Thermal Column Research Articles

English

Primary environmental variables, such as sea surface temperature, wind speed, and chlorophyll, have been used widely in a variety of studies by biological oceanographers to explore the relationship between and, say, distribution and abundance of marine organisms. Fisheries scientists in particular have explored a range of relationships between physics and catch data to understand fish distribution and fishing impacts. The explanatory power of models based on such primary variables is typically limited and may not lead to insight into mechanisms behind the environmental associations. Variables that are more direct measures of habitat, such as thermal fronts, upwelling zones, eddies, and water column descriptors (e.g., mixed layer depth), may yield additional explanatory power. We have developed a suite of these derived variables and demonstrate their utility using examples from Australian fisheries and marine spatial planning. Refinement and access to derived variables may be useful in a range of applications, including catch standardization, habitat prediction, ecosystem models, spatial management, and harvest strategies, and will play an important role in the emerging area of dynamic ocean management.

Gamma residual radioactivity measurements on rats and mice irradiated in the thermal column of a TRIGA Mark II reactor for BNCT.

The current Boron Neutron Capture Therapy (BNCT) experiments performed at the University of Pavia, Italy, are focusing on the in vivo irradiations of small animals (rats and mice) in order to evaluate the effectiveness of BNCT in the treatment of diffused lung tumors. After the irradiation, the animals are manipulated, which requires an evaluation of the residual radioactivity induced by neutron activation and the relative radiological risk assessment to guarantee the radiation protection of the workers. The induced activity in the irradiated animals was measured by high-resolution open geometry gamma spectroscopy and compared with values obtained by Monte Carlo simulation. After an irradiation time of 15 min in a position where the in-air thermal flux is about 1.2 × 10(10) cm(-2) s(-1), the specific activity induced in the body of the animal is mainly due to 24Na, 38Cl, 42K, 56Mn, 27Mg and 49Ca; it is approximately 540 Bq g(-1) in the rat and around 2,050 Bq g(-1) in the mouse. During the irradiation, the animal body (except the lung region) is housed in a 95% enriched 6Li shield; the primary radioisotopes produced inside the shield by the neutron irradiation are 3H by the 6Li capture reaction and 18F by the reaction sequence 6Li(n,α)3H → 16O(t,n)18F. The specific activities of these products are 3.3 kBq g(-1) and 880 Bq g(-1), respectively.

Confirmation of a realistic reactor model for BNCT dosimetry at the TRIGA Mainz.

In order to build up a reliable dose monitoring system for boron neutron capture therapy (BNCT) applications at the TRIGA reactor in Mainz, a computer model for the entire reactor was established, simulating the radiation field by means of the Monte Carlo method. The impact of different source definition techniques was compared and the model was validated by experimental fluence and dose determinations. The depletion calculation code origen2 was used to compute the burn-up and relevant material composition of each burned fuel element from the day of first reactor operation to its current core. The material composition of the current core was used in a mcnp5 model of the initial core developed earlier. To perform calculations for the region outside the reactor core, the model was expanded to include the thermal column and compared with the previously established attila model. Subsequently, the computational model is simplified in order to reduce the calculation time. Both simulation models are validated by experiments with different setups using alanine dosimetry and gold activation measurements with two different types of phantoms. The mcnp5 simulated neutron spectrum and source strength are found to be in good agreement with the previous attila model whereas the photon production is much lower. Both mcnp5 simulation models predict all experimental dose values with an accuracy of about 5%. The simulations reveal that a Teflon environment favorably reduces the gamma dose component as compared to a polymethyl methacrylate phantom. A computer model for BNCT dosimetry was established, allowing the prediction of dosimetric quantities without further calibration and within a reasonable computation time for clinical applications. The good agreement between the mcnp5 simulations and experiments demonstrates that the attila model overestimates the gamma dose contribution. The detailed model can be used for the planning of structural modifications in the thermal column irradiation channel or the use of different irradiation sites than the thermal column, e.g., the beam tubes.

Reactive Transport Modeling of Thermal Column Experiments to Investigate the Impacts of Aquifer Thermal Energy Storage on Groundwater Quality

Aquifer thermal energy storage (ATES) systems are increasingly being used to acclimatize buildings and are often constructed in aquifers used for drinking water supply. This raises the question of potential groundwater quality impact. Here, we use laboratory column experiments to develop and calibrate a reactive transport model (PHREEQC) simulating the thermally induced (5-60 °C) water quality changes in anoxic sandy sediments. Temperature-dependent surface complexation, cation-exchange, and kinetic dissolution of K-feldspar were included in the model. Optimization results combined with an extensive literature survey showed surface complexation of (oxy)anions (As, B, and PO4) is consistently exothermic, whereas surface complexation of cations (Ca and Mg) and cationic heavy metals (Cd, Pb, and Zn) is endothermic. The calibrated model was applied to simulate arsenic mobility in an ATES system using a simple yet powerful mirrored axi-symmetrical grid. Results showed that ATES mobilizes arsenic toward the fringe of the warm water bubble and the center of the cold water bubble. This transient redistribution of arsenic causes its aqueous concentrations in the cold and warm groundwater bubbles to become similar through multiple heating cycles, with a final concentration depending on the average injection temperature of the warm and cold ATES wells.

