TACIS Project R 8 0198 TRANSLATION EDITING AND

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TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Beneficiary: Contractor: Local Subcontractor: Budget: Duration: Contract expired: Tacis 2. 02/95 on VVER 440 RPV Integrity Rosenergoatom, Moscow Ed. F, VTT, Fortum Moht & Atomenergoexport 697000 € 24 months December 1999 1

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Objectives of the project • Carry out accelerated re-embrittlement experiments on spare templates from Novovoronezh 3 & 4 RPV for validation of reembrittlement kinetics. • The elaboration of data files (material properties and NDT) needed for the PTS assessment of WWER 440 /230 RPV. • Elaboration of mechanical properties by direct measurements of kinetic hardness of the RPV core region material. • Re-evaluation of the crack initiation toughness (KIc))/ temperature indexation curve by consideration of all typical (representative of WWER 440 / 230 weld materials) results, available in Russia. • Presentation of the results to the local Safety Authorities. Tacis 2. 02/95 on VVER 440 RPV Integrity 2

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Project implementation and results Task 1; Accelerated re-embrittlement experiments for Novovoronesh 3&4 RPV core weld – Templates form the RPV were used for the experimental part – Sub-size test specimens were irradiated in the Kola NPP, Unit 4 – Neutron dose was estimated on routine bases by measuring Mn-54 activity – Irradiation temperature was monitored with melting binary alloys – The test specimens were tested in RRCKI in Moscow after re-irradiation cycle – The increase in yield strength as expected – The shift in transition temperature in re-irradiation after annealing was much smaller than expected (Fig 1 and 2) Tacis 2. 02/95 on VVER 440 RPV Integrity 3

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Fig. 1 Comparison of experimental and calculated embrittlement rates after irradiation-annealing-re-irradiation (IAI) cycle of the RPV core weld of Novovoronesh NPP Unit 3 Tacis 2. 02/95 on VVER 440 RPV Integrity 4

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Fig. 2 Comparison of experimental and calculated embrittleemnt rates after irradiation-annealing-reirradiation cycle of RPV core weld of Novovoronesh NPP Unit 4. Tacis 2. 02/95 on VVER 440 RPV Integrity 5

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Project implementation and results (cont. ) Task 2; Data files for Pressurized Thermal Shock (PTS) assessment; “material properties” • A comprehensive summary of material properties needed for PTS studies was elaborated • The summary included data on mechanical and chemical properties as well as crack initiation and fatigue crack growth • Plant specific material data from Russian VVER 440/230 units • Data from open literature, previous projects and other available sources were collected • RPV core weld embrittlement aspects were a most important issue (influence of neutron irradiation as a function of neutron fluence) • Effect of annealing and post annealing embrittlement was included Tacis 2. 02/95 on VVER 440 RPV Integrity 6

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Project implementation and results (cont. ) Task 2; Data files for PTS analyses; Non-Destructive Testing (NDT) results • Spectrum of expected remaining defects in the RPV was elaborated • Data collected from NDT-results of manufacturing and acceptance control of VVER RPVs • Statistics and experience from manufacturing induced defects was elaborated • Detection probability based on the applied quality control and ISI was evaluated • Influence of cladding was also considered • Corresponding data from Skoda manufacturing procedures was also included • The flaw distribution in Russian and Czeck RPVs was practically the same • The Marshal distribution gives a higher probability of defects (Fig. 1) • No remarkable defects found in any VVER RPVs in ISI Tacis 2. 02/95 on VVER 440 RPV Integrity 7

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Project implementation and results (cont. ) Task 3 Evaluation of the Kinetic Hardness Method (KHM) • The objective to evaluate feasibility of determining mechanical properties by a nondestructive method: KHM • A correlation has been found between the KHM and the tensile strain diagram • According to VNIIAES a correlation has also been confirmed with toughness properties and embrittlement due to irradiation • If so, the KHM method could be used for assessing irradiation embrittlement and toughness properties of the core region material of an operating RPV • This method could accordingly be considered revolutionary • Some controversial opinions do exist regarding the reliable applicability of the method on operating RPVs • In Task 1 above, the correlation could not be confirmed (Fig 4) Tacis 2. 02/95 on VVER 440 RPV Integrity 9

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Project implementation and results (cont. ) Task 4; Re-evaluation of the Fracture Toughness curve KIc – Re-evaluation of the Russian KIc curve by considering all VVER 440/230 RPV results available in Russia – Comparison with similar results from Phare 2. 01/95 – The quality of the available Russian fracture toughness data did not enable upgrading of the KIc curve in a fully reliable way according to the Maters Curve method – The results confirmed that the Fracture Toughness dependence of Eastern and Western type of RPV steels have a similar temperature dependence Tacis 2. 02/95 on VVER 440 RPV Integrity 12

TACIS Project: R 8. 01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination) Tacis R 2. 02/95, “VVER 440 -230, Reactor Pressure Vessel Integrity Assessment” Project implementation and results (cont. ) Global conclusions and recommendations – The embrittlement rate of the core weld at NV Units 3 & 4 was much smaller than expected based on sub-size specimen testing – Fracture toughness of template samples should be determined direct by static bend test of pre-cracked sub-size Charpy specimens – Russian acceptance standard for flaw evaluation and PTS analyses are well established – The correlation between mechanical tensile testing and KHM method was poor – Present Russian fracture toughness test data should be re-evaluated by analysing original load-displacement curves, if available – A more accurate statistical analysis using Master Curve approach should be performed Tacis 2. 02/95 on VVER 440 RPV Integrity 13