Open-pool Australian lightwater reactor

From Wikipedia, the free encyclopedia

OPAL (Open Pool Australian Lightwater reactor) is a 20 megawatt (MW) pool-type nuclear research reactor that was officially opened in April 2007 at the Australian Nuclear Science and Technology Organisation (ANSTO) Research Establishment at Lucas Heights, located in South Sydney, Australia.

The main reactor uses are:

• Irradiation of target materials to produce radioisotopes for medical and industrial applications
• Research in the field of material science using neutron beams and its sophisticated suite of experimental equipment
• Analysis of minerals and samples using the neutron activation technique and the delay neutron activation technique
• Irradiation of Silicon ingots in order to dope them with phosphorus and produce the basic material used in the manufacturing of semiconductor devices

The reactor runs on an operation cycle of 28 days nonstop at fullpower, followed by a stop of 2 days to reshuffle the fuel.

[edit] History

The Argentine company INVAP was fully responsible through a turn key contract for the delivery of the reactor, performing the design, construction and commissioning. The facility is currently in operation.

OPAL was opened on 20 April 2007 by Australian Prime Minister John Howard^[1] and is the replacement for the HIFAR reactor. ANSTO received an operating license from the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) in July 2006, allowing commencement of hot commissioning, where fuel is first loaded into the reactor core. OPAL went critical for the first time on 13 August 2006 and reached full power on November 3, 2006. ^[2]

[edit] Facility details

The OPAL reactor pools. Made of stainless steels and 4.5m wide, it contains demineralised water used for shielding and cooling.

The reactor core consists of 16 low-enriched plate-type fuel assemblies and is located under 10 metres of water in an open pool. Light water (normal H₂O) is used as the coolant and moderator while heavy water (D₂O) is used as the neutron reflector.

OPAL is the centrepiece of the facilities at ANSTO, providing efficient and rapid radiopharmaceutical and radioisotope production, irradiation services (including neutron transmutation doping of silicon), neutron activation analysis and neutron beam research. OPAL is able to produce four times as many radioisotopes for nuclear medicine treatments, and a wider array of radioisotopes for the treatment of disease than the old HIFAR reactor. The modern design includes a cold neutron source (CNS).

The OPAL reactor already has received seven awards in Australia.^[3]

[edit] Neutron scattering at OPAL

The Bragg Institute at ANSTO hosts OPAL's neutron scattering facility. It is now running as a user facility serving the scientific community in Australia and around the world. New fundings have been received in 2009 in order to install further competitive instruments and beamlines. The actual facility comprises the following instruments:

[edit] ECHIDNA

Engineering drawing of the ECHIDNA High-Resolution Powder Diffractometer (August 2003)

The Ge-115 monochromator has been acquired from the Brookhaven National Laboratory.

ECHIDNA is the name of the high-resolution neutron powder diffractometer. The instrument serves to determine the crystalline structures of materials using neutron radiation analogical to X-ray techniques. It is named after the Australian monotreme echidna, as the spiny peaks of the instrument looks like an echidna.

It operates with thermal neutrons. One of the main features is the array of 128 collimators and position sensitive detectors for rapid data acquisition. ECHIDNA allows for structure determinations, texture measurements and reciprocal space mapping of single crystals in most different sample environments serving the physics, chemistry, materials, minerals and earth-science communities. ECHIDNA is part of the Bragg Institute's park of neutron scattering instruments.^[4]

[edit] Components

• Neutron guide

  The instrument is located on the TG1 thermal neutron guide of the OPAL reactor. The distance from the reactor is 58 m. The position is the second on the guide after the WOMBAT instrument. The size of the guide is 300 mm height X 50 mm width and it is plated with supermirror coatings.

• Primary collimator

  There are Söller collimators prior to the monochromator in order to reduce the divergence of the beam and to increase the angular resolution of the instrument. Since this is an intensity compromise, two items of 5' and 10', respectively, can be interchanged or fully removed by an automated mechanism. The collimators cover the full size of the beam delivered by the neutron guide.

• Monochromator

  The monochromator is made by slabs of [115] oriented Germanium crystals which are inclined towards each other in order to focus down the Bragg reflected beam. The device has been acquired from the Brookhaven National Laboratory in the USA after the shutdown of their neutron facility.

• Secondary collimator

  Optionally a secondary collimator with 10' angular acceptance and 200 mm X 20 mm can be placed in the monochromatic beam between the monochromator and the sample, which again influences the resolution function of the instrument.

• Slit system

  Two automated sets of horizontal and vertical pairs of absorbing plates allow to cut down the size of the monochromatic beam prior to the secondary collimator and sample size. They remove unwanted netrons and reduce the background near the detector. In addition, they allow to select the sample position to be studied.

• Beam monitor

  A ²³⁵U fission monitor measures the amount of neutrons incident to the sample. The efficiency is 10^-4 and most neutrons traverse the device undisturbed. The monitor counts are important to correct for beam flux variations due to changes in the reactor or at the upstream instrument.

