Nuclear Power
Basics R/P depends on how it is used. High estimate is about 150 years, low estimate is about 40 years. More on this later Rapid growth in 1970 s and 1980 s then stagnant growth still happening globally, but slowly Future growth in US (and elsewhere) is tied to concerns of Safety of power plants Safe storage of wastes Nuclear weapons
Basics Uranium reserves fairly well distributed Most reserves in: South Africa Niger Canada United States Brazil Australia Russia
2.7 World Net Nuclear Electric Power Gene (Billion Kilowatthours) Region/Country 2004 World Total 2619.178 Europe 967.522 United States 788.5284 France 425.828 Japan 271.577 Eurasia 236.713 Germany 158.973 Russia 137.469 Korea, South 124.184 Canada 85.871 Ukraine 82.692 United Kingdom 73.68 Sweden 73.426 Spain 60.43 China 47.946 Belgium 45.8 Taiwan 37.939 Switzerland 25.612 Czech Republic 25.014 Finland 21.546 Central & South America 18.913 Slovakia 16.179 Bulgaria 15.598 India 15.044 Lithuania 14.347 South Africa 14.28 Africa 14.28 Brazil 11.6 Hungary 11.324 Mexico 8.731 Argentina 7.313 Romania 5.271 Slovenia 5.212 Netherlands 3.629 Armenia 2.205 Pakistan 1.93 Who s got it? 2004 survey DOE\EIA data
Top 10 nuclear power countries
Nuclear power per capita
Nuclear power plant map: 2006
New power plants
US plants: 1970-2005
US: nuclear and electricity
How does it work? Two fundamental types of nuclear energy Fisson: breaking apart Fusion: fusing together
How does it work? Fission: the purposeful breaking up of atoms to release energy Use neutrons as bullets to break up atoms
How does it work? Not all atoms are fissionable, only Uranium 235 and Plutonium 239 occur natural Natural plutonium decayed away Plutonium can be created in a reactor
How does it work? Normally, fission occurs naturally and spontaneously called radioactive decay. In nuclear power plants, we make this happen at the pace we choose
Controlling the pace Because additional neutrons are released when atom breaks up, the process can accelerate exponentially, and a chain reaction results
Controlling the pace We control the pace by controlling the neutrons. Use neutron absorbing materials in control rods that can be pushed into the reactor (slows it down) or pulled out (speeds it up)
Radiation Energy released when atoms break up is called radiation 3 types Alpha Beta Gamma
Radiation types alpha large and slow, same as a helium atom, stopped by paper, but more damaging than beta or gamma if decay occurs inside body by inhaling or eating radioactive material beta faster and smaller, same as electrons, can be stopped by clothing, can cause genetic damage and burning of tissues gamma radiation (like x-rays), very fast and hard to stop, requires thick shielding with dense element such as lead, can cause genetic damage and burning of tissues
Reactor types: boiling water Simplest reactor setup
Pressurized water reactor Isolate the reactor by adding a water loop less efficient as heat energy is transferred
High temperature reactors Cooled with liquid metal (sodium in this case). Allows the reactor to generate or breed more fuel (plutonium)
Breeder reactors These are reactors that use high temperature, fast neutrons to produce Plutonium from Uranium, while heat is also produced to generate electricity. After about 10 years, enough plutonium is produced to operate a second reactor, hence the breeder name.
Breeder reactors These are harder to regulate as they operate at high temperatures and are potentially more hazardous. We use them as experimental reactors and to produce plutonium, there are no breeder reactors used in commercial energy production
Open vs Closed fuel cycle Open fuel cycle: use uranium and when spent, that s it.
Closed fuel cycle Fast breeder reactor is used to make plutonium, which is also used as a fuel
Closed fuel cycle In theory, we could take this one step further, and make Actinides, that can also be made to undergo fission This is still in the testing phase. Closed fuel cycles can stretch your nuclear fuel supplies, by about a factor of two but plutonium can be made into hydrogen bombs which are more powerful than atom bombs
Controlling a nuclear reactor Remember that a chain reaction is possible as extra neutrons are formed In fact, if you pack the fuel in tightly enough, you get an atom bomb In energy producing reactors, the fuel is not packed that tightly, and a nuclear explosion is not possible
Controlling a nuclear reactor But too much heat is possible if the reaction is not properly controlled. This can lead to a meltdown of the reactor core (where the uranium is), and it can lead to too much steam being produced that can explode, like Chernobyl.
