RD&D-Programme 2004 - SKB

The system analyses will be largely based on other supporting material that is collected and
documented in preparation for the applications. The most important supporting documents are:
• System descriptions.
• Facility descriptions.
• Preliminary safety reports (PSRs) for the facilities.
• Alternative studies regarding technical solutions for encapsulation, transportation and deep
disposal.
• Safety assessment.
The execution of the safety assessments, especially Sysinka, has been planned in detail and the
work has begun. Their initiation has been carried out in dialogue with the authorities, within the
framework of the established consultation process.
A2.3.3 Long-term safety
The ultimate purpose of large parts of the implementation programme for spent nuclear fuel is
to bring about a safe repository for spent nuclear fuel. Since the development work on the KBS
concept started in the late 1970s, SKB has established a number of principles which together
can be said to comprise the safety philosophy for achieving this purpose. These principles are
summarized below, in accordance with the wishes expressed by the authorities in conjunction
with the regulatory review of RD&D-Programme 2001. In addition, a summary is given of the
plans for reporting of safety assessments in conjunction with the permit applications for the
encapsulation plant and the deep repository. The method for SKB’s safety assessments is dealt
with from a more technical perspective in Chapter 14.
Safety principles
Spent nuclear fuel is hazardous for a very long time. The first principle is therefore to find
a long-term stable environment for a repository. Natural variations in the climate mean that
we can expect dramatic changes with permafrost and continental ice sheets in Sweden within
time frames on the order of thousands of years. Society is changing at a much faster rate.
Far-reaching and unpredictable changes cannot be ruled out, even in comparatively short
time frames. Human-induced climate changes may also occur much sooner than the expected
natural variations. In view of considerations such as these, geological environment at depths of
hundreds of metres are seen as being the most realistic for a repository. Geological conditions in
Sweden have led to the selection of granitic crystalline bedrock as the most suitable geological
environment.
The repository will be built on a site where the bedrock can be assumed to be of no economic
interest to future generations. For example, it must not contain minerals that might become
economically attractive in the future.
Another principle is to surround the spent fuel with multiple protective barriers. The purpose of
the barriers is primarily to isolate the fuel, and, if this isolation should be breached, to retard the
dispersal of any radionuclides that might be released. The fuel is placed in corrosion-resistant
copper canisters with a cast iron insert that lends the canisters mechanical strength. The copper
canisters are surrounded by a buffer of bentonite clay in deposition holes at a depth of approximately
500 metres in the crystalline bedrock. The bentonite protects the canisters from minor
rock movements and retards the ingress of the corrosive substances that are present in low
concentrations in the groundwater. The rock in itself comprises a mechanically and chemically
long-term stable environment for canisters and bentonite. The canisters are therefore an isolating
barrier with a very long lifetime in the environment offered by the buffer and the rock.
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