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Nuclear Science and Engineering

Irradiated Materials Laboratory

IML
Conducts research on the behavior of commercial nuclear reactor materials, including fuel cladding, pressure vessels, and other in-reactor components.

The Irradiated Materials Laboratory (IML) has capabilities for handling, testing, and analyzing irradiated materials. The facility was designed to conduct postirradiation examinations of structural components for reactor development. Capabilities have been expanded to include testing of reactor components and fuel-rod cladding. The research has helped increase knowledge of irradiated materials behavior and properties for commercial power reactors and research reactors. The facility has also been used to provide data for development and testing of advanced alloy materials for the DOE fusion program. Testing capabilities include tensile and creep-rupture under vacuum or inert atmosphere up to 800°C, slow-strain-rate tensile testing (SSRT), fatigue and SCC crack growth rate (CGR) tests up to 320°C in controlled PWR and BWR water environments, fracture toughness testing up to 320°C in a controlled water environment, and a LOCA integral test apparatus for subjecting irradiated cladding to high-temperature steam oxidation followed by cold-water quench. Sample preparation capabilities include a remotely operated electric discharge machine (EDM) for cutting precise test specimens from irradiated materials.

The IML consists of four air-atmosphere, centi-curie beta/gamma hot cells. The interior of each cell is 6 ft wide x 5 ft deep x 9.7 ft high and is maintained at a negative air pressure. Each cell is equipped with movable doors that allow the cell equipment to be easily installed, removed, and reconfigured to support the mission of the cell.

Hot Cell Configuration

  • One cell has a 0.5 ton hoist for removal of vertical cask lids.
  • Multiple 4 in. diameter and two 12 in. diameter access ports on the side wall of each cell. Multiple internal ports connect the four cells.
  • Viewing windows at the front (30 x 50 in.) and side (12 x 18 in.) of each cell.
  • Three laboratory hoods for sample preparation.

Testing Equipment

  • Instron 8511 servohydraulic driven tension/compression/ cyclic testing machine in radiological glovebox with Pb glass shielding for contaminated and activated materials.
  • Integral radiant furnace capable of test temperatures up to 1300°C and burst pressures of 2000 psig in flowing gas environments.
  • Custom-built SSRT and CGR apparatus capable of testing in water or gas environment up to 320°C.
  • Modified Instron 8500 and 8800 dynamic testing systems capable of fracture toughness and fatigue studies (1/4 or 1/2–T CT) in water or gas environment up to 320°C.

Ancillary Equipment

  • Hansvedt DS2 Electric Discharge Wire-Cutting Machine with Computer Numeric Control (CNC) for remote machining of precise test specimens from irradiated materials. Minimum wire size is 0.004” and CNC precision is ±0.0002”.
  • Macro-cameras for magnifications from 1X to 20X.
  • Contact and dial-gauge micrometers.
  • Jet polishing apparatus for preparation of TEM specimens.
  • High-temperature furnaces (radiant and resistance), computer–controlled for controlled heating cycles up to 1400°C.
  • Vacuum heat treatment furnaces.

Support Facilities

  • Pb glass-shielded gloveboxes for optical microscopy specimen preparation and imaging .
  • Astro Arc (TIG) welder and pressurization/laser-welding system for fabricating sealed, high-burnup cladding rodlets.
  • Programmable furnace used to simulate drying/storage temperature histories for used-fuel cladding.
  • LECO machines for measuring oxygen, nitrogen and hydrogen contents of irradiated materials.
  • Electron Microscopy Center, with its 1.2– MeV electron microscope and high-resolution analytical microscope.
  • Advanced Materials Fabrication Facility providing alloy preparation and casting, secondary fabrication, assembly and welding, and inspection services.
  • Scanning and transmission electron microscopes to examine radioactive specimens.

Optical Microscope (OM)

The optical microscope is used for micron-level examination of commercial fuel cladding following irradiation, simulated post-irradiation drying, dry-cask storage, and cask transport, and simulated reactor accidents. It is currently being used to measure fuel cladding outer- and inner-surface oxide layers and cladding wall thickness for as-polished surfaces. Examinations of etched surfaces reveal the morphology, orientation, and distribution of precipitated zirconium hydrides, which are predominantly oriented in the circumferential direction following normal reactor operation. Drying of post-irradiation assemblies in storage canisters and/or casks results in elevation of temperature and internal fuel-rod pressure. During slow cooling from elevated temperature, hydrides that precipitate under pressure-induced circumferential stress may reorient in the radial direction, which causes a decrease in ductility and possible embrittlement in response to external circumferential loading. Optical microscope images of etched surfaces are examined to determine the extent of radial hydride precipitation. For cladding samples subjected to a simulated loss of coolant accident, measurements are also made of the thickness values of the metallic oxygen-stabilized alpha layer and the metallic beta layer. Given that the steam-oxidized and the oxygen-stabilized-alpha layers are brittle, cladding ductility is reduced to the point of embrittlement as the beta layer decreases in thickness and increases in oxygen content with increased oxidation time at elevated temperature.

Scanning Electron Microscope (SEM)

Scanning electron microscopy is a powerful technique for surface characterization and quantitative analysis for corrosion- and stress-induced degradation of neutron-irradiated reactor materials. A Phenom XL desktop SEM has been installed inside the IML with added lead shielding for radioactive reactor-material samples. This SEM has a large sample stage (50×50 mm) and is equipped with both backscattered electron and secondary electron detectors. It also has an energy-dispersive X-ray spectroscopy (EDS) detector for chemical analysis and elemental mapping. Neutron-irradiated specimens and radioactive reactor components have been examined in this SEM following mechanical tests conducted at reactor-relevant coolant temperature, pressure, and chemistry. Results for failure analysis and surface characterization have been used to better quantify and understand the combined effects of neutron irradiation, corrosion, and stress on cracking and crack growth rates.

Transmission Electron Microscope (TEM)

Transmission electron microscopy is a powerful tool to investigate crystallographic defects down to the nanoscale level and is a critical technique to study the microstructure of irradiated materials. The IVEM-TANDEM Hitachi-9000 TEM, which is in the same building as the IML, has a resolution of 0.25 nanometers. This TEM has been used to characterize irradiation-induced defects and defect evolution in neutron-irradiated reactor materials. The results aid in the understanding of damage and degradation mechanisms in reactor materials subjected to neutron irradiation.

Advanced Photon Source (APS)

The Advanced Photon Source has been used to examine the in-situ, real-time behavior of many materials, including current and advanced fuel cladding and reactor materials. Many universities, supported by grants from the DOE Office of Nuclear Energy, use APS for fundamental research. Samples irradiated in the Idaho Advanced Test Reactor (ATR) are too contaminated and too high in combined dose rate for direct shipment to APS. The IML serves the intermediate role of receiving, decontaminating, mounting, and transferring (to APS) samples for examination in APS. Following APS examination, the samples are returned to the IML for packaging and shipment back to Idaho. Materials processed by the IML for APS examination include programmatic fuel cladding samples, iron and steel alloys, and U-bearing fuels. Some of the universities who have used the IML facilities include the University of Illinois, Pennsylvania State University, and Purdue University.