Takahisa Yamamoto

Three-Region Core Design for 200-MW(electric) Molten-Salt Reactor with Thorium-Uranium Fuel

In this paper, an improved design for a small molten-salt reactor (MSR) that uses neutron flux flattening, which is referred to as FUJI-U3, is proposed. This reactor is a 200-MW(electric) power reactor, and its core contains graphite (as the moderator) and fuel salt. The fuel salt is composed of ThF4 as the fertile material, 233UF4 as the fissile material, and LiF-BeF2 as both the solvent and heat transfer medium. A basic improvement in FUJI-U3 is the introduction of the design concept of a three-region core in order to avoid the replacement of graphite, which is achieved by reducing the maximum neutron flux. Since there is a limit for irradiation growth in graphite, this reduction in the maximum neutron flux contributes to a longer lifetime of the graphite. Based on calculations using the nuclear analysis code SRAC95 and the burnup analysis code ORIGEN2, it is concluded that there is no need to replace the graphite moderator of FUJI-U3 for 30 yr. Further, the chemical-processing interval of the fuel salt is studied for 7.5, 15, and 30 yr. An increase in this time interval will also contribute to reduce maintenance and cost.

Steady State Analysis of Molten Salt Reactor in Consideration of the Effect of Fuel Salt Flow

The Molten Salt Reactor (MSR) is a thermal neutron reactor with graphite moderation and operates on the thorium-uranium fuel cycle. The feature of the MSR is that fuel salt flows the inside of the reactor accompanying nuclear fission reaction. In the previous study, the authors had developed numerical model to simulate the effects of the fuel salt flow on the reactor characteristics. This paper applies the model to the steady state analysis of the small MSR system and estimates the effects of the fuel flow. The model consists of two group diffusion equations for fast and thermal neutron fluxes, balance equations for six-group delayed neutron precursors and energy conservation equations for fuel salt and graphite moderator. The following results are obtained: (1) the fuel salt flow affects the distributions of the delayed neutron precursors, especially long-lived one, and (2) the extension of residence time in the external loop system and the rise of fuel inflow temperature slightly show negative reactivity effects, decreasing neutron multiplication factor of the small MSR system.Copyright

A novel high-performance low-NOx fuel-rich/fuel- lean two-stage combustion gas and steam turbine system for power and heat generation

Abstract This paper proposes, describes, and analyses a novel high temperature and performance reheat gas turbine (GT) cogeneration system. This newly proposed system employing two-stage fuel-rich and fuel-lean combustion system is named as the ‘Fuel Rich-Lean Combustion Reheat GT Cogeneration System’ (RLCC). Energy and exergy analyses (the latter mainly to evaluate and demonstrate the reduction in exergy loss of this combustion process compared with conventional single-stage and fuel lean-lean combustion) of the proposed cogeneration system were performed and compared with a conventional cogeneration system. The proposed RLCC system is predicted to have an overall power generation efficiency of up to 53.0 per cent (low heating value (LHV) basis), exergy efficiency up to 61.9 per cent, and specific power up to 524.3 kJ/kg. Compared with a conventional cogeneration (CGC) system, its energy utilization efficiency was as high as 95.0 percent, 4.0 percentage points higher than that of the CGC system, the overall power generation efficiency was higher by 6.2 percentage points, and the exergy efficiency was higher by 7.8 percentage points, and the overall power-based NO x emissions was reduced by up to 34.0 per cent.

Volumes of Velopharyngeal and Glossopharyngeal Airway Were Not Changed after Uvulopalatopharyngoplasty: Report of Three Cases

Objective. The aim of this study was to investigate the changes in velopharyngeal and glossopharyngeal airway morphology and volume after uvulopalatopharyngoplasty in three adult obstructive sleep apnea syndrome patients who had bilateral large tonsils using three-dimensional computed tomography. Case Report. All three patients (one male and two females) who presented with a history of heavy snoring and excessive daytime sleepiness were examined with overnight nocturnal polysomnography, which indicated moderate-to-severe obstructive sleep apnea syndrome. Because all patients had large tonsils, uvulopalatopharyngoplasty was expected to enlarge the pharyngeal airway. Polysomnography and three-dimensional computed tomography scanning were performed and compared, both before and 3 months after uvulopalatopharyngoplasty. Results. Unexpectedly, although the morphology of the glossopharyngeal airway clearly changed after UPPP, the volume changes in the velopharyngeal and glossopharyngeal airways were negligible.

Mechanisms Underlying Improvement in Obstructive Sleep Apnea Syndrome by Uvulopalatopharyngoplasty

In a previous case report, we determined for the first time that uvulopalatopharyngoplasty (UPPP) does not change the volume of the upper airway but causes morphological changes in the entire upper airway. The objective of this study is to elucidate the mechanisms underlying the improvement in obstructive sleep apnea syndrome (OSAS) by UPPP. We present an additional case involving a patient with OSAS treated using UPPP. Morphological and numerical parameter changes after surgery were compared with the corresponding preoperative values. Anatomically accurate upper airway computational models were reconstructed from computed tomographic imaging data. In addition, computed fluid dynamics analysis was performed to reveal inhalation flow characteristics before and after UPPP and clearly assess the effect of UPPP on airflow patterns in the patients upper airway. An important benefit of UPPP is the morphological changes in the entire upper airway, in addition to widening the restricted area. These morphological changes induce laminarization of the pharyngeal jet. To obtain sufficient efficacy of UPPP in OSAS, the morphological changes in the upper airway and the airflow pattern after the surgery must be controlled.

