significant and may lead to partial redesign, which
requires total mastery of the design and justifications
of the choices made. The ageing management
programme includes therefore a long-term
maintenance of knowledge approach to "pass the
baton" to those generations who did not take part in
the original design choices or construction.
This problem is shared with other utility companies.
It is covered by the Euratom programme.
In the USA, where the loss of knowledge and of
undocumented know-how has been identified in the
Energy sector, a study [EPRI 1] noted the risk of the
disappearance of knowledge, particularly knowledge
of design and modifications, which concern us here.
It also raises the question of the maintenance of
knowledge of feedback, but this is subject to a
specific organisation in France.
2 THE PROBLEM OF 900 MW NPP
RELAY CIRCUITS
2.1 The I&C of 900 MW power plants
Relay technology is highly significant for
instrumentation and control (I&C) in the oldest
nuclear units of the French reactor stock, the 900
MW nuclear power plants (NPP), where there are
tens of thousands of relay circuits, involved in all
functions. The traceability of documentation (design,
modifications, feedback) has always been very
important.
In so far as design documentation is concerned, it
mainly dates back to end of the 1970's, the period of
construction and commissioning of the 900 MW
power plants. The engineers (operation,
instrumentation, automatic control) who were at the
start of the design of these power plants, are coming
to the end of their careers.
2.2 Knowledge of relay circuits
The first of the players, the operator, has no worries
with relay systems: the relay circuits has not
changed, they have aged a little, but its excellent
reliability has protected it from modifications and
replacements. The documents are as is, hardly ever
amended but often reproduced. The installations
themselves change little, therefore modifications are
rare.
When knowledge is no longer put into practice, it
tends to be forgotten. Therefore, in operation,
knowledge appears to crystallise on components,
boards and relays. The overview of the installation is
less important, the "memory of installations"
(design, modifications) often disappears as
personnel leave.
Engineering offices are the guardians of "the
memory of installations". This memory is in the
extensive and highly diverse documentation
(functional design diagrams, logic specification
diagrams and wiring diagrams …), accessible in
CAD systems. The design of these diagrams is given
in writing, but know-how is transmitted orally,
through training sessions or apprenticeships.
The memory of installations "goes down" to the
memory of equipment. In this case, the combination
is very important, given the large number of
equipment configurations and their use. Once again,
oral know-how of the options adopted during the
design phase and the choice of modifications is
important; it is often heuristics that limit or classify
combination.
Essential knowledge is therefore of two kinds; semi-
formal representation on the one hand (design,
specification, production rules and forms of
representation of diagrams) and, on the other,
practical oral knowledge of the interpretation of
previous knowledge. This is what interests us.
3 CONSTRUCTION OF A
COMMON LANGUAGE
3.1 Our approach
The awareness of this very important combination
and an initial analysis of knowledge has enabled us
to avoid two pitfalls; that of non standardised
modelling [we use standard ISO 704], without a
consistency check, and preliminary, non modifiable
modelling. As we shall see below, we have
linearised the problem by describing it in the form of
a tree-structure and not a graph. This modelling is
incremental and involves all players.
The questions which will be raised over the next 10
years and beyond, are partially unknown. The first
stage for us, ensuring that the knowledge of relay
circuits could make sense later, was to ensure that
they are shared, whatever the situation, profession
and activities of all those concerned, whether in a
context of preserving or renewing technology. The
last pitfall, and not the least, would be not to make
such knowledge independent of the context. We
shall also see how the solution adopted meets this
challenge.
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