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Neutron Irradiation Effects on VVER Reactor Internals

This international project aimed to provide assistance to the Russian Federation in ensuring the safety and structural integrity of VVER reactors. It involved reviewing the current status, conducting experiments, and evaluating neutron flux and structural integrity. The project resulted in a comprehensive report and recommendations for NPP design and operation.

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Neutron Irradiation Effects on VVER Reactor Internals

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  1. ROLE of JSC OKB "GIDROPRESS", JCS “GNC NIIAR” and CNII KM "PROMETEY" in INTERNATIONAL PROJECT ТАСIS 2002 (R2/01.02) V.M. Komolov, V.V. Evdokimenko, V.A.Piminov, I.O.Tregubov, V.I. Tsofin (JSC OKB "GIDROPRESS") B.Z.Margolin, A.A.Sorokin, A.I.Minkin (NRC “Kurchatov Institute” - CNII KM “Prometey”) I.Yu.Zhemkov, V.S. Neustroev, V.K.Shamardin (JCS “GNC NIIAR”)

  2. V.M. Komolov V.V. Evdokimenko V.A. Piminov Acting Tregubov V.I. Tsofin

  3. I.Yu. Zhemkov V.S. Neustroyev V.K. Shamardin

  4. B.Z. Margolin А.А. Sorokin A.I. Minkin

  5. Structure of VVER-1000 RP internals

  6. Internals of VVER-1000 Protective tube unit Core barrel Core baffle

  7. Project Title: Effect of neutron irradiation on properties of materials for VVER reactor internals Project No:R2.01/02 Beneficiary Country:Russian Federation Customer organization: European Commission, Bureau for European Assistance and Collaboration, Directorate A. Project starting date: March 01, 2006. Duration: 39 months Project target Global target: The global target was to render assistance to the Russian Federation on all safety-related issues dealing with design and operation of NPP with VVER reactors to make sure they no longer arouse concern of such international nuclear organizations as International Atomic Energy Agency (IAEA) and Nuclear Energy Agency (NEA). . INTERNATIONAL PROJECT (R2/01.02)ТАСIS 2002 PROGRAM. PROJECT SUMMARY

  8. Particular target:The particular target of the project was to provide Rosatom (former Minatom) and “Rosenergoatom” operating organization with a full set of verified experimental data and scientific / technical methods that consider state-of-the-art international experience and must be used for solving an issue of structural integrity of internals after long-term irradiation. Planned results: 1. Comprehensive review of the state-of-the-arts in science in the issues of internals ageing, embrittlement and integrity of VVER internals, including different material degradation mechanisms. 2. Report on mechanical tests of reference specimens in both irradiated and non-irradiated states. 3. Report on neutron flux distribution assessment in the internals of fore different configurations of the cores of selected reference NPPs with VVER. 4. Report on strength analyses of VVER internals that contains the assessment of loads and stresses acting on the internals under different conditions.

  9. Activities under the Project: Task 1. Project preparation. Task 2. Review of current status on structural integrity of VVER internals. Task 3. Evaluation of neutron flux on reactor internals. Task 4. Analysis of structural integrity of internals. Task 5. Program of experiments to achieve the project results. Task 6. Irradiation of selected specimens of internals material 08X18H10T and respective weld. Task 7. Tensile and fracture toughness tests of irradiated material (08X18H10T with weld) in comparison with non-irradiated material of internals (reference material). Task 8. Stress corrosion cracking (SCC) test of irradiated materials in comparison with non-irradiated reference materials of internals. Task 9. Study of swelling effect in irradiated material of internals. Task 10. Assessment of general scientific and technical significance of the results. Recommendations on NPP design development and operation. Task 11. Project finalization.

