Nuclear Criticality, Shielding, and Thermal Analyses of Separations Processes for the Transmutation Fuel Cycle

The first step in any transmutation strategy is the separation of radionuclides in used nuclear fuel. The current separation strategy supporting the Advanced Fuel Cycle Initiative (AFCI) program is based on the use of a solvent extraction separation process to separate the actinides, fission products, and uranium from used commercial nuclear fuel, and on the use of pyrochemical separation technologies to process used transmuter fuels. To separate the fission products and transuranic elements from the uranium in used fuel, the national program is developing a new solvent extraction process, the Uranium Extraction Plus, or UREX+, process based on the traditional solvent extraction reprocessing technologies. As the volume of waste requiring treatment increases, a higher probability exists that fissionable isotopes of plutonium, neptunium, and curium can accumulate and form a critical mass. Criticality concerns warrant an assessment of the effective neutron multiplication factor, or keff, to prevent a possible sustained fission reaction. Maintaining keff below a safe level (\u3c0.95) prevents criticality events. This parameter can be computed for any combination of fuel and geometry using Monte Carlo neutron transport codes. Monte Carlo simulations establish the best means of examining the criticality safety of the proposed separation processes, and allow engineers to develop proper safety measures for the reprocessing and fabrication of actinide fuels. Candidate storage containers also require analysis to assess the need for radiation shielding. Since minor actinides generate significant amounts of heat through radioactive decay, proposed containment measures must be designed to avoid excessive temperatures. Radioactive decay also generates heat that can lead to melting of the fuel during storage and handling

The Impact of Child Maltreatment on Suicidal Ideation, Polysubstance Use, and Sexual Risk Behaviors

Child maltreatment is a global public health and human rights issue, with severe lifelong consequences. Previous research has linked experiences of child maltreatment with suicidality, sexual risk behaviors, and polysubstance use. However, little is known about these associations with child maltreatment longitudinally, collectively, and in specific regions of the world. Few studies have examined suicidality among youth in sub-Saharan Africa, and youth living in the slums of Kampala, Uganda are a vulnerable population that is drastically understudied and at risk for suicidal ideation. Additionally, research in the U.S. has been conducted on child maltreatment, sexual risk behaviors, and polysubstance use; however, few studies have examined these associations longitudinally across adolescence into adulthood. These studies seek to expand on previous research on the associations between child maltreatment and 1) suicidality, 2) polysubstance use, and 3) sexual behaviors. Using data from Kampala, Uganda, the impact of child maltreatment on suicidal ideation was examined in the context of current and problematic alcohol use as well as negative future expectations using structural equation mixture modeling. Child maltreatment had a direct effect on suicidal ideation, after accounting for negative future expectations and alcohol use. Using data from the U.S., the association between child maltreatment and polysubstance use was examined using both latent class and latent transition analyses. Lastly, the association between child maltreatment and sexual behaviors was examined a similar analytic approach. The second and third studies aimed to determine if changes between substance use profiles and sexual behaviors differed by child maltreatment patterns. Child maltreatment impacted profiles of substance use and sexual behaviors at specific time points, and previous substance use and sexual behavior profiles influenced profiles at later waves. While there was no interaction between maltreatment and previous profiles of substance use and sexual behaviors, there was an indirect effect of maltreatment on subsequent profiles through the elevated uniform impact of maltreatment in previous waves. Future studies should incorporate additional types of child maltreatment and contextual information on timing, severity, and perpetration

The Association of Major Depression and Selected Health Behaviors among HIV-positive Adults Receiving Medical Care in Georgia: Findings from the Georgia Medical Monitoring Project, 2009-2012

