HFIR Experiment Facilities
Neutron Scattering Facilities
The fully instrumented HFIR will eventually include 15 state-of-the-art neutron scattering instruments, seven of which will be designed exclusively for cold neutron experiments, located in a guide hall south of the reactor building. The currently available instruments and the status of new instruments can be found at the HFIR Instrument Systems link. Particularly prominent in the cold neutron guide hall are the two small-angle neutron scattering (SANS) instruments, each terminating in a 70-ft-long evacuated cylinder containing a large moveable neutron detector. In addition to the instruments, laboratories are equipped for users to prepare samples.
Perhaps the most exciting development at HFIR is the successfully commissioned cold source in 2007. The HFIR source has a brightness measured to be the best in the world. The cold source increases the available neutron flux from 4 to 12 Å. For neutron scattering experiments, it’s ideal to match the wavelength and energy of the neutron to the length and energy scales, respectively, of the materials under investigation. Therefore, for studying large-scale structures (e.g., molecular organization, nanopore-size distributions, and aggregate size and shape) and low-energy excitations (e.g., excitations in frustrated systems and various problems in magnetism, superconductivity, and correlated electron systems), the best neutrons are those with long wavelengths and low energies—cold neutrons.
The thermal neutron spectrum of a reactor produces neutrons with wavelengths on the order of a few tenths of a nanometer, well matched to the study of atomic lengths scales and lattice vibrational energies. By passing the thermal neutrons through a vessel of low-temperature liquid hydrogen, the neutrons are slowed down by inelastic collisions with the hydrogen. This produces slower, long-wavelength neutrons better suited for studies of soft matter and low-energy excitations.
Cold neutrons reflect well from some surfaces and thus can be transported over long distances with little loss. Neutron guides can, therefore, be constructed to transport the cold neutron beam to the guide hall outside the reactor building where there is more room to work and where the sensitive instruments can be located in a very low radiation background. The HFIR source illuminates four such neutron guides, bringing beams to seven new instrument positions in the cold neutron guide hall. Two of these guides currently serve the two operational SANS instruments. Instruments on the other guides are being installed or are in development.
Hydraulic Tube Facility
The High Flux Isotope Reactor (HFIR) hydraulic tube facility consists of the necessary piping, valves, and instrumentation to shuttle a set of 2-inch long aluminum capsules containing materials to be irradiated between the flux trap and the capsule loading station during reactor operation. The capsule loading station is located in one of the storage pools adjacent to the pool containing the reactor vessel. This facility provides the capability to irradiate materials for durations less than the standard cycle length of ~22 days. This makes the facility ideal for short-term irradiations and for the production of short half-life medical isotopes that require retrieval on demand. A full facility load consists of nine vertically stacked capsules. Figure 7 is a sketch of a typical capsule.
Normally, the heat flux from neutron and gamma heating at the surface of the capsule is limited to 74,000 Btu/h-ft² (2.3 x 105 W/m²). Furthermore, the neutron poison content of the facility load is limited such that the reactor cannot be tripped by a significant reactivity change upon insertion and removal of the samples.
Target Positions
Thirty-one target positions are provided in the flux trap (see Figure 8). These positions are designed to be occupied by target rods used for the production of transplutonium elements; however, other experiments can be irradiated in any of these positions. Figure 9 and Figure 10 show views of a transplutonium production rod. A similar target capsule configuration can be used in numerous applications. A third type of target is designed to house up to nine 2 inch long isotope or materials irradiation capsules that are similar to the rabbit facility capsules. The use of this type of irradiation capsule simplifies fabrication, shipping, and post-irradiation processing which translates to a cost savings for the experimenter.
Target irradiation capsules of each type must be designed such that they can be adequately cooled by the coolant flow available outside the target-rod shrouds. Excessive neutron poison loads in experiments in target positions are discouraged because of their adverse effects on both transplutonium isotope production rates and fuel cycle length. Such experiments require careful coordination to ensure minimal affects on adjacent experiments, fuel cycle length, and neutron scattering beam brightness. Two positions are now available for instrumented target experiments: positions E3 and E6 (see Figure 8).
