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Thermal Shield Damage Recovery Program,Final Rept,App a: Effects of Core Barrel Bypass Flow on Fuel Assemblies Testing & Analyses
	ML20083M587
Person / Time
Site:	Millstone
Issue date:	03/31/1984
From:	; NORTHEAST NUCLEAR ENERGY CO.
To:	;
Shared Package
ML20083M564	List: B11087, Forwards Thermal Shield Damage Recovery Program,Final Rept, App A:Effects of Core Barrel Bypass Flow on Fuel Assemblies Testing & Analyses, Per; ML20083M587;
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1 NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 THERMAL SHIELD DAMAGE RECOVERY PROGRAM FINAL REPORT APPENDIX A EFFECTS OF CORE BARREL BYPASS FLOW ON FUEL ASSEMBLIES TESTING AND ANALYSES Docket No. 50-336 MARCH,1984 h YO

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I A.1 Experimental Investigation of Core Shroud Bypass Flow I

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EXECUTIVE

SUMMARY

This report summarizes an experimental investigation to determine the velocity and breadth of flow Icaking through a full-scale model of a structural ocam in the core fuci shroud assembly. The test program provides data which can be used to assess the flow-induced vibration of fuci rods adjacent to the shroud assembly. The work was donc at this timo to support evaluation of potentini effects of holcs drilled recently in the core barrel of the Millstone 2 Plant to arrest a crack.

Tests were conducted in a full-scale model of a sector of the core barrel / shroud assembly. The full-scale model was used to make direct measurements of the Icakage velocity at several values of downcomer-to-core pressure drop specified by Northeast Utilitics for these tests. The results show that the Icakage velocity is approximately 50% of the velocity of the flow through the crack-arrestor hole for the configuration which was tested. At the I

specified pressure drop of 25 psi, a velocity of 30 f t/sec was measured over a ;

span of about 2.25 inches through a scam 0.015 inches wide. Further, measurcments in the model indicate that the 1cakage velocity is proportional to

! the squaro root of scam width and to the square root of downcomer-to-coro pressure drop. ,

A flow visualization model was used to provide a qualitative assessment of the flow patterns which catablish the conditions for this leakage flow. Some data are prevented which show that tho height of the Icakago flow is restricted to a small region of the scam icngth equivalent to a few diameters of the inlet jet and is beunded by the girth rib at the inlet jet clovation. Pressure

mensurements vero also made in the region between the core barrol and thn core shroud. There measurements and observations are used to develop a brief description of the flow phenomena and to support calculationa vc have performed.

A scif-conr.istent description of the velocity distribution throughout the model in presented and compared with theory.

I Crearo R&D Incorporated carried out tnin work for Northeast Utilitics j

Gervice Company under Purchase Order 828493. Tests in the full-scale model vero l conducted following Quality Asouranco procedures mocting the requirements of i ANSI N45.2. The Northeast Utilitics reprocentative for thin work was Frank Hello; the authors vero responcibic for carrying out the test program.

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TABLE OF CONTENTS Page EXECUTIVE

SUMMARY

. . . . .. ... .............. i TABLE OF CONTENTS . .. . ......... ..........ii LIST OF TABLES. . . . . . . . . . . . . . . . . . . . . . . . .iii LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . iv 1 INTRODUCTION. ...................... ... I 2 FULL-SCALE MODEL TEST PROCRAM . . ... ............ 2

2.1 Test Model . . . . . . . . . . . . . . . . . . . . . . . . 2

. 2.2 Test Facility. . . . . . . . . . . . . . . . . . . . . . . 2 l

2.3 Test Measurements. . ...... . . . . . . . . . . . . 10 3 FULL-SCALE MODEL TEST DATA. . . . .. . . . . . . . . . . . . 14 4 FLOW VISUALIZATION MODEL STUDIES. .. ............16 4.1 The Flow Vinualization Model . . . . . . . . . . . . . . 16 4.2 Flow Observations. . . . . . .. ............16 4.3 Stagnation Prennure Measurenento . ...........21 5 INTERPRETATION OF PHENOMENA . . . . . . . . . . . . . . . . . 26 6 REFERENCES. . . . ............. . . . . . . . . . 29 APPENDIX At ' Documentation of Proliminary Data APPENDIX B Velocity Vector Dingrams from FLUENT Calculations l

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LIST OF TABLES Table Page, 1

1. Test Measurement Uncertaintics. . . ............13 2 .- Flow Visualization Testa lleight of Seam Exit Flow . . . . . . 23 4

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LIST OF FIGURES !

