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1
Q

What is the distribution coefficient?

A

the conc. of component in org. phase / conc. of comp. in aqueous phase

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2
Q

What is the distribution coefficient a function of? What is it not a funciton of?

A

nature of the solvent, temperature, equilibrium cpomosition of the aqueous and organic phases but independent of the amount of either phase

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3
Q

Why can the solvent extract more compoment from aqueous feed?

A

Because the concentration of component in the aqueous feed is higher than that in the aqueous residue from which the org. phase is in equilibrium with.

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4
Q

What are the 6 principal factors affecting the distribution coefficient value?

A
  1. Element being extracted
  2. Oxidation-reduction potential of aqueous phase
  3. Nature of solvent
  4. Conc. of complexing agent
  5. Conc. of salting agent
  6. Hydrogen ion conc. in aq. phase
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5
Q

How do we measure the ease or difficulting of separation by fractional extraction?

A

By alpha which is the ratio of the distribution coefficient of component i divided by the distribution coefficient of comp j.

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6
Q

What needs to be added to fractional extraction flowsheets when we need to extract one more comopment?

A

a scrubbing and stripping section per component extracted.

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7
Q

What main characteristic the metallic element to be extractable by an organic solvent inmmisicible with water needs to have?

A

The element must be capable of forming an organic-soluble, electrically neutral complex compound with the solvent or with an added complexing agent.

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8
Q

What are coordination bonds?

A

sharing of electrons from the complexing agent to complete previously unfilled orbits of the cation.

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9
Q

What is the coordination number?

A

the number of complexing groups that are attached to the cation.

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10
Q

What needs to happen in terms of distribution coefficients for two elements to be separated?

A

For them to have different distribution coefficients.

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11
Q

How is Pu separted from U in the purex process?

A

A reducing agent is added to reduce Pu to Pu3+ which makes it extractable to water while uranium stays in the organic phase?

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12
Q

What agent is used to reduce Pu but not U in PUREX process (an example)?

A

ferrous salt.

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13
Q

Why are complexing agentes used?

A

to increase or decrease the Distribution coefficient of a metallic component between aqueous solution and kerosene.

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14
Q

Is the addition of a complexing agent necessary?

A

In some cases where the metallic component like Zr(No3)4 is not extracted by the kerosene solvent a complexing agent is used as a vessel through the organic phase to extract the component.

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15
Q

What is the effect of adding solutes to the aqueous phase?

A

Increase distribution coefficient of extractable components.

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16
Q

Why does the distributionc oefficient increases with addition of of a solute as nitrate concentration in aqueou sphase?

A

Because addition of nitrate ion tends to increase the conc. of unionized uranyl nitrate by shifting the equilibrium to the right of the following equation:
UO2(2+) + 2NO3(-) -> UO2(NO3)2
therefore converting it into a more extractable form.

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17
Q

Does the presence of nitric acid decreases the distribution coefficient of Uranium? Why?

A

For nitric acid concentrations less than about 5M the uranium distribution coefficient is greater the higher the concentration of acid. Beyond 5M increasing acid conc. will decrease U distributionc oefficient. Below 5M this happens because of the salting effect of nitrate ion.

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18
Q

What are some qualities of a good solvent for the separation of metals by fractional extraction?

A
  • Selective (high ratio of distribution coefficient)
  • Good extraction capacity
  • It should be readily stripped
  • relatively immiscible with water
  • Different density from water, low viscosity, and high interfacial tensions
  • nonvolatile, nonflammable, nontoxic
  • readily purified by fractional distillation
  • stable in precesenc of chemical agents used in the process.
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19
Q

What is the ingestion toxicity of mill tailings dominated by? Give two example radioisotopes.

A

Decay daughters of uranium isotopes such as Th-230 and Ra-226

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20
Q

Is toxicity of the uranium ore high enough to warrant measures?

A

No, just those in mill tailings.

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21
Q

When does the radiotoxicity of mill tailings start to decrease? Why?

A

10,000 years because of the decay half-life of Th-230 is 80,000 years which is the most dominant contributor to the radiotoxicity of mill tailings.

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22
Q

How does the toxicity of depleted uranium behave with time? Is the toxicity plateau lower or higher than that of the uranium ore?

A

At the start, it has relatively low toxicity but as the U isotopes decay, they generate decay daughters which cause U to increase its toxicity with time. The plateau is lower than that in the ore.

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23
Q

What are the 6 main types of radioactivity?

A
  • Alpha Decay
  • Beta Decay
  • Gamma Emission
  • Positron Emission
  • Electron Capture
  • Spontaneous Fisison
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24
Q

What is the energy of alpha particles in alpha decay?

