ABSTRACT

ACKNOWLEDGEMENTS

The results contained in this paper were obtained by the authors during the course of investigations for Atomic Energy of Canada Ltd. under AECL Purchase Order No. WS-17J-53380 with Acres Consulting Services Ltd. Dr. H. Y. Tammamagi acted as technical project officer for AECL. The views and opinions expressed in this paper are those of the authors and do not necessarily represent those of AECL.

The work described in this paper was a portion of a much larger effort for AECL. The authors wish to acknowledge the technical contributions of R. G. Charlwood, who was the program manager for Acres, M. A. Mahtab and T. D. Wiles of Acres, and P. F. Gnirk of RE/SPEC Inc. Ms. Julie S. Annicchiarico is also gratefully acknowledged for the typing of the manuscript.

INTRODUCTION

Atomic Energy of Canada Limited (AECL) initiated a program in 1975 to develop techniques for the ultimate disposal and isolation of high-level nuclear waste in deep geologic formations. A series of preconceptual design studies has since been carried out by Acres Consulting Services Limited, in association with RE/SPEC Inc., Dilworth, Secord, Meagher, and Associates Limited, and Hagconsult AB for a 1,000-m deep vault in a pluton in the Canadian Shield. Phase I of the studies dealt with design concepts, feasibility assessment, costs, and research and development requirements for a reprocessing waste vault. Phase II of the study involved detailed investigations of key design aspects of the vault, including room stability, waste container emplacement concepts and design concepts for ventilation and cooling systems. No specific constraints (thermal, mechanical or other) were placed on the design of the vault during Phases I and II of the studies.

Phase III of the studies involved a review of the basic design criteria and development of vault design concepts for both reprocessing waste (RW) and immobilized fuel (IF). The specifications used in the study included constraints on temperature of the backfill and container skin, as well as the long-term mechanical behavior of the rock mass. Results presented in this paper are for granite. In the thermal mechanical analyses, the vault was modeled in three geometric zones: container near field, room and pillar, and far field. This paper is concerned with the thermal analyses of the IF and RW vaults in the three geometric zones. Particular attention is given to the characteristic transient thermal response of the RW and IF containers, emplaced backfill and the host rock mass. The influence of backfill and rock thermal conductivity, vault extraction ratio and container arrangement within a room is presented to define the combinations of these variables which satisfy particular maximum temperature constraints.

The temperature histories resulting from the emplacement of CANDU* RW are typical of those arising from the reprocessing wastes from other reactor types (i.e. PWR and BWR) previously reported in the literature by numerous investigators. However, the temperature history arising from the emplacement of CANDU IF varies significantly from that which has been predicted for a PWR or BWR spent fuel repository. This variation is because of the difference in initial fuel composition, burnup, and subsequently different proportion of radiogenic heat producing transuranic elements and isotopes in the spent fuel.

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