Thermal analysis of repository for spent EPR-type fuel

    Research output: Book/ReportReport

    Abstract

    This report contains the temperature dimensioning of the KBS-3V type nuclear fuel repository in Olkiluoto for the EPR fuel canisters, which are disposed at vertical position in the horizontal tunnels in a rectangular geometry according to the preliminary Posiva plan. The disposed canisters produce residual heat due to decay (or disintegration) of radioactive products. The decay heat is conducted to surrounding rock mass. The thermal diffusivity of the rock is low and the heat released from the canisters is spread into the surrounding rock volume quite slowly causing thermal gradient in the rock close to canisters and the canister temperature is increased re-markably.

    The maximum temperature on the canister surface is limited to the design temperature of +100°C. However, due to uncertainties in thermal analysis parameters (like scattering in rock conductivity or in predicted decay power) the allowable calculated maximum canister temperature is set to 90°C causing a safety margin of 10°C. The allowable temperature is controlled by adjusting the space between adjacent canisters, adjacent tunnels and the distance between separate panels of the repository and the pre-cooling time affecting on power of the canisters.

    The temperature of canister surfaces can be determined by superposing analytic line heat source models much more efficiently than by numerical analysis, if the analytic model is first calibrated by numerical analysis (by control volume method). This was done by comparing the surface temperatures of a single canister calculated numerically and analytically.

    For the Olkiluoto repository of one panel having 945 EPR canisters was analyzed. The analyses were performed with an initial canister power of 1830 W. The analyses gave as a result the canister spacing (7.7-10.9 m), when the tunnel spacing was 25 m or 40 m and the burn-up value was 40, 50 or 60 MWd/kgU.
    Original languageEnglish
    Place of PublicationOlkiluoto
    PublisherPosiva
    Number of pages37
    ISBN (Print)951-652-138-X
    Publication statusPublished - 2005
    MoE publication typeD4 Published development or research report or study

    Publication series

    SeriesPosiva Report
    Number2005-06
    ISSN1239-3096

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