Peripheral Target Positions
Six peripheral target positions (PTPs) are provided for experiments located at the outer radial edge of the flux trap (see Figure 8). Fast-neutron fluxes in these positions are the highest accessible in the reactor, although a steep radial gradient in the thermal-neutron flux exists at this location (see Figure 6).
Figure 11 shows a standard PTP capsule that can be used in numerous applications. Like the target positions, another type of PTP capsule is available that houses up to nine 2 inch long isotope or materials irradiation capsules that are similar to the rabbit facility capsules. The use of this type of irradiation capsule simplifies fabrication, shipping, and post-irradiation processing which translates to a cost savings for the experimenter.
PTP irradiation capsules of each type must be designed such that they can be adequately cooled by the coolant flow available. Typical experiments contain a neutron poison load equivalent to that associated with 200 g of aluminum and 35 g of stainless steel distributed uniformly over a 20-in. (50.8-cm) length. PTP experiments containing neutron poison loads in excess of that described are discouraged because of their adverse effects on isotope production rates, fuel cycle length, and fuel element power distribution.
Experiment Facilities in the Beryllium
Reflector
Large Removable Beryllium Facilities
Eight large diameter irradiation positions are located in the removable beryllium (RB) near the control region. These facilities are designated as RB-1A and -1B, RB-3A and -3B, RB-5A and -5B, and RB-7A and -7B. These are generally referred to as the RB* positions. The vertical centerline of these facilities is located 10.75 in. (27.31 cm) from the vertical centerline of the reactor and they are lined with a permanent aluminum liner having an inside diameter of 1.811 in. (4.6 cm). These facilities are designed for either instrumented or non-instrumented experiments. The instrumented capsule design can also employ sweep or cooling gases as necessary. Instrument leads and access tubes are accommodated through penetrations in the upper shroud flange and through special penetrations in the pressure vessel hatch.
Figure 12 illustrates schematically the routing of instrument leads, access tubes, and gas lines associated with typical experiments in the RB* positions. Figure 13 shows an uninstrumented "quad holder," used for the production of radioisotopes. When not in use, these facilities contain beryllium or aluminum plugs. Because of their close proximity to the fuel, RB* experiments are carefully reviewed with respect to their neutron poison content, which is limited because of its effect on fuel element power distribution and fuel cycle length.
These positions can accommodate (i.e., shielded) experiments, making them well suited for fusion materials irradiation.
Uses for the RB* facilities have included the production of radioisotopes; High Temperature Gas-Cooled Reactor (HTGR) fuel irradiations; and the irradiation of candidate fusion reactor materials. The later type of experiment requires a fast neutron flux. As seen in figure 6, a significant fast flux is present in addition to the thermal flux. For this application the capsules are placed in a liner containing a thermal neutron poison for spectral-tailoring. These experiments are carefully reviewed with respect to their neutron poison content and limited to certain positions to minimize their effect on adjacent neutron scattering beam tubes.
Small Removable Beryllium Facilities
Four small diameter irradiation positions are located in the removable beryllium (RB) near the control region (see Figure 5). These facilities are designated as RB-2, RB-4, RB-6, and RB-8. The vertical centerline of these facilities is located 10.37 in. (26.35 cm) from the vertical centerline of the reactor and have an inside diameter of 0.5 in. (1.27 cm). The small RB positions do not have an aluminum liner like the RB* facilities. When not in use, these positions contain beryllium plugs.
The use of these facilities has been primarily for the production of radioisotopes. Figure 14 shows a typical irradiation capsule for one of these facilities. The neutron poison content limits and the available pressure drop requirements for experiments in these facilities is the same as in the RB* facilities previously discussed.
Control-Rod Access Plug Facilities
Eight 0.5-in. (1.27-cm) diameter irradiation positions are located in the semipermanent reflector. The semipermanent reflector is made up of eight separate pieces of beryllium, four of which are referred to as control-rod access plugs (see Figure 5). Each control-rod access plug contains two unlined irradiation facilities, designated CR-1 through CR-8. Each of these facilities accommodates an experiment capsule similar to those used in the small removable beryllium facilities. The vertical centerlines of all control-rod access plug irradiation facilities are located 12.68 in. (32.2 cm) from the vertical centerline of the reactor. Only non-instrumented experiments can be irradiated in these facilities. When not in use, these facilities contain beryllium plugs. A pressure drop of 10 psi (6.89 x 104 Pa) at full system flow is available to provide primary system coolant flow for cooling experiments.
