Nuclear power stations

Question 1

What is the most useful product of nuclear fission for generating energy?

Answer 1

the thermal energy

Question 2

How is nuclear fission used to generate energy?

Answer 2

• fuel rods containing uranium undergo fission and release energy
• thermal energy is taken by a coolant (e.g. water) that is pumped through the reactor to a container of water, which is then heated
• steam is produced which causes turbines to rotate and turn a generator to produce electricity
• the steam is cooled back into water in a condenser so it can be used again

extra thermal energy is released from cooling towers, or into the sea

Question 3

basic layout of the reactor

Answer 3

a coolant such as water is pumped through the reactor

contains fuel rods and control rods

coolant flows out of the reactor core in a connected pipe to be heated, then cools down and flows back in

Question 4

features for controlling the chain reaction (5)

Answer 4

concrete shield - prevents radiation and stray neutrons escaping from the core

fuel rods and control rods in an interlocking/close pattern - neutrons that escape from one fuel rod can be absorbed by another

control rods absorb neutrons to keep the reaction from increasing in size

lowering a control rod further reduces fission reactions

also contains a moderator that fills the core that is used to slow down the neutrons so that fission can occur

Question 5

a moderator

Answer 5

a material such as graphite or water that is used to slow down neutrons so that fission of the uranium-235 nuclei can occur

it does not absorb neutrons

Question 6

Explain how the control rods work in a nuclear power station [3]

Answer 6

the control rods absorb neutrons

if the control rods are pushed down further, more neutrons are absorbed and the chain reaction slows down

if they are pulled out, fewer neutrons are absorbed and the chain reaction speeds up

Question 7

Describe how nuclear fuel is used in power stations [2]

Answer 7

nuclear fuel undergoes fission to release huge quantities of thermal energy

this is used to heat water to produce steam

Question 8

Describe what happens to the products of nuclear fission [2]

Answer 8

the radioactive daughter products need to be disposed of safely

they are usually stored until the activity has decreased to a safe level

Question 9

Explain how pulling control rods out of the core of a nuclear reactor can increase the amount of thermal energy released by the reactor [4]

Answer 9

control rods absorb some of the neutrons produced by the fission of uranium nuclei so these neutrons cannot cause other uranium nuclei to fission

if the control rods are pulled out of the core they will absorb fewer neutrons so more fission reactions will happen and more heat energy will be released

Question 10

Evaluate the use of nuclear fuel to produce electrical energy compared with fossil fuels [6]

Answer 10

should consider 6 from:

• energy released per unit mass/kg
• radioactive waste
• greenhouse gases
• availability of fuels
• threat of nuclear disaster
• decommissioning costs
• reliability of fuels
• lifetime left of fuels for use in power stations

-conclusion