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1. Full-Scale Test !!odel (Partially Assembled) . . . . .... ............. 3 i

2. Test Model Dimensions. ... ..... . . . . . . . . . . ~ . + . 4 j

l 3. Core Barrel Hole in Relation to Former Plate l (Viewed from " Core") . . . . . . . . . . . . . . . . . . . . .. 5 l

4. Plenun Chamber Details . . . . . . . . . . . . . .... ..6 j

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5. Assembled Test Model . . . . . . . . . . . . . . . . . . . ... 7 t

6. Assembled Test Model in Test Facility. . . . ... . . . . . . . 8 -

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7. Test Facility Schematic. ............ ..... .. 9 l

8. Stagnation Probes at Scap Exit . . . . . . . . . . . . . . . .

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9. Heasured Scam Leak Flow Velocity . . . . . . . . . . . . . . 15 ,

10. Flow Visualization Model Dimensions. . . . . . . . . . . . . 17

11. Flow Visualization of Core Jet . ..............18 ,

12. Locations of Flow Visualization Skirte. . . . . . . c . .'..Ih .

13. Flow Patterns in Wedge Region (Artist's Rendition) .... ..... . . . . . . . . . . . 20 r

14. Flow Visualizaton of Scam tankago. ....... ... .'. . . 22

15. StaBnation Precouro Hannurements in Wedge. . . . ..... . . 24 -

16. Scam Exit Velocity vs. Scam Width ..............28 ;

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1 1NTRODUCTION This report describes an experimental project carried out by Creare R&D Inc. to measure the velocity of flow icahing through a structural scam in a full-scale model of the core fuci shroud assembly. This leaking flow is supplied from the flow through a crack-arresting hole in the core barrel, driven by the downcomer-to-core differential pressure. The Icakage flow is of concern because it can impact directly on a fuct rod located at the exit of the scam, l

possibly causing crosion or vibration-induced damage to the fuel rod.

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l Tcat measurements were made at several downcomer-to-core differential

. pressure values, bracketing the target operating pressure drop of 25 psid r specified by Northeast Utilitics. The test model was supplied by Northeast Utilitics and assembled to have a nominal seam width of 0.015 inch which was specified by Northeast Utilitics.

l A separate flow visualization model was also constructed to provide additional experimental verification of the extent of the flow Icaking through

'- the scam and direct observation of the overall flow patterns.

Section 2 of this report describes the test model, facility and instrumentation used in the tests of the full-scale model. The renuits of the l quality-assured tests carried out in that full-scale rodel are presented and I

discuaned in Section 3. Section 4 describen the flow visualization model and l the flow measurements and obacrvations derived f rom that model. An interpretation of the observations from the flow visualization studies is given l in Section 5. Additional measurements f rom prelininary tento in the full-scale l

model are documented in Appendix A. Those measurements show the effect of

dif ferential pressure and naam width on the velocity of flow 1 caking through the scam.

l The test program described in Sections 2 and 3 was carried out under Quality Assurance procedures described in the Test Plan and Procedures document (Reference 1).

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2 FULL-SCALE MODEL TEST PROGRAM This section describes the test model and facility used to produce data on the velocity of flev leaking through the seam in the shroud assembly.

2.1 Test Model The measurements of flow velocity were made in a full-scale mockup of an approximately 30* sector of the fuel shroud assembly. The partially assembled test section is shown in Figure 1. It consists of a steel fabrication which provided a realistic full-scale simulation of the important region between the core barrel and the shroud assembly. The shroud seam is formed at the intersection of two panels which form the central " wedge" of the shroud assembly. All dimensions in the mockup were maintained at nominal full-scale values. The vertical extent of the test section spanned the height of three former plates (girth ribs). The as-built dimensions of the model are shown in Figure 2.

The three girth tibs in the model were fabricated from 1.5 inch thick steel plate with one edge of each rib having a radius of curvature of about 73.7 inch (estimated from measurements of the are height and length). Steel plates (0.75 inch thick) were welded between the girth ribs, intersecting at right angles, to form a sector of the fuel shroud assembly. In.the lower half of the mockup the panels forming.the central vedge were fabricated from acrylic plates and were adjustable in order to establish the specified seam . width for the tests.

Additional support brackets were used near the apex of these wedge panels to stabilize the seam width during tests.

The core barrel was simulated in the model using a 0.375 inch thick steel plate having a radius of curvature which conformed to the shape of the girth ribs. The core barrel plate was bolted to 0.375 inch thick flat bars welded to the girth ribs. These hars provided a fixed clearance gap in the model between the inner surface of the core barrel plate and the girth ribs.

In order to simulate the conditions for flow through the core barrel l creck-arresting hole, a 1.125 inch diameter hole was drilled through the core l barrel plate and through a 1.25 inch thick steel block attached to the plate. ]

The total hole length was 1.625 inch. The core hole was centered in the plane of the seam with its centerline elevation one-half of the hole diameter below the bottom of the middle former plate. Figure 3 clearly shows the alignment of the hole relative to the former plate. ,

An inlet flow plenum chamber was attached to the core barrel plate as shown in Figure 4. The plenum chamber provided a relatively stagnant flow situation in the tests and was used to define the downcomer-to-core differential pressure.

