Thermal Blanket System

The AHTR appears to have excellent safety attributes. The combined thermal capacity of the graphite core and the molten salt coolant pool offer a large time buffer to reactor transients. The effective transfer of heat to the reactor vessel increases the effectiveness of the RVACS and DRAGS to remove decay heat, and the excellent fission product retention characteristic of molten salt provides an extra barrier to radioactive releases. The low-pressure, chemically nonreactive coolant also greatly reduces the potential for overpressurization of the reactor containment building and provides an important additional barrier for fission product release. The most important design and safety issue with the AHTR may be the performance and reliability of the thermal blanket system, which must maintain the vessel within an acceptable temperature range. 

Fig. 2.8. Schematic showing a vertical cross-section for an AHTR thermal blanket system.

Thermal blanket system test facility (engineering). The AHTR requires a thermal blanket system to insulate the reactor vessel from the elevated core and coolant salt. Appropriate high-temperature tests for a variety of transient conditions are required to test alternative insulation... 

If two blocks of metal, one at a high temperature and the other at a low temp-eramre Tj [Fig. 6.10(a)] are separated by a perfect heat insulator, and the system as a whole is surrounded by a thermal blanket that permits no transfer of heat in or out, then no change in internal energy can occur with time. If the insulator between the blocks is removed, the hotter block will decrdease in temperature and the cooler one will increase in temperature until the uniform temperamre T2 is reached. This transformation is spontaneous. At/ is zero. But a loss of capacity to perform work has occurred. In the initial state, we could insert a thermocouple lead in the block at Ts and another in that at Tj and obtain electrical work. Insertion of thermocouple leads in the same positions in the double block at T2 cannot generate any work. At the conclusion of the spontaneous transformation without the thermocouple, the internal energy is stiU the same as that at the outset, but it is no longer in a condition where it has the capacity to do work. 

T0782 Terra-Kleen Response Group, Inc., Solvent Extraction Technology T0783 Terrapure Systems, L.L.C., Palladized Iron Remediation Technology T0784 TerraTherm Environmental Services, Inc., Thermal Blanket for In Situ Thermal Desorption... 

The thermal heating blanket is an in situ thermal desorption system that combines thermal desorption and vacuum extraction to separate organic compounds from in-place contaminated soil. It can be used on soils in situ or ex situ. 

TerraTherm Environmental Services, Inc., a subsidiary of Shell Technology Ventures, Inc., has developed the in situ thermal desorption (ISTD) thermal blanket technology to treat or remove volatile and semivolatile contaminants from near-surface soils and pavements. The contaminant removal is accomplished by heating the soil in sim (without excavation) to desorb and treat contaminants. In addition to evaporation and volatilization, contaminants are removed by several mechanisms, including steam distillation, pyrolysis, oxidation, and other chemical reactions. Vaporized contaminants are drawn to the surface by vacuum, collected beneath an impermeable sheet, and routed to a vapor treatment system where contaminants are thermally oxidized or adsorbed. 

Instrumental. The Mettler TA2000B thermal analysis system is equipped with an interface system, and Hewlett-Packard 9815 desk top calculator and 7225 plotter. Samples, weighing 5-10 mg, sealed in aluminum pans and under a nitrogen blanket, were heated in the calorimeter at a rate of 10 deg/min from -35 or 10 deg C to 180 deg C respectively, for specific heat and kinetic scans. Specific heat measurements were calibrated with alumina to an accuracy of 3%. Temperatures and enthalpies were calibrated with an Indium sample. The accuracies were .02 deg C and 2% (Indium 28.5 J/g), respectively. 

While thermal blankets may treat contaminants near the surface, thermal wells offer the ability to treat contamination at much greater depths. In thermal well systems, heater wells are inserted into the contaminated soil to volatilize contaminants in situ. The generated off-gas is then collected in combination heater-vacuum wells and sent to an APC system. The number of heater-vacuum wells, and the well spacing, depend on site-specific parameters, but typically, one-third of the wells are heater-vacuum wells and the well spacing is 1.8-2.1 m. " With heaters operating at up to 800°C, thermal well systems are able to achieve soil temperatures of 300-500°C between wells. In order to fully remediate contaminated sites, the wells are inserted up to 0.9 m below the contaminated layer and operate for 30-60 days depending on the soil characteristics and contaminants of concern. ... 

Much like thermal blankets, thermal well systems do not require costly excavation and they also offer additional benefits. They have been used to treat contaminants at depths up to 5.5m below the surface and much of the contaminants are destroyed in situ through oxidation or pyrolysis reactions.Furthermore, thermal well systems offer uniform heating and consequent treatment of contaminants is effective across a wide range of soil types. The long residence time favors desorption mechanisms that may be time dependent. ... 

Three peak coolant temperatures were evaluated 705, 800, and 1000°C, for the AHTR — Low Temperature (AHTR-LT), the AHTR — Intermediate Temperature (AHTR-IT), and the AHTR— High Temperature (AHTR-HT), respectively. The respective thermal-to-electric efficiencies are 48.0, 51.5, and 56.5%. The AHTR-LT uses existing code qualified materials, the AHTR-rr uses existing materials that have not been fully tested, and the AHTR-HT uses advanced materials. The AHTR-LT has a metallic blanket system that separates and insulates the reactor vessel from the reactor core so that the fuel and coolant can operate at higher... 

Liquid Shields. A cheaper cryogenic liquid like nitrogen has at times been used as a thermal blanket to shield either expensive or hazardous fluids including liquid helium, hydrogen, or fluorine from ambient temperatures. In such a system, the inexpensive liquid nitrogen, in its own container, surrounds the main fluid, which in turn resides in a vacuum-jacketed inner vessel as shown in Fig. 7.14. 

Case PB/Pt Relative poison in core Relative poison in blanket BR 1 + 0(23 A 23,/A Bi X 1Q6 (core) M-is, kg A 23/A"Bi X 10 (blanket) Mis, kg Average thermal flux in core system Average thermal flux in blanket system... 

The effective therm conductivity values generally obtained in practice are at least a factor of two greater than the one-dimensional thermal conductivity values measured in the laboratoiy with carefully controlled techniques. This degradation in insulation thermal performance is caused by the combined presence of edge exposure to isothermal boundaries, gaps, joints, or penetrations in the insulation blanket required for structure supports, fill and vent hnes, and high lateral thermal conductivity of these insulation systems. 

Thermal conduction (also referred to as electrical conductive heating or in situ thermal desorption) supplies heat to the soil through steel wells or with a blanket that covers the ground surface. As the polluted area is heated, the contaminants are destroyed or evaporated. Steel wells are used when the polluted soil is deep. The blanket is used where the polluted soil is shallow. Typically, a carrier gas or vacuum system transports the volatilized water and organics to a treatment system. 

The presence of water, or water vapour, affects the chemistry of thermal modification and heat transfer within the wood (Burmester, 1981). Under dry treatment conditions, the wood is dried prior to thermal modification, or water is removed by the use of an open system, or a recirculating system equipped with a condenser. In closed systems, water evaporated from the wood remains as high-pressure steam during the process. Steam can also be injected into the reactor to act as a heat-transfer medium, and can additionally act as an inert blanket to limit oxidative processes. Such steam treatment processes are referred to as hygrothermal treatments. Where the wood is heated in water, this is known as a hydrothermal process. Hydrothermal treatments have been extensively studied as a... 

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