Tacis 2.02/95 on VVER 440 RPV Integrity TACIS Project: R8.01/98 – TRANSLATION, EDITING AND...

Tacis 2.02/95 on VVER 440 RPV Integrity Slide 1Rev.: 4.10.2005

TACIS Project: R8.01/98 – TRANSLATION, EDITING AND DIFFUSION OF DOCUMENTS (Result Dissemination)

Tacis R2.02/95, “VVER 440-230, Reactor Pressure Vessel Integrity Assessment”

Beneficiary: Rosenergoatom, MoscowContractor: EdF, VTT, FortumLocal Subcontractor: Moht & AtomenergoexportBudget: 697000 €Duration: 24 monthsContract expired: December 1999




Objectives of the project

• Carry out accelerated re-embrittlement experiments on spare templates from Novovoronezh 3 & 4 RPV for validation of re-embrittlement 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.




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)




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




Fig. 2 Comparison of experimental and calculated embrittleemnt rates after irradiation-annealing-reirradiation cycle of RPV core weld of Novovoronesh NPP Unit 4.




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




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





Fig 3. Probability of defect size larger than a





Task 3 Evaluation of the Kinetic Hardness Method (KHM)

• The objective to evaluate feasibility of determining mechanical properties by a non-destructive 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)




Fig 4. Comparison of Rp0,2 values from real

tensile testing with the KHM method for NV 3 core weld




Fig 5. Comparison of Rp0,2 values from

real tensile testing with the KHM method for NV 4 core weld





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




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 TACIS Project: R8.01/98 – TRANSLATION, EDITING AND...

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