Operation and Maintenance & Research and Development Activities in Czech Republic at the field of LTO and AM Technical Working Group on Life Management of Nuclear Power Plants 25-27 February 2015, IAEA,Vienna Miroslav Žamboch 25. 2. 2015
Structure 1. General information 2. Modernization of RPV EDU LifeTime and Integrity Assessment 3. Reflection of the Doel and Tihange events at Czech NPPs 4. Evaluation of the Swelling development 5. First steps of NDT development to identify swelling 6. Environmental Fatigue
Structure 1. General information 2. Modernization of RPV EDU Life Time and Integrity Assessment 3. In Service Inspection program modification 4. Reflection of the Doel and Tihange events at Czech NPPs 5. Computational Evaluation of the Swelling development 6. First steps of NDT evolution to identify swelling 7. Environmental Fatigue
NPP Dukovany 4 PWR units - VVER 440/213 type Operation since 1985 Power up-rate to 500 MWe finished in 2012 6 reactor coolant loops with horizontal steam generators, 2 turbine generators Original projected life time 30 years (excluding RPV which has 40 years) Unit 1 goes in 2016 in LTO 3
NPP Temelin 2 PWR units - VVER 1000 V320 type Operation since 2002 Power up-rate to 1055 MW 4 reactor coolant loops with horizontal steam generators, 1 turbine generator Original projected life time 30 years (excluding RPV which has 40 years) 4
Structure 1. General information 2. Modernization of EDU RPV LifeTime and Integrity Assessment 3. Reflection of the Doel and Tihange events at Czech NPPs 4. Computational Evaluation of the Swelling development 5. First steps of NDT evolution to identify swelling 6. Environmenta Fatigue
Lifetime and Integrity Assessment of RPV EDU The original design project including RPV computational documentation corresponds to the state of art of 60ties and 70ties of the last century The existing analysis were not taken as sufficient for LTO The new Lifetime and Integrity assessments were developed based upon Modern FEM model of the RPV Geometry (global, local) based upon information from original design documentation and where necessary measured on the VVER 440 RPV (Škoda JS, Paks) Material (type, heat, properties) from components passports Real operational load history sequence of operational regimes and its realistic extrapolation Loads (mechanical, newly calculated temperature transients) 6
Examples of original drawings 7
Measurement on abandoned RPV 8
Laser scanning of RPV head (HRK nozzle flange) - results 9
Benefits of new Assessments Lifetime and Integrity Assessments corresponding to the LTO requirements and current stat of art were elaborated Fatigue TLAA of RPV for 40 years of operation Identification of critical point from fatigue point of view Preparation of remedial action to ensure lifetime 60 years Modification of ISI Modification of operational procedures Modification of CSAMP Pressure vessel Sources for updating of related technical documentation 10
Structure 1. General information 2. Modernization of RPV EDU Life Time and Integrity Assessment 3. Reflection of the Doel and Tihange events at Czech NPPs 4. Evaluation of the Swelling development 5. First steps of NDT evolution to identify swelling 6. Environmental Fatigue
Reflection of Doel and Tihange events in Czech Republic In 2012 on Doel 3 and Tihange 2 RPV unit were discovered thousands indications of hydrogen induced flaws. As consequence were evaluated in Czech republic: Producing technology of VVER 440 and VVER 1000 material and vessels Scope of the In Service Inspection Program with respect to Doel and Tihange indications position The used NDT method sensitivity to the hydrogen flakes like indication As result it was stated that: Used technology of material and vessels production should exclude occurrence of this type defects Potential occurrence of the defect shall be identified during postproduction examination carried out by manufacturer The scope of the ISI and NDT methods used are reliable for identification of potential defects of this type 12
Structure 1. General information 2. Modernization of RPV EDU Life Time and Integrity Assessment 3. Reflection of the Doel and Tihange events at Czech NPPs 4. Evaluation of the Swelling development 5. First steps of NDT evolution to identify swelling 6. Environmental Fatigue
Evaluation of WWER-1000 core baffle shape change due to irradiation swelling VVER-1000 core baffle is important part of reactor internals Main functions are: Decreasing neutron flux on RPV Ensuring cooling of the core Irradiation swelling is considered as one of the main degradation mechanisms influencing VVER 1000 internals Assessment of the of the effects of the irradiation swelling was performed according to methodology described in Appendix C of VELFIFE standard ver. 2014* * It has not been officially published up till now 14
Evaluation of WWER-1000 core baffle shape change due to irradiation swelling - results It was calculated that at the end of assumed LTO period 60 years: Maximal value of radiation swelling of core baffle 15.3% The Radial displacements (positive)of the outer core baffle surface in critical points could be larger then design gap between core baffle and core shroud Radial displacements (negative) of the inner core baffle surface will not exceed design gaps between core baffle and fuel assembly after 60 years of operation Temperature distribution during typical operation campaign, reactor on working parameters 15
