Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2002. / Includes bibliographical references (p. 79-86). / This thesis describes the development and experimental verification (via liquid state nuclear magnetic resonance techniques) of new methods for controlling open quantum systems. First, methods that improve coherent control through the use of both strong control fields and detailed knowledge of the system's Hamiltonian are demonstrated. With the aid of numerical search methods, pulsed irradiation schemes are obtained that perform accurate, arbitrary, selective gates on multi-qubit systems. For a 3-qubit system, implementations show that the control sequences faithfully implement unitary operations with simulated gate fidelities on the order of 0.999 and experimentally determined projections of 0.99. Next, methods for controlling a quantum information in the presence of collective phase noise is demonstrated through the use of a decoherence free subspace (DFS). In addition to demonstrating the robustness of the DFS memory for both engineered and natural noise processes, a universal set of logical manipulations over the encoded qubit is realized. Dynamical control methods at the encoded level are used to implement noise-tolerant control over the DFS qubit in the presence of engineered phase noise significantly stronger than observed from natural noise sources. / (cont.) Finally, we explore the use of noiseless subsystems, which offers the most general and efficient method for protecting quantum information in the presence of noise that has symmetry properties. We demonstrate the preservation of a bit of quantum information against all collective noise operators by encoding it into a 3 qubit noiseless subsystem. A complete set of input states were used to determine the superoperator for the implemented one-qubit process and confirm that the fidelity of entanglement is improved for a large, non-commuting set of engineered errors. To date, this is the largest set of error operators that have been successfully corrected for by any quantum code. / by Evan M. Fortunato. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (v. 2, leaves 177-181). / by Hisham A. Hasanein. / Sc.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (leaves 48-49). / by Nicholas D. Levitt. / B.S.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (leaves 69-70). / by Amr S.G. Mohamed. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references (leaves 174-177). / by Weng-Sheng Kuo. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994. / Includes bibliographical references. / by Abdul I. Barakat. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2004. / Includes bibliographical references (p. 109-113). / Gas-Cooled Fast Reactors (GFRs) are among the GEN-IV designs proposed for future deployment. Driven by anticipated plant cost reduction, the use of supercritical CO₂ (S-CO₂) as a Brayton cycle working fluid in a direct cycle is evaluated. By using S- CO₂ at turbine inlet conditions of 20 MPa and 550⁰C - 700⁰C, efficiencies between 45% and 50% can be achieved with extremely compact components. Neutronic evaluation of candidate core materials was performed for potential use in block-type matrix fueled GFRs with particular concentration on lowering coolant void reactivity to less than $1. SiC cercer fuel was found to have relatively low coolant void worth (+22 cents upon complete depressurization of S-CO₂ coolant) and tolerable reactivity- limited burnup at matrix volume fractions of 60% or less in a 600 MWth core having H/D of 0.85 and titanium reflectors. Pin-type cores were also evaluated and demonstrated higher kff versus burnup, and higher coolant void reactivity than the SiC cercer cores (+$2.00 in ODS MA956-clad case having H/D of 1). / (cont.) It was shown, however, that S-CO₂ coolant void reactivity could be lowered significantly - to less than $1 - in pin cores by increasing neutron leakage (e.g. lowering the core H/D ratio to 0.625 in a pin core with ODS MA956 cladding), an effect not observed in cores using helium coolant at 8 MPa and 500⁰C. An innovative "block"-geometry tube-in-duct fuel consisting of canisters of vibrationally compacted (VIPAC) oxide fuel was introduced and some preliminary calculations were performed. A reference tube-in-duct core was shown to exhibit favorable neutron economy with a conversion ratio (CR) at beginning of life (BOL) of 1.37, but had a coolant void reactivity of +$ 1.4. The high CR should allow designers to lower coolant void worth by increasing leakage while preserving the ability of the core to reach high burnup. Titanium, vanadium and scandium were found to be excellent reflector materials from the standpoint of ... and coolant void reactivity due to their unique elastic scattering cross-section profiles: for example, the SiC cercer core having void reactivity of +$0.22 with titanium was shown to have +$0.57 with Zr₃Si₂. / (cont.) Overall, present work confirmed that the S-CO₂-cooled GFR concept has promising characteristics and a sufficiently broad opion space such that a safe and competitive design could be developed in future work with considerably less than $1 void reactivity and a controllable [delta]k due to burnup. / by Michael A. Pope. