Kozloduy NPP units 5&6

Transcription

1 Kozloduy NPP units 5&6 Ageing management of Buried and Underground Piping and Tanks at NPPs Technical Meeting 621-I2-TM IAEA / EPRI, Charlotte Daniel Genov

2 Agenda 1. Kozloduy NPP Plc - Introduction 2. Buried / Underground Piping 3. Underground Tanks 4. Plant Life Extension (PLEX) 5. Ageing Management 6. Summary 1

3 Kozloduy NPP Plc Units 5&6 in operation Design: VVER-1000 V-320 KNPP MP measures Rated output power: 2000 MWe Plant design life: 30 years Unit 5: Commissioned: 1987 End of original design life: 2017 Unit 6: Commissioned: 1991 End of original design life: 2021 Comprehensive Modernization Program (MP) Time frame: Total budget: over 500M EUR. Over 200 measures implemented The MP is based on the issued by IAEA document: Safety Issues and Their Ranking for VVER-1000 model 320 NPPs First stage of PLEX Plant Life Extension project of units 5&6 undergoing 2

4 Spray Ponds (x6) Circulating Water Station (CWS) 3,4 Buried / Underground Piping Simplified Scheme Cavity Pumping Houses (CPH) (x6) 5DGS 5RB Turbine Hall - 5 6DGS 6RB Turbine Hall - 6 Pressure Piping - QF Drain Piping - QF Additional water CWS Redundant Piping Additional water CPH External fire protection ring *RB Reactor Building 3

5 Buried / Underground Piping Piping of system QF QF Essential Service Water System Cross-section of piping Drain piping between Reactor Building and Spray Ponds Pressure piping between Spray Ponds and DGS Pressure piping between Diesel Generator Station and Reactor Building 4

6 Buried / Underground Piping Piping of system QF Design data and и Normative requirements Overview of system QF: Assure the operation of the Safety Systems. Conduct the heat from primary circuit during accident and normal operation conditions. 1 st seismic category (determined by NP *) In accordance with IAEA Safety Guide 50-SG-D15 (now NS-G-1.6) Materials: steel pipes with diameters DN600,800,1000,1200 Base metal: Стомана 20 (Carbon steel 1020) by technical specifications TU **, TU ** Corrosion-proof coating *Gosatomnadzor Russian regulatory body **Russian codes and standards 5

7 Buried / Underground Piping Piping of system QF Operational condition and current status Laying method filled up in a trench on a sand bed laid in reinforced concrete channel Design pressure and temperature Pressure pipes: temperature: 12 0 C to 45 0 C (55 0 C to 70 0 C during accident conditions) pressure: 0,46 Mpa Drain (gravity) pipes: temperature: 5 0 C to 33 0 C pressure: 0,2 Mpa Design flowrate: 3000 m 3 /h 6

8 Buried / Underground Piping Piping of system QF Plant life management (PLiM) Seismic qualification Measure of Modernization Program Seismic resistance of Maximal Design Earthquake is verified (0.2g Peak Ground Acceleration) Ageing management measures Monitoring level of corrosion through technical means without excavation Visual inspections by remote TV camera Water chemistry upgrade Repairs: 1 significant repair reported Replaced 8 m part of pressure pipe with DN1000 leakage in result of heavy corrosion Base metal break is detected as well as past compromised section of waterproof coating around metal ruptures Cause: mechanical damage during improper lay down of piping 7

9 Buried / Underground Piping Piping of system QF Water chemistry Program to Corrective treatment of ESWS consumers through spray pond water Targets: incrustation free operational condition of equipment inhibition of corrosion process control of microbiological contamination Chemical reagents Depositrol BL-5300; Depositrol PY-5200; Spectrus BD-1501E; Spectrus OX-1201; Spectrus NX-1167 Instrumentation and Control System Monitoring of parameters such as: ph, temperature, rate of corrosion, electrical conductivity, degree of concentration Output: Decreased rate of metal corrosion below prescribed rate of 0,1 mm per year 8

10 mm/year Buried / Underground Piping Piping of system QF Data by 1 st channel of QF system Rate of corrosion Replacement of sensor measured norm 9

11 Buried Piping Piping of additional water by Circulating Water Station Description Part of Service Water System - VB System of normal operation In accordance with the Technological manual for safe operation of units 5 and 6 of NPP Kozloduy Design steel pipelines High rate of corrosion and repair events Redundant piping is installed Redundant piping of PEHD piping layout follows design ones pressure pipe, filled up in a trench on a sand bad operational parameters are in full compliance with design piping Fluid velocity is within 3 m/s Specification Diameters: 400х23,7; 280х16,6 Standard: EN Material: PE100 SDR17 Design criteria: material strength according to ISO

12 Buried Piping Piping of additional water by Circulating Water Station Seismic classification of the redundant piping Unavailability of Codes and Standards for Polyethylene Pipes for Nuclear Power Plants during design and construction The redundant piping is not approved by regulatory body as independent element Design requirements are selected by ASME B Appendix VII, Nonmandatory Procedures for the Design of Restrained Underground Piping Piping is designed for half of Maximal Design Earthquake (0,1 g Peak Ground Acceleration) 11

