Text

Containment Emergency Sump Performance.Technical Findings Related to Unresolved Safety Issue A-43
	ML20074A975
Person / Time
Issue date:	04/30/1983
From:	Serkiz A; Office of Nuclear Reactor Regulation
To:	;
References
	REF-GTECI-A-43, REF-GTECI-ES, TASK-A-43, TASK-OR NUREG-0897, NUREG-0897-FC, NUREG-897, NUREG-897-FC, NUDOCS 8305170118
	Download: ML20074A975 (129)
	v • d • e

. - - - _ _.

L NUREG-0897 l

For Comment Containment Emergency Sump i

Performance Technical Findings Related to Unresolved Safety Issue A-43 U.S. Nuclear Regulatory l

Commission Office of Nuclear Reactor Regulation A. W. Serkiz, Task Manager p " "%,

p o

Ogg5 g e e3o43o 0897 R pyg

NOTICE Availability of Reference Materials Cited in NRC Publications Most documents citec in NRC publications will be available from one of the following sources:

1. The NRC Public Document Room,1717 H Street, N.W.

Washington, DC 20555

2. The NRC/GPO Sales Program, U.S. Nuclear Regulatory Commission, Washington, DC 20555

3. The National Technical Information Service, Springfield, VA 22161 Although the listing that follows represents the majority of documents cited in NRC publicatidns, it is not intended to be exhaustive.

Referenced documents available for inspection and copying for a fee from the NRC Public Docu-ment Room include NRC correspondence and internal NRC memoranda; NRC Office of Inspection and Enforcement bulletins, circulars, information notices, inspection and investigation notices; Licensee Event Reports; vendor reports and correspondence; Commission papers;and applicant and licensee documents and correspondence.

The following documents in the NUREG series are available for purchase from the NRC/GPO Sales Program: formal NRC staff and contractor reports, NRC-sponsored conference proceedings, and NRC booklets and brochures. Also available are Regulatory Guides, NRC regulations in the Code of Federal Regulations, and Nuclear Regulatory Commission Issuances.

Documents available from the National Technical Information Service include NUREG series reports and technical reports prepared by other federal agencies and reports prepared by the Atomic Energy Commission, forerunner agency to the Nuclear Regulatory Commission.

Documents available from public and special technical libraries include all open literature items, such as books, journal and periodical articles, and transactiols. Federal Register notices, federal and state legislation, and congressional reports can usually be obtained from these libraries.

Documents such as theses, dissertations, foreign reports and traslations, and non NRC conference proceedings are available for purchase from the orgmintion sponsoring the publication cited.

Single copies of NRC draft reports are available free upon w.itten request to the Division of Tech-nical Information and Document Control, U.S. Nuclear Regulators Commission, Washington, DC 20555.

Copies of industry codes and standards used in a substantive manner in the NRC regulatory process l

are maintained at the NRC Library, 7920 Norfolk Avenue, Bethesda, Maryland, and are available there for reference use by the public. Codes and standards are usually copyrighted and may be purchased from the originating organization or, if they are American National Standards, from the l

American National Standards Institute,1430 Broadway, New York, NY 10018.

t l

~__,--

NUREG-0897 For Comment Containment Emergency Sump Performance Technical Findings Related to Unresolved Safety issue A-43 Minuscript Completed: March 1983 D te Published: April 1983 A. W. Serkiz, Task Manager Division of Safety Technology Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20666 f..

s,

/

l l

l 1

ABSTRACT This report summarizes key technical findings related to the Unresolved Safety Issue A-43, Containment Emergency Sump Performance, and provides recommendations for resolution of

-attendant safety issues.

The key safety questions relate to:

(a) effects.of insulation debris on sump performance; (b) sump hydraulic performance as determined by design features, submergence, and plant induced effects; and (c) recirculation pump performance wherein air and/or particulate ingestion can occur.

The technical findings presented in this report provide information relevant to the design and performance evaluation of the containment emergency sump.

These findings have been derived from extensive experimental measurements, generic plant studies and assessment of pumps utilized for long-term cooling.

These results indicate a less severe post-LOCA situa-tion than previously hypothesized (e.g.,

low levels of air ingestion over a wide range of sump designs and flow conditions, a debris hazard situation that is not widespread, and pump designs that can accommodate low levels of air ingestion).

Therefore, these findings provide a technical basis for the development of changed proposed to the Standard Review Plan and Regulatory Guide 1.82.

l l

F i

iii l

~..

l TABLE OF CONTENTS PAGE iii Abs tra c t--

Foreword------------------------------------------------ xi t

A c k n owl edgme n ts----------------------------------------- x i i i

1.0 INTRODUCTION

'l

1. l' Safety Significance--------------------------------

1 1.2 Background-------------------------------------__--

1.3 Technical Issue------------------------------------

2 1.4 Summary of Recommendations-------------------------

2 2.0 K EY F7. N DI NG S S UMMARY------------------------------------

5 2.1 Pump Performance-----------------------------------

5 2.2 Effects of Debris on Sump Performance--------------

6 2.3 Sump Hydraulic Perf ormance Finding s----------------

7 3.0 TECHNICAL FINDINGS--------------------------------------

10 3.1 Introduction--------------------------------------

10 3.2 Performance of Residual Heat Removal and

'l Containment Spray System Pumps -- Technical Findings-------------------------------------------

11 3.2.1 Characteristics of RHR and CSS Pumps---------------------------------------

11 3.2.?

Effects of Air or Particulate Ingestion, Cavitation, and Swirl on Pump Performance---

13 3.2.3 Calculation of Pump Inlet Conditions--------

25 3.3 De b r i s A s s e s sme n t----------------------------------

28 3.3.1 Plant Insulation Survey Findings------------

28 3.3.2 Calculational Methods for Assessing Debris Hazards------------------------------

33 3.3.3 Application of Methodology to 5 Sample Plants-----------------------------

41 3.3.4 Experimental Studies On Debris--------------

43 13.4 Sump Hydraulic Performance-------------------------

49 3.4.1 E nve lope An a ly s i s---------------------------

52 3.4.2 General Sump Performance (All Tests)---------------------------------

58 3.4.3 Sump Performance During Accident

{

Conditions (Perturbed Flow)-----------------

58 v

..-__.-...~._.._,.___.____.__,.....,,_.m____,,

TABLE OF CONTENTS (Cont'd)

PAGE 3.4.4 Geometric and Design Ef fects

-(Unperturbed Flow Tests)---------------

59 3.4.5 Design or Operational Items of Spe cial Conce rn in ECCS Sumps---------------

59 4.0 I N DE PE NDE NT PROG RAM REV I EWS-----------------------------

63 4.1 S ump Pe r f o rm a n ce Rev i ew----------------------------

63 4.2 I nsula t ion De br i s E f f e c ts Rev ie w-------------------

64 5.0

SUMMARY

OF SUMP PERFORMANCE FINDINGS--------------------

69 5.1 General Overview-----------------------------------

69 5.2 S ump H yd r a u l i c Pe r f o rm a n ce-------------------------

69 5.3 Debris Assessments---------------------------------

78 5.4 Pump Performance Under Adverse Conditions----------

80 5.5 C om b i n e d E f f e c t s-----------------------------------

83 R E FE R E N C E S- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - --

85 APPENDIX A-- PLANT SUMP DESIGN AND CONTAINMENT LAYOUTS-------- A-1 APPENDIX B--A PROCEDURE FOR ESTIMATING DEBRIS GENERATION, TRANSPORT, AND SUMP BLOCKAGE POTENTI A L----------- B-1 APP 3NDIX C--INSULATION DEBRIS FORMATION UNDER JET FLOW CONDITIONS--------------------------------------- C-1 i

l i

l vi

l i

u, LIST OF FIGURES PAGE

- 3.1 -

-Assembly schematic of centrifugal pump typical of those used for RHR or CSS service-------

14 3.2a' Performance and cavitation curves for'RHR and CSS pumps.

Head versus flow rate data

. normalized by' individual best ef ficiency point l

values.

NPSH required data normalized by best efficiency point head------------------------------

15 3.2b Performance-and-cavitation-curves for CSS pumps.

head vs. flow rate data normalized by individual best-efficiency point values.

NPSH required data normalized by best efficiency point head------

16 3.3 Typical head degradation curves due to cavitation at four flow rates (01 to 04)----------------------

18 3.4 Reduction in NPSH requirements as a function of liquid temperature---------------------------------

19 3.5 Head degradation under air ingesting conditions as a function of inlet' void fraction (percent by volume)-----------------------------------------

21 3.6 Effect of air ingestion on NPSH requirements for a ce n t r i f u g a l p um p---------------------------------

22-3.7 Schematic of suction-Systems for Centrifugal Pump-----------------------------------------------

26 3.8 Outline of methods---------------------------------

35 3.9 Approach flow perturbations and screen blockage I

schemes--------------------------------------------

51 3.10 Break and drain flow impingement-------------------

53 3.11 Void fraction (percent of volume) as a function of Froude number; horizontal outlet configuration--

54 3.12 Surface vortex type as a function of Froude number; horizontal outlet configuration------------

55 3.13 Swirl as a function of Froude number; horizontal outlet configuration-------------------------------

55 3.14 Void fraction data for various Froude numbers; vertical outlet configuration----------------------

56 vii l

l

LIST OF FIGURES (Cont'd)

PAGE

' 3.15 Surface vortex type as a function of Froude number; vertical outlet configuration--------------

57 3.16 Swirl as a function of Froude number; vertical outlet configuration-------------------------------

57 3.1 Technical' considerations' relevant to

. containment emergency sump performance-------------

70 5.2 Flow chart for calculation of pump inlet conditions-----------------------------------------

81 5.3 Codbined technical considerations for sump.

pe r fo rma nc e ----- ---- ---- -- ---- - -- --- - ------- ---- ---

84 4

viii i

I l

LIST OF TABLES PAGE 3.1 RHR and CSS pump data------------------------------

12

'3.2 Reactor plants selected for insulation survey------

29 3.3 Types and percentages of insulation.used within the primary coolant system shield wall in plants surveyed---------------------------------

31 3.4 Reactor plants selected for detailed investigation of insulation debris generation potential------------------------------------------

42 3.5 Summary table for 5 plant sample calculations------

44 3.6 Summary of findings--------------------------------

46 l

5.1 Zero air-ingestion hydraulics design findings------

72 5.2 Hydraulics design findings-------------------------

73 5.3 Geometric design envelope findings-----------------

74 5.4 Additional considerations related to sump size and placement ---------------------------

75 1

5.5 Screen, grate, and cover plate design findings-----

76 5.6 Findings for selected vortex suppression devices---- 77 5.7 Debris assessment considerations-------------------

79 l

ix

FOREWORD NUREG-0897 is being issued for public comment.

