Decommissioning Earlier Reactors

Scientists inside the High Flux Australian Reactor known as HIFAR prior to 2007.

ANSTO - adhering to strict national and international safety requirements - has fully decommissioned one of its two former research reactors and is preparing to decommission the second which is now permanently shut down.

The High Flux Australian Reactor or HIFAR, which shut down in 2007 after 49 years of operation, is being managed in a care and maintenance program while full decommissioning plans are concluded and approved.  Moata, which ended 34 years service in 1995 was dismantled in 2009-2010 and the area – inside a building – remediated and made available for alternative purposes.

The 10 megawatt HIFAR was a multi-purpose reactor of the DIDO class and was 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 almost identical reactors at Harwell in the United Kingdom and Riso in Denmark. The Harwell project began in 1990 and is due to be completed in 2016. The Riso project began in 2000 and is expected to be completed in 2014.

The experiences gained at Harwell and Riso 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 100 kilowatt Argonaut type Moata reactor was used for fundamental physics research, training, activation analysis and neutron radiography of materials.  The decommissioning of Moata was undertaken in 2 steps the first being removal of internal components undertaken in July 2009 and the second - the demolition and removal of the concrete bio shield - was undertaken between March and September 2010 following a rigorous approvals process by the regulator ARPANSA.

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.

For Moata samples taken in early 2008 of the biological shield near Moata's core indicated that the activation zone was very much less than calculations performed some years earlier had suggested and resulted in considerably less active waste than originally anticipated.  As part of planning for the dismantling of HIFAR a similar sampling and characterisation program is being planned.

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 several bucketsful); 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 the decommissioning of Australian reactors refer to the following links:

• HIFAR
• Moata

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

Depending on the structure of the particular reactor the dismantling is 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 waste monitoring, handling and suitable storage systems are required for testing, encapsulation, and for on-site storage as intermediate level waste or disposal at a low level radio-active waste site.
 

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