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A New Generation of Steam Generator Inspections R. Lévy, A. Bouchinet Intercontrôle/Framatome, France Contact

INTRODUCTION

When steam generator tube inspections began in France around 1976 (pre-service), no one could have imagined what equipment would be used in the year 2000.
In a quarter of century, this sector of activity has evolved from "stone age" to the era of digital technologies, benefiting from the contemporary evolution of other techniques.
A general problem linked to the surveillance of a constantly evolving structure is that the tools for the surveillance cannot remain the same. A specific problem linked to the surveillance of a nuclear component is the necessity to ensure the continuity in the records of the information.
It is therefore easy to reach a point where the quantity of equipment needed for an inspection becomes utterly incompatible with the concept of industrial productivity. Putting into operation a new generation of equipment always represents an important effort with financial, technical and human consequences.

THE CONTEXT

In 1975, the only type of nuclear power plant existing in France was the 900 MW PWR.
Today, two more exist : 1300 MW and 1450 MW, consistently different as far as the design of the steam generator is concerned. The manipulator which brings the probe in front of each tube must now be compatible with this diversity of designs.
On the first In-Service Inspection (ISI) in 1979, eddy current data were digitised for the first time, at the output of analogue instruments. Since 1992 one digital instrument has replaced three pieces of equipment in the acquisition line. The bobbin coil probe is still used but, in addition, rotating probes scan the roll transition area, the tube at the level of any support plate or the U-bend, searching for cracks of all sizes and orientation, or corrosion. All these probes developed in successive steps have required dedicated control units and driving systems.
The data acquisition teams no longer carry cases with pieces of equipment, a mobile unit called shelter now includes the data acquisition equipment and is ready to start upon arrival on site.
Data analysis teams have had to face the increase of workload resulting from the increase of indications in the ageing steam generator tubes. Automatic analysis software has mainly helped the analysts in making a better use of their actual skill to solve real interpretation problems.
Even though some efforts had been made to upgrade the equipment, the complete line still looked like a "patchwork" reflecting the successive additions made necessary by the occurrence of new degradations.

THE MODIFICATIONS

When the inspection scope started to remain approximately constant, it became possible to consider modifications of the equipment in order to reduce the number of installations and removals, to reduce the sources of breakdowns and to reduce the time spent on training.

The Manipulator
The basic concept of a manipulator in close contact with the tubesheet has very positive consequences on the average lifetime of all sorts of probes, in addition to an unequalled positioning accuracy. It was therefore decided to keep the same concept in the new line of equipment.

The challenge of having the same manipulator body with interchangeable sets of grippers, each adapted to one design of tubesheet, was made harder by the introduction of the dual guide tube allowing to inspect two tubes simultaneously, (Figure 1). The pneumatic jack pushing the manipulator against the tubesheet was made more powerful to face the new weight introduced by the two probes and their sheath.

Fig 1: The Ritmic manipulator with dual guide-tube


The control unit is replaced by a software programme and the automatic sequences of inspection can cover all inspection plans decided by the Utility and movements are optimised for the shortest duration between two positions.
Some peripheral tubes make it necessary to operate the manipulator in a single tube configuration but such changes are made intrinsic part of the programme.

The probe pusher
Three systems, having each its own control unit are now replaced by the eddy current probe pusher (Figure 2). The new system manages all translation movements, including a specific function for the optimisation of the length of the flexible conduit in which the probes travel.

Fig 2: The pusher-puller for all eddy current probes, in situation of inspection.


The previous driving system consisting of a set of wheels lacked power to push the probes in some tubes because of the reduced contact between the wheels and the sheath ; moreover, it had destroyed too many probes ; it was therefore replaced by a completely new design, enabling a stronger contact on the probe sheath surface. The forced air device is kept for the movements of the probe in tight U-bends.
As for rotating probes, two models of motorization are mounted on the new probe pusher : one for the inspection of the roll-transition area featuring a powerful motor which remains in the flexible conduit linking the pusher to the manipulator ; the other for the inspection of tube sections at support plate level or for the U-bends, allowing now triple lifetime and a significant reduction of the noise level.

