TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 1 Rev.: 05/10/2005 Main Project Data  Beneficiary: GOSATOMNADSOR  Contractor: RISKAUDIT, AEA-T, GRS & VTT  Local Subcontractor: SEC NRS  Budget TACIS (1992): € (1992)  Duration: 24 months  Contract started in: November 1996  Contract expired in: November 1998

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 2 Rev.: 05/10/2005  Overall Objective:  Strengthen GAN and its TSOs in the field of assurance of Reactor Pressure Vessel integrity, focussing on VVER 440/230 units (Novovoronezh 3/4 & Kola 1/2)  Main Targets:  Assess the results of the TACIS project R1.1/91 (Reactor Vessel Embrittlement), which is known as the “industrial project”, dedicated to the assessment of the materials aspects of RPV integrity of the VVER 440/230 units using samples taken from Novovoronezh 2, 3 & 4  Analysis of the loading of the RPV during Pressurised Thermal Shock (PTS) transients and the In-Service Inspection of the RPV 1. Objectives of the Project

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 3 Rev.: 05/10/2005  The working plan included 6 technical tasks, including drawing conclusions:  Task 1: Main factors influencing the Embrittlement  Task 2: Reduction of Embrittlement by Annealing  Task 3: Loss of Integrity of the RPV due to Brittle Fracture  Task 4: Review of In-Service Inspection Programme  Task 5: Structural Integrity of the RPV after Boat Sampling  Task 6: Technical Recommendations for RPV issues  5 interim (task) reports and a final report have been delivered (all in English) 2. Implementation

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 4 Rev.: 05/10/ Main factors influencing the Embrittlement  Codified KIc curves (see figure 1), for base and weld materials respectively, are experimentally based  Ductile to brittle reference temperature Tk is determined from dynamic Charpy V results, but indexed upon the true room temperature yields stress  For VVER 440 RPVs, empirical treatments of Charpy V results have led to the following codified formulae: A F = 800. (P[%] + 0,07. Cu[%]), for an irradiation temperature of 270°C A F = 800. (P[%] + 0,07. Cu[%]) + 8, for an irradiation temperature of 250°C

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 5 Rev.: 05/10/ Main factors influencing the Embrittlement ( Cont. )  No surveillance programme is implemented on VVER 440/230 RPVs. Therefore, the codified prediction laws are applied  The “industrial project” dealt with detailed experimental investigations on samples of Novovoronezh 2 (a decommissioned for-runner of the VVER 440/230 series, operated [270°C] during 20 years) and characterisation of boat-samples of Novovoronezh 3 & 4 (both operating [270°C] VVER 440/230s) RPVs  Conclusions and recommendations have been proposed on the basis of the evaluation of the available results of the “industrial project” and additional information

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 6 Rev.: 05/10/2005  3 fundamental re-embrittlement models have been considered. An early (1989) technical- normative document has recommended the conservative model  The horizontal shift model appears conservative for Novovoronezh 3 & 4 embrittlement history reconstruction (annealing / re-embrittlement). This conclusion applies also for other available results (Novovoronezh & Kozloduy 1)  Pre-established linear sub-size / standard Charpy correlations have been confirmed 3.2 Reduction of Embrittlement by Annealing

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 7 Rev.: 05/10/2005  Key features and assumptions for predicting the (re-) embrittlement kinetics in the “industrial project” have been discussed :  Techniques for determining the neutron doses and chemical compositions  Standard Charpy V testing and results’ evaluation have been performed according to Russian (equipment & type of specimens) and international standards  Sub-size / standard Charpy correlations are used to normalise the results  The method applied for determining T k0 and uncertainties and errors in the assessment of the input data should be considered for consolidating the proposed prediction model for re- embrittlement kinetics 3.2 Reduction of Embrittlement by Annealing ( Cont. )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 8 Rev.: 05/10/2005  RPV integrity assessment is based upon the comparison of the maximal stress intensity factors which may occur at the tip of postulated cracks (various sizes, shapes, orientations and positions) during situations which can cause potential over- pressurisation effects (normal operation and the most severe PTS transients) with the fracture toughness of the material (depending upon the temperature and correlated with T k at the end of the operating period considered) 3.3 Loss of Integrity of the RPV due to Brittle Fracture

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 9 Rev.: 05/10/2005  The Russian procedure (PNAE 89), originally developed for design purposes, is similar to those in use in Western countries; differences resulting from materials and safety factors  Different aspects important for Russian RPV integrity assessments have been reviewed (techniques, procedures and major assumptions)  Realistic modelling, conservative initial and boundary conditions and safety factors on the material properties is common practice  Conclusions and recommendations haven been be drawn as a result of the extended review 3.3 Loss of Integrity of the RPV due to Brittle Fracture ( Cont. )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 10 Rev.: 05/10/ Review of In-Service Inspection Programme  PNAE-G, GOST-series and the Type Inspection Programme for VVER 440 (AIE-2-95) prescribe the scope and frequency, the organisation, the types and techniques, the methodology as well as the Quality assessment norms  Plant specific Work Programmes, prepared by the plant owner and approved by the on-site inspectorate of GAN, contain detailed information upon the component to be inspected, the inspection tools, procedures, methodologies, and requirements for personnel, etc  Equipment and pipelines are classified in 3 safety groups (A, B & C)  PNAE G prescribes the scope of inspection to be performed with each appropriate non-destructive examination technique for each category (I, II & III) of components (e.g. welds), directly related to the safety classes (A, B & C) and further considerations (subcategories a, b & c relate to operational pressure).

