Inspection report details 
Licence holder:Director of National Parks
Location inspected: South Alligator Disposal Facility
Licence number: F0093
Date of inspection: 13-15 and 26 October 2020
Report number: R20/10510

An inspection was conducted as part of ARPANSA’s baseline inspection program 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 facility licence F0093. 

The scope of the inspection included an assessment of the Director of National Parks’ (DNP) performance at the South Alligator Disposal Facility (SADF) against the Facility Performance Objectives and Criteria (POCs). The inspection consisted of a review of records, interviews, and physical inspection of the facility.

A recent change to the management and the environmental monitoring arrangements for the facility has been proposed and is under assessment by ARPANSA and pending approval. The changes aim to improve the management of the facility and utilise the technical knowledge and experience present in the Supervising Scientist Branch (SSB) of the Department of Agriculture, Water and the Environment. If the proposal occurs, staff of the SSB will take on the roles and responsibilities of the site manager, radiation safety officer and perform the environmental monitoring functions for the facility. However, DNP will remain the licence holder. Arrangements are already in place via a memoranda of understanding and a contract between DNP and SSB. This has enabled a dedicated staff member to be appointed who has spent the last six weeks collating information associated with the facility and putting in place arrangements for the future management of the facility. This work has identified some future actions that are required. SSB has committed to fulfilling these actions. This is considered to be a mature and positive approach to management of the facility. This inspection examined the existing arrangements and those that are proposed for the future.


Uranium mining was conducted in the South Alligator River Region of the Northern Territory in the late 1950s and 1960s. Approximately 875 tonnes of U3O8 was produced from 13 mines. However, these sites were abandoned at the end of mining with minimal remediation. A hazard reduction program was conducted in 1990/1991 and an intervention conducted in 2009. This involved the construction of a near surface disposal facility and the relocation of low level naturally occurring radioactive material (NORM) from the treatment of uranium ore into this containment facility. This was undertaken by the Australian Government in an agreement with the traditional landowners.

The facility holds approximately 22,000 m3 of waste. At the time of emplacement, the waste was surrounded by compacted clay liners which were placed above and below the waste. Each liner was 500 mm thickness of local clay. The lower liner was located five metres above the highest level of the water table. The upper clay liner was covered by a 2 metre thick layer of soil to act as a growth medium for the Acacias which were originally planted in order to adopt an evapotranspiration approach to managing the rainfall anticipated to occur each wet season. The design of the facility aimed to visually blend into the local environment. 

Six boreholes were sunk in the nearby vicinity in 2006 when studying the suitability of the site. A further five boreholes were sunk during construction of the facility along with the placement of a meteorological station, two surface runoff monitoring stations, and three monitoring sites which each had 59 sensors, devices and sampling ports located above, below, and within the waste. Licence conditions on facility licence F0093 require DNP to monitor the environment surrounding the facility to ensure there is negligible release of radioactive materials from the facility.

The main codes and standards applicable to this facility are those that appear in section 59 of the Regulations plus: 

  • Code for Disposal Facilities for Solid Radioactive Waste (2018) (RPS C-3) 


Performance reporting and verification

A contract and memorandum of understanding has been developed and agreed between the DNP, who holds the licence, and SSB who intend to take over the management of the facility. The revised plans and arrangements (P&A) implement the agreement and document the responsibilities associated with the facility. Since this agreement occurred, SSB, in collaboration with DNP, has collected and collated the available records associated with the facility. These have been reviewed and the recommendations and actions identified in these reports have been transcribed into a spreadsheet. The vast majority of the actions have been completed. The inspection reviewed those recommendations that have not been completed or where there is insufficient evidence to demonstrate they have been completed. In some cases it is a moot point. In other cases it is difficult to confirm whether the action was taken and consequently actions have been placed on the future works program for the facility. Furthermore, outstanding actions will be reported internally to the nominee along with any other aspects important to safety.

The aforementioned spreadsheet that is being developed to house all relevant and important information related to the facility has not yet been finalised and as such not yet placed on the official records management system used by SSB. Official records are stored in duplicate on-site and backed-up to a remote location. This is expected to mitigate the risk that records may be lost in a catastrophic event. 

