U.S. DEPARTMENT OF ENERGY LABORATORY ACCREDITATION PROGRAM (DOELAP) FOR PERSONNEL DOSIMETRY SYSTEMS

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1 U.S. DEPARTMENT OF ENERGY LABORATORY ACCREDITATION PROGRAM (DOELAP) FOR PERSONNEL DOSIMETRY SYSTEMS F. M. Cummings ^ R. D. Carlson^ R. M. Loesch INTRODUCTION Accreditation of personnel dosimetry systems is required for laboratories that conduct personnel' dosimetry for the U.S. Department of Energy (DOE). Accreditation is a two-step process which requires the participant to pass a proficiency test and an onsite assessment. The DOE Laboratory Accreditation Program (DOELAP) is a measurement quality assurance program for DOE laboratories. Currently, the DOELAP addresses only dosimetry systems used to assess the whole body dose to personnel. A pilot extremity DOELAP has been completed and routine testing is expected to begin in January It is expected that participation in the extremity program will be a regulatory requirement by January THE ACCREDITATION PROCESS The Performance Evaluation (PE) Program Administrator coordinates the accreditation process for personnel dosimetry systems. To obtain accreditation, the DOE contractor first submits an application through the DOE field office to the PE program administrator. The application identifies key personnel in the dosimetry program, identifies the categories in which accreditation is sought, and describes the dosimetry system and the calibration methodology. The performance of the dosimetry system is evaluated by irradiating dosimeters in each category during three rounds of testing conducted over a three- to six-month period and comparing the reported results to delivered dose equivalents. If the performance of the dosimetry system is within the criteria, an on-site assessment is conducted by two DOE/DOE-contractor personnel from other sites. The areas that are scrutinized during the assessment include the quality assurance program, documentation of procedures and U.S. Department of Energy, Radiological and Environmental Sciences Laboratory. U.S. Department of Energy, Office of Health Physics and Industrial Hygiene Programs (EH-411). 427

2 practices, personnel training, personnel competency, facilities and equipment, equipment maintenance and calibration, and record keeping. If the contractor uses a commercial processor, the processor facility is assessed as well. Deficiencies noted during the assessment must be addressed in a corrective action plan submitted to the DOE field office. When the contractor has met all the criteria in the standard, the PE program administrator recommends accreditation to the DOELAP Oversight Board for approval. The Oversight Board, consisting of DOE/DOE contractor personnel recommends ' accreditation to the DOE Headquarters (DOE/HQ) DOELAP administrator or tables the accreditation pending the receipt of further information. The DOELAP administrator will issue a certificate of accreditation to the DOE contractor if the recommendations of the Oversight Board are accepted or rejects accreditation pending the receipt of further.information or testing. If accreditation is rejected, an appeal board has been established to allow the contractor to appeal this decision. WHOLE BODY DOSIMETRY PERFORMANCE TEST The performance test includes irradiating dosimeters in the categories for which accreditation is sought and conducting a one-time study of the angular response and lower limit of detectability characteristics of the dosimeter. The categories include two accident level categories and five protection level categories. The accident level categories extend from 10 to 500 rad at a depth of 1000 mg/cm2 (Deep) and utilize either the M-150 x-ray beam (specified by the National Institute of Standards and Technology [NIST]) or a 137Cs photon source. The protection level categories extend from 0.03 to 10 rem at Deep and/or Shallow (7 mg/cm2) as specified. The test depths for the photon categories in the protection levels include both the Deep and Shallow depths. The general low-energy, x-ray category utilizes NIST-specified beams, M-30 (20 kev-effective), S-60 (36 kev-effective), M-150 (70 kev-effective), and H-150 (120 kev-effective). The plutonium series x-ray category includes K-fluorescence beams at 17.5 kev and 59 kev, as well as the 241 Am source (59 kev). The high-energy photon category utilizes a 137Cs source. The beta categories test only at the Shallow depth and include 204T1, ^Sr/^Y and uranium. The radioisotopic sources are used in the point irradiation geometry and the level of doses extends from 0.15 to 10 rem. The uranium source is a slab source and the dose levels extend from 0.15 to 5 rem. The neutron category includes bare and D20-moderated 252Cf. The dose level extends from 0.2 to 5 rem and the test depth is Deep. The final category is a mixture category. It includes various mixtures of the above irradiations. A mixture irradiation is one that utilizes one source from one category and one source from another category (e.g., M-150 and 137Cs). The standard specifies that the ratio of dose equivalents from the two sources may not exceed 3. The test depths for photon mixtures and beta/high-energy photon mixtures are specified to be both Shallow and Deep. The dose levels extend from 0.05 to 5 rem for photon mixtures and 0.2 to 5 rem for photon/beta mixtures. The neutron/photon mixtures are evaluated at the Deep depth only, and the dose levels extend from 0.3 to 5 rem. 428

