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Radiation Safety Program |
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Performing Close-out Surveys in Radioisotope Laboratories |
| Background | Responsible Users of unsealed radioactive materials
are required to perform several actions prior to termination of their approval
to use radioactive materials or prior to termination of the use of radioactive
materials in a laboratory.
The U.S. Nuclear Regulatory Commission (NRC) requires
that a "close-out" survey be performed to assure that all radioactive materials
are properly disposed or transferred, and that there is no contamination
detectable above regulatory requirements. This survey must be performed
prior to releasing a laboratory area for unrestricted use.
The USDA uses the contamination limits found in "Guidance for Decontamination of Facilities and Equipment Prior to Release for Unrestricted Use or Termination of Licenses for Byproduct, Source, or Special Nuclear Material", published by the NRC in July, 1982, and the contamination limits specified in the USDA license application as the basis for this guidance. |
| Survey Requirements | The Responsible User should consult with their Location
Radiation Protection Officer (LRPO) prior to initiating a close-out survey.
The LRPO will provide necessary assistance and technical support. The Responsible
User or LRPO should also contact the Radiological Safety Staff to coordinate
the close-out survey with any other permit termination actions.
The Responsible User must make a reasonable effort
to eliminate residual contamination from the laboratory. All contaminated
areas or equipment must be decontaminated.
Radioactive contamination on the surfaces of equipment
or work areas must not be covered by paint, plating, or other covering
material unless the contamination is less than the levels specified in
Table 1.
The accessible surfaces of all pipes, drain lines, or ductwork must be surveyed to determine the levels of radioactivity. Monitoring should be performed at appropriate access points, assuming that any contamination found is likely to be representative of the entire pipe or ductwork. If only hydrogen-3 was used, wipe tests should be taken and analyzed. |
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| Survey Requirements
(con't) |
Work surfaces and equipment should be surveyed in
areas where no radioactive materials were used to verify that radioactive
material use was contained within the controlled areas.
Radioactive materials signs, labels, and warning
tape must be removed from all surfaces and equipment in the laboratory.
However, the "Caution - Radioactive Materials" sign at the entrance to
the area must remain until the close-out survey is approved and accepted
by the Radiation Safety Staff.
A close-out survey consists of the following actions:
- A review of radioisotope inventory records to assure proper disposal or transfer of all radioactive materials. - A survey of radiation levels of the laboratory area using an appropriate meter to check for fixed contamination. Areas to survey include: - Bench top work surfaces - Radioisotope storage areas - Inside of hoods and cabinets - Sink drains and traps - Floor - A survey of the laboratory area for removable contamination (swipe survey). Generally, one swipe should be performed for every 18 inches of bench space and for every square yard of floor space. Close-out surveys typically require ten to twenty swipes. Areas to survey include: - Bench top work surfaces - Radioisotope storage areas - Inside of hoods and cabinets - Sink basins and drains - Refrigerators and freezers - Incubators - Isotope handling equipment - Counting equipment - Door handles - Telephones - Floor - Non-laboratory office space The results of both the meter survey and the swipe survey must be recorded on a laboratory survey form. All results must be recorded in Disintegrations per Minute (DPM), with normal background values subtracted from the reported results. |
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| Survey Requirements
(con't) |
Recording these results requires that the detection
efficiency of the survey meter for the energy of the radiation surveyed
for, and the counting system efficiency for the swipe tests, must be known.
The minimum detectable activity (MDA) of the counting
systems must also be known. Survey results that are less than the MDA should
be recorded on the form as < MDA, not as zero. Separate guidance on
determining minimum detectable activity for radiation measurements is available
from the Radiation Safety Staff.
The efficiency and the minimum detectable activity must be recorded on the survey form along with the manufacturer, model, serial number, and calibration date of the counting equipment and survey meter used. |
| Release Limits | A laboratory area can be released from radiological controls when the contamination is less than the limits shown below: |
| Table 1: Acceptable contamination levels for release of facilities from radiological controls. |
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Type of Radioactive Material |
Average Fixed Contamination ( DPM/100 cm2 ) |
Maximum Fixed Contamination ( DPM/100 cm2 ) |
Maximum Removable Contamination ( DPM/100 cm2 ) |
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| Beta or Gamma-ray Emitters not Listed Below | 5,000 | 15,000 | 1,000 | |
| I-125, I-129, Ac-227,
Pa-231, Ra-226, Ra-228, Th-228, Th-230, and Transuranics |
100 | 300 | 20 | |
| Natural Uranium, U-235,
U-238, and Associated Decay Products |
5,000 | 15,000 | 1,000 | |
| Natural Thorium, Th-232, Sr-90, Ra-223, Ra-224, U-232, I-126, I-131, and I-133 | 1,000 | 3,000 | 200 |
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Note: For purposes of laboratory surveys, the average fixed contamination can be calculated by taking the average of the measurements. |
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| Documentation | The following documents must be submitted to complete
the close-out survey requirements:
- A memorandum to the Director, Radiation Safety Staff requesting release of an area from radiological controls. This memorandum must be sent through the Location Radiation Protection Officer (LRPO) and the senior management official of the facility for their concurrence. |
| The information in the memorandum must include:
- A listing of all rooms or areas included in the survey. - The status of the Responsible User's radioactive materials inventory. - A summary of the results of the survey. If areas
of the laboratory are contaminated above the release limit despite repeated
attempts at decontamination, that should be noted, along with a request
for assistance from the RSS.
- Copies of all survey forms completed during the survey. |
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| Release from Controls | Access to the area must be restricted until approval of the survey documents has been obtained from the Radiation Safety Staff. At that time, the "Caution - Radioactive Material" signs can be removed from the entrance to the area. |
| Records Retention | The close-out survey documents must be retained
by the LRPO as long as radioactive materials use is permitted at the facility.
The RSS maintains close-out survey documents for the duration of the USDA radioactive materials license. |
| Questions | If there are any questions regarding the information
in this bulletin, contact:
Radiation Safety Staff
Phone: (301) 504-2440
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| Approved:
Date: 8/14/95
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By:
John T. Jensen /S/
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