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EASC 238 (Natural Resources) > Topic 6: Nuclear fuels > Flashcards

Topic 6: Nuclear fuels Flashcards

1
Q

What is chemical vs nuclear energy? differences?

A

chemical: breaking and joining of atomic bonds, with an electron transfer. Atoms maintain their identities

Nuclear: changes in forces that hold together atomic nuclei. The character of atom or element has changed

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2
Q

What is radioactive decay? what is a half life?

A
  • spontaneous disintegration of an atom
  • releases atomic particles, heat energy, gamma radiation
  • decays from parent to daughter nuclide
  • Half life- time take for half original volume of parent to decay to daughter
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3
Q

What is radioactivity?

A
  • the propensity for a material to undergo radioactive decay, based on ratio of protons to neutrons in nucleus
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4
Q

What are isotopes?

A
  • atoms of the same element with different numbers of neutrons - thus different atomic mass
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5
Q

what is ionizing radiation?

A
  • emitted subatomic particles or electromagnetic waves
  • energetic enough to detach electrons from atoms or molecules
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6
Q

What is alpha radiation?

A
  • emission of alpha particles, 2 protons and neutrons
  • very destructive but travels short distances
  • can be stopped by paper
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7
Q

What is beta radiation?

A
  • emission of beta particle, high energy electron
  • travels further than alpha, but less destructive
  • can be stopped w few cm metal
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8
Q

What is gamma radiation?

A
  • emission of gamma rays, photons of very high frequency and very short wavelength EM spectrum
  • far-travelling, very destructive to cell tissues
  • can be stopped w thick shield of lead/concrete
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9
Q

What is nuclear fission

A
  • breakdown of large nucleus into smaller daughter nuclei
  • small amount of matter converted into large amounts of energy during fission
  • bc mass of atomic nucleus is less than mass of constituent protons/neutrons = missing mass is converted into energy
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10
Q

Fission is a type of decay. it cannot be slowed, but it can be accelerated. How?

A
  • bombarding radioactive nuclei with neutrons
  • having sufficient numbers of radioactive nuclei so natural rate of neutron emission increases decay rate
  • ex. bombardment of 235U results in a self sustaining chain reaction, so fission creates more fission. run-away rain reaction may cause nuclear bomb
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11
Q

Where are some uranium sources found on earth?

A
  • igneous sources - found in low concentration crustal rocks, concentrated in fine stage residual melts and pegmatites. may be bound in minerals (apatite). May be found in rich veins next to granites (skarns)
  • metamorphic sources- deposited in skarns, adjacent to granitic intrusions
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12
Q

What is hydrogenic uranium? Where is it found and how is it formed?

A
  • it is our main economic source of uranium
  • formed when reduced U4+ is oxidized into U6+, this combines with oxygen to form UO2
  • relies on very specific formation environment
  • found in surface and oxic ground waters
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13
Q

What is detrital uranium?

A
  • Precambrian fluvial sandstones and conglomerates
  • low oxygen precambrian atmosphere results in little or no conversion of U4+ to U6+, preserves un-leached uranium = presents as uraninite ore
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14
Q

How do we find uranium on earth?

A
  • standard prospecting tech
  • also gross count survey (Geiger-Muller detector)
  • gamma ray spectrometry survey (detects radiation specific to different elements)
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15
Q

what us beneficiation and enrichment of uranium?

A

Beneficiation:
- uranium ore is very low grade in U3O8, less than 1%. thru mechanical and chemical concentration, a concentrate of enriched U3O8 is produced (called yellowcake)

enrichment:
- production of nuclear fuel (235U) from yellowcake

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16
Q

What is gaseous diffusion?

A
  • U3O8 converted to uranium hexafluoride gas (UF6), by being passed thru porous barriers
  • INCREDIBLY expensive. ~30% total nuclear fuel cost.
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17
Q

What are nuclear fuel rods?

A
  • enriched UF6 oxidized into UO2 and converted to ceramic powder
  • compacted into small fuel pellets, and loaded into metallic fuel rods, then placed into elements.
18
Q

What is reactor burning?

A
  • the actual process of producing nuclear energy
  • fuel rods loaded into reactors
  • irradiated with neutrons to initiate fission, chain reaction occurs, which produces energy for 3-5 yrs.
  • rods are replaced when they are no longer able to support chain reaction
19
Q

What are waste rods and how are they dealt with?

A
  • nuclear fuel rods that are not longer able to support chain reaction (all fissionable material is used up)
  • when removed, they are still ‘hot’ and contain highly radioactive but short-lived isotopes
  • temporarily housed in water tanks to cool and absorb radiation for several months
  • afterwards permanently stored in geologic strata (buried)
20
Q

What is the natural geologic reactor??

A
  • geologic evidence for fossil natural fission reactors in gabon west africa
  • natural hydrogenic uranium deposit, that has depleted 235U content and increased nuclide content - which suggests former nuclear fission
  • occurred around 2 billions yrs ago
21
Q

what are power generating reactors

A
  • machines that help slow neutrons (via light elements) to capture natural uranium and support/cause fission
22
Q

What are some examples of power generation reactors?