It provides a concise-and self-contained reference which summarizes technical findings relevant to the unresolved Safety Issue A-43,

" Containment Emergency Sump Performance." NUREG-0897 is not a substitute-for the requirements set forth in General Design

~

Criteria 16, 35, 36, 37, 38, 40 and 50 in Appendix A to 10CFR50, nor a substitute for requirements set-forth in NRC's Standard Review Plan or Regulatory Guides.

The information contained herein is of a technical nature which can be used as background relevant to the proposed revisions to SRP Section 6.2.2 and Regulatory Guide 1.82.

l f

l l

l i

l l

l xi

ACKNOWLEDGMENTS The technical findings relevant to the Unresolved Safety Issue A-43, Containment Emergency Sump Performance, set forth in this report are the result of the combined efforts of staff at the Nuclear Regulatory

. Commission, the Department of Energy, Sandia National Laboratories (SNL),

Alden Research Laboratory (ARL), Burns & Roe (B&R), Inc. and.Creare, Inc.

The following persons deserve special mention-for their participation and

- contributions:

W. Butler, NRC/DSI G. Otey, 3NL D. Dalghren, SNL.

N. Padmanabhan, ARL G. Hecker, ARL P. Strom, SNL D. Jaffee, NRC/DL W. Swift, Creare M. Krein,.SNL G. Weigand, SNL A. Millunzi, DOE M. Wester, SNL-P. Norian, NRC/ DST J. Wysocki, B&R F. Orr, NRC/DSI In addition, acknowledgment is given to persons whose efforts are referenced herein; and to those persons who participated in " peer" reviews of results obtained and the application of such results.

Particular acknowledgment is given to Gilbert Weigand who played a major role in maintaining technical quality and continuity throughout these efforts, and to George Hecker for his keen insight and questioning regarding the application of results obtained.

i l

[

h I

i 4

Xiii

1.0 INTRODUCTION

1.1 Safety Significance Following a loss-of-coolant accident (LOCA) in a pressurized water reactor (PWR), water discharged from the break will collect

~

on theecontainment floor and within the containment emergency sump.

Although the emergency core cooling systems-(ECCS) and containment spray systems (CSS) initially draw water from the refueling water storage tank (RWST), long-term core cooling is affected by realignment of these ECCS pumps to the containment emergency sump.

Thus, successful long-term recirculation depends upon the sump providing adequate, debris-free water to the recir-culation pumps for extended periods of time.

Moreover, the flow conditions through the sump and associated piping must not result in pressure losses or air entrainment that would inhibit proper pump operation.

Without a proper sump design, long-term cooling could be significantly impaired.

1.2 Background

The importance of the ECCS sump and safety considerations associated with its design were early considerations in con-tainment design.

Net positive suction head (NPSH) requirements, operational verification, and sump design requirements are issues that have evolved and are currently contained in.the following Regulatory Guides (RG):

RG 1.1

-- Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Systems Pumps, 1970.

RG 1.79 -- Preoperational Testing of Emergency Core Cooling Systems for PWRs, 1974.

RG 1.82 -- Sumps for Emergency Cooling and Containment Spray Systems, 1974.

l Review of these Regulatory Guides reveals that the concerns l

of the Nuclear Regulatory Commission (NRC) staff regarding emer-gency sump performance were evolutionary in nature.

Initially, staff concerns were addressed through in-plant tests (per RG 1.79) with a transition to containment and sump model tests in the pid-1970s.

At that time, considerable emphasis was placed l

on " adequate" sump hydraulic performance during these model tests, and vortex formation was identified as the key determinant.

The main concern was that formation of an air-core vortex would result in unacceptable levels of air ingestion and, subsequently, in severely degraded pump performance.

l

There was also concern about sump damage or blockage of the flow as a result of LOCA generated insulation debris, missiles etc.

These concerns led to the' formulation of some of the guide-lines set forth in RG 1.82 (cover plates, debris screen, < 50 percent screen blockage, etc.).

In 1979, as a result of continued staff concern for safe operation of ECCS' sumps, the Commission designated the issue.as Unresolved Safety Issue (USI) A-43, " Containment Emergency Sump Performance."

To assist in its resolution,.the Department of Energy (DOE) provided funding for construction of a-full-scale

' test facility at the Alden Research Laboratory (ARL) of Worcester Polytechnic Institute (WPI) (Reference 1).

At.'about the same time, Task Action Plan.(TAP) A-43 was developed to address all aspects of this safety issue.

1.3 Technical Issue The principal concern is summarized in the following question:

In the recirculation mode following a LOCA, will the pumps receive ~ water sufficiently free of debris and air and at sufficient pressure to satisfy NPSH requirements so that pump performance is not impaired?

i This concern can be divided into three areas for technical consideration:

sump design, insulation de. -is ef fects, and pump performance.

The three areas are not independent, and certain combinations of effects must be considered as well.

l This report presents the technical findings derived from I

extensive, full-scale experimental measurements, generic plant calculations, and residual heat removal (RHR) and CSS pump per-formance assessments.

These technical findings provide a basis for resolving USI A-43.-

1.4 Summary of Technical Finding s The following key determinations are derived from the technical findings contained in Section 3.

l l

2

~

l i

1. 'The' hydraulic performance of. containment emergency sumps should1be based-primarily on~1evel of air ingestion into.the sump-suction inlet (s). ~ Visual-

~

-observations cannot be used-to quantify the amount of air ingestion occurring. - However, observations of-sump surface. vortex activity, principally the lack thereof, can be used to infer'the absence of

air ingestion.

2.

- Relative to acceptable levels-of air ingestion, two options are available:

a) O percent air ingestion, and~b) < 2 percent air' ingestion, provided NPSH requirements at the pump inlet ~are satisfied.

For sumps with marginal flow conditions or designs, vortex suppressors can-reduce air' ingestion to

~zero.-

3 3.

The sump design information, contained in Section'3.2, can be used to evaluate hydraulic design and perform-ance.

If the sump operational envelope falls'outside of the A-43 experimental envelope,oor recommended sump geometric features, additional analyses or data may be needed for support of proposed design.

4.

The general sump design information set forth in RG 1.82, " Sumps for-Emergency Core Cooling and Con-tainment Spray Systems," such-as une of screens and 4

trash racks should be maintained.

However, the currently specific 50 percent screen blockage can lead to non-conservative results.

Finding 5 (below) addresses the question of screen blockage in a more rigorous manner.

5.

The insulation debris evaluation methods, described in Section 3.3, provide a conservative means to determine quantities of debris that would be generated by a LOCA, the resulting screen blockage, and the attendant pressure drop.

6.

Plant insulation surveys have shown that a variety of insulations have been employed in plants and in large quantities.

Nonencapsulated insulations (particularly

- mineral wool and fibrous types) have beers shown through plant specific calculations (see Section 3.3) to have the potential to result in total screen blockage following a LOCA.

Plant specific studies have shown a strong plant layout and type of insulation dependence due to debris migration to the sump.

3

,._,,__....,-,-.-..,,-.,,_.m...-.~.-.__,--.,_m.__.____---m_.

7.

' Recirculation pump operation can be assessed using the findings-and methods provided in Section 3.2..

Low levels of' air ingestion (12 percent) will not degrade pumping capability.

However, as noted in Item 2, non-zero air entrainment conditions. identified at the sump. suction. inlets should be evaluated for NPSH effects.

Ingestion of small particles will not pose a pumping problem; however, pump seal systems warrant review from the viewpoint of possible clogging.

Pumps tht use water lubricated bearings or pumped fluid for bearing coolant warrant review because of the possible effects of debris on bearing operation.

8. BWRs need not be reviewed in as much detail as PWRs for determination of long-term recirculation capabilities.

For the sake of completeness, some BWR-RHR suction con-figurations (representative of Mark I, Mark II and Mark III desicus) were tested to determine air ingestion characteristics.

The results reveal low levels of air ingestion (see Section 3.4); this data set can be used to evaluate BWR designs.

The limited BWR insulation survey that was conducted revealed a high utilization of reflective metallic insulation and, therefore, debris effects are not believed to be significant.

s 4

4 U

. 2.0 KEY FINDINGS -

SUMMARY

2.1 Pump Performance Sustained operation of RHR and CSS pumps-in the recirculating mode presents two principal areas of concern:

Possible degradation of the hydraulic performance of the pump _(inability of pumps to-maintain sufficient recircu.

lation flow as a result of sump screen blockage, cavitation effects, or air ingestion).

Possible degradation of pump performance over the long-or short-term due to mechanical problems'(material erosion due to particulates or severe cavitation, shaft-or bearing failure _due.to unbalanced loads, and shaft or impeller seizure due to particulates).

Pumps used in RHR and CSS systems are primarily single stage centrifugal designs of low specific speed.

CSS pumps are gener-ally rated at flows of about 1500 gpm, heads of 400 feet, and require about 20 feet of NPSH at their inlet; RHR pumps are generally rated at about 3000 gpm, heads of 300 feet, and-require about 20 feet NPSH at maximum ficw.

Rating points and submergence requirements for the pumps are plant specific.

Pump materials are generally highly resistant to erosion, corrosion, and cavitation damage.

Test results show that under normal flow conditions and in the absence of cavitation effects, performance is only slightly degraded when air ingestion is less than 2 percent.

This value l

i would be a conservative estimate for acceptable performance.

l For higher amounts of air ingestion, pump performance is depen-dent on many variables, but air ingestion in excess of 15 percent l

almost completely degrades the performance of pumps of this l

type.

Submergence or net positive suction head requirements (NPSHR) for RHR and CSS pumps (routinely determined by manufacturers' tests) are established by a percent degradation in pump output l

pressure.

(Individual specifications determine that NPSH required be set according to a 1 percent or 3 percent criterion.)

No standard exists for the percent degradation criterion, nor for the margin between NPSH available and that required in setting RHR and CSS pump submergence.

Air ingestion affects NPSHR.

g Test data on the combined effects of air ingestion and cavitation are limited, but the combined effects of both increase the NPSH required.

