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Kozloduy NPP units 5&6
Daniel Genov
Ageing management of Buried and
Underground Piping and Tanks at NPPs
Technical Meeting 621-I2-TM-47031
IAEA / EPRI, Charlotte 13-15.10.2014
1
Agenda
1. Kozloduy NPP Plc - Introduction
2. Buried / Underground Piping
3. Underground Tanks
4. Plant Life Extension (PLEX)
5. Ageing Management
6. Summary
2
Kozloduy NPP Plc
• Units 5&6 in operation – Design: VVER-1000 V-320
– 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: 1998-2008
– 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
KNPP MP measures
3
Buried / Underground Piping
Simplified Scheme
Sp
ray P
on
ds (
x6)
5DGS
6DGS
Turbine
Hall - 5
Turbine
Hall - 6 Circu
latin
g W
ate
r
Sta
tio
n (
CW
S)
3,4
6RB
5RB
Cavity Pumping Houses (CPH) (x6)
Pressure Piping - QF Redundant Piping
Drain Piping - QF Additional water CPH
Additional water CWS External fire protection ring
*RB – Reactor Building
4
• QF – Essential Service Water System
Buried / Underground Piping
Piping of system QF
• Drain piping between Reactor
Building and Spray Ponds
• Pressure piping between Spray
Ponds and DGS
• Pressure piping between Diesel
Generator Station and Reactor
Building
Cross-section of piping
5
• 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.
• 1st seismic category (determined by NP-031-01*)
– 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 14-3-808-78**, TU 14-3-190-82**
• Corrosion-proof coating
*Gosatomnadzor – Russian regulatory body
**Russian codes and standards
Buried / Underground Piping
Piping of system QF
6
• 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: 120C to 450C (550C to 700C during accident
conditions)
– pressure: 0,46 Mpa
• Drain (gravity) pipes:
– temperature: 50C to 330C
– pressure: 0,2 Mpa
– Design flowrate: 3000 m3/h
Buried / Underground Piping
Piping of system QF
7
• Plant life management (PLiM)
– Seismic qualification • Measure 21241 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
Buried / Underground Piping
Piping of system QF
8
• 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
Buried / Underground Piping
Piping of system QF
9
• Data by 1st channel of QF system
Rate of corrosion
mm
/ye
ar
measured norm
Replacement of
sensor
Buried / Underground Piping
Piping of system QF
10
• 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 12201
• Material: PE100 SDR17
• Design criteria: material strength according to ISO 9080
Buried Piping
Piping of additional water by Circulating Water Station
11
• 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 B31.1-1995 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)
Buried Piping
Piping of additional water by Circulating Water Station
12
• 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 3th safety class
• according to 50-SG-D1 (now SSG-30)
– Classified as 1st seismic category
• According to 50-SG-D15 (now NS-G-1.6)
Buried Piping
Piping of additional water by Cavity Pumping Houses
13
• 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.
Buried Piping
Piping of additional water by Cavity Pumping Houses
14
• 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 BDS2592 1971
• 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 : 1982-1984
Underground Piping
External fire protection ring
15
• Cross-section view
1 Dense bituminous concrete
2 Porous bituminous concrete
3 Concrete covering кл.В30
4 Padding paper
5 Sand
6 Gravel
7 Consolidated loess soil
1 2
3
4
5
6
7
fire protection pipe
reinforced concrete chanel
with roof slab
Underground Piping
External fire protection ring
16
• 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 12201-1:2005, 12201-2:2005, 12201-3:2005
– Laying method: excavation-free technology
• Project is approved by Regulatory Body (Bulgarian Nuclear
Regulatory Agency)
Underground Piping
External fire protection ring
Petrol tanks in DGS
3x100m3: QC15,25,35B01
• per unit
17
Underground tanks Overview
100м3
Oil tanks in DGS
2x25m3 QD16B01 – Emergency oil
purge tank
2x5m3 QD17B01 – Drainage tank
25м3 5м3
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.
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.
18
Underground tanks
Condition evaluation
• Measure 21241
– Within the Modernization Program the seismic resistance of the
safety-related and important to operation structures has been
checked and upgrading measures developed
– Performed 2002-2004
– Underground tanks for oil and petrol
• Seismic calculation performed with the software product
STARDYNE – “Structural Analysis Systems”
• Maximum Design Earthquake resistance verified (0,2g)
• PLEX
– 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”
19
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
20
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
21
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
22
Summary
Comprehensive MP, PLEX and PLiM
Replacement, R&M, Monitoring
PEHD piping alternative
Seismic Qualification
Regulatory body concerns PNEG-7-008-89 do not address non-metalic materials
NUREG-1793 Supplement 2 express uncertainty about PEHD