|ANSTO - Secondary Standards Dosimetry Laboratory
|Date of inspection
|13 July 2022
An inspection was conducted to assess compliance with the Australian Radiation Protection and Nuclear Safety Act 1998 (the Act), the Australian Radiation Protection and Nuclear Safety Regulations 2018 (the Regulations), and conditions of source licence F0244.
The purpose of this inspection was to verify the survey report provided in support of ANSTO’s request to surrender facility licence F0244.
Licence holder is authorised under section 32 of the Act to operate an irradiator (prescribed radiation facility). The ANSTO Secondary Standards Dosimetry Lab (SSDL) once provided a traceable calibration for instruments used at radiotherapy centres in hospitals throughout Australia. However, the facility had been used increasingly less frequently in the period up to 2016 and has not been used for irradiations since 2017. The Co-60 source was transferred to the ANSTO Waste Management licence (F0260) in October 2021. A request to surrender the licence, accompanied by a radiation survey report, was received by ARPANSA in April 2022. ANSTO intends to continue to use the structure of the facility for storage.
The main codes and guidance applicable to this licence are:
- RPS C-1 Code for Radiation Protection in Planned Exposure Situations (Rev 1) (2020)
- ARPANSA Regulatory Guide: Decommissioning of controlled facilities
The ARPANSA survey was undertaken to confirm that there is no detectable contamination present in the facility and no controlled material remains. The primary potential source of contamination would be as a result of a leak of the Co-60 or Sr-90 source. The survey intended to compare the results with the survey performed and provided by ANSTO. The licence holder has prime responsibility for safety and ARPANSA’s survey provides independent verification.
The apparatus used in the SSDL contained a cobalt-60 source manufactured by ANSTO. The source is encapsulated in stainless steel, has a sealed source certificate from 1999, and is not expected to leak. Health physics surveys including smear tests have not detected any signs of leakage. However due to configuration and detection limits, there is a small chance that source capsule leakage could have occurred and not been detected.
Measurements were taken using calibrated radiation detection equipment including an ionisation chamber and CsI (Tl) scintillation gamma probes and a 100 cm2 Phoswich scintillation detector for alpha and beta measurements. Measurements were taken in a grid as well as looking for hotspots. Several wipe test samples were taken and analysed in ARPANSA’s Radioanalytical Laboratory.
Radioactive material was detected in the walls of the facility. The main radionuclide identified by gamma spectroscopy was thorium most likely due to naturally occurring radioactive material (NORM), such as monazite, from construction materials. This may be from infill material used in the stack bonded concrete blocks. The construction is estimated to be more than 50 years old, and details of the construction material were not provided. The measured dose-rate of around 1 μSv/hr does not indicate hazardous levels of radiation for workers in the area but does indicate that the material is likely to be above the levels defined by the Regulations as requiring regulatory control – i.e. Exemption and clearance consistent with Requirement 8 of the International Atomic Energy Agency General Safety Requirements No. GSR Part 3 Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards. This result is consistent with the survey results provided by ANSTO.
Measurement of wipe test samples did not identify any material above 0.1 Bq/cm2 gross alpha/beta and 0.02 Bq/cm2 for Co-60, indicating no removable surface contamination. This is consistent with the survey results provided by ANSTO.
The results of ARPANSA’s independent verification were broadly consistent with those presented in the ANSTO survey report. While no removable contamination was detected, elevated levels of radioactive material were present in the construction material. This is not believed to be associated with operation of the SSDL.
Under the Act, such material must remain effective control under a source or facility licence until adequate sampling confirms the activity of the material and an application to dispose of controlled material has been approved by ARPANSA as applicable. Ultimate disposal of the material associated with this facility should be clearly covered under the waste management arrangements, in accordance with the expectations set out in ARPANSA’s Regulatory Guide Plans and arrangements for managing safety (ARPANSA-GDE-1735WEB).
The inspection revealed the following area for improvement:
- Durable markings on the walls, such as a plaque, should make it clear that any future construction, drilling, or demolition work take into account the nature of the material present.
It is expected that improvement actions will be taken in a timely manner.