Number 4 (June 1977)

A Status Report on the Bayou Darter, Etheostoma rubrum, and the Bayou Pierre System. By R.D. Suttkus and G. Clemmer, plus News Notes, 4 pp

TCODE: a computer code for analysis of tritium and vacuum systems for tokamak fusion reactors

TCODE can be used for either near-term experimental reactors or for commercial reactors. The code provides options for items that may be included in a commercial reactor such as a divertor, neutral beam heating, and a breeding blanket. The code was used to calculate tritium and vacuum system parameters for the near term reactors ITR, TNS-UP and EPR as well as for some commercial reactor designs, the UWMAK series. A selected sample of the tritium and vacuum parameters for these reactor designs is shown. Also shown are parameters for a hypothetical reactor UWMAK-III M having similar characteristics to UWMAK-III but with a higher fractional burnup (5.0% cf. 0.83%). The impact of the reactor design scenario upon major tritium and vacuum systems is discussed

Development of tritium breeding blankets for DT-burning fusion reactors

This study examines the status of understanding of blanket tritium recovery and the performance of potentially viable tritium breeding materials under conditions anticipated in a DT-fueled fusion reactor environment. The existing physicochemical, thermophysical, and ceramographic data for candidate liquid and solid breeders are reviewed and appropriate operating conditions defined. It is shown that selection of a breeding material and an appropriate tritium recovery method can impose significant constraints upon blanket design, particularly when considerations of breeder/coolant/structure compatibility and temperature limitations are taken into account

Tritium-handling considerations for ETF and STARFIRE

The tritium handling requirements for both the ETF and the STARFIRE fusion reactor designs are analyzed. The use of a limiter/vacuum system for STARFIRE produced a high fractional burnup (0.42) which resulted in a low tritium inventory in the fueling system. The importance of a fast process flow rate is achieving a rapid cleanup after a tritium release is demonstrated; another important factor is the rate at which HTO is released from building surfaces. A complete fusion reactor tritium facility is described

Modeling of tritium transport in lithium aluminate fusion solid breeders

Lithium aluminate is a candidate tritium-breeding material for fusion reactor blankets. One of the concerns with using LiAlO/sub 2/ is tritium recovery from this material, particularly at low operating temperatures and high fluences. The data from various tritium release experiments with ..gamma..-LiAlO/sub 2/ and related materials are reviewed and analyzed to determine under what conditions bulk diffusion is the rate-limiting mechanism for tritium transport and what the effective bulk diffusion coefficient should be. Steady-state and transient models based on bulk diffusion are developed and used to interpret the data. Design calculations are then performed with the verified models to determine the steady-state inventory and time to reach equilibrium for a full-scale fusion blanket

The LISA-1 and TRIO in-pile tests

The in-pile tests TRIO and LISA-1 involve measurement of in-situ tritium release as a function of time, temperature and sweep gas conditions. These in-situ tritium recovery experiments are similar in concept to other in-pile tests such as the VOM series, Exotic, and the LILA series. TRIO used a single capsule with lithium aluminate. The results from TRIO have been compiled, evaluated and reported. The LISA-1 experiment had six test capsules: one lithium aluminate, one lithium orthosilicate (Li/sub 4/SiO/sub 4/), and four lithium metasilicate (Li/sub 2/SiO/sub 3/). A previous report gives a description of the experimental setup, experimental observations, and preliminary results. Presented herein is a more detailed evaluation of the LISA-1 experimental results for the three breeder materials. The results from LISA are then compared to those of TRIO

Liquid Li-Pb-Bi, a new tritium breeder

In light of their potential utility as tritium breeder-blanket materials, a study was conducted to identify and characterize low-melting phases in the lithium-lead-bismuth system. It is found that a low-melting ternary phase field did in fact exist, e.g., compositions with less than or equal to 20 atom percent lithium and Pb/Bi = 0.773 melted at or below 140/sup 0/C. In addition, the qualitative reactivity of Li-Bi-Pb alloys with water was tested, and although minimal evidence of exothermic chemical reaction was observed, a physical vapor explosion did occur in one of the tests

Adsorption Isotherms of Hydrogen: The Role of Thermal Fluctuations

It is shown that experimentally obtained isotherms of adsorption on solid substrates may be completely reconciled with Lifshitz theory when thermal fluctuations are taken into account. This is achieved within the framework of a solid-on-solid model which is solved numerically. Analysis of the fluctuation contributions observed for hydrogen adsorption onto gold substrates allows to determine the surface tension of the free hydrogen film as a function of film thickness. It is found to decrease sharply for film thicknesses below seven atomic layers.Comment: RevTeX manuscript (3 pages output), 3 figure

Narratives of self and identity in women's prisons: stigma and the struggle for self-definition in penal regimes

A concern with questions of selfhood and identity has been central to penal practices in women's prisons, and to the sociology of women's imprisonment. Studies of women's prisons have remained preoccupied with women prisoners’ social identities, and their apparent tendency to adapt to imprisonment through relationships. This article explores the narratives of women in two English prisons to demonstrate the importance of the self as a site of meaning for prisoners and the central place of identity in micro-level power negotiations in prisons

Electronic transport in polycrystalline graphene

Most materials in available macroscopic quantities are polycrystalline. Graphene, a recently discovered two-dimensional form of carbon with strong potential for replacing silicon in future electronics, is no exception. There is growing evidence of the polycrystalline nature of graphene samples obtained using various techniques. Grain boundaries, intrinsic topological defects of polycrystalline materials, are expected to dramatically alter the electronic transport in graphene. Here, we develop a theory of charge carrier transmission through grain boundaries composed of a periodic array of dislocations in graphene based on the momentum conservation principle. Depending on the grain boundary structure we find two distinct transport behaviours - either high transparency, or perfect reflection of charge carriers over remarkably large energy ranges. First-principles quantum transport calculations are used to verify and further investigate this striking behaviour. Our study sheds light on the transport properties of large-area graphene samples. Furthermore, purposeful engineering of periodic grain boundaries with tunable transport gaps would allow for controlling charge currents without the need of introducing bulk band gaps in otherwise semimetallic graphene. The proposed approach can be regarded as a means towards building practical graphene electronics.Comment: accepted in Nature Material