Analysis of Pebble-Bed VHTR Spectrum Shifting Capabilities for Advanced Fuel Cycles

Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of achieving ultra-long life VHTR (Very High Temperature Reactor) configurations by utilizing minor actinides as a fuel component. The present analysis takes into consideration and compares capabilities of pebble-bed core designs with various core and reflector configuration to allow spectrum shifting for advanced actinide fuels. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. By altering the moderator to fuel ratio, a shift in the spectrum is observed. The use of minor actinides as fuel components relies on spectrum shifting capabilities. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities are apparent and effects of altered moderator to fuel ratio, and Dancoff factor are investigated. This will lead to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems.This paper is based upon work supported by the U.S. Department of Energy under Award Number DE-FC07-05ID14655 (05-094)

Low-Cost and Sustainable All-Iron Redox Flow Battery Energy Storage

Redox flow batteries are promising grid-scale energy storage devices as they are able to decouple battery power and capacity as either property can be independently scaled. Herein a novel all aqueous all-iron redox flow battery was developed. Iron was selected because of its low cost and due to its low-toxicity, the all-iron RFB is likely to have minimal detrimental effect on the environment. Using ferrocyanide as the redox active material in the positive electrolyte and iron triethanolamine in the negative electrolyte a columbic efficiency of >80% was achieved. A redox flow battery using ferrocyanide in the positive electrolyte and iron triisopropanolamine in the negative electrolyte was also developed which achieved >81% columbic efficiency. Capacity loss was seen over 25 cycles in all battery experiments, this was found to be due to the crossover of the negative redox active material over the membrane. Both Nafion-117 and BTMA membranes were evaluated to attempt mitigation of crossover. Further scale up of the design is hindered by limiting solubility of the negative electrolyte redox active material, however, future work into improving the solubility by adding additives to the electrolytes may improve efficiency. Additives may also improve the stability of the redox active material during the charging and discharging process and avoid crossover of species

Neutronic analysis of pebble-bed cores with transuranics

At the brink of nuclear waste repository crises, viable alternatives for the long term radiotoxic wastes are seriously being considered worldwide. Minor actinides serve as one of these targeted wastes. Partitioning and transmutation in fission reactors is one possible incineration option and could potentially serve as a source of nuclear fuel required for sustainability of energy resources. The objective of this research was to evaluate the neutronic performance of the pebble-bed Very High Temperature Reactor (VHTR) configurations with various fuel loadings. The configuration adjustments and design sensitivity studies specifically targeted the achievability of spectral variations. The development of several realistic full-core 3D models and validation of all modeling techniques used was a major part of this research effort. In addition, investigating design sensitivities helped identify the parameters of primary interest. The full-core 3D models representing the prototype and large scale cores were created for use with SCALE 5.0 and SCALE 5.1 code systems. Initially the models required the external calculation of a Dancoff correction factor; however, the recent release of SCALE 5.1 encompassed inherent double heterogeneity modeling capabilities. The full core 3D models with multi-heterogeneity treatments are in agreement with available pebble-bed High Temperature Test Reactor data and were validated through benchmark studies. Analyses of configurations with various fuel loadings have indicated promising performance and safety characteristics. It was found that through small configuration adjustments, the pebble-bed design can be tweaked to produce desirable spectral shifts. The future operation of Generation IV nuclear energy systems would be greatly facilitated by the utilization of minor actinides as a fuel component. This would offer development of new fuel cycles, and support sustainability of a fuel source

Characterization Methodology for Decommissioning Low and Intermediate Level Fissile Nuclide Contaminated Buried Soils and Process Piping Using Photon Counting

A new approach to- and method for characterization of fissile nuclide contaminated soils and process piping has been developed and implemented for low and intermediate level wastes, using new calibration bases for photon counting. The method has been validated by integrating the capabilities of MCNP5 and ISOCS for a LaBr scintillator detector in combination with known radioactive standards. In addition, the developed methods consider nuclear safety as the priority while retaining realistic fissile mass and enrichment estimation techniques. The impact of a quick, portable non-destructive assay process to the decommissioning and remediation arena is extremely valuable. Traditional methods have inherent limitations in time consumption, resources, stability, and rigidity. In addition to optimizing a material blending and storage program, gaining a real-time understanding to the nature of fissile material prior to disturbance aids a nuclear safety program and culture invaluably. In this dissertation, detailed detector-waste models were developed and utilized to create a quick uranium mass and enrichment estimation process by taking advantage of the resolution and discrimination capabilities of the LaBr equipped InSpector 1000 instrument. The analysis takes into account multiple possible scenarios that may be encountered during decommissioning and remediation of a fuel fabrication and buried nuclear waste facility, while keeping nuclear safety controls in mind. As an inherent part of the process, the models were validated by performing a series of code-to-software and software-to-standard benchmarking procedures, which provided substantiation for use of the detector for the derived purposes, in addition to ensuring that the Monte Carlo-based calibration approach was conservative, as compared to other methods. The scenarios analyzed for the calibration basis were selected based on historical knowledge and in-field experience at the Westinghouse Hematite Decommissioning Project. The techniques developed in this dissertation offer a new characterization method for fissile material quantity and enrichment with a portable, passive non-destructive gamma assay system without relying on continual macroscopic system analysis. In addition, it provides early detection of large quantities of fissile material prior to exhumation or disturbance to enhance nuclear safety processes. This places the first priority on nuclear and radiological safety while preserving the time and money saving aspects of production-based projects

