Lithuania’s reactors get new plant process computer systems28 January 2000
As part of a major safety upgrade programme, the Ignalina Nuclear Power Plant installed a new plant process computer system at its unit 1 RBMK reactor. Following the system’s initial period of operation, which began in October 1998, the project’s main contractor and supplier, Data Systems & Solutions, was also given the job of replacing the old computer system at unit 2.
In 1996 a contract was signed with the Ignalina Nuclear Power Plant (INPP) to replace the plant process computer system, referred to as TITAN, at its unit 1 reactor, one of the station’s two RBMK-1500s. The replacement project successfully met a compressed two-year schedule and the system began operation in October 1998. This project represents the first replacement in history of a plant process computer system for a Russian designed RBMK reactor.
The new TITAN system installed in INPP unit 1 by Data Systems & Solutions, greatly improves the ability of the operating staff to acquire real-time data, to analyse plant conditions, to determine proximity to operating and safety limits, to view useful real-time and historical information, and to archive historical data for future use. One of the major benefits of replacing the old computer system is that the new system is capable of executing the main core physics, thermal hydraulics, and other applications programs 18 to 25 times faster than the original TITAN system. The new process computer’s real-time database manages a total of 140 000 data points, including the 23 000 field input/output points, making it the largest plant process computer system in the world.
The new information system is based on the technologies that have been installed in many nuclear power plants in the US. It fully meets the technical requirements of INPP. The computation capabilities of the system will increase the operational safety of the plant. For example, one nuclear application that took almost 20 minutes to execute on the original TITAN executes in less than 5 seconds on the new host computer and is executed every 5 seconds. The new system provides the control room operators with much more timely information with which to operate the plant.
Following the excellent performance of their upgraded TITAN system, the INPP management soon decided that a similar, full replacement of the TITAN system hardware and software of unit 2 was called for.
In 1999, the Lithuanian government, owner of INPP, approved the decision to upgrade the unit 2 system and selected Data Systems & Solutions as the prime contractor and system supplier for the project. As in the case of unit 1, the project financing involves a long-term loan obtained by the Lithuanian government to be supported by US Export-Import Bank. The new system for unit 2 will be completed in phases by 2002. The first phase will cover reactor operator information and the last phase, turbine operator and secondary unit operator information.
Following completion of the unit 2 upgrade, operators of both units will be much better able to monitor important safety parameters using a modern, standardised human-machine interface. The new TITAN plant process computer system also provides the necessary interfaces with other safety systems, such as upgrades of the INPP control system and protection systems, secondary diverse reactor shutdown systems. Interfaces to a future safety parameter display system can be easily added.
The upgrade of these computer information systems are part of the INPP Safety Improvement Program, which was approved by the Lithuanian Nuclear Power Regulatory Agency VATESI and several international advisory committees (see panel).
RBMKs have a number of features which differ from LWRs that must be considered in designing a process computer system.
These channel-type reactors are boiling water cooled and graphite moderated. Each reactor at INPP has 1661 individual cooling channels which contain fuel elements (known as cassettes). After passing through the reactor channels, the coolant (a water and steam mixture) flows into drum-separators which are mounted above the active zone of the reactor core. The water settles in the drum-separators, while the steam is directed to the main turbines. Steam exhausting from the main turbines is condensed, and then the feed pumps return it to the same drum-separator, where it is mixed with the water which was separated from the steam. The main circulation pumps return the heated fluid to the active zone, where part of it is again converted into steam.
RBMK reactors are refuelled on-line. At normal operating conditions and reactor power, 1-2 fuel cassettes have to be replaced each day. The refuelling mechanism allows for replacing five cassettes a day.
THE PLANT MONITORING SYSTEM
INPP’s RBMK reactors have the following control parameters:
• Reactor power density distribution.
• Integrity of fuel channels and fuel cladding.
• Coolant flow in fuel channels and control channels.
• Steam quality in the fuel channels.
• Temperature of the graphite and metal constructions.
The plant information system provides information on the operation of the reactor and each fuel channel. The main parameters include: core power / flux; temperatures; flow rates; flow valve positions; and pressures. It also provides performance and equipment status information on primary and secondary plant systems as well as auxiliary systems such as ac and dc electric power, service water and other systems.
All the information obtained from the control and monitoring systems is then processed automatically by the information computer system. This computerised system collects data from the technological process measuring elements (eg pressure, temperature and other sensors), and communicates to the redundant host computers, which validate and process the data and calculate the physical parameters of the reactor. The primary host computer presents the final information to the control room operators at three principal workstations: SRO (reactor operator), STO (turbine operator), and SEUC (secondary unit), each with multiple display screens. Each workstation can call up more than one hundred displays. In addition, new displays to meet special monitoring needs can be rapidly built using a variety of available templates. Examples of INPP displays are shown on the previous page.
