Databank

POSIVA Report 1996-11

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Name:

Criticality Safety Calculations for the Nuclear Waste Disposal Canisters

Writer:

Markku Anttila

Language:

English

Page count:

27

ISBN:

951-652-010-3; 1239-3096

Summary:

Working report: CRITICALITY SAFETY CALCULATIONS FOR THE NUCLEAR WASTE DISPOSAL
CANISTERS




The criticality safety of the copper/iron canisters developed for the final disposal of the Finnish
spent fuel has been studied with the MCNP4A code based on the Monte Carlo technique and with
the fuel assembly burnup programs CASMO-HEX and CASMO-4.

Two rather similar types of spent fuel disposal canisters have been studied. The differences
between the canisters result from properties of the spent fuel assemblies planned to be disposed of
in them. One canister type has been designed for hexagonal VVER-440 fuel assemblies used at
the Loviisa nuclear power plant ("IVO canister") and the other one for square BWR fuel bundles
used at the Olkiluoto nuclear power plant ("TVO canister").

A spent fuel disposal canister must meet the normal criticality safety criteria. The effective
multiplication factor must be less than 0.95 also when the canister is in the most reactive credible
configuration (optimum moderation and close reflection). Uncertainties in the calculation methods
may necessitate the use of an even lower reactivity limit.

Based on the results of this study the IVO canister loaded with eleven similar VVER-440
assemblies with the initial enrichment of 3.6% fulfills the criticality safety criteria, if the discharge
burnup of the assemblies is more than 4 MWd/kgU. The TVO canister loaded with eleven BWR
assemblies with the initial enrichment of 3.5% and without burnable absorbers meets the same
criteria, if the discharge burnup of the assemblies is more than 10 MWd/kgU. An increase of the
average enrichment by 0.1 percentage might be compensated by increasing the minimum
discharge burnup by one MWd/kgU.
CRITICALITY SAFETY CALCULATIONS FOR THE NUCLEAR WASTE DISPOSAL
CANISTERS




The criticality safety of the copper/iron canisters developed for the final disposal of the Finnish
spent fuel has been studied with the MCNP4A code based on the Monte Carlo technique and with
the fuel assembly burnup programs CASMO-HEX and CASMO-4.

Two rather similar types of spent fuel disposal canisters have been studied. The differences
between the canisters result from properties of the spent fuel assemblies planned to be disposed of
in them. One canister type has been designed for hexagonal VVER-440 fuel assemblies used at
the Loviisa nuclear power plant ("IVO canister") and the other one for square BWR fuel bundles
used at the Olkiluoto nuclear power plant ("TVO canister").

A spent fuel disposal canister must meet the normal criticality safety criteria. The effective
multiplication factor must be less than 0.95 also when the canister is in the most reactive credible
configuration (optimum moderation and close reflection). Uncertainties in the calculation methods
may necessitate the use of an even lower reactivity limit.

Based on the results of this study the IVO canister loaded with eleven similar VVER-440
assemblies with the initial enrichment of 3.6% fulfills the criticality safety criteria, if the discharge
burnup of the assemblies is more than 4 MWd/kgU. The TVO canister loaded with eleven BWR
assemblies with the initial enrichment of 3.5% and without burnable absorbers meets the same
criteria, if the discharge burnup of the assemblies is more than 10 MWd/kgU. An increase of the
average enrichment by 0.1 percentage might be compensated by increasing the minimum
discharge burnup by one MWd/kgU.

Keywords:

File(s):

Criticality Safety Calculations for the Nuclear Waste Disposal Canisters (pdf) (332.4 KB)


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