application of orifice plate for measurement of feed water

Application of Orifice Plates forMeasurement of Feedwater Flow

EdF Plant Experience

Technical Report

LI

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NS E D

M A T E

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WARNING:Please read the License Agreementon the back cover before removingthe Wrapping Material.

P L A N TP L A N T S U P P O R S U P P O R TT E N G I N E E R I N G E N G I N E E R I N G

EPRI Project ManagerR. ShankarT. Eckert

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

Application of Orifice Plates forMeasurement of Feedwater Flow:EdF Plant Experience

1003040

Final Report, December 2001

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THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS ANACCOUNT OF WORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCHINSTITUTE, INC. (EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THEORGANIZATION(S) BELOW, NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

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iii

CITATIONS

This report was prepared by

EdF R&D6 quai WatierChatou, France

Principal InvestigatorH. Jeanneau

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

Application of Orifice Plates for Measurement of Feedwater Flow: EdF Plant Experience, EPRI,Palo Alto, CA: 2001. 1003040.

v

REPORT SUMMARY

BackgroundAccurate measurement of feedwater flow may allow nuclear plant operators to increase thermalpower without affecting plant reliability and safety. The U.S. NRC has approved small thermalpower uprates of commercial nuclear plants if the licensee implements certain feedwater flowmeasurement instrumentation with accuracy to within ±2%. The uprates to the current ratedpower can vary from 0% to as high as 1.5%. The amount of the power increase is equal to thedifference between the original 2% margin established by the NRC in 1973 and the demonstrableaccuracy of the instrumentation being used. For example, if the instrumentation can bedemonstrated to measure thermal power to within 0.6%, then a 1.4% power increase could beobtained.

Consequently, commercial nuclear plants have the capability to increase both generated electricalpower and revenue. Successful use of this technology requires that the plant ensure that thenuclear steam supply system (NSSS) safety requirements are met and that balance-of-plantconsiderations accommodate the allowable uprate.

The new instrumentation so far approved by the NRC uses ultrasonic technology to measureflow rates and sometimes requires an expensive piping retrofit. According to EPRI report1000607, Small Power Uprates Under Appendix K: Benefits and Considerations, the cost ofsuch a retrofit varied widely although the return on investment in all cases was attractive.

U.S. nuclear plants may have an opportunity to use orifice plates for accurate feedwater flowmeasurement. Orifice plates have been used at EdF nuclear plants and have achieved accuraciesto within ±0.8%.

Objectives• To document the use and performance of orifice plates for the measurement of feedwater

flow at plants operated by EdF

• To develop a project plan that evaluates the accuracy of orifice plates for pipingconfigurations that are typical of some U.S. nuclear plants

ApproachEdF has operating experience using orifice plates for the measurement of feedwater flow forcalorimetric calculations at certain plants. The accuracies are high enough to consider theseinstruments as alternatives to justify power uprates for U.S. nuclear plants.

vi

This report describes EdF plant experience with orifice plates. Based on feedback from thisreport, EdF will assess their actual performance in typical installation conditions (reproducingthe lack of upstream straight lengths) at the EdF EVEREST flow test loop.

ResultsFeedwater flow measurement by orifice plate is reviewed, and the EdF plant experience isdescribed. The review covers operating principles, installation requirements, and maintenancerequirements.

EPRI PerspectiveIn most plants, it is more cost effective to increase plant productivity than to add new plantcapacity. Consequently, nuclear utilities are striving to maximize economic production fromexisting assets. The availability of more accurate feedwater flow measurement instrumentationwith the simultaneous relaxation of margins and focus on reduced costs have motivated manynuclear utilities to consider increasing thermal power. This report provides an assessment of theuse of orifice plates for accurate flow measurement; however, its applicability to U.S. nuclearplants will have to be evaluated and demonstrated.

