No abstract available

No abstract available

[en] This paper summarizes the development of an advanced digital computer thermal hydraulics model for nuclear power plant simulation. A review of thermal hydraulics code design options is presented together with a review of existing engineering models. CAE has developed an unequal temperatures-unequal velocities five equation model based on the drift flux formalism. CAE has selected the model on the basis that phase separation and thermal non-equilibrium are required to simulate complex and important phenomena occurring in systems such as reactor cooling systems (RCS) and steam generators (SG). The drift flux approach to phase separation and countercurrent flow was selected because extensive testing and validation data supports full-range drift flux parameters correlations. The five equation model was also chosen because it conserves important quantities, i.e. mass and energy of each phase, and because of numerical advantages provided by the case of coupling phasic mass conservation equations with phasic energy conservation equations. The basis of CAE's model as well as supporting models for convection and conduction heat transfer, break flow, interphase mass and heat transfer are described. Comparison of code calculations with experimental measurements taken during a small break LOCA test with the OTIS facility are presented. The use of such advanced thermal hydraulics model as plant analyzer considerably improves simulation capabilities of severe transient as well as of normal operation of two phase systems in nuclear power plants. (orig./HP)

[en] This paper summarizes the development of an advanced digital computer thermal hydraulics model for real-time full scope power plant simulators which as been carried out by the authors. A review of thermal hydraulics code design options is presented together with a review of existing engineering models. They developed an unequal temperatures-unequal velocities 5 equation model based on the drift flux formalism

[en] This paper presents the first experimental results of the thermal behavior of AECL's CANSTOR spent fuel dry storage module. The CANSTOR module is an air-cooled concrete vault about 22 m long, 8 m wide and 7 m high. It can store 12000 CANDU spent fuel bundles inside 200 baskets which are stacked into two rows of 10 storage cylinders. The first module was built on the site of Hydro-Quebec's Gentilly-2 station during the summer of 1995. Dissipation of the residual heat generated by the spent fuel is a major factor in spent fuel dry storage design and one of the key elements for its licensing. The fuel temperature must be kept below 160 deg C to avoid oxidation. Experiments on a mock-up and calculations showed that the air cooling circuit provides at least 15 deg C margin for the fuel with 6-year cooled fuel subject to the ambient design temperature of 40 deg C. Nevertheless, the Atomic Energy Control Board of Canada (AECB) requested Hydro-Quebec to monitor the temperatures and limit the age of the fuel to more than 8-year cooled. During the construction, fourteen temperature sensors were installed to measure the temperature of the air, concrete and top of storage cylinders. A computer based data acquisition system has been used to collect the data, starting before the first fuel was loaded. The first loading campaign occurred during the fall of 1995, mainly during the months of October and November. The module was half filled with 6000 bundles that had been cooled in the spent fuel bay for more than 8 years, in accordance with the AECB license. No loading was done during the 1995-1996 winter. This provided a few months of data with quasi-constant power dissipation. This paper presents this data and compares it with the calculations used in support of the licensing submission. It is shown that fuel of much less than 8-year cooled could be loaded into the CANSTOR module. (author)

[en] A postulated rupture in one of the large diameter pipes in the primary circuit of a CANDU reactor could lead to degraded fuel cooling in several fuel channels. The resulting increase in the sheath temperature could lead to failure of fuel sheathing and release of fission products. For scenarios where Emergency Core Cooling Injection is not available (LOECI), the resulting increase in the sheath temperature would be much more significant and the amount of the fission products would be much more important. This paper describes the investigation of a new analysis methodology for calculating the source term for fission products released to the containment and for evaluating the radiological consequences (doses) to equipments in containment. (author)

[en] The objective of this paper is to identify standardized ways of data exchange between scientific codes compared to the current ad-hoc case by case approach. The Hierarchical Data Format (HDF) developed by the National Center for Supercomputing Applications (NCSA) is recommended. To demonstrate feasibility, a prototype application of HDF for data exchange between two Canadian Industry Standard Toolset (IST) codes, SMART (fission product behaviour in containment) and ADDAM (atmospheric dispersion and public dose calculation), was successfully developed and tested. (author)

[en] PARSOAR project is one of the scientific projects on hydrogen risk in nuclear power plants co-sponsored by the European Commission in the Fifth Euratom Framework Program and the Swiss government. It is one of the components of the 'Safety Accident Management' (SAM) cluster that is focusing on review of severe accident risks and on development of countermeasures for defence-in-depth. The first objective is to carry out a state-of-the-art on passive autocatalytic recombiners (PAR) to constitute a database helpful for the PAR-designers, nuclear power plant designers and utilities, and safety authorities. The second objective is to elaborate a handbook guide that defines an approach for implementing catalytic recombiners in nuclear power plants, and that proposes recommended practices to support the detailed implementation by individual nuclear actors. The third objective is to identify the needs in terms of complementary experimental qualification or computer code developments about the hydrogen risk in nuclear power plants. It is also recommended that future experimental tests and numerical modelling should concentrate on the remaining issues of (a) lowering of existing uncertainties about hydrogen sources as core reflood or the reactions between boron carbide and steam or uranium and steam, (b) completing the experimental qualification of catalytic recombiners for existing and future nuclear power plant applications, and (c) performing well-qualified couplings between computational fluid dynamics computer codes and numerical models simulating PAR-behaviour (thanks to some global and well-instrumented experiments reproducing a complete reference accident sequence in presence of catalytic recombiners). Such areas to be considered for future work could be integrated in the scope of a European hydrogen network of excellence, in the framework of the Sixth Euratom Framework Program (2002-2006)

[en] It has recently been demonstrated that the dramatic effects of plasma precipitation and convection on the composition and dynamics of the polar thermosphere and ionosphere include a number of strong interactive, or feedback, processes. To aid the evaluation of these feedback processes, a joint three dimensional time dependent global model of the Earth's thermosphere and ionosphere was developed in a collaboration between University College London and Sheffield University. This model includes self consistent coupling between the thermosphere and the ionosphere in the polar regions. Some of the major features in the polar ionosphere, which the initial simulations indicate are due to the strong coupling of ions and neutrals in the presence of strong electric fields and energetic electron precipitation are reviewed. The model is also able to simulate seasonal and Universal time variations in the polar thermosphere and ionospheric regions which are due to the variations of solar photoionization in specific geomagnetic regions such as the cusp and polar cap

[en] This paper deals with the thermal performance of the MACSTOR spent fuel dry storage system. The thermal performance of this air cooled storage structure is one of the key factors for its design and licensing. The results of some experiments aimed at demonstrating the thermal performance of a full-scale mock-up of the MACSTOR module are presented. The experimental results of MACSTOR tests reinforce AECL's confidence in its design. Calculations using a PRESCON2 model of the MACSTOR mock-up were compared to the experimental values and shown to be conservative for the prediction of maximum concrete temperature and concrete temperature gradient, two key elements for the licensing of spent fuel dry storage systems. Therefore, this exercise demonstrates that the thermal performance of dry air cooled structures can be modeled by a relatively simple analytical tool. It is planned to use these validated analytical capabilities to assess the thermal performance of the CANSTOR module. (author) 3 refs., 1 tab., 7 figs