Sixteen irradiation positions located in the permanent reflector are referred to as the small vertical experiment facilities (VXF). Each of these facilities has a permanent aluminum liner having an inside diameter of 1.584 in. (4.02 cm). The facilities are located concentric with the core on two circles of radii 15.43 in. (39.2 cm) and 17.36 in. (44.1 cm), respectively (see Figure 5). Those located on the inner circle (11 in all) are referred to as the inner small VXFs. Those located on the outer circle (five in all) are referred to as the outer small VXFs. Normally, non-instrumented experiments are irradiated in these facilities. VXF-7 is dedicated to one of the pneumatic irradiation facilities that supports the Neutron Activation Analysis Laboratory and is unavailable for other use.
A pressure drop of approximately 100 psi (6.89 x 105 Pa) at full system flow is available to provide primary system coolant flow for cooling experiments. When not in use, these facilities may contain a beryllium or aluminum plug or a flow-regulating orifice and no plug.
Large neutron poison loads in these facilities are of no particular concern with respect to fuel element power distribution perturbations or effects on fuel cycle length because of their distance from the core; however, experiments are carefully reviewed with respect to their neutron poison content, which is limited to minimize their effect on adjacent neutron scattering beam tubes.
Large Vertical Experiment Facilities
Six irradiation positions located in the permanent reflector are referred to as the large vertical experiment facilities (VXF)(see Figure 5). These facilities are similar in all respects (as to characteristics and capabilities) to the small vertical experiment facilities described in the preceding section except for location and size. The aluminum liners in the large VXFs have an inside diameter of 2.834 in. (7.20 cm), and the facilities are located concentric with the core on a circle of radius 18.23 in. (46.3 cm). When not in use, these facilities contain beryllium or aluminum plugs.
Large neutron poison loads in these facilities are of no particular concern with respect to fuel element power distribution perturbations or effects on fuel cycle length because of their distance from the core; however, experiments are carefully reviewed with respect to their neutron poison content, which is limited to minimize their effect on adjacent neutron scattering beam tubes.
Neutron Activation Analysis (NAA)
Laboratory and Pneumatic Tube Facilities
Two pneumatic tube facilities are installed in the reactor in support of neutron activation analysis. Pneumatic Tube, PT-1, small vertical experiment facilities (in VXF-7) and pneumatic Tube, PT-2 is located in the EF-1 slant engineering facility that intersects the outer edge of the permanent beryllium eflector.
These facilities, operated by the Analytical Chemistry Division, consist of flight tubes, air supply and exhaust lines, loading stations at which sample containers (rabbits) are introduced into the flight tubes, and irradiation stations to which the rabbits move to be irradiated (see Figure 15). The inner diameter of the flight tubes is 0.62 in. (15.88 mm), and the outer diameter of the rabbit is 0.56 in. (14.48 mm). Both flight tubes accept the same rabbits, which have an internal volume of about 1 cm³. Both systems operate with air entering both ends of the flight tube. Capsules are inserted into the reactor and returned to shielded loading stations in the laboratory. The capsules stop on an air column which permits them to be made of graphite as well as plastic. Graphite capsules can be irradiated for many hours, thus making NAA extremely sensitive for many elements. The capsules can be stopped at decay stations in the pool if they are temporarily too radioactive to return to the laboratory. The facilities are used to measure the trace element content in a variety of materials by neutron activation analysis. About 65 of the chemical elements can be measured in the range of 10-6 to 10-15 g. The induced radioactivity of the samples is measured with high-resolution germanium detectors interfaced to a personal computer-based analyzer.
PT-1 was installed in the HFIR in 1970. This tube carries the sample to VXF-7 in the permanent beryllium reflector about 7 in. (180 mm) from the edge of the fuel element. The thermal flux in PT-1 is about 2.8 x 1014 neutrons/(cm²·s). The thermal/epithermal flux ratio is approximately 40.
