P2 7 Energy from the Nucleus

Question 1

What is nuclear fission?

Answer 1

Nuclear fission is the splitting of a nucleus into two approximately equal fragments with the release of two or three neutrons along with radioactive waste

Question 2

Energy released from nuclear fission:

Answer 2

Energy in the form of radiation plus kinetic energy of the fission neutrons and the fragment nuclei

Question 3

Fissionable isotopes:

Answer 3

Uranium-235 or Plutonium-239 A neutron hits the nucleus of one of these isotopes and the nucleus splits A chain reaction then occurs in a nuclear reactor as each fission event causes further fission events

Question 4

Nuclear Reactor Diagram:

Answer 4

Question 5

Nuclear Reactor Components:

Answer 5

A nuclear reactor consists of uranium fuel rods spaced evenly in the reactor.

The reactor core contains the fuel rods, control rods and water at high pressure

Fission neutrons are slowed down by collisions with water molecules

This is important as fast neutrons do not cause further fission of U-235

The water is a moderator as it slows down the fission neutrons

Control rods- absorb surplus neutrons. Depth of rods is adjusted to maintain a steady chain reaction

Water acts as a coolant. Its molecules gain KE from neutrons and fuel rods. Then the water gets pumped through the core to and from a heat exchanger.

Water transfers energy for heating to the heat exchanger from the core

Question 6

Nuclear Fission Reaction:

Answer 6

Question 7

What is nuclear fusion?

Answer 7

Nuclear fusion is the process of forcing two nuclei close enough together so they form a single larger nucleus

Question 8

Nuclear fusion and Energy release:

Answer 8

Nuclear fusion releases energy only if the relative mass of the nucleus formed is no more than about 55 (about the same as an iron nucleus). Energy must be supplied to create bigger nuclei

Question 9

How is nuclear fusion brought about?

Answer 9

Nuclear fusion is brought about by making two light nuclei collide at very high speed

Question 10

The sun and nuclear fusion:

Answer 10

• Two protons (i.e. hydrogen nuclei) fuse, they form a ‘heavy hydrogen’ nucleus 2H1. Other particles are created and emitted at the same time
• Two more protons collide separately with two 2H1 nuclei and turn them into heavier nuclei
• The two heavier nuclei collide to form the helium nucleus 4He2
• The energy released at each stage is carried away as kinetic energy of the product nucleus and the other particles emitted

Question 11

Nuclear Fusion:

Answer 11

Question 12

Fusion reactor conditions:

Answer 12

• The reactor needs to be at a very high temperature
• This is because the two nuclei approaching each other will repel each other due to their positive charges. If they are moving fast enough, they can overcome the force of repulsion and fuse together

Question 13

What happens to the plasma in a fusion reactor?

Answer 13

• The plasma is heated by passing a very large electric current through it
• The plasma is contained by a magnetic field so it doesn’t touch the walls.
• If it does, it would go cold and fusion would stop

Question 14

The promising future of nuclear fusion:

Answer 14

• Fuel for fusion reactors is readily available as heavy hydrogen is naturally present in sea water
• The reaction product, helium is a non-radioactive inert gas so it is harmless
• The energy released could be used to generate electricity
• But still in the development stages

Question 15

What is radon gas?

Answer 15

Radon gas is an alpha emitting isotope that seeps into houses in certain areas through the ground

Question 16

What are methods to reduce the exposure to radon gas?

Answer 16

Pipes under buildings can be installed and fitted to a suction pump to draw the gas out of the ground before it seeps into the building

Question 17

Could Chernobyl happen again?

Answer 17

• Most nuclear reactors are of a different design
• The Chernobyl accident did not have a high-speed shutdown system like most reactors have
• The operators at Chernobyl ignored safety instructions
• There are thousands of nuclear reactors in the world. They have been working safely for many years

Question 18

Radioactive Risks

The effect on living cells of radiation from radioactive substances depends on:

Answer 18

• The type and amount of radiation received (dose)
• Whether the source of radiation is inside or outside the body
• How long the living cells are exposed to the radiation

Question 19

Complete the sentence

The larger the dose of radiation someone gets…

Answer 19

the greater the risk of cancers developing. High doses kill living cells

Question 20

Complete the sentence:

The smaller the dose…

Answer 20

the lower the risk- but it is never zero

Question 21

How can workers reduce their exposure to radiation?

Answer 21

• They can stay far away from the source of radiation. Eg: using special tools with long handles
• They can spend as little time as possible in ‘at-risk’ areas
• They can shield themselves from the radiation by staying behind thick concrete barriers and/or using thick lead plates

Question 22

What is done to nuclear waste after its use?

Answer 22

The nuclear waste is stored in safe and secure conditions for many years after unused uranium and plutonium (to be used in the future) are removed from it