Project General Data Beneficiary: Rosenergoatom Contractors: Empresarios Agrupados et.al. Local Subcontractor: MOCHT Sector of activities: Design Safety Sites: Kola & Novovoronezh NPP Installations: VVER 440/230 Status: Completed Budget: 827 000 € Duration: 20 months

Russian Organisations involved   The following Russian Organizations were involved, assuring an approach likely to be shared globally in the Russian Nuclear Community: -Concern «Rosenergoatom» the Beneficiary -Kola NPP and Novovoronezh NPP; -FSUE «Atomenergoproekt» (AEP), -Atomtechenergo (ATE) -VNIIAES -RRC KI (Kurtshatov Institute), -OKB-GP (Gidropress), -Regulatory Authority of RF Gosatomnadsor (GAN RF).

Objectives of the Project With this project the leak tightness of the confinement in Kola and Novovoronezh NPP (VVER-440/230-type reactors) was to be analyzed Current Russian Nuclear Regulatory Requirements had to be observed Special attention had to be paid to relevant improvements made in Bohunice and Kozloduy. Concrete proposals for improvement had to be defined.

Scope of the Work to be performed (1) The project covers the following phases: Review and estimation of leak tightness state of structures and equipment installed to provide leak tightness of the Hermetic Boundary Systems (HBS), using design and construction documentation as well as the previous tests results; Elaboration of proposals and guidelines to draw up documents, which describe criteria and methods for HBS improving; Review of Local and Integral Tests Programs to estimate the leak tightness state of HBS structures and equipment of the NPP Units mentioned above.

Scope of the Work to be performed (2)   Elaboration of criteria to provide the following: - comparison of requirements of Regulatory Authorities of Russia and Western countries and create a unified approach; - analyzing the geometrical characteristics of the confinement penetrations; - modification of the confinement using methods adopted at NPP Bohunice in Slovakia and NPP Kozloduy in Bulgaria; - adaptation of technical facilities and review leak tightness Procedures used at Western NNP, for applying at these four Russian units as far as possible; - sharing the operation experience, obtained during modernization in Slovakia and Bulgaria

Areas of leak tightness activities (1)   Proposing changes or using new leak tightness elements or compositions; Proposing more effective Procedures for inspection and finding the local leakage points; Recommendations for installation of permanent devices for periodic examination of local tightness; Proposals for modification or modernization of design of penetrations and other leak tightness equipment; Procedures of Local and Integral tests; Proposals for confinement modernization; repair Procedures Tighten leaks as far as possible within the given project’s budget

Areas of leak tightness activities (2)   Criteria on leak tightness were defined and adopted as follows: Decrease the leakage as low as possible or Total removal of leakages through all types of penetrations by the following means: Repair of damaged penetrations; Use of more effective hermetic materials being better adapted for surrounding conditions; Use of new locking and leak tightness systems; Removing standby penetrations as much as possible; Replacement of penetrations for more tighter structures.

Methods applied to measure leak tightness   First stage: Apply a maximal pressure of 100 mm water column, using ventilation systems П-2, П-4, fulfill HBS inspection, find and remove the defects; Second stage: Increase the total pressure inside HBS, up to maximal level of 1,3 kg/cm2, inspect confinement pressure-retaining boundary and find the defects and remove the defects found. Apply a vacuuming test with systems В-2, В-4, inspection and finding defects inside HBS;

Main components found, affecting leak tightness Electrical penetrations (because of their large quantity and unqualified leak tightness technology, using hermetic, which deteriorates with time); KUD valves Shaft leak tightness unit of re-circulating fan as the shaft leak tightness system does not meet requirements of leak tightness at shaft rotation; Welded units of hermetic lines; Rubber of sealing. Leak tightness rubber sealing in leak–proof doors, ventilation valves, valve ducts, ducts equipment and etc. have major leakages, due to aging Ventilation systems isolating valves; Shut-off valves of process systems.

Equipment to be tightened with priority (1)   The following equipment was considered to be most important for tightness: Pipe penetrations I & C Penetrations Electrical Penetrations Reactor shaft cover dome Fuel storage pond Hatches above the main cooling pump Hatches above Steam Generator and recycling ventilation system

Equipment to be tightened with priority (2) Welded joints of hermetic pipe lines Leak tightness doors Valve shaft extensions Steam dump ventilation shafts Pipelines isolating valves KUD-Valves Penetrations of air ducts and ventilation valves

Summary (1) As a result of the detailed review of the design documentation of the a.m. NPP Units, Tests Procedures, Test Programs and Inspection of the Units, the confinement’s existing leakages were significantly decreased by the following: Elaboration of leak tightness criteria and methods; Review and approval of Procedures, programs and methods to test the tightness; Elaboration of recommendations for separate items on the confinement boundary for increasing leak tightness extent up to the level required and sealing for new constructions and materials;

Summary (2) Replacement of material and sealing for new constructions and materials; Local tests for leakages indicate and further removing; Integral tests to value the leakages and compare with set leak tightness criteria.