I&C progress at Paks3 June 2002
The extensive I&C upgrade at Paks is reaching its final stages. A major milestone of the programme was the implementation of the new reactor protection system. By Miklos Ignits
The Paks nuclear plant (4xVVER-440) in Hungary was originally equipped with Soviet-supplied I&C systems. The original plant computer and data acquisition systems were of Soviet construction for units 1 and 2, and those of units 3 and 4 were made in Hungary. These systems were operated with minor modifications, but without significant upgrading. In 1997, a safety improvement programme was initiated at the plant, which aimed to:
• Meet stricter safety requirements.
• Replace inadequate systems.
• Address findings of safety reviews.
• Reduce maintenance and operational costs.
A new plant computer system
In the first phase of the plant computer system (PCS) two-phase upgrade programme, a highly reliable and flexible system was to be developed that would fully cover the functionality of the existing system. Also, new advanced safety features had to be implemented, such as the Critical Safety Function Monitoring (CSFM) System. Prior to system installation on the reactor unit, a functionally identical system (including the reactor protection system interface) had to be installed at the Simulator Centre. The system was to be designed so that additional functions that were to be developed in the second phase could be added on.
The second phase of the upgrade programme consisted of the implementation of functions and services that are not essential for safe operation, but support and simplify the operation of the main control room. These systems form the basis for diagnostic and management functions. The timetable of the milestones of the PCS upgrade programme was as follows:
• 1996: Supervisory Control and Data Acquisition (SCADA) system investigation and pre-selection of Intellution's FIX-32.
• 1997: Establishment of a pilot project, installation and testing.
• 1998: System replacement invitation to tender, negotiation, and contracting.
• 1999: System installation in the training simulator.
• 1999: Installation of the reactor protection system (RPS) information and archive subsystem.
• 2000: System installation (during outages) in units 1 and 2.
• 2001: Installation of PCS on unit 3.
After the commissioning of the systems for unit 1 and 2, the system designers and the Paks process and IT personnel performed an evaluation of the new systems. Both the "factory" and the individually developed software elements were evaluated from the user aspects of the process engineers and the computer engineers. The findings of the evaluation formed the basis of the unit 3 system design.
The major changes in comparison with the system for units 1 and 2 included the new version of the SCADA software and adjustment of the data acquisition units to the PCS. In addition, the FDDI network connection had to be changed to Fast Ethernet.
The formation of the parallel data paths for the data acquisition units and the provisional installation of the new PCS in the computer centre was followed by the one-month parallel operation of the old and new computers. During that period, the database and process diagrams of the new system were validated.
The final installation and testing of the PCS was performed during the maintenance outage of unit 3. At present, the new PCS is fully operational at unit 3, maintaining uninterrupted process services.
Plant computer System structure
The PCS can be divided into three logic levels. The bottom level includes the existing data acquisition units and the RPS information gateway computer for the coupling of the RPS signals. The intermediate processing level includes the processing and archiving of the data received from the bottom level. The third level accommodates the man-machine interface (MMI) for user information supply.
The computers of the PCS have Intel processors running the Windows NT 4.0 operating system (server and workstation). The new PCS is based on the Intellution FIX-32 SCADA software, which provides the basic data processing and display functions of the system. Further essential system functions — such as communication with data acquisition units, archiving and archive listings, representation of archived trends, central clock management, self-diagnostic and monitoring programs — required specific purpose-made application software. The logic scheme of the system at unit 3 is shown in the Figure on the opposite page.
The functions of the individual components are as follows:
Intermediate level servers
• Duplicated RVR servers, for receiving and processing the coupled signals from the RPS GW and archiving the received signals locally into the service archives.
• Duplicated XFRT-A and -B servers, for receiving and processing the signals from the XFRT signal acquisition unit.
• Duplicated computation servers, for executing the secondary calculations (modules implementing the CSFM function), and handling the external data interfaces of the PCS.
• Duplicated SQL-based archive servers, storing the off-line database and the process archive.
• Web server, handling the external ("remote") display units.
• Operation server for the execution of the programs handling the operational activities and for the maintenance of the off-line database.
Top level displays
The operational displays (14 units in total) facilitate the availability of the PCS data for the operational personnel.
Network tools — for the internal communication between the PCS components and for external system interfaces — ensure the separation of the data transfer by the different subsystems and prevent the propagation of potential network errors between the systems. The switch centre is also fully duplicated using switching and routing functions. The local area network (LAN) of all four Paks units is supervised by two central star-switch subsystems as well as by a management station. The physical network is constructed from optical and metal Fast Ethernet wiring, and the protocol used is TCP/IP.
fix system functions
Data acquisition servers
Duplicated data acquisition servers are connected to the data acquisition units of the RPS and the XFRT servers. These computers are responsible for receiving and primary processing of signals. The measured signals are transferred into the distributed database of the FIX system. These servers provide the data for the computation servers and display units using the FIX system.
The PCS ensures the synchronisation of the internal clock of the computers based on the base time received from the master calendar of the Paks plant. The system can handle the summer/winter time changeover.
The most important task of the SCADA servers is the receiving and primary processing of the arriving data. The data resulting from the primary processing is stored in its own FIX SCADA database.