A value of 3. percent degradation criterion in pump output pressure for the combined effects of air ingestion and cavitation appears to be a realistic value.

i

---w yy.-w 3-9'-3 y--re

-w-v -,m.--9

-,i w

y g

3 w-+9,py

-yw

---mmw

- - - --.gimy,.., wry,-w.rv,-y yr y,yw +9,w yvp,.ww m

w-y,,.-,-yw wy---

y,v.m e*

-yv.y-iy---~

y

J 1

The types'and quantities'of debris which are likely to reach.the pump should not impair long term hydraulic per-formance.

In pumps with mechanical shaft seals,~ accumulated

' quantities of soft or abrasive debris in the seal flow passages may result in clogging or excessive wear; both of which may lead

'to increased seal' leakage.

Catastrophic failure of a shaft coal' as a result: of debris ingestion is considered unlikely.

In the event of complete failure of shaft seals, the pump leakage would-be restricted by the' throttle or safety-bushing incorporated in these seals.

Debris may cause failure of water lubriated bearings.

These systems should be evaluated on a case by case basis.

4 2.2 Effects of Debris on Sump Performance The safety issues related to debris effects on sump perform-ance concern screen blockage and attendant potential loss of pump suction pressure.

-Results of-the insulation debris studies are summarized

+

.below.

j Types of insulations'used vary from plant to plant, with newer plants generally using reflective metallic insula-tion that is ' not likely to cause blockage prob 1ccas.

Types of insulation used in the 19 plants surveyed in

[

this study'are shown in Table 3.3.

I Detailed methods were developed for determining the quantities, sources, and transport mechanisms of debris that could be generated during a LOCA'and for: assessing l

the~ consequences of the blockage of sump inlets that

(~

might result-(see Figure 3.8).

The methods developed for debris assessment'were eval-uated by application to 5 selected plants to establish variability due to plant design, type (s) of insula-tion employed and sump design. ' Table 3.5 summarizes the-calculated results as a-function of break location and plant selected.

Screen blockages greater than 5' percent were calculated, with 2 of the plant calculat ons resulting in 100 percent screen blockage. -For the Salem l

plant, low flow velocities, large screen area, sump design and location resulted in~1ow pressure losses ~through the-

-blocked screen.

Therefore, NPSH requirements were not impacted.

For the Maine Yankee plant, large quantities of nonencapsulated mineral wool were calculated to be trans-ported.to a small'aump screen area.

In this case, a 100 percent screen blockage with high pressure drop was predicted.

Although conservative assumptions have been j

embodied into these analyses methods, the variabilities 6

l

due to plant design and types of insulations employed illustrate the need for plant specific evaluations.

Mirror (reflective type) insulations do not appear to pose screen blockage problems.

Velocities required for migration of such insulation is relatively high.

Low. density insulations, having a closed cell structure, l

will float and are not likely to impede flow through the pump screens except where the screens are not. totally submerged.

Low density hygroscopic insulation having equilibrium densities greater than water require a plant specific assessment of screen blockage effects.

Non-encapsulated insulation (particularly mineral fiber, fiberglass, or mineral wool blanket) require a plant. specific evaluation to determine the potential for sump screen blockage.

(Section 3.3, Section 5.3, and Appendix B provide a conservative method for assessing screen blockage effects.)

Some debris will not be collected on sump screens by virtue of its size and shape distribution.

2.3 Sump Hydraulic Performance Findings Data obtained from full-scale sump tests provide a sound

[

base for assessing pump hydraulic performance.

Both side-suction and bottom-suction designs were tested over a wide range of design parameters, and the effects of elevated water temperatures were assessed.

Scaling experiments (1:4, 1:2, 1:1) were also l

conducted to provide a means for assessing the validity of pre-l vious scaled model tests.

The effectiveness of certain vortex l.

suppression devices was also evaluated.

For completeness, plant specific and LOCA-introduced effects (condenser drain flow, break L

flow impingement, large swirl and sump circulation effects, and i

sump screen blockage) were evaluated experimentally at' full scale.

Results of this test program are summarized below.

i The broad data base from the sump studies resulted in the development of envelope curves for reliably quantifying the expected upper-bound for the hydraulic performance of any given sump whose essential features fall approxi-mately within the flow and geometric ranges tested.

Vortices are unstable, randomly formed, and, for cases where air ingestion occurs, cannot be used to quantify air ingestion levels,_ suction inlet losses, or intake pipe fluid swirl.

The full-scale tests show that for l

water submergences greater than B feet, and inlet water velocities of less than 7 ft/sec, significant vortex activity disappears.

l o

7 l

. _ _ _ _ _ _. - _ _. ~, _

Based on void fraction measurements,-air ingestion was found to be less-than 2 percent in most cases;-only highly perturbed flow conditions associated with large.

screen blockage and/or deliberately induced approach water swirl at low submergences and high flow resulted in-high levels of air ingestion.

(These tests revealed the importance of measuring void fraction and demon-strated the ineffectiveness of visual observations of vortices as a means of quantitatively evaluating air entrainment.)

Swirl angles in suction pipes were generally found to have decreased to about 4* at 14 pipe diameters from' inlets: angles of up to 7* at 15 pipe diameters from

~

inlets were observed in tests at low' submergence with

' induced floe perturbations.

Hydraulic grade line measurements for all experime'ts revealed that the sump loss coefficient was insensitive to sump design-variation.

Loss coefficients are basi-cally a function of intake geometry, and the measured values are consistent with those obtained from standard hydraulic handbooks.

i High temperature testing (up to 165'F) revealed water temperature (or previously hypothesized Reynolds number i

effects) had no measurable effect on surface vortexing, air ingestion, pipe swirl,. or loss coefficient.

Vortex suppressor testing revealed that cage-type and submerged grid-type designs generally (a) reduce surface vortexing from a-full air-core vortex to surface swirl only; (b) reduced air ingestion to or near zero; (c) reduced pipe swirl to less than 5*; and-(d) had no signif-icant effect on loss coefficient.

)

There were no major differences in the hydraulic perform-L ance of vertical outlet sumps and horizontal outlet sumps of the same geometry and flow conditions.

Comparison of the different scale model results showed that scale modeling down to 1:4 scale, using Froude number similitude, adequately predicted the performance variables (void fraction, vortex type, swirl, and loss i

coefficient) of full-scale tests.

Tests on 1:4, 1:2, l

and 1:1 scale versions of the same sump under comparable operating conditions showed no significant scale effects in the modeling of air-withdrawal due to surface vortices or in free surface vortex behavior.

Additionally, swirl and inlet losses were accurately predicted by model tests providing specified Reynolds number criteria were maintained.

8

A parametric; assessment of nonuniform approach flow into the sump due to specific structural features aid not reveal any-significant adverse effects.

Drain flew impingement on the sump water surface resulted in extensive. turbulence that tended to reduce vortexing and did not lead to increased air ingestion.

Break flow impingement tests resulted in; findings similar to those for drain flow; significant air entrain-ment did not occur.

Screen blockage tests, in most inLtances, did not reveal significant increases in air ingestion or subsequent degradation in the hydraulic performance of the sump.

There were some cases where certain screen blockage schemes, up to 75 percent screen area blocked, resulted in significant air ingestion (see Figures 3.11 and 3.14).

However, in each case, the use of a vortex suppressor eliminated the air-core vortex and reduced the air inges-tion to zero or negligable levels.

Thus, the effectiveness

.of vortex suppressors (even submerged floor grating

~

designs) has been demonstrated.

The full-scale test program has resulted in an extensive d4ta base that has broad applicability and can be used in

'.ieu of model tests, or in-plant tests (provided the sump design j

falls within the experimental envelope investigated).

l l

r L

l l

l 9

3.0 TECHNICAL FINDINGS

~ Introduction 3.l Prior to the development of a plan for the resolution of Unresolved Safety Issue A-43, the following key safety questions were identified:

1.

What are the performance capabilities of pumps used in containment recirculation systems, and how tolerant are such pumps to air entrainment, cavitation and the potential ingestion of debris and particulates that may pass through screens?

2.

Were a LOCA to occur, would the amount and type of debris generated from containment insulation (and its subsequent transport within containment) cause-significant sump screen blockage and, if so, would such blockage be of sufficient magnitude to reduce NPSH available below NPSH required?

3.

Can geometric and hydraulic sump system designs be established for which acceptable sump performance can be assured?

It was recognized that resolution of USI A-43 depended upon successful responses to these questions.

This effort was under-taken in three parallel tasks, each designed to respond to one of the key safety questions.

The first question was addressed through an evaluation of the general physical and performance characteristics of RHR and CSS pumps used in existing plants.

Conditions likely to cause degraded performance or damage to pumps were identified, i

and the effects of such conditions on pump performance were evaluated.

This effort was undertaken by Creare, Inc., and the results are reported in Reference 2.

The second question was addressed in three parts:

(a) a survey was conducted of 19 power reactor plants concerning the quantity, types, and location of insulation used within contain-ment; (b) detailed methods were developed for determining the l

quantities and sources of debris that could be generated during a LOCA.

This information, used in conjunction with the develop-i ment of criteria for the initiation and continuation of debris u

movement, allowed estimates to be made of the quantities and character of insulation debris that could potentially be trans-ported to sump screens.

(c) Calculational methods were also developed that can provide estimates of head losses as a result of such debris buildup on sump screens.

This work was undertaken by Burns and Roe, Inc., and is reported in References 3, 4, and 5.

Experimental determinations were made of these parameters 10

a (debris generation by jets, velocity requirements for the onset and continuation of debris migration, the phenomena of

' debris' buildup on sump screens and associated-head losses) at Alden Research Laboratory.

Results of these efforts are reported in References 6 and 7.

The third key safety question was addressed in an.investi-gation of_the behavior of ECCS sumps under diverse flow condi-tions that_might occur during a LOCA. ~The test program was designed to cover a broad range of geometric and flow variables representative of emergency sump designs.

This work was undertaken jointly by Alden Research Laboratory, of Worcester

' Polytechnic Institute, and Sandia National Laboratories, and is reported in Reference 9, 21, 22, and 23.

3.2 Performance of Residual Heat Removal and Containment Spray System Pumps -- Technical Findings This section summarizes the general physical and performance characteristics of RHR and CSS pumps used in a sample of existing plants. 'All plants in the sample are PWRs.

Effects likely to cause degraded performance or damage are identified, and_results from an analysis of these effects on RHR and CSS pump perfor-

-mance are presented.

