236 - 233 = 3

(ii) The graph below shows the binding energy per nucleon plotted against nucleon number A.

 

Mark on the graph the position of each of the three nuclei in the equation.

three correct positions on x-axis (one mark if two correct)

(iii) Hence determine the energy released in the fission process represented by the equation.

binding energy of U-235 nucleus = 235 × 7.5 = 1763 MeV

binding energy of Sr-98 = 98 × 8.6 = 843 MeV

binding energy of Xe-135 = 135 × 8.3 = 1121 MeV

binding energy released = 1121 + 843 – 1763 = 201 MeV (±30MeV)

(6 marks)

(b)

(i) Use your answer to part (a)(iii) to estimate the energy released when 1.0 kg of uranium, containing 3% by mass of , undergoes fission.

235g of U-235 is one mole

1 mole of U-235 releases 6.02 × 1023 × 201 MeV

= 1.21 x 1026 MeV = 1.21 x 1032 eV

Converting to joules:

energy released by one mole of uranium-235 = 1.21 x 1032 × 1.6 × 10–19J

= 1.94 × 1013 J

1.0 kg of uranium containing 3% U-235 contains 30g of U-235

energy from 1.0kg of uranium = 1.94 × 1013 x 30/235 = 2.5 × 1012J

 

(ii) Oil releases approximately 50 MJ of heat per kg when it is burned in air.

State and explain one advantage and one disadvantage of using nuclear fuel to produce electricity.

Advantage:

Less mass of fuel used because more energy per kilogram

Less harm to environment because does not generate greenhouse gases

Disadvantage:

Hazardous waste because fission products are radioactive

Long term responsibility because waste needs to be stored for many years

 

(7 marks)

(Total 13 marks)