U1.03/02 B2 - Zaporozhye NPP - Pilot Valves for Pressurizer Safety Valves Units 1-4 (AP ref 7.2.1.1 partim)

In the framework of the “Tacis Nuclear Safety Programme”, it was decided to increase the nuclear safety of the units 1 through 6 at the Zaporozhye NPP by improving the protection of the primary circuit from overpressure under normal and emergency modes.

The Zaporozhye NPP consists of six units of the VVER 1000/320 type. In order to protect the primary circuit from overpressure, the pressurizer of each unit is equipped with 3 independent safety relief valves which are installed in parallel on the steam dump pipeline. During construction, units 1 – 4 of the power plant were fitted with pressurizer safety valves manufactured by the German valve manufacturer, Sempell. Units 5 and 6 were fitted with pressurizer safety valves manufactured in the Soviet Union.

Due to functional reliability problems with the pressurizer safety valves installed on units 5 and 6, it was first decided to replace these valves through competitive tendering (see project U2.03/96). For units 1 – 4 on the other hand, it was established that the desired safety improvements could be achieved with the greatest cost/benefit ratio by upgrading the already installed pressurizer safety valves. This required a direct agreement with the original valve manufacturer. This work was covered by the present contract and is described below.

At the units 1 - 4, each of the 3 independent pressurizer safety valves installed in parallel on the steam dump pipeline is controlled by 2 pilot valves. Two of the 3 safety valves are the so-called "Operating Valves". The 3rd safety valve, the so-called “Control Valve”, is additionally equipped with a separate impulse line actuated by a remote-controlled solenoid valve, the so-called "Discharge Valve", and a motor-driven stop valve; the latter, is normally opened.

The generic purpose of the intended improvements was to:

• Eliminate the deviations from the Ukrainian safety regulations and rules;
• Enable the core heat removal under emergency conditions (Bleed-and-Feed function);
• Enable the protection of the primary vessel from cold overpressure.
• Enable the application of state-of-the-art testing methods for the valves and thus to exclude potentially dangerous and imperfect testing methods.

In order to achieve the above goals, the improvement measures included the following:

• Provision of the possibility to remotely control (open - close) any and each of the 3 safety valves from the main control room, as well as the emergency control room, to achieve the “Bleed and Feed” function and to protect the primary circuit from cold overpressure. This would be achieved by supplementing an additional control line with a remote-controlled "Discharge Valve" and a stop valve on each of the 2 "Operating Valves";
• Making the necessary modifications to the main valves (replacement of a number of components) required to achieve the qualification of the safety valves for operation with steam, water, water-steam mixture and nitrogen;
• Installation of position indicators (open/closed) on all pilot valves, with the possibility to transmit the related signals to the main and emergency control rooms;
• Provision of the possibility to connect a mobile system for adjusting and testing the pilot valves, thus enabling to achieve these works without having to increase the parameters of the primary coolant system up to the actual set pressure for the opening of the valve;
• The equipment to be supplied also included the required I&C and power supply interfaces.

The Supplier’s scope of work comprised the design, manufacture, testing, certification, delivery and supervision of the installation of the equipment. The Supplier’s scope also included the development of all necessary documentation including that required for licensing purposes, the provision of training to the End User’s personnel and warranty on the supplied equipment.

In July 2004, the EC approved direct negotiations with the supplier of the original valves to be upgraded: Sempell/Germany. A technical meeting was performed with Sempell and the EC where the scope of delivery and technical issues were discussed and agreed. Based on the meeting’s result the final Technical Specification for procurement of the equipment was developed and issued.

The Supplier submitted its quotation in March 2005 and following negotiations the supply contract was signed by all parties by 30 June 2005.

The kick-off meeting with all involved organisations was performed at ZNPP in July 2005. The design and licensing approval of the supplies, being already approved by the Technical Specification for Supply (TSfS) of the Tacis project U2.03/96, because the delivered mechanical components are identical, was significantly simplified.

The I&C part of the valves was subcontracted to Khartron Company/Ukraine.

The factory acceptance tests for the mechanical parts and for the control system were successfully performed respectively at Sempell's premises in August 2006 and at Khartron premises in October 2006.

ZNPP performed, together with the Supplier, the first installation in Unit 4 during the outage in January/February 2007. After commissioning and testing in mid February, the Provisional Acceptance Certificate (PAC) for the first installation was issued on 26.02.2007. Similar successful installation steps were performed at the second installation (Unit 1) during the outage in May/June 2007, at the third installation (Unit 2) during the outage in July/August 2007 and at the last installation (Unit 3) during the outage in October/November 2007. The respective PACs were issued in July, August and December 2007. The warranty periods were monitored and no failure reports were issued.