Configuration management

Revised arrangements for the management of this facility have been proposed to ARPANSA. Although this is still under review, SSB has started preparing to implement the revised P&A. The revised approach to the future management of the facility intends to identify what needs to be done to demonstrate the safety of the facility and utilising the available skill sets of staff within SSB, consultants (where appropriate) and park rangers. Related actions will be tracked to completion. SSB has undertaken to conduct a review of the environmental monitoring program. This will consider the information that needs to be collected to demonstrate the safety of the facility over the long term. This is an area for improvement. 

SSB has also undertaken to prepare a safety case for the facility. This would bring the facility in-line with modern practices and ARPANSA’s expectations. It is expected that this will describe the evolution of the facility to date and any deviation from the previously evaluated prediction of future performance of the facility. It is presumed that this safety case will be based on a revised safety assessment, be periodically updated and used for communicating with stakeholders over the life of facility. This is also identified as an area for improvement below. 

A register of who has accessed the facility and for what purpose has been in place since 2012. However, this is not a complete list as it does not include previous ARPANSA inspections or previous SSB inspections that have occurred over the life of the facility. Since the new facility manager was employed a register of people who have been inducted into the site has been recorded and a separate and comprehensive register of access to the facility maintained. The facility manager recently engaged with rangers and inducted them into the facility. This is consistent with the proposed approach based on building and maintaining a relationship with strong communication channels between SSB and the rangers. 

Inspection, testing and maintenance 

The licence holder’s current understanding of the behaviour and performance of the facility is informed by four types of inspections. Until recently, these inspections were undertaken either by contractors or staff of the SSB. In the future, SSB may undertake all types of inspections. These inspections obtain monitoring data, groundwater data, radiation data, landform stability, vegetation coverage and maintenance of the facility. 

The facility was constructed with monitoring stations consisting of numerous sensors emplaced below, within and above the waste. It is estimated that there were initially some 180 sensors, devices and stations. The understanding of the behaviour and performance of the facility is informed by the measurements taken by these sensors. However, over time many of these sensors have failed. This is presumed to be due to either ageing infrastructure or the impact of settling and compaction of the waste and the overlying soil on the sensor cables. As the majority of the sensors/devices are below ground they cannot be maintained or repaired. It is understood that the initial design anticipated a degree of sensor/device failure would occur and accounted for this. However, at some point over the design life of the facility all of the sensors/devices are expected to fail. 

There are currently many facets to the monitoring program each of which has associated data points which have accumulated over the life of the facility. Noting the failure of the monitoring sensors/devices that have occurred to date and the questions over the location of the boreholes, SSB has undertaken to conduct a review of the passive and active aspects of the monitoring program. This will aim to identify what is important to demonstrating the safety of the facility, what are the objectives of the measurement, and identify criteria to be used in assessing the performance of the facility. This is an area for improvement. This can be provided to the current contractors. While SSB is currently satisfied with the performance and capability of the contractors used at the facility, SSB intends to obtain and hold the raw data collected by the contractors.

The plan and design of the facility undertaken prior to construction analysed the predicted steady-state seepage of four scenarios (base case, worst case and two alternate cases with differing designs). For the base case and the worst case it was predicted that the net percolation rate into the waste volume would be 70 mm/year and 207 mm/year respectively. Furthermore, it was predicted that the seepage flux exiting the facility would be 57 mm/year and 173 mm/year respectively for these two designs. The most recent data from the monitoring suggests that the measured seepage rates from the middle of the facility peaked at 2.5 mm/day and over the 2019-2020 period sustained a rate of around 1 mm/day for the entire year. This would equate to approximately twice the seepage rate predicted by the worst case scenario. 

Prior to the creation of the facility eleven boreholes were created in the nearby vicinity. These were initially used to assess the suitability of the location and to provide a better understanding of the hydrology.  These were drilled to a variety of depths and are fitted with screens at various levels. The boreholes have been monitored every year since 2012 in both the wet and dry seasons. Although the timing does fluctuate a little, the objective is to capture the data before and after the wet season. The monitoring of the boreholes involves the collection of groundwater and subsequently the performance of a series of measurements including pH, electrical conductivity, the concentration of a variety of elements (including uranium), and activity concentration of radium-226. The measured values are comparable to those obtained prior to construction of the facility. Although these do not show any indication of movement of radioactivity in the environment SSB has undertaken to perform a thorough review of the current and historical groundwater results to identify any necessary changes to the groundwater monitoring program and feed this into the development of the safety case.

