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Health Physics > Nuclear Fuel Cycle and Radioactive Waste Management > Flashcards

Nuclear Fuel Cycle and Radioactive Waste Management Flashcards

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1
Q

Nuclear Fuel Cycle

Overview

A
  1. Mining and Milling
  2. Gas Conversion
  3. Enriching - Increases 235 concentration to enrichment levels (3 - 5% 235U)
  4. Fuel Rod Fabrication - Combines 235U into useable fuel elements for a nuclear power reactor
  5. Power Reactor - Spent fuel elements of depeleted uranium with levels around 0.6% 235U
  6. Fuel Reprocessing Plant
  7. High Level Waste repository
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2
Q

Describe

Mining and Milling

(Nuclear Fuel Cycle)

A
  • Extracts U3O8 (“yellow cake”) from ore at natural enrichment levels of 0.711% 235U
  • This leaves low grade crushed rock and sand as byproducts.
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3
Q

Describe

Gas conversion

(Nucleaer Fuel Cycle)

A

Converts U3O8 to a UF6 gas

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4
Q

Define

Mine Tailings

(Nuclear Fuel Cycle)

A
  • During mining and milling, hundreds and gallons of water are used for each ton of ore processed.
  • This wastewater contains significant concentrations of radium and uranium.
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5
Q

Describe

UMTRAP

(Nuclear Fuel Cycle)

A

Uranium Mill Tailngs Remedial Action Program

  • Clean up the mill sites
  • Reduce radon emanation from tailings to acceptable levels by burying them
  • Restore the land to unrestricted use
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6
Q

Describe

What changes when uranium ore is transformed to yellowcake

(Nuclear Fuel Cycle)

A
  • One ton of uranium ore usually yields between 2 and 3 kilograms of yellow cake.
  • Yellow cake has 95% of the uranium contained in the original ore, but only 14% of the total radioactivity.
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7
Q

What are the three classes of low level waste?

A
  • A (least radioactivity)
  • B
  • C
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8
Q

What is the basic principle of dealing with radwaste?

A
  • High Level: Concentrate & contain
  • Low Level: Dilute & disperse
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9
Q

What is 10 CFR 61?

A

Licensing Requirements for Land Disposal of Radioactive Waste

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10
Q

What are requirements for classification as class A LLW?

A
  • Cannot contain more than 1% freestanding liquid
  • Nonexplosive
  • Not biologically hazardous
  • Not pyrophoric
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11
Q

What are requirements for classification as class B LLW?

A

Must meet special conditions as to form to ensure that the waste does not structurally degrade and affect overall stability of the site through slumping, collapse, or other failure of the disposal unit, leading to water infiltration.

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12
Q

What are requirements for classification as class C LLW?

A

It must meet the stability requirements of class B, but extra precautions must be taken by the disposal site to protect against inadvertent intrusion.

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13
Q

Applied Processing Techniques

Increasing the concentration of solids

A

Compaction

  • Involves crushing and baling under compression.
  • Typical volume reduction of 3 to 7 times, but big problem of airborne activity as a result of crushing operation.

Incineration

  • Particularly useful with animal carcasses which are radioactive.
  • Typical volume reduction of 10 to 15 times, but produces radioactive gases and particulates in addition to solid ash residue.
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14
Q

High Level Liquid Solidification

Overview

A
  1. Initial Volume Reduction
  2. Tank Storage
  3. Solidification ⇒ Evaporation, nitrate removal, calcination, vitrification or ceramic formation
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15
Q

High Level Liquid Solidification

What is initial volume reduction?

A
  • Needed to reduce the overall size
  • Typically done via evaporators because tank farms are very expensive
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16
Q

High Level Liquid Solidification

Tank Storage

A
  • Utilized in the overall management of the waste to allow for substantial radioactive decay before the solidifcation is attempted.
  • This prevents decay heat from causing temperature variations (and subsequently other related faults) in the final product produced.
17
Q

Define

Mixed Low-Level Radioactive and Hazardous Waste

A

Waste that satisfies the definition of LLW in the Low-Level Radioactive Waste Policy Amendments Acts of 1985 and contains hazardous waste that either: (1) is listed as a hazardous waste in Subpart D of 40 CFR 261 or (2) causes the LLW to exhibit any of the hazardous waste characteristics of Subpart C of 40 CFR 261.

