A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

U

ultimate heat sink:
A medium to which the residual heat can always be transferred, even if all other means of removing the heat have been lost or are insufficient.
This medium is normally a body of water or the atmosphere.

unrestricted linear energy transfer, L:
See linear energy transfer (LET).

unrestricted use:
See use.

uptake:
1.   A general term for the processes by which radionuclides enter one part of a biological system from another.
Used in a range of situations, particularly in describing the overall effect when there are a number of contributing processes, e.g. root uptake, the transfer of radionuclides from soil to plants through the plant roots.
2.   The processes by which radionuclides enter the body fluids from the respiratory tract, gastrointestinal tract or through the skin, or the fraction of an intake

uranium:

uranium enriched in the isotope 235 or 233:
Uranium containing the isotope 235 or 233 or both in an amount such that the abundance ratio of the sum of these isotopes to the isotope 238 is greater than the ratio of the isotope 235 to the isotope 238 occurring in nature. [57]

uranium series:
The decay chain of uranium-238.
Namely, uranium-238, thorium-234, protactinium-234, uranium-234, thorium-230, radium-226, radon-222, polonium-218, lead-214, bismuth-214 and polonium-214, lead-210, bismuth-210, polonium-210 and (stable) lead-206, plus traces of astatine-218, thallium-210, lead-209, mercury-206 and thallium-206.

use:

! There may be other restrictions on the use of the area or materials, such as planning restrictions on the use of an area of land or restrictions related to the chemical properties of a material.  In some situations, these restrictions could, in addition to their primary intended effect, have an incidental effect on radiation exposure, but the use is classified as unrestricted use unless the primary reason for the restrictions is radiological.

V

validation:
The process of determining whether a product or service is adequate to perform its intended function satisfactorily.
Validation is broader in scope, and may involve a greater element of judgement, than verification.

  • model validation: The process of determining whether a model is an adequate representation of the real system being modelled, by comparing the predictions of the model with observations of the real system.
    Normally contrasted with model verification, although verification will often be a part of the broader process of validation.
    There is some controversy about the extent to which model validation can be achieved, particularly in relation to modelling the long term migration of radionuclides from radioactive waste in repositories.

vehicle:
A road vehicle (including an articulated vehicle, i.e. a tractor and semi-trailer combination) or railroad car or railway wagon.  Each trailer shall be considered as a separate vehicle.

vendor:
A design, contracting or manufacturing organization supplying a service, component or facility.

verification:
The process of determining whether the quality or performance of a product or service is as stated, as intended or as required.
Verification is closely related to quality assurance and quality control.