SP4h Nuclear Energy and Fission

Question 1

What are advantages of nuclear fuels? (4)

Answer 1

.do not burn so do not need air for the release of energy (useful is powering submarines)
.do not produce carbon dioxide
.store a lot of energy
.uranium is a non-renewable fuel but supplies of it last much longer than fossil fuels

Question 2

What are disadvantages of nuclear fuels? (3)

Answer 2

.they produce waste that will stay radioactive for millions of years
.decommissioning them and waste treatment is very expensive
.if there is an accident large areas can be affected (for example Chernobyl)

Question 3

Nuclear fission?

Answer 3

the process by which one atomic nucleus splits to form two atomic nuclei. If the splitting nucleus has an atomic number above 26 (the atomic number of iron) the nuclear reaction releases energy.

Question 4

What occurs during nuclear fission?

Answer 4

.a heavy nucleus is made even less stable by capturing an additional neutron
.the nucleus fissions into two daughter nuclei and some free neutrons (the fission products are highly radioactive)
.the nucleus has lost mass - this mass has been converted into energy

Question 5

How do chain reactions occur in fission?

Answer 5

neutrons released can be captured by other U-235 nuclei and so on, giving a chain reaction. This can only occur if there is a critical mass of U-235 (the smallest amount of fission material needed for a sustained chain reaction)

Question 6

What are nuclear chain reactions used in? (2)

Answer 6

.nuclear chain reactions are uncontrolled and will grow exponentially so are used in nuclear bombs
.in power stations they can be controlled so nuclear energy can be transferred to thermal energy

Question 7

How do moderators control nuclear reactions?

Answer 7

.neutrons released from fission are too fast to be absorbed by other U-235 nuclei
.a moderator such as graphite or water is used to slow down neutrons released
.it converts extra kinetic energy of the fast neutrons into thermal energy
.a coolant is required to carry the thermal energy away

Question 8

Control rods inside reactor core? (3)

Answer 8

.made from boron or cadmium
.absorb spare free neutrons to stop exponential growth of the chain reaction
.they can be inserted deeper between fuel rodes to decrease or compeletly shut down the reaction

Question 9

Fuel rods inside reactor core? (2)

Answer 9

.containing U-235 and U-238 in pellet form
.enriched fuels contain a greater proportion of U-235
.they are the nuclear fuel for a nuclear reactor

Question 10

Water, moderator and coolant inside reactor core?

Answer 10

.convect (transport) around the fuel rods, slowing neutrons and heating up

Question 11

What occurs in nuclear power stations? (5)

Answer 11

.water heated to made steam
.energy from nuclear reactions heats coolant
.hot collant sent to heat exchanger
.steams turn turbines
.turbines turn generators