Front End Flashcards
(14 cards)
Where do we get nuclear fuel?
What is this “fuel cycle” thing?
Pre-irradiation
Mining → Milling → Conversion of U3O8 to UF6 → Enrichment → Fuel Fabrication.
Post-irradiation (back end)
* On-site storage (reactor pool, dry cask storage)
* Permanent waste disposal
* or reprocessing and recycling of Pu
Why Must be enriched up to about 3-5% for commercial fuel?
Preventing nuclear weapons development, IAEA Safety Standards.
Separative Work Unit
F = amount (kg) of feed material
* P = amount (kg) of enriched product
* W = amount (kg) of waste
* xf = w/o of 235U in the feed (0.711% in Nat. U)
* xp = w/o of 235U in the product (depends on Tcycle)
* xw = w/o of 235U in the waste (0.2-0.3%)
Seperative Work Unit
Where
* PU = price of natural uranium, $/kgU
* PC = cost of conversion of U3O8 to UF6, $/kgU
* lC = conversion losses,
* PS = price of SWU, $/SWU
* S = SWU factor, SWU/kgU
* PE = price of enriched U, $/kgU
What is criticality safety?
What are the effects of a criticality event?
What are the consequences of a criticality event?
- The prevention of a self-sustainable nuclear chain reaction
- The uncontrolled release of ionising radiation and energy
- Acute radiation effects
Criticality safety is concerned with preventing both critical and supercritical states
Criticality controls with design
Geometry
Fissile Mass
Isotropic Enrichment
Moderation
Heterogeneity
Shape
Interaction and Seperation
Neutron absorbing materials
When is criticality possible?
Criticality not possible unless fissile material > min critical mass
Criticality controls
Administrative control
Established limits on the amount of fissionable material allowed
*Posted mass limits
*Zone markings
* Training programs
How to reduce chance of criticality through design?
Geometry: Using specific shapes and configurations to minimize neutron interactions.
Fissile Mass Limits: Ensuring the amount of fissile material stays below the minimum critical mass.
Isotropic Distribution: Controlling how fissile material is spread to avoid concentrated areas.
Enrichment Control: Limiting the percentage of fissile isotopes in nuclear fuel.
Moderation Management: Regulating materials that slow down neutrons, such as water or graphite.
Heterogeneity: Designing fuel assemblies with varied compositions to disrupt neutron propagation.
Shape Optimization: Using non-spherical configurations to reduce neutron reflection.
Interaction and Separation: Keeping fissile materials physically apart to prevent unintended reactions.
Neutron Absorbing Materials: Incorporating materials like boron or cadmium to absorb excess neutrons.
What is Isotropic Distribution
Controlling how fissile material is spread to avoid concentrated areas.
Baiscs of U235, U238 and UO2
Fissile U-235 is only ~0.7%
* Requires enrichment
U-238 breeds Pu and higher actinides
* Weapons material proliferation
* Waste is radioactive in a very long term
UO2 is a good fuel matrix
* Radiation damage stability
* Vast experience
what is the most reaactive shape
sphere is.
Slab or cylinder → beneficial due to increase neutron leakage
* Leads to the term “geometrically favourable” or “safe by shape
Control strategy
* Geometrically favourable dimensions that confine the material to subcritical levels
waste management options
isolate from man
dilute to low concentrations
multi barrier approahc
destroy
recycle Pu
Different types of fuel
Homogeneous fuel
* higher NU requirements and higher FCC
* Micro heterogeneous fuel
* Modest improvement can be achieved at the expense of
* higher design complexity
* lower thermal margin
* Macro heterogeneous fuel
* Breakeven (with UO2) FCC and NU utilisation
* More favourable worth of reactivity control materials
* Has mechanical, thermal, and materials design issues
* All can be addressed, actively studied in Russia
* All 3 design concepts are feasible in principle
