We develop a method of directly incorporating additional Shell Model (SM) components in the One-Body Density Matrix (OBDM) by treating Core Polarization (CP) as a two-body operator in a limited SM space. We show that inclusion of such SM configurations in CP through the use of first-order Perturbation Theory in a calculation of the OBDM can be accomplished by the introduction of segmented Two-Body Density Matrices (TBDM) between the appropriate inital and final SM states. Comparisons between "exact" SM calculations and the CP approach are presented, as are attempts to assess the role of spuriosity and different treatments of the Hartree-Fock condition in the latter.

A description of the measurement of quasielastic interference structure functions for the nucleus $\sp{12}$C is presented. Longitudinally polarized electrons with an average polarization of 39 $\pm$ 4% and an initial energy of 660.0 MeV were scattered through 33.4 degrees from a graphite target. The scattered electrons were detected with a large magnetic spectrometer in coincidence with the knockout protons which were detected simultaneously by either of two small magnetic spectrometers placed out of the electron scattering plane. The forward-backward asymmetry A$\sb{91}$ and the beam helicity induced asymmetry A$\sbsp{01}{\prime}$ were measured, and the longitudinal-transverse interference structure functions $f\sb{01}$ and $f\sbsp{01}{\prime}$ were extracted for the $\sp{12}$C p-shell knockout reaction at a missing momentum of 115.0 MeV/c and a Q$\sp2$ of 0.13 (GeV/c)$\sp2$. This experiment was the first attempt in a series of $(\vec e,e\sp{\prime}p)$ experiments using multiple out-of-plane spectrometers to detect hadrons in isolating several interference structure functions simultaneously through precise asymmetry and cross section measurements. The equipment for these measurements was installed from 1995 to 1996 at the Bates Linear Accelerator Center in Middleton, Massachusetts, and this experiment was carried out in September of 1996.

While the agreement between theory and experiment is excellent for the π 0 → 2γ reaction, other reactions that proceed through the axial anomaly have been poorly tested. For example the existing measurement of the γ → 3π amplitude, F3π, is in poor agreement with theory. In the limit of low s and t, the γp → π+π 0n reaction is sensitive to F 3π. In this thesis preliminary cross sections for the γp → π +π0n reaction are presented using the CLAS with tagged photon energies between 1 and 2 GeV and over a range in s and t up to 1 GeV2. The π+ was detected using the time-of-flight and tracking systems. The π0 was detected via reconstruction of the invariant mass of its two decay photons, which were detected by an electromagnetic calorimeter. The presence of the neutron was inferred via missing mass. The sensitivity of these cross sections to F3π in the low t region is studied for s = [special characters omitted] and s = [special characters omitted] at Eγ = 2 GeV. The results show a momentum dependence of the F3π and are consistent with a calculation that includes the effects of ππ final state interactions on the chiral perturbation prediction for F 3π.

Nuclei in the light rare-earth, for values of N ≥ 90, are textbook examples of the evolution of nuclear structure with respect to excitation energy and angular momentum in deformed nuclei. In the high-spin region (J ≥ 10ħ), effects such as backbends and shape changes occur, ending with termination of the lower energy collective structures. First backbends occur before 20ħ Findings also reflect a spectacular return to collectivity in the "ultra-high spin" region (J ≥ 50ħ). Thanks to recent developments in both detectors and accelerators, gamma-ray spectroscopy has been able to probe the upper ends of the high-spin region, and begin probing into the ultra-high spin regime. Data from two experiments form the basis of this work. One study was an ultra-high-spin analysis of the Z=67, N=90 ¹⁵⁷Ho nucleus at Argonne National Laboratory with Gammasphere. The findings were that remarkable correlations were observed to the neighboring isotone, ¹⁵⁸Er, in which termination states and ultra-high spin structures had been previously observed. A high-spin investigation of Ytterbium (Yb) and Erbium (Er) isotopes was performed at FSU. This study used an intense radioactive ¹⁴C beam, available at FSU, in order to study these heavy, neutron-rich nuclei in regions of angular momentum and excitation energy not attainable with stable beams. The reactions of ¹⁷⁰Er(¹⁴C,5n/4n/α4n) generated new information in ¹⁶⁹Yb, ¹⁷⁰Yb, and ¹⁶⁶Er, respectively. Due to the recently upgraded digital FSU Gamma-Ray Array, aided by JBSMILE, triple ᵧ-ray coincidences were able to be viewed in these nuclei for the first time at FSU. The result was the investigation of rotational alignments in both the yrast and non-yrast multi-quasiparticle bands in these nuclei. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2018. / November 19, 2018. / Includes bibliographical references. / Mark A. Riley, Professor Directing Dissertation; Oliver Steinbock, University Representative; Samuel L. Tabor, Committee Member; Alexander Volya, Committee Member; Laura Reina, Committee Member.