2.2 Test Facility In these experiments the fully-assembled mockup (Figure 5) was placed inside a tank and the plenum .was connected to a water supply manifold using the 4 hoses as shown in Figure 6.. The test facility is shown in Figure' 7. '. Flow to .

the model was.provided from a supply tank using a centrifugal pump with' ^

i sufficient hcad to achicyc the desired inlet plenum pressure. The flow'rcte to -

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4 the model was regulated using bypass and flow control valves to establish the target inlet plenum pressure. The water leaving the model (through the shroud scam and through the cicarance gaps between the core barrel and the shroud assembly) was returned to the supply tank through the overflow line near the top of the test tank.. In the tests the model was fully submerged in the tank and the static (no flow) elevation of the water was 26.4 inch above the upper former plate ( 44.63 inch above the centerline elevation of the core hole). With an 4 inlet plenum pressure of 25 psid, the flow rate into the model was about 155 gallon / minute. (For that flow rate, the water level in the tank head was increased 4.5 inch; this minor change is accounted for in reducing the test data.)

2.3 Test Measurements The principal measurement of interest in these experiments was the velocity of the flow leaking through the sean in the shroud assembly. Stagnation probes were installed at the exit of the seam to measure the total pressure of the leaking flow, as shown in Figure 8.

These stagnation probes measure the flow velocity according to the relationship:

AP = K 2g0 (1) c where AP is the difference between the total pressure measured with flow and l the pressure measured with no flow (1bf/ft2) 1 K is the probe pressure coefficient p is the fluid density. (lbm/f t 8)

V is the fluid velocity (ft/s) g" is the gravitational proportionality constant (32.174 lbm ft/lbf s)2 For the stagnation pressure probe design used in this test program, the pressure coefficient K is taken to'bc unity (Reference 2). Thus, the velocity is calculated'from:

2g AP V=( c

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P 4- The probes were fabricated from 0.020 inch diameter stainless steel tubing 4

- having an inner diameter of 0.010 inch. The probe tips were placed- l

.approximately 0.020 inch from the exit plane of.the seam and were aligned to be !

on the centerline of and perpendicular to the seam. Seven probes were used to )

define the velocity profile in the region of the maximum expected leak flow velocities and extending approximately 3.25. inch.below the. middle'former plate.

The probes were connected to a: single pressure transducer using:

water-filled lines and isolation valves. During the tests-the valves were used 10

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to select individual probe outputs to be measured by the transducer. The j voltage readings from the transducer were converted to pressure using the i calibration-data for the transducer. This calibration was performed using mercury manometers for the standard reference pressure.

The plenum pressure was the only variable in the quality-assured tests.

Plenum pressure was measured using calibrated pressure gauges connected to the plenum at two locations. One gauge measured the pressure from the end of the i- plenum, while the second gauge was connected to the side of the plenum, at approximately mid-length. These two gauges always read within 0.5 psi of each j -- other. The plenum pressure readings, corrected for elevation and averaged i together, defined the downcomer-to-core differential pressure for these tests.

The flow rate to the model was measured using an orifice meter designed and i installed in accordance with standard practice established by ASME (Reference 3). The orifice meter was fabricated from 2 inch diameter, schedule 40 pipe with flange taps. The orifice plate had a diameter of 1.551 inch (B=0.75), and i an orifice coefficient (K-factor) in these tests of 10.61. A differential l pressure transducer measured the orifice pressure drop.

1 All tests were conducted with cold water, in the range from 50*F to 60*F.

Water temperature was measured in the supply tank using a dial-stem thermometer.

f Table 1 provides a list of the test measurements, instruments, and estimates of the uncertainty in the measured and the reduced parameters, i

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TABLE 1 Test Measurement Uncertainties Test Measurement Instrument Instrument Uncertainty in Uncertainty Reduced Data Inlet plenum pressure gauge (2) 0.5 psi 0.5 psi (0 to 30 psig range)

Stagnation pressure transducer 0.1 in. Hg 0.5% of (0 to 20 in. Hg velocity at range) 30 ft/s i

Flowrate transducer across 0.1 in. Hg 5% of

! orifice plate flowrate at

(0 to 20 in. Hg 150 gpm*

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Temperature dial-stem 3*F <0.1% of thermometer density at (0 to 250*F range) 60'F L

This uncertainty in flow rate also includes the combined uncertainty in the orifice discharge coefficient and other possible error sources.

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3. FULL-SCALE 140 DEL TEST DATA A series of Quality Assured tests were carried out in the full-scale model, measuring the Icak flow velocity at the scam exit for three values of downcomer-to-core differential pressure. The nominal pressures selected for these tests ranged from 22.5 to 27.5 psid, covering the specified differential pressure of 25 psid and variations of ! 10% around that value. For the tests described in this section the model had a seam width varying between 0.015 inch and 0.017 inch over the height of the test section. In the region of the test section where the stagnation probes were situated the scam width was measured as a uniform 0.015 inch.

The tests were conducted following the procedures described in the test plan report (Reference 1). The basic procedure was to adjust the inlet flow rate to the model to achieve the target inlet plenum pressure. Then, with steady flow established the stagnation pressure frorc. each of the seam exit probes was recorded. After a full set of probe readings for one flow condition, the flow rate was adjusted for a new inlet plenum pressure and the stagnation probe readings were again recorded. This process was repeated for each of the three inlet pressures values.