KeywordsThermal performanceOrifice plateFlow measurementFeedwater flowEdF plant experience

EPRI Licensed Material

vii

CONTENTS

1 SYMBOLS ........................................................................................................................... 1-1

2 OVERVIEW OF FEEDWATER FLOW................................................................................. 2-1

Overview of the Feedwater Flow at EdF Nuclear Plants ..................................................... 2-1

Measurement of the Nominal Thermal Power of a PWR ................................................ 2-1

Feedwater Flow Measurement in BIL100....................................................................... 2-2

Orifice Plates Used for Calorimetrics .................................................................................. 2-2

3 ORIFICE PLATE DESCRIPTION......................................................................................... 3-1

Measurement Principle....................................................................................................... 3-1

Types of Orifice Plates ....................................................................................................... 3-2

Orifice Plate Thickness and Beveling ................................................................................. 3-2

Beta Ratio and Measured Pressure Drop ........................................................................... 3-4

Total Pressure Drop from the Plate .................................................................................... 3-4

4 ORIFICE PLATE ACCURACY............................................................................................. 4-1

Calibration Requirements at EdF........................................................................................ 4-1

Installation Requirements at EdF........................................................................................ 4-1

Upstream and Downstream Lengths of Piping (L/Ds)..................................................... 4-2

Cost Benefits ................................................................................................................. 4-4

Special Orifice Plate Alignments .................................................................................... 4-4

Pressure Differential Instrument Accuracy Requirements .............................................. 4-4

Pipe Roughness and Circularity Requirements.............................................................. 4-4

5 EDF EXPERIENCE WITH ORIFICE PLATE MAINTENANCE............................................. 5-1

Plate Inspection.................................................................................................................. 5-1

Upstream Pipe Inspection .................................................................................................. 5-1

Routine Diameter Measurements ....................................................................................... 5-1

Differential Pressure Transmitter Maintenance................................................................... 5-1


viii

6 LICENSE EVENT REPORTS RELATED TO EDF FEEDWATER FLOW ............................ 6-1

7 IMPLEMENTATION REQUIREMENTS AT U.S. NUCLEAR PLANTS................................. 7-1

8 COST BENEFIT ANALYSIS FOR NUCLEAR PLANTS ...................................................... 8-1

Cost of Installing a Differential Pressure Device ................................................................. 8-1

Manufacturing Cost........................................................................................................ 8-1

Installation Cost ............................................................................................................. 8-2

Operating Cost............................................................................................................... 8-2

Summary of Costs ......................................................................................................... 8-4

9 REFERENCES .................................................................................................................... 9-1


ix

LIST OF FIGURES

Figure 2-1 Installation Diagram Showing the Measurement Points Needed for BIL100 ........... 2-2

Figure 3-1 Orifice Plate ........................................................................................................... 3-1

Figure 3-2 Orifice Plate, Rear View......................................................................................... 3-3

Figure 3-3 Orifice Plate Location ............................................................................................. 3-4

Figure 4-1 Evaluation of Orifice Plate Installation Conditions on the EVEREST Loop:Pipework Configuration ................................................................................................... 4-3

Figure 4-2 Evaluation of Orifice Plate Installation Conditions on the EVEREST Loop:Bias Versus Flow-Rate .................................................................................................... 4-3


xi

LIST OF TABLES

Table 7-1 Required Straight Lengths Between Orifice Plates and Fittings Without FlowConditioners (Values Expressed as Multiples of Internal Pipe Diameter D) ..................... 7-2

Table 8-1 Estimate for Supplying a Venturi Tube and Orifice Plate ......................................... 8-1

Table 8-2 Cost for Installing a Sensor in the Bugey (900 MW) Nuclear Power Plant ............... 8-2

Table 8-3 Comparative Pressure Losses - Orifice Plate/Venturi .............................................. 8-3

Table 8-4 Comparative Costs of Measurement Systems......................................................... 8-4


1-1

1 SYMBOLS

Symbol Definition Dimension SI unit

C Coefficient of discharge dimensionless -

d Diameter of the orifice (or throat) of the primary deviceat working conditions

L m

D Upstream internal pipe diameter at working conditions L m

e Thickness of the orifice of the primary device atworking conditions

L m

E Thickness of the plate of the primary device atworking conditions

L m

ec Distance between the centerline of the orifice and thecenterlines of the pipes on the upstream anddownstream sides

