IB Physics HL E.4 Fission Questions

SLSL HLHL

Practise IB Physics HL E.4 by analysing fission chains, binding-energy changes, reactor physics and extended nuclear evidence.

35 questions in this syllabus scope, with question parts counted together.

Exam points & syllabus

Exam points

Balance both A and Z in neutron-induced fission; include the incoming neutron before finding the number emitted.
Identify kinetic energy of fission fragments or gamma radiation as an immediate energy output.
For maximum energy from a fuel mass, count U-235 nuclei and multiply by energy per fission, converting MeV to joules.
Find specific fission energy from energy per reaction divided by the mass of one fuel nucleus; convert u to kg for J kg⁻¹.
Convert a fission rate to events over the stated time, then multiply by one fuel nucleus mass to find fuel consumed.
Calculate useful electrical power as fission rate × energy per event × efficiency; report joules per second as watts.
Explain enrichment in the stated reactor by low natural U-235 abundance and an increased U-235 fraction supporting the intended fission chain.
Explain how neutron absorption by U-238 or accumulated waste removes neutrons needed to sustain further fissions.
Link waste accumulation to early fuel replacement: neutron absorption can hinder the chain before the uranium is fully consumed.
Explain moderation as neutron slowing that increases thermal-neutron fission probability; name neutrons rather than unspecified particles.
Give the moderation mechanism: neutron collisions transfer KE to moderator atoms or molecules.
Distinguish control-rod absorption from moderator slowing; lowering control rods decreases the overall fission rate.
For a requested comparison, give both component differences and a valid similarity, such as affecting reaction rate or interacting with neutrons.
Choose poor neutron absorption for an ideal moderator and good neutron absorption for control material.
State that the heat exchanger transfers thermal energy from reactor coolant to water or steam; the transfer must be explicit.
Trace the plant energy chain: fission energy becomes thermal energy of coolant, then steam and turbine KE, then electrical energy in the generator.
State two concrete accepted nuclear-safety problems, such as radiation leakage and radioactive-waste processing, handling or storage.
When using the stated safety rubric, name meltdown risk rather than a vague explosion; keep separate problems distinct for the two marks.

Covered syllabus points

E.4.1—Fission energy release E.4.2—Chain reactions E.4.3—Nuclear power plant roles E.4.4—Fission products and waste

Exam points

For maximum energy from a fuel mass, calculate the number of U-235 nuclei, convert MeV per fission to joules and multiply.
Calculate specific nuclear energy by dividing energy per fission by the mass of one U-235 nucleus, expressing the result in J kg⁻¹.
State kinetic energy of the fragments or gamma radiation as an immediately released form of fission energy.
Convert fissions per second into fissions per day, then multiply by the mass of one fuel nucleus to find the mass fissioned.
Calculate useful power as fission rate × energy per fission × efficiency; convert MeV to joules before reporting watts.

[Maximum number: 4]

(a)

A nuclear power station uses U-235 as fuel. Assume that every fission reaction of U-235 gives rise to 180 MeV of energy.

[ 4 ]

(i)

Estimate, in $\mathrm{Jkg}^{-1}$ , the specific energy of U-235.

[ 2 ]

see «energy = » $180 \times 10^{6} \times 1.60 \times 10^{-19}$ AND «mass =» $235 \times 1.66 \times 10^{-27}$ $7.4 \times 10^{13} \ll \mathrm{~J} \mathrm{~kg}^{-1} \gg$

(ii)

The power station has a useful power output of 1.2 GW and an efficiency of 36 %. Determine the mass of U-235 that undergoes fission in one day.

[ 2 ]

$\text { energy produced in one day }=\frac{1.2 \times 10^{9} \times 24 \times 3600}{0.36}=2.9 \times 10^{14} \ll \mathrm{~J}>\text { }$

Exam points

For the stated uranium reactor, explain that natural ore contains much more U-238 than U-235, leaving too little U-235 for the intended chain reaction.
Explain enrichment as increasing the fraction of U-235, which more readily undergoes the required thermal-neutron-induced fission.
In the stated reactor, neutron absorption by U-238 leaves fewer neutrons available to induce further U-235 fissions.
Explain early fuel replacement through accumulating neutron-absorbing waste: fewer neutrons remain to sustain the chain before all uranium is consumed.

[Maximum number: 3]

Outline the reason why fuel enrichment is necessary for the fuel used in a commercial nuclear reactor.

Exam points

State that the moderator slows neutrons or removes their KE, increasing the chance of U-235 fission at thermal-neutron energies.
Explain moderation through neutron collisions that transfer energy to moderator atoms or molecules.
Control rods regulate fission rate by absorbing neutrons; lowering them decreases the overall reaction rate.
When comparing components, distinguish absorption by control rods from slowing by moderators, then give the requested shared effect or interaction.
For ideal materials, choose a moderator that absorbs neutrons poorly and a control material that absorbs them well.
Describe a heat exchanger as transferring thermal energy from the reactor coolant to water or steam; explicitly state the transfer.

[Maximum number: 3]

This question is about energy sources.

A small island is situated in the Arctic. The islanders require an electricity supply but have no fossil fuels on the island. It is suggested that wind generators should be used in combination with power stations using either oil or nuclear fuel.

A nuclear reactor requires both control rods and a moderator to operate. Outline, with reference to neutrons, one similarity and two differences in the function of each of these components.

[Maximum number: 2]

State two other safety problems associated with nuclear power.

1.

2.

Question 1

Question (a)

Question (i)

Question (ii)

Question 1

Question 1

Question 1