Over the past few years, there has been a sustained interest in the development of small modular reactors (SMRs) evident by the number of global initiatives focused on SMR development. This desktop study was performed to review the viability of SMRs based on their benefits and flexibility, focusing predominantly on the light water NuScale and the gas cooled AHTR designs. In assessing the level of safety, the typical general design and safety criteria were reviewed to establish a basis to compare the NuScale and AHTR designs. The need for flexibility to support grid operators and the ability of a nuclear plant to load follow were reviewed to confirm their flexibility. The principal of cogeneration and the feasibility for cogeneration and energy storage with SMRs was explored to determine the potential industrial application. Finally, the technical readiness and uncertainties, the potential market and economic competitiveness of SMRs were reviewed. The review established that SMRs with safety performance levels exceeding those of current reactor designs are definitely viable. The ability to prevent fuel failure through passive cooling simplifies the design by eliminating the need for complex safety systems and reduces the constraints associated with siting, opening up energy markets where previously nuclear reactors would not have been viable. Their flexibility and the ability to add additional units over time enable them to integrate into any size electrical network and a variety of energy markets. As a clean energy source, SMRs are well suited to support strategies to reduce greenhouse gas emissions and replace fossil-based energy sources. SMRs operating at high temperatures have the added option of considering thermal storage as a means to provide additional flexibility. The biggest uncertainty in the deployment of SMRs is associated with the regulatory and licencing processes. However, there is a large potential market for SMRs and the lower capital cost per unit, the shorter period until a revenue stream is established and the ability to stagger the financial impact of additional units are expected to make SMRs easier to finance than large nuclear units. This preliminary review concluded that SMRs are definitely viable, but until a SMR design has been successfully licenced, constructed and operated, the uncertainty associated with the licencing of a new technology and the potential for long delays during construction are likely to prevent any large-scale deployment in the near future.

The moisture separator forms part of the moisture separator reheater (MSR) component used in a steam cycle in a nuclear power plant, to reduce the risk of erosion of the low-pressure (LP) turbine and to improve cycle efficiency. The performance and optimisation of moisture separators is well studied in literature; however, there have been few investigations on the impact of moisture separator degradation on MSR performance. To investigate this impact a mathematical model, representing the steam flow through the MSR, is developed and used to simulate and analyse the impact of degradation conditions. The mathematical model was developed for design conditions, calibrated and validated against manufacturer specifications. The model was then augmented to include two moisture separator degradation conditions. The first degradation condition is the partial blockage of separator vane channels due to fouling, and the second is separator material deterioration resulting in steam bypass of the moisture separator. The model uses known properties of the MSR inlet steam and predicts the properties of steam exiting the MSR, given the simulated degradation of the moisture separator. The outcomes of the model simulations demonstrated that partial blockage of moisture separator vane channels increases steam velocity though the separator and consequently improves MSR performance, but with a noted pressure drop. The velocity increased until a theoretical upper limit, above which re-entrainment of droplets back into the steam flow reduces MSR performance. It was concluded that there is margin in the separator surface area design, where a minimal reduction in separator surface area (represented in the model as blockage of the vane channels) would improve the performance of the MSR, while still allowing for a buffer against the re-entrainment velocity upper limit. Equally, an unexpected improvement in MSR performance may be an indication of blockage of separator vane channels that, if not monitored and managed, could surpass the critical velocity limit where re-entrainment adversely affects the MSR performance. The simulation results demonstrated that steam bypass of the moisture separator is a credible degradation condition which affects MSR performance. It was found that steam bypass of the moisture separator leads to a decline in the quality of steam exiting the separator and a decline in MSR performance. The simulation of a fully bypassed moisture separator showed that the MSR performance declines by more than three times the design value when compared to the scenario where there is no bypass of the moisture separator.

No description available.

South Africa is poised to expand significantly its nuclear power generation industry. Considering that the current South African nuclear safety regulatory approach is applied to regulate the operation and maintenance of one mature nuclear power plant, it is expected that significant adaptation of this approach will occur for the regulatory system to accommodate the planned industry expansion. This dissertation tests the hypothesis that the optimal nuclear safety regulatory approach for South Africa’s planned nuclear industry can already be determined by systematically comparing the suitability of various alternatives in use in the international nuclear industry. Investigating the validity of this hypothesis improves the understanding of the possibilities available for future nuclear safety regulation in South Africa and aids preparations and decision-making in this regard. Research was conducted on the various nuclear safety regulatory approaches applied internationally and on what determines the suitability of each approach in different circumstances. The characteristics of South Africa’s current and planned nuclear power generation industry were investigated. Applying multi-criteria decision making analysis methodology, a test was developed and used to systematically assess the relative suitability of the various regulatory approaches to the South African context. The three primary approaches to nuclear safety regulation considered were the prescriptive approach, the performance based approach and the goal-setting approach. Based on currently available information, the test results show that the goal-setting regulatory approach is the optimal approach for South Africa’s planned nuclear power industry. However research findings also show that the state level bilateral cooperation the South African government would pursue to develop South Africa’s fleet approach to the 9,6 gigawatt nuclear new build programme may have sufficient influence on South Africa’s nuclear industry to change South Africa’s optimal nuclear safety regulatory approach or make this plant specific. The benefits of aligning South Africa’s nuclear safety regulatory approach with the approach applied in the fleet vendor company’s country of origin may outweigh other considerations. The vendor company for South Africa’s nuclear new build programme is not yet known. Even though systematic comparison of the suitability of various regulatory approaches shows that the goal-setting nuclear safety regulatory approach is the optimal approach for South Africa, the hypothesis is shown to be false. The optimal nuclear safety regulatory approach for South Africa’s planned nuclear industry cannot already be determined, since bilateral cooperation with the nuclear new build fleet vendor company’s country of origin may be the dominant factor in shaping South Africa’s nuclear safety regulatory approach. In the interim and in the event that strategic regulatory alignment for the new build fleet is not embarked upon, the research findings and test results have an important implication: Applying the goal-setting approach as the dominant nuclear safety regulatory approach can optimize nuclear safety regulation of South Africa’s nuclear industry.

