## Abstract

This report contains the temperature dimensioning of the KBS-3H type nuclear fuel repository, where the fuel canisters are disposed at horizontal position in the horizontal tunnels according to the preliminary SKB (Swedish Nuclear Fuel and Waste Management Co) and Posiva plan.

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) 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 power of the canisters. With reasonable canister and tunnel spacing the maximum temperature 90°C is achieved with an initial canister power of 1700 W.

It became apparent that 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 verified and calibrated by numerical analysis. This was done by comparing the surface temperatures of the central canister in a single infinite canister queue calculated numerically and analytically. In addition, the results from SKB analysis were used for comparison and for confirming the calculation procedure.

For the Olkiluoto repository a reference case of one panel having 1500 canisters was analysed. The canisters are disposed in a rectangular geometry in a certain order. The calculation was performed separately for both Olkiluoto BWR canisters and Loviisa PWR canisters. The result was the minimum allowable spacing between canisters.

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) 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 power of the canisters. With reasonable canister and tunnel spacing the maximum temperature 90°C is achieved with an initial canister power of 1700 W.

It became apparent that 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 verified and calibrated by numerical analysis. This was done by comparing the surface temperatures of the central canister in a single infinite canister queue calculated numerically and analytically. In addition, the results from SKB analysis were used for comparison and for confirming the calculation procedure.

For the Olkiluoto repository a reference case of one panel having 1500 canisters was analysed. The canisters are disposed in a rectangular geometry in a certain order. The calculation was performed separately for both Olkiluoto BWR canisters and Loviisa PWR canisters. The result was the minimum allowable spacing between canisters.

Original language | English |
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Place of Publication | Olkiluoto |

Publisher | Posiva |

Number of pages | 43 |

ISBN (Print) | 951-652-125-8 |

Publication status | Published - 2003 |

MoE publication type | D4 Published development or research report or study |

### Publication series

Series | Posiva Report |
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Number | 2003-11 |

ISSN | 1239-3096 |

## Keywords

- spent nuclear fuel
- repository
- decay heat
- temperature dimensioning