A
  • magnox reactor
  • CANDU reactor
  • AGR’s (advanced gas-cooled reactors)
  • boiling and pressurized water reactors
  • fast breeder reactors
23
Q

What are some potential future technologies we can use in nuclear reactors?

A
  • small modular reactors (miniaturized reactor tech, much smaller scale for places with modest power needs, require no human intervention to maintain.)
  • fusion reactors (controlled fusion of nuclei to release huge amounts of energy)
24
Q

What is fusion?

A

joining of two lighter atoms to make a heavier one

25
Q

What are some causes of nuclear accidents?

A
  • inherent complexity (the more complex a system, the more possible fail points exist)
  • design/modelling errors (any unexpected behavior of reactor or fissionable material may exceed a systems ability to cope, any emergencies not forseen will not have plans in place to help solve them)
  • mechanical failure (equipment not built for encountered conditions, or poor maintenance/cost-saving results in failure)
  • human error (design stage, improper operation, improper decommissioning)
  • intentional sabotage or attack
  • natural disaster (major nat disasters can cause damage to reactors and disable safety mechanisms)
26
Q

What are some types of nuclear accidents?

A
  • loss of coolant (which can cause overheating of the reactor or steam explosion is water is cooled)
  • melt-down (reactor core becomes too hot, causes fuel to melt, can melt thru reactor housing and into the ground)
  • Waste fuel accidents (failures in cooling ponds for waste fuel rods, or low-grade leaks from reprocessing plants/fuel containers)
  • processing accidents (low-grade leaks and danger of criticality)
27
Q

What was chernobyl? What caused it?

A
  • Ukraine, 1980’s
  • the worst nuclear accident in history, level 7 event
  • experiment for emergency systems causes reactor power output to become unstable, core overheats and reactor heats resulting in huge surge of reactant power and output
  • steam explosion causes more increase in reactor power output, then a second explosion causes a runaway fission cascade, graphite moderator catches fires - which disperses radioactive material
28
Q

What were the main causes of chernobyl?

A
  • human error, bad design, no containment structure
29
Q

What was the worst nuclear accident in North America?

A
  • Three mile island, Pennsylvania in 1979
30
Q

What occurred at three mile island?

A
  • loss of coolant, partial core meltdown, major contamination of coolant fluid and power station site.
  • minor hydrogen explosion due to exposed fuel rods reacting with steam
  • radioactive steam vents into the atmosphere
  • contamination occurring at plant and around plant
31
Q

What was the worlds 2nd level 7 nuclear disaster?

A

Fukushima Daichi boiling water reactors in Japan in 2011

32
Q

What occurred at Fukushima?

A
  • plant built on subduction zone
  • earthquake causes tsunami, damaged onsite equipment
  • reactors 1,2,3 SCRAM’d, 4,5,6 were already shut down
  • tsunami wave flooded backup generators
  • emergency battery ran out, reactors 1,2,3 overheat and meltdown
  • hydrogen explosions occur
  • release of radiation into ocean
33
Q

What is SCRAM?

A

A rapid emergency shutdown of a nuclear reactor

34
Q

What are the front-end sources of nuclear waste?

A
  • waste generated in fuel processing
  • mining waste (not very radioactive)
  • depleted uranium
35
Q

What are the back-end sources (after fission) of nuclear waste?

A
  • spent fuel rods, containing fission products
  • neutron poisons
36
Q

What are low level nuclear wastes?

A
  • paper, rags, tools, clothing
  • these contain small amounts of shortlived radioactivity
  • more of a precautionary thing
  • typically dealt with by shallow burial and incineration
37
Q

What are intermediate level wastes?

A
  • higher radioactivity than low level waste,
  • resins, chemical sludge, reactor fuel cladding, contaminated materials from reactor decommission.
  • can be solidified in concrete or bitumen for disposal
  • typically deposited/buried deeper underground if long-lived contaminants
38
Q

What are high-level wastes?

A
  • waste produced by nuclear reactors
  • fission products, elements from reactor core that are highly radioactive and thermally hot
39
Q

What are disposal methods for high-level radioactive waste? intermediate treatment, for materials with concerns over long-lived radioactive elements

A
  1. vitrification (radioactive waste bonded with glass in steel containers, welded shut. Stable for 1000+ yrs)
  2. ion exchange (ferric hydroxide used to concentrate radioactive contaminants into sludge, mixed with concrete + buried)
  3. synroc (mineral-based substrate absorbs liquid high-level waste, turns into synthetic rock)
40
Q

What are disposal methods for high-level radioactive waste? For long term management and disposal

A
  1. re-use and reprocessing (some elements extracted for industry applications, such as food irradiation, radio-medicine, or nuclear assisted hydrogen production methods for oil recovery)
  2. transmutation (placing highly radioactive elements in breeder reactors to bombard with neutrons and convert to less dangerous elements)
  3. space disposal (but very dangerous and costly)
  4. Geologic disposal (burial of nuclear waste into deep geologic formations

EASC 238 (Natural Resources) (10 decks)

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