3.2.1 Characteristics of RHR and CSS Pumps in PWRs A study of' pumps used in 12 operating nuclear plents has shown that although individual pump details are plant specific, the pumps used in RHR and CSS services are similar in type, mechanical construction, and performance.

Similarities in the types of pumps are shown in Table 3.1,-

which lists the manufacturer, model number, and rated conditions for each of the pumps utilized in the plants surveyed.

The t-column labeled " Specific Speed" provides a parameter conven-tionally used by pump manufacturers to specify hydraulic charac-teristics and, hence, the overall design configuration of a l

pump.

As the table shows, all pumps are in the specific speed j

rangeaof 800-1600 with specific speed defined as Na " (Speed)

(Volumetric Flow)l/2/(Head)3/4 Thus, all are relatively high head, centrifugal pumps with nearly radial impellers.

5 The class of pumps used for RHR and CSS service have similarities in mechanical construction:

11

~

- ~

Table'3.1 RHR and CSS Pump Data

Rate d Conditions-------

Manufacturer */%odel RHR CSS (RPM)

(PT)

(GPM) Specific Plant Speed Head Flow Speed Arkansas Unit #2 I-R 6x23 WD 1800 350 3100 1238 I-R 8x20 WD 1800 525 2200 851 Calvert Cliffs I-R 8x21 AL.

1780 360 3000 1205 1&2 B&W 6x8x11 HSMJ 3580 375 1350 1544 Crystal River #3 W 8HN-184 1780 350 3000 1205 W6HND-134 3550 450 1500 1407 Ginna Pac 6" SVC 1770 280 1560 1016 Haddom Neck Pac 8" LX 1770 300 2200 1152 Pac 8" LX 1770 300 2200 1152 Kewaunee B-J 6x10x18 VDSM 1770 260 2000 1222 I-B 4x11 AN 3550 475 1300 1257 McGuire 1&2 I-K 8x20 WD 1780 375 3000 1144 I-R 8x20 WD 1780 380 3400 1205 Midland #2 B&W 10x12x21 ASMK 1780 370 3000 1156 B&W 6x8x135 MK 3550 387 1300 1467 Millstone Unit 2 I-R (No Model #)

1770 350 3000 1198 G3736-4x6-13DV 3560 477 1400 1370 Oconee #3 I-R 8x21 AL 1780 360 3000 1180 I-R 4x11 A 3550 460 1490 1380 Prairie Island B-J 6x10x18 VDSM 1770 285 2000 1141 I-R 4x11 AN 3550 500 1300 1210 Prairie Island B-J 6x10x18 VDSM I-R 4x11 AN 1780 280 2000 1156 1&2 3550 5100 1300 1210 Salem #1 I-R 8x20W 1780 350 3000 1205 G 3415 8x10-22 1780 450 2600 929 CPac -- Pacific I-R -f Ingersoll-Rand i

4 W,- Worthington j

G -- Gould

\\ B&W -- Babcock & Wilcox

's-J -- Byron Jackson i

Specific Sphed is defined as N, = Speed (Flow)I/2 (Head)1/4

/

In this definition:

Speed is in rpm, flow in gpa and head in ft.

12

Impellers and casings are usually austenitic stainless steel -- highly resistant to damage by cavitation, corrosion and erosion.

Impellers are shrouded, with wear rings to minimize leakage.

Shaft seals are the mechanical type.

Bearings are grease or oil lubricated ball-type.

A pump assembly typical of pumps used for RHR and CSS service is shown in cross-saction in Figure 3.1.

S imilarities in the performance of pumps used in RHR and CSS service are shown in Figure 3.2.

Performance and cavitation data from each of the pumps listed in Table 3.1 have been plotted for comparison.

Performance data are given in terms of normalized head vs. normalized flow rate where the best-efficiency-point head and flow are used for the reference values.

Cavitation data are given in terms of NPSH required.

3.2.2 Effects of Cavitation, Air or Particulate Ingestion, and Swirl on Pump Performance Several items have been identified as potential causes of long-or. short-term degradation of CSS and RHR pumps:

Cavitation -- may cause head degradation and damage to impellers Air ingestion -- may cause head degradation L

Particulate ingestion -- may cause damage to internal parts Swirl at the pump inlet -- may cause head degradation l

l All of these effects also have the potential for inducing hydraulic or mechanical unbalanced loads.

L Cavitation Net positive suction head is defined as the total pressure L

at the pump inlet above vapor pressure at the liquid temperature, expressed in terms of liquid head (pressure / specific weight),

and is equivalent to the amount of subcooling at the pump inlet.

If.the NPSH available at the pump is less than the NPSH required, some degree of cavitation is assured and some degradation of performance and perhaps material erosion is

-likely.

13 1 - - --

y8 60 @ 8 i

I 1

(

1 r

=

I k 8.

08G p:.

==:

s T$

$i y

g-i?";)(f]y9l~

f a

%k.s Sq"~Rl N

b MP

~

t:

A

~

O O

OOG e e

i SyOS@@

O6888 m M. 4 a

3 (q

_q

-'c::: = :':'

Figure 3.1.

ASSEMBLY SCilEMATIC OF CENTRIFUGAL PUMP TYPICAL OF TilOSE USED FDR RiiR OR CSS SERVICE

RHR Pumps 1.5 O

a-Arkansas Unit 82 b-Calvert Cliffs 1&2 g

c-Crystal River #3 g,4 J

d-Cinna e-Haddam Neck f-Kewaunee q

l,k,f g-McQuire 1&2 h-Midland 62 g,g h,C, f i-Millstone unit 2

\\

j-Oconee 83 g

k-Prairie Island 1&2 h 1-Salem #1 1.2 1.1

~.

2 5

1.0 50 0 o'

5

=

0.9 40.0 Ms5s l

=

0.8 30 0 g

c

==

0.7 g, j 200 l

08 20 l

/

b,e k,f,d 05 O.0 to 0.2 44 R$

0.4 1.0 1.2 1.4 1.6 i

NORNAtlZED FL0f RATE, (0/Qbep)

Figure 3.2a.

Performance and Cavitation Curves for RHR Pumps.

Head vs. Flow Rate Data Normalized by Individual Best Efficiency Point Values.

15

I CSS Pumps I

I 4

i i

I 4

a-Arkansas Unit 82 g

b-Calvert Cliffs 162 c-Crystal River 83 I.4 d-ednna gj e-Haddam Neck f-Kewaunee g-McGuire 1&2 I.3 C'f h-Midland e2 i-M211 stone Unit 2 j

j-Oconee #3 k-Prairie Island 1&2 d g l1-Salem #1 1.2 0

~

1.1 3

n!E 50.0 1.0 af5

=

s 3

0.5

\\

40.0 5

d

t 5

t l

=

0.8 b,g 30 0,e l

=

20 0 0.T e

.0 J,k 10 0 06 f, i 05 O.0 0.0 0.2 0.4 06 0.8 1.0 12 1.4 1.6 NORWALIZED FLOW RATE, (0/0bep) l Figure 3,2b.

Performance and Cavitation Curves for CSS Pumps.

l Head vs. Flow Rate Data Normalized by Individual Best Efficiency Point Values.

16

There is no fixed standard for~ identifying the NPSH required.

for a given' pump.- Unless stipulated by specifications, manufac-turers have used some percentage (1 percent or 3. percent) in i'

head degradation as the criterion for establishing the NPSH

. required at some flow condition.. These are empirically estab-lished values for which.very rapid degradation occurs and severe' erosion'is likely to occur.

Figure 3.3 illustrates the changes in pump performance at several flow rates as a function offnet positive suction head.

(The curves are' typical of those obtained by pump manufacturers to define the NPSH required for their pumps.)

As NPSH is_ reduced for each flow rate shown (01-04), a point.i:s reached below the 3 percent limit at which

. substantial degradation begins.

Fluid system designers may:

choose to apply some' margin to the NPSH requirements for a pump when designing RHR and CSS systems, but currently no standard margin between NPSH required and NPSH available has

'been established by NRC regulations.

Some conservatism may be introduced in the calculation of NPSH following guidelines established in RG 1.1 where no credit is allowed for. increased containment pressure.

However RG 1.1 does not address sub-atmospheric conditions in containment with i

respect to NPSH.

Cavitation behavior of pumps changes at elevated liquid temperatures.

Figure 3.4 from the Hydraulic Institute Standards (Reference 10), shows that as liquid temperatures increase, less NPSH is required by the pump.. As a result, increases in-liquid temperature have two effects on NPSH:

(1) the vapor pressure increases, which reduces NPSH available; (2) the NPSH required is reduced by an amount given in Figure 3.4.

The austentic stainless steels specified for impellers-and

-casings in RHR and CSS pumps are highly resistant to. erosion damage caused by cavitation.

Erosion rates for extended opera-l tion are not significant as long as the NPSH available exceeds l

the NPSH requirement of the pump.

l I

Air Ingestion L.

The key findings derived for RHR and CSS pumps with respect to air ingestion are based primarily on data from carefully.

conducted tests in air / water mixtures on pumps of a scale and specific speed range comparable to RHR and CSS pumps.*

Test i

(

All relevant test data were gathered through reviews of tech-nical papersfand interviews with pump manufacturers.

Manufac-turers' test data on air / water performance of pumps are sparse, applying primarily to the development of commercial pumps for the paper industry.

Although these pumps are similar to those used for RHR and CSS service, test methods and results are generally poorly documented.

Therefore, manufacturers' data 17

I i

3%

\\

t

\\

Ql l

I

{

3%

\\

I 02 f

(

INCREASING FLOW RATES

\\g

\\

03 t

HEAD Np l

g

\\

37s

\\

l 04 i

l l

NPSHR VALUES i

AT 01-04 l

NPSH Figure 3.3 TYPICAL HEAD DEGRADATION CURVES DUE TO CAVITATION AT i

FOUR PLOW RATES (01, 02, 03 AND 04) 1 i

i i

40 i

I i

l 1

l l

-g h

3.0 E

or M

~

i

~

g 2.0 s

z 5

~

g

{ l.0 g

i N

i I

I I

j 0

I i

100 150 200 250 300 TEMPERATURE (*P) 1 i

i Figure 3.4.

REDUCTION 'IN PUMP NPSil REQUIREMENTS AS A FUNCTION OF LIQUID TEMPERATURE (REFERENCE 12).

i l

'l data from independent programs on different pumps have been plotted in Figure 3.5 to illustrate the degradation in head at different levels of air ingestion (percent by volume) at several operating points.

