Alice Y. Ying

The effects of imperfect insulator coatings on MHD and heat transfer in rectangular ducts

Abstract The integrity of the electrically insulating coating at the coolant channel walls represents a feasibility issue for a self-cooled liquid metal blanket. The effects of cracks in the insulating layer on MHD pressure drop are investigated, for various crack locations, sizes and resistivities. It is shown that, once the crack resistance exceeds the Hartmann layer resistance, the MHD pressure drop increases significantly. Using the 2-D fully-developed MHD flow code, it has been found that the crack location has a large impact on the MHD pressure drop: for the same crack sizes and resistivities, the pressure gradient increases as the cracks move towards the central plane. The effect of the insulation on heat transfer is discussed. The heat transfer capability is reduced in the presence of the insulator coating.

Numerical and experimental prediction of the thermomechanical performance of pebble beds for solid breeder blanket

In this paper, recent numerical modeling and experiment work for predicting the effective thermal and mechanical properties of solid breeder blanket pebble bed materials is presented. The numerical modeling is based on the micro-mechanics displacement method in conjunction with an iterative process of successive releasing of the contact force of particles. Initial and final packed states for particle assembly and the contact forces for particles have been studied. In addition, a test article has been constructed to measure the thermal stress induced by the thermal expansion of the solid particle and to estimate the characteristic properties of particle materials. Corresponding experiments are carried out with aluminum and Li2ZrO3 pebble beds. Empirical correlations for the moduli of deformation are presented. These experiment data are compared with the numerical modeling results.

Mechanical behavior and design database of packed beds for blanket designs

Abstract The mechanical behavior and properties of particle beds relevant to fusion ceramic breeder blanket designs are addressed through a combination of experimental and analytical studies. A series of uniaxial compression tests are performed in a INSTRON hydraulic-press test facility in which compressive loads are applied to Li 2 ZrO 3 and aluminum packed beds. The experimental data shows that the mechanical properties such as the bed effective modulus are stress dependent and consistent with the analytical model predictions. Nevertheless, the experimental data shows that the bed effective modulus is approximately two orders of magnitude lower than that of the solid material.

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.

Benefits of natural convection in solid breeder blankets with poloidal coolant channels under LOFA conditions

Abstract This paper analyzes natural circulation flow in solid breeder blanket designs with poloidal channels under a LOFA condition. Analyses couple the flow transient behaviors with transient heat transport models. While two-phase natural circulation exists in the system, a homogenous mixture model is used. The results of example calculations performed for an ITER solid breeder design concept indicate that in a 3-loop system with an elevation head ( ΔZ ) of 20 m, the removal of the afterheat (energy stored in the blanket elements and decay heat) depends on two-phase natural circulation flow with a quasi-equilibrium flow quality of 26% at the outlet of the blanket segment. However, if the available hydrostatic head is about 15 m or less, the amount of natural circulation flow is reduced due to significant increases of friction and acceleration losses in a two-phase system. To rely on natural circulation flow as an afterheat removal mechanism, the design of coolant system with its flow channels should be addressed analytically and experimentally to permit stable steady-state operation under conditions of the presence of vapor in the coolant channels.

Application of reliability analysis method to fusion component testing

Abstract The purpose of this paper is to discuss a basic reliability analysis method that is beneficial to fusion component test planning. Emphasis is placed on formulating the problem to be solved and on determining the required test time and the number of test articles needed to verify a performance or a failure criterion. While an increasing failure rate is likely to be the case for the fusion component resulting from irradiation effects, analysis is performed to show how the life characteristics impact the test requirements. Taking into account the available data from similar technology experiences, calculations based on the Bayesian approach indicate a possible saving on the test time requirement.

Thermo-mechanical Analysis of ITER Test Unit Cell under Pulse Operation

In this paper, a 3-D finite element model has been built to do thermo-mechanical analysis about an ITER test unit cell with edge-on configuration under pulse operation. In previous works, the constitutive equations of effective material properties, which are dependent on local temperature and stress, have been empirically derived. In our program, these material properties of ceramic pebble beds (lithium breeders & beryllium neutron multipliers) are implemented the model Based on current simulation results, it can provide the stress and temperature magnitude and distribution inside the blanket structure when it is under pulse radiation heating. These structural responses due to deformation of particulate materials and material thermal creep are important for assessment of thermo-mechanical behaviors and characterization of tritium release

CHARACTERISTICS OF HELIUM PURGE FLOW IN SOLID BREEDER PEBBLE BED AND ITS IMPACT ON DESIGN CONSIDERATIONS

One of the design objectives of helium purge in the solid breeder is to keep the HT partial pressure in the purge system low to minimize the tritium inventory and permeation through the clad. The helium purge flow rate is set at the highest possible value to achieve this criterion. A distinguishable feature of the helium purge flow in a pebble bed design is its velocity jet due to high local porosity near the wall. Thermalhydraulic calculations based on 2-D non-Darcian momentum equations showed that the peak velocity is about 8 times or more higher than the bulk velocity at Reynolds number relevant to solid breeder blanket application. This velocity profile results in reducing the tritium permeation rate through the cald based on the low tritium partial pressure at the wall associated with this peak velocity by a factor of 2 or more.

Solid breeder thermal transient under purge-line-break accidents

Abstract The breeder thermal performances under a purge line break have been analyzed for two blanket design options: a blanket design using a packed breeder bed and a blanket design using a sintered breeder product. Under a purge line break open to a vacuum environment, the packed bed breeder temperature exceeds its operating temperature limit at a faster rate than that of the sintered breeder blanket design for the same breeder temperature gradient. Depending on the breeder material and nominal operating conditions, the breeder reaches its maximum operating temperature in time ranging from 32 seconds to 125 seconds for a break area of 10 cm 2 in packed bed designs. However for the sintered product design, the consequence of this transient might not result in the breeder exceeding its maximum operating temperature if a reasonable contact pressure could be established at the interface. To reduce the safety hazards, the tritium concentration build up in the vacuum vessel in conjunction with the purge gas pressure inside the blanket module should be used as a measure for initiating the reactor shutdown for this type of accident. The consequence of the purge line break outside the vacuum vessel on the breeder transient thermal performance is less significant because of a longer transient time involved.