L m

eCn ec component in the direction perpendicular to thepressure tap

L m

ecl ec component in the direction parallel to the pressuretap

L m

F Angle of the bevel dimensionless -

He Feedwater enthalpy at the steam generator inlet ML2T-2mol-1 J/mol

Hv Feedwater enthalpy at the steam generator outlet ML2T-2mol-1 J/mol

Hp Blowdown enthalpy at the steam generator outlet ML2T-2mol-1 J/mol

n Number of loops dimensionless -

p Absolute static pressure of the fluid ML-1T-2 Pa

QARE Feedwater flow MT-1 kg/s

Qp Blowdown flow MT-1 kg/s

qm Mass rate of the flow MT-1 kg/s

β Diameter ratio (d/D) dimensionless -

∆p Differential pressure ML-1T-2 Pa

ω∆ Pressure loss ML-1T-2 Pa

ρ Density of the fluid ML-3 kg/m3


2-1

2 OVERVIEW OF FEEDWATER FLOW

Overview of the Feedwater Flow at EdF Nuclear Plants

Measurement of the Nominal Thermal Power of a PWR

The nominal thermal power of a given pressurized water reactor (PWR) unit is periodicallymeasured (at least once a month) by plant testing teams. On French PWRs, the procedurefollowed is known as BIL100 (thermal balance at 100% licensed thermal power). The procedureserves as a reference for calibrating nuclear measuring channels and for measuring the thermalbalance established by control sensors (the BIL KIT procedure for 900-MW units and BIL SPINfor 1300-MW units). BIL100 is performed on the secondary circuit, at the inlet and outlet of eachof the steam generators.

With the BIL100 procedure, thermal power is defined by:

kr Wn

iH i

pH ivn

Q pH i

eH ivQiW ARE −∑

=

−−−=

1)()( Eq. 2-1

where:

Wr = thermal powern = number of loopsQARE = feedwater flowHv = feedwater enthalpy at the steam generator outletHe = feedwater enthalpy at the steam generator inletQp = blowdown flowHp = blowdown enthalpy at the steam generator outletWk = primary power not coming from the core (heaters, primary pumps)

Since EdF’s PWRs are based on the original Westinghouse design (through a license toFramatome), this BIL100 procedure is identical to the procedure performed by WestinghousePWRs (see Figure 2-1).


Overview of Feedwater Flow

2-2

Figure 2-1Installation Diagram Showing the Measurement Points Needed for BIL100

Feedwater Flow Measurement in BIL100

The predominant term in the calculation of uncertainty for BIL100 is the uncertainty related tofeedwater flow, which accounts for 80% of the uncertainty related to thermal power. Theuncertainty of BIL100 for a 1400-MW unit (known as the N4 unit) is ± 0.4 %, and the realuncertainty of the feedwater flow is ± 0.8 %.

This feedwater flow measurement in BIL100 is extremely important for determining the primaryflow by means of the primary/secondary enthalpic balance method, which is performed by allPWRs in the world today. This determination of primary flow rate is periodically required bysafety authorities to guarantee that the rate of cooling of the core remains between the lower limit(to ensure sufficient cooling of the reactor vessel) and the higher limit (to ensure stability of thevessel internals).

Orifice Plates Used for Calorimetrics

The most common measurement tool for industrial flow measurement is a pressure differentialdevice (venturi tube, orifice plate, or nozzle). This is governed by international standardsdescribed under ASME, ISO, and others.


Overview of Feedwater Flow

2-3

In all French PWRs, each feedwater line is fitted with two flow measurement devices:

• A control flowmeter (always a venturi), whose reading serves to regulate power in the I&Csystem.

• A “test” flowmeter, whose reading is used in the BIL100 procedure for a more accuratedetermination of the feedwater flow rate. The test flowmeter is an ISO standard orifice plate.

The control flowmeter does not require extreme precision because it is regularly recalibrated bycomparison with the test flowmeter measurement, which must have maximum precision.Depending on whether the plant design is PWR or BWR, these two feedwater flowmeasurements are performed either by identical devices (two venturi tubes, for example) or bydifferent devices (a venturi and an orifice plate, as is the case in France). It is therefore clear thatthe risk of systematic error due to the measurement method varies from one PWR to another.

Considering the importance of feedwater flow measurement in PWR calorimetrics, EdF’s designengineers for the PWR fleet decided to have two different flowmeters in series on each feedwaterline.


3-1

3 ORIFICE PLATE DESCRIPTION

Measurement Principle

The measurement principle consists of inserting a primary device (see Figure 3-1) in a fluidflowing under pressure in a pipe, creating a differential pressure (ûS� EHWZHHQ WKH XSVWUHDP

length and the throat of this element (downstream). According to the Bernoulli principle, thisdifferential pressure is proportional to the square of the velocity of the fluid.

Figure 3-1Orifice Plate (Drawing from ISO Standard 5167)


Orifice Plate Description

3-2

The equation for calculating the mass flow of the circulating fluid is:

ρεπ

)p(2dCA4

q 2f ∆=m Eq. 3-1

where:

qm = mass flowC = discharge coefficientAf = 1/¥��4) = velocity of approach factor0 = expansion factor (= 1 for incompressible fluids)ûS = differential pressure! = fluid density� = d/D = beta ratiod = diameter of orificeD = diameter of pipe

This measurement method is described in ISO Standard 5167 and EPRI report TR-101388.