Numerical Simulation for Intranasal Transport Phenomena

More than 10million people in Japan suffer some of nasal diseases every year (Haruna (2003)); the paranasal sinusitis (so-called the empyema), hypertrophic rhinitis and inferior concha inflammation. Nebulizer treatment has been used for the nasal diseases. The effectiveness of the nebulizer treatment has been confirmed from clinical view points until now. However there are a few researches that evaluate the effect of the nebulizer treatment theoretically and quantitatively, i.e., the transport characteristics of medicinal droplets and their deposition on the inflammation areas of nasal wall. The development of medical image processing technique is in progress and now gives us exquisitely detailed anatomic information. Some researchers calculated blood flow inside vital arteries and intranasal airflow characteristics by means of the medical image processing technique as well as Computed Fluid Dynamics (CFD) analysis. As for the CFD analysis of intranasal flow, Weinhold et al. constructed both a transparent resin model and numerical three-dimensional anatomy model with nasal cavities using a patient’s CT data (Weinhold & Mlynski (2004)). They subsequently made clear airflow characteristics in the nose experimentally and numerically, and found that pressure drop was a main factor of nasal airflow. Lindemann et al. focused at a case which underwent radical sinus surgery (Lindemann et al. (2004; 2005)). In their case, both the lateral nasal wall and the turbinates, inhibiting physiological airflow, were removed by the surgery to realize the enlargements of the nasal cavity volumes and to increase the ratio between nasal cavity volume and surface area. However the researches mentioned here dealt with only a few patient-cases even though there are individual differences in the shape of human nasal cavity and in the grade of medical conditions. The past researches considered the individual differences insufficiently. The authors analyzed intranasal transport phenomena for several patient cases and compared each others in the past study (Monya et al. (2009); Yamamoto et al. (2009)). From the results characteristics of airflow and medicinal droplet transportation strongly depend on inflow conditions such as inflow angle, velocity and size of particle even if there are the individual differences for the shape of patient’s nasal cavity. 24

Reactor Controllability of 3-Region-Core Molten Salt Reactor System: A Study on Load Following Capability

The Molten Salt Reactor (MSR) systems are liquid-fueled reactors that can be used for actinide burning, production of electricity, production of hydrogen, and production of ssile fuels (breeding). Thorium (Th) and uranium-233 (233 U) are fertile and ssile of the MSR systems, and dissolved in a high-temperature molten fluoride salt (fuel salt) with a very high boiling temperature (up to 1650K), that is both the reactor nuclear fuel and the coolant. The MSR system is one of the six advanced reactor concepts identified by the Generation IV International Forum (GIF) as a candidate for cooperative development [1]. In the MSR system, fuel salt flows through a fuel duct constructed around a reactor core and fuel channel of a graphite moderator accompanied by fission reaction and heat generation, and flows out to an external-loop system consisted of a heat exchanger and a circulation pump. Due to the motion of fuel salt, delayed neutron precursors that are one of the source of neutron production make to change their position between the ssion reaction and neutron emission events and decay even occur in the external loop system. Hence the reactivity and effective delayed neutron precursor fraction of the MSR system are lower than those of solid fuel reactor systems such as Boiling Water Reactors (BWRs) and Pressurised Water Reactor (PWRs). Since all of the presently operating nuclear power reactors utilize solid fuel, little attention had been paid to the MSR analysis of the reactivity loss and reactor characteristics change caused by the fuel salt circulation. Sides et al. [2] and Shimazu et al. [3] developed MSR analytical models based on the point reactor kinetics model to consider the effect of fuel salt flow. Their models represented a reactor as having six zones for fuel salt and three zones for the graphite moderator. Since their models employed the point reactor kinetics model and the rough temperature approximation, their results were not sufficiently accurate to consider the effect of fuel salt flow.Copyright

Low Heating Value Fuel Combustion: Flamelet Combustion Model and NO Formation Model

This study has performed the numerical simulations of turbulent low-heating-value fuel (LHVF) combustion and NO emissions using a flamelet model and a newly developed NO formation model. The emphases of this study are that the flamelet model employs a flamelet library specialized to LHVF combustion reaction, and a NO formation model involves not only the Zeldovich mechanism but also Fenimore mechanism. The calculated results of temperature and chemical species concentrations are compared with the measured ones. In consequence, it is clarified that the flamelet model can predict temperature and chemical species distributions of experimental results well, and the NO formation model developed in this paper shows good agreement with experimental results quantitatively.