4.4 NUCLEAR FISSION + FUSION

Question 1

What is nuclear fission?

Answer 1

The splitting of large, unstable nuclei to
form smaller more stable nuclei (+the
emission of spare neutrons).

Question 2

Give an example of a fissionable isotope.

Answer 2

Uranium - 235

Question 3

What usually needs to happen to induce

fission?

Answer 3

● The unstable nuclei must absorb a
neutron
● Spontaneous fission (where no
neutron absorption occurs) is rare

Question 4

Alongside two smaller nuclei, what else

is emitted in a fission reaction?

Answer 4

● Two or three neutrons
● Gamma rays
● Energy

Question 5

What form of energy do all fission

products have?

Answer 5

Kinetic energy.

Question 6

What takes place during a chain reaction

in a nuclear reactor?

Answer 6

● An unstable nucleus absorbs a neutron
● The nucleus undergoes fission and
releases 2 or 3 further neutrons
● These induce more fission, which results
in a chain reaction

Question 7

What is the consequence of an

uncontrolled chain reaction?

Answer 7

● The rate of fission events becomes to
high and results in the production of
too much energy
● This can lead to a nuclear explosion

Question 8

What are the three main components of

the core a nuclear reactor?

Answer 8

1. Fuel rods
2. Control rods
3. Moderator

Question 9

What is the role of the moderator in a

nuclear reactor?

Answer 9

To slow down the neutrons so they are
travelling at speeds which allow them to
be absorbed by fissile nuclei and cause
fission.

Question 10

How is the chain reaction in a fission

reactor kept under control?

Answer 10

● Control rods are positioned in between the fuel
rods
● The rate of fission is controlled by moving
these rods up and down
● The lower the rods are inserted, the slower the
rate of fission

Question 11

What term is used to describe nuclei in
which fission can be induced through the
absorption of slow neutrons?

Answer 11

Fissile Nuclei

Question 12

What is nuclear fusion?

Answer 12

The joining of two light nuclei to produce

a heavier nuclei and release energy.

Question 13

Name two isotopes of hydrogen which

are commonly used in nuclear fusion.

Answer 13

Deuterium and Tritium

Question 14

Which releases more energy, nuclear

fission or nuclear fusion?

Answer 14

Nuclear fusion.

Question 15

Explain the difficulty of generating

energy through nuclear fusion.

Answer 15

Fusion requires very high temperatures
which in itself requires large quantities of
energy and also requires casing which
can withstand them.

Question 16

Explain why nuclear fusion is currently
not a viable way to produce energy on
Earth.

Answer 16

With current equipment/techniques, the
energy required is greater than the
energy produced, resulting in a net
energy loss.