4.8 Nuclear Fission and Fusion

Question 1

When an uranium atom undergoes fission, it goes on to produce bout 2.5 further neutrons per fission, which go on to do what 3 things?

Answer 1

1. Escape without causing further fission.
2. Be absorbed by a neighbouring nucleus, without causing further fission
3. Cause further fission in a neighbouring nucleus

Question 2

Define a chain reaction

Answer 2

When enough neutrons go on to cause further fission, and the reaction sustains itself

Question 3

Define a coolant

Answer 3

The material used to transfer energy away from the nuclear reactor to generate electricity

Question 4

3 Examples of coolants

Answer 4

Water, CO2 or liquid sodium

Question 5

Define a moderator

Answer 5

Something which sows down neutrons in between fissions

Question 6

3 examples of a moderator

Answer 6

Graphite, water or heavy water

Question 7

What is AGR

Answer 7

A graphite moderated fission reactor

Question 8

Define critical size

Answer 8

The minimum size if a nuclear reactor core so that sufficient numbers of neutrons are retained within the reactor core to sustain the chain reaction

Question 9

Define control rods

Answer 9

Used to change the fission rate by capturing excessive neutrons before they can cause further fission

Question 10

What is reactor shielding

Answer 10

The shield used to prevent potentially dangerous radiation esp, v penetrating gamma rays and neutrons from pprenetrtng the reactors walls

Question 11

Define nuclear fusion

Answer 11

A nuclear reaction in which atomic nuclei of low atomic no. Fuse to form a heavier nucleus with the release of energy

Question 12

Why must the plasma be heated to such a high temperature for nuclear fusion

Answer 12

Because the protons must be projected at each other at an extremely high speed to overcome the repulsion between the two positive charges and get close enough to fuse

Question 13

Define plasma

Answer 13

In a plasma, all the electrons have broken free of the atoms and the gas becomes a mixture of electrons and ions

Question 14

Name the three ways to confine plasma

Answer 14

Gravitational, Inertial and Magnetic

Question 15

How does gravitational plasma confinement work in stars

Answer 15

The inward gravitational pull of the stars huge mass balances the outward forces created by the photons mpactng on the particles of the gas plasma

Question 16

How does Inertial plasma confinement work

Answer 16

Involves directing intense ion or laser beams at a solid fuel pellet. The beams provide energy to heat the pellet. The idea is to produce fusion for long enough to extract the energy before the plasma escapes

Question 17

How does magnetic plasma confinement work

Answer 17

Magnetic fields are used to hold the charged particles in the plasma in what is sometimes called a magnetic bottle without touching the sides of the vessel.

Question 18

Plasma containment problems (2)

Answer 18

1. Plasma must be kept contained at a high enough temp for long enough to obtain an adequate no. Fusion reactions
2. Must produce more energy than it is initially supplied

Question 19

What is the chemical equation for the Deuterium-Tritium reaction

Answer 19

2.1H + 3.1H arrow 4.2He + 1.0n +17.6MeV

Question 20

Where is deuterium found

Answer 20

Sea water

Question 21

Where is tritium obtained

Answer 21

Lithium

Question 22

Give 2 reasons why the D-T reaction is used for fusion

Answer 22

1. Produces a greater energy release than other similar reactions\
2. Limited waste products (neutron-irradiated products) so no long-term storage needed
   (3. Deuterium and tritium are easily accessible)

Question 23

How are fusion reactors inherently ‘fail-safe’

Answer 23

The fuel must be continuously fed into them. If the feed is stopped, the reaction ceases.

Question 24

What does ITER stand for?

Answer 24

International Thermonuclear Experimental Reactor

Question 25

What are the ITER’s beryllium blankets for

Answer 25

They provide shielding from the high-energy neutrons produced by the fusion reactions

Question 26

How does ITER use changing magnetic fields to generate heat for fusion

Answer 26

The changng magnetic fields produce. Large current by electromagnetic induction. This current passes thru the plasma causing ions and electrons to collide and gain Ke and collide.

These collisions result in resistance, producing a Heating effect. However, ths heating effect also slows the current and the heating effect then decreases.

Question 27

How does ITER use a beam of deuterium ions to heat the plasma

Answer 27

A beam of deuterium ions is accelerated by an electric field to a high velocity. They pass thru another electric fired on way to become neutral then collide w the ions and electrons in the plasma, heating it up

Question 28

How dos the ITER use high-frequency microwaves to heat up the plasma

Answer 28

High frequency microwaves are directed into the plasma nd transfer their energy to the particles.
3 specific wavelengths matched to. Specific type of ion or electron to maximize efficiency

Question 29

How does CO2 in the earth’s atmosphere trap solar energy

Answer 29

By radiating nfrared radiation emitted from the planets surface back to the earth

Question 30

when was the Chernobyl disaster

Answer 30

1986

Question 31

When was the Fukuyshima disaster

Answer 31

2011