Types of Orifice Plates

In French PWRs, two types of orifice plates (made of stainless steel) are used. These plates arecharacterized by their pressure taps.

The vena contracta plates are characterized by an upstream tap at distance D from the plate and adownstream tap dependent on the diameter ratio β. This orifice plate is used on all 900-MWunits.

The other type of orifice plate has pressure taps at distance D upstream of the plate and D/2downstream and has replaced the vena contracta design.

Orifice Plate Thickness and Beveling

The requirements in ISO Standard 5167 concerning the thickness and angle of the bevel are thefollowing:

• The thickness (e) of the orifice bore shall be between 0.005D and 0.02D. The variance in themeasured values of e at any point on the orifice should be less than 0.001D.

• The thickness (E) of the plate shall be between e and 0.005D.

• The angle of the bevel (F) shall be 45° ± 15°.

In French PWRs, the thickness of the plate is 10 mm (3/8 inch) and the bevel angle is 45°.



3-3

Figure 3-2 shows a rear view of an orifice plate, and Figure 3-3 shows the flange fitting wherethe orifice plate is placed.

Figure 3-2Orifice Plate, Rear View



3-4

Figure 3-3Orifice Plate Location

Beta Ratio and Measured Pressure Drop

The diameter ratio (�=d/D) is always less than or equal to 0.75. Within the limits described in theISO 5167 standard, the value of � may be chosen by the user.

An orifice plate generates a pressure loss of around 60% in the differential pressure measured.This value is high compared to other pressure differential devices; the drawback is a loss ofenergy in thermal power. To minimize this loss, the orifice plates used in French PWRs havehigh opening ratios (� � 0.64). This ratio makes it possible to decrease the differential pressureand have a minimal resulting loss in production costs (see below).

For feedwater flow measurement in all French 3:5V� WKH YDOXH RI � VKRXOG UDQJH EHWZHHQ ��

and 0.75, the maximum limit allowed under ISO. The measured pressure drop is around 1 bar(16 psi or 105 Pa).

Total Pressure Drop from the Plate

The pressure loss ( ω∆ ) is related to the differential pressure (ûp) by the equation:

pC)C1(1

C)C1(1224

224

∆β+−β−

β−−β−=ω∆ Eq. 3-2



3-5

where:

ω∆ = pressure loss� = diameter ratio (d/D)C = discharge coefficientûS = differential pressure

This pressure loss is the difference in static pressure between the pressure measured at the wallon the upstream side of the orifice plate (approximately 1D upstream of the orifice plate) and thatmeasured on the downstream side of the orifice plate (approximately 6D downstream of theorifice plate).

An approximation value of Equation 3-2 is:

9.11p

β−=∆

ω∆Eq. 3-3

where:

ω∆ = pressure lossûp = differential pressure� = diameter ratio (d/D)

For example, for �= 0.65, the total pressure drop is around 56%; for � = 0.71, it is 47%.Typically, for the French PWR plants, the total pressure drop is approximately 13 psi (9E1 kPa)�IRU � ��


4-1

4 ORIFICE PLATE ACCURACY

Calibration Requirements at EdF

In Equation 3-1, the term C (discharge coefficient) was introduced to take into account thepressure losses at the orifice plate. This coefficient was determined on the basis of numeroustests performed in laboratories around the world to empirically determine the dischargecoefficient.

This significant amount of testing makes it possible to estimate a global uncertainty for C:

C = ± 0.5% when � �0.6C = ± (1.667 x � - 0.5)% when � is between 0.6 and 0.8

No calibration laboratory is used because the requirements of ISO Standard 5167 are met.Nevertheless, EdF R&D has carried out various tests in their laboratory facility in Chatou tocheck the principal installation configurations (see “Upstream and Downstream Lengths ofPiping” later in this section).

Installation Requirements at EdF

The installation requirements at EdF are described in ISO Standard 5167. The main requirementsare the following :

• The pipe must be full of fluid at the section being measured.

• The primary device shall be fitted between two straight sections of cylindrical pipe ofconstant diameter and of specified minimum lengths in which there is no obstruction orbranch connection other than those specified in “Upstream and Downstream Lengths ofPiping” later in this section.