Following the tests the stagnation probe readings were converted to velocity according to the relationship in Eq. 2. The test results are shown in Figure 9. In that figure the velocity measured at each probe is plotted as a function of probe position relative to the bottom of the former plate with plenum pressure as a parameter. The size and clevation of the core hole are shown on the figure for reference.

The ecasured volumetric flow rate and the calculated Core Jet Velocity are also tabulated in Figure 9 at cach of the test pressures. Core Jet Velocity is the ideal velocity which would be attained by a jet of water flowing through an orifice having a pressure drop equal to the tabulated plenum-to-core difierential pressure.

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AP = plenum-to-core differential pressure (lb f/ft ) 2 The data in Figure 9 show a peak seam flow velocity of about 35 ft/s at the probe located near the centerline elevation of _the core hole (Probe 58). That peak velocity was measured for the test condition with the highest inlet plenum pressure (27.3 psid). At the specified pressure drop of 25 psid, the peak velocity at the scan exit was 34 f t/s. The peak velocity was still lower for the lowest pressure tested. These peak velocitics are about 50% of the velocities achieved in the jet flow through the core barrel hole. j For all three test pressures the velocity profiles at the scam exit have the same characteristic form. The peak velocitics occurred at the elevation of the core jet with lower scan flow velocities at elevations below the jet.

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SYM B0 L PLENUMT0 CORE FLOW RATE CORE JET AP (psid) (GPM) VEL 0 CITY (ft/ sed CORE BARREL O 27.3 164 64 H01.E O 24.7 155 61 Q- 22.3 149 58 0 ,

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4 FLOW VISUALIZATION MODEL STUDIES Brief flow visualization studies were' performed to support the quality-assured data in the full scale model. The main purpose of these studies was to increase confidence in the identification and understanding of the flow phenomena, although some supportive data were also obtained. The work involved direct observation and manual interaction with the flow.

4.1 The Flow Visualization Model A model of one sector (vedge) was constructed at full size, but reduced height. Figure 10 shows the model dimensions. Tlye model stands 15 inches tall (approximately half of full height) and includes upper and lower horizontal plates, a vertical 90* wedge sector of the core shroud, and a vertical (flat) plate to simulate a section of the core barrel.

The model was submerged in cold water in a 300 gallon open trough having approximate dimensions 3 f t by 10 f t by 18 inches tall (liquid icvel) . Baffling was inserted into the trough to reduce flow recirculation in order to suppress water surface turbulence and improve the flow visualization.

This model had two useful features which we exploited, namely accessibility

and visibility. The model was small enough, and in an open tank, such that measurements could be mado quickly and without questions of probe orientation or location. In this way simple traverses could be easily performed to survey the I

. entire flow field. Spaces were large enough that a human hand could be moved through the flou to survey its main features. The model was constructed entirely of plastic to enable flow visualization (See Section 4.2).

Despite these useful features, this flow visualization work is for support information only. The data from this model are not quality assured and the model is not intended to be a precise replica.

4.2 Flow Observations

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Figure 11 is a top v'iew of the transparent model. Kater is injected through a 1 inch pipe (1.05 inch I.D.) at the left of the photo. This pipe is-installed at the bottom of the model for ease of flow visualization, and is

, correctly positioned relative to the base plate. (Gravity is irrelevant in a submerged flow.)

i The Flow Between the Core Barrel and the Thermal Shroud The flow is visualized by two skirts labeled A and B and located as in Figure 12. The individual black strips in these skirts deflect in the direction of the. flow. ' Figure 11 shows that the water jet is narrow near the injection pipe and has, a width about the size of the injection pipe.- Near.the corner the jet becomes a " corner flow" with flow toward the walls across the entire width l except very near the side walls.

1 Similar flow observations throughout the region indicate the general flow pattern sketched in Figure 13. This artist's conception shows a compact jet entering at the bottom, turning' upward in the corner, and turning back toward 16 -

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Figure 13. FLOW PATTERNS IN WEDGE REGION (Artist's Rendition) 20

l the core barrel at the top. There is considerabic diffusion and turbulent mixing of this jet. In turn, this induces a major recirculating flow within the model.

The injected flow rate was varied over a factor of 5 range without observable change in either the overall flow pattern or the specific pattern scen in Figure 11.

The Flow through the Scam Figure 12 shows the installation of a flow visualization skirt, labeled C, positioned outside the wedge. Skirts A and B and their support bars were removed during the tests of the flow through the slot, so as not to block the jet. The individual strips deflect according to whether there is a local flow through the seam. Figure 14 is a photograph taken at a 45"~ angle through the top of the model showing a typical flow pattern. The skirts deflect over a height h measured from the bottom; above this height no deficction is seen.

The height' h of the seam exit flow depends on the flow rate and velocity of the injected jet. We performed a series of tests at various injection velocities and obtained the data given in Table 2. For comparison purposes, the range of injection velocities *of the quality-assured data presented in Section 3 is 58 to 64 ft/s.

