RRFM 2009 Transactions - European Nuclear Society

4
2.2 The strategy at the Montreal SLOWPOKE facility
The following are the seven facets of our strategy for the management of ageing:
Along with components and materials, the reactor documentation may also age, in the sense
that it may become out of date. We have recently developed a formal Quality Assurance
Programme that ensures that all reactor documentation is kept up to date. According to the
QA programme, the Operating Manual is continually revised and the procedures in it,
especially the maintenance procedures, are continually updated. The QA programme also
ensures that the operating personnel are knowledgeable of modified systems and the
associated documentation. The operating personnel also follow a documented Continuing
Training Programme.
The ageing of the operating personnel should also be considered. At the Montreal facility, a
training programme for new operators was developed and two new reactor operator
candidates have now almost completed their training. It was found that an overlap of a
retiring operator and his replacement of at least one year is necessary.
The most important goal of the ageing management strategy is to preserve the integrity if the
reactor fuel, because if any fuel degradation occurs it cannot be repaired. When the reactor
was commissioned with LEU fuel in 1997, it was necessary to carry out power excursions to
demonstrate the self-limiting behaviour of the reactor, but these were limited to powers less
than 80 kW to minimise their possible effect on the fuel. The mechanism which caused the
degradation of the aluminium-clad HEU fuel is not expected to occur with the zirconium-clad
LEU fuel. No sign of degradation has been observed after 24 years of operation of the
Kingston, Canada reactor with identical LEU fuel. The most important aspect of the
preventive maintenance is to maintain the purity of the reactor water. It is verified weekly and
the resistivity is maintained above 2 Mohm-cm. The radioactivity of the reactor water is also
measured each week. An increase in the concentration of gaseous or solid fission products
in the reactor water will be the first indication of fuel degradation.
The reactor control system, the pneumatic irradiation systems, the radiation monitoring
systems, the pool cooling system and the purification systems for the reactor water and the
pool water have many components that are more than 30 years old. It is generally accepted
[6] that the risk of failure of such components increases with age, and it may be wise to
replace them before they fail to reduce the risk. We do not totally agree with this logic, for two
reasons. First, we know our reactor well enough to be confident that the failure of a
component of any of these systems will not lead to an unacceptable situation from the point
of view of safety. Second, we have found these systems to be acceptably reliable up to now
and we are not convinced that new components will improve reliability. Therefore, our
strategy is to continue operating these systems until failures occur. Then the failed
components will be replaced. The reactor may need to remain shut-down until the
replacement is completed. In order to minimise down-time, our strategy is to ensure that the
eventual repairs can be completed as quickly as possible.
Many of the original components are now obsolete and it may take considerable time to find
or have manufactured suitable replacements and then to install and verify them. For critical
components, such as the temperature recorder and the self-powered neutron detector of the
control system, replacements were purchased several years ago and are available. A
network, with the participation of the five operating SLOWPOKE reactors in Canada, has
been set up. Each is drawing up a list of spare parts on hand and has agreed to make them
available to the other facilities as needed. As many spare parts as possible have been
salvaged from two SLOWPOKE reactors that have already been decommissioned and more
will be obtained from the next reactor to decommission. Most of the parts will be stored at the
Montreal facility.
307 of 455