Analysis of the Pebble-Bed VHTR Spectrum Shifting Capabilities for Advanced Fuel Cycles

Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of achieving ultra-long life VHTR (Very High Temperature Reactor) configurations by utilizing minor actinides as a fuel component. The present analysis takes into consideration and compares capabilities of pebble-bed core designs with various core and reflector configuration to allow spectrum shifting for advanced actinide fuels. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. By altering the moderator to fuel ratio, a shift in the spectrum is observed. The use of minor actinides as fuel components relies on spectrum shifting capabilities. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities are apparent and effects of altered moderator to fuel ratio, and Dancoff factor are investigated. This will lead to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems.This paper is based upon work supported by the U.S. Department of Energy under Award Number DE-FC07-05ID14655 (05-094)

Real-world effectiveness of admissions to a tertiary treatment-resistant psychosis service: 2-year mirror-image study

Background Treatment-resistant schizophrenia is a major disabling illness which often proves challenging to manage in a secondary care setting. The National Psychosis Unit (NPU) is a specialised tertiary in-patient facility that provides evidence-based, personalised, multidisciplinary interventions for complex treatment-resistant psychosis, in order to reduce the risk of readmission and long-term care costs. Aims This study aimed to assess the long-term effectiveness of treatment at the NPU by considering naturalistic outcome measures. Method Using a mirror image design, we compared the numbers of psychiatric and general hospital admissions, in-patient days, acuity of placement, number of psychotropic medications and dose of antipsychotic medication prescribed before and following NPU admission. Data were obtained from the Clinical Records Interactive Search system, an anonymised database sourced from the South London and Maudsley NHS Trust electronic records, and by means of anonymous linkage to the Hospital Episode Statistics system. Results Compared with the 2 years before NPU admission, patients had fewer mental health admissions (1.65 ± 1.44 v. 0.87 ± 0.99, z = 5.594, P < 0.0001) and less mental health bed usage (335.31 ± 272.67 v. 199.42 ± 261.96, z = 5.195 P < 0.0001) after NPU admission. Total in-patient days in physical health hospitals and total number of in-patient days were also significantly reduced (16.51 ± 85.77 v. 2.83 ± 17.38, z = 2.046, P = 0.0408; 351.82 ± 269.09 v. 202.25 ± 261.05, z = 5.621, P < 0.0001). The reduction in level of support required after treatment at the NPU was statistically significant (z = −8.099, P < 0.0001). Conclusions This study demonstrates the long-term effectiveness of a tertiary service specialising in treatment-resistant psychosis

Association of physical health multimorbidity with mortality in people with schizophrenia spectrum disorders: Using a novel semantic search system that captures physical diseases in electronic patient records

OBJECTIVE Single physical comorbidities have been associated with the premature mortality in people with schizophrenia-spectrum disorders (SSD). We investigated the association of physical multimorbidity (≥two physical health conditions) with mortality in people with SSD. METHODS A retrospective cohort study between 2013 and 2017. All people with a diagnosis of SSD (ICD-10: F20–F29), who had contact with secondary mental healthcare within South London during 2011–2012 were included. A novel semantic search system captured conditions from electronic mental health records, and all-cause mortality were retrieved. Hazard ratios (HRs) and population attributable fractions (PAFs) were calculated for associations between physical multimorbidity and all-cause mortality. RESULTS Among the 9775 people with SSD (mean (SD) age, 45.9 (15.4); males, 59.3%), 6262 (64%) had physical multimorbidity, and 880 (9%) died during the 5-year follow-up. The top three physical multimorbidity combinations with highest mortality were cardiovascular-respiratory (HR: 2.23; 95% CI, 1.49–3.32), respiratory-skin (HR: 2.06; 95% CI, 1.31–3.24), and respiratory-digestive (HR: 1.88; 95% CI, 1.14–3.11), when adjusted for age, gender, and all other physical disease systems. Combinations of physical diseases with highest PAFs were cardiovascular-respiratory (PAF: 35.7%), neurologic-respiratory (PAF: 32.7%), as well as respiratory-skin (PAF: 29.8%). CONCLUSIONS Approximately 2/3 of patients with SSD had physical multimorbidity and the risk of mortality in these patients was further increased compared to those with none or single physical conditions. These findings suggest that in order to reduce the physical health burden and subsequent mortality in people with SSD, proactive coordinated prevention and management efforts are required and should extend beyond the current focus on single physical comorbidities