The last column of Table 2, labeled h "by finger probe" is a significant support measurement. An engineer reached around the top plate of the model and felt the flow issuing out of the slot with his index finger. The seam flow is very narrow, of order of the seam width which is 0.015 inches, and is so weak that the finger must be moved about to " find" the flow.

Comparison of the two methods used to measure h indicates that the skirts are slightly more sensitive than an index finger. It is difficult to imagine any sub.stantial structure such as a rod being affected in the slightest by the very weak flow leaking through the seam.'

In one series of measurements at an injection velocity of 54 f t/s (highest value) the flow visualization skirt was moved to the top of the' model. The finger probe felt an outflow through the seam over about one inch of height and the skirts gave a deflection over 1.5 inches of height. The flow felt weaker (to the finger) at the top of the seam than at the bottom. .

4.3 Stagnation Pressure Measurements Additional supportive stagnation pressure measurements were made in the flow visualization model using hand-traversed probes. One probe was oriented to stagnate flow with direction toward the scam (horizontal) whereas the second probe stagnated flow in the vertical upward direction. The probes were both 1/8 inch in diameter and were located in the apex of the wedge at the inlet to the seam.

Figure 15 shows the stagnation _ pressure prof,iles in the flow visualization model at two inlet flow rates. The test data are displayed on two scales -

stagnation pressure and the corresponding flow velocity - as a function of probe elevation above the bottom plate. The data clearly show a well defined corner 21

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TABLE 2 FLOW VISUALIZATION TESTS '

IIEICllT OF SEAM EXIT FLOW

. Core llole Flow Core Jet Velocity (l) Span of Exit Flow (

(gpm) (ft/s) Skirts Finger (in. ik") Probe (in. th")

41 15.2 3.5 , too weak to feel 62 23 4.75 3.25 100 37.1 6.0 5.0 145 53.8 7.5 6.0 145 53.8 [1.5] Top (3) [1.0] Top (3)

(1) The core jet velocity is calculated from the measured flow rate for a core hole diameter of 1.05 inch.

(2) The span of the exit flow is measured (inches) from the bottom plate of the model, with inlet jet at the bottom.

(3) The measurement in brackets is the span of the exit flow at the top of the model, with the inlet jet located at the bottom.

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- INLET INLET WEDGE VELOCITY SEAM EXIT 1 SYMBOL VELOCITY COM PONENT VELOCITY (FLOW(ft/sec) 9Pm) ( f t/see)

O 49 18.2 HORIZONTAL 7 0 49 18.2 V E RTIC AL 7 O 103 38.2 HORIZONTAL 17 i A 103 38.2 VERTIC AL 17 6 3 $

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I i i 1 0 .

10 . 20 . 30 40 l VELOCITY (f t/sec)

Figure 15. STAGNATION PRESSURE MEASUREMENTS IN WELGE l

24 I

flow close to the scam. The vertical extent of the horizontal component of the i corner flow was measured to be only about 2 to 2.5 inches in height. The l vertical vpflow velocity (stagnation pressure) was also quite distinct, and was f airly uniforn over the height of the model examined with the probes.

Compare the corner flow profile (Figure 15) with the measurements made with the flow skirts (Table 2) . The height of the horizontal jet in the corner flow is less than half of the height of the scam flow. For example with a core inlet jet velocity about 37 f t/sec, Figure 15 gives a height of about 2.2 inches while the flow skirt gave a height of about 5 to 6 inches. The corner flow measurement is insensitive to core inlet velocity, as was the corner flow visualization, but the seam flow height is sensitive to core inlet velocity.

A single stagnation probe was also situated at the exit of the seam, 0.5 inch up from the bottom plate at the elevation of the inlet hole. The velocity of the flow leaking through the seam is shown in the tabulated data on Figure

15. For the two flow rates tested, the Icak flow velocity was less than 50% of the inlct jet velocity.

These stagnation pressure measurements along with the flow visualization studies aid us in understanding the complex flow patterns in the region between the core barrel and the shroud assembly and provide confidence that we have

- located and measured the significant regions of leakage through the seam.

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25

5 INTEEPRETATION OF PHENOMENA In an earlier letter report (Reference 4) we provided some qualitative descriptions of the phenomena acting to drive a small leakage flow through the scam in the shroud assembly. The recently ccmpleted experiments in the full-scale mockup, and the observations and measurements in the flow visualization model reinforce this early understanding of the flow behavior and provide quantitative data. In this section we offer new details to summarize and extend our earlier description of the flow phenomena.

Qualitative Description of Phenomena Core Barrel llole Jet - Driven by stagnation pressure in the downconer, a water jet flows through the hole drilled in the core barrel. This jet contracts to some degree so that its diameter is smaller than the hole. Based on measured flow rate data in the full-scale model tests, the discharge coef ficient, C for the core barrel hole is estimated to be 0.83, implying a minimum jet diamcEe,r equal to 91% of the hole diameter (D /D g=/C{) .

Free Jet - The jet enters the region between the core barrel and core shroud assembly. Bounded by the upper former plate, the jet remains relatively intact.

