RD&D-Programme 2004 - SKB

adiation shield. The radiation shield has two telescopic parts. The upper part is fixed and fitted
with a movable radiation-shielding hatch on top. The lower part can move vertically so that
the canister can be raised and lowered. At the bottom is a turntable that can rotate the canister,
which is required for electron beam welding, machining and nondestructive testing. The canister
is prepared for welding in the preparation station (5). The canister is docked from beneath in a
similar manner as at the handling cell. (Applies to the following work stations as well.)
The atmosphere in the canister is changed via a valve in the steel lid, the air is evacuated and
the canister is filled with argon. The steel lid is then leak-tested. In the cell, the canister’s joint
surface is also inspected and cleaned if necessary, after which the copper lid is lifted down onto
the canister.
Electron beam welding: At the welding station (6), the copper canister is docked to a vacuum
chamber inside the station. After docking, the copper lid is lifted up and the chamber is vacuumpumped,
as is the gap between the insert and the copper shell. The copper lid is then put back
and the copper canister is sealed by EBW. During welding the canister is rotated around its axis
on the turntable in the transport frame.
Friction stir welding: At the welding station (6), the canister is docked from beneath in a
similar manner as at the handling cell. The copper canister is sealed by FSW. During welding,
a clamping system holds the canister and the lid while the welding head rotates around the
canister.
In the Non Destruction Testing (NDT) station (7), the weld joint is tested with respect to the
quality of the weld. The methods used are radiographic and ultrasonic testing. Depending on
what the final quality requirements on the welds are, eddy current testing may also be used.
If the weld fails NDT but contains reparable defects, the canister is taken back to the welding
station, where it is repaired. Then the quality of the weld is checked once again. In cases where
the weld cannot be repaired, the transport frame with the rejected weld is put aside so that it
does not obstruct normal production. At a suitable opportunity, the canister is transported back
to the station for machining, where the copper lid is cut open by means of the milling machine.
The copper lid is then lifted off, after which the canister is transported to the handling cell.
There the fuel is transferred to an empty transfer canister standing in one of the drying positions.
The copper canister is decontaminated in the active workshop (19) and the copper shell is sent
to recycling. The insert is reused in a new canister. The unloaded fuel assemblies in the handling
cell are transferred to a new canister.
If the canister meets the quality requirements, it is transported to the machining station (8),
where the weld joint and the area around it are machined to a smooth finish in accordance with
the canister’s other shape and dimensional requirements. In the transfer position in the transport
corridor (9), the canister is lifted out of the canister sleeve, after which the canister sleeve is
lifted out of the transport frame. In the decontamination cell (10), smear tests are performed on
the canister to make sure it is free of surface contamination. If decontamination is necessary, a
high-pressure water jet is used, after which new smear tests are performed. The surface dose rate
is also measured before the canister leaves the cell.
In the transfer position in the dispatch hall (11), the canister is loaded into the transport cask,
after which the transport cask lid is fitted. Via the dispatch hall (12), the canister transport
cask is moved to the transport air lock (13), where it is lifted down onto a transport frame and
secured in the horizontal position. In the transport air lock the cask is inspected, after which it is
removed by a terminal vehicle. If transport to the deep repository does not begin immediately,
the cask is placed in a store awaiting transport. The store is also a temporary holding site for
empty canister transport casks.
96 RD&D-Programme 2004