C.3 Nuclear Fission and Fusion Flashcards
Why is nuclear fusion an ideal source of energy for the future?
The fuel is cheap and abundant and no radioactive waste or greenhouse gas is produced.
When does nuclear fusion occur?
When two light nuclei like hydrogen nuclei fuse together to make a larger one releasing large quantities of energy, the binding energy per nucleon increases during the reaction.
What is binding energy?
The amount of energy required ro break a nucleus into individual proton and neutron (nucleons) or the amount of energy released when the nucleons come together to form a nucleus - the greater the binding energy per nucleon the more stable the nucleus.
How does the binding energy per nucleon change over the elements?
It increases from hydrogen to iron and then decreases as the nuclei get larger.
How must a fusion reaction balance?
The sum of the atomic masses and atomic numbers on left and right sides of the equation must balance.
What does the fusion reaction generate?
The fusion reaction generates a larger more stable nucleus in which the binding energy per nucleon is greater than in deuterium. The extra binding energy is released as heat.
When is absorption spectrum produced?
It is produced when specific frequencies of light are absorbed form a continuous spectrum. When an atom absorbs light, its electrons are promoted to higher energy levels. The visible absorption spectrum of hydrogen is created when electron in main energy level 2 are promoted to higher energy levels - it appears as a series of black bands within a continuous spectrum that get closer together at higher frequencies.
What is nuclear fission?
Nuclear fission involves the splitting of heavy nuclei into smaller nuclei of comparable mass. The binding energy per nucleon increases in a fission reaction.
What is the typical fuel used in a fission reaction?
Uranium - 235, when bombarded with neutrons it becomes unstable and spits into two smaller nuclei. The increase in binding energy per nucleon causes the reaction to release a lot of energy in the form of heat. Uranium does not always split into the same two nuclei.
What happens to neutrons related in the fission reaction?
They are able to cause the fission of further uranium 235 nuclei which releases more neutrons which cause more fission - this is called a chain reaction.
What happens when there is only a small quantity of uranium 235 present?
Many neutrons escape from the sample without causing fission - a chain reaction does not occur. Above a certain mass of uranium 235 - the CRITICAL MASS - there is enough material to ensure that at least one neutron from each fission process is captured by another uranium nucleus to cause another fission process and a chain reaction occurs, the reaction is self sustaining.
What is a breeder reactor?
A nuclear reactor that produces more fissionable material than it consumes.
Why are breeder reactors useful?
A naturally occurring sample of uranium contains mostly uranium 238 which does not undergo fission. In a breeder rector this can be converted by bombardment with fast neutrons to Plutonium 239 which does undergo fission.
What are issues associated with nuclear power?
Health issues - exposure to radiation can cause radiation poisoning, cancer and brith defects
Meltdown - if the chain reaction becomes uncontrollable or cooling systems malfunction the core can overheat and fuel rods may melt causing radioactive material to escape into the environment.
Nuclear weapons - plutonium breeder reactors and fuel reprocessing can be used to construct nuclear weapons that have the potential to cause mass destruction and severe loss of life.
What are some properties of low level nuclear waste?
Lower activity - usually contains isotopes with shorter half lives
Normally associated with items that have been contaminated with radioactive material or have been exposed to radioactivity like gloves and tools
They may be stored on site until it has decayed or buried underground near surface disposal in individual concrete canisters