However, it must travel a distance of order 10 times its diameter. As it does so, it entrains stagnant fluid and diffuses (spreads and slows down).

Recirculation Patterns - A complex three-dimensional flow is established in the space between the core barrel and the shroud assembly. Because the cicarance gap between the shroud assembly and the core barrel is very large (flow area =

90 inz ) compared with the flow area of the jet (1.0 in2 ) or the 0.015 inch wide crack (0.36 in2 ), most of the jet flow leaves through this opening. That is, the jet turns and flows out the gap. There is also some inflow through the gap to feed the fluid entrainment by the jet. The sketch of flow patterns in Figure 13 is based on our observations in the flow visualization model.

While the flow patterns are quite complex, they have only a secondary impact on the jet. The measured jet stagnation pressures in the flow visualization model (Figure 15) show that the jet has retained approximately 60%

of its inlet velocity by the time it reaches the apex of the " wedge".

Corner Flow - As the jet diffuses, there is little pressure recovery and the static pressure remains near zero. When the jet approaches the* corner of the shroud assembly, it is deflected from horizontal to vertical. In turning the

, jet, an elevated static pressure is developed at the stagnation point in the corner of the shroud assembly, i.e. at the location of the scam inlet.

This corner flow occurs in a region of the order of one to three local jet diameters. That is, the corner region is about 3 inches on each side.

The flow continues vertically in the corner of the shroud assembly as a well defined jet, continuing to diffuse. As it approaches the former plate, the jet turns to the horizontal, toward the core barrel, again creating an increased static pressure in the corner of the shroud assembly.

26

O Scam Flow - The static pressure developed by turning the jet drives a tiny leakage flow through the scam. The " width" (height) of this flow corresponds with the rice in static pressure due to the corner flow, but is somewhat greater due to diffusion within the seam. The velocity of the leakage flow is no more than the ideal velocity that could be achieved by converting the static pressure to dynamic head. In the flow visualization model tests the leakage flow velocity was only about 50% of the ideal velocity due to friction in the scam.

Coupling - The scam flow is much too small to influence the flow patterns elsewhere. That is, the inlet jet, the free jet, the recirculatory patterns, and the corner flow are insensitive to the size of the seam. The static pressure in the corner and the ideal velocity in the scam are the same whether the seam has width 0.010 inch 0.015 inch, or 0.020 inch. The shape and width of the seam only affect friction in the scam. Based on results of preliminary tests described in Appendix A, the leakage flow velocity is proportional to the seam width b to the 1/2 power (/b) .

Manual Calculations For a scam velocity in the range 20 to 30 ft/sec, the Reynolds number and Fanning friction factors are tabulated below for a crack width of 0.015 inch.

Cold Hot (Model Test) (Reactor)

Re 3500-5000 18,000-27,000 b

flow transitional turbulent f 0.02 - 0.05 0.025 Figure 16 tabulates and plots the velocity exiting the scam V , as a function of driving static pressure P,, friction factor f, and craEk width b.

Based on the measured stagnation pressures in the flow visualization model, we estimate a calculated leakage flow velocity of 16 to 20 ft/s leaving the scam. The experimental data in the flow visualization model show a velocity of approximately 17 ft/s. Thus, the measured behavior is consistent with simple theory.

O l

1 i

27 O

Y Y 1

SEAM EXIT VELOCITY VS. ' SEAM WIDTH i

Ve EXIT VELOCITY i Vi IDEAL VELOCITY 00RRESPONDlilG TO STA0!!ATION PRESSURE AT SEAM , IN ABSENCE OF FRICTION 5

y, .j 2PPo .

1.0 i i f 3 0.02 0.8 -

y .0.05 1

s ,

d 0.6 - -

O.::

g VELOGITY RATIO V,/Vi I 5 *

~

. SEAM FRIOTI0ll FACTOR, f

~

El WIDTH, b 0.02 0.05 t- 0. 01 in. 0.70 0.52 i 0 0.015 in. 0.77 0.60 0.02 in. 0 . 81 0.66 _

I R

l l 1 1 0

0 0 .01 0.02 0.03 0.04 i

~

SEAM tilDTH, b (INCH) -

Figure 16. SEAM EXIT VUIDCITY VS. SEAM WIDTil - i 28

' in

..- - -_ 1_ _ - _ _ _ . ,,_

"r 6 REFERENCES I

,' 1. Dolan, F.X. , Rothe, P.H. and Sellew, S.S. ; CORE JET TEST PROGRAM TEST

- PLAN AND PROCEDURE; Rev. 2, TM-952, Creare R&D Inc., Dec. 8, 1983.

2. Dean, R.C., Jr.; AERODYNAMIC MEASUREMENTS; Cas Turbine Laboratory, MIT, 1953.

3. Bean, U.S. , ed. ; FLUID METERS. THEIR THEORI AND APPLICATION; 6th ed.,

New York, NY: - ASME, 1971.