• The pipe bore shall be circular over the entire minimum length of straight pipe required (see“Upstream Pipe Inspection” in Section 5).

• The interior of the pipe shall be clean at all times. Dirt that can readily detach from the pipeshall be removed. Any metallic pipe defects, such as metallic peeling, must be removed.

• The pipe may be provided with drain holes and/or vent holes to permit the removal of soliddeposits and entrained fluids; however, there shall be no flow through either drain holes orvent holes during the flow measurement process. Drain and vent holes should not be locatednear the primary device.


Orifice Plate Accuracy

4-2

Upstream and Downstream Lengths of Piping (L/Ds)

To ensure the uncertainty of the discharge coefficient, ISO Standard 5167 imposes proceduresthat allow very little deviation for manufacturing and mounting the orifice plates. The primarydevice must be installed in the pipeline at a position such that the conditions immediatelyupstream approximate those of swirl-free, fully developed fluid flow.

The required length upstream between the orifice plate and the first non-straight pipe section(bends, valves, or tees) must be greater than 46D (see Section 7 for more details). If these lengthrequirements are not met, the potential error must be increased (typically by ± 0.5%).

The required length downstream between the orifice plate and the first non-straight pipe sectionmust be greater than 7D (see Table 7-1).

The values of the required lengths are given in a table in ISO Standard 5167. They depend on thekind of non-straight section in the pipeline (single bend, double bend, angle of the bend, reducer,expander, etc.). The values also depend on the diameter ratio �.

The values given in ISO Standard 5167 (see Table 7-1) were determined experimentally with avery long straight length of pipe upstream of the fitting in question so that the flow immediatelyupstream of the fitting was considered as fully developed and swirl-free. It is stronglyrecommended that a flow conditioner be installed downstream of the header (for example, aconditioner whose cross-sectional area is approximately equal to 1.5 times the cross-sectionalarea of the operating flow meter tubes) because there will always be distortion of the flow profileand a high probability of swirl.

Those requirements are met for most of the French PWRs; but for some of EdF 1300-MW units,this is not the case. The orifice plate is positioned 26D downstream from a combination of aventuri tube and a 90° elbow, although ISO Standard 5167 requires 28D for a guaranteedaccuracy of ± 0.7%. Although the difference appears to be small, it does not allow strictapplication of ISO accuracy values. The 0.5% increase required by the ISO standard has to beapplied for those 1300-MW units because the feedwater flow orifice plate installation conditionsdo not meet the ISO requirements.

An experimental study relating to orifice plate installation conditions was carried out on theEVEREST experimental loop at EdF Chatou. The feedwater pipework was simulated, and theinfluence of the orifice plate installation conditions was evaluated. Figure 4-1 depicts the pipeconfiguration that was mounted in the EVEREST testing section.



4-3

Figure 4-1Evaluation of Orifice Plate Installation Conditions on the EVEREST Loop:Pipework Configuration

Figure 4-2 represents the bias between the reference and the measured flow rate for two series oftests done with the orifice plate positioned at 28 and 26 pipe diameters from the elbow.

Figure 4-2Evaluation of Orifice Plate Installation Conditions on the EVEREST Loop:Bias Versus Flow-Rate

Figure 4-2 seems to show a difference between the two flow rates of about 0.4%, but since thefigures of “bias versus flow rate” are within the accuracy limits of the ISO standard, the accuracyof the orifice plate measurements is considered not to be affected by the installation conditions.



4-4

Cost Benefits

An increase of 0.5% on the accuracy in each of four feedwater sections will yield an increase of

0.25% in thermal power accuracy (0.5%/ 4 = 0.25%). This increase represents a difference of 9MWth because the estimate of the thermal power uncertainty is reduced from ± 24 MW to ± 15MW (3867 nominal reactor thermal power). In terms of electrical power, it leads roughly to anannual gain of 3 MWe, which is a gain of $300,000 per unit. For the total number of 1300-MWunits (12), this 0.5% uncertainty decrease has resulted in $3.6 million a year additional revenues.

Special Orifice Plate Alignments

The orifice plate should be perpendicular to the centerline of the pipe to within 1°.

The orifice plate should be centered in the pipe. The distance (ec) between the centerline of theorifice and the centerlines of the pipes on the upstream and downstream sides should bemeasured. For each pressure tap, the components of the distance between the centerline of theorifice and the centerline of the pipe in the directions parallel to and perpendicular to the axis ofthe pressure tap should be measured.