Numerical Investigation of the Formation of a Convective Column and a Fire Tornado by Forest Fires

Computational modeling of the formation of a convective column by forest fires has been carried out. It has been established that in the case of an unstable atmosphere stratification the basic factor influencing the thermal column formation is the intensification of the processes of turbulent mixing and that at a stable atmosphere stratification a more significant factor determining the convective column formation is the action of the buoyancy force. It has been shown that a swirling flow in the convective column is formed due to the appearance of a tangential velocity component as a consequence of the local circulation arising against the background of large-scale motion owing to the thermal and orographic inhomogeneities of the underlying surface.

Design and construction of a thermal neutron beam for BNCT at Tehran Research Reactor

An irradiation facility has been designed and constructed at Tehran Research Reactor (TRR) for the treatment of shallow tumors using Boron Neutron Capture Therapy (BNCT). TRR has a thermal column which is about 3m in length with a wide square cross section of 1.2×1.2m2. This facility is filled with removable graphite blocks. The aim of this work is to perform the necessary modifications in the thermal column structure to meet thermal BNCT beam criteria recommended by International Atomic Energy Agency. The main modifications consist of rearranging graphite blocks and reducing the gamma dose rate at the beam exit. Activation foils and TLD700 dosimeter have been used to measure in-air characteristics of the neutron beam. According to the measurements, a thermal flux is 5.6×108 (ncm−2s−1), a cadmium ratio is 186 for gold foils and a gamma dose rate is 0.57Gyh−1.

Ultracold neutron source at the PULSTAR reactor: Engineering design and cryogenic testing

Construction is completed and commissioning is in progress for an ultracold neutron (UCN) source at the PULSTAR reactor on the campus of North Carolina State University. The source utilizes two stages of neutron moderation, one in heavy water at room temperature and the other in solid methane at ~40K, followed by a converter stage, solid deuterium at 5K, that allows a single down scattering of cold neutrons to provide UCN. The UCN source rolls into the thermal column enclosure of the PULSTAR reactor, where neutrons will be delivered from a bare face of the reactor core by streaming through a graphite-lined assembly. The source infrastructure, i.e., graphite-lined assembly, heavy-water system, gas handling system, and helium liquefier cooling system, has been tested and all systems operate as predicted. The research program being considered for the PULSTAR UCN source includes the physics of UCN production, fundamental particle physics, and material surface studies of nanolayers containing hydrogen. In the present paper we report details of the engineering and cryogenic design of the facility as well as results of critical commissioning tests without neutrons.

Rotating turbulent Rayleigh–Bénard convection subject to harmonically forced flow reversals

The characteristics of turbulent flow in a cylindrical Rayleigh–Bénard convection cell which can be modified considerably in case rotation is included in the dynamics. By incorporating the additional effects of an Euler force, i.e., effects induced by non-constant rotation rates, a remarkably strong intensification of the heat transfer efficiency can be achieved. We consider turbulent convection at Rayleigh number Ra = 109 and Prandtl number σ = 6.4 under a harmonically varying rotation, allowing complete reversals of the direction of the externally imposed rotation in the course of time. The dimensionless amplitude of the oscillation is taken as 1/Ro* = 1 while various modulation frequencies 0.1 ≤ Roω ≤ 1 are applied. Both slow and fast flow-structuring and heat transfer intensification are induced due to the forced flow reversals. Depending on the magnitude of the Euler force, increases in the Nusselt number of up to 400% were observed, compared to the case of constant or no rotation. It is shown that a large thermal flow structure accumulates all along the centreline of the cylinder, which is responsible for the strongly increased heat transfer. This dynamic thermal flow structure develops quite gradually, requiring many periods of modulated flow reversals. In the course of time, the Nusselt number increases in an oscillatory fashion up to a point of global instability, after which a very rapid and striking collapse of the thermal columnar structure is seen. Following such a collapse is another, quite similar episode of gradual accumulation of the next thermal column. We perform direct numerical simulation of the incompressible Navier–Stokes equations to study this system. Both the flow structures and the corresponding heat transfer characteristics are discussed at a range of modulation frequencies. We give an overview of typical time scales of the system response.

