Background
In the framework of the TACIS 1996 programme, the Commission contracted RWE Energie (later continued by Kernkraftwerk Gundremmingen – KGG) to provide on-site Assistance to Novovoronezh NPP (NvNPP) [R1.07/96T1 & T2 – 24698 & 24699]. The programme of work to be implemented by RWE Energie / KGG included, inter alia, the management of the implementation of the project R1.07/96A “Confinement Tightness Improvement in Units 3 and 4”.
The confinement of a VVER 440 nuclear reactor is the final barrier to radioactive release into the environment. The confinement is constructed as a system of pressure retaining hermetic rooms. In order to maintain and operate systems inside the confinement pipes, cables, etc penetrate the confinement wall. In case of an accident leading to pressurised confinement, these penetrations are a potential pathway for leakage and thereby release of radioactivity to the environment. Therefore, correct sealing of the penetrations is essential.
The project for the improvement of the confinement leak-tightness made use of results previously obtained at other VVER-440 V-230 units, and in particular the results of the project R1.10/91 (see 22129). Leak tests showed the different contributors to the high leak rate from the confinement, which had been identified by the IAEA as a Category III safety issue for first generation VVER-440 reactors (IAEA-TECDOC-640, Ranking of Safety Issues for WWER-440 Model 230 Nuclear Power Plants, February 1992). The main contributor was the poor quality of the welded seams of the hermetic steel liner of the confinement. Other major contributors included the rubber seals around doors and hatches, electrical cable penetrations and the ventilation system (the installation of fast acting isolation valves in the ventilation system at Kola NPP had resulted in 20-30% reduction in the confinement leakage rate). The End User (NvNPP) embarked on a programme of activities to improve the leak-tightness, addressing each of the different contributors. As a contribution to these activities, the Commission included the project R1.07/96A in the Tacis 1996 programme.
The project was divided into three parts:
• R1.07/96A-R: Rubber sealing material for hatches and doors
Hatches and doors are large penetrations of the confinement and most crucial elements for tightness of the confinement. Hatches and doors are provided with seal rubbers to ensure that the potential radioactive release to the environment around the hatches and doors is below the limits specified in the plant operation conditions. The existing rubber materials did not ensure leak-tightness during normal operation and under emergency conditions.
It was proposed to install new, sufficiently thick seal rubbers, vulcanized at the corners, to hatches and doors. Prior to installation of new seal rubbers the old seal rubbers had to be removed and the sealing surfaces checked and repaired if necessary.
• R1.07/96A-V: Installation of fast acting isolation valves in the ventilation system
In order to prevent radioactive release from the confinement into the environment, piping systems penetrating the confinement are designed with isolation valves to allow isolation of the confinement after specific incidents. To ensure reliable isolation of the confinement against radioactive release inside the confinement, fast-acting isolation valves are installed. Reliable operation of the isolation valves especially under harsh accident condition inside the confinement is required.
It was proposed to install isolations valves in the air ducts of the intake ventilation system of the confinement. Those valves are open under normal condition. In case of emergency, and via the signal "confinement overpressure", the valves have to close and prevent medium release beyond the confinement boundary. In this case the direction of medium flow is opposite to the normal medium flow because the pressure in the confinement will be higher than the atmospheric air pressure. Signals for operating the isolation valves are generated by the plant protection system.
• R1.07/96A-S: Sealing of electrical cable penetrations
Cable penetrations are crucial elements of the confinement leak-tightness. Sealant of cable penetration has to ensure that the potential radioactive release to the environment through the cable penetrations is below the limits specified in the plant operation conditions.

The OSA Consultant KGG, itself, supplied the rubber sealing materials.
Due to the length of time required to prepare for competitive tendering of the isolation valves for the ventilation system, the End User decided to take this project over itself, and it was cancelled from the Tacis programme.
The present contract was for the supply and installation of sealing material for the electrical cable penetrations (R1.07/96A-S).
Objective
The purpose of the supply and services provided by the present contract was to help to improve the confinement tightness of NvNPP Units 3 and 4 (VVER-440 V-230) by enhancing the sealing of the existing cable penetrations with elastic, heat-proof, fireproof and radiation-resistant sealants.
The existing cable penetrations were in operation since 1971 (Unit 3) and 1972 (Unit 4). The configuration, with stuffing boxes, did not ensure long term leak-tightness and the sealing glands were difficult to repair.
The selected supplier had to develop/provide the sealing methodology and supply sufficient sealant for 1636 cable penetrations, as well as 10% additional sealant as spare to cover contingencies or losses. The supplier also had to provide the process equipment required to prepare, install, inspect, test and repair the penetration seals (4 sets to allow simultaneous installation works).
Other duties of the supplier included the provision of associated documentation, training of End User’s staff and supervision of the sealing installation works performed by the End User personnel.
End User staff had to be trained in the sealing techniques, the preparation and application of the sealants, inspection and testing, and maintenance of the seals. The six End User personnel to be trained included trainers, who would later train other End User staff.
The existing penetrations had to be sealed without dismantling, disassembly or other operations which could damage the cables in the penetrations. The sealant should not lead to changing of the temperature conditions of the cables in the penetrations.
The sealants had to be able to perform its function in normal operating conditions, accident and emergency conditions and during fire.
Results
The contract was awarded to the company Mecatiss of France and was signed on 16 January 2004. Technical and design work was completed in the first half of 2004, but the first fire test results were not satisfactory. Further design work and new fire tests were required.
Equipment delivery was completed successfully and the Provisional and Final Acceptance certificates were signed in November 2006. However, at the end of 2006, the design failed to obtain the certification testing in Russia in order to meet the fire safety requirements. Further design and testing work was performed by the End User prior to installation at the NPP. Despite having received the Provisional and Final Acceptance Certificates and having received final payments, Mecatiss supported the End User in their further design and testing work.