RD&D-Programme 2004 - SKB

SKB has devised a quality system for the different fabrication processes used in canister fabrication.
This system includes procedures that describe how qualification of both suppliers and
fabrication processes is done.
Conclusions in RD&D 2001 and its review
The choice of methods for sealing and testing the canister influence the design of the encapsulation
plant and should also have been made at the time of the application for a permit to build the
plant. At that time there will also be a programme for qualification of the methods. Qualification
of the methods will be done at a later stage, prior to encapsulation of the spent fuel.
SKI’s viewpoints on qualification of the sealing method are largely the same as their viewpoints
on nondestructive testing (see below).
Newfound knowledge since RD&D 2001
A strategy has been devised for establishing the reliability, robustness and repeatability of
the welding methods for canister sealing. This strategy is based on statistical methods. Such
methods have been used with great success since the 1950s to develop and design industrial
processes. Experiments based on a statistical approach are often used to model and optimize the
response of a system, but the focus may also be on studying the system’s stability (the variance
of the response). The choice of a suitable experimental plan for a given welding method has
been made on the basis of the number of factors involved and the degree of detail with which
the studied domain is to be described. A more detailed description of the programme has been
published and is presented in Chapter 6 under the relevant welding method.
Programme
Welding trials and testing of welds will, according to plans, be conducted during 2004.
Evaluation of the results will take place during 2005. The results are important both for the
choice of welding method and for obtaining input data regarding the encapsulation process for
the deep repository’s safety assessment.
SKB plans to carry out a project during 2004 aimed at studying the prerequisites and the
overall forms for qualification of fabrication and welding methods. SKB intends to present a
programme for this at the time of the permit application. SKB will keep SKI informed of the
preparation of this programme.
A milestone that can already be defined now is the preparation of a programme by mid-2006
for determining the reliability of the fabrication methods. The programme will be carried out in
preparation for the planned safety assessment for the deep repository, SR-Site.
The connection between qualification and safety assessment is important, since the qualification
goals for fabrication and welding processes as well as nondestructive testing must be set so
that safety in the deep repository is guaranteed. Figure 7-1 shows the timetable for compiling
supporting material for the various safety assessments. Data from the probabilistic safety
assessment are also expected to be available prior to SR-Can, see section 14.2.
As is evident from the timetable, efforts during the period 2005–2008 will be aimed at gathering
data on the reliability of the fabrication processes for SR-Site.
88 RD&D-Programme 2004