Radiation Shielding - std3028

DOE-STD-3028-2000

protection against all perils such as major fires and earthquakes; design of the facility and of the

storage array are expected to address these considerations.

A.7.3 Radiation Shielding

Uranium-233, with its associated contaminant isotope 232U, presents more severe external

radiation hazards than any of the naturally occurring uranium isotopes do. Massive biological

shielding is required, where high concentrations of 232U occur, to protect personnel from the

2.6 MeV (4.17E-6 erg) gamma emission of 232U daughter product, 208Tl. The occupational

radiation exposure should be kept as low as reasonably achievable (ALARA) and radiation

protection be provided as specified in 10 CFR 835, "Occupational Radiation Protection." Dose

rates are dependent on the source (e.g., activity, geometry, and matrix), shielding, and source-

to-detector configuration, so expected dose rates for actual conditions should be determined on

a case-by-case basis.

Except for spontaneous fission, neutrons are not directly produced during the radioactive decay

of any of the uranium isotopes or the sequential decays. However, alpha-neutron reactions, in

which alpha particles react with low-Z isotopes such as 6Li, 7Li, 9Be, 10B, and 19F, (and to a

lesser extent 27Al and 28Si), generate neutrons. Depending on the material storage system used,

the facility itself may serve as a shield.

A.7.4 SNM Safeguards

DOE requirements for safeguards are given in DOE O 470.1, DOE O 471.2A, DOE O 472.1B,

DOE 474.1, and DOE 5632.7A.