Background
The project intended to implement at Kalinin Unit 2 (VVER 1000 type) a system allowing for diagnostic and monitoring of small leaks in equipment and piping of primary coolant circuit pressure boundary located inside the reactor containment.
A leak detection system was required to improve reliability and safety of the plant by detecting and locating small leaks in selected equipment and piping of the primary coolant circuit pressure boundary located inside the reactor containment and to evaluate associated leak values. This monitoring could allow in an early stage of leak development to take appropriate measures to prevent further incident/ accident.
Objectives
The leak detection system improved the reliability and safety of the plant by detecting and locating small leaks in the equipment & piping of the reactor coolant pressure boundary and according to the criterion Leak before Break (LBB) preventing the development of the leaking cracks to avoid any consequential damage.
The system operated in both automatic and dialogue mode ensuring continuous (24 hours/24 hours) monitoring of sensor signals for all channels. In automatic mode the system provided performance of the whole set of functions: from data acquisition up to output of signals to be used for analysis of results.
The system was able to automatically and manually check and test the conditions of the whole sensor network, of other system elements and to generate warnings about failures of the system components.
The system included the necessary services and equipment for detection of unidentified leaks in the following equipment ranked according to their priority:
Lot 1: Flanges of control rod housing on reactor vessel cover;
Lot 2: Isolation valves on primary loops (hot legs)
Lot 3: Drain lines of the primary loops
Project Results
The supply included the design, manufacturing, shop testing, delivery, supervision of installation and field testing of a leak detection system, as well as the training of the plant personnel to operate and maintain the system. The leak detection system was able to detect unidentified internal leakage to the containment atmosphere, and was based upon humidity and/ or acoustic measure.
The leak detection system was able to detect and locate all leakage to the plant containment atmosphere with the sensitivity and response time needed to detect a leakage rate, or its equivalent, of one gpm in less than one hour.
The leak detection system based on humidity detection had to assure that there will be no influence due to external humidity. The system consisted of the following components:
-moisture sensitive tapes and its attachments to equipment and piping
-multiplexing unit and connecting wiring to the sensors
-control station
-processing unit with alarm and signal unit
The leak detection system based on acoustic detection continuously monitored the operating noise, detecting and locating leaks by discriminating the sound level from the background noise, and evaluating the leakage rate to achieve a complete leakage monitoring of the equipments and piping.
The system consisted of the following components:
-ultrasonic pickups
-preamplifier
-signal station
-ultrasonic transmitter
-data transient storage
-alarm and signal unit
-evaluation computer
The control station of each of the humidity and acoustic detection systems was able to detect presence of leakages, each with their own sensitivity, accuracy and timing as a stand alone system. In case of leakage detection they would communicate to the overall processing unit all needed information (leakage alarm, localisation, intensity) to allow for possible systems outputs correlation. The system assessed the volume rate and the mass rate of the leakage, the operator having the possibility to choose the value to be monitored.
The overall processing unit provided:
- needed relevant alarms to the Main Control Room;
- detailed diagnostic for maintenance crews;
- extrapolation of the leak progress;
The system assured the needed back-up and archive (for control stations and own elaborated information) and the ways and means for processing and displaying this information).
The first Call for tender was launched on January 8, 2001, but the tender procedure was unsuccessful, because none of the received bids were compliant technically. After discussions, it was agreed to proceed with another tender to be launched with an adapted Technical Specification. Decision to re-launch the tender was taken in June 2001. The updated specification was sent to JRC for comments on June 14, 2001 and the updated version of Evaluation Criteria was sent to JRC on August 20. They both have been approved on August 30. A proposal for new tender dossier was prepared by the Procurement Agent, Italtrend, in November 2001, commented by OSA-Utility at Kalinin NPP, Tractebel, and sent to EC. A final version, taking into account comments from EC was sent mid of February 2002, and publication occurred in July with a deadline for the tenderers fixed on September 16, 2002. The evaluation was done end of September and only one bid was found technically compliant, but with a price exceeding the budget. EC agreed to increase the budget for this project, allowing its full implementation.
The contract was signed on 30 September 2003. The kick-off meeting was organized on November 17-18, 2003.
The leak detection system was designed and manufactured for a 30-year continuous operating time under normal operating conditions, except for those components subject to normal maintenance or replacement.
The supplier provided the following on site assistance:
-delivery and checking of the equipment
-installation supervision
-commissioning
-training of Kalinin staff
-acceptance testing
The supplier subcontracted part or all of following activities to a Russian company adequately qualified:
- Development of the system technical project in compliance with requirements of Russian regulatory documents.
- Development of design documents for system arrangement;
- System installation
- Start up tests during putting system into pilot operation and carrying out of system pilot operation
- System operating documentation development and its inclusion into the Power Plant design documentation.
The leak detection system was classified N according IEC 1226 and 4N according point 2.5 of OPB-88 as failure of this system does not violate normal operating conditions of reactor and can not lead to design basis or beyond design basis accident.
Metrological characteristics of the system were certified by the Russian GOSSTANDARD bodies.
Factory acceptance tests were carried out at supplier premises with Russian representatives involvement. The factory acceptance inspections and tests demonstrated that the leak detection system integrating all hardware and software meet the set-up requirements. The supplier provided all needed simulation means that were necessary for system testing.
The site acceptance inspections and tests verified that:
-the system, equipment and sensors were correctly installed;
-the system functioned properly when connected to -and integrated in- existing Kalinin NPP equipment/ systems.
Training of operation and maintenance teams of the End User was held on Kalinin NPP site and in Russian language, and was related to.
- use of leak detection system;
- maintenance configuration, diagnostic and modification of leak detection system.
The project implementation was split into the following phases:
- engineering studies (including technical project, documentation and system arrangement design documentation)
- manufacturing
- installation, training, testing and putting into pilot operation
- pilot operation (including certification tests performance)
The installation, testing and commission were done during the refuelling outage period.
The Provisional Acceptance certificate was signed on 18 December 2006.
Final acceptance was pronounced after the warranty period.