Previous SG safety valves experienced several design shortcomings:
- No qualification under water and steam-water mixture: operating reliability is not guaranteed, inducing a risk of stuck open or closed valve
- Availability of spare parts is not guaranteed, as supplier is not existing any more
- Difficulties in maintenance and in adjusting opening/closing set points
- Deviation from Ukrainian regulations
These points led to the need for replacement of SG safety valves at Rovno NPP.
The present TACIS project U1.01/95C aims at replacing the 12 SG (steam generator) safety valves (2 per SG) of each unit 1 and unit 2 of Rovno NPP. The new safety valves should have the following functions:
- High level of reliability for opening and closing
- Qualification to all fluids, which can go through SG safety valves: steam, water, steam-water mixture
- Ability to withstand water hammer load in case of overfilling of SG
- Automatic opening and closing, with good accuracy of set points
- Ability to open/close SG steam valves from main control room for feed and bleed
Technical specifications and tender dossier were prepared by OSA utility EDF (Electricité de France) in the frame of general OSA contract U1.01/95. These TS were prepared in close cooperation with Rovno NPP and Energoatom. Invitation to tender was launched on 20th May 1998, and technical tender evaluation took place in December 1998. Financial evaluation took place in July 1999. Then, French company SEBIM was selected, and supply contract was signed on 25th February 2000.
Implementation of the supply contract:
Tasks performed by the contractor were the following,
- Establishment of a work plan and a quality assurance plan
- Studies for implementation of the detailed design of new safety valves
- Writing and delivery of design and operational documentation
- Manufacturing of new safety valves
- Supply of safety valves at Rovno NPP
- Certification and support to licensing
- Supervision of on-site installation
- Testing and commissioning
- Warranty period.
Other partners have been involved in the implementation of the project, outside contractor’s scope:
- Rovno NPP: validation of all steps of the project, installation, commissioning, licensing
- Energoatom: validation of all steps of the project, licensing
- KIEP: studies of integration of new safety valves to Rovno NPP systems
- EDF (OSA utility): general follow-up of the project, and general support, in the frame of general OSA contract U1.01/96
- UNRA + Riskaudit: licensing
Technical description of the supply:
Each Rovno NPP unit 1 and unit 2 has 6 SG. Each SG is equipped with 2 safety valves. Selected contractor SEBIM proposed a technology of safety valves with a single main valve equipped with a spring (normal mechanical opening/closure) and a pilot valve (small valve motored by steam of main valve: this pilot valve actuates itself main valve).
In case of steam pressure increase, pilot valve detects this steam pressure increase and, at a certain threshold, actuates the opening of main valve. Once steam depressurisation reaches another threshold, pilot valve actuates the re-closure of main valve. This gives a high accuracy and a high reliability of opening and closure.
In addition, SEBIM valves are qualified for any fluid, which the safety valve could contain (steam, water, steam-water mixture).
SG safety valves are equipped with a remote control system: they can be opened/closed from main and emergency control rooms, in order to perform feed and bleed when requested by accident management procedures.
Ukrainian side requested the installation of an additional system of electrical opening/closure of SG safety valves. It consists in the installation of pressure sensors and an I&C box for opening/closing safety valves at certain thresholds.
SG safety valves are designed and manufactured to withstand design basis seismic loads, and are classified for safety.
Time schedule of the implementation phase:
- 25th February 2000: supply contract signature
- Project kick-off meeting was held at Rovno NPP in March 2000
- Manufacturing of safety valves for unit 1 was completed in January 2001, and for unit 2 in May 2001
- Factory acceptance tests were performed at SEBIM facilities in February 2001
- Certification of the safety valves was issued in July 2001
- Delivery of SEBIM safety valves for unit 1 at Rovno NPP was completed in March 2001, and for unit 2 in May 2001
- Installation of safety valves was performed on unit 1 during outage in April-May 2001, and on unit 2 in July-August 2001
- Provisional acceptance of safety valves was issued for unit 1 on 5th June 2001, and for unit 2 on 17th August 2001
- 1-year warranty period run without problems. Final acceptance was signed in June 2002 for unit 1 and in August 2002 for unit 2.