ML12300A221

Attachment 11: BWROG-TP-12-012, Revision 0, Task 4 - Operation in the Maximum Erosion Rate Zone (Cvds Pump)

ML12300A221
Person / Time
Site:	Monticello, Boiling Water Reactor Owners Group
Issue date:	08/31/2012
From:	Kalra A Sulzer Pumps (US), BWR Owners Group
To:	Office of Nuclear Reactor Regulation
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ML123000308	List: ML12300A219 ML12300A220 ML12300A221 ML12300A222 ML12300A224
References
BWROG-12051 BWROG-TP-12-012, Rev 0
Download: ML12300A221 (17)

Text

Containment Accident Pressure Committee Task 4 - Operation in the Maximum Erosion Rate Zone (CVDS Pump)

Author: Ankur Kalra (Sulzer Pump) Project Manager: Kenneth Welch (GEH) Committee Chairman: John Freeman (Exelon) BWROG-TP-12-012 Revision 0 August 20 12 BWROG-TP-12-012 REV 0 INFORMATION NOTICE Recipients of this document have no authority or rights to release these products to anyone or organization outside their utility.

The recipient shall not publish or otherwise disclose this document or the information therein to others without the prior written consent of the BWROG, and shall return the document at the request of BWROG. These products can, however, be shared with contractors performing related work directly for the participating utility, conditional upon appropriate proprietary agreements being in place with the contractor protecting these BWROG products. With regard to any unauthorized use, the BWROG participating Utility Members make no warranty, either express or implied, as to the accuracy, completeness, or usefulness of this guideline or the information, and assumes no liability with respect to its use. BWROG Utility Members CENG - Nine Mile Point Chubu Electric Power Company DTE - Fermi Chugoku Electric Power Company Energy Northwest

- Columbia Comisión Federal de Electricidad Entergy - FitzPatrick Hokuriku Electric Power Company Entergy - Pilgrim Iberdrola Generacion, S.A. Entergy - River Bend/Grand Gulf Japan Atomic Power Company Entergy - Vermont Yankee J-Power (Electric Power Development Co.) Exelon (Clinton) Kernkraftwerk Leibstadt Exelon (D/QC/L) South Texas Project Exelon (Oyster Creek) Taiwan Power Company Exelon (PB/Limerick) Tohoku Electric Power Company FirstEnergy

- Perry Tokyo Electric Power Company NPPD - Cooper NextEra - Duane Arnold PPL - Susquehanna PSEG - Hope Creek Progress Energy

- Brunswick SNC - Hatch TVA - Browns Ferry Xcel - Monticello

BWROG-TP-12-012 REV 0 2 Executive Summary This BWROG Technical Product provides an evaluation of the impact of cavitation on the service life of the Sulzer CVDS pump model used at the Monticello station and other BWR stations. The evaluation considers the potential effects of operating in the range of NPSH A that result in the maximum erosion rate.

Implementation Recommendations This product is intended for use to address (in part) issues raised in the NRC Guidance Document for the Use of Containment Accident Pressure in Reactor Safety Analysis (ADAMS Accession No. ML102110167). Implementation will be part of the BWROG guidelines on the use of Containment Accident Pressure credit for ECCS pump NPSH analyses.

Benefits to Site This product provides a technical response to the NRC concerns raised about the potential for cavitation wear during long term pump operation in a post-accident environment.

QUALITY LEVEL SULZER PUMPS (US) INC. DOCUMENT ASME CODE SECTION Direct DOC. NO: E12.5.1912 Indirect ORDER NO:

CLASS NO. CODE EDITION (YEAR) TITLE: Task 4 - Operation in Maximum Erosion Rate Zone Sulzer Pumps (US) Inc.

SEASON YEAR Monticello - 12x14x14.5 CVDS RHR Pump CUSTOMER GE-HITACHI Nuclear Energy Americas LLC PROJECT Monticello Nuclear Power Station, Monticello, MN CUSTOMER P.O. NO.

437054820 CONTRACT NUMBER SPECIFICATION NO.

ITEM / TAG NUMBER CUSTOMER APPROVAL NUMBER: CUS TOMER APPROVAL REQUIREMENT Yes No Information Only SPACE FOR CUSTOMER APPROVAL STAMP CERTIFIED AS A VALID SULZER PUMPS (US) INC. DOCUMENT (when applicable/available)

For Outside Vendor

For Manufacture at Sulzer Pumps (US) Inc.