Numerical control ensures reliable and highly flexible automated inspection sequences. The whole system has been qualified for use on site for two years now; the reduction in installation time and switching time from one type of inspection to the other is clearly demonstrated as well as the expected reduction in maintenance and training duration.

The annular gallery terminal
In this case again, three pieces of equipment have been replaced by one.
The orders to the manipulator and the information in return for the tube co-ordinates were managed by one PC type computer in the shelter, an electronic system called "scrutator" also in the shelter and an equivalent "scrutator" in the annular gallery. These components had become obsolete and are now replaced by the annular galley terminal, connected to the shelter by an Ethernet link, with TCPIP protocol.

The Supervisor
Initially developed in the 90s, the Supervisor is a software product managing the complete acquisition process. The new version has been rewritten under Windows NT environment and is now a real time multitask system, benefiting from the NT technology and ensuring reliable high speed transfer of information.

On-site operation
The complete line of equipment will be tested on site in the last term of this year.
In January 2001, three complete lines will be operational and progressively, the sixteen shelters operated by the company will be linked to as many sets of new equipment for the new generation of steam generator inspections.

NEW GENERATION OF ANALYSIS TEAMS

Data transmission
The current organisation of inspection teams systematically implies the travel of acquisition and analysis personnel on the site of the inspection. Intercontrôle has considered for several years now, the possibility to keep the analysis teams in the facilities of the company, in a specific area, adequately equipped. Data would then be transferred from the inspected site to this location where all the working forces and the experts would remain "concentrated". The constant presence of the experts allows an immediate tracking of the analysis results and reduces the probability of false calls.
The various technologies available have been evaluated and satellite transmission was found to be a best compromise between performances and costs.
This new way of operating must also be fully accepted by the Utility and the complete process requires time before an official implementation.
The progress made in information technologies will have an impact on the social life of data analysts who can now remain in a location and receive data from anywhere. Those for whom travels were an attractive feature of their work sometimes resign ; others are pleased to see an improvement in their family life. A new distribution of skills will be necessary.

Analysis networking
Once the concept of data transmission is made part of the current practice, then the optimisation of available resources becomes the unavoidable following step.
When equipment and competence are gathered on one spot, they must be used in the best way in terms of efficiency, quality of work and costs.
Network organisation is the optimal solution ; each analyst can in fact be trained to be operational on the limited number of existing configurations. Data are then distributed, as they arrive, to the available operator regardless of the origin making thus the most efficient use of working hours. Moreover, all storage and loading operations made necessary in absence of network disappear and with them, all the inherent risks of errors.

Borderless analysis
Since January 1998, Intercontrôle is a subsidiary of Framatome S.A. and is integrated in the Nuclear Services of the Group, together with other subsidiaries such as Framatome Technologies Inc., (FTI), in the U.S.A. Since then, a very fruitful collaboration has been initiated between Intercontrôle and FTI.
Eddy current data analysts from each company were successfully trained to become certified in the system prevailing in each country, thus being qualified to perform eddy current data analysis indifferently in one or the other company.
French data analysts have already participated in five jobs, in FTI facilities, interpreting data from US plants. FTI analysts have been trained in the early 2000 and should be busy, interpreting data from French plants in the fall of this year.
The next step envisaged is to continue this co-operation but without having to travel from one facility to the other : data will be sent across the ocean via satellite link and analysis results will be sent back.
Shortage in skilled manpower should no longer be a problem.

CONCLUSION

The new generation of steam generator tube inspections incorporates technological and social trends that are dictated at a larger scale by a new worldwide economic context.
The driving force is a general optimisation of resources for an increased productivity.
The financial investment which leads to putting into operation new systems has human consequences since personnel works on more reliable equipment, requiring less exposure to radiation, reduced maintenance and more efficient training.
Advanced technologies also impact upon inspection personnel by modifying the way they work and sometimes the way they live: a different organisation of skills is taking place inside inspection companies.
Man remains an essential element in an fully automated environment !

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