Introduction: Currently there are approximately 1.2 million people in the United States living with HIV and it is estimated that 25.6% of HIV-positive adults suffer from depression. The purpose of this study is to examine the contribution of depression on substance use and medication adherence specifically among HIV-positive adult Georgians receiving medical care for HIV. Methods: Secondary data with a probability sample of 608 HIV-positive adults who took part in the 2009-2012 Georgia Medical Monitoring Project (MMP) were analyzed. Descriptive analysis and multivariate logistic regression models were conducted to assess relationships between depression with current cigarette smoking, injection drug use, other non-injection drug use, and medication adherence, adjusting for sociodemographic covariates (age, gender, race, and education). All analyses accounted for non-response and complex sampling design and were performed using SAS 9.2 (Cary, NC). Results: Among HIV-positive adults in Georgia, approximately 9.2% met the criteria for major depression; 15.2% of women and 6.9% of men had major depression. Heterosexual adults also had a higher percentage of major depression (11.9%) compared to adults who identified as bisexual (8.3%) or homosexual (6.1%). Major depression was also highest among young adults (17.1%) and adults with high school diploma or GED (13.0%). Major depression was associated with a greater odds of current cigarette smoking (3.04; 95% CI: 1.48, 6.23); injection drug use (5.62; 95% CI: 0.96, 32.81), and other non-injection drug use (2.17; 95% CI: 1.10, 4.25), after adjusting for sociodemographic variables. Major depression was also associated with a greater odds of ART medication non-adherence, 2.52 (95% CI: 1.20, 5.28), after adjusting for gender. Conclusion: As previously found in the general population, we found significant associations between depression and smoking and other non-injection drug use among HIV-positive adults. Major depression was also associated with a greater odds of ART medication non-adherence, which is also consistent with the literature. Because HIV-positive adults have ongoing encounters with healthcare providers, screening and treatment for depression and other co-morbid substance use is needed to reduce an additional health burden in this population

Radiation Transport Modeling of Beam-Target Experiments for the AAA Project

The AAA program will rely on the use of an accelerator-based transmuter to expose spent nuclear fuel to high-energy neutrons. The neutron flux will be sufficient to activate or fission the long-lived isotopes of Tc, I, Pu, Am, Cm, and Np that present a significant safety hazard in commercial spent fuel. Transmuter fuel will be subcritical and a high-energy proton accelerator is needed to maintain the necessary neutron flux through the use of a neutron spallation target. The maximum neutron energy produced by spallation (~ 600 MeV) is significantly higher than that produced by a commercial light water reactor (~ 2 MeV). To design the nation’s first transmuter, the neutronics code MCNPX will be used to model the distribution of neutron flux within the fuel blanket and to determine the neutron multiplication, keff. However, the cross section libraries and computational methods used by MCNPX at these neutron energies still have some uncertainty and will require validation. To lessen the uncertainties in the MCNPX libraries, the Department of Energy, through its national laboratories, is in the process of conducting several experiments utilizing protons produced by the Los Alamos Neutron Science Center (LANSCE) accelerator at the Los Alamos National Laboratory. MCNPX simulations provide valuable information for the design of experiments in addition to their use in analysis of experimental to validate and improve the codes and databases. We propose a research project wherein UNLV students and faculty will contribute to these critical experiments by performing computational work using the latest versions of MCNPX and its associated data libraries. This research project will be conducted in close coordination with AAA leads and researchers in both experimental projects and code and database development

Fabrication and Characterization of an Extracellular Matrix Hydrogel for Aortic Valve Applications

With an estimated 5 million people suffering from valve disease in the United, valve disease is currently the leading cause of cardiovascular disease. Each year, between 80,000 and 85,000 aortic valve replacements are performed in order to treat the stenotic heart valves. Despite this being a worldwide epidemic, the current valve replacement options that are on the market have distinct limitations. Furthermore, a viable alternative does not exist for the patients that are not candidates for the current treatment methods. Our proposed solution to this epidemic is to create a highly viable injectable scaffold that would allow for the minimally invasive delivery of human adipose-derived stem cells (hADSCs), as well as to provide necessary biological cues for growth and remodeling to the scaffold. A process was created to create a hydrogel derived from decellularized porcine aortic cusp tissue. The aortic cusp was solubilized using an acid-pepsin solution, neutralized and reformed as a hydrogel structure. This processing was analyzed for effectiveness of decellularization, retention of the extracellular matrix components, scaffold architecture, and cell interaction and viability. Histology showed proper decellularization while maintaining the components of the extracellular matrix throughout the fabrication process, collagen content analysis provided further evidence of this. Quantitative analysis of H&E sections revealed a highly porous scaffold, conducive to cell migration. Rheological studies revealed shear thinning properties that is advantageous for the ability of the scaffold to be injected. A Live/Dead assay of the scaffold showed an extremely viable scaffold in static conditions, as well as a tendency of the cells to contract and remodel the hydrogel. Present studies have optimized the technique for creation of the hydrogel, characterized the biological and physical properties of the scaffold, and determined the viability of the scaffold for seeding of hADSCs. These aortic cusp-derived scaffolds provide an environment that mimics the aortic cusp ECM. This research will advance cardiovascular tissue engineering and further aid in the search for the ideal tissue engineered heart valve

