Inspection report: Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, 10 December 2020

Purpose

The purpose of this inspection was to verify the health physics survey report provided in support of ANSTO’s request to surrender facility licence F0240. 

Background

ANSTO is authorised under section 32 of the Act for the operation of a non-medical irradiator. The Gamma Irradiator Suite (GIS) was a general-purpose irradiation facility for the gamma irradiation of samples for radiobiology research including low dose animal research. The facility was licensed to contain a cobalt-60 source of up to 32.8 TBq.  

The facility has been shut down since 2017 following a mechanical malfunction. The source in its housing was removed and transferred to ANSTO Waste Operations on 16 September 2020. 

A request to surrender the licence accompanied by a health physics survey report was received by ARPANSA on 26 October 2020.

Survey objectives

ARPANSA performed a survey of both rooms of the facility to confirm that there was no detectable contamination present in the facility, consistent with the ANSTO survey. The primary potential source of contamination is as a result of a leak of the Co-60 source. However, this is not likely and there was no evidence of such leakage in past routine monitoring. This survey also provides assurances that any other previous uses of the laboratory did not result in detectable contamination.

The apparatus contained a cobalt-60 source manufactured by ANSTO. The source is encapsulated in stainless steel and is not expected to leak. While there is no source certificate available, ANSTO estimated an activity of 71 TBq in December 1996, which was loaded in the refurbished GIS in 2003 at which time the source was estimated to be 32.8 TBq. The source is now less than 4 TBq in 2020. Annual health physics surveys were performed including smear tests of the unit head and collimator and did not detect any signs of leakage. However due to configuration of the equipment and detection limits of the surveillance method used, there is a small chance that source capsule leakage could have occurred and not been detected. This could have resulted in contamination above the exemption limits listed in the ARPANS Regulations. These limits are considered as part of any request to surrender a licence.

Survey method

Measurements were taken with sensitive calibrated radiation detection equipment. Equipment included a 2-inch sodium iodide gamma probe and a 100cm² 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 the ARPANSA’s Radioanalytical laboratory. 

Survey results

Measurements taken did not detect any material above the exemption value of 10⁵ Bq for Co-60, or any significant variations from background. This indicates that no radioactive material contamination was found. 

Wipe testing sample measurements did not detect any material above 10 Bq, alpha or beta, and therefore no contamination greater than 0.4Bq/cm² was detected. This indicates that no removable surface contamination was found. 

Findings

The results of ARPANSA’s independent verification were consistent with those presented in the ANSTO survey report.  No contamination was detected.

The inspection revealed the following area for improvement:

1. Surveys conducted in association with decommissioning or surrender of licence should reference minimum detection limits or otherwise allow for comparison with release criteria consistent with ARPANSA Regulatory Guide: Decommissioning of controlled facilities.