Evaluation of WWER-1000 core baffle shape change due to irradiation swelling - results Radial displacements distribution in 60th campaign at the working parameters As precondition for LTO of VVER 1000 reactor it is necessary to evaluate and measure development of irradiation swelling 16
Structure 1. General information 2. Modernization of RPV EDU Life Time and Integrity Assessment 3. Reflection of the Doel and Tihange events at Czech NPPs 4. Computational Evaluation of the Swelling development 5. First steps of NDT development to identify swelling 6. Environmental Fatigue
Firsts step in the development of irradiation swelling measurement methodology Based upon precise measurement of core baffle geometry With use of underwater laser beam Limited amount of commercial products with requested irradiation resistance and accuracy measurement (problems with refraction, turbulences, limited spaces) Manufacturers are ready to cooperate with development of the technology High cost expected With use of mechanical equipment Measurement of the core baffle channels deformation (for relative quantification of the swelling) Measurement of the core baffle inner surface deformation, tested at Krymska NPP, realised on JU NPP, only limited information available Measurement in agreement with ETE calculations 18
Firsts step in the development of irradiation swelling measurement methodology At this stage of development it was decided to use mechanical approach: To measure inner dimension of the core baffle at different level of the Z axis The same measurement was realised during assembly of the RVI prior the operation, easy verification of swelling zero state Plans to realise it in 2021 19
Structure 1. General information 2. Modernization of RPV EDU Life Time and Integrity Assessment 3. Reflection of the Doel and Tihange events at Czech NPPs 4. Computational Evaluation of the Swelling development 5. First steps of NDT evolution to identify swelling 6. Environmental Fatigue
World wide experience with environmental fatigue The effect of environment on fatigue was many times identified in the world during past years. The most advanced procedures were developed in the USA and Japan. In fatigue assessments of Czech NPP components, environmental effect was never taken into account. During SALTO mission at NPP Dukovany, this approach was identified as an issue. Due to these facts, research projects were established in the Czech republic, funded by both, Ministry of Industry and Trade, and CEZ company (owner of Czech NPPs). Western formulae for environmental effect on fatigue could not be used due to different materials used, different procedure for fatigue assessment. 21
Normative requirements on environmentally assisted fatigue in Czech Republic The Russian Standards for Strength Evaluation of Component and Piping of Nuclear Power Plants, PNAE G-7 002-86 do not provide any recommendation on reduction of fatigue lifetime due to effect of environment The same situation was in older versions of the Czech Standard Technical Documentation of the Association of Mechanical Engineers Only reduction of allowable amplitude of fictitious stress due to welding is taken into account: [σ af ] s = φ s. [σ af ] where [σ af ] s - allowable amplitude of fictitious stress for weld, [σ af ] - allowable amplitude of fictitious stress without effect of weld, φ s - reduction coefficient for weld (dependent on type of weld and post-weld heat treatment, φ s < 1) The new Czech Standard Technical Documentation uses the same formal approach for reduction of allowable amplitude of fictitious stress due effect of environment. 22
Research projects realisation Fatigue tests were performed on selected materials of VVER primary circuit in autoclaves simulating VVER primary circuit environment (chemistry, temperature, pressure). Test facility with autoclave PLUTO manufactured in UJV Rez was used. 23
New Czech procedure Based on tests as presented above, new procedure was included into Standard Technical Documentation of the Association of Mechanical Engineers, rev. 2013 The formula for the effect of welding (presented above) [σaf]s = φs. [σaf] is used in extended manner considering effect of corrosive environment, irradiation and welding, where s = min { PR, F, W} PR - reduction coefficient for environment F - reduction coefficient for irradiation W - reduction coefficient for weld (to avoid overconservativeness, minimum of the coefficients is used, not multiplication) In the other words find the allowable number of cycles (based on formulae from standard) for the increased amplitude of fictitious stress [σ af ] s / φ s. 24
Unresolved tasks The fatigue tests should be performed for materials of VVER vessel that are in contact with medium There is not common agreement how to use original safety coefficient for number of cycles and applied stress with respect to safety environmental safety coefficient Further research, cooperation and agreement with broad scientific community is necessary 25