Extended Missions: the inspector takes control

For a nuclear power plant, the inspection and maintenance of steam generators are vital operations that must be carried out during a planned shutdown. The overall performance of these activities depends on the extent to which the schedule deadlines are met by sub-contractors and plant outage teams. Because the financial consequences of an overrun of an outage are significant, steam generator tube inspection is managed by France’s national utility, EDF, as a project in its own right.

THE CONCEPT

The extended mission has three main objectives: reduce the duration of the set of interventions on the steam generator; reduce the cost; and reduce the levels of exposure.

In developing the extended mission concept, Intercontrôle realised that reductions in outage time will only by possible when the tasks carried out before and after the NDE campaign, usually by subcontractors, are co-ordinated. Extending its role to include task co-ordination and integration is also an effective way for Intercontrôle to improve the preparation of the work plan, which will help minimise the number of interventions, thus keeping doses low during an outage, and generally help improve safety and the quality of the service.

The extended mission concept also frees the utility from having to manage a variety of operations related to tube inspection, since each inspection requires equipment and procedures specific to the NDE method being implemented.

The sub-contractors co-ordinated by Intercontrôle are selected from an EDF approved list. Each subcontractor remains fully responsible for its portion of the work and of the management of its personnel and equipment. However, tube inspection now becomes the central activity in the chain of inspection and maintenance tasks carried out on the steam generators.

“The main difference between an extended mission and a classical mission,” remarked Biagio Airo of Sotrasi, one of the subcontractors, “is that Intercontrôle becomes the main interface for subcontractors.”

PLANNING – CO-ORDINATION – INTEGRATION

For an extended mission, Intercontrôle drafts an optimal intervention plan. In co-operation with EDF and its partners, Intercontrôle identifies those tasks which, while traditionally either preceding or following the tube inspection, could be carried out in parallel. In this way, for example, one contractor could work on the cold leg while another is working on the hot leg.

Planning must take account of existing safety controls. In France, the company in charge of the steam generator tube NDE becomes “responsible” for the component on receiving the permit to work on it. This formality goes together with a so-called “cleanliness visit” carried out jointly be a representative of the utility and a representative of the contractor. This situation also applies to other interventions, such as the opening and closing of manhole covers, the drying of steam generators or the installation of nozzle dams in the channel heads. Furthermore, safety restrictions forbid the simultaneous presence of two different contractors on the same components.

The extended mission modifies the starting point with the inspection contractor taking responsibility for the interventions preceding and following the inspection. As a first consequence, only one permit to work is delivered and only two “cleanliness visits” are necessary: one at the beginning of the work and one at the end.

Two possibilities then exist:

• If the subcontractor carrying out one of the tasks prefers to receive his orders from the utility, Intercontrôle acts as a co-ordinator and a specific procedure will be used which allows for the intervention of the two companies simultaneously.

• If the company accepts to act as an Intercontrôle subcontractor, the entire responsibility is on Intercontrôle.

During the whole process, Intercontrôle coordinates all tasks, taking into account the priorities set by EDF outage managers. As work progresses, Intercontrôle keeps the plant informed on progress and problems encountered.

In this way Intercontrôle reduces interface-related time wastage for the operator and allows it to refocus its efforts on overall project monitoring.

Intercontrôle may also integrate peripheral tasks into its basic inspection activities, such as the opening and closing of steam generators, the drying and remote TV inspection of channel heads. Such new activities are either subcontracted or carried out by qualified Intercontrôle teams.

SITE EXPERIENCE

Eight extended missions have been carried out since the fall of 1996. These included:

• In April 1996, Intercontrôle co-ordinated an extended mission on the Fessenheim site involving both axial and rotating probe inspections on all three steam generators.

The workscope also covered maintenance operations, including deplugging, replugging, specific work on tubes located in areas where support plate degradation has been found, and TV inspection of channel heads. These were planned with the help of two sub-contractors.

The extended mission required the co-ordination of the NDE and maintenance tasks and the integration of the sub-contractors involved in opening of man-hole covers, installation of nozzle dams and drying of steam generators. By entrusting Intercontrôle, EDF gained a full 4 days on the total time required for the interventions, despite several problems encountered.

• In March 1997, six days were gained during the 10-year inspection of Paluel 3.

For this inspection, in addition to axial and rotating probe examinations, helium testing was to be carried out. This required preparing the secondary side with a mixture of helium and air. The preparation of the SGs for these tests was carried out with the assistance of a local contractor.

Included in the maintenance works programme, deplugging was to be carried out on the three SGs. One unit experienced unexpected problems forcing the NDE operation to be started on another steam generator. The extended mission arrangement allowed more flexible management of the inspection planning and made it possible to reduce channel head immobilisation times.

Despite several modifications of the task plan made by Intercontrôle, the five days reduction in outage initially anticipated during contract negotiations was improved by one day.

The optimisation of operation, the preclusion of redundant activities and the use of common biological protection devices, also resulted in the reduction of total exposures, in full compliance with ALARA principles.