Z. Gorbis

Study of Effective Solid-to-Solid Contact Thermal Resistance and its Application to Solid Breeder Blanket Design For ITER

AbstractCharacterization of solid-to-solid contact thermal resistance is important for ITER solid breeder blanket designs utilizing sintered blocks of Be and/or solid breeder1. In order to fully assess the thermal performance of such blankets, including their ability to accommodate power variation, the thermal resistances of the Be/clad and solid breeder/clad contacts need to be characterized. In this paper, factors affecting the gas and solid conductances in the contact zone are analyzed. They include: roughness, contact pressure, temperature and curvature of restrained Be block. The study is carried out based on the models of Yovanovich2 and Shlykov3 and available experimental data from the literature. Recommendations are provided for the ITER solid breeder blanket design applications and for corresponding R&D requirements.

Model for determining the effective thermal conductivity of particle beds with high solid-to-gas thermal conductivity ratio

A Be-packed bed between the high-temperature breeder and low-temperature coolant has been proposed for an ITER solid breeder base blanket. The design offers the possibility of adjusting the solid breeder temperature through active control of the packed-bed effective conductivity; such control can potentially be achieved by varying the pressure or flow rate of the helium purge flowing through the Be-packed bed. A modeling effort directed at estimating the effective thermal conductivity of pebble beds with high solid-to-gas conductivity ratios (such as Be and He) is described. The model can account for different particle sizes and surface contact characteristics which are particularly important in determining the extent to which the bed effective thermal conductivity can be controlled through pressure variation for high ratios of solid-to-gas conductivity.<<ETX>>

Design and analysis of the Prometheus wetted wall IFE reactor cavity

The design and engineering of a wetted wall cavity are in progress at UCLA as a part of an inertial fusion energy (IFE) reactor study led by McDonnell Douglas. The authors outline the design methodology, analyze the thermal, mechanical, nuclear and energy conversion attributes of the cavity, and present possible solutions to outstanding problems. The choice of a wetted wall cavity was made following an assessment of previous IFE cavity designs and evaluation of a number of key design goals, including: safety and environmental attractiveness, reliability, ease of maintenance, high thermal cycle efficiency, and long component lifetime. Design of the present wetted wall concept considers several important issues, including: (1) limits on cavity clearing time due to the requirement to conduct heat out radially; (2) film flow uniformity, wetting, and drainage; and (3) mechanical response of the first wall system.<<ETX>>

A helium-cooled solid breeder concept for the tritium-producing blanket of the international thermonuclear experimental reactor

The usefulness of the tritium-producing blanket in the International Thermonuclear Experimentall Reactor (ITER) to the fusion research and development program can be maximized by selecting design parameters, features, and options that are reactor relevant without significantly increasing the risk in key areas such as device safety and operational reliability. For that reason, a helium-cooled solid breeder (SB) blanket is proposed since it combines the operation of the SB at high reactor-relevant temperatures with the operation of helium at moderate temperature and pressure to minimize risk. Results of the analysis done for this blanket concept indicate that it is very attractive. It can achieve a high tritium breeding ratio without breeding in the space-limited inboard region, It offers important safety features, including the use of inert gas with no chemical reaction or corrosion, low activation SB, and multiple containment of tritium. the concept provides great operational flexibility to accommodate changes in ITER operating parameters, such as power level, and to optimize the operating temperature of the structure. A novel and practical concept is proposed for the thermal resistance gap between the coolant and SB to allow their operating temperatures to be optimized.

Analysis of wall-packed—bed thermal interactions

Abstract One of the major issues remaining for ceramic breeder blankets involves uncertainties in heat transfer and thermomechanical interactions within the breeder and multiplier regions. Particle bed forms are considered in many reactor blanket designs for both the breeder and Be multiplier. The effective thermal conductivity of beds and the wall—bed thermal conductance are still not adequately characterized, particularly under the influence of mechanical stresses. The problem is particularly serious for the wall conductance between Be and its cladding, where the uncertainty can be greater than 50%. In this work, we describe a new model for the wall—bed conductance that treats the near-wall region as a finite-width zone. The model includes an estimate of the region porosity based on the number of contact points, and the contact area for smooth surfaces. It solves the heat conduction in a near-wall unit cell. The model is verified with existing data and used to predict the range of wall conductances expected in future simulation experiments and in reactor applications.