Chernobyl Now encased in a concrete sarcophagus
Controlling the reaction In addition to control rods of boron or graphite, we also control the reaction using cooling water to help carry the extra heat away. If the cooling water is lost, the heat is too much for the structure of the reactor building
Uranium lifetime issues At current use rate (6% of global energy), R/P is about 40 years This could grow to 75 years by tapping military supplies for energy production Build new, more efficient reactors and you get 70 years to 130 years (depending on use or no use of military uranium) Use closed fuel cycle to stretch the fuel and you can double the R/P
Uranium lifetime issues Lets take the maximum R/P of about 250 years With a growth in energy needs of 3% per year, energy demand will be 4 times higher by 2050. Nuclear needs to increase by 16 times to meet all energy needs If nuclear supplies ALL energy, it will need to increase by 66 times (4 x 16)
Uranium lifetime issues To meet this increase in R/P, nuclear needs to grow by 30% per year R/P goes to zero by 2020
Uranium lifetime issues Suppose nuclear only meets 50% of needs R/P goes to zero by 2030
Uranium lifetime issues Bottom line: its hard to envision a scenario in which nuclear provides a substantial fraction of all energy, and lasts beyond 2040 or so
Fusion Another type of nuclear reaction is the fusing of atoms to release energy, this is how the sun works
Fusion Energy in deuterium in the ocean is 1,230,000,000 times more than all fossil fuels But we cannot produce useful energy from fusion. Thus far, it takes more energy to get a fusion reaction going than energy released by fusion.
Future of fusion? Why can t we control fusion? Very high temperature (like inside the sun), this is a challenge for finding materials out of which we can make the reactor High density of hydrogen, got to pack it in tight Confinement of the process Only useful fusion produced thus far is hydrogen bomb, which uses an atom bomb to produce the heat and density
Future of fusion? We have not managed to control fusion yet, despite over 40 years of work. It s not looking good Keep in mind that fission was working 4 years after we started trying to control it
Problems with nuclear Three main issues Safety of power plants Storage of wastes Proliferation of nuclear weapons
Safety Engineered for safety in older plants means redundant valves, pumps, etc. Result was overly complex power plants that were prone to human error there are over 40,000 valves and switches in a typical nuclear power plant there are about 4,000 in a comparable coal fired power plant. The result is very costly plants that are prone to construction errors and operator errors irony is that such plants are not fail safe
Simplify reactors to gain safety Passive safety systems: Example Old: if core gets too hot, pump water into core area, use two or three sets of pumps as backups New: put extra water on top of core, if core gets too hot, open a valve and let gravity do the work Result: pump failure is not an issue
Simplify reactors to gain safety Passive safety systems: Example #2 New: surround the core with low pressure water containing boron (to absorb neutrons), if high pressure cooling water fails and the water pressure drops, the boron water floods the core. Result: No switches, no pumps to fail.
Passive stability systems Disperse uranium in small pellets, then encase pellets in ceramic, and then encase ceramic in graphite This result is uranium that can produce useful heat, but which cannot get hot enough for a meltdown Trades efficiency for safety
General principles: Nuclear waste 2 levels of radioactive waste high level waste - very radioactive, such as fuel rods low level waste - less radioactive, such as clothes, medical waste Materials are both radioactive and poisonous Radioactivity is a problem over thousands to tens of thousands of years. We have no experience as nations or as societies with such time scales.
Decay of nuclear energy Total energy "Safe safe level level" Time
Radioactive decay The "safe level is hard to define. Radiation occurs naturally, and we have evolved in the presence of radiation. But radiation causes mutation and some cancers. What is acceptable in terms of additional radiation exposure? The curves may not converge for 10,000 years or more. Can we monitor the waste for such a long time?
Options for waste storage Options are: Keep it at the place it was generated Store it underground Store it at the surface Reprocess some the high level waste Permanent "temporary" storage Shoot it into outer space There are pros and cons to each approach, what are they?
How much of this stuff do we Volume is in 1000 m 3, activity (radioactivity) is in mega Curies. have?
Waste observations Most of the volume of waste is military, but most of the activity is commercial. Spent fuel accounts for nearly all of the activity, but little volume. Low level waste has low activity, but high volume.
Underground storage Yucca Mountain, Nevada is the future commercial and military storage facility Waste Isolation Pilot Project (WIPP) is the high level storage facility (Rocky Flats waste goes here)
WIPP and Yucca Mtn Both have highly impermeable rock to minimize water seeping through (rots barrels and carries waste away) Groundwater table is well below storage area Not prone to earthquakes Minimal population nearby But, all of these are changeable, particularly considering the time scale involved
Yucca Mountain
Yucca Mountain Waste would be stored in pits inside the tunnels, which would be backfilled with rock after reaching capacity. Note deep groundwater level, which needs to remain well below tunnel depth for safe storage but water levels change
Yucca Mountain When Yucca Mountain opens, it will not stay open long. By the time it is completed (about 2015), there will be more waste in existence than space in the repository.
Mostly military waste WIPP
Salt deposit is used WIPP
Like Yucca Mountain, WIPP is an isolated location WIPP
Note the containers Trupact containers developed for this purpose (expensive!) note the name: Trupact instead of Trupack why? First shipment in 1999
Trupact Containers
What do we do with our waste now? Store high level waste on site at reactors Some reprocessing in England and Russia Low level waste is buried at sites in Washington State, Nevada and South Carolina Ocean dumping: prior to 1970, waste was dumped in the ocean by the US, Europeans dumped in the ocean until 1983
Weapons proliferation This is a concern if fuel is reprocessed and the plutonium removed, also if breeder reactors become common. Also a concern for atom bombs, which need the same purified Uranium 235 that reactors use. Nuclear weapons technology is not a secret, however, so the tie between nuclear power and nuclear weapons is not that obvious. Terrorism involving nuclear power plants is perhaps a larger concern