Risk Release Inspection Report # ________________

Other (specify)

_______________________ APPROVALS (SIGNATURE) Date Engineering 04/23/12 Quality Assurance CERTIFICATION (when applicable)

Originating Advance Engineering This Document is certified to be in compliance Dept: with THE APPLICABLE PURCHASE ORDER, By: SPECIFICATIONS, PROCEDURES, AND ADDITIONAL REQUIREMENTS LISTED IN Ankur Kalra THE APPENDICES. Title: Hydraulic Design Engineer Date: 11/7/2011

__________________________________________ Professional Engineer APPLICABLE S.O. NUMBERS: ___________ _____________________________

100072780 State Registration No.

Date _______________

E12.5.1912 0 Rev. DOCUMENT IDENTIFICATION Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 1 TABLE OF CONTENTS

1.0 PURPOSE

.......................................................................................................................

.......................................... 2

2.0 BACKGROUND

....................................................................................................................

.................................. 2

3.0 SCOPE

.........................................................................................................................

............................................. 3 4.0 ANALYSIS.......................................................................................................................

......................................... 4

5.0 CONCLUSION

..............................................................................................................................

......................... 12

6.0 BIBLIOGRAPHY

..............................................................................................................................

..................... 13

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 2 1.0 PURPOSE To evaluate the impact of cavitation on the service life of a Monticello RHR pump impeller. Cavitation in a pump can result in pump vibration, noise and component erosion. This report addresses the

material erosion aspects of an impeller under cavitation. The material erosion of an impeller under

cavitation is predicted using formulae from Gülich's Book; Centrifugal Pumps [Ref 1]. These formulae

were developed in an EPRI study [6] from empiri cal data collected for various pump types for predicting the number of hours an impeller will su rvive under reduced Net Positive Suction Head (NPSH). The purpose of this evaluation is to show t hat the impeller service life is at least 30 days (720

hours) of operation when operating at reduced NPSH margin.

2.0 BACKGROUND

The service life of an impeller can be predicted based on a defined percentage of material loss due to cavitation erosion and on a known or predicted cavitation bubble length. The three primary factors

influencing cavitation erosion are : 1) The hydrodynamic cavitation intensity. 2) The cavitation

resilience of the material. 3) Time duration over which the cavitation is acting. The hydrodynamic

cavitation intensity is related to the volume of the cavitation vapor (related to bubble length) in the flow

and the differential pressure (p-p v) driving the implosion of the bubbles. The cavitation resilience is purely a function of the mechanical properties of the material. The rate of cavitation erosion will then

depend on the hydrodynamic cavitation intensity, the material cavitation resilience and the time

duration during which the cavitation is occurring. The service life of an impeller undergoing cavitation

depends strongly on absolute pressure of the fluid (suction pressure minus vapor pressure) which

drives the gas-bubble implosion, the impeller materi al properties (strength and modulus of elasticity), and on the flow characteristics and liquid properties. Gülich [Ref 1] explains that cavitation erosion

occurs only when the hydrodynamic cavitation intensity (dependent on flow and fluid properties)

exceeds the cavitation resistance (dependent on material properties; fixed for a given material and

temperature) of the impeller material and that "hydrodynamic cavitation intensity increases with the

total volume of all vapor bubbles created in the flow".

The length of the cavitation bubble is related to the bubble volume, which in turn is an indicator of the

damage producing potential. The optimal way to determine the true bubble length for a given impeller geometry while operating under a given set of inlet conditions (flow rate and NPSHa) is by flow

visualization from model testing. Recently, with the advent of advanced CFD techniques it is possible to simulate the bubble length as a function of inlet conditions.

[[

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 3 ]] Relationships between cavitation bubble length and the rate of material erosion have been derived empirically.

3.0 SCOPE

For evaluating impeller damage due to cavitation erosion; impeller material properties, flow properties, and available NPSH are considered for this analysis.

a) Impeller life due to cavitation damage is predicted using Gülich's empirical formulae and CFD analysis results [8]. b) Validity of the impeller life prediction formulae conducted during experimental and field operation analysis work is briefly discussed. c) Impeller life prediction method is presented in a step-by-step format. Calculation steps include methods for bubble length, material resilience, erosion power, erosion rate and impeller life

calculation. Several conservatisms, which are listed in section 5, are incorporated in the

calculation.

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 4 4.0 ANALYSIS A CFD study of the Monticello RHR impellers using a commercial CFD package was conducted to

predict NPSH 3%, bubble lengths, and bubble location under varying flow rates and NPSH margins

[8]. Figure 1 shows bubble lengths versus NPSH margin predicted by the CFD analysis for four

different pump flow rates. As would be expected, Figure 1 shows the bubble length grows as the

NPSH margin decreases.