Performance degradation is indicated by the ratio of the two-phase (air / water) pressure rise to the single-phase (water) pressure rise.

Figure 3.5 shows that for low levels of air ingestion, the degradation in pump head follows the curve (dashed line) predicted by the change in average fluid density due to the air content.

Above 2 percent void fraction, the data depart from this theoretical line and the rate of degradation increases.

Above void fractions of about 15 percent, pump perforicance is almost totally degraded.

The degradation process between 2 and 15 percent void fraction is dependent on operating condi-tions, pump design, and other unidentified variables.

(These findings closely approximate the guidelines empirically estab-lished by pump manufacturers:

at air ingestion levels of less than 3 percent, degradation is generally not a concern; for air ingestion levels of approximately 5 percent, performance is pump and site dependent; for an ingestion greater than 15 percent, the performance of most centrifugal pumps is fully degraded.)

For CSS or RHR pump operation at very low flow rates

( < about 25 percent of best efficiency point) even small quanti-ties of air may accumulate resulting in air " binding" and com-plete degradation of pump performance.

1 Combined Effects of Cavitation and Air Ingestion Few data on the combined effects of cavitation and air ingestion are available.

Figure 3.6, using test results from Reference 11, shows that as air ingestion rates increase, the have not been used to establish the air / water performance characteristics of pumps in this report.

(Manufacturers' data and testimonials do, however, corroborate published data.)

Only sources of information meeting the following criteria were used:

Subject pumps must be low specific speed (N, = 800-2000)

Subject pumps must be of " reasonable" design -- pumps hav-ing efficiencies of >60 percent and impellers >6" diameter.

Reasonable care must have been used in experimental techniques and in the documentation of results.

Test results meeting these criteria were then reduced to common, normalizing parameters and plotted for comparison.

20

1.2 g

g g

i g

i Merry () O MurakamisMinemura[12) w 1.Q Florgencic [13] W w N O E 0.8 Oh ~ Q E G C: 3y 0.6 3 N h E S i y 0.4 Symbol 9/9ben i O Open Symbols 0.6 I 9,y Closed S' pols 0.8 5 O Half-Closed 1.0 0 Symbols Dashed Lines - Density Effect l l l l I l l l I I l 0 4 8 12 16 20 PUMP INLET VOID FRSCTIO:1 - % i Figure 3.5. HEAD DEGRADATION UNDER AIR INGESTING CONDITIONS AS A FUNCTION OF INLET VOID FRACTION (% OF TOTAL FLOW RATE BY VOLUME). 21

l l 1 I 1.1 r i i l i i S!med=29/0 ron "1 m = MO am l' cad = 301 (t / - 34 h"Ad denradatiori r

1.0 20 f - IM]

C G e o v l h i \\ e s 4 ~ c n=2% g,3,3% l N w N M l l l ~ g 0.9 n-c,. e,s n I g N c. at NPSIf recuired !:i 0.9 I (2% air) 41'S!t reauired (zero 1 l ~ l i air) l l l I 0.7 o 10 20 30 l NPSH (f t) l J Figure 3.6. EFFECT OF AIR INGESTION ON NPSII REQUIREMENTS FOR A CENTRIFUGAL PUMP. i

4 NPSH requiremeht for. a. pump also increases. The curves for. 'this particular pump show that air ingestion levels of about 2 percent results in a 50 percent increase in.the NPSH required (allowed head degradation based upon 3 percent degradation from the liquid head performance). ~ Particulate Ingestion The assessment of pump performancefunder particulate -ingesting conditions is based on estimates of the type and concentrations of debris likely to be transported through the. screens to the pump inlet. In the absence of comprehensive test data to quantify types and concentrations of debris which -will reach the pumps it has been estimated.that concentrations of fine, abrasive precipitated hydroxides are of the. order of 0.1-percent by mass and. concentrations of fibrous debris are of_the order of l' percent by volume.* The effects of particu-lates.in these quantities has been assessed on the basis of known behavior of this type pump under.similar operating circumstances.

Ingestion of particulates through pumps is not likely to cause performance degradation for the, quantities and types of debris estimated above.

Due to the presence of upstream screens, l particulates-likely to reach the pumps should be small enough-to pass directly_through the_ minimum cross-section passages of the pumps. Because of generally low pipe velocities on.the_ pump suction side, particulates reaching'the pumps should be of near neutral buoyancy and,- therefore, behave like the pump fluid, i Manufacturers tests and experience-with these types of l pumps.have shown that abrasive slurry mixtures up to concentra-tions of 1 percent by mass should cause no serious degradation in performance. Similarly, tests on pumps of similar construc-tion to evaluate the capability of pumps of this type to handle fibrous paper stock have shown that quantities up to 4' percent should cause no appreciable-degradation. A major concern in the effects of particulates on perform-i ance and operability of the pumps has been the effects of fibrous or other debris (such as paint chips) on pump-seal and bearings systems. It is possible that porting within cyclone separators l l

The concentration for abrasive A10(H) was obtained from Reference 16 where 3000 pounds of precipitate was estimated to develop in 30 days and recirculate with 3.7 million pounds of water (Reference 16).

The 1 percent by volume concentration of fibrous debris is based on the quantity of fibrous insulation l reaching the sump screens from Maine Yankee plant (Table 3.6) i mixing with 200,000 gallons from RWST and being recirculated through the pumps. 23 __... _ _ ~, _ _. _ _.. _. _ _ _ _. _. _ _ _ _ _. _ _ _ _ _. _ _ _ _ _ _.. _ _. _ _ _

and in the flush ports for mechanical shaft seals or water lubricated bearings may become clogged with debris. In such an event, seal or bearing failure is likely. In the PWR plants which were reviewed, pumps used oil.or permanent lubricated bearings and mechanical shaft seals. For these con-figurations, the seals may be subject to failure due to clogging, but the bearings are not. The construction of mechanical face seals used in these pumps is such that complete pump degradation or failure is not likely even in the event of seal failure. For situations where the pumps incorporate water lubricated bearings (in some BWRs) loss of lubricant due to clogging of passages is likely to cause bearing failure. Swirl The effects of swirl due to sump vortices on pump performance are negligible if the pumps are located at significant distances from sumps. Tests discussed in Section 3.4 of this report indi-cate that swirl angles in the suction pipe 14 pipe-diameters from the outlet of the sump were typically 4* (swirl will decay with distance in a pipe). RHR and CSS pumps are generally preceded by valves, elbows, and piping with characteristic lengths on 'the order of 40 or more pipe diameters; this system of piping components is more likely to determine the flow distributions (swirl) at the pump inlet than is the swirl caused by sump hydraulics. For pumps with inlet bells directly in the sumps, vortices and accompanying swirl in the inlet bell can cause severe problems, due to asymmetric hydraulic loads in the impeller. This configuration should be avoided. 24

3.2.3 Calculation of Pump Inlet Conditions Given the findings noted above, the following steps outline the resulting calculational procedure for assessing the inlet conditions to.the pump. The procedure follows routine calculation methods used for estimation NPSH available, except that steps are also incorporated which allow for air ingestion effects. Figure 3.7 shows a schematic of the pump suction system with appropriate nomenclature. 1. Determine the hydrostatic water pressure (gage), P at sg, the sump suction inlet. centerline, accounting for temp-erature dependency and minimum water level. 2. Based on the sump hydraulic assessment, determine the potential level of air ingestion at the sump suction pipe a as discussed in Section 5.2. s, 3. Calculate the pressure losses in the suction pipe between the sump and the pump inlet flange. Pressure losses are calculated for each suction piping element (i.e., inlet loss, elbow loss, valves, pipe friction) using the average velocity through each element Vi, and a loss coefficient, Ki, for each element. The total pressure losses are then: 2 ('y/144) [Ki 1 /2g V P = y where y is the specific weight of water (lb/ft3) and 144 is the conversion from psf to psi. The loss coefficients are defined as: hyi K E i 2i /29 V where: hfi is the head loss in ft of water in l element i, g is the acceleration due to gravity, and vi is the average velocity in element i in fps. Loss coefficients can be found in standard hydraulic data references such as found in Reference 10. 4. Calculate the absolute static pressure at the pump inlet Pp. Pp = Psa - Py + Ph-Pd 25

i i i l P - CONTAINMENT ABSOLUTE PRESSURE c l Psg - HYDROSTATIC PRESSURE OF SUMPSCREENS SUMPSUCTION INLET Pc Zw - WATER ELEVATION Zs - SUMP SUCTION CENTER LINE ELEVATION [ f e - - - { l.- - 1, Zw Zr _ PUMPINLETFLANGECENTER l ~ l -T7 / LINE ELEVATION M l

ls

/, REDUCER I SUMP PUMP SUCTION SUMPSUCTION VALVE PUMP [ PIPE L' l // //// 1 l Figure 3.7. Schematic of Suction Systems for Centrifugal Pump

I where: Psa is the total absolute pressure at the sump suction pipe centerline which is the sum of the hydrostatic pressure, Psg, and the containment absolute pressure. P (determined c, in accordance with RG 1.1 and 1.82 for'NPSH determination). Py is the suction loss determined in Step 3. Ph is the hydrostatic pressure due to the elevation difference between the sump suction pipe centerline, Zs, and the pump inlet flange centerline, Z p. Ph= (y /144) (Zs - Zp) Pd is the dynamic pressure at the pump inlet flange using the average velocity at the pump suction flange, Vp. 2 y V Pd= 144 2g The value for P will be used to correct the volumetric p flow rate of air at the sump suction pipe for density changes. If air ingestion is zero, Steps 4, 5 and 6 can be ignored. 5. Calculate the corrected air volume flow rate at the pump inlet, ap, based on perfect gas, isothermal process: l l l ap sPsa/Pp)a r s l l 6. If ap is greater than 2 percent, inlet conditions l are not acceptable. l 7. Calculate NPSH at the pump inlet flange, taking into account requirements of RG 1.1 and 1.82. l NPSH = (Pc+Psg - Py + Ph - Pyp) (144/y) where Pyp is the vapor pressure of the water at evaluation temperature. 8. If air ingestion, ap, is not zero, NPSH required from the pump manufacturer's curves must be modified to account for air ingestion. 27

p = 0.50 (ap) + 1.0 where ap is the air ingestion level percent by volume at the pump inlet flange. Then: NPSH required (air / water) =sx (NSPH required for water) 9. If NPSH from Step 7 is greater than NPSH required from Step 8, pump inlet conditions should be satisfactory. 3.3 Debris Assessment i The safety concerns related to LOCA generation of debris resulting from the breakup of thermal insulation, and the potential-for sump screen blockage were addressed generically as follows: 1. A survey of nineteen reactor power plants was conducted to identify insulation types used, quantities and distribution, methods of attachment, components and piping insulated, variability of plant layouts, sump designs and location. 2. A calculational procedure was developed for estimating quantities of insulation which the pipe break jet might destroy or dislodge, for estimating debris migration during the recirculation mode and for esti-mating the degree of -screen blockage that might occur. A series of engineering models were established and concise review methods were developed. 3. The debris calculational methods described in 2, above, were then applied to five PWRs to determine the influence of various types of insulations and plant layout effects (i.e., sump location versus break location). In addition, the calculational methods and results obtained'were subjected to external, independent technical review (i.e., peer panel reviews). 4. Experiments were conducted to establish the onset of insulation debris generation from typical mineral wool and fiberglass insulations, their buoyancy and migration characteristics, and the potential of such insulations and their debris to create screen blockage. r The results are summarized in the following subsections. 3.3.1 Plant Insulation Survey Findings Table 3.2 lists the plants surveyed. The results of these insulation surveys are summarized in Table 3.3, wherein tabulations of the respective insulations are made for the respective plants and comparison of the 28

