[en] The objective of this study is to advise FSA on the extent to which its current models for calculating air concentration and deposition for continuous releases close to sites with many buildings are adequate, whether there are circumstances for which the explicit modelling of building wake effects is required, and, if so, to recommend an appropriate model for this. The study considered the predictions of simple Gaussian models and the ADMS model. Results from the models are presented and compared, for a range of on-site building configurations and release locations. In addition, the extent to which details of the buildings on the site are required in ADMS is considered. The results indicate that buildings only affect the predicted concentration in a relatively small area around the site (less than 1 km from the site even for tall buildings). For dose calculations beyond 1 km, no allowance is required for modelling building effects. The results suggest that modelling the effects of buildings can be sensitive to a number of parameters and care should be used in interpreting results for locations within the region affected by buildings. However, because ADMS explicitly treats these factors, it is considered a better model for use than those based on a simple Gaussian approach. (author)

[en] Residual radioactive material guidelines for uranium were derived for the Ventron site in Beverly, Massachusetts. This site has been identified for remedial action under the Formerly Utilized Sites Remedial Action Program of the US Department of Energy (DOE). The derivations for the single radionuclides and the total uranium guidelines were based on the requirement that the 50-year committed effective dose equivalent to a hypothetical individual who lives or works in the immediate vicinity of the Ventron site should not exceed a dose of 100 mrem/yr following remedial action. The DOE residual radioactive material guideline computer code, RESRAD, which implements the methodology described in the DOE manual for implementing residual radioactive material guidelines, was used in this evaluation

[en] General Electric (GE) has proposed an advanced boiling water reactor, the Simplified Boiling Water Reactor (SBWR), which will utilize passive, gravity-driven safety systems for emergency core coolant injection. The SBWR design includes no recirculation loops or recirculation pumps. Therefore the SBWR will operate in a natural circulation (NC) mode at full power conditions. This design poses some concerns relative to stability during startup, shutdown, and at power conditions. As a consequence, the NRC has directed personnel at several national labs to help investigate SBWR stability issues. This paper will focus on some of the preliminary findings made at the INEL. Because of the broad range of stability issues this paper will mainly focus on potential geysering instabilities during startup. The two NC designs examined in detail are the US Humboldt Bay Unit 3 BWR-1 plant and Dodewaard plant in the Netherlands. The objective of this paper will be to review operating experience of these two plants and evaluate their relevance to planned SBWR operational procedures. For completeness, experimental work with early natural circulation GE test facilities will also be briefly discussed

[en] The primary coolant system in light water reactors is subjected to corrosion on surfaces and to the deposition of corrosion products on surfaces. These conditions occur both in-core and out-of-core and inhibit the thermal transfer across the layers. The deposition of such crud layers on reactor fuel element surfaces is a recognized problem that can affect performance and potentially limit the maximum power rating of the fuel. When boiling is present with such crud layers, wick boiling has been postulated to be the dominant mode of heat transfer, at least when it can be assumed that the structure of the deposit includes chimneys, i.e., large pore holes that penetrate deeply into the deposit and almost perpendicularly to the surface on which the deposit has formed. The wick boiling mechanism is explained. In this study, the wicking limit for porous deposits with chimneys is investigated. The major highlights gained from this study include: (1) the dryout heat flux for a heating surface may be caused by the Helmholtz instability due to high-velocity gas jets or by the wicking limit. (2) The dryout heat flux based on the wicking limit decreases very rapidly with decreasing porosity, with decreasing size of particles in the porous layer, and with increasing crud thickness. (3) Physically, it is expected that the chimney population would increase with increasing heat flux. Using a power law relation between heat flux and chimney population density, much lower wicking limits or thinner deposits are predicted

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[en] Experiments on collective ion acceleration by means of the formation of a virtual cathode have been carried out for a number of years in the Soviet Union and in the United States. Recently, there has been renewed interest in the subject as a possible means of accelerating ions to very high energies. By understanding the physics underlying the acceleration process it may be possible to determine the feasibility of virtual cathode staging for very high energy ion production. For this reason, a theoretical and computational effort is underway at Los Alamos in order to clarify the basic issues of collective ion acceleration by means of virtual cathodes. To support the theoretical effort, simulations were done with the fully electromagnetic and relativistic particle-in-cell code ISIS (in a one-dimensional mode) and the electrostatic one-dimensional code BIGONE. In the simulations, an electron beam of density 6 x 10¹¹cm^-3 is injected into a one-dimensional box of length L. To supply the necessary ions for collective acceleration, a plasma source containing both ions and electrons was initialized near the emitting boundary. Of prime interest in this study was to understand the dynamics of virtual cathode formation and the dynamics of the acceleration process for the ions. In particular, the question of whether the ions are accelerated by a moving potential well or hydrodynamic pressure due to ambipolar expansion is of primary interest. 3 refs., 5 figs

[en] The CEBAF RF control system uses a heterodyne scheme to convert the cavity frequency of 1497 MHz down to a more manageable IF frequency of 70 MHz. At this IF frequency all the signal processing is done. Because of the tight system requirements of ±0.2 degree phase stability and ±2·10^-5 amplitude stability, CEBAF uses new technologies such as high speed analog circuits at 70 MHz. Major themes include components for signal processing in the control system and recent system performance tests. 6 refs., 6 figs

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