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 11 Rev.: 05/10/ Review of In-Service Inspection Programme ( Cont. )  Pre-Service Inspection (PSI) is required to register the initial status of the components. The inspections’ intervals are depending on the safety group  The NDT procedures are developed by specialised organisations and approved by GAN  NDT personnel taking part in manual inspections is certified (by specialised institutes authorised by GAN) according to PNAE G Inspection personnel for automated inspection systems are qualified within specialised organisations  The assessment has shown that Russian documentation covers all the major issues related to effective performance of ISI of RPV (areas covered are similar, but administrative measures should be improved)

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 12 Rev.: 05/10/ Review of In-Service Inspection Programme ( Cont. )  Differences in practice exist in ISI of Russian NPPs related to the variety of mechanised inspection equipment and tools (Russian original and Western are coexisting). Limitations should be compensated (accessibility). Systematic registration of indications is done. Better conservation of the data and use of modern assessment tools should be introduced  Russian system for certification of NDT personnel differs from the one applied in Western Countries, based upon EN 473, but the requirements and, consequently, the competence of certified personnel are considered to be very similar  The qualification of ISI systems (equipment, procedure, personnel) is still under development (ENIQ methodology is suggested to serve as a basis )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 13 Rev.: 05/10/ Structural Integrity of the RPV after Boat Sampling  The objective of this task was to assess the effects of the grind-outs (after sampling) at the inner surface of the RPV on the local stress fields during normal and upset conditions and the allowable transition temperature T k a during typical PTS transients  The increase of the local peak stresses (few percent at maximum / negligible 40 mm away from the grind-outs) for normal and upset conditions are very limited. These effects are considered insignificant (Framatome and EDO Gidropress)  GRS and EDO Gidropress performed specific studies for typical PTS transients to assess the influence of the grind-outs and the maximum defect size. The effect (decrease of T k a of 6 to 7°C due to the grind-outs) is depending upon many parameters (load path, critical temperature range and crack configuration) and needs to be assessed with appropriate methods to avoid over-conservatism.

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 14 Rev.: 05/10/ Main Conclusions & Recommendations  This project has been performed within the planned period and produced a set of good technical reports addressing all aspects of integrity assessment of RPV  VVER 440/230 units have been the main focus, but the review expanded to a broader scope  The systematic review has provided for thematic information summaries, which are valuable bases for building appropriate case-by- case regulatory statements  The recommendations issued are of high importance in that respect. Periodic updating according to the actual situation at the plants is necessary

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 15 Rev.: 05/10/2005  Recommendations  The methodology for assessing the embrittlement effects in Russia is based on similar elements (experimentally based correlations and formulas) as in Western Countries. Continuous improvements are necessary to take advantage of technical developments. With this respect the following is proposed: T k (similar to RT NDT ) relates poorly with K Ic, but retrospective access to T k0 should also be consolidated (correlation with chemical composition) Improving the KIc / (T-Tk) correlation on a statistical basis or replacing it by alternative advanced concepts e.g. “Master Curve” Standard AF is recognised to be conservative (possible revision should be based on ΔKIc), but the temperature effect needs further study 4 Main Conclusions & Recommendations ( Cont. )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 16 Rev.: 05/10/2005  Recommendations  The horizontal shift model conservatively predicts the annealing efficiency and the re-embrittlement kinetics, but the related uncertainties should be considered. Moreover : A methodology should be developed for this purpose Mean line and the associated error in the mean line should be considered in the sub-size / standard Charpy V correlations Sampling for direct characterisation of the RPV at Kola NPP 1 & 2 and further accelerated irradiation in a host reactor of spare specimens is strongly supported 4 Main Conclusions & Recommendations ( Cont. )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 17 Rev.: 05/10/2005  Recommendations  In the future, best estimate (advanced) methods (including uncertainties analyses) are needed for treating sensitive (law margin) cases of RPV integrity assessment. Consequently : Participation in international codification and benchmarking exercises is recommended to the Russian experts for improving mutual knowledge and recognition, as well as further validation of the Russian codes Although implified analytical methods for the calculation of stress intensity factors at the crack tip are reasonable and acceptable for uncladded vessels, advanced fracture mechanics methods are needed for cladded vessels In case of small margins in terms of Tka, a sensitivity analysis on various parameters of the defect could help in assessing the situation Calculated allowable defects should be regarded in the context of the performance and results of the ISI. 4 Main Conclusions & Recommendations ( Cont. )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 18 Rev.: 05/10/2005  Recommendations  The Russian documentation for ISI covers all the major issues related to effective performance of ISI of RPV. The areas covered in the inspection programme are similar to those addressed in western practices. In addition : Appropriate administrative measures should enforce the implementation of the practical work programmes It is recommended to replace the outside inspections of the RPV by inspections from inside in order to compensate for some limitations (mainly accessibility) The Russian practice, which is to register all indications is appreciated for its capability to ensure for monitoring of subsequent inspections, but assessment by modern techniques should be used For improving definitely the ISI practice in Russia, the European Methodology for Inspection Qualification (developed by ENIQ) is suggested to serve as a basis 4 Main Conclusions & Recommendations ( Cont. )

TACIS Project: R8.01/98 - DISSEMINATION OF RESULTS: "TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS" Licensing Related Assessments of Reactor Vessel Embrittlement TACIS R/TSO/VVER-01C Page 19 Rev.: 05/10/2005  Recommendations  Several VVER 440 /230 RPVs (e.g. Novovoronezh 3 & 4) have grind- outs left (following boat sampling), typically 7-10 mm depth and curvature radius between 200 & 300 mm. Studies confirmed very limited increase of the local peak stresses (few percent at maximum / negligible 40 mm away from the grind-out) for normal and upset conditions. These effects are considered insignificant In contrast to the situation during normal and upset conditions, grind- outs should be considered in PTS events assessments 4 Main Conclusions & Recommendations ( Cont. )