• Archives of Pharmacal Research
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• v.22 no.3
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• pp.237-242
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• 1999

A proteinacious inhibitor with a molecular weight of 1,600 Da which inhibits S-adenosyl-L-methionine-dependent transmethylation reactions was purified from porcine liver to homogeneity by procedures including boiling, Sephadex G-25 column chromatography and repeated HPLC. Employing both Nuclear Magnetic Resonance (NMR) and Fast Atom Bombardment-Mass (FAB-Mass) spectroscopy, S-adenosylhomocysteine was conclusively identified as an integral part of the inhibitor. The purified S-adenosylhomocysteine was competitive with S-adenosyl-L-methionine with Ki value of $6.3{\times}10^{-6}$ M towards protein methylase II.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.1013-1021
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• 2020

A combination of simultaneous thermal analysis, evolved gas analysis and non-ambient XRD techniques was used to characterise and investigate the conversion reactions of ammonium uranates into uranium oxides. Two solid phases of the ternary system NH₃ - UO₃ - H₂O were synthesised under specified conditions. Microspheres prepared by the sol-gel method via internal gelation were identified as 3UO₃·2NH₃·4H₂O, whereas the product of a typical ammonium diuranate precipitation reaction was associated to the composition 3UO₃·NH₃·5H₂O. The thermal decomposition profile of both compounds in air feature distinct reaction steps towards the conversion to U₃O₈, owing to the successive release of water and ammonia molecules. Both compounds are converted into α-U₃O₈ above 550 ℃, but the crystallographic transition occurs differently. In compound 3UO₃·NH₃·5H₂O (ADU) the transformation occurs via the crystalline β-UO₃ phase, whereas in compound 3UO₃·2NH₃·4H₂O (microspheres) an amorphous UO₃ intermediate was observed. The new insights obtained on these uranate systems improve the information base for designing and synthesising minor actinide-containing target materials in future applications.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.176-189
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• 2019

This paper presents a feasibility study for producing the medical isotope $^{99m}Tc$ using the hazardous and currently wasted radioisotope $^{99}Tc$. This can be achieved with the nuclear resonance fluorescence (NRF) phenomenon, which has recently been made applicable due to high-intensity laser Compton scattering (LCS) photons. In this work, 21 NRF energy states of $^{99}Tc$ have been identified as potential contributors to the photo-production of $^{99m}Tc$ and their NRF cross-sections are evaluated by using the single particle estimate model and the ENSDF data library. The evaluated cross sections are scaled using known measurement data for improved accuracy. The maximum LCS photon energy is adjusted in a way to cover all the significant excited states that may contribute to $^{99m}Tc$ generation. An energy recovery LINAC system is considered as the LCS photon source and the LCS gamma spectrum is optimized by adjusting the electron energy to maximize $^{99m}Tc$ photo-production. The NRF reaction rate for $^{99m}Tc$ is first optimized without considering the photon attenuations such as photo-atomic interactions and self-shielding due to the NRF resonance itself. The change in energy spectrum and intensity due to the photo-atomic reactions has been quantified using the MCNP6 code and then the NRF self-shielding effect was considered to obtain the spectrums that include all the attenuation factors. Simulations show that when a $^{99}Tc$ target is irradiated at an intensity of the order $10^{17}{\gamma}/s$ for 30 h, 2.01 Ci of $^{99m}Tc$ can be produced.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1676-1685
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• 2021

We develop a new high-fidelity multiphysics model to simulate boron chemistry in the porous Chalk River Unidentified Deposit (CRUD) deposits. Heat transfer, capillary flow, solute transport, and chemical reactions are fully coupled. The evaporation of coolant in the deposits is included in governing equations modified by the volume-averaged assumption of wick boiling. The axial offset anomaly (AOA) of the Seabrook nuclear power plant is simulated. The new model reasonably predicts the distributions of temperature, pressure, velocity, volumetric boiling heat density, and chemical concentrations. In the thicker CRUD regions, 60% of the total heat is removed by evaporative heat transfer, causing boron species accumulation. The new model successfully shows the quantitative effect of coolant evaporation on the local distributions of boron. The total amount of boron in the CRUD layer increases by a factor of 1.21 when an evaporation-driven increase of soluble and precipitated boron concentrations is reflected. In addition, the concentrations of B(OH)₃ and LiBO₂ are estimated according to various conditions such as different CRUD thickness and porosity. At the end of the cycle in the AOA case, the total mass of boron incorporated in CRUD deposits of a reference single fuel rod is estimated to be about 0.5 mg.