The plant monitoring system replacements delivered by Data Systems & Solutions are based on the company’s SAIPMS real-time data management software and the SDS/DV human-machine interface (HMI) software. The SDS/DV HMI supports many different graphic output formats. SAIPMS-based real-time systems are currently installed in 72 operating nuclear power plants in the US plus two in Russia, one in Lithuania, one in Taiwan and one in Armenia.
The system functions of this real time monitoring system fall into the following main categories:
• Data acquisition
• Signal validation
• Value derivation and transformation
• Processing and annunciation of alarms
• Log and report production
• Displaying to the operators
• Database maintenance
• System and Network maintenance
• Data transfer to the local area network (LAN) of the power plant
The functional subsystems of SAIPMS are described in the panel at right.
|Ignalina and nuclear power in Lithuania|
|The Ignalina Nuclear Power Plant houses two RBMK-1500 reactors. With nominal capacities of 1500 MWe, the two units are the largest operating reactors in the world, although safety concerns limit operation to a total of 2760 MWe. INPP was built as part of the former Soviet Union's North-West energy system; the first unit began working at the end of 1983, followed by the second one in August 1987. After Lithuania regained its independence as a nation, INPP became the property of the Republic of Lithuania. Direct ownership of INPP lies with the Lithuanian Ministry of Economy. The plant itself is located in the northeast of the country, near Visaginas, on the south coast of Drukso Lake in the Ignalina district. Vilnius, the capital of the Republic of Lithuania, is 130 km away. The State Company 'INPP' was registered with Ignalina District Administration on 31 May 1995 and was established in accordance with the law of the State and Municipal Companies of the Republic of Lithuania. Lithuania relies on nuclear power for generation of over 80% of its electrical power. One of the main strategic goals for Lithuania is the preparation of the Lithuanian energy sector for integration into the European Union (EU). The Lithuanian National Energy Strategy states that safety improvement programs should be put into practice at INPP in order to accommodate EU requirements. Therefore, efforts to improve safety at the plant have become more active, especially after the government took control of the electric power station. The INPP management, together with international nuclear energy experts, prepared a Safety Improvement Program (SIP) that was approved by the Lithuanian Nuclear Power Regulatory Agency, VATESI. This resulted in financial support for 20 projects in the spheres of operational safety, technical improvement and repairs, construction, the purchase of repair equipment and instruments, radiation monitoring, and renewal of project documentation. The INPP Safety Improvement Program includes renewal of the TITAN plant information system, engineering studies of the secondary emergency shutdown system, installation of fire-prevention and hydrogen explosion safety systems and renewal of other systems.|
|Main functional subsystems|
|The following describes the main functional subsystems of the new computer system: Application Executive Subsystem. This subsystem includes the system initialisation, system status (health) monitor and system time maintenance functions. After the system is started and initialised, all critical processes are monitored. The System performs a failover such that no data is lost longer than ten seconds due to failures caused by any hardware and/or software malfunctions. The Application Executive monitors the resource status, such as CPU utilisation and memory usage. This information is then reported back to the user. The system clock is monitored and synchronised, if necessary, to maintain correct timing of the acquired data. Data Acquisition, Processing and Archive Subsystem. This subsystem performs the functions of collecting and error checking external field inputs, generates derived or calculated values and stores data in global memory for downstream processes. It also performs historical data archiving if the change of data value exceeds a prescribed magnitude . The external inputs are in the form of individual field signals or data streams of semi-processed data from another computer system. This functional subsystem is also responsible for providing analog as well as digital outputs. Alarm Processing Subsystem. This subsystem monitors alarm conditions and provides alarm annunciation to the user. Alarm information is displayed on the Satellite Display Stations (SDS) and/or is printed on a hard copy device. All dynamic SDS elements that change their condition to "abnormal" are displayed as blinking for visual annunciation and are returned to the normal condition (without blinking) when acknowledged. Human-Machine Interface Subsystem. This subsystem provides a host-based interface with the Satellite Display Stations (SDS) user workstations. It receives and interrogates information from the workstation and prepares information that is sent back to the requesting workstations for display to the user. Data Retrieval Subsystem. This subsystem provides a means of recalling archived historical data. The data is displayed on the SDS workstation or is printed on a hard copy device. This subsystem provides on-line data storage in the form of disk files that are accessed for the storage and retrieval of data, and also provides archival storage on optical disk and/or magnetic tape that is accessed for data that has been stored for long periods of time. Database Subsystem. This subsystem provides the capabilities of generation, modification, and maintenance of the SAIPMS database. It also provides the function of generating user-requested database reports. Log and Report Subsystem. This subsystem generates disk-based or hard copy reports in accordance with prescribed formats. The following logs are supported: Tabular Logs, Periodic Logs, Post-Trip Logs, Free-Format Logs, SOE Logs, Database Change Logs, and Configuration Management Logs. Utilities and Software Support Subsystem. This subsystem is provided to facilitate the development and testing of SAIPMS software modules. It also provides a means of generating data files needed for the proper operation of the SAIPMS. An SAIPMS rebuilding mechanism is provided to rebuild the software from individual software modules.|