Four fault tolerant architectures were evaluated for their potential reliability in service as control systems of nuclear power plants. The reliability analyses showed that human- and software-related common cause failures and single points of failure in the output modules are dominant contributors to system unreliability. The four architectures are triple-modular-redundant (TMR), both synchronous and asynchronous, and also dual synchronous and asynchronous. The evaluation includes a review of design features, an analysis of the importance of coverage, and reliability analyses of fault tolerant systems. An advantage of fault-tolerant controllers over those not fault tolerant, is that fault-tolerant controllers continue to function after the occurrence of most single hardware faults. However, most fault-tolerant controllers have single hardware components that will cause system failure, almost all controllers have single points of failure in software, and all are subject to common cause failures. Reliability analyses based on data from several industries that have fault-tolerant controllers were used to estimate the mean-time-between-failures of fault-tolerant controllers and to predict those failures modes that may be important in nuclear power plants. 7 refs., 4 tabs.

Schlieren imaging techniques were used to study the density depressions created by the ATA electron beam 37 cm after the entrance foil. Typical channel depressions were 5--10% of ambient density per pulse. Under IFR guiding channel depths as deep as 30% were seen on single pulse operation. Pulse 5 of the 5 pulse burst has passed through a channel reduced to 30% of ambient density. To lowest order, one would expect channel density depressions to scale as ({Delta}n/n) {proportional to} ({number sign} of pulses * I{sub beam}/channel area). Channel depth observations scaled roughly with beam current, {number sign} of pulses, and inversely with channel area. Pressure scaling was anomalous in that {Delta}n appeared to be less sensitive to pressure than the linear dependence expected. This would require that the energy deposition (stopping power) is independent of pressure and is a surprising result which can only be explained with collective effects. Scaling of channel expansion rates with pressure suggest classical diffusion (D {proportional to} 1/n) for times up to 200 mS. During these early times, the diffusion constant was, however, 3--5 times larger than the classical value. At later times, large scale turbulence was observed and the effective diffusion constant increased …

We have developed an assay for detecting variant erythrocytes that occur as a result of in vivo allele loss at the glycophorin A (GPA) locus on chromosome 4 in humans. This gene codes for an erythroid- specific cell surface glycoprotein, and with our assay we are able to detect rare variant erythrocytes that have lost expression of one of the two GPA alleles. Two distinctly different variant cell types are detected with this assay. One variant cell type (called N{O}) is hemizygous. Our assay also detects homozygous variant erythrocytes that have lost expression of the GPA(M) allele and express the GPA(N) allele at twice the heterozygous level. The results of this assay are an enumeration of the frequency of N{O} and NN variant cell types for each individual analyzed. These variant cell frequencies provide a measure of the amount of somatic cell genotoxicity that has occurred at the GPA locus. Such genotoxicity could be the result of (1) reactions of toxic chemicals to which the individual has been exposed, or (2) high energy radiation effects on erythroid precursor cells, or (3) errors in DNA replication or repair in these cells of the bone marrow. Thus, the GPA-based variant cell frequency …

The use of a 1-kg solid-lithium x-ray and debris shield around each fusion fuel pellet prevents vaporization of, and destructive shock waves in, the Cascade blanket granules thereby increasing their lifetime. The shield vaporizes as it absorbs energy and the vapor flows into the blanket several centimeters. The shield also increases tritium breeding and enhances vacuum pumping of high Z materials that are vaporized in the fuel pellet. Using heavy ion beams allows illumination of the fuel pellets with the restricted geometry present in Cascade. We used a 5 MJ driver with 18 beams (one 3 {times} 3 array from each end).

Fe, Ni, and V are considered trace impurities in heavy crude oils and tar sand bitumens. In order to understand the importance of these metals, we have examined several properties: (1) bulk metals levels, (2) distribution in separated fractions, (3) size behavior in feeds and during processing, (4) speciation as a function of size, and (5) correlations with rheological properties. Some of the results of these studies show: (1) V and Ni have roughly bimodal size distributions, (2) groupings were seen based on location, size distribution, and Ni/V ratio of the sample, (3) Fe profiles are distinctively different, having a unimodal distribution with a maximum at relatively large molecular size, (4) Fe concentrations in the tar sand bitumens suggest possible fines solubilization in some cases, (5) SARA separated fractions show possible correlations of metals with asphaltene properties suggesting secondary and tertiary structure interactions, and (6) ICP-MS examination for soluble ultra-trace metal impurities show the possibility of unexpected elements such as U, Th, Mo, and others at concentrations in the ppB to ppM range. 39 refs., 13 figs., 5 tabs.