4. Dolan, F.X. and Rothe, P.H.; Technical Memorandum to Frank Mello, Northeast Utility Service Co.; TM-950, Crearo R&D Inc., Nov. 23, 1983.

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APPENDIX A Documentation of Preliminary Data Prelininary tests conducted in the full-scale model provide additional data which suppert predicted trends and calculations of leakage flow velocity. This Appendix describes the results of two such preliminary tests which show the effects of scam width and downcomer-to-core differential pressure on seam leakage velocity. Because these tests were not fully quality-assured we have not incorporated the results in Section 3. However, it is our opinion that the data are correct and that the results are useful, and so we include them here

. for completeness.

Effect of Differential-Pressure on Scam Exit Velocity An early series of tests in the full-scale model covered the range of ;

plenum-to-core differential' pressures from 15 to 25 psid, compared with the 1 quality-assured tests which covered a narrow range around 25 psid. For these early tests, the measured seam exit velocity showed a very clear trend with differential pressure. Table A-1 displays the data from these early tests having a scam width of 0.017 inch to 0.020 inch. In order to simplify the data tabulation, the leakage velocities measured at probes 57, 58, 59 and 60 are averaged together at each differential pressure AP , These probes cover the first 1 inch of seam height below the rib plate, wEcre the maximum leakage velocities were measured. For the tests in Table A-1 the variation in velocity over this height was less than 1 f t/s. The column labeled " Normalized Velocity" compares the average seam velocity to the ideal core jet' velocity as determined from Eq. 3. In these tests the leakage velocity was about 55% of the ideal core jet velocity and is proportional.to /AP over the range of pressures tested.'

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l Table A-1 Effect of Inlet Pressure on Scam Exit Velocity (

Inlet-to-Core Calculated Measured ( ) Normalized Differential Core Inlet Leakage Flow Velocity Pressure, AP ity, V 1 city, V V/V

. (psid) Jk2]1(ft/s)

V (ft/s) 3 14.7 46.7 25.8 0.55 19.5 5,3.8 28.8 ,

0.54 24.4 60.2 33.3 0.55 24.5 60.3 33.8 0.56

( ) Data from tests with seam width variation from approximately 0.017 inch to 0.020.

( V is the calculated velocity of the inlet jet through core barrel hble,seeEq.3.

( } Tabulated velocity V is average of measurements from probes 57, 58, 59, 60.

Effect of Cap Width on Leakage Velocity Figure 16 (Section 5) predicts a trend of increasing leakage flow velocity

. with increasing seam width b due to a reduction in friction' pressure drop. The results from one early test confirm this basic trend. In that test the seam width was set at 0.02 inch, rather than the desired 0.015 inch. Tests were conducted in this configuration with inlet differential pressures of 22.3, 24.8 and'27.3 psid. _The velocity measured with the stagnation pressure probe located at the centerline elevation of the inlet jet (Probe 59) is 10% to 12% higher in the' tests with the 0.020 inch scam as compared to tests with the 0.015 inch seam at the same inlet pressures. This increase in velocity is consistent with the expected trend for the scam widths tested and'for a Fanning friction factor f=0.05.

APPENDIX B Velocity Diagrams from FLUENT Calculations Introduction Creare's proprietary computer-code FLUENT was used in early phases of this investigation to provide some insight into the overall flow patterns and

-magnitudes of velocities which might be expected in the experimental phase.

Examples of velocity vectors and profiles calculated using FLUENT are presented in this appendix as supplementary information. The flow patterns shown agree with our general assessment and descriptions of the phenomena in Section 4.2.

Physical Model The physical model which was used in the calculations is a full-scale representation of the region bounded by the inner core barrel wall and the central wedge of the shroud, and by former plates on the top and bottom.

Clearance gaps between the former plates and core barrel and between the shroud and core barrel were maintained at full-scale. The core barrel was simulated with a flat plate to simplify the configuration of the finite-element mesh. The hole through the core barrel was modeled as a square opening having an area equivalent to the area of a circular opening with a diameter of 1 1/8 inch.

, Fluid properties for water at prototype reactor operating conditions were assumed, and a core barrel hole pressure drop of 20.6 psid was used in the calculations.

Velocity Diagram Figures B-1 through B-6 display calculated velocity vectors and profiles in two views of the core barrel / fuel shroud geometry. Velocity direction at a location is indicated by the arrow alignment and magnitude is scaled from the vector length relative to the longest vector in the displayed field. The maximum velocity is given in m/sec in the lower Icf t of each figure.

The three velocity profile diagrams provide additional details of the local patterns .and changes in distribution of a single component of velocity in a planc. Again, the velocity scale factors are given in the lower Icf t figure labe1.

7 m

G v 4 w

WP w hv 1

Symmetry

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ORIENT = 2 --

IET FLOW DISTRIBUTION STUDY VELOCITY VECTORS PLANE - 18 FLUENT 3-D DOMAIN - n=

MAX. - 1.93182E+ 1 l l

Figure B-1. VELOCITY VECTOR DIAGRAM HORIZONTAL PLANE THROUGH {

CENTERLINE ELEVATION OF CORE JET l

.. l

I

= l l

Symmetry Core Jet Plane i f (1/2 width)

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MAX. = 1.92949E+ 1 .

