Dosimetry Results for AECL Personnel Involved in Maintenance Activities at Off-Shore CANDU Stations

Abstract

Atomic Energy of Canada Limited (AECL) is intermittently involved in maintenance work on domestic and off-shore CANDU nuclear power plants. Maintenance activities, such as fuel-channel replacement (FCR), small-scale spacer location and relocation (SLARETTE) and primary-side steam-generator tube cleaning, require work in high-radiation fields. This may lead to appreciable radiation doses. AECL staff experience has been that these radiation doses accrue mostly from external gamma fields, with a minor internal dose component from the uptake of tritiated water vapour. There are no significant uptakes of other radionuclides. AECL practice for SLARETTE and FCR work at off-shore CANDU stations has been to equip AECL personnel with 1 set of thermoluminescent dosimeters (TLDs) and 1 direct-reading personal alarming dosimeter (PAD). These TLDs are read at the Chalk River Laboratories of AECL. In addition, off-shore site radiation protection personnel issue AECL personnel with a TLD. This TLD is subsequently read at the off-shore site. Consequently, there are often three independent measurements of dose from external fields for AECL personnel. Internal dose assessments rely on offshore radiation protection personnel. All offshore CANDU stations use urine bioassay methods for tritiated water uptakes. Most offshore CANDU sites also have lung or whole-body gamma spectrometry capabilities or both, which, if necessary, can be used to assess doses from uptakes of gamma-emitting airborne contaminants (e.g., from 60Co, 95Zr, 95Nb, etc.). This paper discusses some internal and external dosimetry data for AECL personnel involved in recent FCR and SLARETTE work at off-shore CANDU stations. The data show that the whole-body dose contribution from uptake of tritiated heavy water is small. The data also show that three independent external dosimetry systems give dose results that are in relatively close agreement. Such information is invaluable in promoting confidence in the various dosimetry systems used under field conditions and allows Sheridan Park Health Physics staff to address any spurious measurements. The dosimetry data are also useful in planning future maintenance work.