The component in the direction parallel to the pressure tap Ecl and the component in the directionperpendicular to the pressure tap ecn should meet the requirements of ISO Standard 5167.

It is necessary when holding the orifice plate between flanges to allow for its free thermalexpansion and to avoid buckling and distortion.

Pressure Differential Instrument Accuracy Requirements

The pressure differential instrument accuracy must be ± 0.15% of the measured value (MV). Theglobal uncertainty must be bounded to ± 0.2% of the MV during the 20-minute measurement (theduration of data acquisition for sampling and averaging).

Pipe Roughness and Circularity Requirements

The requirements for EdF are governed by ISO Standard 5167. EdF R&D has carried out variousevaluations on the effects of the roughness and the circularity of the pipe and found therequirements under the standard to be adequate.


5-1

5 EDF EXPERIENCE WITH ORIFICE PLATEMAINTENANCE

Plate Inspection

Plant operators make periodic inspections (one in three or four orifice plates is inspected at thetime of each unit outage), and no problems have been detected. The uncertainties allowed arewithin the limits in ISO Standard 5167.

Upstream Pipe Inspection

The pipe bore should be circular over the entire length of straight pipe required. The crosssection may be assumed to be circular if it appears so by visual inspection. The circularity of theoutside of the pipe can be taken as a guide, except in the immediate vicinity (2D) of the primarydevice where special requirements apply.

Routine Diameter Measurements

The internal diameter is measured at the installation of the orifice plate. It is measured on threedifferent sections and on four diameters on each section (12 measurements).

Differential Pressure Transmitter Maintenance

The EdF procedure specifies that the differential pressure transmitter must be calibrated everynine months. A number of statistical studies have been done by EdF R&D on this subject. Inparticular, in 2000 a study on drift indicated that no differential pressure transmitter showed anydrift after being installed for nine months. The calibration interval may change to once a yearinstead of once every nine months.


6-1

6 LICENSE EVENT REPORTS RELATED TO EDFFEEDWATER FLOW

No license event was ever reported that was caused by using orifice plates for feedwater flowmeasurement. Most of the problems were related to the reinstallation of the orifice plates after anoutage and were due to human error:

• An orifice plate was remounted with a bad tightening torque. EdF has written a newprocedure to help the technicians.

• In another plant, technicians had reinstalled the orifice plate in the wrong direction (facingupstream instead of downstream). A new procedure specifies that two people must be presentto reinstall an orifice plate: one to do the job and another one to double check the work.

No fouling has been seen in any EdF plant since the orifice plates were installed; some of theplates were installed 20 years ago.

The upstream length-to-diameter ratios (L/Ds) required by ISO Standard 5167 are not met in allFrench PWRs. The plant operators who identified the problem called EdF R&D to determinewhether to increase the uncertainty as required by the ISO standard. As detailed in Section 4 (seeFigure 4-2), there was no need to increase the uncertainty because it was within the ISO limits.


7-1

7 IMPLEMENTATION REQUIREMENTS AT U.S. NUCLEARPLANTS

The implementation requirements for U.S. nuclear plants are those described in ISO Standard5167 (see “Upstream and Downstream Lengths of Piping (L/Ds)” in Section 4).

Table 7-1 gives the required straight lengths for several fittings. The values are the same as in theISO standard.

The ISO standard also gives the values in case a flow conditioner is used.

A study specifically for U.S. nuclear plants is necessary to precisely determine the followingpoints:

• The best diameter ratio �

• The total lost pressure drop (depends on the diameter ratio)

• The accuracy of the feedwater flow measurement by an orifice plate in the various U.S. plantconfigurations

If the required straight lengths cannot be found in the U.S. plants, there are two options:

• Option 1: The uncertainty has to be increased as described in the ISO standard.

• Option 2: Some tests on the EVEREST loop can be carried out to determine if there is a needto increase the uncertainty given by ISO Standard 5167. This amounts to a specificcalibration of the orifice plate.

Such tests have been done for some EdF PWRs. It was experimentally demonstrated that theuncertainty overestimation of 0.5% was unjustified, and this allowed EdF to save U.S. $3.6million a year (see Section 4 for the required straight lengths).