[[ ]] Figure 1: Bubble Growth versus NPSH margin

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 5 The bubble lengths and the corresponding NPSHa values obtained from the CFD results are then

used in the Gulich formulae to predict maximum erosion rate at different pump flow rates and NPSH

margins. Figure 2 shows impeller erosion rate (µm/hr) versus NPSH margins at different flow rates. It is observed that the maximum erosion occurs at

[[ ]] for an NPSHa margin of

[[ ]]. A sample maximum erosion rate calculation for the

[[ ]] flow is provided in the following sections of the report along with the corresponding impeller service life calculation.

[[ ]] Figure 2: Erosion Rate versus NPSH Margin NPSH values corresponding to the full diameter impeller (14.5") are used for this analysis. The current

Monticello trim diameter is

[[ ]] (approximately

[[ ]] trim). [[ ]]

Given:

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 6 Impeller Material:

[[ ]] SI units Imperial units Tensile strength, R m [[ ]] [[ ]] [Ref 3] Young's modulus, E 2.01 x 10 11 N/m 2 29,200 kpsi [Ref 4]

Impeller blade thickness at

cavitation length 2 , e [[ ]] [[ ]] Density of water, (at 95ºF) 994 kg/m³ 0.994 S.G. Gravitational constant, g 9.81 m/s² 32.2 ft/sec²

Impeller outer diameter, D 2 [[ Impeller eye diameter, D 1 Circumferential velocity 3 at impeller eye, u 1

Eye Area (each side)

]]

[[ ]]

Meridional velocity 4 , c 1 [[ ]] NPSH 3% [[ ]] (as predicted by CFD)

The formulae used in this report for predicting im peller erosion rate and impeller service life have been empirically derived from a large pool of cavi tation test results obtained from several pump manufacturers for different pump types [6]. These test results were used to develop a correlation between NPSH, cavitation resistance, vapor density, speed of sound, gas content, and the erosion

rate.

These formulae have been verified through experimentation using visual inspection techniques. Bruno

Schiavello in paper, "Pump Cavitation - Various NPSHR Criteria, NPSHA Margins, and Impeller Life

Expectancy" [Ref 5] validates Gülich's erosion rate formulae by comparing the cavitation damage depth on impellers in the field with the predicted values. Several other field tests and research papers

have verified the use of these formulae for accurately predicting impeller service life.

2 [[

]]

3 Calculated as x (impeller eye diameter) x (revolutions per second) 4 Meridional velocity is calculated as flow rate, Q, divided by eye area

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 7 Following steps outline the impeller life prediction method in a step-by-step approach.

Step 1: Calculate resistance to cavitation damage (U R) for the impeller material This quantity depends only on the impeller material properties. For

[[ ]] at 35°C (95°F):

[[ ]] Step 2: Estimate cavity length Cavity length data is generally obtained experimenta lly using flow visualization techniques or analytically from CFD simulation results. In the case of the Monticello RHR pumps, cavity lengths

were determined via CFD, see Figure 1. A bubble length of 0.05 m, obtained from the CFD analysis

for 3900 gpm at the NPSH margin of 2.0 (predicted maximum erosion zone), is used for this sample

calculation.

When the cavity length data is absent and there is an NPSH margin (additional NPSH available above

the NPSH 3% required), the following formula can be used to estimate cavity length based on impeller geometry and coefficients derived from the NPSH values.

[[

]]

Depending upon flow conditions and the impeller inlet geometry the bubble formation can occur at the suction side, the pressure side or both sides of the impeller blade inlet (Figure 3 shows the general

effect of incidence angle on cavitation bubble formation). Generally, zero incidence angle (i = 0)

occurs at the BEP flow rate. However, 1-D Excel based flow calculation tools, and the CFD analysis

results provide evidence that for the Monticello impeller design the positive flow incidence angle is

observed at the blade inlet (suction side cavitation) even at the highest flow rate considered for the analysis ([[ ]]). Therefore, only suction side erosion calculation methods are used for the impeller life analysis. In the case of Monticello RHR impeller, the vertical red line (Figure 3), zero

incidence occurs at approximately

[[ ]] of BEP flow. Further, Figure 3 below also shows a Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 8 general trend for NPSH i (inception cavitation), NPSH 3%, Noise and Erosion as a function of inlet flow incidence.

