Science Terms Definitions - F

False Positive Results - Results which show an effect when one is not there.

Feasibility Study - Analysis of the practicability of a proposal; e.g., a description and analysis of potential cleanup alternatives for a site such as one on the National Priorities List. The feasibility study usually recommends selection of a cost-effective alternative. It usually starts as soon as the remedial investigation is underway; together, they are commonly referred to as the "RI/FS". A small-scale investigation of a problem to ascertain whether a proposed research approach is likely to provide useful data.

Federal Facilities Compliance Act (FFCA or FFC Act) - An amendment to RCRA, the FFCA waives immunity for DOE and other Federal Agencies, allowing States and the EPA to impose penalties for non-compliance and requires DOE to develop plans for treating the hazardous components of radioactive wastes subject to RCRA requirements.

Fertile material - A material, which is not itself fissile (fissionable by thermal neutrons), that can be converted into a fissile material by irradiation in a reactor. There are two basic fertile materials, uranium-238 and thorium-232. When these fertile materials capture neutrons, they are converted into fissile plutonium-239 and uranium-233, respectively.

Fissile Material - A material consisting of atoms whose nuclei can be split when irradiated with low energy (ideally, zero energy) neutrons.

Fissile Uranium - These isotopes can be split by low to zero energy neutrons in a self-sustaining chain-reaction to release enormous amounts of energy. Natural uranium consists of only 0.711 % U-235, 99.28305 % U-238, and 0.0054 % U-234. U-235 is so fissionable with slow neutrons that a self-sustaining fission chain-reaction can be made to occur in a reactor constructed from natural uranium and a graphite moderator. Standard nuclear reactors use uranium that has been enriched to 3 or 4 % U-235.

Fissile Waste - A subcategory of the other radioactive waste types (LLW, TRU, HLW) that contains U233, U235, Pu238,Pu239, and Pu241 of sufficient percentage to release energy by fission after absorbing neutrons.

Fission - The splitting of the nucleus of an element into fragments. Heavy elements such as uranium or plutonium release energy when fissioned.

Fission Product - Any atom created by the fission of a heavy element. Fission products are usually radioactive.

Flocculation - Process by which clumps of solids in water or sewage aggregate through biological or chemical action so they can be separated from water or sewage.

Fly-ash - Small solid ash particles from the noncombustible portion of fuel that are small enough to escape with the exhaust gases.

Food Chain - Dependence of a series of organisms, one upon the other, for food. The chain begins with plants and ends with the largest carnivores.

Fossil Fuel - Natural gas, petroleum, coal, and any form of solid, liquid, or gaseous fuel derived from such materials for the purpose of creating useful heat.

Frank-effect Level (FEL) - Exposure level which produces unmistakable adverse effects, such as irreversible functional impairment or mortality, at a statistically or biologically significant increase in frequency or severity between an exposed population and its appropriate control.

Fuel Cycle - The complete series of steps involved in supplying a fuel. Most often refers to the fissionable fuel for a nuclear reactor and includes management of spent fuel.

Fuel Reprocessing - The complete series of steps involved in supplying a fuel. Most often refers to the fissionable fuel for a nuclear reactor and includes management of spent fuel.

Fusion - The combining of two nuclei to form a heavier one. Fusion of the isotopes of light elements such as hydrogen or lithium gives a large release of energy.