Radiations In Uranium Facilities

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

equivalent, and international standards are based on the ambient dose equivalent concept. The depth of

interest is typically 1 cm of soft tissue, as specified in 10 CFR 835.

The personal dose equivalent, Hp(d), is the dose equivalent in soft tissue at the appropriate depth, d,

below a specified point on the body. Obviously, personnel dosimeters should be calibrated in terms of

personal dose equivalent.

In reality, most instruments and personnel dosimeters used at DOE facilities are calibrated in

terms of dose equivalent. For example, consider the case in which personnel neutron dosimeters are

calibrated on acrylic plastic phantoms at a specified distance from a calibrated neutron source. For

DOELAP testing, the dose equivalent at this point has been calculated in accordance with NBS Special

Publication 633, Procedures for Calibration of Neutron Personnel Dosimeters. These calculations are

based on the Grundl-Eisenhauer energy spectrum and the conversion coefficients from NCRP Report 38

(NCRP 1971), which are for the "old" values of dose equivalent from cylindrical phantom calculations.

In most instances, the present methods based on dose equivalent overestimate effective dose

equivalent. In cases where personnel are approaching dose limits, it may be prudent to more accurately

evaluate effective dose equivalent using special calibrations. Depending on the irradiation geometry and

energy, effective dose equivalent may be as much as a factor of two less than dose equivalent.

6.2 RADIATIONS IN URANIUM FACILITIES

As outlined in Section 2.0 of this TS, the uranium isotopes are primarily alpha-emitters and their

progeny emit a wide variety of radiations, including alpha and beta particles, as well as more penetrating x

rays and gamma rays. Alpha-neutron interactions (and the small cross-section for spontaneous fission) add

the potential for neutron exposure to the radiation mix. This section outlines methods to calculate

the dose equivalents from radiations emitted by uranium and its progeny. Examples of measured dose

rates are also included.

The design of an external dose control program, including instrument and dosimeter selection, is

dependent upon the type and intensity of the radiation fields to which the workers will be exposed. Many

factors can affect the radiation field:

enrichment (mix of uranium isotopes),

emissions from parent radionuclide(s),

emissions from daughter radionuclide(s),

emissions from impurity radionuclide(s),

type of radiation emitted (beta, gamma, etc.),

energies of emitted radiation,

specific activity of the source material,

self-shielding of source material,

shielding provided by process equipment,

shielding provided by protective clothing, or

distance and geometry factors.

The ratio of uranium isotopes in a specific process (a function of enrichment) will determine the

source term by which the radiation fields can be predicted. This mix of uranium isotopes and daughter

radionuclides may be estimated by using an equation developed to predict specific activity as a function

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