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

Transcription

1 Nuclear Power

2 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

3 Basics Uranium reserves fairly well distributed Most reserves in: South Africa Niger Canada United States Brazil Australia Russia

4 2.7 World Net Nuclear Electric Power Gene (Billion Kilowatthours) Region/Country 2004 World Total Europe United States France Japan Eurasia Germany Russia Korea, South Canada Ukraine United Kingdom Sweden Spain China Belgium 45.8 Taiwan Switzerland Czech Republic Finland Central & South America Slovakia Bulgaria India Lithuania South Africa Africa Brazil 11.6 Hungary Mexico Argentina Romania Slovenia Netherlands Armenia Pakistan 1.93 Who s got it? 2004 survey DOE\EIA data

5 Top 10 nuclear power countries

6 Nuclear power per capita

7 Nuclear power plant map: 2006

8 New power plants

9 US plants:

10 US: nuclear and electricity

11 How does it work? Two fundamental types of nuclear energy Fisson: breaking apart Fusion: fusing together

12 How does it work? Fission: the purposeful breaking up of atoms to release energy Use neutrons as bullets to break up atoms

13 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

14 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

15 Controlling the pace Because additional neutrons are released when atom breaks up, the process can accelerate exponentially, and a chain reaction results

16 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)

17 Radiation Energy released when atoms break up is called radiation 3 types Alpha Beta Gamma

18 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

19 Reactor types: boiling water Simplest reactor setup

20 Pressurized water reactor Isolate the reactor by adding a water loop less efficient as heat energy is transferred

21 High temperature reactors Cooled with liquid metal (sodium in this case). Allows the reactor to generate or breed more fuel (plutonium)

22 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.

23 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

24 Open vs Closed fuel cycle Open fuel cycle: use uranium and when spent, that s it.

25 Closed fuel cycle Fast breeder reactor is used to make plutonium, which is also used as a fuel

26 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

27 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

28 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.

29 Chernobyl Now encased in a concrete sarcophagus

30 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

31 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

32 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 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)

33 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

34 Uranium lifetime issues Suppose nuclear only meets 50% of needs R/P goes to zero by 2030

35 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

36 Fusion Another type of nuclear reaction is the fusing of atoms to release energy, this is how the sun works

37 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.

38 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

39 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

40 Problems with nuclear Three main issues Safety of power plants Storage of wastes Proliferation of nuclear weapons

41 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

42 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

43 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.

44 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

45 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.

46 Decay of nuclear energy Total energy "Safe safe level level" Time

47 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?

48 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?

49 How much of this stuff do we Volume is in 1000 m 3, activity (radioactivity) is in mega Curies. have?

50 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.

51 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)

52 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

53 Yucca Mountain

54 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

55 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.

56 Mostly military waste WIPP

57 Salt deposit is used WIPP

58 Like Yucca Mountain, WIPP is an isolated location WIPP

59 Note the containers Trupact containers developed for this purpose (expensive!) note the name: Trupact instead of Trupack why? First shipment in 1999

60 Trupact Containers

61 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

62 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