13 Buried Piping Piping of additional water by Cavity Pumping Houses Description Backup water supply to Spray Ponds for recover of water losses due to evaporation, drift, filtrations, etc. Backup water supply of auxiliary buildings and systems Pressure pipes, filled up in a trench on a sand bad Especially required by regulatory body Plant project of 2001 Piping is classified as safety relevant Classified as 3 th safety class according to 50-SG-D1 (now SSG-30) Classified as 1 st seismic category According to 50-SG-D15 (now NS-G-1.6) 12

14 Buried Piping Piping of additional water by Cavity Pumping Houses Ageing mechanisms PLEX report Critical component: pressure pipeline between the CPH and SP Damages and flaws: heavy corrosion of visible sections Ageing mechanism: general corrosion Index: COR01 Current status Pipeline operation conditions: exposure to nonaggressive ground waters with unstable level due to the direct interconnection between ground waters and Danuve Rive waters The mode of the pipeline continuous wetting and drying adversely affects the corrosion process developing in the pipeline metal Virtually the pipeline is near the end of its design life. A decision for replacement with PEHD is under consideration. 13

15 Underground Piping External fire protection ring Description: supply of suficient quantity of water at required pressure to building and rooms where fire extinguishing system exist. The main consumers are as follows: Reactor Building, Turbine Hall Auxiliary Building OSK combined auxiliary building Oil-petrol storage facility Water source: CWS 3,4 (Danube river) Pipe specification: 90% (6532 m) of total length of the ring is comprised of pipes with diameters within range of DN200 do DN300 Spirally welded steel pipes (such as system QF) Carbon steel type ВСт3 по BDS Laying method: In most part the pipeline is laid down into U-shaped channel with reinforced concrete roof slab. Channel depth vary within 0,9 to 2,5 m. Construction and Commissioning :

16 Underground Piping External fire protection ring Cross-section view 1 Dense bituminous concrete 2 Porous bituminous concrete 3 Concrete covering кл.в30 4 Padding paper Sand 6 Gravel 6 7 Consolidated loess soil 7 fire protection pipe reinforced concrete chanel with roof slab 15

17 Underground Piping External fire protection ring Operational experience: There are 15 cases of unscheduled repairs for a period of 7 years ( 2012) Damaged corrosion protection mainly during construction period Technical solution Project for replacement with PEHD pipes with analogous hydraulic characteristics New PEHD pipeline PEHD 100, PN1,6 Mpa; Diameters 110 to 355 mm BDS, EN :2005, :2005, :2005 Laying method: excavation-free technology Project is approved by Regulatory Body (Bulgarian Nuclear Regulatory Agency) 16

18 Underground tanks Overview 100м 3 Petrol tanks in DGS 3x100m 3 : QC15,25,35B01 per unit The structure is made of monolithic reinforced concrete B20 and reinforcement steel A-I and A-III. The steel liner placed on the innner surface has a thickness of 3 mm. 25м 3 5м 3 Oil tanks in DGS 2x25m 3 QD16B01 Emergency oil purge tank 2x5m 3 QD17B01 Drainage tank The structure is made of monolithic reinforced concrete B20 and reinforcement steel A- I. The steel liner placed on the innner surface has a thickness of 3 mm. 17

19 Underground tanks Condition evaluation Measure Within the Modernization Program the seismic resistance of the safety-related and important to operation structures has been checked and upgrading measures developed Performed Underground tanks for oil and petrol PLEX Seismic calculation performed with the software product STARDYNE Structural Analysis Systems Maximum Design Earthquake resistance verified (0,2g) Ageing management Ultrasonic thikness measurement (steel liner) Visual inspection (inner volume and overgrade parts) Waterproof coating repair Two layer corrosion protection of inner surface Tankguard Storage protection used (phenol-epoxid coating) thickness measurement: callipers Mititoyo 18

20 Ageing Management Plant Life Extension Project Operating licenses of units 5 and 6 require assessment of the actual condition of the Systems Structures and Componentws undertaking Comprehensive assessment of the actual condition and residual lifetime analysis of Kozloduy of SSC completed Program of Kozloduy NPP Units 5&6 Preparation for Extended Lifetime - undergoing Underground Piping System QF (essential service water closed loop chemically treated water) Corrosion rate monitoring and early leak detection Special chemical treatment Replacement if necessary System VB (service water Danube river water) Condition monitoring of the design piping (Maitanance&Repair) until Independent operation of newly installed redundant PEHD piping Need regulatory body approval Seismic qualification concerns 19

21 Ageing Management Plant Life Extension Project Underground Piping System UK (backup water by artesian wells) Replacement with PEHD piping Need regulatory body approval Seismic qualification concerns Underground Tanks System QC (petrol) and UN (oil) seismic qualification corrosion protection monitoring 20

22 Ageing mechanisms PLEX Project General corrosion Description General surface corrosive damage of metal during contact with an electric conductive solution Critical elements Invisible underground parts of pipelines Inner and outer surface Damages, defects Loss of integrity of pipes insulation and leakages Pitting Change of size Ageing mechanisms Steel pipes corrosion 21

23 Summary Comprehensive MP, PLEX and PLiM Replacement, R&M, Monitoring PEHD piping alternative Seismic Qualification Regulatory body concerns PNEG do not address non-metalic materials NUREG-1793 Supplement 2 express uncertainty about PEHD 22

24 Kozloduy NPP Plc Thank you for your attention!!! 23