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references. / A proton core imaging system has been developed and extensively used for measuring the nuclear burn regions of inertial confinement fusion implosions. These imaging cameras, mounted to the 60-beam OMEGA laser facility, use the penetrating 14.7-MeV protons produced from the fusion of deuterium and 3-helium to obtain spatial images of the nuclear burn. The technique relies on penumbral imaging, with symmetric or asymmetric reconstruction algorithms used to extract the source distribution. The hardware and design considerations required for the imaging cameras are described and the fidelity of the reconstructed burn profiles is verified. The spatial characteristics of the nuclear burn profile of directly driven capsule implosions were, for the first time, extensively studied. For thick plastic-shell capsules, with initial radii of-- 430 pun, the characteristic burn radii were found to be - 30 pun. The effects of gas pressure, shell thickness, laser energy, laser smoothing, capsule size, and capsule composition on the burn radius were systematically examined, resulting in radii ranging from 20 m to 80 pim. This new set of absolute burn profile measurements, in combination with other important implosion diagnostics, constitute a significant advance in that it imposes an exacting, integral test of the complex dynamics of imploding capsules. / by Joseph Loreto DeCiantis. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (p. 154). / Modifying material properties provides another approach to optimize coated particle fuel used in pebble bed reactors. In this study, the MIT fuel performance model (TIMCOAT) was applied after benchmarking against the experiment results. The optimization study focuses on the fracture toughness of silicon carbide and Bacon anisotropy factor (BAF) of pyrocarbon. The variations on the silicon carbide toughness show that higher fracture toughness leads to a lower fuel failure probability, as expected. However, the results from the BAF variations reveal that a higher BAF lowers a fuel failure probability. This quite contradicts the generally believed notion that a higher BAF would increase fuel failures. In addition to the fuel design optimization, the failure characteristics of coated particle fuel are explained and the key factors influencing such characteristics are identified. / by Chaiyod Soontrapa. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005. / Includes bibliographical references (leaves 62-65). / The bystander effect is the observation that non-irradiated cells near a cell traversed by radiation express biological responses such as micronuclei formation and genomic instability. Most published studies of the bystander effect have been conducted using alpha particles, a high LET radiation. A few studies have been done with low LET radiation. This project studies the bystander effect from both low LET x-rays and high LET Fe particle beam irradiation. Using a transwell insert system, the bystander effect was studied in hTERT immortalized human keratinocytes. Cells are plated in a 6-well plate and in a companion permeable membrane insert. Cells in the 6-well plate are irradiated using conventional 250 kVp X-rays or 1000 MeV/nucleon Fe ion beam, LET of 151 keV/pm, from the NASA Space Radiation Laboratory at Brookhaven National Lab. After irradiation, inserts are immediately placed into the 6 well plate so that the irradiated and unirradiated cells are sharing medium but are not in contact. For both beams, frequency of micronuclei, chromatin bridges, and p21 wafl induction as well as cell cycle phase analysis were determined in both directly irradiated and bystander cells from 0.1 Gy to 5 Gy. From x-rays, a two-fold bystander effect at 24 h after irradiation with elevated p21' wafl induction and micronuclei was seen but in Fe ion irradiation, the p21 wafl bystander effect was delayed to 40-50 h after irradiation and no MN bystander effect was observed. / (cont.) Cell cycle analysis showed a slight G2 arrest in keratinocytes 5 h after x-rays but a strong G2 arrest until 40-50 h was seen after Fe ion irradiation. Bystander keratinocytes co-cultured with directly irradiated human fibroblasts AGO 1522 cells showed a two-fold p21 wafl and MN bystander effect 24 h after x-rays, and a potential 2-fold MN bystander effect 50 h after Fe ions. Bystander AGO1522 cells co-cultured with directly irradiated keratinocytes showed a two-fold MN bystander effect 24 h after x-rays, but no MN bystander response was seen at any time points studied from Fe ions. Striking differences in the bystander response were shown from the two radiation types, but the reason remains to be clarified. / by Vered Anzenberg. / S.M.