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3. Results
3.1 Impact of the thermal output of the waste on the repository's dimensions
The minimum lengths of the galleries for disposal of SF and HLW are derived from heat dissipation
calculations by ensuring that the temperature limitations are respected; in the disposal concepts considered
in this study these are that the temperature has to remain below 100 °C in the bentonite
buffer for granite and at the interface between the gallery liner and the host formation for clay. As
the thermal output of the ILW canisters is negligible, the length of the ILW galleries is determined
by the number and size of the disposal containers. An overview of the estimated lengths of the SF
and HLW disposal galleries is given in Table 1.
Table 1: Estimated lengths of the SF and HLW disposal galleries
Fuel cycle scenario
Granite
A1 A2 A3 B1 B2
SF + HLW gallery length (m/TWhe) 8.89 11.12 5.52 3.63 4.49
relative SF + HLW gallery
length
Clay
(-) 1.00 1.25 0.62 0.41 0.51
allowable thermal output (50 a) (W/m) 353 332-376 365 379 379
SF + HLW gallery length (m/TWhe) 5.92 5.74 3.48 1.88 2.89
relative SF + HLW gallery
length
(-) 1.00 0.97 0.59 0.32 0.49
3.2 Evaluation of the radiological impact in the case of the reference scenario
The dose to a member of the reference group in the case of the reference scenario, which is associated
with radionuclide transport in groundwater, was calculated by making a number of simplifying
assumptions. For granite it was assumed that the canisters will fail between 1300 and 10 000 years,
and that waste matrix lifetimes are 72 000 years for HLW, 10 million years for uranium oxide SF
and 1 million years for MOX SF. For clay the canister lifetime was assumed to be 2000 years, and
the waste matrix lifetimes 100 000 years for HLW and 200 000 years for SF. For granite sorption
on the buffer and on minerals of the host formation was taken into account, whereas for clay sorption
on the buffer was neglected. The calculated doses, normalised per produced electricity, are
shown in Figs. 3 and 4 for a repository in granite and clay respectively. The radiotoxicity released
from the repository into the environment was also calculated. Table 2 compares the radiotoxicity
released over a 10 million years period with the initial radiotoxicity in the disposed waste. In most
recent safety cases, a time cut-off of 1 million years is used; however for the purpose of Red-Impact
it was considered more appropriate to consider a longer time scale of 10 million years to illustrate
that also at the very long-term no considerable change in the radiological impact has to be expected
from P&T.
Table 2: Comparison between initial radiotoxicity in the disposed SF and HLW (50 years cooling
prior to disposal) and the radiotoxicity released from the geological repository into the environment
over a 10 million years period.
Fuel cycle
Initial radiotoxicity (50 Released radiotoxicity (10
a)
Ma) Containment factor
(Sv/TWhe) (Sv/TWhe) (-)
145