This is where the alarm and event handling signal transfer to the archive takes place, as well as less sophisticated data processing (such as averaging, correction, or rate-of-change calculation).
Secondary signal processing
Secondary signal processing refers to:
• Logic and secondary validity checks.
• Generation of the analogue and discrete variables (process calculations).
The more sophisticated algorithmic calculations are performed on the computation server receiving the input data required for the calculations from the SCADA servers. The derived data resulting from the calculations can be handled in the same way as the measured data.
Alarm and event message generation
The event and alarm messages generated by the system have an important role in providing information for the operating personnel. An event is essentially a signalling that calls the attention of the operator in a textual or graphical format to a change in the status of a process component or in the value of a characteristic process parameter. An alarm can be considered a discrete signal characterising the current or past status of a process component or a process parameter. Thus an event represents change, whereas an alarm characterises a status.
Operator support system
These complex functions aim to provide the operators with wide-ranging and integrated information about the status of the process and safety systems, the expected processes and measures to be taken. These functions are implemented by the computation server.
The new operator support system functions are:
• Dynamic processing (calculation of limit violations) and displaying of plant technical specifications (TS) document. Displaying general and specific aspects of TS according to the dynamic process parameters, with textual presentation of the given TS paragraph.
• Checking of minimum controllable power conditions.
• Determination of critical reactor parameters.
• Computerised support of technological and protection system testing.
• Displaying plant technical documentation.
• Integrating and displaying CAD pictures.
A further advanced function is the PLASMA (PLAnt Safety Monitoring and Assessment) subsystem.
• Main features include: online monitoring of the current safety status of the plant; online monitoring of the critical safety function status trees; and displaying the emergency operating procedures (EOPs) in a computerised form, and the dynamic parameters referenced in them.
• Main functions of the modules: CSFM I/O server (obtaining all required input signals from other servers); plant state identification (determination of reactor operation mode, monitoring actuation and system status); critical safety function status tree monitoring — subcriticality, core cooling, secondary heat removal, vessel integrity, containment integrity, primary circuit inventory; and EOP selection and display of the dynamic parameters referenced.
• Data is accessible by plant operators and remote users.
Displaying is divided into operational and external displays so that the external displays do not disturb the servers involved in the processing of essential data.
The frame integrating the operational displays of the PCS is the FIX View software package. The operational displays of the PCS receive the data from the active SCADA server computers. The PCS provides the following functions for the users via the operational displays:
• Schematic drawings and trend displays.
• Archive listings and trends.
• Critical safety function monitoring.
• Handling of the parameters specified in the Technical Specification.
• Alarm and event management.
• Online database management.
• Offline database queries and listings.
The external (not operational) displays are operated from the web server. The continually updated process data is available from the user interface of the external displays without installation of application programs. The users of the external displays have access to the following functions:
• Schematic drawings and trend displays.
• Archive listings and trends.
• Offline database queries and listings.
The data generated in the system is stored and archived for subsequent long-term processing. The archived data is available for the purposes of listings, logging, statements and analyses. For the process signals, the significant changes are archived. The archive is based on the Microsoft SQL server package.
The system facilitates making data printouts. The data can be presented in the logs of the process status or in the lists generated by different listings, checks and user activities.
Process data management
During the data management inside the system, the real-time (online) database is distinguished from the (offline) database which contains the master data of the system. The static data is loaded into the online databases from the offline database. The data to be loaded into the online database of the signal acquisition computers is copied from the server computer. The activities concerning offline database maintenance are logged, thus any database record modifications can be traced.
For central administration of the distributed system and for an even load distribution, the description data of the system is stored on a separate server called the operational server. The operational server stores the central directories containing the data files of the schematic drawings, log schemes, trends and filters.
Operational and diagnostic functions
The system provides comprehensive operational services and the diagnostic system ensures the traceability of the status of the system as a whole and its individual parts at each level. The major functions of the supervision and diagnostic services are:
• Checking of system status and operation — handling of
redundancy, state of equipment, action-list (event and error messages), diagnostic data.
• System saving and backup utilities, and maintenance of disk directories.
• Operational and service menu functions.
• Management of subsystem protection and authorisation.
• Error detection and handling.
• Central system supervision.
• Network management.
• Providing O&M and development documentation.
The main tasks for the immediate future are:
• The implementation of the unit 4 system in 2002.
• Unification of the systems based on the unit 4 installation, backfitting units 1 and 2 and the training simulator.
• Upgrading the process information system of the plant information centre based on the experiences of the PCS upgrade programme.
• Development and implementation of further operator support functions within the PCS (for example, introduction of computerised alarm response guidelines, model-based early fault detection combined with online fault diagnostics, operator advisory services using the plant's electronic documentation).
• Expand diagnostic services for intelligent I&C systems.
• Ensure long-term archiving of process data.
• Event investigation support.
• Connections to the company's strategic tasks of power uprating, plant lifetime extension, ageing management, and data exchange with the business system (SAP).
Operational experience to date is excellent. The I&C systems allow for nearly 100% availability. The operators are now accustomed to the displays and their functions, some of them having been intensely involved in the design of the MMI functions and the display formats. Future upgrading activities are expected to further improve the systems' capabilities and efficiency.
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