U1.03/02 B1 - Zaporozhye NPP -Steam Generators Safety Valves for 6 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.

Proper functioning of the SG SV ensures keeping the steam generator as well as associated pressure piping within the design limits and ensures overpressure protection. In case of loss of feedwater, the SG SVs can be used as an ultimate means to provide a secondary heat sink function, i.e. depressurize the SG to allow for low pressure injection into the steam generators from alternative sources (e.g. fire pumps). The qualification of the SG SV for two-phase flow (steam-water mixture) is however an important pre-condition in order to avoid a physical disintegration of the safety valves and associated piping.

Because VVER 1000/320 design is highly standardized in terms of use the same equipment types, replacement of SG SV sets was implemented sequentially at all six ZNPP Units. With regard to licensing requirements, SG SV should be first installed at one Unit, and after a period of successful pilot operation, the regulator would give permission for SG SV installation to continue at other units. Project implementation was therefore divided into two Lots of safety valves.

The European Commission programmed the preparation phase of the project to replace SG SV 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.

This project aimed at installing new state of the art Steam Generator Safety Valves (SG SV), which are part of the steam supply system of VVER 1000 Units operated at Zaporizhzhya Nuclear Power Plant (ZNPP). There are six 1000 MW units (VVER 1000/320) in operation. Each unit is equipped with four steam generators; at each steam generator there are two (2) safety valves installed.
The original SG SVs were not compliant with the requirements of Nuclear Safety Rules and Regulations that came to force in 1990, in particular due the following reasons:

• Missing control function from the main control room or the emergency control room;
• Inadequate qualification status for operation with steam, water and water-steam mixture;
• Missing position indicators (opened/closed) on all safety valves and pilot valves, with the possibility to transmit the related signals to the main and emergency control rooms;
• Missing function to check the functionality and to test the safety valves at low parameters;
• Missing features to perform a diagnosis of the valve condition

The overall objective of this project was to procure and install the new, state of the art SG SV, at six ZNPP Units.

The contract was awarded to French company Weir/Sebim, a winner of the European Commission tender. The contract was signed in September 2004 and involved three Lots; in Lot 1 the supplier delivered, installed and tested set of SG SV for Unit 1 and Lot 2 included the supply of SG SV for remaining 5 units. In addition there was a Lot 3 which included delivery of a mobile test bench for testing the main valves, a mobile set-up device for check and setup of the pilot valves as well as respective training in their use and some replacement solenoids and spare parts.

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.
Since the beginning, this project suffered delays mainly due to different views between the Beneficiary and the Supplier over the design of the SG SV control system. This was finally resolved and the project was able to proceed.

The Factory Acceptance tests (FAT) for Lot 1 (8 SGSVs for Unit 3) and Lot 2-part 1 (8 valves for Unit 1) took place from 25 – 27 July 2006. Due to the comments of SNRIU/SSTC on the valve qualification, a meeting was held at the Supplier’s premises in October 2006, and all open issues were solved, and Technical Decision for Installation was eventually approved by SNRIU in November 2006. Consequently, SG SVs were installed in the first unit (Unit 3). The partial Provisional Acceptance Certificate (PAC) for Lot 1 has been signed December 2006.
FAT for Lot 2-part 2 (16 valves for Units 2 and 4) was successfully performed in February 2007 at Weir/Sebim premises.

The second installation took place in Unit 1 during the outage in May/June 2007. ZNPP received the SNRIU approval for operation in June 2007. The installation, commissioning and testing itself was successful, after the Unit reached full power level a small leakage at a pilot pipe flange was detected and preliminary tightened. The PAC was signed in august 2007.
The third installation took place at Unit 2 during the outage in June-August 2007. The NPP received the approval for operation in August 2007 from SNRCU. The installation, commissioning and testing itself was successful, after the Unit operated some weeks at full power level; the PAC was signed in august 2007.

The 4^th installation (Unit 4) was successfully completed in March 2008, followed by the Provisional Acceptance in April 2008.

The last batch of 16 valves (Lot 2-part 3; Units 5 and 6) was subject to the final Factory Acceptance Tests in Marseilles in two stages in February and May 2008. The valves arrived at ZNPP warehouse at the beginning of April 2008 and in mid July 2008 respectively.
The 5th installation (Unit 6) was successfully completed in May 2008, followed by the Provisional Acceptance in June 2008 and the 6th (last) installation (Unit 5) was successfully completed in September 2008. The Provisional Acceptance was signed in October 2008.
Last delivery of remaining Lot 3 equipment took place in November 2008. Partial Provisional Acceptance was issued in November 2008.

First Final Acceptance Certificate (FAC - Unit 3) was issued in December 2008. Subsequent FACs were issued for each Unit after a two year warranty period following the respective PACs. However, the FACs for Units 5 and 6 were suspended due to the discovery of problems during the warranty period related to corrosion of the bellows of the valves. Following a period of investigation, the supplier agreed to provide replacement bellows which allowed issue of the last FACs in 2012.