TABLE 3.2 Reactor Plants Selected for Insulation Survey Plant and Location Reactor Rating Start-Up Date Utility Architect / Engineer Oconee Unit 3 B&W-PWR 860 MWe 1974 Duke Power Co. Duke Power Co. Seneca, SC Crystal River Unit 3 B&W-PWR 825 MWe 1977 Florida Power Corp. Gilbert Red Level, FL Midland Unit 2 B&W-PWR 805 MWe 1983* Consumers Power Co. Bechtel Midland, MI Haddam Neck W-PWR 575 MWe 1968 Connecticut Yankee Stone & Webster Haddam Neck, CT Atomic Power Co. Robert E. Ginna W-PWR 490 MWe 1970 Rochester Gas & Gilbert Ontario, NY Electric Corp. H. B. Robinson W-PWR 665 MWe 1971 Carolina Power & Ebasco Hartsville, 6C Light Co. Prairie Island 1 & 2 W-PWR 520 MWe 19739 Northern States Fluor Power Services Red Wing, MN Power Co. Kewaunee W-PWR 535 MWe 1974 Wisconsin Public Fluor Power Services Carlton, WI Services Corp. Salem Unit 1 W-PWR 1090 MWe 1977 Public Service Public Service Salem, NJ Electric & Gas Co. Electric & Gas Co. McGuire Units 1 & 2** W-PWR-1180 MWe 1981* Duke Power Co. Duke Power Co. Gowans Ford, NC 1

Estimated dates Unit 2 start-up date is 1974 Source: Nuclear News, August 1981
- Unit 2 estimated start-up date is 1983 Source: Nuclear News, February 1981

1-s TABLE 3.2 (C ntinusd) Plant and Loca1 tion Reactor Rating Start-Up Date Utility Architect / Engineer i Sgquoyah Unit 2 W-PWR 1148 MWe 1982* Tennessee Valley. . Tennessee Valley I Dr.isy, TN Authority Authority i Maine Yankee CE-PWR 790 r4We 1972 Maine Yankee Atomic Stone and Webster Wiscassett, ME Power Co. i Millestone Unit 2 CE-PWR 870 MWe 1975 Northeast Utilities Bechtel Waterford, CT 1 St. Lucie Unit 1 CE-PWR 777 MWe 1976 Florida Power & Ebasco l Hutchinson Island, FL Light Co. s l Calvert Cliffe CE-PWR 850 MWe 1975** Baltimore Gas & Bechtel Units 1 & 2 Electric Co. Lusby, MD Arkansas Unit 2 CE-PWR 858 MWe 1980 Arkansas Pcwcr & Bechtel j g Russellville, AR Light Co. 4 Waterford Unit 3 CE-PWR 1165 MWe 1983* Louisiana Power Ebasco Taft, LA & Light Co. ) l Cooper GE-BWR I 778 MWe 1974 Nebraska Public Burns and Roe j Brownsville, NB Power District l l WPPSS Unit 2 GE-BWR II 1150 MWe 1983*- Washington Public Burns and Roe l Hanford, WA Power Supply System

Estimated dates 4

i j

- Unit 2 start-up date is 1977 l

Source: Nuclear News, August 1981 i i i, l i 4

i TABLE 3.3 Types and Percentages of Insulation Used Within the Primary Coolant System Shield Wall in Plants Surveyed

Types of Insulation and Percentage *-------------------

Mineral Calcium Reflective Totally Fiber / Wool Silicate Unibestos Plant Metallic Encapsulated Blanket Block Block Fiberglass Oconee Unit 3 98 2 ) Crystal River Unit 3 .94 5 1 Midland Unit 2 78 22 Haddam Neck 3 959 1 Robert E. Ginna 5 80 10 l H. B. Robinson 15 85 Prairie Island Units 1 & 2 98 2 i Kewaunee 61 39 Salem Unit 1 39 8 53** McGuire Units 1 & 2 100 l Sequoyah Unit 2 100 w l Maine Yankee 13 48 25 13 1 Millstone Unit 2 25 35 5 30 St. Lucie Unit 1 10 90 Calvert Cliffs Units 1 & 2 41 59 Arkansas Unit 2 46 53 1 ) Waterford Unit 3 15 85 j Cooper 30 70 WPPSS Unit 2 100 T 4

Tolerance is + 20 percent i

l

- Both totally and semi-encapsulated Cerablanket is used, however, inside containment only totally j

encapsulated is employed. 9Unibestos is currently being replaced by Calcium Silicate. However, both types of insulation have the same sump blockage characteristics. i l

respective amounts of insulations used in a particular plant is provided on a percentage basis. Additional detailed information for each plant surveyed has been assembled into reference data packages and has been published as NUREG/CR-2403 and NUREG/CR-2403, Supplement No. 1 (References 3 and 4). These reports detail the types and amounts of insulation employed, their location -in containment, components insulated, material characteristics, methods of installation, etc. In addition, the plant sump designs and screen details are provided in simplified drawings for ease of reference. Appendix A of this report illustrates the plant specific sump designs and plant layouts, the variability plant-to-plant is quite evident. Plant design information was obtained for plants representative of the 4 U.S. light water reactor vendors and the selected sample consisted of plants designed by 8 U.S. architect-engineering firms. New and old plants were surveyed. The types of insulation employed in nuclear power plants-are as follows: 1. Reflective metallic insulation, generally constructed from stainless steel, although aluminum internal foils have also been used. 2. Totally encapsulated insulation panels which utilize more effective thermal insulators (e.g., mineral wool fiber, fiberglass, calcium silicate, etc.). The principal point of distinction is that the encapsula-tion material (i.e., stainless steel) provides a container that is resistant to break jet forces and promotes the maintenance of the insulation in large blocks. 3. Nonencapsulated insulations (e.g., mineral wool, fiber wool, calcium silicate blocks, fiberglass blankets, unibestos block, etc.) which, if directly l impacted by the break jet and subsequently immersed i in the steam-water environment within containment, can be viewed to pose screen blockage problems and must be evaluated. The plant variability and selection / utilization variability noted above preclude a singular generic debris assessment. Rather, the prevalant situations lead to the necessity of developing logical and consistent debris calculational methods for assessment and quantification of debris generated and screen blockage severity. The following subsection outlines calcula-tional methods and models for systematically performing debris calculations. Past evaluations have relied to a great extent on R.G.1.82 which addresses an assumed acceptable limit of 50 percent screen blockage, but does not require an engineering i 32 l l I

W-cotimate of the amounts of insulation.dsbris'which a LOCA L . might-. generate, nor an assessment of the attendent sump screen blockage. 4 I 3.3.2 Calculational Methods for Assessing Debris Hazards The calculational methods' described herein were developed. j by Burns'& Roe, Inc., engineering staff and are applicable for analyzing the diversity of plant layouts, sump locations, insulation types and piping runs typified by the plant surveys conducted (see Section 3.3.1 and Appendix A). I' These calculational methods (which are described in greater detail in Reference 5 and Appendices B and C) provide an analysis tool which allows a systematic' estimation of the quantities of debris generated.- The assumption is made at the outset that the postulated pipe ruptures are those defined in NRC's Standard Iteview Plan (NUREG-0800), Section 3.6.2, and use is made of the break jet models provided in References 17 and 24. In the treatment given here, the jet model in Reference 17 has been modified to provide more conservatism in the results. In 4 addition, jet impingement effects are calculated *, short-term transport due to blowdown forces and long-term transport due to the flow of recirculated water are estimated as is the screen blockage by debris. _ As can be expected, plant layout,. types of insulation employed, and quantities thereof are the controlling inputs. Since the< majority of postulated rupture locations (PRLs) are I located within.the crane wall region, and attention _to that portion of the plant is required. Reflective metallic insula- .tions will sink and transport will be.along the plant flows. Low density insulation (if non-hygroscopic) will float and i migrate to the screens--but will not cause blockage if water levels are high enough. Nonencapsulated insulations will be subjected to direct high temperature, high pressure water and steam jets. Destruction, dispersion and displacement will f likely occur. Encapsulated insulation sections will tend to maintain a geometric structural shape which is large, and although migration could occur, a densely packed (or blocked) screen situation is less likely. The insulation material of primary. concern is the nonencapsulated, or free (due to jet breakup) fibrous insulation as characterized by mineral wool, l fiber glass, wool blanket materials. It has been demonstrated t l

In recent NRC supported research of two-phase jet phenom-l'

.ena'and jet loads (References 18, 19, and 24). stagnation pressure lin two-phase jets and pressure loading on two-dimensional targets were investigated. This research has shown that the target load depends upon the thermodynamic conditions immediately upstream of the break and the distance to the target. For highly subcooled vessel conditions a potential exists for extremely high pressures (greater than 2000 psia for PWRs) on targets within several diameters of the break. 33

