Decommissioning earlier reactors
HIFAR reactor
ANSTO will decommission its two permanently shut-down nuclear research reactors, adhering to strict national and international safety requirements.
The reactors, the High Flux Australian Reactor or HIFAR, which shut down in 2007 after 49 years of operation, and Moata, which ended 34 years service in 1995, are being managed in care and maintenance programs while full decommissioning plans are concluded and approved.
The 10 megawatt HIFAR was a multi-purpose reactor used for research and making radioactive products for Australian nuclear medicine and industry. Moata was a very small 100 kilowatt reactor used mainly for materials testing and teaching.
The first stage of reactor decommissioning, as in the case of HIFAR, is shutting it down, removing its fuel and draining fluids such as the heavy water that cooled its core.
Now, under HIFAR's care and maintenance program, it is being kept in a safe state while short-lived radioactive materials within it decay.
For HIFAR's ultimate decommissioning plans, ANSTO has the advantage of being able to draw upon the extensive experience gained by other operators around the world that have safely closed down, dismantled and stored any remnant radioactive materials from now obsolete research reactors.
About 90 research reactors and eight power reactors around the world have been fully decommissioned, with resulting wastes managed in national stores. The decommissioning proposals for HIFAR and Moata are consistent with this sequence.
The details of the process for HIFAR are expected to be similar to those followed to decommission an almost identical reactor at Harwell in the United Kingdom. This project began in 1990 and is due to be completed in 2016.
However, the experience gained at Harwell will enable faster decommissioning of HIFAR. It is also expected to be completed in 2016, at a cost of $50 million.
While the ultimate use of the HIFAR site is to be decided, non-radioactive components such as concrete and building structures will progressively be demolished or dismantled and properly disposed of as industrial waste or for recycling.
The decommissioning of Moata is further advanced, with dismantling expected to begin in April 2009, subject to necessary approvals.
A critical safety aspect of dismantling nuclear reactors is gaining a very accurate knowledge of the levels of radioactivity in its concrete biological shield and other internal components.
Samples taken in early 2008 of the biological shield near Moata's core indicated that the activation zone is very much less than calculations performed some years ago had suggested. Testing of other internal components continues.
Waste
Any radioactive materials from HIFAR and Moata will eventually be removed to a proposed Commonwealth nuclear waste store.
The anticipated volumes are:
- Low level radioactive waste. Moata 61 cubic metres (about three 10 foot shipping containers); mostly graphite and concrete, and smaller volumes of activated steelwork; HIFAR up to 460 cubic metres (about six 40 foot shipping containers).
- Intermediate level waste. Moata 0.15 cubic metres (about a bucketful); mainly lead shielding; HIFAR up to 492 cubic metres (just over six 40 foot shipping containers).
Although it has only recently begun operations, the new OPAL reactor has been designed for minimal waste generation when it is eventually decommissioned after its expected 40 year-plus service life.
The United Nations' International Atomic Energy Agency (IAEA) has established main goals of nuclear reactor decommissioning.
They are unrestricted release of the reactor building and site; reduction of contamination below clearance levels following IAEA safety standards; clearance of materials; and minimisation of radioactive waste.
Decommissioning plans for ANSTO's reactors must be approved by the independent national nuclear regulator, the Australian Radiation Protection and Nuclear Safety Agency, which will also monitor their implementation.
For more information on Australian reactors currently being decommissioned:
Decommissioning
Decommissioning is the process by which an operating nuclear reactor is permanently shut down. This process involves the removal of fuel and cooling liquids and, the structure of the reactor, the containment and associated buildings being dismantled.
The process can be divided into three stages:
Step 1
Shutdown of the plant, fuel removal, draining of circuits (99 per cent of radioactivity removed), dismantling of non-nuclear facilities. Reactor containment maintained, with controlled access.
Step 2
Dismantling of remaining non-nuclear buildings, and those nuclear buildings excluding the reactor buildings, evacuation of wastes to storage facilities, ongoing containment and surveillance of the reactor core and buildings.
Step 3
All materials, equipment and structures in which radioactivity levels exist above prescribed limits removed. Site released for alternative use - no radiological restrictions
Dismantling
The dismantling would be undertaken in a series of steps, one for each of the major components, such as gas manifold, neutron shield, graphite moderator, internal support structure and the pressure vessel itself. Remote handling equipment, including manipulators, hoists, transfer and viewing equipment would require installation before starting. In addition a waste monitoring system for testing, encapsulation, shielded boxes for on-site storage as intermediate level waste or disposal at a low level waste site.