NATURAL CIRCULATION MODELLING

The prediction of nuclear reactor thermal-hydraulic behaviour under operational and accidental conditions can potentially be made by 

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TABLE XXIV-7. THERMAL-HYDRAULIC RESULTS CALCULATED WITH NATURAL CIRCULATION MODEL... 

The natural recourse for this situation is to use numerical solution methods for both steady-state and transient analyses. The systems-analysis codes that are used for design and safety studies can all handle the coupled NCL case. At the same time, local special- and general-purpose natural-circulation models, methods, and codes are being developed for applications to Gen IV reactor concepts. 

Blumenkrantz and Taborek (1971) applied the density effect model of Boure to predict instability in natural-circulation systems in thermosiphon reboil-ers used in the petrochemical industry. An important conclusion of their work was that similarity analysis in terms of the model s dimensionless groups can be used to extrapolate threshold stability data from one fluid to another. 

Modeling efforts aimed at simulating the worldwide diffusion of the cloud begin to appear preliminary results gave rather faster transit times than have actually been observed (Capone et al., 1983 Pitari et al., 1984). While these results may be due to the scarce resolution of the circulation models, they may also point to the rather complex nature of the aerosol dynamics (see e.g. Crescentini and Fiocco, 1983). Related anomalies were found by us in utilising the meridional distribution model of Cadle et al. (1976), in efforts to simulate the effects of Mt. Agung (Fiocco et al., 1977). 

Covey C., Schneider S. H. and Thomson S. L., Global atmospheric effects of massive smoke injections from a nuclear war results from general circulation model simulations. Nature (submitted) (1984). 

Joussaume S., Jouzel J., and Sadourny R. (1984) A general circulation model of water isotope cycles in the atmosphere. Nature 311, 24-29. 

Most of the evaluation of the He plumes in the ocean has been qualitative or semi-quantitative in nature. However, there are increasing attempts to incorporate He into Ocean General Circulation Models (OGCMs) in order to understand how such models ventilate the mid-depth and deep-water masses. An early attempt of He simulations in an OGCM has been documented by Farley et al. (1995). The results of the model simulations indicate that the model can roughly close the helium balance and reproduces most of the major observed features of the He field in the ocean. At the same time, the simulations show many shortcomings of the model and future work will contribute to... 

Figure 13 (Right) Global ocean circulation model results from 12 different coarse-resolution models participating in OCMIP-2 compared to WOCE data for natural A C on a meridional Pacific section. The model groups are identified in each subpanel and in Table 1 All of the models used the same chemistry and boundary conditions.

Several thermohydraulic calculations and other analyses were carried out to determine success criteria for the event tree modelling, support the event sequence development and assist the initiating event analysis. These analyses were performed by the Paks NPP and by the KFKI Atomic Energy Research Institute supporting the SPSA activity. The thermohydraulic calculations were performed for several LOCA scenarios during cooldown and during natural circulation. 

ABSTRACT This study addresses the time-variaut reliability assessment in relation to systems exhibiting a non-stationary random process during their operation, such as thermal-hydrauhc passive systems for advanced reactors, relying on natural circulation. The reliability assessment efforts conducted so far don t deal with this specific aspect the dependence upon time is usually ignored, or at most the system unavaUabUity is intended to he assessed per mission time, during which the parameter values, as t-h parameters for instance, are assumed as constant quantities. The paper presents an effort for a consistent approach to model and evaluate the natural circulation passive systems, in terms of time-variant performance parameters, as for instance mass flow-rate and thermal power, to cite any. 

An integral sodium experiment has been carried out with a partial core model composed of seven subassemblies, inter-wrapper gaps, an upper plenum and dipped cooler. The tests for core-plenum and cooling system interaction were almost completed. A series of tests is under way focusing inter-wrapper flow under conditions of natural circulation decay heat removal. 

Global climate models Computer models (general circulation models) which simulate past, present, and future climates from changes in greenhouse gas concentrations and natural forcing factors. 

During normal operation of the reactor, core heat is removed by the natural circulation of Pb-Bi coolant. The coolant at 1173 K enters the fuel tube in the lower plenum, absorbs the reactor heat, and at 1273 K reaches the upper plenum. Twelve sodium heat pipes transfer heat from the upper plenum to the system of heat utilizing vessels. Thermal-hydraulic analyses were carried out to study natural circulation and the effect of orificing in the primary loop. A computer model based on the law of conservation of momentum was developed for this analysis a simplified model of the primary loop is shown in Fig. XXIX-7. 

The RCCS modelling and qualification are supported by the tests performed in a High Pressure Natural Circulation Rig (CAPCN) and covering thermal hydraulics and reactor... 

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