A

2 to 8 MeV

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25
What is the energy of beta particles in beta decay?
10,000 eV to 4 MeV
26
What is the most serious hazard among the three emitted particles (beta, alpha, gamma)?
gamma
27
With what speed and energy are neutrons born in fission reaction?
avg energy of 2 MeV (speeds of 1.955E7 m/s)
28
What are moderators?
materials like hydrogen, deuterium beryllium or carbon that are used to cause elastic collisions with neutrons to slow them down for them to reach thermal equilibrium with surrounding medium
29
How do you overcome leakage in fast reactors due to high vneutron velocities?
by using a high concentration of fissionable material (plutonium or highly enriched U-235).
30
What is the neutron flux?
Is the product of the number of neutrons per unit volume and the neutron speed
31
What is the physical significance of the neutron flux?
It is the total distance traveled in unit time by all the neutrons present in unit volume
32
What are typical volumes of neutorn flux in a reactor?
10^11 to 10^14 n/cm2s
33
What does the heat release of spent fuel depend on qualitatevly ?
- rate of fission of fuel when in reactor - length of time in reactor - length of time to cool
34
What is an issue with using throium as fertilfe fuel int erms of processing?
In fission Th-232 absorbs a neutron to produce Th-233 which then decays to Pa-233 and further decays into U-233 but with thermal fluxes above 5E13 an appreciable fraction Pa-233 absorbs a neutron to make Pa-234 which then decays to U-234
35
What is an important nuclear parameter in terms of breeder? What is a good value and why?
n which is the # of fission neutrons produced per neutron absorbed in the fuel. It must be at least two since one goes to keep the chain reaction while the otherbreeds fuel.
36
What is the typical energy of a neutron in a fast reactor?
2E5 eV
37
What is nu, the # of fission neutrons produced per neutron absorbed for Pu-239 in the fast spectrum?
2.3
38
What is burnup?
The amount of heat liberated by the fuel through fission and other nuclear reactions in MWd/MT (other units exist.
39
What is reactivity?
the difference between the rate of neutron production by fuel and the rate of neutron consumption, divided by the rate of neutorn production
40
Why does reactivity decreases with increasing burnup?
Because the increase in Pu-239 and Pu-241 content is not sufficient to compensate for the decrease in U-235 content and because U-236, Pu-240, Pu-242 and FP whose content increases are neutron absorbing poisons.
41
What are the five main objectives of fuel and poison management?
- keep reactor critical during long-term changes in fuel comp and reactivity - shape power dens distribution to max power output - maximize heat production from fuel - obtain uniform irradiation of fuel - max productive use of neutrons
42
At the beginning of operation with all fresh fuel in a PWR is the flux and power density distribution nonuniform?
Yes
43
How can you flaten the power distribution from a fuel and poison management perspective?
This can be done by placing fuel of lower enrichment in the middle and fuel with higher in the peripherial or by concentrating poisons in the middle region.
44
What are the buckled zones?
peripheral regions of the reactor
45
What is the advantage other than providing more uniform power density of zoned loading?
provides uniform burnup for the fuel in the region of the reactor where the flux is uniform
46
What is the disadvantage of zone loading?
Use of higher fuel enrichment and hence more cost than with uniform loading, also, the burnup in the buckled zone is nonuniform
47
How does partial batch replacement help a chiave a more uniform burnup?
partial replacement of the fuel at the end of life instead of complete replacement. The burned fuel is replaced by fresh fuel and the rest is left in the reactor until the next time fuel has to be replaced.
48
What is the advantage and disadvantage of partial batch replacement?
fuel discharged each time has farily uniform composition while the disadvatanges are the need to open the reactor more frequently for refueling and the peaking in flux and power density that occurs every time fresh fuel is charged to the center .
49
How can flux peaking be reduced when refueling?
By scatter refueling,
50
What does scatter refueling consist on?
On creating groups of assemblies (e.g. 4 groups) in which each only one assembly is replaced per cycle and so on.
51
What are the benefits of scatter refueling?
an overall flatter flux distribution since the fuel in the center is highly burned, fuel can be irradiated to higher burnups than in batch irradiation, and less control poison is needed. Additionally, depleted fuel acts as control poison to absorb excess neutrons to productively make plutonium
52
Is the power density flatter in scatter refueling? Why?
No, there is still power density peaking in the freshest assembly that is replaced per cycle.