3 Fifteen dosimeters are tested in each category, in three groups of five, over a four- to five-month period. The only categories which are identified at the time dosimeters are returned to the contractor for processing are the accident categories and neutron categories. Performance of the dosimetry system is satisfactory if \B\ + S - \E\ L where B is the bias, or mean of the performance indexes, S is the standard deviation of the performance indexes, and E is a category-specific uncertainty term associated with the test irradiations. The S term is not employed for low-energy beta sources. The value of L is 0.3 for all categories except mixture categories and low-energy beta sources where the value of L is 0.4. Contractors pursuing accreditation are also required to conduct a one-time angular dependence study and a lower limit of detectability study as specified in the standard. There are no criteria for passing or failing these tests, only the stipulation that they be conducted using the sources specified in the standard. EXTREMITY DOSIMETRY PERFORMANCE TEST The performance test includes irradiating dosimeters in the categories for which-accreditation is sought and conducting a one-time study of the angular response and lower limit of detectability for the dosimeter. The categories include one accident level category with two sources and three protection level categories. All doses are delivered at the shallow (7mg/cm2) depth. The accident level category extends from 10 to 500 rad and utilizes either the M-150 x-ray beam (specified by NIST) or a 137Cs photon source. The protection level categories extend from 0.25 to 10 rem. The general low-energy x-ray category utilizes NIST-specified beams M-30 (20 kev-effective) and M-150 (70 kev-effective). There is no plutonium series x-ray category as in the whole body standard. The high-energy photon category utilizes a 137Cs source. The beta categories include 204T1, ^Sr/^Y and uranium. The radioisotopic sources are used in the point irradiation geometry and the natural and depleted uranium sources are used in the slab geometry. The neutron category includes bare and D20-moderated 252Cf. The fluence-to-dose conversion used in the extremity DOELAP standard is the same as the one used in the whole body DOELAP standard. The factor is currently under investigation and will be changed as appropriate even though the concept of neutron dose equivalent to extremities is technically inappropriate. There are no mixture categories in the extremity DOELAP standard. Extremity dosimeters are usually employed in well-characterized fields where the response of the dosimeter has been measured or estimated. Therefore, the participants are notified regarding which source was used to irradiate each dosimeter. One further difference in the extremity DOELAP and whole body DOELAP is that all dosimeters, including those irradiated on the uranium slab, are irradiated on phantom. 429

