Glossary

Breeder fast reactor

A nuclear reactor that uses high-energy neutrons to produce more fissile material than it consumes during its operation.

Blanket fuel

A nuclear reactor zone containing fertile material that is used for the purpose of breeding fissile material by nuclear reactions. A sub-critical assembly zone in an externally-driven system (EDS) is also sometimes referred to as a blanket, particularly if the zone only contains fertile material, but not in general (i.e., the “blanket zone” in an EDS could also contain fissile material).

Capacity factor

A ratio of the actual electrical energy output over a given period of time to the maximum possible electrical energy output over that period (i.e., continuous full-power operation).

Conditioning

Processing of spent nuclear fuel into packages that are appropriate to store, transport, and dispose.

Continuous recycle

A fuel cycle strategy in which fuel is recycled indefinitely, either in the same nuclear fission system or another fission system. Only high-level waste and low-level waste associated with (re)processing of the fuel are disposed of; no intact spent nuclear fuel is disposed of in continuous-recycle fuel cycle options.

Conversion of Uranium

A step in the uranium fuel preparation process in which UF₆ is produced, starting from yellowcake. The UF₆ is then used in the enrichment process.

De-conversion of depleted uranium

A process that changes the chemical form of depleted uranium from UF₆ to the more chemically stable U₃O₈ for the purpose of disposal.

Depleted Uranium (DU)

Uranium that has a lower content of the fissile isotope uranium-235 than the naturally-occurring uranium in the environment. It is produced as a by-product of the uranium enrichment process used to produce fuel for some nuclear reactors.

Discharged Fuel (DF)

Nuclear fuel that is discharged from an irradiation system, such as a nuclear reactor, after irradiation.

Discount rate

The discount rate is a quantitative measure of the time value of money. It can be theoretically defined as the opportunity cost of investing in a certain project rather than in an alternative investment featuring equivalent risk.

Disposal cost of depleted uranium

Cost of permanent disposal of depleted uranium in the U₃O₈ chemical form.

Driver fuel

Fuel with high fissile content that is necessary to sustain criticality in the fast reactor.

Equilibrium (mass balance)

The calculations presented in this website are performed for fuel cycles at mass balance equilibrium (assuming a fully developed and deployed system), which implies that all the mass streams (flow rates) in a given fuel cycle do not change with time, or from one cycle to the next, and that each fuel cycle facility is preceded and followed by a sequence of identical facilities, with identical cash flow profiles in constant dollars. This assumption allows the evaluation of the performance of fuel cycles independent of the factors required to reach equilibrium situations.

Enrichment

The process by which the fraction of isotope ²³⁵U in a given uranium sample is increased, and the concentration of isotope ²³⁸U is correspondingly decreased.

Evaluation Group (EG)

The group of Fuel Cycle Option Groups created by considering the similarities between Fuel Cycle Option Groups (see Option Group below). Each Evaluation Group consists of one or more Fuel Cycle Option Groups, and results from the process of combining groups based on the principles of similarity of resource requirements, fuel mass usage and compositions, and disposal needs.

Fabrication cost of nuclear fuel

The cost of producing nuclear fuel elements in their final form, ready for reactor irradiation, excluding the cost of purified uranium, enrichment (if present), addition of other fissile materials, and other fuel additives (e.g., burnable poisons), but including the cost of the assembly hardware (e.g., cladding, grids, spacers, wire wrappers, end caps, etc.).

Fission products (FP)

This is a lower-weight element that results when a heavier element is split into two or more parts following a nuclear fission reaction. Some examples are cesium, barium, strontium, iodine, samarium, krypton, molybdenum, and xenon, which are some typical FPs from the fission of uranium-235, plutonium-239, etc.

Fuel cycle

This is the complete nuclear energy system involving elements from mining to disposal. A fuel cycle could be once-through or recycle (limited or continuous) fuel cycle. The functions in a fuel cycle could include fuel resource acquisition (uranium and/or thorium fuel), power generation (uranium enrichment, fuel fabrication, critical and/or sub-critical reactors, storage, reprocessing, waste generation, storage and transportation), and nuclear waste disposal.

Geologic disposal

An excavated, underground facility that is designed, constructed, and operated for safe and secure permanent disposal of high-level radioactive waste including the fission product bearing waste from reprocessing and intact spent nuclear fuel.

High-level waste (HLW)

A highly radioactive material (which consists primarily of fission products and actinides from processing losses) resulting from the reprocessing of spent nuclear fuel.

Interest rate during construction

The cost of capital (in real terms, i.e., net of inflation) during the plant construction phase.