53
What is the main constraint of scatter refueling?
that reactors are at most a couple of few hundred assemblies large meaning six assemblies per group is practically the upper limit. The more groups the more the reactor needs to be shutdown for refuelin.g
54
What type of reactors are not subject to the constraints of scatter refueling?
graphite moderated, gas cooled reactor which have thousand of assemblies and are equiped to change assemblies withouth shutting down.
55
What is the shared disadvantage of graded ans scatter refueling?
flux is higher in the center of the reactor than at the outside although nonuniformity is not as great as a simple batch irradiation since highly burned fuel will always be present at the center of the reactor.
56
What is the shared disadvantage of graded ans scatter refueling?
flux is higher in the center of the reactor than at the outside although nonuniformity is not as great as simple batch irradiation since highly burned fuel will always be present at the center of the reactor.
57
What is out-in refueling and what are the benefits?
fuel is divided into annular zones of equal volume. It depresses the flux and power density further at the center. It consists of moving fuel zones further in and removing the center one always.
58
What are the disadvantage of out-in refueling?
In large reactors, the depression in flux and power density at the center of the reactor is too high.
59
What are the implications of reprocessing and volume reduction in terms of structural materials?
All structural materials consisting of fuel assembly except for the fuel are now regarded as either High-Level Solid Waste or TRU waste. We many need to prepare a separate repository for this type of wastes in addition to the HLW repository.
60
Does reprocessing and volume reduction really reduce volume? Why?
The repository footprint is determined by heat generation intensity which comes mainly from FP. The heat generation per volume is almost the same for both solidified HLW and SNF canisters. Therefore volume reduction effect by reprocessing is not obvious. It mostly facilitates transportation and handling and allows us to extract useful materials from spent fuel.
61
What type of waste do YM, WIPP, and Barnwell hold?
- YM: HLW - WIPP: TRU (Defense) - Barnwell: Class A, B, and C
62
Who is the operator for YM, WIPP, and Barnwell?
- YM: DOE - WIPP: DOE - Barnwell: Energy Solutions
63
Who is the regulator for YM, WIPP, and Barnwell?
- YM: NRC - WIPP: NRC - Barnwell: South Carolina Department of Health and Environmental Control
64
What are some related regulations for radiological safety related to YM, WIPP, and Barnwell?
- YM: NWPA, EPA, 10CFR-63 - WIPP: Federal Waste Isolation Pilot Plant Land Withdrawal Act of 1992, Resource Conversation and Recovery Act of 1991 (RCRA), 40 CFR-191 and 194 (EPA) - Barnwell: RCRA and Atomic Energy and Radiation Control Act, 10 CFR 20.2002.
65
Amount disposed of so far in YM, WIPP, and Barnwell.
- YM: 0 - WIPP: 85000m3 (2013) - Barnwell: 230,000ft3 (2004)
66
What is the capacity of YM, WIPP, and Barnwell?
- YM: 70000 MT - WIPP: 173,600m3 (2013) - Barnwell: 575,000ft3 (2004)
67
Name the environment, depth below the surface and above the water table, type of rock, barriers, and nearest town of Yucca Mountain.
- Environment: Dry climate - Depth: 300m below surface and 300m above water table - Type of Rock: unsaturated rock layers - Barrier: Capillary Barriers - Nearest Town: 70 km from the mountain
68
Name the depth below the surface type of rock, and barriers of WIPP
- Depth: 2150 ft underground - Type of Rock: salt bed with an absence of flowing freshwater - Barriers: rock salt heals its own fractures because of its plastic quality
69
Name the depth below the surface type of rock of Barnwell
- Near Surface Soil | - Clay Rich Soil
70
What is the waste form of YM?
UO2 or borosilicate glass
71
What is the waste form of WIPP?
Mixed Waste (tools, cloathing, sludges, etc.)
72
What is the waste form of Barnwell?
Mixed Waste
73
What is the package used in YM?
TAD (Transportation, Aging, and Disposal Canister)
74
What is the package used in WIPP?
Transuranic Packaging Transporter Model 2 (TRUPACT-II), HalfPACT and TRUPACT-III
75
What is the package used in Barnwell?
Approved high integrity containers by the South Carolina Department of Health and Environmental Control
76
What is the buffer used in YM?
Drip Shields
77
What is the buffer used in WIPP?
Crushed Salt, MgO
78
What is the buffer used in Barnwell?
Clayey Soil
79
What are the implications of higher solubility limits in terms of radionuclide release? A higher initial mass?
If the solubility limit is higher, then more radionuclide release will occur and will occur sooner than previously predicted. A higher initial mass could cause precipitation and therefore radionuclide will be solubility limited release.

Waste 2 (2 decks)

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