PT-2 was installed in the HFIR in 1986. This tube carries the sample to the EF-1 slant engineering facility that intersects the outer edge of the permanent beryllium reflector. This places the sample approximately 12.5 in. (320 mm) from the fuel element. The thermal flux for the facility is about 5.9 x 1013 neutrons/(cm²·s). The thermal/epithermal ratio is approximately 200. PT-2 is expected to permit thermal-neutron NAA that is unusually free of interferences caused by fast neutrons. Additionally, PT-2 has a special delayed neutron counter (DNC) for fissile nuclide analysis. The DNC can be operated in a manual or automatic mode.
The NAA systems support ORNL (DOE) programs, are used in work-for-others projects, and are available for use by students and faculty of universities through Oak Ridge Associated Universities and other programs.
From 1975 to 1985, approximately 100,000 samples were analyzed for uranium by the DNC in the ORR system. Most of those samples were generated by the National Uranium Resources Evaluation and the remaining ones from the Formerly Utilized Sites Remedial Action Program.
NAA at ORNL was also used to analyze evidence related to the 1961-62 French-connection heroin case and the 1963 assassination of President Kennedy. More recently, it has been used in environmental analysis and in determining levels of uranium in materials used in the semiconductor industry and debunked a widely held theory that President Zachery Taylor was assassinated using arsenic poisoning.
Slant Engineering Facilities
Provision has been made for installation of up to two engineering facilities to provide additional positions for experiments. These facilities consist of 4-in. (10.16-cm)-O.D. tubes that are inclined upward 49° from horizontal. The inner ends of the tubes terminate at the outer periphery of the beryllium. The upper ends of the tubes terminate at the outer face of the pool wall in an experiment room one floor above the main beam room.
One of the engineering facilities houses the PT-2 pneumatic tube, which was installed in 1986.
Gamma Irradiation Facility
Since 1968, a large variety of materials have been subjected to high gamma fluxes generated from the decay of fission products in the spent HFIR fuel assemblies in the HFIR pool. The current Gamma Irradiation Facility design is a nominal 3-in diameter can that is placed in the flux trap of the fuel while stored in the spent fuel racks. A cadmium lined post in the flux trap shields any neutrons from the sample so that it does not become activated. Air supply and off-gas lines are available to the irradiation can to provide a sweep gas and for temperature control of the environment. The fuel assemblies used for these irradiations range in decay time (since reactor shutdown) from 30 hours to 7 months, depending on the experiment. The initial (maximum) dose rate in the facility is approximately 1 x 108 R/h.
To date, such experiments have included studies of the effects of gamma radiation on salt, insulating materials, paint samples, and a variety of other materials. An excellent use of this facility is the environmental qualification of commercial grade equipment for nuclear application.
Quality Assurance Requirements
The quality assurance (QA) program for the High Flux Isotope Reactor (HFIR) is based on 10 CFR 830, Subpart A requirements and implementation practices from ASME/NQA-1. All experiments, rabbit capsules, and isotope targets to be irradiated in HFIR must be designed and fabricated under an equivalent set of controls. The experiment's quality program will be reviewed for approval by the Research Reactors Division (RRD) QA personnel prior to acceptance of an experiment into the irradiation program. Experimenters are expected to exercise strict controls over material certification, traceability, and handling, fabrication dimensional tolerances and inspection, containment integrity testing, and cleaning.
The specific design of the experiment will be reviewed and approved by RRD technical personnel following an established process. Deviations and nonconformances to approved designs are required to be reviewed and approved by RRD. Experiment fabrication facilities may be audited by RRD QA personnel for program implementation compliance. The experiment's fabrication records will be reviewed and approved prior to acceptance of the hardware for irradiation in HFIR.
Contacts
For information on the experiment review
and approval process, contact the Research
Reactors Division Experimenter Interface
or the Experiment Coordinator:
Experimenter
Interface
Steve
Burnette |
Experiment
Coordinator
Randy
Hobbs |
Oak Ridge National Laboratory
P.O. Box 2008, MS 6398
Oak Ridge, TN 37831-6398
Phone: (865) 576-0214 |
Oak Ridge National Laboratory
P.O. Box 2008, MS 6423
Oak Ridge, TN 37831-6423
(865) 574-8789 |
|