Figure 3: NPSH, Noise and Erosion versus Inlet Incidence The erosion formulae and the CFD results have been used to develop the relationship between

erosion rate and the flow incidence angle (Figure 4) for the different flow rates. As shown in Figure 4, the lowest erosion rate zones are found at BEP ([[ ]]) and at low incidence angles

([[ ]]). i < 0i > 0 NPSH [m] Inception3% 0% Erosion, noise Inlet Incidence (i = 0)

NPSH A Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 9 [[ ]] Figure 4: Maximum Erosion Rate versus Incidence angle Step 3: Determine absolute pressure p at the impeller inlet

This is the differential pressure that drives bubble implosion. It is dependent upon NPSH A. For this calculation, NPSHa is equal to

[[ ]] times the NPSH 3% ( See Figure 2 - maximum erosion zone at

[[ ]]). 2 3 2 3 2 1 1)47.6(2/994)2.13)(/81.9)(/994(2)(mkgsmmkg cNPSHgppp A V = [[ ]] p 1 = suction pressure at impeller inlet p v = vapor pressure at impeller inlet Step 4: Determine erosion power P ER [[

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 10 ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

° ° ° ° °

° ° ° ]] Erosion power is calculated as follows (Gülich, equation 6.1.2):

44.0'36.0 3 1 2 ref ref ref x ref cav mat cor ref ER a a L L F F p p C P Where:

C 1 = 5.4 x 10

-24 W/m² for suction side erosion (constant from empirical data) p =

[[° ° ° ° ° ° ° ° ° ° °

° ° ° ]] (for [[° ° ° ° ° ° ° °

° ° ° ]] flow rate) p ref = 1 N/m² (used by Gülich in empirical calculations)

F cor = corrosion factor = 1 for fresh water (Sulzer Handbook 1.008.004 Table 3)

F mat = material factor = 1 for ferritic steel (Sulzer Handbook 1.008.004 Table 3)

Lcav

= [[° ° ° ° ° °

° ° ° ]] (From CFD analysis for

[[° ° ° ° ° ° ° °

° ° ° ]] flow rate)

L ref = 0.010m (used by Gülich in empirical calculations) x 2 = 2.83 for suction side erosion (constant from empirical data)

a = speed of sound in the fluid = [[° ° ° ° ° ° ° °

° ° ° ]] (water at

° ° ° ° ° ° ° ) (Using Lubber and Graff's eqs) a ref = 1497 m/s (water at 20°C) (Using Lubber and Graff's eqs) = gas content of fluid = [[° ° ° ° ° ° ° °

° ° ° ]] ([[° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° ° °

° ° ° ]]) ref = 24ppm (reference: ordinary, untreated water) " = density of saturated vapor = [[° ° ° ° ° ° ° ° ° °

° ° ° ]] (water at

° ° ° ° ° ° ° ) " ref = 0.02 kg/m³ (water at 20°C)

For [[° ° ° ° ° ° ° °

° ° ° ]]: ° ° ° ° ° ° °

Step 5: Calculate erosion rate E R

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 11 [[ ]] E R = [[ ]] for [[ ]] flow Step 6: Calculate expected impeller life LI, exp )))(((3600))((exp, R I Een L

LI, exp = expected impeller life in hours n = defined proportion of impeller material lost at end of service life e = original thickness of impeller blade at site of cavitation

= [[ ]] = duration of service at particular load considered The function would be used in situations where the impeller was subject to different cavitation conditions over the course of its service life. In this study only one cavitation situation is being considered for the estimation of impeller service life, so = 1. [[ ]] [[ ]]

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 12

5.0 CONCLUSION

The cavitation erosion and the impeller service life calculations for the maximum erosion zone show that the Monticello RHR impeller would operate for at least

[[ ]] while operating at the flow rate and NPSH margin corresponding to the maximum erosion rate, [[ ]] and [[ ]] respectively. This service life is

[[ ]] times the minimum required service life of

[[

]] Based on the above analysis, the impeller life at the maximum erosion rate greatly exceeds the

[[ ]] mission time. Hence, it can be concluded that the impeller integrity is assured.

Task 4 - Operation in Maximum Erosion Rate Zone E12.5.1912 12x14x14.5 CVDS 13 6.0 BIBLIOGRAPHY

[1] J. Gülich Centrifugal Pumps (2008), Springer-Verlag publishers Section 6.6 "Cavitation erosion" [2] Speed of Sound in water -

http://resource.npl.co.uk/acoustics/techguides/soundpurewater/content.html#LUBBERS

[3] ASTM Standards A487A/487M-93 (Reapproved 2007)

[4] ASME B31.1-1995

[5] Bruno Schiavello, "Pump Cavitation - Various NPSHR Criteria, NPSHA Margins, and Impeller Life Expectancy".

[6] Gülich JF: Guidelines for prevention of cavitation in centrifugal feedpumps. EPRI Report GS-6398, Nov 1989.

[7] Philippe Dupont and Gary Fitch, "Impeller Life Prediction in Pumps", 10 th European Fluid Machinery Congress, April 2008.

[8] Philippe Dupont, Bruno Maroccia - Investigation Report 2012, Numerical prediction of NPSH 3% by means of an impeller only CFD calculation for Monticello 12x14x14.5CVDS.