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Reactor & Isotope: Reactors
Technetium (Tc-99m) is the most widely used radioisotope in nuclear medicine. It accounts for 80% of all diagnostic nuclear medicine procedures. This amounts to 7 million diagnoses per year in Europe and 8 million per year in the USA. The present world demand for molybdenum (Mo-99), the parent radioisotope of Tc-99m, is estimated at 10.000 to 12.000 Ci per week (reference: 6 days after production day). Most of the world's supply of Mo is produced by fissioning of U-235 in highly enriched uranium targets.
ANSTO's Open Pool Australian Lightwater (OPAL) reactor is a state-of-the-art 20 Megawatt reactor that uses low enriched uranium fuel and is cooled by water.
Opened by the Prime Minister in 2007, OPAL is one of a small number of reactors with the capacity for the
 commercial production of radioisotopes. This capacity, combined with the open pool design and operating utility, places OPAL among the best research reactors in the world.
While OPAL is the centerpiece of ANSTO's research facilities, the suite of neutron beam instruments housed next to the reactor building represent a significant addition to ANSTO's research capabilities.
These facilities, operated by the Bragg Institute, are supported by the Minister for Innovation, Industry, Science and Research, Senator Kim Carr, who recently described ANSTO's contribution to Australian science by saying: "Having started out as a specialist organization tied to this site at Lucas Heights, ANSTO is now driving innovation in nuclear science and technology right around the country. The Government is very aware of how important this work is."
While virtually every reactor is unique, OPAL is one of a number of similar production facilities around the world, including the Safari-1 reactor in South Africa, the HFR reactor at Petten in the Netherlands and the NRU reactor at Chalk River in Canada.
These reactors play a vital role in society by helping us understand the world at the atomic level. They function as 'neutron factories' producing isotopes for several important purposes, including the production of radioisotopes for cancer detection and treatment.
OPAL's operation staff cooperates with their international colleagues in sharing information and knowledge both directly through formal collaboration agreements and via various international organizations and forums.
The heart of the reactor is a compact core of 16 fuel assemblies arranged in a 4x4 array, with five control rods controlling the reactor power. OPAL uses low enriched uranium fuel with just under 20 per cent uranium-235. In terms of security and nuclear safeguards, this is a distinct advantage over earlier research reactors; some of which required as much as 95 per cent enriched uranium (weapons grade).
OPAL's fuel assemblies are cooled by demineralised light water (ordinary water) and are surrounded by a zirconium alloy 'reflector' vessel which contains heavy water. It is positioned at the bottom of a 13-metre-deep pool of light water. The open pool design makes it ease to see and manipulate items inside the reactor pool. The depth of the water ensures effective radiation shielding of staff working above the pool.
HFR Petten, The Netherlands
 The High Flux Reactor (HFR) at Petten is owned by the Institute for Energy (IE) of the Joint Research Centre (JRC) of the European Commission (EC). Its operation has been entrusted since 1962 to the Netherlands Energy Research Foundation Nuclear Research and consultancy Group (NRG). Since February 2005, NRG became also the license holder of the HFR. Together with the hot cells of NRG at the Petten site, the HFR has provided for over four decades, an integral and full complement of irradiation and post-irradiation examination services as required by current and future R&D for nuclear energy, industry and research organisations. Since 1963, the HFR has a recognized record of consistency, reliability and high availability with more than 280 days of operation per year. The HFR operates at a constant power of 45 MW. The HFR is a tank in pool type reactor which has 20 in-core and 12 poolside irradiation positions, plus 12 horizontal beam tubes.
The High Flux Reactor is the most prominent nuclear facility in Petten. It is an indispensible facility for the production of radio-isotopes for the medical sectors, covering some 60% of European demand. In addition it plays a key role in international (nuclear) research projects, among which are projects on materials for fusion reactors.
NRU, Chalk River, Canada
Designed as a 200 MWt reactor, NRU began operating in 1957, and is still one of the world's best-performing research reactors. It produces a high percentage of the world's medical and industrial radioisotopes, including molybdenum-99, a critical isotope used for medical diagnoses. NRU's large irradiation space has been an important factor in the testing of fuel bundles and fuel-channel components for CANDU reactors. NRU is used for research into reactor fuels, materials and components, and is the centre for neutron beam research in Canada. Originally designed for operation with natural uranium, NRU was converted to high-enriched uranium in 1964. AECL has been operating NRU with low-enriched uranium (LEU) fuel since 1991.