Measurements of the ambient gamma dose rate and the radon exhalation flux have been performed every two years. However, it is anticipated that this monitoring will in future be performed every five years. This is because the measured values are low and do not statistically differ from values measured prior to construction of the facility. Hence it has been concluded that exposure to radon or gamma radiation from the facility does not currently present a radiological hazard to people accessing the site. These measurements are relevant to the assessment of dose to workers and visitors to the facility. An assessment of scenarios concluded that a maximum effective dose of 6 µSv/annum can be expected. A dose constraint of 30 µSv/annum effective dose for both workers and the public has been established. A condition on facility licence F0093 requires the licence holder to conduct a review each year of the performance of the facility against the dose constraint and provide the results to ARPANSA. Only records relating to measurements conducted every second year and not annually were provided. Hence this is a non-compliance.  

While visiting the facility the inspector took ambient gamma dose rate measurements above the facility. These values were consistent with the range of normal background dose rates found in Australia and were also consistent with the range of dose rates that have previously been measured by ARPANSA inspectors and by SSB staff at the facility. SSB staff also periodically measure the radon exhalation flux density from the facility. These measurements have shown some variation. The values peaked in 2012 and have been decreasing ever since. SSB has concluded that the variation in the level of moisture in the local environment at the time of measurement is leading to this variation in the measured radon levels. Conducting the measurements at approximately the same time of year (relative to the wet season) may result in a more consistent level of moisture in the environment and enable more meaningful comparison of measurements performed over time.

SSB has conducted annual inspections of the facility. Photographs are taken as evidence when issues are identified. These photographs are considered to be a useful tool in recording the history of the development of the facility over time. The inspections assess the landform stability and evidence of erosion. For instance, minor cracks have previously been observed on the southern side of the facility. SSB has undertaken to continue to monitor the facility to ensure that the landform is not slipping down gradient. The inspections also assess vegetation coverage and identify any necessary maintenance of the facility. The most recent inspection performed by SSB concluded no significant change in the composition or density of vegetation cover at the facility from the previous year. The ARPANSA inspector agrees with this conclusion but notes that when viewed over a longer timescale the vegetation cover appears to be thickening.


The revised arrangements for the management of the facility have created the role of facility manager. This has been done in advance of the proposed changes and is not considered to have any significant safety implications. This role is responsible for ensuring the appropriate inspection and maintenance activities occur along with recording details of the facility from a knowledge management perspective. This role was filled for the first time six weeks prior to the inspection. The criteria for the job were developed by the management team and took into account the anticipated role and the internal capabilities already present within the organisation. Hence radiation protection knowledge and experience was not explicitly required but a good understanding of compliance with regulatory requirements was identified. The successful applicant had experience in this area and also experience in environmental monitoring which is also relevant to this facility. Since taking on the role of facility manager, the individual has been introduced to ARPANSA’s legislation, guidance materials and relevant codes of practice applicable to the facility. Training in the data loggers used for the environmental monitoring program has been undertaken and a Radiation Safety Officer course has been booked.

Other SSB staff also play a role in the management of the facility. A Radiation Safety Officer (RSO) has been assigned for the facility. This individual has a doctorate in radioecology and over 10 years experience in radiation safety roles across a variety of organisations and as a research scientist focussed on radiation protection associated with uranium mining.

Other personnel such as contractors, rangers, and other SSB staff also visit and work at the facility from time-to-time. There is no record of these individuals receiving appropriate training in radiation safety and training with respect to the facility. This is a considered a non-compliance with licence condition 4 of Schedule 2 of facility licence F0093. It appears in this instance that there may be some confusion as the SSB representatives interviewed as part of the inspection were still trying to collate all of the relevant records associated with the facility. They only became aware of this requirement shortly prior to the inspection as they did not have a copy of the current facility licence (nor the previous licence), which had been provided to the licence holder, the DNP. This particular requirement was imposed as a condition on the licence issued in 2019. Furthermore, a facility induction including the radiation protection aspects of the facility was prepared immediately prior to the inspection and presented to the inspectors as part of the visit to the facility.

