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This paper presents a performance study of deep borehole heat exchangers. The coaxial borehole heat exchanger (BHE) has been selected because for the present conditions it has a better performance ...

In this paper a simplified and not fully discretized numerical model is used to simulate the performance of a non-grouted (water filled) borehole heat exchanger (BHE). The model enables simulation ...

The endemic fish fauna of the Southern Ocean are cold-adapted stenotherms and are acutely sensitive to elevated temperature. Many of these species lack a heat shock response and cannot increase the production of heat shock proteins in their tissues. However, some species retain the ability to induce other stress-responsive genes, some of which are involved in cell cycle arrest and apoptosis. Here, the effect of heat on cell cycle stage and its ability to induce apoptosis were tested in thermally stressed hepatocytes from a common Antarctic fish species from McMurdo Sound in the Ross Sea. Levels of proliferating cell nuclear antigen were also measured as a marker of progression through the cell cycle. The results of these studies demonstrate that even sub-lethal heat stress can have deleterious impacts at the cellular level on these environmentally sensitive species.

High temperature cleaning of producer gas from biomass gasification has been investigated with a granular filter. Field tests were performed for several hours on a single filter element at about 550 °C. The results show cake filtration on the granular material and indicate good filtration of the biomass gasification producer gas. The relatively low pressure drop over the filter during filtration is comparable to those of bag filters. The granular filter can operate with high filtration velocities compared to bag filters and maintain high efficiency and a low residual pressure. This work is a part of the BioSOFC-up project that has a goal of utilizing the producer gas from the gasification plant in a solid oxide fuel cell (SOFC). The BioSOFC-up project will continue to the end of 2007.

Purpose: The aim of this study was to construct a 6 Li filter and to improve penetration of thermal neutrons produced by the fission converter–based epithermal neutron beam (FCB) for brain irradiation during boron neutron capture therapy (BNCT). Methods and Materials: Design of the 6 Li filter was evaluated using Monte Carlo simulations of the existing beam line and radiation transport through an ellipsoidal water phantom. Changes in beam performance were determined using three figures of merit: ( 1 ) advantage depth (AD), the depth at which the total biologically weighted dose to tumor equals the maximum weighted dose to normal tissue; ( 2 ) advantage ratio (AR), the ratio of the integral tumor dose to that of normal tissue averaged from the surface to the AD; and ( 3 ) advantage depth dose rate (ADDR), the therapeutic dose rate at the AD. Dosimetry performed with the new filter installed provided calibration data for treatment planning. Past treatment plans were recalculated to illustrate the clinical potential of the filter. Results: The 8-mm-thick Li filter is more effective for smaller field sizes, increasing the AD from 9.3 to 9.9 cm, leaving the AR unchanged at 5.7 but decreasing the ADDR from 114 to 55 cGy min −1 for the 12 cm diameter aperture. Using the filter increases the minimum deliverable dose to deep seated tumors by up to 9% for the same maximum dose to normal tissue. Conclusions: Optional 6 Li filtration provides an incremental improvement in clinical beam performance of the FCB that could help to establish a therapeutic window in the future treatment of deep-seated tumors.

Laboratory studies, confirmed by field studies at both large and small scales, elucidated behavior of a granular panel bed for gas filtration with accumulation of filter cakes on gas-entry surfaces (filtering occurring by a sieving mechanism). Filtration is cyclic: intermittently, flow of dusty gas is interrupted, and the panel is subjected to a sharp “reverse” puff of gas (a “puffback”), producing a body movement of sand toward gas-entry faces, dumping both dust cake and a relatively small quantity of sand from each face.

A Phase I/II clinical trial of neutron capture therapy (NCT) was conducted at Harvard–MIT using a fission converter epithermal neutron beam. This epithermal neutron beam has nearly ideal performance characteristics (high intensity and purity) and is well-suited for clinical use. Six glioblastoma multiforme (GBM) patients were treated with NCT by infusion of the tumor-selective amino acid boronophenylalanine-fructose (BPA-F) at a dose of 14.0 g/m 2 body surface area over 90 min followed by irradiation with epithermal neutrons. Treatments were planned using NCTPlan and an accelerated version of the Monte Carlo radiation transport code MCNP 4B. Treatments were delivered in two fractions with two or three fields. Field order was reversed between fractions to equalize the average blood boron concentration between fields. The initial dose in the dose escalation study was 7.0 RBE Gy, prescribed as the mean dose to the whole brain volume. This prescription dose was increased by 10% to 7.7 RBE Gy in the second cohort of patients. A pharmacokinetic model was used to predict the blood boron concentration for determination of the required beam monitor units with good accuracy; differences between prescribed and delivered doses were 1.5% or less. Estimates of average tumor doses ranged from 33.7 to 83.4 RBE Gy (median 57.8 RBE Gy), a substantial improvement over our previous trial where the median value of the average tumor dose was 25.8 RBE Gy.