U.S. Solid Breeder Blanket Design for ITER

The US blanket design activity has focused on the developments and the analyses of a solid breeder blanket concept for ITER. The main function of this blanket is to produce the necessary tritium required for the ITER operation and the test program. Safety, power reactor relevance, low tritium inventory, and design flexibility are the main reasons for the blanket selection. The blanket is designed to operate satisfactorily in the physics and the technology phases of ITER without the need for hardware changes. Mechanical simplicity, predictability, performance, minimum cost, and minimum R D requirements are the other criteria used to guide the design process. The design aspects of the blanket are summarized in this paper. 2 refs., 7 figs., 3 tabs.

Thermal control of solide breeder blankets

Abstract An assessment of the thermal control mechanisms applicable to solid breeder blanket designs under ITER-like operating conditions is presented in this paper. Four cases are considered: a helium gap; a sintered block Be region; a sintered block Be region with a metallic felt at the Be-clad interface; and a Be packed bed region. For these cases, typical operating conditions are explored to determine the ranges of wall load which can be accomodated while maintaining the breeder within its allowable operating temperature window. The corresponding region thicknesses are calculated to help identify the practicality of each concept and the design tolerances.

LOCA Study for a Helium-Cooled Solid Breeder Design for ITER

The analysis of thermal processes after a loss-of-coolant accident (LOCA) in a solid breeder blanket is important because of the first wall and solid breeder maximum allowable temperature constraints. The objective is to design for a LOCA so that following a LOCA, the maximum solid breeder and structure temperatures are less than the limit beyond which irreversible damage is done, which would lead to loss of investment. The temporal temperature profiles for the solid breeder and first wall regions of a helium-cooled solid breeder design for ITER were calculated based on afterheat values for adiabatic and non-adiabatic conditions and the results are presented in this paper. It is found that, for this design, even when excluding radiation to the cooled inboard, a LOCA can be recommended by energy removal through a flowing purge with a reasonable flow rate.

High-Heat-Flux Removal by Phase-Change Fluid and Particulate Flow

A new concept based on particulate flow in which either or both the particulates and the fluid could undergo phase changes is proposed. The presence of particulates provides not only a mechanism for additional heat removal through phase change but also the potential for increasing the rate of heat transfer by enhancing convection through surface region/bulk [open quotes]mixing[close quotes], by enhancing radiation, particularly for high-temperature cases; and for the case of multiphase fluid, by enhancing the boiling process. One particularly interesting coolant system based on this concept is [open quotes]subcooled boiling water-ice particulate[close quotes] flow. A preliminary analysis of this coolant system is presented, the results of which indicate that such a coolant system is better applied for cooling of relatively small surface areas with high local heat fluxes, where a conventional cooling system would come short of providing the required heat removal at acceptable coolant pressure levels. 14 refs., 8 figs.

Helium-cooled solid breeder blanket for ITER

This paper summarizes the latest results of a design study of a helium-cooled solid breeder blanket for ITER. Attractive features of this design include the following: (1) There is a significant design margin since only part of the allowable solid breeder temperature window needs to be used. (2) There is an expanding data base available from solid breeder experiments carried out internationally. (3) The solid breeder can be designed to operate at high reactor-relevant temperature, while the helium is kept at moderate temperature and pressure for safety and reliability. In addition, since helium is a gas, it can be run so as to optimize the structure temperature and accommodate long term power variation without incurring any substantial pressure penalty. (4) The use of helium, an inert gas minimizing any chemical reaction and corrosion, in combination with a low activation solid breeder, is a safety advantage. An extensive list of the blanket operating parameters is provided and key factors are discussed.