Fossil Fuels n Nuclear

Question 1

What are unconventional reserves of fossil fuels?

Answer 1

• Shale, ‘tight’ gas or oil in low permeability/low yield rock
• Hydraulic fracking of rock required
• Amounts to an extra 50% on top of existing hydrocarbon reserves
• Issues involved such as water pollution and increased seismic activity

Question 2

Describe the CCGT process?

Answer 2

• Comprises of two power cycles - a gas (Brayton) and a steam (Rankine) for single fuel input
• Brayton cycle comprises of an air compressor, gas combustion chamber, gas turbine and an electrical generator. Hot air and fuel mixture moves turbine blades which turn drive shaft connected to a generator
• Rankine cycle comprises a steam turbine, electrical generator, a pump and a condenser. Waste heat from the first cycle is used to generate steam to power another turbine and generator
• Cycles are connected by a heat exchanger
• Reduces overall losses and raises efficiency to around (55% to 60%)

Question 3

Describe a coal power plant process?

Answer 3

• Utilises a Rankine cycle, coal is pulverised and then burned, this heat is used to create steam which spins the turbines connected to generators

Question 4

What are the associated Co2 emissions with coal, oil and gas generation?

Answer 4

(kg/kWh)
Coal = 0.9
Oil = 0.7
Gas = 0.2

Question 5

Describe the fission process?

Answer 5

• Fuel comes from naturally occurring uranium, only contains about 0.8% U235 and most of the remainder is U238
• Uranium is enriched to increase U235 to 2-3%, technically challenging and costly
• Enriched uranium is processed into fuel pellets and turned into fuel rods
• Impact of neutron with a U235 nucleus causes fission process
• Fuel is used to power a Rankine Cycle (heat is used to turn water into steam to drive turbines n generator)
• Spent fuel from nuclear process is reprocessed to improve efficiency

Question 6

How are Pressurised Water Reactors different to conventional reactor?

Answer 6

• Conventionally, a coolant is used to heat up the water into steam (such as gas) with water used a moderator
• PWR use water as a moderator AND a coolant

Question 7

What does the coolant and moderator do?

Answer 7

Moderator slows down the released neutrons, increasing the probability of further fission events
Coolant part cools the core and removes heat generated from the fission reaction and transfer it to the electrical generators

Question 8

What are the issues associated with nuclear power?

Answer 8

• Primary waste is spent uranium fuel rods with no long-term storage solution
• High capital costs and long lead times
• Catastrophic consequences if something goes wrong in the reactor
• Uranium is a non-renewable resource (estimated 100 years left)

Question 9

What are breeder reactors?

Answer 9

• Initially charged with plutonium, therefore only requiring natural (or depleted) uranium as input
• Generates less waste than a normal reactor
• Generates more fissile material than it consumes