Implementation Requirements at U.S. Nuclear Plants

7-2

Table 7-1Required Straight Lengths Between Orifice Plates and Fittings Without Flow Conditioners (Values Expressed as Multiples ofInternal Pipe Diameter D)

Upstream (Inlet) Side of the Orifice Plate Downstream(Outlet) Side

DiameterRatio β

Single 90°bendTwo 90° bendsin any plane(S>30D)*

Two 90°bends in thesame plane(30D>S>10D)*

Two 90°bends inperpendicularplanes(S<5D)*

Single90° tee

Single 45° bendTwo 45° bends inthe same plane(S>22D)*

Reducer 2D to Dover a length of1.5D to 3D

Full bore ballvalve or gatevalve fullyopen

Any fittings(columns 2to 8)

0.40 16 10 50 9 30 5 12 6

0.60 42 30 65 29 30 9 14 7

0.67 44 44 60 36 44 12 18 7

0.75 44 44 75 44 44 22 24 7

* S is the separation between the two bends measured from the downstream end of the curved portion of the upstream bend to the upstream end of the curvedportion of the downstream bend.


8-1

8 COST BENEFIT ANALYSIS FOR NUCLEAR PLANTS

Cost of Installing a Differential Pressure Device1

Manufacturing Cost

Differential pressure devices listed in decreasing order of manufacturing cost are:

• Orifice plates

• Nozzles

• Traditional venturi tubes

The orifice plates and nozzles, however, must be used with measurement tubes. The ISOstandard requires straight lengths of 10D upstream and 4D downstream with a very lowroughness coefficient that can be guaranteed only by proper surface machining.

The EdF facility in Chatou asked for an estimate for supplying a venturi tube and an orifice plateto measure feedwater flow in an N4 design plant (These are 1400-MWe generating units; atpresent there are four such units in France). The cost estimate from a European manufacturer isshown in Table 8-1.

Table 8-1Estimate for Supplying a Venturi Tube and Orifice Plate

PressureDifferentialDevice

Proposal Price

Orifice plate The plate is of stainless steel and centered on the flanges.

The mounting has an upstream length of 10D and adownstream length of 4D, fully machined. The machiningmeets the criteria imposed by the ISO standard.

$10,326

Venturi tube With a so-called cast convergent (or “as-cast”), in keeping withISO Standard 5167:

• Pressure taps using welded vortex chambers

• Inlet cylinder length = 3D

• Divergent angle = 8°

$9,449

1 All costs are based on typical cost schedules and labor rates in France.

EPRI Licensed MaterialCost Benefit Analysis for Nuclear Plants

8-2

The manufacturer offered to calibrate the venturi tube prior to mounting. The calibration testsincrease the price by some $1,369.

In conclusion, the manufacturing costs are roughly identical for the two devices if all criteria ofmanufacturing and mounting stipulated in the ISO standard are met.

To this cost for the pressure differential device, the cost of the differential pressure sensor mustbe added. Table 8-2 details the items and cost involved.

Table 8-2Cost for Installing a Sensor in the Bugey (900 MW) Nuclear Power Plant

Description Cost

Pressure sensor $1,096

Manifolds $ 411

Bosses – 10 m impulse line – preparation – insulation valves and mounting $1,917

Cabling and plan (from an existing network) $2,396

Study (plan and launch of works on a nuclear site) $1,369

Cost for one calibration $ 342

Total $7,532

Installation Cost

The venturi can be mounted on shorter pipe lengths than an orifice plate; therefore, additionalsupports can be eliminated. The conditions under which a venturi must be installed are also lessrestrictive (less constraint with respect to relative roughness).

The cost has been estimated by an EdF Engineering Support Team. The figures come from anestimate for replacing a feedwater flow orifice plate in the Bugey plant. The cost of the service is$10,956. This includes cutting, welding, inspecting the weld, hydrotests, and studies.

For the purposes of this report, consider that the installation costs are the same for the threedevices.

Operating Cost

On EdF’s PWR fleet, sensors are calibrated every year at a cost estimated at $480 each; thisincludes not only calibration but also mounting and demounting the sensor, as well asverification of the mounting. Every three or four years, the plate is removed and inspected; thecost is around $2,464 or $820 per year.

On the U.S. fleet of PWRs, dimensional inspection of the venturis has been performed regularlysince the problem of fouling was first detected. Because it takes longer to inspect a venturi than a


8-3

plate, the cost is estimated at $1,369. This presupposes that the venturi is mounted betweenflanges and is easy to demount (access platform).

The essential difference between the operating cost of a venturi and that of an orifice plate is dueto the pressure loss with the orifice plate, which is greater than with the venturi. To estimate theadvantage with the venturi, the N4 plant series was chosen as an example. The calculation dataare shown in Table 8-3.

