UCD McClellan Nuclear Radiation Center

Mutagenized populations have become indispensable resources for introducing variation and studying gene function in plant genomics research. In this study, fast neutron (FN) radiation was used to induce deletion mutations in the soybean (Glycine max) genome. Approximately 120,000 soybean seeds were exposed to FN radiation doses of up to 32 Gray units to develop over 23,000 independent M2 lines. Here, we demonstrate the utility of this population for phenotypic screening and associated genomic characterization of striking and agronomically important traits. Plant variation was cataloged for seed composition, maturity, morphology, pigmentation, and nodulation traits. Mutants that showed significant increases or decreases in seed protein and oil content across multiple generations and environments were identified. The application of comparative genomic hybridization (CGH) to lesion-induced mutants for deletion mapping was validated on a midoleate x-ray mutant, M23, with a known FAD2-1A (for fatty acid desaturase) gene deletion. Using CGH, a subset of mutants was characterized, revealing deletion regions and candidate genes associated with phenotypes of interest. Exome resequencing and sequencing of PCR products confirmed FN-induced deletions detected by CGH. Beyond characterization of soybean FN mutants, this study demonstrates the utility of CGH, exome sequence capture, and next-generation sequencing approaches for analyses of mutant plant genomes. We present this FN mutant soybean population as a valuable public resource for future genetic screens and functional genomics research.

The University of California/Davis McClellan Nuclear Radiation Center (UCD/MNRC) was originally constructed by the U.S. Air Force as a nondestructive testing tool to detect moisture and corrosion in large honeycomb filled structures of aircrafts. The MNRC was transferred to UCD in February of 2000 as part of the Base Realignment and Closure (BRAC) process of McClellan Air Force Base. UCD MNRC has a sound base of research and industrial partnerships. Jet Propulsion Laboratory, Pasadena, CA. approached UCD MNRC with the need to image the condition of brushes contained in motors used in their space related projects. JPL explained that they were unable to see what they needed to see with X-rays. They wanted to know if we could see the carbon brushes in these motors. Using their samples, we initially performed two computed radiography (CR) shots 90 degrees apart through the diameter. Furthermore, another shot along the rotational axis was taken. The brushes could not be seen in the shot along the axis. The exposures through the diameter showed an inconsistency between the two motors’ brushes. We then performed neutron computed tomography (CT) on both motors with one degree projection. Reconstruction clearly showed that the motor with the inconsistent shape brushes had the brushes installed incorrectly. There is a significant difference in both time and cost between CR and CT of the motors. CR took about 30 minutes from beginning of the set up to the complete evaluation, while CT took about five hours to finish. UCD/MNRC was not completely satisfied with just saying that there is an inconsistency between the two motors. Through working outside the envelope, a complete picture of the brushes condition was seen with CT in about 30 minutes.

Use of the RELAP5 thermal-hydraulic code to support the safety analysis for reactor power upgrade from 1.0 to 2.0 MW

The UCD/ MNRC inherited NDT capabilities from the US Air Force and even though it is now mainly a research facility, it has kept this acquired asset performing at a production level. The UCD/MNRC facility is equipped with a hexagonal grid, natural convection water cooled TRIGA reactor designed to operate at a nominal 2 .0 MW steady state power as well as in pulse and square wave mode. The reactor utilizes a specially designed annular graphite reflector accommodating four removable units to accept four separate source ends of beam tubes. These tangential beam tubes lead to four large investigation bays with neutron radiography setting. The design basis for these beam tubes is to provide a path for primary thermal neutrons with minimum scattering and attenuation between the reflector inserts and radiography bays. Typical unperturbed beam parameters are summarized in the following: Each beam tube ends with a bulk shield as the primary beam stopper and a separate boron-included fast shutter to initiate and complete a neutron exposure. Traditional film system and more recently computed radiology system utilizing reusable storage phosphor imaging plate (SPIP) are extensively used as 2D imaging recording media. Bay 3 is designed with a charge coupled device (CCD) camera with system control hardware and software to perform 3D neutron tomography. Bay 4’s beam tube, different from the others, has an 11”-thick sapphire crystal filter to provide an even higher quality beam, i.e. much lower contamination from fast neutrons and gamma rays, for 2D neutron radiography. UCD/ MNRC is committed to offering state-of-the-art neutron imaging experiences for non-destructive testing projects. Our unique capabilities enable us to provide effective solutions to the customer’s needs. Providing quality assurance of complicated titanium castings for aircraft, inspecting metal loss of pressurized tanks for fighting forest fires, examining binding between corrosion-resistant coatings and base metal for spent fuel containers, are a few of many services rendered.

Depletion calculations have been performed for the McClellan reactor history from January 1990 through August 1996. A database has been generated for continuing use by operations personnel which contains the isotopic inventory for all fuel elements and fuel-followed control rods maintained at McClellan. The calculations are based on the three-dimensional diffusion “theory code REBUS-3 which is available through the Radiation Safety Information Computational Center (RSICC). Burnup-dependent cross-sections were developed at zero power temperatures and full power temperatures using the WIMS “code (also available through RSICC). WIMS is based on discretized transport theory to calculate the neutron flux as a function of energy and position in a one-dimensional cell. Based on the initial depletion calculations, a method was developed to allow operations personnel to perform depletion calculations and update the database with a minimal amount of effort. Depletion estimates and calculations can be performed by simply entering the core loading configuration, the position of the control rods at the start and end of cycle, the reactor power level, the duration of the reactor cycle, and the time since the last reactor cycle. The depletion and buildup of isotopes of interest (heavy metal isotopes, erbium isotopes, and fission product poisons) are calculated for all fuel elements and fuel-followed control rods in the MNRC inventory. The reactivity loss from burnup and buildup of fission product poisons and the peak xenon buildup after shutdown are also calculated. The reactivity loss from going from cold zero power to hot full power can also be calculated by using the temperature-dependent, burnup dependent cross-sections. By calculating all of these reactivity effects, operations personnel are able to estimate the total excess reactivity necessary to run the reactor for the given cycle. This method has also been used to estimate the worth of individual control rods. Using this approach, fuel management and core loading can be optimized such that each individual fuel element and fuel-followed control rod is used to its full potential before being replaced with fresh fuel. This fuel management strategy allows a significant cost saving to MNRC by reducing fuel replacement costs and maximizing the usefulness of each element in the inventory.

Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) where the accelerator and detectors will be subjected to large fluences of hadrons, leptons and gamma’s over their life. Examples are NdFeB magnets considered for the damping rings and final focus, electronic and electro-optical devices to be utilized in detector readout and accelerator controls and CCDs required for the vertex detector. Effects of gamma’s on many materials have been presented and our understanding of the situation for rare earth permanent magnets at the Particle Accelerator Conference 2003. Here we give first measurements of the fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD/MNRC) together with the induced radioactivities. Damage appears to be proportional to the distances between the operating point and Hci.

The elemental losses from ashes of common biomass fuels (rice straw, wheat straw, and wood) were determined as a function of temperature from 525 8C to below 1525 8C, within the respective melting intervals. The experimental procedure was chosen to approach equilibrium conditions in an oxidizing atmosphere for the specific ash and temperature conditions. All experiments were conducted in air and used the ashes produced initially at temperatures of 525 8C as reactants. Losses during the initial ashing at 525 8C were negligible, except for a K2O loss of 26% for wood and a Cl loss of 20% for wheat straw. Potassium losses are positively correlated with temperature for all fuel ashes. The K2O loss for wood ash commences at 900–1000 8C. Carbonate is detected in the wood ashes to about 700–800 8C and thus cannot explain the retention of K2O in the ashes to 1000 8C. Other crystalline phases detected in the wood ashes (pericline and larnite) contain little or no potassium. Petrographic examinations of high temperature, wood ash products have failed to reveal potassium bearing carbonates, sulfates, or silicates. The release of potassium, thus, appears to be unrelated to the breakdown of potassium-bearing crystalline phases. The straw ashes show restricted potassium loss compared to wood ash. The potassium content declines for both straw ashes from about 750 8C. Cristobalite appears in the straw ashes at about 700–750 8C and is replaced by tridymite in the rice straw ash from about 1100 8C. Sylvite (KCl) disappears completely above 1000 8C. The Cl content starts to decline at about 700 8C, approximately at the same temperature as potassium, suggesting that the breakdown of sylvite is responsible for the losses. The K–Cl relations demonstrate that about 50% of K (atomic basis) released from breakdown of sylvite is retained in the ash. The presence of chlorine in the ash is, therefore, best attributed to the presence of sylvite. Potassium is easily accommodated in the silicate melt formed at temperatures perhaps as low as 700–800 8C from dehydration, recrystallization, and partial melting of amorphous components. Loss of potassium persists for ashes without remaining sylvite and points to the importance of release of potassium from partial melt at temperatures within the melting interval for the fuel ashes.

The University of California McClellan Nuclear Radiation Center was originally developed by the U.S. Air Force as a nondestructive testing tool to detect moisture and corrosion in large honeycomb filled surfaces of aircraft. MNRC was transferred to UCD in February of 2000 as part of the closure process of McClellan Force Base. UCD MNRC has a firm base of research and industrial partnerships. The United States Forest Service contracted Dyncorp Inc. to upgrade and perform safety checks fire fighting systems carried aboard Air National Guard C-130 aircraft. These fire fighting systems, "Modular Airborne Firefighting Systems", MAFFS, were fabricated in the early to mid 70’s. The tanks, tubing, and fittings that make up these systems are made of aluminum. They have been exposed to various fire retardant formulas. Following use, the systems are flushed with water and air dried. The result of these caustic and corrosive cycles was not known. Working through UC Davis' office of Technology Industry Alliances, Dyncorp turned to the neutron radiography facility at UC Davis' McClellan Nuclear Radiation Center to determine the effect of these cycles. The U.S. Forest Service, UC Davis and Dyncorp are partners in the Center of Excellence for Aircraft Health Management. Other partners include NASA Ames Research Center, Aerobotics Inc., Hill Engineering LLC and Eclypse International.

Many materials and electronics need to be tested for the radiation environment expected at linear colliders (LC) to improve reliability and longevity since both accelerator and detectors will be subjected to large fluences of hadrons, leptons and gammas. Examples include NdFeB magnets, considered for the damping rings, injection and extraction lines and final focus, electronic and electro-optic devices to be utilized in detector readout, accelerator controls and the CCDs required for the vertex detector, as well as high and low temperature superconducting materials (LTSMs) because some magnets will be superconducting. Our first measurements of fast neutron, stepped doses at the UC Davis McClellan Nuclear Reactor Center (UCD MNRC) were presented for NdFeB materials at EPAC04 where the damage appeared proportional to the distances between the effective operating point and Hc. We have extended those doses, included other manufacturer's samples and measured induced radioactivities. We have also added L and HTSMs as well as a variety of relevant semiconductor and electro-optic materials including PBG fiber that we studied previously only with gamma rays.