Event protection

A cover system for the facility was chosen to provide a growth medium for establishing a sustainable vegetation cover. This cover aims to reduce soil erosion, the rate of net percolation into the waste, and achieve aesthetics consistent with the surrounding area. Some challenges have been encountered in the maturation of the vegetation cover. For instance, the first wet season following construction was unusually heavy and resulted in significant erosion gullies forming as the vegetation had not matured and the soil comprising the growth medium did not have time to compact under its own weight. Diversion channels were created up gradient of the facility, rock armouring was installed at three drainage points on the down gradient side of the facility, and the growth medium was repaired. Bushfires passed through the facility in November 2014 and June 2019. This caused minor damage to monitoring equipment which has consequently been repaired and resulted in changes to the dominant vegetation species above the facility. While these natural events have caused damage to the facility they were anticipated given the facility is surrounded by bushland in a national park and subject to the wet and dry seasons common to the Northern Territory. The damage due to these events has been repaired and in some instances alterations made to limit the likelihood and/or consequences of future damage due to similar events. 

The facility was designed with the objective of containing and minimising the transportation of radioactivity for a period of 300 years and maintaining the stability of the landform for a period of 1000 years. Prior to the construction of the facility, substantial effort went into analysing and modelling the predicted capacity of the facility to contain and isolate the waste and limit the movement of nuclides into the environment. It was predicted that over a period of 300 years a negligible amount of nuclides would migrate a distance of 5 metres below the facility which is anticipated to be the point where the nuclide could meet local groundwater. The predicted activity concentration of radioactivity accessible to enter the groundwater would be less than measurable levels. From this point the groundwater is expected to move any radioactivity laterally through the ground towards the river approximately 1 km to the south. No radioactivity was expected to reach the river in an appreciable timeframe.

The relatively long time scales require a relatively long-term view when judging the performance of the facility. The monitoring data suggests that a higher than anticipated rate of water infiltration into the waste volume may be occurring. It has been hypothesised that this may be a localised effect which has ironically been caused by the presence of the monitoring system itself as it may enable an easier pathway for water to infiltrate into the waste volume. However, moving forward SSB is assessing the performance of the facility on the conservative assumption that the measured rate of infiltration is occurring evenly across the whole cap.

The previous ARPANSA inspection in 2018 discussed the role that the safety assessment and safety case plays in assessing, documenting and demonstrating to stakeholders the safety of the facility. SSB has undertaken to re-evaluate the performance of the facility in light of the experience gained to date, document the assessment, and prepare a safety case. It is anticipated that these documents will reflect the review and assessment of the performance of the facility and be a useful tool in communication with relevant stakeholders.


The facility is accessible via a short dedicated track from the nearest road. The track is not sign-posted so it is unlikely that members of the public passing through the area would notice the presence of the facility; it’s also in an area which is inaccessible by road during the wet season. Furthermore, the facility is encircled by security fencing which is expected to deter passing tourists, prevent occupation (i.e. camping) and inadvertent intrusion into the waste.

A number of locks have historically been used to secure the main access gate. In recent times one of these locks was removed and replaced as key holders were unknown. This aims to give SSB positive control of access to the facility. The facility manager maintains a register of all access to the facility.

Representatives of SSB indicated that no safety or security incidents have occurred at the facility since the last ARPANSA inspection and no signs of any unauthorised access to the facility were identified during the visit to the facility. The most recent SSB inspection of the landform stability, vegetation coverage and maintenance of the facility conducted in July 2020 identified a gap between the ground and the access gate and recommended that this be addressed to control both animal access to the facility and for security purposes. ARPANSA supports licence holders identifying, reporting and rectifying issues themselves. Hence, the actions identified by SSB staff are encouraged.

Radiation protection

As part of the planned transition of some responsibilities to SSB, a revised set of P&A have been prepared. The revised P&A indicate that personal dosimetry is not needed when visiting the site provided the site (in particular the growth layer and clay cap) is not going to be disturbed. However, the P&A are silent on some other operational aspects of radiation protection. For instance, it is not stated whether any PPE or radiation detector is needed when accessing the site and whether any controls are required to clear any pumps or equipment leaving the site. These should be explicitly stated following a review based on radiological risk.

