Flow Accelerated Corrosion. in Angra 1 and Angra 2 Nuclear Power Plants. Lucio Ferrari Tomás D. S. Costa

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1 Flow Accelerated Corrosion in Angra 1 and Angra Nuclear Power Plants Lucio Ferrari Tomás D. S. Costa December/008

2 Angra Site Angra 1 Power: 657 MW Start of Operation: 198 Westinghouse Angra Power: 1390 MW Start of Operation: 000 Siemens/KWU

3 Historical Background 1986 Surry Catastrophic failure of 18-inch MFW pump suction line elbow. Four workers died. May, 1989 US NRC issued Generic Letter 89-08, Erosion/Corrosion-Induced Pipe Wall Thinning requested US licensees to implement long-term erosion/corrosion monitoring programs to maintain the structural integrity of all carbon steel systems carrying high-energy fluids.

4 Historical Background 1993 Start of Angra 1 Wall Thickness Monitoring Program Procedure: (1) Selection of piping systems and locations for ultrasonic inspections based on US experience EPRI () Evaluation of the results of ultrasonic testing (UT) examinations (3) Calculation of minimum wall thickness required (4) Replacement of piping pieces with thickness smaller than required Weak Points: (a) Lack of program with predictive models (b) Lack of baseline thickness measurements (c) Inconsistency of UT measurements poor grid

5 Historical Background 09/08/004 Mihama 3 Rupture of a condensate pipe downstream of a flow orifice. Five workers died. Material: Carbon Steel Pressure: 9 bar Temperature: 146 o C Flow Velocity:,1 m/s Outer diameter: 558.8mm (in) Original wall thickness: 10.0mm (0.4in) Minimum wall thickness of the ruptured area: 0.4mm (0.0in) Rupture Section Orifice Plate

6 Historical Background 005 Acquisition of COMSY software by ELETRONUCLEAR Revision of Angra 1 piping monitoring program Implementation of flow accelerated program in Angra Improvements: (a) Implementation of predictive plant model (b) Evaluation of susceptible systems (c) Modeling of piping lines to determine critical points (d) Implementation of full-coverage grid (e) Implementation of measurement protocols (f) Implementation of data bank (g) Determination of trend curves

7 Inspection Improvements Preparation of full-coverage grid Inspection Protocol

8 Replacements Steam Extraction Line DN 16

9 Wear Rate x Piping Length

10 Wall Thickness x Time

11 ANGRA 1 Piping Pieces Inspected 1P15a (008) 109 Distribuição das peças inspecionadas por sistema GS EX HD FW Distribuição das peças inspecionadas por tipo Curva Placa de Orifício Redução Restritor de Fluxo Tê Tubo 81 6 Distribuição das peças inspecionadas por diâmetro nominal Válvula Systems Quant. Piping Pieces Quant. DN (inches GS Turbine Gland Steam EX Extraction Steam 4 1 Elbow Flow Orifice Reducer Flow Restrictor HD Heater Drain FW - Feedwater Tee Tube Valve

12 ANGRA 1 Classification According Wall Thinning Classification No wear Quant. 318 % 87,1 Distribuição das peças de acordo com a perda de espessura verificada 318 Initial wear 30 8, Sem perda Perda inicial Significant wear 16 4,4 Perda avançada Perda crítica Critical wear 1 0, Identification of the piece with Critical Wear SYSTEM PIPING ISOMETRIC LINE IDENTIFICATION DN NUMB ER TYPE NOM. THICKNESS (mm) MINIMUM THICKNESS (mm) FW GH01T-TU4-00-FL FW G 16 7 Tube 1,7 8,0

13 ANGRA Piping Pieces Inspected P6 (008) Distribuição das peças inspecionadas por sistema Distribuição das peças inspecionadas por tipo Distribuição das peças inspecionadas por diâmetro nominal LAB LAH LBA LBJ LCA LCJ LCM MAG Controlador de Fluxo Curva Placa de Orifício Redução Tê Tubo Válvula System Quant. Piping Pieces Quant. DN Quant. LAB - Feedwater 0 Flow Restrictor 15 4 LAH - LBA Main Steam 30 3 Elbow Orifice Plate LBJ Moisture Reheating LCA Main Condensate LCJ LP Preheater LCM MAG Reducer Tee Straight Tube Valve

14 ANGRA Classification According Wall Thinning Classification Quant. % Distribuição das peças de acordo com a perda de espessura verificada No wear 180 9,8 180 Initial wear 5,6 Sem perda Perda inicial Perda avançada Significant wear 7 3,6 Perda crítica Critical wear 1, System Piping Isometric Type DN Nominal Thickness (mm) Minimum Thicknee (mm) LAH XJ-LAH31BR001-F Rev.04 Orifice Plate 50 3,6,3 LBJ XJ-LBJ0BR001-F Rev.03 Valve 150 7,1 4,1

15 Summary of Results ANGRA 1 ANGRA Inspected Systems CW / EX / FW / GS / HD / MS Inspected Systems LAB / LAH / LBA / LBJ / LCA LCJ / LCM / LCQ / MAG Period of application - 5 Outages 1340 piping pieces inspected 43 replacements Period of application - 3 Outages 554 piping pieces inspected 3 replacements

16 Conclusions The internal degradation of piping by flow accelerated corrosion mechanism is not visible and can cause severe accidents An effective flow accelerated corrosion program will increase personnel safety, plant safety and plant availability The continuing occurrence of failures caused by piping wall thinning evidences that plant programs for FAC mitigation should be maintained and improved as industry knowledge evolves and more operating and plant data become available

17 Thank you for your attention!