Levelized cost of electricity at equilibrium (LCAE)

The cost of electricity which renders the net present value of the project cash flow equal to zero. For a reactor, the costs included in the LCAE are those associated with capital investment, operation and maintenance, fuel, waste disposal, and decommissioning the plan at the end of life, while the revenue is obtained by the sale of products (i.e., wholesale electricity for a reactor). The difference between the LCAE used here and the more commonly used LCOE (Levelized Cost of Electricity) is that the LCAE highlights specifically the assumption of mass balance equilibrium for the economic performance quantification, while the LCOE could also be used to quantify the economic performance of transitioning systems.

Limited recycle

A fuel cycle strategy in which fuel is recycled one or a few times, either in the same nuclear fission system or another fission system, after which the spent fuel is disposed as waste. Essentially, intact spent nuclear fuel, high-level waste, and low-level waste are disposed of in limited-recycle fuel cycle options.

Low-enriched uranium oxide fuel (UOX)

Uranium that contains the isotope uranium-235 in a concentration greater than 0.7% (naturally occurring uranium) and less than 20% (highly enriched uranium).

Minor actinides (MA)

Actinide elements in nuclear fuel other than uranium and plutonium (primarily neptunium, americium, and curium).

Mixed oxide (MOX) fuel

Fuel containing plutonium-oxide mixed with natural or depleted or recovered uranium oxide or thorium oxide.

Natural Uranium (NU)

Refers to uranium with the same isotopic ratio as found in nature. It contains about 0.7% uranium-235, 99.3% uranium-238, and a trace amount of uranium-234 by mass. In terms of the amount of radioactivity, approximately 2.2% comes from uranium-235, 48.6% from uranium-238, and 49.2% from uranium-234.

Once-through fuel cycle

A fuel cycle strategy in which fuel is used only once in the nuclear fission system, followed by storage and disposal. A fuel cycle that processes intact spent nuclear fuel for waste management purposes only (e.g., to separate long-lived isotopes from short-lived isotopes and then dispose of them) but does not include re-use of such fuel is considered to be a once-through fuel cycle.

Operation and maintenance (O&M) fixed costs ($/kWe-y)

The annual fixed costs of operating and maintaining a functioning nuclear power plant, excluding fuel and capital repayments, but including payments for repairs and improvements, personnel, taxes and fees, and the annual contributions to the decommissioning escrow fund. It is expressed here as a quantity normalized to the net electrical output of the reactor, in units of $/kWe-y.

Operation and maintenance (O&M) variable costs ($/MWh)

The part of the cost of operating and maintaining a functioning nuclear power plant that is proportional to the electricity generated, expressed as $/MWh.

Overnight cost

The (total) overnight cost is the base construction cost plus applicable owner's, contingency, and first core costs. Overnight cost excludes escalation, fees, and interest during construction, which need to be added to the overnight cost to arrive at the total construction cost.

Pressurized water reactor (PWR)

A light water reactor in which the water absorbs the heat from fission in the reactor core, while staying in liquid form due to pressurization, and transfers the heat to a steam generator to produce electricity. Most of the world's nuclear power plants are PWRs.

Recovered Uranium (RU)

Any form of uranium that has been recovered by (re)processing of irradiated fuel and with or without chemical separation to be used for fuel fabrication or storage and/or disposal.

Separative work unit (SWU)

A unit of measure for the amount of work needed to separate uranium isotopes during enrichment. It is a non-linear function of the U-235 concentrations in the feed, product, and tails.

Spent Nuclear Fuel (SNF)

Intact irradiated fuel destined for direct disposal.

Uranium hexafluoride (UF₆)

A chemical form of uranium that is gaseous at relatively low temperatures and is therefore suitable for the purpose of uranium enrichment (which separates isotopes by weight).

Used Nuclear Fuel (UNF)

Irradiated fuel that is reprocessed to recover one or more elements for recycle, with the resulting high-level wastes requiring waste disposal.

Yellowcake

The solid form of various uranium oxides which are produced from uranium ore in the uranium recovery (milling) process. Yellowcake was commonly referred to as only U₃O₈, because that particular chemical compound comprised the majority of the yellowcake produced by uranium recovery facilities utilizing conventional milling methods. Most modern uranium recovery facilities utilize in situ recovery methods and produce a yellowish compound comprised mostly of uranyl peroxide dihydrate. Here, yellowcake is used to refer generically to the product sent to a uranium conversion facility, where it is transformed into uranium hexafluoride (UF₆), in preparation for fabricating fuel for nuclear reactors.