OPAL capabilities

ANSTO's neutron guide hall adjacent to
the reactor will eventually house
ten instruments

See larger image

With its many capabilities, OPAL accommodates a broad range of needs for Australian industrial, medical, scientific and mining communities.

OPAL utilisation facilities are sub-divided into:

• Neutron beam research; and
• Irradiation for radioisotope production, neutron-activation analysis of materials, and silicon ingot doping for the semiconductor industry.

Neutron beam research

OPAL is specially designed to sustain neutron scattering related research, with three different sources supplying neutrons of varying energy ranges:

• Cold neutron source: this provides very low energy neutrons with long wave lengths required for biological applications of neutron scattering. In this field, larger objects can be studied, rather than objects of atomic size.
• Thermal neutron source: provides medium range energy neutrons such as molecules in an energy range comparable to room temperatures. Two examples of thermal neutron use are the investigation of fluids, or tumour therapies.
• Hot neutron source: Although not yet available, there is a further provision for a future option to provide a hot neutron source for higher energies. These are needed for experiments on fluids. Their scattering image has to be a snapshot of the atomic order so the operator needs short interaction time and a high velocity of neutrons.

Five assemblies situated around the core extract the neutron beams, which are then led towards the neutron guides.

The neutron guides conduct the neutrons from the sources with minimum reduction in quality towards the neutron beam hall instruments, which can be as far as 40 metres away from the reactor core.

Cold neutron source

Scientist inspects the guide
positioning in Quokka

In order to slow down neutrons produced at the core, there is a special device, a cold neutron source (CNS), installed in the reflector vessel which surrounds the reactor core. The CNS uses liquid deuterium (an isotope of hydrogen) and operates at very low temperatures (about -250⁰C). The CNS is supported by a cryogenic plant and a 500 kW compressor. The CNS moderator is cooled by helium vapour circulating through the heat exchanger and in an outer cooling jacket.

With this device, neutrons are 'moderated' to lower energies: the neutrons have around three times less energy than in the thermal guides. The cold neutron source is located as near as practical to the peak in the thermal neutron flux (~50 cm from the core, centre to centre).  

Neutron guides

The best way to use neutrons for research investigations is by conducting neutron beams through neutron guides to special equipment on which scientists can do their neutron research. 

At present OPAL has two thermal and two cold neutron guides extending into the neutron guide hall. There is capacity for further expansion, including potential for a second neutron guide hall. Neutron super-mirrors are devices used for transporting, bending and focusing neutron beams. Neutrons are reflected off the surfaces of the inside of these guides, made by sputtering layers of nickel and titanium onto a surface. The guides are operated under vacuum, because neutrons are scarce: there are 10 billion more air molecules than neutrons in a cubic centimetre of a guide.

The neutron guides begin 1.5 metres from the reactor core and continue through beam shutters, without windows, until the outer perimeter of the reactor. These neutron guides are 50 mm wide and between 50 mm and 300 mm high. The guides are very slightly curved between the reactor face and the exit of the guide bunker, to beyond line-of-site, reducing contaminating radiation.

Irradiation facilities

There are provisions in OPAL for the following irradiation facilities:

• General purpose irradiation facilities
• Bulk irradiation facilities
• Large volume irradiation facilities used for irradiating silicon
• Neutron activation delayed neutron activation facilities

The irradiation facilities are contained in various tubes within the reflector vessel that access neutron fluxes of varying wavelengths as required for the material being irradiated and its end purpose. For example, the large volume irradiation facilities used for irradiating silicon, so that it may be "doped" by neutron transmutation, are located around the outer part of the reflector vessel.

The irradiation facilities are supported by extensive pre- and post-irradiation facilities handling stations in the reactor service pool, and a number of hot cells which shield radioactive material. However, no processing of irradiated material takes place within the OPAL facility. Instead, there is a pneumatic shuttle system between OPAL and radiopharmaceutical processing and transport centre operated by ANSTO's radiopharmaceutical division.