An immunologic tool based on manipulation of the boron neutron capture reaction was previously proposed in the context of heart transplantation research to examine the temporal relationship between parenchymal rejection (representing immune cell infiltration) and transplantation-associated arteriosclerosis (characterized by progressive vascular occlusion). Critical to the development of this method is the uptake of boron by specific cells of the immune system, namely T cells, without adverse effects on cell function, which may be assessed by the ability of boron-loaded cells to produce IFN γ , a protein with substantial impact on rejection. This work presents the evaluation of two carboranyl thymidine analogs. Advantages of this type of boron compound are reduced risk of leakage and effective dose delivery based on their incorporation into cellular nuclear material. Results indicate that uptake of these boronated nucleosides is high with no adverse effects on cell function, thereby warranting the continued development of this technique that has potentially wide applicability in immunological models.

Purpose : A Phase I trial of cranial neutron capture therapy (NCT) was conducted at Harvard-MIT. The trial was designed to determine maximum tolerated NCT radiation dose to normal brain. Methods and Materials : Twenty-two patients with brain tumors were treated by infusion of boronophenylalanine-fructose (BPA-f) followed by exposure to epithermal neutrons. The study began with a prescribed biologically weighted dose of 8.8 RBE (relative biologic effectiveness) Gy, escalated in compounding 10% increments, and ended at 14.2 RBE Gy. BPA-f was infused at a dose 250–350 mg/kg body weight. Treatments were planned using MacNCTPlan and MCNP 4B. Irradiations were delivered as one, two, or three fields in one or two fractions. Results : Peak biologically weighted normal tissue dose ranged from 8.7 to 16.4 RBE Gy. The average dose to brain ranged from 2.7 to 7.4 RBE Gy. Average tumor dose was estimated to range from 14.5 to 43.9 RBE Gy, with a mean of 25.7 RBE Gy. Conclusions : We have demonstrated that BPA-f-mediated NCT can be precisely planned and delivered in a carefully controlled manner. Subsequent clinical trials of boron neutron capture therapy at Harvard and MIT will be initiated with a new high-intensity, high-quality epithermal neutron beam.

The performance of the prompt gamma neutron activation analysis (PGNAA) facility at the MIT Research Reactor has been improved by a series of modifications. These modifications have increased the flux by a factor of three at the sample position to 1.7 × 107 n/cm2 s, and have increased the sensitivity, on average, by a factor of 2.5. The background for many samples of interest is dominated by unavoidable neutron interactions that occur in or near the sample. Other background components comprise only 20% of the total background count rate. The implementation of fast electronics has helped to keep dead time reasonable, in spite of the increased count rates. The PGNAA facility at the MIT Research Reactor continues to serve as a major analytical tool for quantifying 10B in biological samples for Boron Neutron Capture Therapy (BNCT) research. The sensitivity for boron-10 in water is 18 750 cps/mg. The sensitivity for pure elements suitable for PGNAA analysis is reported. Possible further improvements are discussed.

As a part of the IEA Bioenergy, Task X-Conversion, Combustion activity, an international round robin test of a wood stove supplied with a catalytic afterburner (JOTUL 3TDCI-2) has been performed to investigate and compare the emission level of CO, particles/tar, hydrocarbons and NO x . The participating countries were Austria, Canada, Denmark, Finland, the Netherlands, Norway, Sweden. U.K. and U.S.A. The wood stove was tested according to national standards and test procedures. In addition, a comparison of the calculation procedures used to convert measured transient volumetric emission levels into average emission levels in g/kg dry fuel was performed, based on both arithmetic and weighted averaging. The results uncovered significant differences in ways of doing environmental evaluation. Particle emission measurements were found to be the best method to evaluate the environmental acceptability of the tested stove, since the particle emission level was least dependent of the national standards, test procedures and calculation procedures used. Finally, transient particle emission measurements are presented, which reveal a close relationship between particle and hydrocarbon emissions.