18
Q

Define

Transuranic wastes

A
  • Wastes containing elements with a Z > 92, the Z of uranium.
  • Have extremely long-lived nuclides and often decay by alpha particle emission.
19
Q

Define

Byproduct material

A
  • Any radioactive material (except special nuclear material) yielded in, or made radioactive by, exposure to the radiation incident to the process of producing or using special nuclear material.
  • Example ⇒ The tailings/wastes produced by the extraction of uranium or thorium from ore processed primarily for its source material content.
20
Q

Define

Source material

A

Uranium or thorium or any combination of the two in any physical or chemical form.

21
Q

Define

Special nuclear material

A
  • Ores that contain, by weight, 0.05%, or more, of uranium, thorium, or any combination of the two.
  • Source material does not include special nuclear material.
22
Q

Define

Discrete source

A

A radionuclide that has been processed so that its concentration within a material has been purposely increased for use for commercial, medical, or research activities.

23
Q

What are three types of fissile material?

A
  • Burn naturally occurring U-235 directly
  • Irradiate U-238 (produces Pu-239)
  • Irradiate Th-232 (produces U-233)
24
Q

What are different methods of uranium enrichment?

A
  • Electromagnetic
  • Gaseous diffusion
  • Gaseous centrifugation
  • Laser excitation
  • Gas nozzles
  • Chemical exchange
25
Q

What are four exposure pathways from mill tailings?

A
  • γ-radiation
  • Dust blowing radioactive radium and arsenic
  • Groundwater
  • Radon exhalation
26
Q

What are the requirements for nuclear fuel?

A
  • Fissionable (235U, 233U, 239Pu)
  • Reliable
  • Relatively low cost
  • No release of radionuclides to the coolant
27
Q

How do you control criticality?

A
  • Geometry of fissile assembly
  • Concentration of fissile material
  • Interaction between 2 or more critical assemblies
  • Presence/absence of moderator (water)
  • Presence/absence of a neutron reflector (human body)
  • Presence/absence of a neutron absorber (poison)
28
Q

Graph

Thermal fission product yield (Percent Yield vs. Mass Number)

A
29
Q

Graph

Fission cross section vs. neutron energy

A
32
Q

Define

Transuranic waste

A
  • Material contaminated with transuranic elements (artificially made radioactive elements such as neptunium, americium, and others) that have atomic numbers higher than uranium on the periodic table.
  • Primarily produced from recycling spent fuel or using plutonium to fabricate nuclear weapons
  • T1/2 > 20 years
  • Concentrations > 100 nCi g-1
33
Q

Why segregate transuranic from high level waste?

A
  • After 6 years only 9 fission products (and progeny) contribute significantly to total activity.
  • After 100 years 90Sr/90Y and 137Cs/137mBa makeup 90% of fission product activity.
34
Q

List the 4n series decay chains.

A

AUNT

  • 4n + 3 ⇒ Actinium (U-235)
  • 4n + 2 ⇒ Uranium (U-238)
  • 4n + 1 ⇒ Neptunium
  • 4n + 0 ⇒ Thorium (Th-232)
35
Q

List the effects of a nuclear weapon detonation

A
  • Blast ⇒ High temperatures and radiation cause a gas to move outward radially in a thin, dense shell called the hydrodynamic front (40 – 50%)
  • Thermal radiation ⇒ The “flash” from the nuclear detonation emits large amounts of visible, infrared, and ultraviolet light (30 – 50%)
  • Ionizing radation ⇒ Neutrons, gamma-rays, alphas, and electrons, moving at the speed of light (~5%)
  • Nuclear fallout ⇒ Radioactive material (e.g., fission fragments) released to the environment/atmosphere.
  • Electromagnetic pulse ⇒ Electrons produced during detonation are caught by the earth’s magnetic field at altitudes between 20 – 40 km. The pulse lasts 1 msec, but is powerful enough to generate thousands of volts in long metal objects which can destroy unshielded electronics

Health Physics (17 decks)

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