Project Continuation Proposal: Radiation Transport Modeling of Beam-Target Experiments for the AAA Project

The AAA program will rely on the use of an accelerator-based transmuter1 to expose spent nuclear fuel to high-energy neutrons. The neutron flux will be sufficient to activate or fission the long-lived isotopes of Tc, I, Pu, Am, Cm, and Np that present a significant radiological hazard in commercial spent fuel. Transmuter fuel will be subcritical and a high-energy proton accelerator is needed to maintain the necessary neutron flux through the use of a neutron spallation target. The maximum neutron energy produced by spallation (~ 800 MeV) is significantly higher than that produced by a commercial light water reactor (~ 2 MeV). To design the nation’s first transmuter, the neutronics code MCNPX will be used to model the distribution of neutron flux within the fuel blanket and to determine the neutron multiplication, keff. However, the cross section libraries and computational methods used by MCNPX at these neutron energies still have some uncertainty and will require validation. During the second year of the project, the goals include: • Continue analyses of the neutron leakage tests completed in July 2002 and to be conducted on LANSCE in December, 2002. • Prepare simulations of the December 2002 tests to provide input on the test design. • Complete work started in the first year on a benchmark program for the validation of MCNPX for transmutation studies. This program will be designed along the lines of the international nuclear criticality benchmark series

Radiation Transport Modeling of Beam-Target Experiments for the AAA Project: Quaterly Report, June 01- August 31, 2002

The national development of technology to transmute nuclear waste depends upon the generation of high-energy neutrons produced by proton spallation. Proton accelerators, such as LANSCE at the Los Alamos National Laboratory, are capable of producing 800 MeV protons. By bombarding a lead /bismuth target, each proton may generate up to 25 neutrons that can activate fission of transuranic isotopes. Students at UNLV have been involved in radiation transport calculations in collaboration with researchers at the Los Alamos National Laboratory and at the Argonne National Laboratory

Letter to Ruth Corry regarding SEAALL membership, October 27, 1958

A letter from Grace Culbreth to Ruth Corry enclosing a check for SEAALL membership dues

Breaking Apart the Reinforcement Learning Deficit in Schizophrenia

Reinforcement learning deficits have long been associated with schizophrenia. However, tasks traditionally used to assess these deficits often rely on multiple processing streams leaving the etiology of these task deficits unclear. In the current study, we borrowed a recent framework from computational neuroscience, which separates reinforcement-learning into two distinct systems, model-based and model-free. Under this framework, the model-free system learns about the value of actions in the immediate context, while the model-based system learns about the value of actions in both immediate and subsequent states that may be encountered as a result of their actions. Using a decision task that has been previously validated to assess relative reliance on each system we showed that individuals with schizophrenia demonstrated decreased model-based but intact model-free learning estimates. Furthermore, parameter estimates of model-based behavior correlated positively with IQ, suggesting that model-based deficits in schizophrenia may relate to reduced intellectual function. These findings specify reinforcement-learning deficits in schizophrenia by showing both intact and disturbed components. Such findings and computational frameworks provide meaningful insights as researchers continue to characterize decision-making circuitry in schizophrenia as a means to discover new pathways for interventions

Radiation Transport Modeling Using Parallel Computational Techniques

The Advanced Fuel Cycle Initiative (AFCI) program will rely on the use of accurate calculations and simulations of criticality and shielding for the separation process of the longlived isotopes that present a significant safety hazard in commercial spent fuel. To help design and verify the safety of the separation process, the neutronics code MCNPX will be used to model the distribution of neutron flux within the fuel blanket and to determine the neutron multiplication, keff. However, the cross section libraries and computational methods used by MCNPX at these neutron energies still have some uncertainty and will require validation. Currently MCNPX relies on a hand created input deck, which can be time consuming to produce and prone to errors. One way to solve this problem is to create a graphical user interface (GUI) to help the user create the input deck. Also, to achieve accurate results in a short period of time there is a need to increase the efficiency of the parallel version of MCNPX. We propose to involve UNLV students and faculty in this endeavor to create a GUI, to increase the speed of MCNPX on parallel clusters of computers, and to continue application of MCNPX to solve practical AFCI problems. The project proposed for year three of the project will consist of three parts: • Optimization and validation of MCNPX on multiple platforms using Message Passing Interface (MPI). • Create a graphical user interface (GUI) to help users generate input files for MCNPX. • Continue MCNPX simulations in support of AFCI work