  10. Project arrangement diagram European Commission (EC) • Steering Committee: • - Project Manager (EC); • Representative of Beneficiary; • - Consultant Team Leader. Beneficiary Rosenergoatom Concern Consultant IBEDROLA Experiment Leader OKB “GIDROPRESS”

  11. Project arrangement diagram of Experiment Leader

  12. Activity Target of Task 1 Investigated Problems Several problems were singled out in the technical issues of structural integrity of VVER reactor internals: 1. Insufficient amount of experimental data on the changes of metal properties of VVER internals (mainly made of stainless austenitic steel 08X18H10T) under acute irradiation; 2. Method of interpretation of similar data and their usage in the developed models is still the subject matter of scientific/engineering discussions at international level; 3. Provision of availability of internationally recognized methods of calculations of stresses in the internals at different conditions in the core and also for safety criteria to be used in the Official Safety Reports. 4. Provision of availability of knowledge and mutual understanding among the international experts in the field of inspection of the internals for PWR NPPs, Russian VVER reactors included. Documents below were developed by EL within the framework of accomplishing Task 1: 1. Inception Report. 2. Logical basis of Experiment Leader. 3. Quality Control Program for TACIS R2.01/02 project activity implementation. Project preparation

  13. Activity Target of Task 2 Analysis of available experimental data for the stated problem and assessment of the current status. The review included: data on the internals of VVER-440 and VVER-1000; analysis of available methods on structural integrity of internals and determination of the list of materials required for the analyses; information on the materials of internals of VVER-440 and VVER-1000; preliminary conclusion on the effect of irradiation on mechanical properties of chromium-nickel austenitic steels type 18-10; preliminary conclusion on the effect of irradiation on swelling and irradiation creep of chromium-nickel austenitic steels type 18-10; preliminary conclusion on the effect of irradiation on fracture toughness of chromium-nickel austenitic steels type 18-10; preliminary conclusion on the effect of irradiation on fatigue crack resistance in chromium-nickel austenitic steels type 18-10; preliminary conclusion on the impact of high temperature water environment on fatigue resistance of chromium-nickel austenitic steels type 18-10. Review of current status on structural integrity of VVER internals

  14. Activity Target of Task 3 Evaluation of neutron flux in four different core configurations using the information from design documents of prototype Units and calculational models. Two prototype Units were considered: for VVER-440 reactor: Kola NPP, Unit 2; for VVER-1000 reactor: Balakovo NPP, Unit 1 Evaluation of neutron flux on reactor internals

  15. The Case for VVER-440 reactor dealt with: full loading of the core; core loading with 36 shield fuel assemblies. The Case for VVER-1000 reactor dealt with: the core with fresh FAs over the periphery; the core with reduced neutron leakage. Task 3involved determination of values of fast neutron flux with energy above 0.1 MeV acting on metal of internals including distribution over the azimuth, height and thickness of reactor internals. Rates of accumulation of the number of displacements per atom in the metal of reactor internals were also determined.

  16. Activity Target of Task 4 The work was performed in two stages. Stage 1 comprised: Determination of stresses from taken loads for VVER-440, VVER-1000; Determination of stresses in the most irradiated components of internals (core barrel, core baffle, basket) from the power determined in Task 3. Analysis of structural integrity of internals

  17. Stage 2 comprised: Determination of boundary conditions for the mode of start-up, normal operating conditions, shutdown mode, large-break LOCA; Determination of temperature fields and stresses in components of internals in steady-state start-up mode. Determination of temperature fields and stresses in components of internals in scheduled shutdown mode. More accurate calculations of stresses in the components of internals at large-break LOCAs; Determination of most critical points of internals and critical sizes of cracks for them. Activities performed under Task 4: 1. Strength analysis of internals under a break of main coolant pipeline of VVER 440. 2. Strength analysis of internals under a break of main coolant pipeline of VVER 1000. 3. Determination of power induced stresses in the most irradiated components of internals for VVER-440 and VVER-1000. 4. Determination of temperature fields and stresses in components of internals in start-up, steady-state shutdown and large break loss of coolant accident. 5. Determination of the most critical points of internals and critical sizes of cracks for them.

  18. Activity Target of Task 5 The purpose of the work was to prepare full program of irradiation and tests of specimens for its subsequent implementation according to the requirements of TACIS R2.01/02 Project. The program defines the type and quantity of specimens for irradiation and tests as well as the general requirements for the testing conditions that were established in accordance with the requirements of the Project. The strategy of the LE experiment established the requirements for the selection of the investigated materials, manufacturing of the specimens, Program and the requirements for irradiation of the manufactured specimens as well as the Program, requirements and conditions of specimen testing in the initial and irradiated states and the Program for subsequent experimental processing of the results. Program of experiments to achieve the project results

