| United States Department
of Agriculture
Office of Procurement & Property Management (OPPM) Radiation Safety Staff |
| Permit Conditions
for Tritium Bioassay and Effluent Monitoring |
| Background | Permit Holders requesting the use of milliCurie
quantities of hydrogen-3 (tritium) must take special care to prevent the
release of tritium to the environment and to prevent its accidental ingestion
or inhalation.
This document describes the procedures that must be accomplished for obtaining a bioassay for tritium intake and for monitoring effluent releases. |
| In this
Document |
This document covers the following topics: |
| Topic | See Page | |
| Policy | 2 | |
| Limits on Uptake | 2 | |
| Effluent Limits to Unrestricted Areas | 2 | |
| General Precautions | 2 | |
| Bioassay Collection Method | 3 | |
| Effluent Air Collection Method | 3 | |
| Sample Preparation | 3 | |
| Instrument Calibration | 3 | |
| Formula for Determining Concentration | 3 | |
| Formula for Determining Minimum Detectable Activity | 4 | |
| Records Retention | 4 | |
| Using Program Forms and Worksheets | 4 | |
| Questions | 5 |
| Continued on Next Page |
| Policy | A tritium bioassay is required: |
| If the operation is conducted in a ... | And the activity of volatile H-3 exceeds: | |
| Open room or on a laboratory benchtop | 100 mCi | |
|
Fume hood of adequate face velocity |
1,000 mCi |
| An individual's urine must be evaluated for tritium
content:
- No earlier than 24 hours after the use, and - No later than 72 hours after the use. |
|
| Limits on Uptake | This table shows the limits on concentration of hydrogen-3 in urine. |
| Criteria | Limit | |
|
Weekly Limit for Whole Body Uptake |
2 x 10-3 µCi / ml | |
|
Permit Holder Investigation Level |
6 x 10-4 µCi / ml | |
|
Radiation Safety Staff Notification Level |
2 x 10-4 µCi / ml |
| Effluent Limits to Unrestricted Areas | The concentration of hydrogen-3 released to unrestricted
areas can not exceed an average of 1 x 10-7 µCi / ml.
This value can be averaged over a period of time that exceeds the actual time of the operation. It is RSS policy to limit the time to 8 hours. Additional time can be allowed upon approval of the RSS. |
| General Precautions | All procedures involving milliCurie quantities of
tritium (where the tritium compound is or could become volatile) must be
conducted in a properly operating chemical fume hood. This includes:
- Opening of packages; - Dilution of stock solutions; and - Chemical procedures.
Individuals handling tritium compounds shall wear a lab coat and protective gloves. |
| Continued on Next Page |
| Bioassay Collection Method | Each individual requiring a bioassay shall collect, handle, and count their own samples. This shall be done by collecting all of the urine in a single urination-void, withdrawing a 1-10 ml sample and discarding the remainder. |
| Effluent Air Collection Method | When sampling effluent air for hydrogen-3, the air sample should be passed through a cold trap (such as acetone/dry ice) to remove the water vapor from the air stream. This assumes that the tritium is in the form of tritiated water. If a different chemical compound is known to be released, special chemical or physical filters must be used. |
| Sample Preparation | No specific sample preparation is required. Low
potassium glass or plastic vials should be used to minimize background
counts. The sample vials should be allowed to dark adapt in the scintillation
counter for one hour prior to counting to minimize fluorescence.
The RSS must review and approve each sample preparation and analysis procedure used for tritium bioassay. |
| Instrument Calibration | Portable survey instruments are inappropriate for
monitoring the weak beta particle emitted by hydrogen-3.
A liquid scintillation counter is adequate for counting contamination wipes and bioassay samples. This counter should be calibrated on an annual basis using National Institute of Standards and Technology (NIST) traceable standards. |
| Formula for Determining Concentration | The concentration of tritium in the sample in units
of µCi / ml can be calculated using the following formula:
Concentration = [ Cs - Cb ]/
[ ( 2.22x106 ) E V ]
where: Cs = Gross sample counts per minute Cb = Background counts per minute E = Counting efficiency for tritium V = Volume of sample 2.22x106 = DPM per µCi |
| Continued on Next Page |
| Formula for Determining Minimum Detectable Activity | The minimum detectable activity for the counter
in units of µCi / ml can be calculated using the following formula:
MDA = {[ 2.71 / T ]+4.65(Rb T)1/2}/
[ ( 2.22x106 ) E V ]
where: Rb = Background count rate T = Counting time E = Counting efficiency for tritium V = Volume of sample 2.22x106 = DPM per µCi The calculated MDA must be lower than the limits
on uptake or the effluent limits or the counting procedure is not valid.
Additional information on calculating minimum detectable activity can be found in the Radiation Safety Staff's Technical Bulletin titled "Determining Lower Limit of Detection (LLD) and Minimum Detectable Activity (MDA) for Radiation Measurements". |
| Records Retention | The following worksheet is used in this program:
- Tritium Bioassay Worksheet (RSS-40)
This worksheet must be retained by the facility LRPO for three years. Copies must be submitted to the RSS for review. |
| Using Program Forms and Worksheets | The forms and worksheets used with this document
provide the basis for an individual to document the surveys and assessments
performed.
All of the worksheets describe the policy that must
be met for radiation safety surveys and include the minimum amount of information
needed to provide traceability and repeatability of the measurements, if
needed.
The procedures section assures that the proper calculations
have been performed.
Upon receipt of the forms by the RSS, the calculations are entered into a spreadsheet to verify the calculations. |
| Continued on Next Page |
| Questions | If there are any questions regarding the information
in this document, contact:
USDA Radiation Safety Staff
|
|
|
| Approved:
3/11/96 Date |
By:
/s/ John T. Jensen Director, Radiation Safety Staff |