Slow neutron reactions in inverse kinematics for isotope production: a primer

Slow neutron inverse-kinematic reactions offer unique advantages since their kinematical conditions can be tuned to utilize very high resonance cross-sections and to separate transmuted-isotopes online. New advances in plasma sciences and thermal neutron facilities can usher practical applications of this type of reactions in some special cases. Production and implantation of isotopically-pure short-lived and spin-polarized radiotracers has been identified as a probable first application. The production rates for 110m,gAg radio-nuclides in 109Ag(n, γ) capture, that occur when a beam of 109Ag ions traverses a thermal neutron column, have been calculated and the results are presented. To develop the idea of inverse reactions in physical grounds, further analyses and advances on the non-trivial technological issues related to the generation and control of high density and high volume particle beams, isotope separation methods, and high flux thermal neutron channels of matching parameters are required and a brief discussion on these aspects are also included.

Solid state detectors for dosimetry in the BNCT beam of the LVR-15 research reactor

Dosimetry measurements have been carried out at the epithermal neutron beam of LVR-15 reactor (Řež) moderated by a polyethylene disk placed through the collimator exit. The spatial distributions of thermal neutron fluence rate and of gamma and fast neutron dose rates have been attained. The contributions to the dose of the radiation field components have been assessed with Fricke-gel-layers, by pixel-to-pixel elaboration of the light transmittance images of samples having different isotopic composition and with thermoluminescence detectors, by analysing the shape of the glow curve. An analogous experiment has been carried out at the thermal column HK1 of the same LVR-15 reactor, aimed at neutronography research. Good consistency of all results was obtained.

Intensified heat transfer in modulated rotating Rayleigh–Bénard convection

Heat transfer in a Rayleigh-Bénard configuration consisting of a vertical cylinder, which is rotating about its axis, can be intensified considerably when the rotation rate is modulated harmonically in time. Such time-dependent rotation introduces an Euler force into the governing equations which leads to a particular modification of the flow that is shown to support a Nusselt number (Nu) that is considerably higher than in case of constant rotation. We use direct numerical simulation of the incompressible Navier–Stokes equations to perform a comprehensive parameter study of the flow-structuring and associated heat transfer investigating primarily the effect of variations in the frequency with which the rotation rate varies. We consider flow in an upright cylinder of unit aspect ratio which is heated from below and cooled at the top. At sufficiently strong Euler forces the temporal variation of Nu shows a striking dynamics with periods of gradual increase in Nu with more rapid oscillations superimposed, next to rather catastrophic events in which the entire flow-structure that supported high levels of Nu collapses entirely and it returns to a value more similar to that attained at steady rotation. During periods of oscillatory build-up of Nu, high levels of turbulence gradually become more pronounced from the outer cylinder wall inward and a gradually stronger thermal column arises along the centreline of the cylinder. This flow structure can support Nu up to 250% larger than without rotation, a value otherwise achievable only by employing phase transition.

Measurement of Thermal Conductivity of Gases Using Thermal Diffusion Columns: Air and Helium

This paper describes a method for determining the thermal conductivity of a gas by using a thermal diffusion column and uses it for finding the thermal conductivity of air and helium upto 140 degree centigrade. The study widens the scope for finding the thermal conductivity of a gas at still higher temperatures.

Using TRIGA Mark II research reactor for irradiation with thermal neutrons

Recently a series of test irradiations was performed at the JSI TRIGA Mark II reactor for the Fission Track-Thermoionization Mass Spectrometry (FT-TIMS) method, which requires a well thermalized neutron spectrum for sample irradiation. For this purpose the Monte Carlo N-Particle Transport Code (MCNP5) was used to computationally support the design of an irradiation device inside the TRIGA model and to support the actual measurements by calculating the neutron fluxes inside the major ex-core irradiation facilities. The irradiation device, filled with heavy water, was designed and optimized inside the Thermal Column and the additional moderation was placed inside the Elevated Piercing Port. The use of the device improves the ratio of thermal neutron flux to the sum of epithermal and fast neutron flux inside the Thermal Column Port by 390% and achieves the desired thermal neutron fluence of 1015neutrons/cm2 in irradiation time of 20h.

Equipment design for thermal cycling absorption process column efficiency test

In order to support the tritium production and recycling in the fuel cycle system of fusion reactors, the thermal cycling absorption process (TCAP), which is a semi-continuous chromatographic process for hydrogen isotope separation, has been developed for years. The hydrogen isotopes separation capacity mostly depends on the efficiency of the separation columns, therefore, evaluating different column structure designs and packing materials for their separation efficiency is significative. In this work, a unique design of separation column apparatus with the hot/cold cycling system has been developed. Its unique feature is the different separation columns can be changed for testing several factors such as particle size of packing material, fill density and uniformity, column structure on the influence of the column efficiency. Moreover, the methods to measure efficiency of the separation column have been introduced. The experimental results show that the displacement chromatographic method is more suitable for this apparatus to analyze the column efficiency.