• Sample stage

  The sample is supported by a heavy load goniometer consisting of a 360° vertical omega rotation axis, x-y translation tables and a chi - phi cross tilt stage of ±20° range. It can hold a few hundred kilograms in order to support heavier sample environment, such as cryostats, furnaces, magnets, load frames, reaction chambers and others. A typical powder sample is filled into vanadium cans which give little, unstructured background. The mentioned sample environment allows to measure changes of the sample as a function of external parameters, like temperature, presser, magnetic field, etc. The goniometer stage is redundant for most powder diffraction measurements, but will be important for single crystal and texture measurements, where the orientation of the sample plays a role.

• Detector collimators

A set of 128 detectors each equipped which a 5' collimator in front are arranged in a 160° sector focusing to the sample. The collimators select the scattered radiation into the well defined ranges of 128 angular positions. All the collimator and detector setup is mounted on a common table which is scanned in finer steps around the sample, to be combinded further to a continuous diffraction pattern.

• Detector tubes

  The 128 linear position sensitive ³He gas detector tubes cover the full opening height of 300 mm behind the collimators. They determine the position of the neutron event by charge division over the resistive anode towards each end of the detector. Overall and local count rates lie in the several 10000 Hz range.

[edit] PLATYPUS

PLATYPUS is a time-of-flight reflectometer built on the cold neutron. The instrument serves to determine the structure of interfaces using highly collimated neutron beams. These beams are shone on to the surface at low angles (typically less than 2 degrees) and the intensity of the reflected radiation is measured as a function of angle of incidence.

It operates using cold neutrons, with a wavelength band of 0.2–2.0 nm. Although up to three different angles of incidence are required for each reflectivity curve, the time-of-flight nature means that timescales of kinetic processes are accessible. By analysing the reflected signal one builds a picture of the chemical structure of the interface. This instrument can be used for examining biomembranes, lipid bilayers, magnetism, adsorbed surfactant layers, etc.

[edit] WOMBAT

WOMBAT is a high-intensity neutron powder diffractometer. The instrument serves to determine the crystalline structures of materials using neutron radiation analogical to X-ray techniques. It is named after the wombat, a marsupial indigenous to Australia.

It will operate with thermal neutrons. It has been designed for highest flux and data acquisition speed in order to deliver time resolved diffraction patterns in a fraction of a second. WOMBAT will concentrate on in-situ studies and time critical investigations, such as structure determinations, texture measurements and reciprocal space mapping of single crystals in most different sample environments serving the physics, chemistry, materials, minerals and earth-science communities.

[edit] KOWARI

KOWARI is a neutron residual stress diffractometer. Strain scanning using thermal neutrons is a powder diffraction technique in a polycrystalline block of material probing the change of atomic spacing due to internal or external stress. It is named after the kowari, an Australian marsupial.

It provides a diagnostic non-destructive tool to optimize e.g. post-weld heat treatment (PWHT, similar to tempering) of welded structures. Tensile stresses for example drive crack growth in engineering components and compressive stresses inhibit crack growth (for example cold-expanded holes subject to fatigue cycling). Life extension strategies have high economic impact and strain scanning provides the stresses needed to calculate remaining life as well as the means to monitor the condition of components since it is non-destructive. One of the main features is the sample table that will allow to examine large engineering components while orienting and positioning them very accurately.

[edit] Others

• TAIPAN - Thermal 3-Axis Spectrometer
• KOALA - Quasi Laue Diffractometer.
• QUOKKA - Small-Angle Neutron Scattering
• PELICAN - Time of Flight Polarisation Analysis Spectrometer
• SIKA - Cold Neutron 3-Axis Spectrometer

[edit] July 2007 shutdown

Following the discovery of loose fuel plates during a routine inspection, the ANSTO announced on July 27, 2007 that the reactor would be shut down for 8 weeks to fix the fuel plates and a minor fault causing light water to seep into the reactor's heavy water.^[5][6]

According to reports, during the examinations no radiation leakages were detected, although it took much longer than 8 weeks to obtain the necessary clearances to complete repairs and readjustments. ANSTO announced on 25 October 2007 that the reactor would remain shut down until early 2008 while it sought approval from ARPANSA to restart the reactor.^[7]

As of March 2008, the reactor remained shut down. According to an ANSTO news release on 22 February 2008, "Late last week, ARPANSA submitted a series of questions on the application, which ANSTO will respond to as quickly as possible. This is expected to take some weeks."^[8]

The supply of radiopharmaceuticals was rationed, causing the postponement of some treatments for patients; this caused some concern amongst doctors in nuclear medicine.^[9]

OPAL returned to full operational power on 23 May 2008, after a 10-month shutdown, following approval by the nuclear regulator, ARPANSA to use a modified fuel design.

[edit] See also

• Research reactors
• Spallation Neutron Source
• Neutron scattering
• Anti-nuclear movement in Australia

[edit] References

[edit] External links

• OPAL
• KOWARI home page
• ECHIDNA home page
• ANSTO Radiopharmaceuticals and Industrials
• Bragg Institute
• INVAP Nuclear Division designs
• Announcement of the new reactor's name
• Nuclear reactor to reopen after six-month shutdown
• Govt expects nuclear reactor to restart this month
• Reactor ready for second try
• Open-pool Australian lightwater reactor is at coordinates 34°03′05″S 150°58′44″E / 34.051339°S 150.978799°E / -34.051339; 150.978799Coordinates: 34°03′05″S 150°58′44″E / 34.051339°S 150.978799°E / -34.051339; 150.978799