(References 7, 14, 15, and 25) experimentally that free fibers .and shreds can migrate (at near neutral _ buoyancy) to the screens where they can adhere and form layers sufficiently thick to result in significant screen blockages with high attendant pressure drops. These methods for sequential evaluation are outlined in Figure 3.8, Sheets 1, 2, 3 and 4,in which the respective steps described below are' identified. STEP 1 -- Identification of the number, orientation, and i location of the PRL to be analyzed. These postulated pipe. ruptures are defined in the NRC-Standard Review Plan, Section 3.6.2, which provides guidance for selecting the number, orienta-tion, and location &- the postulated ruptures within containment.* In general, PRLs are selected'for' analysis as follows: 1. All PRLs which are identified in the Final Safety Analysis Report ( FSAR) 2. From PRLs identified, select breaks that'are: J a) located in large diameter, high energy lines b) or!ented toward principal sources of insulation (steam. generators, coolant pumps, pressurizers, hot legs, cold legs, cross-over piping, etc.). l 3. Four or five breaks are selected for further analysis by noting jet travel direction for unrestrained or l restrained pipes and breaks are selected that project insulation toward the sump area. (Breaks dislodging i the greatest amount of insulation that will be trans-ported toward the sump should be selected without regard for initial transport ~ direction). STEP 2 -- Estimation of the amount of insulation debris that might be generated by postulated pipe rupture. Debris is generated by three mechanisms: 1. Jet Impingement -- generates debris by subjecting the insulation to a high velocity, high differential pres-sure field that strips the insulation from the target. ~ *For piants that have already filed FSARs, the design basis break locations inside containment have been tabulated and may.be found in FSAR's, Section 3.6.2, for plants filing FSARs under the revised format. Information for FSAR plants that filed prior to the revised format effective date may be found in Accident Analysis-l (Chapter 15), Design of Structures, Components, Equipment and Systems. (Chapter 3 ?, and Engineered Safety Features (Chapter 6 or an Appendix). 34

t

Stsp 1 Break Locations and Orientations Step 2 Debris Generation l

l Pipe W ip Pipe Impact Jet Impingement -l l 1 Step 3 Debris Transport Step 3a i Short Term Transport Pipe Wip Pipe Impact Jet Impingement l ~l Debris Location at Termination of-Blowdown i Step 3b l Long Term Transport i i A Figure 3.8 - Sheet 1 i Outline of Methods l l l l 35

s A Containment Recirculation-Qualitative Description Containment Recirculation-Qualitative Method of Evaluation l Insulation Debris Class i i i i i i Mirror Panels Metallic Jacketing Non-Hygroscopic Hygroscopic Fibrous W ] I 1 _ _ _ _ _ _ _ _ J - -i - - - - - - - - - -------'I Transport Transport Sinking Debris Floating Debris j l l l l Force Required Force Available Exposed Screens ~ to Cause Motion to Cause Motion I I lFibrousInsulation Normal Force Velocity Near Sump Hygroscopic Insulation Vortex Formation l j B C D E F G 4 1 Figure 3.8_- Sheet 2 Outline of Methods

B C D E F' G i i Non-Hygroscopic Non-Hygroscopic flygroscopic Floating Debris No voida Volds-100% Migration Less than 100% Migratesl Velocity to Overcome Coefficient of Friction Buoyant Force l I Scoping Analysis Small Diameter i Floating Debris Large Floating Debris l Step 4 Sump Effects i I Head Loss liead Loss Unblocked Screens Due to Debris Accumulations 4 l I I I I I Impermeable Debris Porous Beds of Solid Beds of Type-1 Fibres Individual Fibres [ l I I H I Figure 3.0 - Sheet 3 Outline of Methods 1

H 'I 4 Evaluation of Pressure Drop j Due to Accumulated Debris i l Ede Head Loss llead Loss Due to Increased Due to Debris 1, Flow Rate l l l s l \\. Sump Evaluation \\ \\ 4 +. Figure 3.0 - Sheet 4 Outline of Methods x y i N \\ 4 ,4il 4 \\ g 4 s i .t.

= i J .This-is the. principal debris generation mechanism (i.e., l 90 percent of debris generated). l l

2.. Pipe' Whip -generates. insulation debris due to the motion of unrestrained piping segments.

3. Pipe Impact -- generates additional insulation debris by the impact of unrestrained piping segments with-l 'ir.sulated structures, components, or other piping j systems. Specific methods for calculating the amount of debris generated by each mechanism are given in Reference 5 and Appendices B and C. Methods for calcu-lating the magnitude of jet thrust,. jet impingement forces, stagnation pressure as.a function.of distance, and other hydro- . dynamic effects'were adapted from Standard Review Plan, Section f 3.6.2, and engineering handbooks.. STEP 3 -- Calculation of short-term and long-term transport of insulation debris. 1. Short term transport ~--. debris motion caused by pipe whip, pipe impact, jet impingement mechanisms -- terminates at the end of the blowdown transient. t Velocities of debris caused by pipe whip and pipe impact are assumed to'cause motion in a straight line.that continues until impact with walls or other' obstructions. Debris then drops i vertically to floors, grates, or other structures.. L Debris generated and entrained into the jet by jet impingement will not stop upon impact with obstructing structures, but will change direc-tion. Consequently, debris can pass through I doorways or other openings not directly in line with pipe breaks. The jet force at an obstruc-f tion is determined using the stagnation pressure f equation (Reference 5). t [ 2. 6ong-term transport -- begins with activation of the ^ /- contain Fluid _ velocity, debris,9 enter = circulation system. 'e'7L/ density, debris size, and effects of coolant tr ^ on-debrfs integrity are analyzed to determine if long-term transport could occur. For. debris transport, ~ 1 the migration patterns of dislodged insulation within f

/censainment are established.

Insulation debris may .2 r""b'e-typed - either as Sinking -(mirror panels, metallic ~ jacketing /or hygrosEopic insulation with equilibrium [ s densities greater /than that of water) or Floating .(non# hygroscopic, h'ygroscopic, fibrous). j " sr l ' -" / lP ~y 39 E. L 64 m i g y

40 ?Vi Ni ' Sinking Debris '-- will be transported to the sump.if the water velocity is sufficient to-7 .. overcome) drag force. The' analysis considers the -hydrodynamic -forces needed to move debris ^ un-the containment floor to the-sump inlet, and determines the local. velocities that Lexist within containment.-lExperimentalistudies 1 allow estimates of those velocities. required to transport insulation debris to sump. screens. Floating Debris -- is assumed to migrate to -the sump. The possibility'of sump blockage is determined by evaluating the local veloc-ity required to overcome the buoyant force of 'the ' debris and comparing this value to the local velocity existing at the sump. The -floating debris model is valid'also for pre- ' dicting the behavior near, sump intakes of floating fibrous insulation. Suspended fibrous debris is ass'umed to migrate.to the sump. The effect of : blockage f s determined by evaluating the pressure drop across the resulting debris

- g mat = formed on the sump screen.

1 s .X-STEP 4 *--TDetermination of Screen Blockage and Attendant i Pressure Drops.The results of Steps 1 through 3 can now be used to estimate the. extent of' screen blockage that might occur due to debris migration. .These debris migration models can be used tx) estimate-screen blockages-in terms of the quantities of debris transported and screen blockage patterns can be deduced., Attendant pressure drop is the critical parameter for determining effects on required pump NPSH.- Careful considera- ' tion'should be given to head losses for blocked screens. In the' calculation of blockage by fibrous debris, the equivalent insulation blockage thickness (ti),'should'be calculated as: Volume of debris transported t. = 1 Available Screen Area a Pressure drop calculations, using the above relationship, have been'made on two selected examples where blockage has been t~ calculated'to be total'(Salem Unit 1 and Maine Yankee). Such L calculations; provided'in Reference 5, have made use of the J. methods 'and assumptions present-in the referenced report. In E the estimation of pressure drops at sump screens due to fibrous insulation debris,'the methods provided in Reference 5 and Appendices B and C are applicable. However, the pressure drop versus insulation debris thickness information developed experi-mentally should be used in calculations of sump acceptability (Reference 7). 40 L ye .g,m-t i-----ve----+-=-r-w--*'r---v+*r-ww-r*-=w--,--,--e a -- e t-w-w v'=--w-r--e---n ~=++--=* ewe-e-+w--ei-w-=-ri,====~*---=*w e--*----- =**r-=-+--*

'These four steps of the debris analysis = provide a conserv-ative' method for evaluating the potential for generation of-L-

insulation debris in_a power reactor station, the potential l

for blockage'of the sump' screens due to LOCA-generated insula-tion debris,-and.for assessing the impact of insulation debris ~ i on sustained operation of-the containmentirecirculation system. They.-provide a set of methods for assessingf the potentia] safety hazard'of insulation debris and-can be used to aid in assessing debris effects (screen blockage) in any reactor ~ primary containment. l' [ '3.3.3 Application of. Methods to 5 Gample Plants The methods described in the previous section.were applied ~ to 5 plants selected from the 19 originally surveyed. Sample calculations were performed to prove the methods and to identify l any problem areas for plant or insulation types. Plants of varying design with different insulationLinventories were . Table 3.4 summarizes these plants by type, owner, selected. location,' size, and architect / engineer. Tables 3.2 and 3.3 summarize the types of insulation present in each plant. The tables-show that a broad spectrum of insulation types, both singly and in combinations, were found.to be in use. Table 3.5 describes the location of the emergency sump, l summarizes the location of the.various types of insulation ~in the plant, and provides an assessment of the migration poten-tial of debris generated as a result of a pipe break, as derived from the development provided in Reference 5. l Table 3.6 summarizes, for each plant, the PRLs, the quanti-ties of debris generated, the quantities of debris transported i to the sump screens, unblocked screen areas,. blocked screen ' areas, and the percentages of sump inlet areas that are blocked: -the table concludes with a qualitative indication of the severity of.the potential sump blockage. The estimates provided in this summary derive from Reference 5. l l Although the estimated quantities of debris and attendant i screen blockages show a high variability, the findings are ~ L quite revealing. Large quantities of debris are estimated to ~ be produced. This results-from the conservative assumption Lthat all jet-targeted insulation is stripped and conservative assumptions as to transport to the sump. In addition, . calculated screen blockages vary due to sump screen area variability. Screen blockages in excess of 50 percent (see the Sequoyah #2 results) have been calculated. However, the screen pressure drop at Sequoyah has been-determined to be negligible, since Sequoyah. utilizes all reflective metallic insulation. Plants having large screen areas (i.e., Salem l 41 l a-,; ,.-..a ._.,,-,,.--...-.-.-....-...--...-J

