USNRC Guidelines for Facilities & Equipment (surface)
The following is a listing of the USNRC’s guidelines for decontamination of facilities and equipment prior to release for unrestricted use or termination of licenses for byproduct, source or special nuclear material. This listing came from a USNRC Division of Idustrial and Medical Nuclear Safety document prepared in 1987, and it is consistent with the listing found in the USNRC’s Regulatory Guide 1.86, dated 1977. Because they are performance-based rather than risk-based, they should be used with caution. The values shown below are in units of “disintegrations per minute per 100 square centimeter area”. Interpretations and additional instructions on the use of these values are listed at the bottom of this page.
Ac-227
- Average – 100
- Maximum – 300
- Removable – 20
Beta/Gamma Emitters (other)
- Average – 5,000
- Maximum – 15,000
- Removable – 1,000
I-125 and I-129
- Average – 100
- Maximum – 300
- Removable – 20
I-126, I-131 and I-133
- Average – 1,000
- Maximum – 3,000
- Removable – 200
Pa-231
- Average – 100
- Maximum – 300
- Removable – 20
Ra-223 and Ra-224
- Average – 1,000
- Maximum – 3,000
- Removable – 200
Ra-226 and Ra-228
- Average – 100
- Maximum – 300
- Removable – 20
Sr-90
- Average – 1,000
- Maximum – 3,000
- Removable – 200
Th-natural
- Average – 1,000
- Maximum – 3,000
- Removable – 200
Th-230 and Th-228
- Average – 100
- Maximum – 300
- Removable – 20
Th-232
- Average – 1,000
- Maximum – 3,000
- Removable – 200
Transuranics
- Average – 100
- Maximum – 300
- Removable – 20
U-natural
- Average – 5000 (alpha)
- Maximum – 15,000 (alpha)
- Removable – 1,000 (alpha)
U-232
- Average – 1,000
- Maximum – 3,000
- Removable – 200
U-235 and U-238
- Average – 5000 (alpha)
- Maximum – 15,000 (alpha)
- Removable – 1,000 (alpha)
Additional Instructions
- Where surface contamination by both alpha and beta-gamma emitting nuclides exists, the limits established for alpha and beta-gamma emitting nuclides should apply independently.
- Measurements of average contamination should not be averaged over more than one (1) square meter. For objects of less surface area, the average should be derived for each such object.
- The maximum contamination level applies to an area of not more than 100 square centimeters.
- The average and maximum radiation levels associated with surface contamination results from beta-gamma emitters should not exceed 0.2 mrad per hour at one (1) centimeter and 1.0 mrad per hour at one (1) centimeter, respectively measured through not more than seven (7) milligrams per square centimeter of total absorber.