A computer-based beam monitoring system for boron neutron capture therapy is described. This system provides accurate, sensitive, and rapid on-line readout and recording of the beam components, epithermal and thermal neutron flux, and gamma ray dose rate. Readout of fluxes, fluentes, and corresponding doses in the target are provided in color coded graphic as well as numerical form on the computer monitors. Redundancy of fluence measurement is provided by an independent system using scalers and timers and by utilizing reactor power measuring instruments. Variations in neutron spectrum or spatial distribution of the beam can be rapidly diagnosed with the aid of the monitor readout.

Projects and achievements within the activity “Wood Combustion and Oxidation of Wet Biomass” in the triennium 1992–1994 are reviewed. The projects include modelling of wood combustion and pyrolysis, characterisation of biomass fuels and ashes, emission comparisons, emission reduction techniques, measurement techniques, comparison of test standards, utilisation of contaminated wood waste, oxidation of wet biomass, condensing systems and co-generation and co-firing techniques.

Unconfined turbulent partially premixed propane/air flames issuing from a straight tube into quiescent air at atmospheric pressure and temperature are investigated. Experiments on lifted flames are performed. Flame height and liftoff are reported together with emission indices for oxides of nitrogen (NO[sub 3]). The degree of partially premixing has been varied between a fuel mass fraction of 1.0 to 0.15. Six different nozzle diameters, d[sub 0], of 3.2, 6, 10, 20.5, 23.3, and 29.5 mm have been used. This resulted in outlet velocities, u[sub 0], varying from 1 to 130 m/s, flame heights up to 2.5 m, Froude numbers, Fr, from 3 to 3 [times] 10[sup 5], and thermal heat releases up to 350 kW. Flame height and liftoff show a strong dependence upon the ratio of the nozzle outlet velocity to the outlet diameter, the Froude number, and the fuel mass fraction Y[sub f]. Both modified, simplified, and newly developed expressions for height, liftoff and NO[sub x] emissions are presented and discussed. All the proposed expressions scale with Y[sub f][sup a]Fr[sup b] or Y[sub r][sup a]f(u[sub 0], d[sub 0]). The emission index for NO[sub x] scales very well with a previously developed expression based on the buoyant flame volume.more » The agreement between predictions and experimental data is generally good and well within the underlying experimental and theoretical uncertainties. The results from this study contain new data, as very little focus has previously been directed toward lifted partially premixed free flames of this size.« less

The TITAN reversed-field-pinch (RFP) fusion-reactor study has two objectives: to determine the technical feasibility and key developmental issues for an RFP fusion reactor operating at high power density: and to determine the potential economic (cost of electricity), operational (maintenance and availability), safety and environmental features of high mass-power-density fusion-reactor systems. Mass power density (MPD) is defined as the ratio of net electric output to the mass of the fusion power core (FPC). The FPC includes the plasma chamber, first wall, blanket, shield, magnets, and related structure. Two different detailed designs TITAN-I and TITAN-II, have been produced to demonstrate the possibility of multiple engineering-design approaches to high-MPD reactors. TITAN-I is a self-cooled lithium design with a vanadium-alloy structure. TITAN-II is a self-cooled aqueous loop-in-pool design with 9-C ferritic steel as the structural material. Both designs use RFP plasmas operating with essentially the same parameters. Both conceptual reactors are based on the DT fuel cycle, have a net electric output of about 1000 MWe, are compact, and have a high MPD of 800 kWe per tonne of FPC. The inherent physical characteristics of the RFP confinement concept make possible compact fusion reactors with such a high MPD. The TITAN designs would meet the U.S. criteria for the near-surface disposal of radioactive waste (Class C, IOCFR61) and would achieve a high Level of Safety Assurance with respect to FPC damage by decay afterheat and radioactivity release caused by accidents. Very importantly, a “single-piece” FPC maintenance procedure has been worked out and appears feasible for both designs. Parametric system studies have been used to find cost-optimized designs. to determine the parametric design window associated with each approach, and to assess the sensitivity of the designs to a wide range of physics and engineering requirements and assumptions. The design window for such compact RFP reactors would include machines with neutron wall loadings in the range of 10–20 MW/m2 with a shallow minimum COE at about 18 MW/m2. Even though operation at the lower end of the this range of wall loading (10–12 MW/m2) is possible, and may be preferable, the TITAN study adopted the design point at the upper end (18 MW/m2) in order to quantify and assess the technical feasibility and physics limits for such high-MPD reactors. From this work, key physics and engineering issues central to achieving reactors with the features of TITAN-I and TITAN-II have emerged.