Access to the site has been restricted by a perimeter fence. Warning signs indicating danger and instructing readers to keep out were observed. Concrete monoliths which are more durable surface markers are also used to ensure that information relating to the presence of the site are maintained for future generations. These surface markers indicate that no camping, no fires and no digging should be conducted within 100 metres of the sign; this covers the full area of the facility.

As indicated above, SSB has been periodically measuring the gamma dose rate and the radon exhalation flux density above the facility and at a few points outside the fence line. These measured values are compared against the values obtained prior to the facility being constructed and used to assess dose to workers and the public from the facility. In the most recent assessment, SSB concluded that the measured values are effectively no different from what existed prior to the construction (i.e. local background radiation) and as such concluded that no doses have been incurred due to the facility. The facility licence requires the performance of the facility to be compared against the dose constraint of 30 µSv/annum effective dose for both workers and the public established for the facility. This has only been happening every second year and as such is considered a non-compliance.

The current arrangements for reviewing the performance of the facility do not take a long-term view. Hence, SSB is expected to re-evaluate the purpose and the process of optimising protection associated with this facility. The current approach should be strengthened to involve the integration and analysis of the data from the environmental monitoring program such as from the groundwater monitoring. While still conducting the assessment in an iterative fashion, a more long-term view of optimisation should be implemented to consider doses and risks associated with both normal and potential exposures from the facility and be in accordance with the graded approach to safety. In line with this, SSB has proposed a five-yearly review to accommodate the nature of environmental processes. Predictive modelling of the movement of radioactivity becomes inherently more difficult the further into the future one looks however protection associated with this site should consider the long term nature of the radioactivity present and should provide future generations with a level of protection that is equivalent to what is acceptable today.

Radiological protection has long considered the protection of both people and the environment. However, in recent times approaches to assessing environmental exposures and drawing conclusions regarding environmental protection have been explicitly published at both an international level and in the Australian context. Staff at SSB have a capacity to undertake a screening assessment of environmental protection if further groundwater modelling is performed. This would demonstrate an adequate level of environmental protection. However, to date this has not occurred. This is an area for improvement.

Emergency preparedness & response

The concept of a passive approach to safety has been adopted and largely implemented at the facility. The revised P&A for managing safety associated with the facility consider extreme events such as bushfires and flooding and describe the intended response to these types of emergencies. This involves getting people out of any danger, then after the extreme event has passed assessing the facility and conducting any repairs if necessary. As such, due to the passive approach to safety mentioned above, no need for emergency response in the usual context has been identified. However, some preparedness activities occur. These are associated with minimising the risk of bushfires. This involves the maintenance of the fire breaks located at the perimeter of the facility and surrounding the monitoring equipment, and management of the vegetation cover (specifically the prevalence of introduced species such as annual mission grass) at the facility. The records suggest that annual mission grass invaded the area following a bushfire in November 2014. It is known that mission grass provides more fuel for fire than native species do and can result in much hotter fires which have greater potential to damage the above ground monitoring equipment. SSB has been conducting annual inspections of the facility since it was constructed. These inspections monitor the annual mission grass present and where appropriate recommend treatment to address it. 


The inspection revealed the following non-compliances:

  1. In some instances no radiation safety training has been conducted for people accessing the facility as required by Licence Condition 4 in Schedule 2 of the licence. 
  2. An annual review of facility performance against the dose constraint has not been conducted as required by Licence Condition 6 in Schedule 2 of the licence.

The inspection revealed the following areas for improvement:

  1. Reviewing the environmental monitoring program. SSB has proactively identified the need and committed to doing this.  
  2. Performing a revised safety assessment and preparing a safety case for the facility. SSB has proactively identified the need and committed to doing this.  
  3. Adoption of a more consistent approach to the timing of the measurement of radon exhalation flux density with the aim of having a consistent amount of moisture in the ground. 
  4. Consider assessing environmental radiation protection associated with the facility. This was identified under the heading of radiation protection. 

It is expected that improvement actions will be taken in a timely manner.


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