Research Reactor

Nuclear research reactors are known as the most important source of neutrons and high energy particles in the world and have numerous and extensive applications. Nuclear research reactors can be used for radiopharmaceutical production, industrial radioisotope production, neutron radiography, BNCT: Boron Neutron Capture Therapy, NAA: Neutron Activation Analysis, NDT: Neutron Transmutation Doping for semiconductor industries, solar cells and high power transistors, gem stone coloring, cold neutron applications, neutron diffraction analysis, and etc.
Nuclear research reactors have several beam tubes with different neutron fluxes. In these beam tubes, various radiopharmaceuticals for therapy and diagnostics as well as industrial radioisotopes are produced. There are locations within the nuclear reactor core that can be used for neutron transmutation doping applicable to semiconductor technology. There are some diagonal beam tubes with different dimensions and neutron fluxes for gem stones coloring, material analysis, fuel test, and irradiation. A treatment room and a filtered, collimated neutron beam is required to perform BNCT. There are also pneumatic systems for transfer of samples in order to irradiate products and perform neutron activation analysis. Thermal column with appropriate moderators and filters to cool down neutrons leaking from the core to thermal energy level which can be used for neutron physics study and training. While it may take a significant neutron flux to be useful for most materials irradiations, almost any reactor can use its fuel while shutdown for gamma irradiations.

  • Gemstones Coloration:

Gemstones may be irradiated with neutrons to improve their properties (e.g., change to a more desirable color) in order to increase their demand and monetary value. The most common neutron irradiation being performed at research reactors is for topaz.

  • Neutron Radiography:

Static neutron radiography produces an image on film that has been exposed to the secondary radiation produced when neutrons from the reactor penetrate the specimen and interact with a neutron absorbing screen.

  • Material Structure Studies:

Material structure studies have been performed using research reactors in the low, intermediate and high power level range. While it is still possible to perform some studies using low power level reactors, the use of intermediate and high power level reactors are the most efficient reactors for this application. Many high power level research reactors have been constructed primarily for this application. Material structure studies are performed using reactor produced neutrons that are extracted from the reactor through beam ports. The energy of these emerging neutrons covers a range 31 from below thermal to several MeV. Using various techniques, neutrons within a small energy band are selected for use in experiments. These neutrons are allowed to interact with samples using a wide variety of instruments. The instruments are referred to as “spectrometers” and the experiments as “neutron scattering experiments”. A wide range of experiments from fundamental physics to biological science is now performed using many kinds of neutron spectrometers. While some information on neutron scattering at high power level reactors is presented, this section concentrates on the use of low and intermediate power level reactor neutrons as probes of materials, stressing the experiments that are possible and the spectrometers that could be used.

  • Radioisotope Production:

Some isotope production is possible in a low flux reactor. It should be recognized that in order to be able to realistically produce radioisotopes, the operating cycle of the reactor for all but short lived isotopes needs to be as long as possible. Flux traps are useful for reactors of all power levels and a variety of irradiation facilities is desirable (e.g., pneumatic transfer, hydraulic transfer, irradiating baskets in core, or in beam tubes). Similarly, capabilities for thermal interactions and fast neutron irradiations should be available. A gamma spectroscopy system is needed for quality assurance purposes to provide reliable measurements of radioactivity levels and purity. Indeed a complete quality assurance (QA) program must be in place for any commercial work in this field. 18 The reactor facility should develop encapsulation techniques for the range of fluxes, fluences and irradiation environments available there. After irradiation, a shielded device, often in a fume hood, must be available for opening irradiation capsules safely. There are some significant issues relating to safety analysis, and licensing that must be addressed prior to radioisotope production. It should be determined that possible abnormal occurrences during the production process are within the bounds of the reactor design basis and the operational limits and conditions. In addition, the use of radioisotopes requires licensing by a competent authority. For first time users, the operating organization should be willing to assist the user in the licensing process. Special requirements are necessary for the use of medical isotopes on humans and animals, and this may require special considerations during the production process.

  • Neutron Capture Therapy:

When 10B absorbs a neutron it emits an alpha particle that is highly ionizing and has a range in tissue about equal to the diameter of a cell. Therefore, the methodology in boron neutron capture therapy (BNCT) is to load a tumor with a borated compound and irradiate with neutrons. If the conditions are right, then the tumor dose is much higher than that to the rest of the surrounding tissue, resulting in subsequent preferential killing of tumor cells. Thermal neutrons are desired at the tumor location because the 10B interaction probability is much higher with slower neutrons. Therefore, surface or shallow tumors can be irradiated with thermal neutrons, while those at a depth of a few centimetres can be irradiated with epithermal neutrons which then become thermalized by the overlying tissue. Thermal neutrons are also useful for research involving cell cultures or small animal irradiations. As currently practiced, most neutron capture therapy makes use of boron compounds; however, other compounds (e.g., gadolinium compounds) can also be used. FIG. 13. An arrangement for neutron capture therapy. 41 Most neutron capture therapy research has focused on malignant melanomas and brain tumors, particularly glioblastoma multiform (GBM). While the incidence of GBM is quite low (about 20 per million population per year), its median survival is only about 8.6 months. It should be emphasized that NCT is still in the research phase with no Phase III clinical trials having yet been performed. In addition, it has been concluded that the results of 320 patients treated in BNCT studies have not demonstrated any significant benefit for these patients. Current research efforts are directed toward providing the dose to the tumor in a short time period (minutes instead of hours) and reducing the dose to normal tissue through higher flux, better neutron energy selectors, shielding and collimation and better drugs.

  • Neutron Transmutation Doping:

Neutron transmutation doping (NTD) of silicon is the process of irradiating ingots of high purity silicon with thermal neutrons to convert some of the silicon to phosphorus through an (n, gamma) reaction. The advantage of this doping technique over the non-nuclear techniques is that it is possible to produce better uniformity of the doping material because of the penetrability of neutrons in the silicon. NTD has some attractiveness to reactors because it is a potential income generator. The demand for doped silicon is about 100 tons per year and a large facility can produce 20–30 tons per year. At the time of writing (early 2000), it appears that the production is greater than the demand. However, old reactors will probably produce less and less per year, but this is offset by the fact that several newly constructed and designed reactors have dedicated production facilities built into them.