A feasibility study of the Tehran research reactor as a neutron source for BNCT

Investigation on the use of the Tehran Research Reactor (TRR) as a neutron source for Boron Neutron Capture Therapy (BNCT) has been performed by calculating and measuring energy spectrum and the spatial distribution of neutrons in all external irradiation facilities, including six beam tubes, thermal column, and the medical room. Activation methods with multiple foils and a copper wire have been used for the mentioned measurements. The results show that (1) the small diameter and long length beam tubes cannot provide sufficient neutron flux for BNCT; (2) in order to use the medical room, the TRR core should be placed in the open pool position, in this situation the distance between the core and patient position is about 400cm, so neutron flux cannot be sufficient for BNCT; and (3) the best facility which can be adapted for BNCT application is the thermal column, if all graphite blocks can be removed. The epithermal and fast neutron flux at the beginning of this empty column are 4.12×109 and 1.21×109n/cm2/s, respectively, which can provide an appropriate neutron beam for BNCT by designing and constructing a proper Beam Shaping Assembly (BSA) structure.

Cloning, Expression and Characterization of a Novel Thermophilic Polygalacturonase from Caldicellulosiruptor bescii DSM 6725

We cloned the gene ACM61449 from anaerobic, thermophilic Caldicellulosiruptor bescii, and expressed it in Escherichia coli origami (DE3). After purification through thermal treatment and Ni-NTA agarose column extraction, we characterized the properties of the recombinant protein (CbPelA). The optimal temperature and pH of the protein were 72 °C and 5.2, respectively. CbPelA demonstrated high thermal-stability, with a half-life of 14 h at 70 °C. CbPelA also showed very high activity for polygalacturonic acid (PGA), and released monogalacturonic acid as its sole product. The Vmax and Km of CbPelA were 384.6 U·mg−1 and 0.31 mg·mL−1, respectively. CbPelA was also able to hydrolyze methylated pectin (48% and 10% relative activity on 20%–34% and 85% methylated pectin, respectively). The high thermo-activity and methylated pectin hydrolization activity of CbPelA suggest that it has potential applications in the food and textile industry.

A new rapid neutron activation analysis system at Dalat nuclear research reactor

An auto-pneumatic transfer system has been installed at the Dalat research reactor for rapid instrument neutron activation analysis based on very short-lived nuclides. This system can be used to perform short irradiations in seconds either in the vertical channel 13-2 or in the horizontal thermal column of the reactor. The transferring time of sample from irradiation to measurement position is approximately 3.2 seconds. A loss-free counting system using HPGE detector has been also setup in compacting with the pneumatic transfer system for measurement of sample’s activity, automatically starting for data acquisition at irradiated sample’s arrival. This new facility was tested and shown to have high potential for the determination of short-lived nuclides with half-lives from 10 ¸ 100 seconds. This work presents the results of timing parameter measurements, characterization of irradiation facilities, and application of this system to determining Selenium concentration in several biological reference materials.

Design of an epithermal neutron beam for BNCT in thermal column of Tehran research reactor

The potential of the thermal column of Tehran Research Reactor (TRR) to provide epithermal neutron beam for Boron Neutron Capture Therapy (BNCT) has been investigated using Monte Carlo simulation. A Beam Shaping Assembly (BSA) has been designed and optimized to meet BNCT neutron beam criteria recommended by International Atomic Energy Agency. The suggested BSA configuration in cylindrical geometry consists of 20cm Al as a moderator, 35cm Pb as a reflector, two 5cm Bi slabs as gamma shield, and two 2mm Cd sheets as thermal neutron filters. The results show that epithermal neutron flux at the exit of the BSA can be 0.65×109n/cm2s. In-phantom dose analysis indicates that the designed neutron beam can be used for treatment of deep-seated brain tumors in acceptable time.

Thermal treatment of neutron-irradiated nuclear graphite

The properties of graphite samples from the thermal column of a material testing reactor and from the internals of two different nuclear power reactors were investigated regarding the thermal release of tritium and radiocarbon. These reactor types have been selected due to the different conditions under which graphite has been irradiated with neutrons during the operating time of these reactors. Based on the findings, options for thermal treatment of irradiated graphite are discussed in order to facilitate its final disposal.

Dynamic Simulation of Petlyuk Column for Separation of Ternary Mixtures

The Petlyuk distillation configuration has received considerable attention because of its efficiency to reduce the energy required for the separation of ternary mixtures. The dynamic properties of fully thermal coupling distillation column, which separates ternary mixtures of H2O, ethylene glycol (EG), diethylene glycol (DEG), are analyzed. The possible control configurations were investigated using Relative Gain Array (RGA) Analysis and dynamic simulation. The results indicate that the provided control scheme is able to produce a stable control response for thermally coupled distillation systems and shows better dynamic responses than the conventional distillation sequence.