Analysis of Proliferation Resistance of Small Modular Reactors (SMR) for the Expansion of Civilian Nuclear Power Systems

Analysis of Proliferation Resistance of Small Modular Reactors (SMR) for the Expansion of Civilian Nuclear Power Systems A. S. Mollah Department of Nuclear Science and Engineering Military Institute of Science and Technology Mirpur Cantonment, Dhaka-1216, Bangladesh Abstract Nuclear energy has the potential benefit to make an important contribution for mitigating greenhouse gas (GHG) emissions that cause climate change. Expanding nuclear energy capacity worldwide based on large centralized facilities poses many challenges and risks due to the large capital costs, important safety issues, obstructive public attitude, and persistent concerns about proliferation-that is, the intentional misuse of nuclear technology and material. SMRs, defined as units with a production capacity of less than 300 MWe, may represent a viable alternative to large reactors designs. Among many benefits, SMRs could allow for more proliferation resistant designs, manufacturing arrangements, and nuclear fuel-cycle practices at widespread deployment. In addition, some SMR designs may give rise to less public obstruction from the viewpoint of safety. A principal SMR advantage includes its installation in smaller grids typical of electrical power systems in developing countries. It is observed that there is limited work evaluating the proliferation resistance of SMRs, and existing proliferation assessment methods for large nuclear reactors designs are not well appropriate for these novel arrangements. The objective of this study is to conduct a proliferation resistance evaluation for future nuclear energy deployment driven by SMRs. We develop the scenarios to investigate relevant technical and institutional features that are postulated to enhance the proliferation resistance of SMRs. Different aspects of SMR designs such as: core-life, refueling, burnup, enrichment, fissile material inventory, excess reactivity, fuel element size, breeders etc. are discussed in the context of proliferation concerns

CONSERVATION LAWS OF A NONLINEAR INCOMPRESSIBLE TWO-FLUID MODEL

We study the conservation laws of the Choi-Camassa two-fluid model (1999) which is developed by approximating the two-dimensional (2D) Euler equations for incompressible motion of two non-mixing fluids in a channel. As preliminary work of this thesis, we compute the basic local conservation laws and the point symmetries of the 2D Euler equations for the incompressible fluid, and those of the vorticity system of the 2D Euler equations. To serve the main purpose of this thesis, we derive local conservation laws of the Choi-Camassa equations with an explicit expression for each locally conserved density and corresponding spatial flux. Using the direct conservation law construction method, we have constructed seven conservation laws including the conservation of mass, total horizontal momentum, energy, and irrotationality. The conserved quantities of the Choi-Camassa equations are compared with those of the full 2D Euler equations of incompressible fluid. We review periodic solutions, solitary wave solutions and kink solutions of the Choi-Camassa equations. As a result of the presence of Galilean symmetry for the Choi-Camassa model, the solitary wave solutions, the kink and the anti-kink solutions travel with arbitrary constant wave speed. We plot the local conserved densities of the Choi-Camassa model on the solitary wave and on the kink wave. For the solitary waves, all the densities are finite and decay exponentially, while for the kink wave, all the densities except one are finite and decay exponentially

Analysis of Non-ignorable Missing and Left-Censored Longitudinal Biomarker Data

In a longitudinal study of biomarker data collected during a hospital stay, observations may be missing due to administrative reasons, the death of the subject or the subject's discharge from the hospital, resulting in non-ignorable missing data. Standard likelihood-based methods for the analysis of longitudinal data, e.g, mixed models, do not include a mechanism that accounts for the different reasons for missingness. Rather than specifying a full likelihood function for the observed and missing data, we have proposed a weighted pseudo likelihood (WPL) method. Using this method a model can be built based on available data by accounting for the unobserved data via weights which are then treated as nuisance parameters in the model. The WPL method accounts for the nuisance parameters in the computation of the variances of parameter estimates. The performance of the proposed method has been compared with a number of widely used methods. The WPL method is illustrated using an example from the Genetic and Inflammatory Marker of Sepsis (GenIMS) study. A simulation study has been conducted to study the properties of the proposed method and the results are competitive with the widely used methods.In the second part, our goal is to address the problem of analyzing left-censored longitudinally measured biomarker data when subjects are lost due to the above mentioned reasons. We propose to analyze one such biomarker, IL-6, obtained from the GenIMS study, using a weighted random effects Tobit (WRT) model. We have compared the results of the WRT model with the random effects Tobit model. The simulation study shows that the WRT model estimates are approximately unbiased. The correct standard error has been computed using asymptotic pseudo likelihood theory. The use of multiple weights across the panel improves the estimate and produces smaller root mean square error. Therefore, the WRT model with multiple weights across panels is the recommended model for analyzing non-ignorable missing and left-censored biomarker longitudinal data. Model selection is an extremely important part of the analysis of any data set. As illustrated in these analyses, conclusions, which can directly impact public health, depend heavily on the data analytic approach

Some Travelling Wave Solutions of KdV-Burgers Equation

In this paper we study the extended Tanh method to obtain some exact solutions of KdV-Burgers equation. The principle of the Tanh method has been explained and then apply to the nonlinear KdV- Burgers evolution equation. A finnite power series in tanh is considered as an ansatz and the symbolic computational system is used to obtain solution of that nonlinear evolution equation. The obtained solutions are all travelling wave solutions