4 Fifteen dosimeters are tested in each category, in three groups of five, over a four- to five-month period. Performance of the dosimetry system is satisfactory if \B\ + S <. L where B is the bias, or mean of the performance indexes and S is.the standard deviation of the performance indexes. The value of L is 0.30 for category 1 and 0.5 for other categories. Contractors pursuing accreditation also are required to conduct a one-time angular dependence study and a lower limit of detectability study as specified in the standard. There are no criteria for passing or failing these tests, only the stipulation that they be conducted using the sources specified in the Standard. QUALITY ASSURANCE PRACTICES Several practices are conducted to control and assure that the quality of performance test irradiations is maintained at a high level.. Dosimeters from different participants are irradiated together. A quality control dosimeter which is calibrated and analyzed at the Performance Testing Laboratory (PTL) is included in every irradiation. When dosimeters arrive at the PTL, a bar-coded label is attached to each dosimeter. The label is read at the irradiation station, and software checks are performed to assure that the dosimeter belongs in the group being irradiated and that the group of dosimeters (packet) is being irradiated in the right category. In addition, the dosimeter packet is assigned a bar-coded label that identifies the irradiation source and dose equivalent level to which it will be exposed. Ionization chambers have been positioned in the dosimeter phantoms to provide direct assurance of the delivered doses. A message is displayed on the computer monitor if the discrepancy between the delivered dose and the dose recorded by the in-phantom monitor is greater than 2%. A summary of the pertinent irradiation data is printed at the irradiation station for each irradiation. The 2% flag is included on the printout if appropriate. The entire testing process is automated and controlled by computer to the extent possible to reduce the amount of human interaction. The DOELAP computer is used to maintain the dosimeter database, read the bar-code labels at each station, control the dosimeter irradiations, collect irradiation data (temperature, pressure, in-phantom monitor currents), and generate reports. Strict procedures are employed to store and handle dosimeters not being irradiated. Environmental dosimeters are placed at storage positions to monitor environmental doses and assure that transit doses are not delivered while dosimeters reside at the PTL. Only the dosimeters to be irradiated during a given shift, or on a given day are allowed to be removed from storage and taken to the irradiation facility. The output of DOELAP radiological sources is verified by PTL personnel using the in-phantom monitors at the beginning of each round to assure that the irradiation systems are stable. In addition, the source output is verified quarterly using secondary transfer standards that are directly traceable to standards at the NIST. Annually, the PTL participates in the DOE Radiological Calibration 430

5 Intercomparison program administered by the Pacific Northwest Laboratory. Every two or two and one-half years, the PTL participates in the NIST Measurement Quality Assurance program. Finally, the DOE contracts with the NIST and DOE contractor personnel to conduct periodic oversight audits of the PTL facilities and procedures and the DOELAP program in general. CURRENT STATUS OF THE DOELAP The DOELAP is responsible for accrediting 31 dosimetry systems for 38 DOE facilities under 10 field offices. The facilities are diverse, including small university research groups, environmental restoration programs, defense programs and complex multi-program facilities. The number of routinely processed dosimeters ranges from several dozen per month for small facilities to thousands per month for the large, complex facilities. Currently, 15 dosimetry systems are fully accredited, 6 have passed performance testing and are awaiting onsite assessments, and 10 are in remediation or are participating in performance testing. Of the 31 dosimetry systems, 19 are conducted using dosimeters processed within DOE facilities by DOE contractor personnel, 10 use commercial processors, and two are determining which way to go. All facilities use thermoluminescent dosimeters. Three facilities routinely use CR-39 for neutron dosimetry, and two facilities use commercially available film dosimetry. The DOELAP oversight board consists of five individuals representing five different DOE field offices and the program administrator from DOE/EH. The 23 DOELAP assessors used to conduct the onsite assessments represent 14 DOE/DOE contractor organizations at 9 of the 10 DOE field offices. Their expertise ranges from operating and managing personnel dosimetry programs to conducting research in personnel dosimetry. The whole body DOELAP is currently conducting its fifteenth performance testing session. The extremity DOELAP is available for implementation, and voluntary testing will probably begin concurrent to the sixteenth whole body test session. The two LAPs will eventually be combined into a single accreditation program. POTENTIAL CHANGES IN THE DOELAP Whole Body Personnel Dosimetry It is expected that during 1993, the whole body DOELAP standard and handbook will be revised. The revision may include some revision of the categories and radiological sources, a revision of the Cx conversion factors for photons, and a revision of fluence to dose equivalent conversion factors for neutrons. New sources that will be considered include International Organization for Standardization (ISO) narrow and broad beam x-rays, planar beta radiation sources, and high-energy neutron and photon sources. In addition, changes in existing conversion factors to become compatible with ISO standards or internationally accepted values will be considered. The DOELAP standard refers to a later change in performance criteria for the mixture and lowenergy beta categories. This change has not yet been implemented. The criteria change will be re 431

6 evaluated during the revision of the standard. Additionally, new criteria may be included to routinely test the angular response of personnel dosimeters. Extremity Personnel Dosimetry It is expected that testing of extremity personnel dosimetry systems will be incorporated into routine DOELAP testing in January As with the DOELAP for whole body dosimetry systems, participation will be voluntary for some period of time. Accreditation will then be required for both types of dosimetry and the two programs will be combined under external dosimetry in DOE Order The testing standards for the two dosimetry systems may be combined in the future into a single standard. 432