The Grohnde pressurised water reactor in Germany now has well over a year of operating experience with its new process computer system. The old system was replaced with a modern one based on Siemens’ TELEPERM XP digital process control system. The replacement itself took only ten days, having been preceded by a period of parallel operation lasting approximately three months. The system was replaced due to limited expansion capability, spare parts bottlenecks and a growing performance gap between the old system and current ones.
The Grohnde nuclear power plant has been on line since September 1984, and monitoring tasks at the plant have been handled using a number of individual computer systems, each of which was separately configured and administered.
In addition to standard monitoring tasks, the new system offers the following special functions:
• Nuclear calculations.
• High-speed analog signal acquisition.
• An Aeroball system for recording the power density in the reactor core.
• Status display of protection and protective logic requirements.
• Acquisition and decoding of special alarm annunciations encoded in matrix form.
These individual functions were combined in a closed system.
Signal acquisition and preprocessing, as well as the relevant engineering tasks and diagnostics, are performed by the standard TELEPERM XP functions.
All other processing and display functions are tailored to the special requirements of a nuclear installation, resulting in the TELEPERM XP-IN information system for nuclear power plants.
A NUCLEAR INFORMATION SYSTEM
The TELEPERM XP-IN system includes the following number of signals and logs or displays:
There are ten workplaces with up to four monitors each in the control room alone to handle this vast amount of information. The various displays can be freely assigned. The interactive system is operated exclusively via the screen, replacing the function keyboards used previously. A trackball at each workplace is the only remaining operator control device. To save space, an in-house design in KW48 format (miniaturised control room equipment) was developed.
The operating sequences in the control room at the Grohnde plant were predetermined, and only slightly modified for the new system. Permanently assigned alarm areas provide information to the power plant personnel at the corresponding sections of the console.
The conventional alarm signalling system is acknowledged simultaneously with a computer alarm. Display of the alarm is always given priority when a new alarm arrives for the corresponding alarm area. When a plant display or curve group is selected, for example, the current display is sent to the background. This requirement was easily met, thanks to the high level of flexibility of the TELEPERM XP-IN system. Once the alarm is acknowledged, “last screen” can be selected to reactivate the original display.
In the system, all logged information is stored on magneto-optical disks and can be accessed at the workplaces for on-screen display or output to a printer. A concurrent alarm log exists only in the background and can be activated as needed using a graphics key. The most recent ten minutes of the alarm log are then printed out on request. In addition, the diverse options of continued operation under faulted conditions, the fault display and the supervisor function are still available; these can be used to provide a detailed analysis of the alarm event. Furthermore, comprehensive data searches are possible through analysis of the archives.
At the Grohnde plant, the I&C interlock and enable criteria can be manually selected. This criteria display function is of great help to the control room personnel for plant operation, because it allows any unfulfilled switch-on criteria to be detected early. This function is also used for inservice inspections in the area of the reactor protection system. The approximately 15000 criteria signals are acquired via eight separate bus lines.
A new, Windows-based tool receives and graphically displays the existing configuration data. This solution guarantees an accurate, high-quality data display. In addition, it simplifies handling of the plant documentation for processing purposes.
MAIN INNOVATIONS AND ADVANTAGES
In addition to the desired characteristics mentioned above, such as expandability and ease of maintenance, the new system architecture ensures that all data is freely available on a relational basis. The system also incorporates reserve capacity for future signalling expansion. The processing units (PU) currently operate at 30% of capacity during normal operation. If necessary, they can be replaced by even more powerful units.
The performance of the networks and communications processors likewise affects overall throughput of an information system. Redundancy considerations require well-thought-out information mechanisms and standby strategies at the levels of inter-user communications. Using consistently applied standards, the high-performance data transmission system forms the backbone of the power plant information system. Other systems can be connected much more easily when standard conventions have been used. For example, the system already incorporates the features necessary for the connection of numerous nuclear power plant diagnostics and expert systems. An additional hardware and software function package has been designed to adapt special solutions.
The output level is equipped with standard X-terminals. Windowing to other modern UNIX-based systems is no longer a problem from the viewpoint of data systems technology. Unauthorised access is prevented by gateways.
The special functions are seamlessly integrated both from a data systems technology point of view on the signalling side as well as in terms of configuration.
High-speed analog signals can be easily combined with the remaining signals for evaluation. A “jukebox” system is provided for archiving of all data. The jukebox can store approximately 200 GB of process data on magneto-optical disks (MODs). This entire volume of data can be accessed by the archive evaluation system.
Additional customer advantages result from signal configuration with automatic generation of the necessary documentation. Supplements are implemented step-by-step and in logical sequence through linking specifications. The same process is used for establishing groups and characteristics packages or complex, high-density process-engineering plant displays. The database is used to administer the entire volume of data in a user-friendly manner and to provide effective configuration support. At the Grohnde plant, a total of approximately 25000 data records of various types, each with special detailed information, can be processed. The data were transferred electronically from the older systems. The engineering system (ES 680-IN) can also be used at a later time for processing additional instrumentation and control functions in the area of plant operations.
Another technical improvement which makes maintenance and handling of the system much easier is the TELEPERM XP diagnostics subsystem. Malfunctions or irregularities of any kind produce group alarms in the control room which indicate that something unusual has occurred. The shift electrician receives detailed information in graphical form via the diagnostics terminal.
Due to the control room layout at Grohnde, operators and monitors are in some cases approximately two to three metres apart. This fact was taken into account in the basic design of the displays. Legibility is ensured at the normal working position of the control room personnel. The good operating response times make the monitor-equipped workplaces easy to use. These workplaces were quickly accepted by the control room personnel due not least of all to the ergonomically well-thought-out MMI concept.
PREOPERATIONAL TESTS
Keeping the relevant authorities and independent experts informed and included in the process played an important role in project implementation. All important procedures were co-ordinated with the customer, the Environmental Ministry of Lower Saxony and the Technical Inspectorate (TÜV) of the state of Lower Saxony. The TÜV required extensive pre-operational testing prior to approval of the computer replacement. Therefore, during the course of project implementation scale-back concepts, maximum load tests, verification of redundancy function, inspection and test procedures, etc were prepared.
SYSTEM CHANGEOVER
Changeover of the process information system and control room installation was originally planned for April 1997 during the annual refuelling outage. It would have been necessary to avoid interfering with the regularly scheduled maintenance work. For operational reasons, however, the Grohnde nuclear power plant had to be shut down in November/December 1996. Therefore, the changeover to the new TELEPERM XP system could be completed four months earlier than had been anticipated.