• Nuclear Engineering and Technology
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• v.38 no.6
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• pp.459-482
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• 2006

A geochemical approach to the long-term safety of waste disposal is discussed in connection with the significance of actinides, which shall deliver the major radioactivity inventory subsequent to the relatively short-term decay of fission products. Every power reactor generates transuranic (TRU) elements: plutonium and minor actinides (Np, Am, Cm), which consist chiefly of long-lived nuclides emitting alpha radiation. The amount of TRU actinides generated in a fuel life period is found to be relatively small (about 1 wt% or less in spent fuel) but their radioactivity persists many hundred thousands years. Geological confinement of waste containing TRU actinides demands, as a result, fundamental knowledge on the geochemical behavior of actinides in the repository environment for a long period of time. Appraisal of the scientific progress in this subject area is the main objective of the present paper. Following the introductory discussion on natural radioactivities, the nuclear fuel cycle is briefly brought up with reference to actinide generation and waste disposal. As the long-term disposal safety concerns inevitably with actinides, the significance of the aquatic actinide chemistry is summarized in two parts: the fundamental properties relevant to their aquatic behavior and the geochemical reactions in nanoscopic scale. The constrained space of writing allows discussion on some examples only, for which topics of the primary concern are selected, e.g. apparent solubility and colloid generation, colloid-facilitated migration, notable speciation of such processes, etc. Discussion is summed up to end with how to make a geochemical approach available for the long-term disposal safety of nuclear waste or for the performance assessment (PA) as known generally.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.642-649
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• 2016

Important safety parameters such as the fuel temperature coefficient (FTC) and the power coefficient of reactivity (PCR) of the CANada Deuterium Uranium (CANDU-6) reactor have been evaluated using the Monte Carlo method. For accurate analysis of the parameters, the Doppler broadening rejection correction scheme was implemented in the MCNPX code to account for the thermal motion of the heavy uranium-238 nucleus in the neutron-U scattering reactions. In this work, a standard fuel lattice has been modeled and the fuel is depleted using MCNPX. The FTC value is evaluated for several burnup points including the mid-burnup representing a near-equilibrium core. The Doppler effect has been evaluated using several cross-section libraries such as ENDF/B-VI.8, ENDF/B-VII.0, JEFF-3.1.1, and JENDL-4.0. The PCR value is also evaluated at mid-burnup conditions to characterize the safety features of an equilibrium CANDU-6 reactor. To improve the reliability of the Monte Carlo calculations, we considered a huge number of neutron histories in this work and the standard deviation of the k-infinity values is only 0.5-1 pcm.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.164-170
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• 2010

Thermodynamic consideration was performed for Alloy 617 exposed to an impure helium ($H_2$ 20pa, $H_2O$ 0.5pa, $CH_4$ 2pa and CO 5pa) at $950^{\circ}C$. Oxidation power was decreased in the order Al > Ti > Si > Cr > Mn. Decarburization and carburization reactions were available leading to carbon activity decrease and increase, respectively, depending on carbon and Cr activities. The thermodynamic prediction was compared with the experimental results obtained in similar conditions (($H_2$ 20pa, $H_2O$ 0.05pa, $CH_4$ 5pa and CO 2pa) and $950^{\circ}C$) by others for Alloy 617. The driving force for oxidation of Al, Ti and Si is very large to be oxidized at a given impure helium and the environment is actually carburizing towards the structural alloy, which is consistent with this work.

• Nuclear Engineering and Technology
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• v.28 no.1
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• pp.72-78
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• 1996

A computer program COVAFIT has been developed and applied to the evaluation of experimental cross sections for MeV energy incident particles. The program utilizes weighted least-square linear regression method with high-order polynomials derived in this study. Meeting the growing demand for the treatment of covariances in nuclear data, it deals with the variance and covariance data provided along with experimental cross sections and yields those for the evaluated ones. The evaluated results on two sets of neutron total cross section of oxygen and three sets of proton cross section for $C^{11}$ production reactions confirm the methodology formulated in and the applicability of the program.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1863-1870
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• 2023

Molybdenum-99 (⁹⁹Mo) is used for preparing Technetium-99 m (^99mTc), which is the most widely used isotope in nuclear medicine. In this work, a study for ⁹⁹Mo production based on a high-power electron accelerator has been performed as an alternative approach to produce ^99mTc. In this study, Monte Carlo MCNPX2.6 code has been used to examine a novel idea of simultaneous hybrid production of ⁹⁹Mo via both photoneutron and neutron capture reactions using an electron accelerator in heavy water tank. It is expected that this conceptual design including an arrangement of metallic plates of ¹⁰⁰Mo and ⁹⁸Mo produces total activity of 97.5 Ci at the end of 20-h continuous e-beam irradiation (30 MeV, 10 mA).

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2079-2091
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• 2024

In this paper, a model is developed for calculating pH in the presence of organic impurities due to dissolution of paint and/or continuous injection of organic impurities in the sump. The model is implemented in the AnCheBi code for the analysis of chemical behaviors of the iodine in the containment when the pH changes during a severe accident. Validation of the model is performed with P10T2 and P11T1 experiments carried out by AECL in Canada under the BIP project. Importance analyses of the pH calculation model in the AnCheBi code are then performed with the aforementioned experimental data via Latin hypercube sampling on the reaction coefficients, sensitivity analyses of AnCheBi, and calculation of the correlation coefficients between the reaction coefficients and figure of merits (the pH and the concentrations of the various iodine species). From the importance analyses, we provide the sensitivity of the pH calculation model to the change of pH and the concentrations of the various iodine species and the reaction coefficients related with the dominant phenomena underlying the change of pH and the concentrations of the species.