  19. Scope of assignments for irradiation exposure and testing for Tasks 6, 7, 8 and 9

  20. Activity Target of Task 6 Irradiation of specimens made of materials of the internals (steel 08Х18Н10Т and its weld metal). Irradiation of specimens of steel 08Х18Н10Т and its weld metal was done in BOR-60 research reactor at GNC NIIAR (in Dimitrovgrad). Type and quantity of irradiated specimens were defined in the Terms of Reference of the Program of TACIS R2.01/02 Project. To determine the effect of neutron irradiation on the properties of materials of the internals, the irradiation was performed in the conditions as close as possible to the operating conditions of VVER-1000. Irradiation temperature was 320-350C, irradiation was maintained up to the three different levels of damaging dose (5÷7, 25, 40 dpa) as established in R2.01/02 Project. Irradiation of selected specimens of material of the internals 08Х18Н10Т and respective weld

  21. Activity Target of Task 7 Experimental study aimed at defining the characteristics of mechanical properties under tensile test, fracture toughness and cyclic crack resistance (rate of fatigue strength growth da/dN=f(K)) of materials of VVER internals (steel 08Х18Н10Т and metal of its welds) in the initial (non-irradiated) state and after neutron irradiation with various damaging doses. The tests were performed in the irradiated material study scientific laboratory of CNII KM “Prometey” (Gatchina). Tensile tests of irradiated materials and partially the tests in the initial state were performed in the hot cell laboratory of JSC GNC NIIAR (in Dimitrovgrad). Tensile and fracture toughness tests of irradiated material (08X18H10T with weld), comparison with non-irradiated material of internals (reference material)

  22. Activity Target of Task 8 Tests of irradiation-assisted stress corrosion cracking (IASCC) were performed to determine the sensitivity of irradiated materials to SCC under the conditions of neutron irradiation and high reactor coolant temperatures. Tests were performed in autoclave at high temperature in the environment similar to the primary-side water at the NPPs with VVERs. The purpose of the tests for IASCC was to determine the dynamics of the origination and propagation of the crack as well as the threshold values for its origination, propagation and stopping. Load increase method or other appropriate methods of SCC checking that create the necessary parameters of KISCC corrosion etc. were used as the testing methods. Stress corrosion cracking (SCC) test of irradiated materials in comparison with non-irradiated reference materials of the internals

  23. Activity Target of Task 9 Determination of swelling and assessment of the effect of irradiation damage dose on swelling of materials of VVER internals (steel 08Х18Н10Т and its weld metal). Swelling was determined using the method of comparative study of the density of specimens of the studied materials both in the initial and irradiated states. Scope of testing to determine the swelling of materials in the initial and irradiated states was defined by the Program for TACIS R2.01/02 Project activities. All the tests except for the tests of materials irradiated to 40 dpa were carried out in two irradiated material study scientific laboratories: in CNII KM “Prometey” and JSC GNC NIIAR. The tests of materials irradiated to 40 dpa were carried out in CNII KM “Prometey”. Study of swelling effects in irradiated materialof internals

  24. Activity Target of Task 10 Preparation and issue of the report on analysis of scientific and technical importance of general result obtained during tests and studies performed under the Project. The Report covers: values of critical crack sizes for potentially most critical points of the internals; description of the effect of operational factors on the embrittlement, stress corrosion cracking, swelling and creep of the materials of internals. The report on assessment of scientific and technical importance of the results and recommendations regarding NPP design development and operation has summed up all the results of the work performed under Tasks 19 of R2.01/02 Project, TACIS 2002 Program in accordance with the Terms of Reference for the Project. Assessment of general scientific and technical significance of test results. Recommendations on NPP design development and operation

  25. Activity Target of Task 11 The R 2.01/02 International Project of TACIS 2002 Program was completed by holding the summing up workshop with the presentation of the results of the performed activities in OKB GIDROPRESS on February 25, 2010. The analytical and experimental activities on Tasks 2÷9 were performed in full scope in accordance with the Terms of Reference. The activities under the project were performed by Experiments Leader OKB “Gidropress” in consortium with CNII KM “Prometey” and JSC GNC NIIAR. The analytical and experimental data obtained under the Project were used: in justification of safe operation of the internals of VVER-1000 RP for international customers; in drafting the R&D Programs on the justification of the service life extension of the VVER RP internals up to 60 years; in elaboration of the programs of creating new advanced steel for internals. Project finalization

  26. THANK YOU FOR ATTENTION!

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