This week (11.29) we will cover nuclear energy, as in chapter 10, which was assigned for you to read last weekend. We'll meet Monday, Wednesday and Friday this week, and we'd like to cover these topics on Monday:
- half-lives: see also population curves
- radiation: natural (e.g. radioactivity) and synthetic (e.g. X-rays)
- types of radiation:
- alpha rays-Helium nuclei
- beta rays-fast electrons
- gamma rays-high energy photos
- cosmic rays-very high energy photos
- X-rays-medium energy photos
- UV rays-low energy photos
- neutron radiation-fast or slow (thermal) neutrons: from nuclear explosions or reactors
- Measuring radiation:
- decay rates: 1 Bq = 1 decay per second, 37 billion Bq = 1 Curie
- absorbed dose: 1 Gray = 1 joule/kg, 1/100 Gray = 1 RAD
- dose equivalent: RAD x quality factor (beta, gamma = 1, alpha = 20: slow moving but very large bullets)
- dose equivalent: 1 REM = RAD x QF, 100 REM = Seivert (not often used in US)
- What this means: type of radiation and dose are both important
- ionizing radiation, e.g. knocks electrons out of biological structures, e.g. DNA
- X-Rays most common ionizing radiation, medium energy (Dental strongest, guts medium, backscatter weakest)
- UV radiation is also ionizing, but causes damage to cells at the surface (e.g. sunburns and free radicals)
- most vulnerable to ionizing radiation are DNA (blueprints) including growth regulation elements (cancer)
- fastest growing cells are the most susceptible to fast cancers (e.g. skin, colon, lung, white blood cells)
- radiation damage is compound: Hiroshima victims lost skin and wbc, so many died of infections
- Radiation protection: damage depends on type, exposure, and cumulative damage (you get cancer like mutations several times each day, your body's immune system deals with it very cleverly: peroxidases and others)
- Penetration:
- alpha: skin, paper
- beta: foil
- gamma: lead
- neutron: meters of concrete
- UV: para amino benzoic acid (PABA), zinc oxide, others
- X rays: lead (n.b. when you get a dental or medical x-ray, or at the TSA these days)
- all radiation exposure risks require badges, except the TSA, because they don't need no stinking badges
- Nuclear reactions: Fission and Fusion
- Fisson: heavy stuff (Uranium, Plutonium) splitting into smaller stuff (neutrons, Krypton-superman, Barium-what they do with dead people)
- Fusion: light stuff (Hydrogen, helium) joined to create heavier stuff (Helium, lithium, beryllium, boron, etc.)
- Atomic bombs and present power plants use fission
- Hydrogen (fusion) bombs and future power plants use fusion. So do all stars. Not movie stars, thermonuclear stars.
- H bomb also called a thermonuclear bomb, because the detonator for a fusion reaction/bomb is a fission bomb
- Reactors are contained, hopefully controlled fission reactions
- Fission reaction involves one neutron in, more than one out: capture all but one, and you have a sustaining reaction. Capture more, the reaction slows down and stops. Capture less and you have a runaway reaction. Do it quickly, and you have a bomb. The material needed to form a bomb right away is called critical mass
- Reactor parts: fission
- Fuel: fissionable ("fissile") material, e.g. uranium
- Core: a collection of fuel rods
- Moderator: something that captures fast neutrons and turns them into heat
- Coolant: stuff that carries this heat away to create steam and then electricity
- Reactor types: fission (why is this important? some are more dangerous than others-ask about submarines)
- BWR: boiling water reactor: one loop of coolant, moderator is the coolant
- PWR: pressurized water reactor: two loops, moderator loop (primary) and coolant loop (secondary). As about sodium
- HWR: heavy water reactor, or BWR using Deuterium water, can use low quality uranium
- GCR: gas cooled reactor, e.g. pebble-bed reactor-safer, newer design
- BR: breeder reactor: uses liquid sodium as coolant, very high neutron flux (flow) so creates plutonium (bomb fuel) out of non-fuel U 238
- Fusion reactions (e.g. solar reactions)
- 1 million degrees C, very high temperatures, must be contained in a magnetic field
- Hard to do on earth, but if we get it right, 1/600 parts of seawater contain deuterium, the fuel, so virtually unlimited power
- Safer than fission, because as soon as any of the conditions fail, the reaction ceases.
Part two: environmental concerns
- Fuel issues: Uranium mining
- 0.7% of uranium mined is U235, rest is low quality U238 (see above)
- Mill tailings are leftovers from the refining/processing process. Often toxic
- Any time humans concentrate anything, we create an environmental hazard (uranium, lead, copper, zinc, mercury, etc.)
- Nuclear waste includes all materials involved in fuel processing, reprocessing, reactor operations or exposed machinery
- 16% of global energy comes from nuclear power (highest in France)
- Two major accidents: Three mile island (PA, 1979) and Chernobyl (1986, Pripyat, outside Kiev in the Ukraine, was USSR back then)
- Three mile island: core exposed due to operator error, released radiation, site still too hot to enter
- issues: officials lied initially about release, amounts, and effects
- long term damage: not much radiation was released, but no nuclear plants have opened since then in the US
- exposed flaws in design, operation, maintenance and regulation of plants in the US
- Chernobyl: core exposed due to operator error, control rods burned, reactor exploded, radiation killed 37 firemen, radiation released killed many hundreds of thousands due to increased cancer risk
- Waste issues: Yucca Mountain project, salt mines
- Thermal pollution