Nuclear Energy Flashcards
Nuclear energy generates how much of the global electricity output?
10 %
Differ from countries like in France it provides 70% of electricity demand
What was fewer reactors built from 1980s and onward?
Fewer reactors were built due to a combination of factors. This is due to a combination of anti-nuclear sentiment due to safety concerns and several serious accidents. However, one of the major factors is the low cost of alternative fuels such as coal and gas which has made nuclear uncompetitive
It is worth noting that since the lifetime of a reactor is about 30‐40 years many of the reactors built in the 1970s are now being closed down, requiring new reactors to be built or alternative energy sources to be found.
What is happening to nuclear now?
Because of the phase-out of coal and gas due to CO2 emissions nuclear power has become more prominent and is believed by many to be part of the future energy mix.
It is worth noting that since the lifetime of a reactor is about 30‐40 years many of the reactors built in the 1970s are now being closed down, requiring new reactors to be built or alternative energy sources to be found.
Explain the dominant types of nuclear plants
The dominant types are the light water reactor based on pressurised or boiling water
How does a Pressures Water Reactor (PWR) work?
Current PWR plants generate about 1200 MW, usually have multiple fluid flow loops, and each is consists of a primary and secondary fluid side. The secondary side is a steam generating loop that powers the turbine.
How does a Boiling Water Reactor (BWR) work?
A Boiling Water Reactor (BWR) only has a primary circuit; the steam boils in the reactor vessel and flows directly to the turbine, condenses then returns to the reactor vessel.
What is nuclear fuel made of?
Uranium,
U-235 is the most important one
How does nuclear energy work?
Fission aka. splitting a large atom into several elements and the total mass of the products is less than original. This loss appears as kinetic energy.
Since fission produces neutrons that have high kinetic energy (ie called fast neutrons) they have to be slowed down to increase the likelihood of a reaction. This is done by allowing the fast neutrons to collide with surrounding material (the structure in a reactor to do this is called a moderator). Reactors that slow down the neutrons are called Thermal Reactors, for U-235. Some nuclear fuels (for example U‐238 and Th‐232, thorium) react more readily to fast neutrons and are designed without moderators. They are called Fast Reactors.
What is a breeder reactor?
With U‐238 and Th‐232 is that products of the fission process are elements that are fissile, ie they can to undergo a nuclear reaction to produce energy.
This means if the U238 or Th‐232 is part of the fuel makeup, new fuel can be generated
The material is called fertile if they can produce a new fuel. Breeder refers to the process
What is a key aspect that differs nuclear from coal?
The fuel requirement for a 1000MWe ( eg for electrical output) for coal is 2700000 tons and the nuclear fuel is 30 tons.
While there is auxiliary equipment which makes nuclear fuel handling more complex than coal, the actual heat generating part, the reactor vessel is significantly smaller than a coal-fired furnace.
What has to be done to use current thermal nuclear reactors?
The fuel used needs to be enriched because natural uranium has insufficient U‐235 to maintain a chain reaction. This means an enrichment process is required to take the fuel to 2‐5% U‐235, the remainder is U‐238.
Reactor componentes?
Fuel. Usually, pellets of uranium oxide (UO2) arranged
in tubes to form fuel rods. The rods are arranged into
fuel assemblies in the reactor core.
Moderator. This is material which slows down the
neutrons released from fission so that they cause more fission. It is usually water but may be heavy water or graphite.
Control rods. These are made with neutron-absorbing material such as cadmium, hafnium or boron, and are
inserted or withdrawn from the core to control the rate
of reaction, or to halt it.
Coolant. A liquid or gas circulating through the core so as to transfer the heat from it. In light water reactors, the moderator functions also as a coolant
Pressure vessel or pressure tubes. Usually, a robust steel vessel containing the reactor core and
moderator/coolant, but it may be a series of tubes
holding the fuel and conveying the coolant through the moderator.
Containment. The structure around the reactor core
which is designed to protect it from outside intrusion and to protect those outside from the effects of radiation in case of any malfunction inside. It is typically a metre thick concrete and steel structure
What happens after continous operation?
The fuel rods become less effective at producing energy as the fuel (U‐235) gets used up.
The question now do you try and extract the remaining fuel (U235, plutonium, U238) or do you store it as waste.
What happends with the waste (uranium) afterwards and when plants closes?
It is highly radioactive and a dangerous source of contamination.
Waste has different levels of radioactivity and ranges from low volumes of highly radioactive and long-lived radiation products to large volume of low radiation levels products.
The volumes are considered small compared to domestic waste. However, the HLW is long-lived ( 1000 years) and highly toxic.
At present in the UK there are no political or socially acceptable methods or decision on long-term disposal methods though technical solutions do exist. Current waste is stored on existing reactor sites.
What effect has access to uranium on the viability of nuclear power?
Three countries (Australia, Canada and Kazakhstan) hold 50% of the resources with 75% held by only 7 countries. Current resources could last for about 80 years. However, breeder programmes and fuel reprocessing could be developed to extend the life of proposed reactor technology.