Safari-1, Pelindaba Site (near Pretoria), South Africa 
SAFARI-1 is a tank in pool type reactor of Oak Ridge design which has a design power of 20 MW. The reactor's 9 x 8 core matrix contain 28 MTR type fuel elements and six control rods. The remaining lattice positions are either aluminium or beryllium reflector elements. The locally produced fuel elements consist of 19 flat plates constructed from uranium-aluminium alloy clad with aluminium A five-week operational cycle, which includes one shutdown week, is followed. In-core irradiation positions have neutron fluxes of ~2 x 1014 n.cm-2.s-1 at 20 MW and are primarily used for isotope production.
LVR 15 Reactor - Rez Czech Republic  The reactor LVR-15 is a light water tank type reactor with the thermal power 10 MW. The reactor uses IRT-2M fuel enriched to 36% of 235U and combined water-beryllium reflector. This core composition provides in the core maximum thermal neutron flux of 1.5x1018 n.m-2s-1 and maximum fast neutron flux of 3x1018 n.m-2s-1. LVR-15 operates in three-week cycles, usually 9-10 cycles per year.
The main research projects are aimed to material testing. 5 water loops and several irradiation rigs are used for this purpose. Water loops simulate conditions similar to that existing in reactors of nuclear power stations, such as temperature, pressure, doses and water chemistry. Another significant use of the reactor is irradiation of samples for medical purposes and radio-pharmaceutical production. LVR-15 is also used for irradiation of silicon single crystals, activation analysis and experiments at beam tubes. Some experiments, including clinical tests, were also done at the thermal column in the field of neutron capture therapy.
The OSIRIS Reactor, Saclay, France  OSIRIS is an experimental reactor with a thermal power of 70 megawatts. It is a light-water reactor, open-core pool type, the principal aim of which is to carry out tests and irradiate the fuel elements and structural materials of nuclear power plants under a high flux of neutrons, to produce radioisotopes and semiconductors for the industry.
Located within the French Atomic Energy Commission (CEA) centre at Saclay, it is close to many research teams and inspection laboratories and has a large-scale technological infrastructure. The SACLAY centre (certified ISO 14001) is one of the 9 research sites of the French Atomic Energy Commission (CEA). It is a top-ranking innovation and research centre at the European level. More than 5000 people work in the centre. It plays a major role in the regional economic development. The centre is multidisciplinary, with activities in fields such as nuclear energy, life sciences, material sciences, climatology and the environment, technological research and teaching.
Main Features
In order to maintain direct access to the core, the reactor does not comprise a pressurization vessel, resulting in a high level of flexibility for laying out experiments and handling operations. The fact that the configuration of the core can be changed also means considerable ease of experimentation from a neutronic point of view.
The reactor started operation in 1966 and functions on average 200 days a year, in cycles of varying lengths from 3 to 5 weeks. A shutdown of about 10 days between two cycles is necessary to reload the core with fuel, carry out light maintenance operations and the handling operations required for the experiments. More consequential maintenance operations are carried out during dedicated shutdowns of longer duration.
The gradual conversion of the reactor to using U3Si2 Al fuel enriched to 19.75% began in January 1995 and was completed in April 1997. An on-going refurbishment program has been established to avoid the ageing of the components in the flux and the obsolescence of the materials.
The following major operations have been undertaken to maintain the degree of reliability and improve the safety level of the reactor: rebuilding of the effluent tanks and the de-activation tanks, the overhaul of the control/command system, the replacement of the core housing which maintains the fuel elements, and the replacement of the core vessel surrounding the fuel.
Radio-Isotopes Production
Radio-isotopes used in imagery for medical diagnoses: this involves the use of gamma cameras to examine the operation of organs onto which a radioactive molecule has been fixed. The product most frequently used is 99mTc obtained from targets made of enriched 235U. The targets are in tube form, 160 mm high and 22 mm in diameter.
Production is part of a joint program with the other European reactors in order to ensure a regular supply for hospitals. About 1000 tubes or targets are irradiated each year in the OSIRIS reactor for French and European industrials.
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