Table 8-3Comparative Pressure Losses - Orifice Plate/Venturi

System DifferentialPressure(Measured)

Pressure Loss(Residual)

Orifice plate with pressure taps at D and D/2now in operation at Chooz

820 mbars 380 mbars

“As-cast” venturi 1040 mbars 75 mbars

Difference inpressure loss

305 mbars

Maintaining the water level in each steam generator (SG) is extremely important to plant safety.Feedwater flow is directed to the SGs by a series of feedpumps (for the units at Bugey andFessenheim, for example, three pump systems are used). Continuing to meet the stipulated valueis ensured by a level-control channel that acts on each SG. Its role is to distribute flow among theSGs. Overall control of the flow is ensured by varying the speed of the main feedwater pumps.

For the N4 plant, the delivery head for the main feedwater pumps is 1250 psig (86 bars). Thegain in pump power output due to the difference in pressure loss (4.5 psid or 0.305 bars) betweenthe two devices is negligible in comparison with this pressure. This small difference is offset bythe control channel. For greater pressure losses (> 1 bar), however, a complete calculation mustbe made to estimate the impact on the SG level-control channel.

In conclusion, it is estimated that the economic gain attributable to a venturi in comparison withan orifice plate is nil. Furthermore, U.S. plants with venturis have encountered problems offouling. The percentage power loss due to fouling ranges from 0.8% to 2.2%. Assuming 80%availability and at $0.02/kwH, the annual loss at some operating units can be as high as $2.0million.

The budget for R&D and experience feedback studies is unknown, but the cost of the loss ofoperation and power de-rate is significant.


8-4

Summary of Costs

Table 8-4 presents a summary of the costs of the two measurement devices.

Table 8-4Comparative Costs of Measurement Systems

Orifice Plate Venturi

Investment (I) Manufacturing $10,268 $9,445

Cost of installation andinspection

$10,950 $12,319

Purchase of the sensor andinstallation

$8,213 $8,213

Operation (O) Cost of annual inspection andverification (calibration,dimensional inspection)

$1,300 $1,848

Maintenance contract $0

Yearly cost price (I/10 + O) $4,243 $4,846

The costs are not very different. The advantage of the orifice plate is that no fouling was found inFrench PWRs, thus saving the cost of fouling studies and the loss of revenue through lost MW.Consequently, orifice plates can be considered for accurate and reliable feedwater flowmeasurement.


9-1

9 REFERENCES

1. 10CFR50 Appendix K, paragraph (I)(A), prior to July 2000 rulemaking revision.

2. ACRS letter dated June 22, 1999, from ACRS Chairman D. Powers to Dr. William D.Travers, Executive Director of Operations at NRC, “Revision of Appendix K, ‘ECCSEvaluation Models,’ to 10CFR Part 50.”

3. “ECCS Models,” Federal Register, Vol. 65, No. 106, Thursday June 1, 2000.

4. Feedwater Flow Measurement in U.S. Nuclear Power Generation Stations, EPRI, Palo Alto,CA: 1992. TR-101388.

5. “Improving Power Plant Efficiency and Safety Through Better Knowledge of Flow-Rates:The EdF Approach,” M. Piguet, POWER-GEN EUROPE, 1998.

6. “Measurement of Fluid Flow by Means of Pressure Differential Devices Inserted in CircularCross-Section Conduits Running Full, Part 1: General,” International Standard ISO 5167-2,1999.

7. “Measurement of Fluid Flow by Means of Pressure Differential Devices Inserted in CircularCross-Section Conduits Running Full, Part 2: Orifice Plates,” International Standard ISO5167-2, 1999.

8. NRC Reg. Guide 1.49, Power Levels of Nuclear Power Plants, Revision 1, December 1973.

9. “Nuclear Plant Performance Benefits From Flowmetering Improvements : EdF’s ExperienceFeedback With Various Industrial Flowmetering Techniques,” H. Jeanneau, J. M. Favennec,M. Piguet, EPRI/PSE/NPPI Seminar, Chicago, IL, August 7–8, 2000.

10. “Pipe Flow Modeling for Ultrasonic Flow Measurement,” H. Jeanneau, M. Piguet,FLOMEKO 2000, Salvador, June 2000.

11. Small Power Uprates Under Appendix K : Benefits And Considerations, EPRI, Palo Alto,CA: 2000. 1000607.

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application of orifice plate for measurement of feed water

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