[en] Reaction between Csl, U0₂₊^x, and molybdenum to form CS₂Mo0₄ was observed in a Knudsen cell mass spectrometer between 1100 and 1500 K; however, the reaction only progressed to a small extent and most Csl remained unreacted. The extent of the reaction depends on the oxygen potential of the system as well as the temperature; in these experiments it was controlled by the O/U ratio of the U0₂. However, little difference was observed between unoxidized and slightly oxidized fuel samples, corresponding to O/U ratios of 2.00 to 2.01 respectively. The experiments suggest that under normal operating conditions, Csl is expected to be more stable than CS₂Mo0₄ in the fuel. (author)

[en] This paper reviews the approach of HM Nuclear Installations Inspectorate (NII) to containment integrity in the United Kingdom (UK). NII is that part of the regulatory authority, the Health and Safety Executive (HSE), which administers the UK's nuclear site licensing system. A major part of the licensing process lies in the assessment of licensees' submissions for new and existing plant. The purpose of this paper is to: briefly review our revised Safety Assessment Principles, describe our assessment and inspection activities on the primary containment building of the Sizewell B PWR which is progressing to full power operation in 1994 and, to indicate our views on the possible directions for future research into containment design and performance. (author). 5 refs

[en] A set of phenomenological analyses have been performed for the Byron Nuclear Station containment system to quantify its performance under severe accident conditions. This assessment concludes that the current-generation, large, dry containment system employed at Byron is a robust and reliable barrier to the release of fission products during severe accident sequences. This conclusion suggests that the future containment systems plans should consider those beneficial design aspects present in the current generation of nuclear reactor containment buildings. (author). 2 figs

No abstract available

[en] In the design of reinforced concrete(RC) vessels, we have to deal with many combinations of load cases such as internal pressure, transient temperature distribution and earthquake loading. It seems to be impracticable to confirm the structural safety under each loading condition only by experiments, especially the experiments under high temperature scarcely have been reported. It is important to establish a method to simulate the behavior of the structures up to failure subjected to mechanical and thermal loads simultaneously. The purposes of this study are; 1) to evaluate the elasto-plastic analysis method for RC members under high temperature by the simulation analyses of RC beams exposed to high temperature, 2) to examine the validity of the nonlinear analysis for actual RC structures under high temperatures by the analysis of typical openings of reinforced concrete vessel due to internal pressure, thermal loads and their combined loads using 3-D solid model. In both analyses, computations are done taking into account of nonlinear characteristics of concrete and steel with temperature dependency. From the obtained results, not only qualitative but also quantitative agreement was found between the test results and computed results in the RC beam analyses many cases with respect to thermal deformations, reduction of rigidities and load carrying capacities. The validity of nonlinear analysis of RC members under very high temperatures are proven. From the results of the analyses of opening by 3-D model, the validity of the nonlinear analysis for actual RC structures under high temperatures are also shown and the unresolved issues are discussed. (author)

[en] A passive CANDU containment design has been proposed to provide the necessary heat removal following a postulated accident to maintain containment integrity. To study its feasibility and to optimize the design, multi-dimensional containment modelling may be required. This paper presents a comparison of two CFD codes, GOTHIC and PHOENICS, for multi-dimensional containment analysis and gives pressure transient predictions from a lumped-parameter and a three-dimensional GOTHIC model for a modified CANDU-3 containment. GOTHIC proved suitable for multidimensional post-accident containment analysis, as shown by the good agreement with pressure transient predictions from PHOENICS. GOTHIC is, therefore, recommended for passive CANDU containment modelling. (author)

[en] BUSCA-PSI is a computer code which predicts the aerosol scrubbing taking place when gas bubbles containing fission products rise through stagnant pools of water after a postulated severe accident. A Lagrangian formulation is adopted to follow the path of a bubble as it rises toward the surface of the pool. The BUSCA model includes most aerosol removal mechanisms which are thought to be significant, namely: Jet Impaction at tile orifice, Convection/Diffusiophoresis during steam condensation, Thermophoresis, Sedimentation, Centrifugal Impaction during bubble rise, and Brownian Diffusion. The hydraulic modelling offers a variety of options for the initial globule volume, the stable bubble size, tile bubble rise velocity, and the bubble shape. The heat and mass transfer part of tile model uses correlations found in the relevant literature. BUSCA simulations were performed to determine the decontamination factor (DF) dependence on key aerosol and thermal hydraulic parameters. The decontamination factor increases with height, pool temperature subcooling, and steam content. The decontamination factor exhibits a parabolic dependence on the particle radius. At low particle sizes, the DF is high due to Brownian Diffusion which is the dominant removal mechanism. The DF hits a minimum and then increases with particle size as Centrifugal Impaction and Sedimentation become important. In separate calculations, BUSCA was used to the simulate the aerosol scrubbing experiments performed by EPRI. For cold pool tests, the predicted scrubbing efficiencies were in a good, conservative agreement with the data for both Tin and CsI, and the discrepancies were within the reported measurement errors. For hot pool tests, the code systematically underpredicted the scrubbing DF's; this is potentially due to condensation in the gas space above the pool, a situation not currently modelled by BUSCA. The code was also tested against data produced by the Tepco-Toshiba-Hitachi experiments. The predicted DF factors were again in good, conservative agreement with the data. (author)

No abstract available

[en] Performances of the Containment System under Severe Accident conditions depend on a number of different features and components. The equipment hatch may be considered a critical component because it is a potential main contributor to the total Containment leak rate during a Severe accident and a potential (depending on the design) direct leak path between the containment atmosphere and the environment. The analytical study performed to anticipate the response of the equipment hatch of a large dry steel containment under Severe Accident condition has pointed out some questions of concern. The possible leak tightness failure mechanism are related to: the gaskets elastic characteristics degradation due to thermal and radiological aging; the deformation of the hatch sleeve induced by the containment wall; and the differential expansion between gasket material and steel. Beside, the equipment hatch may be considered a single barrier and although it is equipped with two gaskets, it is not difficult to demonstrate that a backup function cannot be assigned to the external gasket. For these reason it seems to be necessary to realize a wider application of the 'Defence in Depth' criteria in the design of this component. The DEFENDER (DEFENce in Depth Equipment hatch Requalification) might be a solution to increase the margin of safety of the equipment hatch under the Severe Accident condition. (author)

No abstract available