The Fukushima Daiichi Nuclear Power Plant accident created renewed international interest in the behaviour of spent fuel subsequent to a complete loss of water inventory in a spent fuel pool (SFP). The study conducted in this dissertation serves as a starting point in gaining an understanding of the thermal hydraulics and associated heat transfer processes involved when spent fuel assemblies (SFAs) become uncovered in air. The complete loss of cooling in a SFP is a complex 3-D problem, hence several simplifications were necessary in this research to narrow the scope. Further, due to the complexity of this topic, the results obtained serves purely as a first order approximation. Accordingly, the Flownex systems CFD code (version 8.6.1.2630) was used to simulate the thermal response of the uncovered SFAs in the SFP of a typical Pressurised Water Reactor (PWR) during a severe accident scenario. Two network models were developed. The first was to identify the dominant heat transfer mechanisms with-in the spent fuel pool and it therefore accounted for a range of physics. This included convective heat transfer through the composite SFA channel walls, conduction along the vertical axial direction of the SFAs and through the inner and outer rack wall as well as through the fuel building (FB) roof and side walls. The model also took into account the radiative heat transfer from the cladding surface of the composite SFAs to the FB roof and side walls. This network model informed that the heat transfer with-in the SFA during the considered extreme accident scenario is dominated by radiative heat transfer. This informed the development of an improved 2-D network model using conduction elements which were specially calibrated in this work to account for radiative heat loss. An effective conduction for the fuel volume which is dependent on temperature was determined and was used to assess the severe accident. Transient results showed that the spent fuel may reach cladding oxidation temperature within circa 10.5 hrs after a complete loss of inventory.

In this thesis, the excited states ³³P were populated by the ¹⁸O+¹⁸O reaction at E[subscript lab]=24 MeV. The GAMMASPEHRE array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus ³⁶S. The use of Microball enabled the selection of the proton emission channel. It also helped in determining the position and energy of the emitted proton; which eventually helped in calculating more precise direction of the recoils to achieve better Doppler corrections. 16 new transitions and 13 new states were observed in ³³P for the first time. The nearly 4π geometry of GAMMASPEHRE allowed the measurement of γ-ray angular distributions leading to spin suggestions for many states. In a separate experiment conducted at the John D. Fox laboratory in Florida State University, the higher-spin structure of ³⁸Cl (N = 21) was investigated following the ²⁶Mg(¹⁴C, pn) reaction at 30 and 37 MeV. The outgoing protons were detected in an E ‒ ΔE Si telescope placed at 0° close to the target with a Ta beam stopper between the target and telescope. Multiple γ rays were detected in time coincidence with the protons using an enhanced version of the FSU γ detection array. A total of 11 new γ transitions and 6 new states were reported for the first time. DCO ratio analysis and measurement of polarization asymmetry for the emitted γ transitions were performed to assign spins and parities to a number of states. The level scheme was extended up to 8420 keV with a likely spin of 10 ħ. A new empirical shell model interaction was developed in the spsdfp model space. This FSU interaction was built by fitting to the energies of 270 experimental states from ¹³C to ⁵¹Ti. Calculations using the FSU interaction reproduced observed energy states of ³³P and ³⁸Cl rather well, including other spectroscopic properties. The interaction has been used to predict the intruder states of other sd-shell nuclei, along with the configurations of the nuclei belong to the Island of Inversion region of the nuclear landscape. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester 2019. / May 7, 2019. / Higher spin, Intruder states, Nuclear Structure, particle hole excitation, Shell evolution, Shell model / Includes bibliographical references. / Samuel Tabor, Professor Co-Directing Dissertation; Vandana Tripathi, Professor Co-Directing Dissertation; Thomas Albrecht-Schmitt, University Representative; Alexander Volya, Committee Member; Laura Reina, Committee Member.