A prompt gamma neutron activation analysis facility has been constructed at the MIT Research Reactor using a diffracted beam from a multilayered graphite monochromator. A beam of 0.0143 eV neutrons of intensity 6 × 106 n cm 2 s is available at the sample position. Backgrounds are low due to the use of the diffracted beam and are further improved by a sapphire crystal in the beam line. This design allowed the Ge detecting crystal to be placed close to the sample position, ~ 4 cm, with a resultant high detection efficiency. The sensitivity of the facility is reported for several representative pure elements. The major impetus for the construction of this facility was the need for accurate analyses of 10B in biological samples for neutron capture therapy research. Detailed results for this type of analysis are provided. The sensitivity of this diffracted beam facility currently exceeds that of two representative direct beam facilities using reactors of twice the power of the MITR-II. Possible major improvements in sensitivity, more than an order of magnitude, and in background levels are outlined for future development.

Experiments have been performed with coke particles in the freeboard region of a 250 kW Atmospheric Fluidized Bed Combustor (AFBC) with particle sizes ranging from 90 μm to 360 μm in the gas temperature range from 1050 K to 1350 K. Partially burned particles were collected at various heights and residence times. The observed morphological development during combustion indicates clear effects of internal burning resulting in an increase of pore volume and internal surface area. A pore model has been developed to describe the evolution of pores and total surface area, and to calculate the intrinsic reactivity and burning rates. The model is based on a combination of a Thiele analysis and the random pore model.

Results of theoretical estimates and of measurements are reported on emissions of oxides of nitrogen from large methane, propane and natural-gas flames under buoyancy-controlled conditions. The theory employs reduced chemical-kinetic mechanisms for the reaction-sheet regime along with simplified mass, momentum and mixture-fraction balances for the turbulent flame height. Explicit expressions for local, instantaneous NO production rates are derived, involving rate constants of only fourteen elementary steps, and a two-reaction-zone description of the laminar flamelets is adopted, enabling average production rates to be obtained from asymptotics through approximation of a joint probability-density function for mixture fraction and scalar dissipation. The theory predicts significant contributions from the Zel'dovich mechanism in the oxygen-consumption zone and from the prompt mechanism in the fuel-consumption zone but negligible contributions from the nitrous-oxide mechanism and gives an increase in the ratio of prompt to Zel'dovich contributions with increasing strain rates, as extinction is approached. The experiments employ continuous gas analyzers with water-cooled quartz and stainless-steel suction probes and derive emission indices from measured ratios of NO x to CO 2 concentrations. The experimental results are in reasonable agreement with a Froude-number correlation derived from the theory over a range of Froude numbers from 10 to 5×10 5 , wider than available previously.

Bioenergy use and potential, biofuels and bioenergy systems including combustion equipment and technology development are reviewed in the IEA member countries participating in the combustion activity. Focus has been put on pollutant emissions, emission measurement and reduction techniques, energy and emissions from contaminated wood combustion and fuel reactivity and modelling of pyrolysis and combustion. The paper describes the status on these topics within the IEA cooperation agreements.

Experiments with coke particles of various sizes ranging from 90 to 360 μm in the gas temperature range from 1050 to 1350 K were performed in the freeboard region of a relatively large (250-kW) fluidized bed reactor. Burning rates and kinetic parameters have been calculated (based on external surface) by use of both the shrinking particle model and the constant diameter model. The calculations of burning rates give values less than the diffusion limit, indicating the combustion to be limited in various degrees by heterogeneous kinetics and/or pore diffusion, depending on the temperature. The calculations give an overall apparent activition energy of 38 735 cal/mol for the shrinking particle model and 36 500 cal/mol for the constant-diameter model, indicating combustion in the transition between zone I and zone II. The kinetic constants are independent of particle size. The measurements of particle size and apparent density show that the smallest particles burn more internally with an initial sharp decrease in apparent density; the larger particles, however, burn with only a small decease in apparent density but with a sharper decrease in particle diameter. The experiments support an overall apparent reaction order in the range of 0.83–1.0.