Jason T. Harris

47 Ca production for 47 Ca/ 47 Sc generator system using electron linacs

In this work we have studied the feasibility of photonuclear production of (47)Ca from (48)Ca for (47)Ca/(47)Sc generators. Photon flux distribution for electron beams of different energies incident on a tungsten converter was calculated using the MCNPX radiation transport code. The (47)Ca production rate dependence on electron beam energy was found and (47)Ca/(47)Sc yields were estimated for a 40MeV electron beam. It was shown that irradiating enriched targets with a 40MeV, 1mA beam will result in tens of MBq g(-1) (few mCi g(-1)) activity of (47)Sc. The results of the simulations were benchmarked by irradiating 22.5g of CaCl2 powder with a 39MeV electron beam incident on a tungsten converter. Measured (47)Ca/(47)Sc activities were found to be in very good agreement with the predictions.

RADIOLOGICAL EFFLUENTS RELEASED BY U.S. COMMERCIAL NUCLEAR POWER PLANTS FROM 1995-2005

Commercial nuclear power plants release gaseous and liquid radiological effluents into the environment as by-products of electrical generation. In the U.S. these releases are monitored by the Nuclear Regulatory Commission (U.S. NRC) and Environmental Protection Agency (U.S. EPA). Traditionally these releases have always been well below the regulatory limits. However, the tracking and analysis of nuclear power radiological effluents was stopped in 1994 by several government agencies. The purpose of this study was to compile the entire U.S. industry effluent data, identify trends, and calculate average population dose commitments since that time. Data were taken from radioactive material release reports submitted by each nuclear power plant. Industry trends were identified using the Mann-Kendall non-parametric test. Total collective effective and population doses were estimated using UNSCEAR and U.S. NRC methodologies. Overall, industry releases have been level over the study time period. Public doses continue to be well below 1% of the regulatory limits.

Radiological Releases and Environmental Monitoring at Commercial Nuclear Power Plants

The generation of electricity from nuclear power has become increasingly important due to the growing concerns of global climate change. Nuclear energy has long been recognized as a leading energy source that produces minimal pollution to the environment that can contribute to this phenomenon. In addition, nuclear power offers an attractive option for countries looking for energy source diversification. Currently there are 442 commercial nuclear power reactors operating in the world (International Atomic Energy Agency [IAEA], 2010, 2011). These power plants contribute about 19% of the electricity production today. The United States of America (U.S.) has the largest commercial nuclear reactor fleet in the world with 104 operating reactors (U.S. Nuclear Regulatory Commission [USNRC], 2010). Of these reactors, 69 are pressurized water reactors (PWRs) and 35 are boiling water reactors (BWRs), located on 65 sites around the country. These power plants contribute about 20% of the U.S. electricity production. Although it is known that commercial nuclear power plants release small amounts of radioactivity into the environment, there is still the potential for these releases to impact public health. This is especially important today as changes are occurring in nuclear power plant operations including: higher electric generating capacities, increased power levels due to mechanical uprates, and plant life extensions. Public health effects must be reexamined as new light water reactor designs are being considered for construction. In addition, recent events at multiple nuclear power plants in the U.S. involving unplanned releases, especially tritium (3H), have led to increased scrutiny on monitoring and evaluating releases. Changes in radiation protection recommendations and regulations also warrant further and continued investigations in these matters. Although Harris (2007) and Harris & Miller (2008) have performed numerous studies of nuclear power effluent releases and environmental monitoring, data collection and analysis must continue to be performed for the entire nuclear industry. This chapter focuses on recent research that has been conducted in the areas of commercial nuclear power radiological releases and environmental monitoring by the author. Although the emphasis will be on studies performed in the United States of America, international comparisons will be made where appropriate.

Biokinetics of Plutonium in Nonhuman Primates.

AbstractA major source of data on metabolism, excretion and retention of plutonium comes from experimental animal studies. Although old world monkeys are one of the closest living relatives to humans, certain physiological differences do exist between these nonhuman primates and humans. The objective of this paper was to describe the metabolism of plutonium in nonhuman primates using the bioassay and retention data obtained from macaque monkeys injected with plutonium citrate. A biokinetic model for nonhuman primates was developed by adapting the basic model structure and adapting the transfer rates described for metabolism of plutonium in adult humans. Significant changes to the parameters were necessary to explain the shorter retention of plutonium in liver and skeleton of the nonhuman primates, differences in liver to bone partitioning ratio, and significantly higher excretion of plutonium in feces compared to that in humans.

Monte Carlo simulation of in vivo measurement of the most suitable knee position for the optimal measurement of activity.

AbstractA new computational model has been developed using the Monte Carlo (MC) technique to simulate in vivo measurements with the objective of understanding the most precise measurement location with respect to quantifying the activity of 241Am in the bones. To benchmark the model, in vivo measurements were performed on the U.S. Transuranium and Uranium Registries (USTUR) case 0846 leg. Front and lateral measurements of the knee of the USTUR case 0846 leg in a bent position and the same measurements with the leg in a straight position using a HP(Ge) detector were completed. Experimental results concluded that the front measurement of the knee in a bent leg position gave the highest count rate, which is an indication of optimal detection efficiency. Therefore, this geometry and knee-detector position were considered as the most appropriate position for knee monitoring. A computational model using MCNPX version 2.6.0 was used to simulate the experimental measurements by using a leg voxel phantom. The mean value and standard deviation (SD) of peak efficiency due to an isotropic 59.5-keV photon from 241Am were calculated in four different counting geometries. An extra sum of squares F-test was performed on the mean values of the simulated detection efficiencies. The p-value obtained from this statistical test indicates that the differences among the mean values for different counting geometries were significant. These results suggest that the front measurement of a knee in a bent leg position is the optimal counting geometry for in vivo measurement of 241Am deposited in the bones. The computational model was validated through comparison of the measured and simulated detection efficiencies. It was observed that there is no difference at the 0.1 significant levels between the simulated and measured detection efficiencies in assessment of 241Am within the bones.