Associations of presenting symptoms and subsequent adverse clinical outcomes in people with unipolar depression: a prospective natural language processing (NLP), transdiagnostic, network analysis of electronic health record (EHR) data

Objective: To investigate the associations of symptoms of mania and depression with clinical outcomes in people with unipolar depression. Design: A natural language processing electronic health record study. We used network analysis to determine symptom network structure and multivariable Cox regression to investigate associations with clinical outcomes. Setting: The South London and Maudsley Clinical Record Interactive Search database. Participants: All patients presenting with unipolar depression between 1 April 2006 and 31 March 2018. Exposure: (1) Symptoms of mania: Elation; Grandiosity; Flight of ideas; Irritability; Pressured speech. (2) Symptoms of depression: Disturbed mood; Anhedonia; Guilt; Hopelessness; Helplessness; Worthlessness; Tearfulness; Low energy; Reduced appetite; Weight loss. (3) Symptoms of mania or depression (overlapping symptoms): Poor concentration; Insomnia; Disturbed sleep; Agitation; Mood instability. Main outcomes: (1) Bipolar or psychotic disorder diagnosis. (2) Psychiatric hospital admission. Results: Out of 19 707 patients, at least 1 depression, overlapping or mania symptom was present in 18 998 (96.4%), 15 954 (81.0%) and 4671 (23.7%) patients, respectively. 2772 (14.1%) patients subsequently developed bipolar or psychotic disorder during the follow-up period. The presence of at least one mania (HR 2.00, 95% CI 1.85 to 2.16), overlapping symptom (HR 1.71, 95% CI 1.52 to 1.92) or symptom of depression (HR 1.31, 95% CI 1.07 to 1.61) were associated with significantly increased risk of onset of a bipolar or psychotic disorder. Mania (HR 1.95, 95% CI 1.77 to 2.15) and overlapping symptoms (HR 1.76, 95% CI 1.52 to 2.04) were associated with greater risk for psychiatric hospital admission than symptoms of depression (HR 1.41, 95% CI 1.06 to 1.88). Conclusions: The presence of mania or overlapping symptoms in people with unipolar depression is associated with worse clinical outcomes. Symptom-based approaches to defining clinical phenotype may facilitate a more personalised treatment approach and better predict subsequent clinical outcomes than psychiatric diagnosis alone

Inpatient use and area-level socio-environmental factors in people with psychosis

Purpose: There is consistent evidence that socio-environmental factors measured at an area-level, such as ethnic density, urban environment and deprivation are associated with psychosis risk. However, whether area-level socio-environmental factors are associated with outcomes following psychosis onset is less clear. This study aimed to examine whether the number of inpatient days used by people presenting to mental health services for psychosis was associated with five key area-level socio-environmental factors: deprivation, ethnic density, social capital, population density and social fragmentation. Methods: Using a historical cohort design based on electronic health records from the South London and Maudsley NHS Trust Foundation electronic Patient Journey System, people who presented for the first time to SLAM between 2007 and 2010 with psychosis were included. Structured data were extracted on age at presentation, gender, ethnicity, residential area at first presentation and number of inpatient days over 5 years of follow-up. Data on area-level socio-environmental factors taken from published sources were linked to participants’ residential addresses. The relationship between the number of inpatient days and each socio-environmental factor was investigated in univariate negative binomial regression models with time in contact with services treated as an offset variable. Results: A total of 2147 people had full data on area level outcomes and baseline demographics, thus, could be included in the full analysis. No area-level socio-environmental factors were associated with inpatient days. Conclusion: Although a robust association exists between socio-environmental factors and psychosis risk, in this study we found no evidence that neighbourhood deprivation was linked to future inpatient admissions following the onset of psychosis. Future work on the influence of area-level socio-environmental factors on outcome should examine more nuanced outcomes, e.g. recovery, symptom trajectory, and should account for key methodological challenges, e.g. accounting for changes in address