[en] Utilizing a new complex-band-structure technique, the electronic structure of model Si-Si/sub 1-x/Ge/sub x/ and MOS superlattices has been obtained over a wide range of layer thickness d (11 less than or equal to d less than or equal to 110 A). For d greater than or equal to 44 A, it is found that these systems exhibit a direct fundamental band gap. Further calculations of band-edge effective masses and impurity scattering rates suggest the possibility of a band-structure-driven enhancement in electron mobility over bulk silicon

No abstract available

[en] The results are presented of tests conducted at the Trojan nuclear power plant near Rainier, Oregon, to assess the electrical noise filtering capabilities of the input buffer circuits to be used in a solid state plant logic system. The general levels of electrical noise induced in different types of cables laid in a system of 480-V power cables in a typical fashion are analyzed. The tests confirmed that the input buffers had adequate filtering capability when used in typical power plant applications. The test data are discussed pointing out its limitations and the importance of proper cable selection and routing

[en] Dilute chemical decontamination of primary heat transport system of Madras Atomic Power Station (MAPS) 1 and 2 units was carried out successfully in December 1993 and April 1995 respectively. The need for such decontamination campaigns had been recognised quite early at MAPS and exploratory work began in 1989 itself. This paper gives an account of work done at MAPS, like identification of the facilities required, inputs to designers regarding site operational requirements and layout/space constraints, preparatory activities preceding the first campaign in unit-1, the procedure used along with the experiences during the actual campaign. Changes brought about for unit-2 based on operating experience in unit-1 and further improvements that are desirable are presented. (author)

[en] Full text: At present NPCIL has fourteen PHWRs (Pressurised Heavy Water Reactors) and two BWRs (Boiling Water Reactors) under operation. In addition, three PHWRs are under commissioning and two VVERs are in the advanced stage of construction. The achievement of optimum chemistry parameters in the process systems of a nuclear power station during commissioning and operation facilitates safe, efficient and economic plant operation with high availability factors. One of the main concerns in the operation of a nuclear power station is the radioactivity build-up on the out-of-core surfaces of the coolant/reactor systems and high man-rem (Person-Sievert) consumption during maintenance activities. Appropriate technology like In-situ Decontamination techniques need to be developed for reducing the fields. Further, optimisation of the chemical parameters based on the latest developments in the field of Water Chemistry along with the selection of suitable structural materials results in low radiation fields and also helps the PLEX (Plant Life Extension)/ageing management programmes of the station. However these programmes need the support of R and D groups and strong commitment from the management. During the recent years, Flow Accelerated Corrosion (FAC) in the secondary and primary circuits assumed significance and problems like thinning/development of pinholes in carbon steel surfaces have surfaced. In addition to material selection, optimum chemical/process conditions play an important role in mitigating this phenomenon. Further, Corrosion and Biofouling are the major problems in the coastal based power stations (like MAPS and TAPS) where sea water is used for cooling the main condensers. The experience gained during the past few years of operation along with some case studies are presented in this talk

[en] An interferometer for broadband single-cycle THz pulses is developed based on the Michelson configuration. Total internal reflection of THz pulses in high-resistivity silicon prisms provides a nearly 180^o phase shift of one arm relative to the other to achieve destructive interference. We show that due to automatic compensation for laser fluctuations by the interferometer, it is possible to measure the index and absorption of thin-film samples with more accuracy than is achievable with standard THz time-domain spectroscopy. We demonstrate characterization of the complex index of refraction of 2 μm thick Mylar (polyester) films. By measuring the signal amplitude directly in the time domain, the interferometer can be used for rapid measurements of film thickness with a resolution of better than 1 μm. Copyright 2001 American Institute of Physics

[en] The clean up of soils contaminated with petroleum products is associated with several challenges, especially of analytical methodologies and data interpretation. Petroleum products comprise a vast continuum of hydrocarbons from short chain aliphatic and simple aromatic hydrocarbons in gasoline to kerosene, diesel, and heavy oils and to lubricating oils or vaseline, each gradation with increasing carbon chains and complexity. Gasoline alone may contain over twelve hundred compounds. Properties of these vary and this will be of analytical concern. Treatment technology and site remediation progress will lean heavily on analytical techniques that are accurate, reproducible and of real time value. This paper examines the various analytical techniques available along with their special features. Some new methods currently under development are also discussed. These include: (1) High Resolution Chromatograph method which can reveal the detail composition of the contaminants; (2) Supercritical Fluid Extraction which can save time for the analysis; and (3) Fingerprinting which can be used to determine the responsible party for the spill. In addition, the interference due to weathering is also examined

[en] The containment isolation at MAPS is provided by two dampers in series in the supply and exhaust of RB ventilation system ducts. The pneumatically operated isolation dampers are activated by Boiler room pressure high signal or containment high activity signal through respective relay logics and solenoid valves. Scenario of one of the exhaust dampers closing spuriously during reactor operation and during the period of corrective action, the requirement of damper to be kept open was taken up for study. To review the Containment Isolating System (CIS) reliability Risk Spectrum Fault Tree (FT) methodology was used to determine the Probability of Failure on Demand(PFD) and spurious failure rates of CIS dampers. Suggested improvements in the logic design to reduce the PFD and spurious failure rate are discussed. (author)

[en] Madras Atomic Power Station is the first Nuclear Power Station indigenously designed, developed and constructed in India. The commercial operation of unit 1 and unit 2 started during 1984 and 1986 respectively. Over the years of operation after commissioning, many equipment have become obsolete and some of the components required replacement. As a part of the life extension and ageing management, number of up gradation activities were taken up during the planned Enmasse Coolant Channel Replacement Programme in Unit 2. This paper deals briefly about the upgradation activities carried out on mechanical systems. The following benefits were achieved by carrying out the upgradation/ageing management activities. 1) Enhanced reliability on safety related systems 2) improvement in performance 3) replacement of aged/obsolete equipment with latest/improved design. (author)

[en] The effects of rapid solidification and aging of Ti alloys with monotectoid forming W and further additions of eutectoid forming elements such as Ni and Si were investigated. The alloys (in wt%) Ti-36W, Ti-19W-2.6Ni, and Ti-17W-2Ni-0.3Si were rapidly solidified (RS) into ribbons by the chill block melt spinning (CBMS) technique. The RS ribbons were heated at two sub-eutectoid temperatures (550⁰C and 650⁰C) for varying times (1 minute to 170 hr) to evaluate aging response. Aging of Ti-36W at 550⁰C and 650⁰C resulted in hardness peaks of 650Hv and 600Hv, respectively, after 1 hr. The effect of further alloying with Ni, an active eutectoid former, was evident in the aging of Ti-19W-2.6Ni