A Longitudinal Study of Human Exposure to Potential Nuclear Power Plant Risk

This study constructs a potential risk index (PRI) for the 65 U.S.-based commercial nuclear power plant (NPP) sites in relation to their surrounding populations. Four risk levels are defined: low risk, moderate risk, high risk, and very high risk. Discrepancies that exist in the sociodemographic characteristics of the host communities’ populations are examined as sorted by risk-level category. It is found that a greater percentage of minority groups are exposed to the highest levels of risk. In addition, percent “Hispanic” and percent “Other,” a grouping that includes multiracial, mixed, interracial, as well as Hispanic and Latino groups (for example, Mexican, Puerto Rican, Cuban, or Spanish) are categories that show the greatest percent change in both the period 1990–2000 and 2000–2010.

In-core flux sensor evaluations at the ATR critical facility

Abstract As part of an Idaho State University (ISU)–led Advanced Test Reactor (ATR) National Scientific User Facility (NSUF) collaborative project that includes Idaho National Laboratory (INL) and the French Alternative Energies and Atomic Energy Commission (CEA), flux detector evaluations were completed to compare their accuracy, response time, and long-duration performance. Special fixturing, developed by INL, allows real-time flux detectors to be inserted into various Advanced Test Reactor Critical Facility (ATRC) core positions to perform lobe power measurements, axial flux profile measurements, and detector cross-calibrations. Detectors initially evaluated in this program included miniature fission chambers, specialized self-powered neutron detectors (SPNDs), and specially developed commercial SPNDs. Results from this program provide important insights related to flux detector accuracy and resolution for subsequent ATR and CEA experiments and yield new flux data required for benchmarking models in the ATR Life Extension Program (LEP) Modeling Update Project.

Tritium recapture behavior at a nuclear power reactor due to airborne releases.

This paper describes the initiatives taken by Cook Nuclear Plant to study the on-site behavior of recaptured tritium released in its airborne effluents. Recapture is the process where a released radioactive effluent, in this case tritium, is brought back on-site through some mechanism. Precipitation, shifts in wind direction, or anthropogenic structures that restrict or alter effluent movement can all lead to recapture. The investigation was started after tritium was detected in the north storm drain outfall. Recent inadvertent tritium releases by several other nuclear power plants, many of which entered the groundwater, have led to increased surveillance and scrutiny by regulatory authorities and the general public. To determine the source of tritium in the outfall, an on-site surface water, well water, rainwater and air-conditioning condensate monitoring program was begun. Washout coefficients were also determined to compare with results reported by other nuclear power plants. Program monitoring revealed detectable tritium concentrations in several precipitation sample locations downwind of the two monitored containment building release vents. Tritium was found in higher concentrations in air-conditioning condensate, with a mean value of 528 Bq L−1 (14,300 pCi L−1). The condensate, and to a lesser extent rainwater, were contributing to the tritium found in the north storm drain outfall. Maximum concentration values for each sample type were used to estimate the most conservative dose. A maximum dose of 1.1 × 10−10 mSv (1.1 × 10−8 mrem) total body was calculated to determine the health impact of the tritium detected.

Hybrid GPU/CPU Approach to Multiphysics Simulation

Multiphysics simulation is a crucial stage in many current fields of science and industry like solid mechanics, heat transfer, automobile systems, or nuclear systems. Modeling and simulation provides knowledge that would be difficult or even impossible to obtain when trying to experiment with physical objects. Multiphysics simulation is a time and computational demanding process. Therefore great effort has been put forward to apply new technologies which eventually will enhance performance. In the last decade a number of approaches were proposed. One approach takes advantage of classic supercomputers with thousands of Central Processing Units (CPU). Another approach uses modern Graphical Processing Units (GPU) to perform general purpose computing (GPGPU) by adjusting the application to a new environment. In this paper, hybrid approaches that use both CPU and GPU are proposed. The approach assumes executing highly serial parts of code by a classic multiprocessor machine that uses underlying GPU to execute heavy computational and parallel parts of code. The idea is applied to a Finite Element (FE) library called libMesh (a part of the MOOSE Framework). Proposed modification of the FE library does not affect existing applications that use the MOOSE Framework or libMesh alone. Therefore, it is enough to recompile the multiphysics simulation framework of the library. To evaluate performance of implemented modification, software was used to perform a simulation on an empty cylinder sealed from both sides. Obtained results show that the presented approach has potential and may be beneficial to develop this idea by extending the scope of the code executed by GPU.

Lead Slowing Down Spectrometry Analysis of Data from Measurements on Nuclear Fuel

Abstract Improved nondestructive assay of isotopic masses in used nuclear fuel would be valuable for nuclear safeguards operations associated with the transport, storage, and reprocessing of used nuclear fuel. Our collaboration is examining the feasibility of using lead slowing-down spectrometry techniques to assay the isotopic fissile masses in used nuclear fuel assemblies. We present the application of our analysis algorithms to measurements conducted with a lead spectrometer. The measurements involved a single fresh fuel pin and discrete 239Pu and 235U samples. We are able to describe the isotopic fissile masses with root-mean-square errors over seven different configurations to 6.3% for 239Pu and 2.7% for 235U. Significant effort is yet needed to demonstrate the applicability of these algorithms for used-fuel assemblies, but the results reported here are encouraging in demonstrating that we are making progress toward that goal.