U1.03/02 B3 - Zaporozhye NPP - Feedwater Control Valves for some Units (2-3 units) (AP ref. 7.2.1.1 partim)

With 6 VVER 1000 / 320 Units in operation at a single site, ZNPP is the largest nuclear power plant in Europe. It is situated in the south east steppe zone of Ukraine, on the bank of the Kakhovka water reservoir. In the period from 1984 to 1987 the first four power units had been commissioned. Unit 5 was started up in 1989 and unit 6 in 1995.
Feedwater flow control ensures keeping the steam generator water level within the required limits. If the water level is too low or too high, it can lead to a reactor trip. Together with a turbine-driven feedwater pump the feedwater control valve (bypass or main valve) can maintain the SG water level in a large range of power, i.e. 5-100%. A feedwater flow control system is an integral part of the digital automatic turbine control system.
Because VVER 1000/320 design is highly standardized in terms of use the same equipment types, replacement of FWCV sets was implemented sequentially at four ZNPP Units. With regard to licensing requirements, FWCV should be first installed at one Unit, and after a period of successful pilot operation, the regulator would give permission for FWCV installation to continue at other units. Project implementation was therefore divided into two Lots.

This project aimed at installing new Feedwater Control Valves (DN 400), which are part of the feedwater supply system of VVER 1000 Units operated at Zaporizhzhya Nuclear Power Plant (ZNPP).
The original feedwater control valves (FWCV) suffered with low reliability and long response time to control the feedwater flow during plant transients. In addition, valve internal parts considerably eroded throughout the years of operation mainly because their parts were made from low erosion resistant material. Despite the fact that the main and auxiliary feedwater system does not belong to safety related systems, incorrect control of the feedwater flow may result in plant transients with potential to challenge the heat removal (safety) function.
The European Commission programmed the preparation phase of the project to replace FWCV at ZNPP already in the framework of the TACIS 1999 nuclear safety programme. However, the project preparation phase experienced difficulties which resulted in delays, and the implementation phase of the project was eventually programmed in the TACIS 2002 nuclear safety programme.
The overall objective of this project was to procure and install the new, state of the art feedwater control valves, at four ZNPP Units.

The contract was awarded to Russian JSC Atomashexport, a winner of the European Commission tender. The Supplier's scope of work comprised the design, manufacturing, testing, certification, delivery and supervision of the installation of the equipment. A provision of after sales services, warranty, and ZNPP personnel training was also included in the contract.
Lot 1 comprised the delivery and installation of FWCV at one Unit in order to gain experience from the implementation, testing and operation of the new FWCV. Lot 2 comprised the delivery of FWCV for remaining three Units, including a mobile diagnostic device for valve maintenance and testing purpose.
Following installation of FWCV in 2007, several problems were encountered that were associated with unsatisfactory reliability of valve actuators chosen by the supplier to operate FWCV. It was found that these actuators were unable to ensure reliable valve operation in the long term. Several attempts to solve the problems by replacement with repaired actuators failed. A detailed investigative analysis revealed deficiencies in the actuator design. The Provisional Acceptances in 2 units were suspended. The Supplier proposed in January 2008 to replace the delivered actuators by another type from another manufacturer. Following installation and demonstration that the new actuators fulfilled all the requirements, the actuators of the valves of the other units were also replaced.
Key contract data are as follows; the supply contract was signed on 8 July 2005. The supplier JSC Atomashexport manufactured the equipment, performed factory acceptance tests and installed the equipment in 2007 outage. ZNPP has replaced all the original valve actuators in 2008-2009. The Final Acceptance for the first Unit delivery was issued on 25 May 2009, and the other acceptance certificates followed. The project was formally completed on 31 October 2010.