Masters Theses

Date of Award

12-1988

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Paul N. Stevens

Committee Members

Nermin A. Uckan, Hall C. Roland

Abstract

The injection of solid pellets composed of the hydrogen isotopes has become the leading candidate for refueling the next-generation fusion power reactors based on the tokamac concept. The benefits of this refueling scheme depend upon the distance that the hydrogenic pellet penetrates a plasma and deposits its particles into the plasma interior for improving the plasma temperature and density profiles. A general overview of various practical plasma fueling mechanisms such as gas injection (plasma edge fueling) and injection of high-speed hydrogenic pellets (plasma central fueling) was presented. The neutral gas shielding (NGS) model, which describes the ablation rate of a solid hydrogenic pellet injected at high-speeds into a burning plasma, was also discussed. The Oak Ridge National Laboratory (ORNL) pellet ablation code "PELLET", which incorporates the neutral gas and plasma shielding (NGPS) model, has been used in this research to study the physical variables affecting the penetration depths of the injected pellets into a plasma characteristic of the Engineering Test Reactor (ETR). Such variables include initial pellet radius, pellet velocity, pellet molecular mass, neutral cloud thickness, fusion heating power, plasma minor and major radii, and central plasma electron temperature and density along with associated radial profile factors. A multi-dimensional regression analysis, which incorporates the aforementioned plasma and pellet parameters, has been used for developing suitable fitting correlations based on the NGPS model. Comparisons were made between the analytical expressions and the computational correlations for the penetration depths obtained in this study. The computationally developed empirical expressions were found to be in reasonable agreement with the analytical models for a range of ETR plasma and pellet parameters. It was concluded that these empirical expressions can be used along with the other physics and engineering constraints to determine the design envelope for the next-generation fusion Engineering Test Reactors (ETRs).

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