Figure B-2. VELOCITY PROFILE DIAGRAM U-COMPONENT IN HORIZONTAL PLANE THROUGH CENTERLINE ELEVATION OF CORE JET t

l 1

l

______ i s

_._ __ __ ^._: _ _ _ _ . _ _ _

ORien = 2 =====

E7 FLOW D]STRIBUTION STUDY PRT]LES 0: V-VB_D)]TY PUNE = IS-- Fl_UENT 3-D DNAIN sames.

_bjX.= 3.1582 'IE 00 MIN. = -2.75934E 00 Figure B-3. VELOCITY PROFILE DIAGRAM V-COMPONENT IN HORIZONTAL PLANE THROUGH CENTERLINE ELEVATION OF CORE JET

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                                                                                                      ==== =

MAX. - 1.93182E+'l I 3-D DONAlN ) Figure B-4. VELOCITY VECTOR DIAGRAM VERTICAL PLANE THROUGH CENTERLINE OF CORE JET . 9 i ! i 1

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TEF FLOW DISTRIBUTION STUDY ORIENT = Y == VELOCITY VECTORS 'PLN4E - 39 FLUENT HAX. - 1.93182E+ ) l 3-D DONAIN - n-= _ i Figure B-5. VELOCITY VECTOR DIAGRAM (SAME AS FIGURE B-4 WITH MAGNIFIED VECTOR LENGTH) ae

a _ -N N ' N . i

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i ORien - Y == IET FL W DISTRIBUTION STUDY PR T]LES OF W-VELOGITY PUWE - 29_ FLUENT i asem a.

HAX. = 3.27985E 00 l HIN. = -1.0852iE+ 1 3-0 DOMAIN l,

Figure B-6. VELOCITY PROFILE DIAGRAM W-COMPONENT IN VERTICAL PLANE THROUGH CENTERLINE OF CORE JET l

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e k A.2 Effects of Core Shroud Baffle Jetting on Fuel

o o GENERAL DESCRIPTION OF EVALUATIONS Fluid elastic fuel rod response to baffle jet conditions is determined by a concatenation of data obtained from mechanical testing and analysis. The type of data / analyses required to judge rod stability includes the determination of f uel rod mechanical properties and determination of the effective baffle jet momentum flux. These calculations and tests lead to the establishment of an allowable momentum flux criteria. In order to analyze fuel rod motion, the f uel rod mechanical properties must be determined. The properties necessary to characterize fuel rod motion include fuel rod damping, stiffness, mass, and support conditions (BOL and EOL). These parameters are used in the analytical evaluation of the fuel rod natural frequencies and mode shapes. The analytical models are then used in the effective momentum flux calculation. The baifle jet ef fective momentum flux profile, V2h, is determined analytically using the velocity profile obtained from a hydraulic resistance model and verified by f ull scale hydraulic test data presented in Section 1. The effective momentum flux is calculated by normalizing the absolute momentum flux through the core shroud gap to the f uel rod mode shapes. The calculation is performed using the following equation. V2hef f = o/L 2Vh (z)D2(z)dz (1) o/L 62(z)dz where D (z)- the normalized mode shape The fuel rod motion resulting from an applied hydraulic flux excitation was determined experimentally. During hydraulic testing, rod motions were closely monitored to determine the instability points. Once established, the effective momentum flux inducing the instability was used to develop the stability criteria. The stability criteria were based on Comov's stability equation which relates the f uel rod mechanical properties to momentum flux. The equation is given below. V2 h = B 2Fn2D6Mo (2) A where B- The Fuel Assembly Constant Fn - Fuel Rod nth Mode Frequency of Vibration D- Fuel Rod Outside Diameter 6- Fuel Rod Log Decrement Damping Mo- Fuel Rod Mass Per Length A- Fluid Density

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4 o l

                                                   ;          The allowable momentum flux was determined by retrofitting the test data using
;         equation 2 to establish the constant beta, bound by a square distribution at a 95%

confidence level extrapolated to zero failures (instabilities). Once established the measured fuel rod parameters are used in conjunction with beta to determine

the allowable v2h EVALUATION The Millstone Unit No. 2 plant specific analysis was performed utilizing the core shroud seam exit velocity profile determined experimentally as discussed in Section 1. Since the velocities were measured at room temperature, they were converted to the velocities at operating temperature by multiplying the original values by a factor of 1.203 to account for the density effect. Furthermore, the velocity profile was modified to fit the finite-element fuel rod model. The modified velocity profile was slightly more conservative and thus, would yield more conservative results. Figure I shows the original velocity profile t determined experimentally and the modified velocity profile used in the analysis.

The values of momentum flux were calculated for the first nine fuel rod vibration modes. Since the effective V 2h values are less than the allowable V2 h values for all the first nine fuel rod vibration modes, it is concluded that the core shroud seam exit jet flow will not cause fuel rod instability. i j l 1 1 I

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