TABLE 3.4 Reactor Plants Selected for Detailed Investigation of Insulation Debris Generation Potential Plant and Location Reactor Rating Start-L*p Date Utility ' Architect / Engineer Maine Yankee CE-PWR 790 MWe 1972 Maine Yankee Atomic Stone and Webster-Wiscassett, ME Power Co. Arkansas Unit 2 CE-PWR 858 MWe 1980 Arkansas Power & Bechtel Russellville, AR Light Co. Salem Unit 1 W-PWR 1090 MWe 1977 Public Service Public Service Salem, NJ Electric & Gas Co. Electric & Gas Co. j g Sequoyah Unit 2 W-PWR 1148 MWe 1982* Tennessee Valley Tennessee Valley Daisy, TN Authority Authority Prairie Island Unit 1 W-PWR 520 MWe 1973 Northern States Fluor Power Redwing, MN Power Co. Lervices

Estimated date l

4

1 Unit 1 with a 936 ft2 screen) can tolerate large quantities of transported debris. On the other hand, plants with smaller screens and fibrous, nonencapsulated insulation targeted by_ principal pipe breaks (such as' Maine Yankee) have been iden-tified.as having a potential for unacceptable pressure drops. Plant and insulation effects are evident. The methods given l above, however, can be used to evaluate plants for the degree of f screen blockage that various insulations can pose. The-methods have been. tested against a broad spectrum of plants and eval- [ uated independently - (see Section 4.2). The results. point out the deficiency of the 50 percent screen blockage guidance set forth in RG l.82, which has been used in the past at times with-out the benefit of plant specific debris evaluations and atten-dant 'losa in required NPSH. These calculations also show that the answers the analysis method provides can vary over a wide range of blockages; plant dependent features dominate'the block-age calculations. i 3.3.4 Experimental Studies on Debris Following the studies conducted by Burns and Roe, experi-mental work was carried out at Alden Research Laboratory to examine in a preliminary way the generation, buoyancy, and transport characteristics, as well as the potential for sump blockage of typical as-fabricated insulation and insulation debris. These experimtatal studies are reported in References 6 and 7. Susceptability of Fibrous Insulation to Debris Formation Experiments have been reported to study the onset of failure i of as-fabricated fibrous insulation due to jet impingement. These tests were conducted using-incompressible water jets at ambient temperature for various stagnation pressures and for two angles of jet impingement: normal to the insulation surface and 45' to the insulation surface. These. tests demonstrated that the stagnation pressure was the preliminary scaling variable with regard to the forces applied to an insulation panel (some-times referred to as insulation pillows). The experiments studied the stagnation pressure to determine the level required l for damage to the cover fabrics and failure of the insulation panel (fibrous insulation release). Tests were conducted using three types of insulation panels: Type 1 was made of mineral wool' enclosed in a Mylar coated asbestos cover, Types 2 and 3 l were made of fiberglass insulation covered with silicone glass cloth and fiberglass cloth, respectively. The insulation that was the most susceptible to failure was the Type 1 insulating panels. Visable damage occurred at stagnation pressures of about-10 ~ psig. (90

impact) and 15 psig (45' impact); failure of the pillow occurred at stagnation pressures of about 35 psig (90* impact) and 30 psig (45' impact).

visable damage was de-fined as the pressure at which the first signs of structural failure occurred, e.g., fraying of the fibers in the covering, etc.. Failure of the insulation panel was defined as the pres-sure where there was a release of fibrous insulation from the l as-fabricated incalation panel. In both instances the insulation 43 ~.

4 TABLE 3.5 Sumunary Table for 5 Plant Sample Calculations i Final Assessment of Migration' i Plant and Reactor Location of Potential of Debris Generated Nanufacturer Type of Insulation Utilized Emergency Sump as a Result of a P.se Break j ? Outside the reac- ' Plant calculations show that 1 Maine Yankee Reactor vessel uses reflective metal-(CE) lic insulation. Pressurizer, reactor tor coolant system for some of the postulated i (Conbustion coolant pumps, and steam generators shield wall below breaks total screen blockage Engineering) use calcium silicate molded block basement floor. can occur due to the transport j jacketed insulation for nonremovable of unencapsulated fibrous sections and mineral fiber / wool for insulation. Since the sump 2 the removable sections. Primary cool-screen area is small'(108 ft ), j ant piping uses removable mineral fiber / the calculated pressure drop wool blankets. Main steam, feedwater, (6.3 psi) is excessive. Further residual heat removal, and chemical and investigation is necessary to j volume control system piping use calcium' confirm the fibrous bed pres-am silicate or unibestos molded block sure drop correlation employed. insulation. Component cooling lines use i fiberglass jacketed antisweat insulation. 1 Arkansas Unit 2 Reactor coolant piping, reactor vessel Outside the reac-Total debris is large (76,800 2 l (CE) bottom head of steam generator, and tor coolant system Ft ) but is incapable of either pressurizer use reflective metallic shield wall below migrating to the sump (reflec-l insulation. Feedwater. pressurizer safety basement floor. tive metallic) or being drawn l relief valve, and balance of steam gener-into the screens (calcium ator blowdown use totally encapsulated silicate). Extensive blockage calcium silicate or expanded perlite of the inboard screens occurs molded block insulation. Main steam pip-but outboard screens are more ing uses. calcium silicate or expanded than adequate to pass the i perlite block with stainless steel jacket-required flow without' intro-l ing. Chilled water piping uses fiberglass ducing excessive head losses. with stainless steel jacketing.

TABLE 3.5 (Continurd) I Final AE@msment cf Migrction' i Plant and Reactor Location of Potential of Debris Generated Manufacturer Type of Insulation Utilized' Emergency Sump as a Result of a Pipe Break l Salem Unit 1 Reactor vessel, primary coolant piping, Outside the reactor Postulated breaks resulted in ~ (W) pressurizer, reactor coolant pumps,:and coolant system large quantities of debris. l (Westinghouse) bottom part of steam generator use reflec-shield wall below calculations indicate total tive metallic insulation. Upper part of basement floor. screen blockage to occur.. Cal - l steam generator uses semi-encapsulated Water drains _into culations showed that'large i cerablanket insulation. Main steam, emergency sump quantities of debris would be-feedwater, residual heat removal, safety through trenches generated by postulated breaks. injection, and chemical and volume control in the floor in They further showed the poten-4 system piping use totally encapsulated addition to directly tial for total screen blockage. I cerablanket. Service water and component from annular space However, this. plant design has i cooling-water piping use antisweat insula-outside of shield large debris intercept areas, j tion. wall. in addition to the local sump screen. This, when coupled-l j with the low recirculation velocities within containment, results in a low blocked screen 3 AP which does result in Ln insufficient NPSH. Sequoyah Unit 2 All piping and equipment within the Inside the crane While a large percentage of the l (W) shielded crane wall area use reflective shield wall below sump intake area was blocked -metallic insulation. containment floor. (approximately 74%), the j remaining screen area is capa-ble of passing the required recirculation flow without ) excessive head loss. Pump NPSH j requirements are not impaired. j Prairie Island Mirror insulation is used on reactor vessel, Outside reactor The quantity of insulation j Unit 1 (W) steam generator, reactor coolant pump,. pres-coolant shield debris generated is large i surizer, excess letdown heat exchanger, wall, below (>3000 Ft ) but is unable to 2 regenerative heat exchanger, surge line, high basement floor. migrate to the sump since re-l pressure safety injection loop, primary cool-flective metallic is exten-ant piping, steam generator blowdown lines, sively employed. The quantity pressurizer spray piping, chemical and volume ~ of fibrous insulation genera- } control piping, accumulator, low pressure ted is not sufficient to block { safety injection, feedwater, main steam, a sump intake area large j auxiliary feedwater, residual heat removal, enough to cause' excessive -steam generator supports. Fiberglass insu-pressure drop. lation is used on main steam and feedwater hangers and restraints. l 1 ~

TABLE 3.6 Sanmary of Findinga Debris

Debris
Total
Blocked
Percent Plant Break Generated At Sump Sump Screen Sump _ Screen Blockage Note Area Area Sclem Unit 1 Hot Leg 2692 1197 1078**

1078** 100 1 Cold Leg 4737 2290 '1078** 1078** 100 1 Main Steam 0 1078** O O 2 Feedwater 0 1078** O O 2 Arkansas Unit 2 Main Steam 7161 6517 287 95 33 3 Feedwater 1 278 0 287 189 66 4 Feedwater 2 97 5 K:ine Yankee Main Steam 3314 108 6 Hot Leg 1 1071 108 6 Hot Leg 2 1642 108 6 Crossover 1 1642 108 6 Crossover 2 1596 394 108 108 100 7 Cold Leg 431 108 6 Emerg. Feed. 215 108 6 l Sequoyah Unit 2 Feedwater 248 15 41 15 37 8 Hot Leg 2840 27 41 27 66 9 Coolant Pump 1009 15 41 15 37 8 l Hot Leg 2840 27 41 27 66 9 S.G. No. 4 528 20 41 20 49 9 S.G. No. 1 3257 15 41 15 37 8 Loop Closure 5632 15 41 15 37 8 Prairie Island Main Steam 4316 39 60 39 65 8 Unit 1 Feedwater 1299 0 60 0 0 10 Hot Leg 4131 39 60 39 65 8 Cold Leg 1221 0 60 0 0 10 Crossover 5009 39 60 39 65 8 " Units of ft2 l

- Total debris intercept area available in this plant to accept LOCA-generated debris.

2 The sump screen area at the sum is 68 ft, NOTES: l 1. As insulation is fibrous, uniform deposition is assamed (i.e., 100% of sump screens l are blocked). Pressure drop is insufficient to adversely affect NPSH. 2. No de8ris reaches the sump region due to gratings as shown in Figure A-24. 3. Entire inboard screen blocked; outboard screen has sufficient unblocked area. 4. Entire outboard screen blocked; inboard screen has sufficient unblocked area. 5. Scoping analysis -- Feedwater 1 was more severe. 6. These cases are parts of a scoping analysis. Cold leg failure was most limiting. l 7. Screen blockage is calculated to be total. Calculated pressure drop across fibrous debris bed is sufficient to offset any available NPSH margin, subject to assumption of total sump screen blockage with no credit for debris capture in transport. 8. Blockage acceptable from pressure drop standpoint. 9. Blockage as percentage of screen area is high, but pressure drop is acceptable. 10. Insulation does not reach sump. 46

panal-was subjected for a period of five minutes to an impact from a two~ inch diameter, incompressible water jet'at a constant I . stagnation pressure, Po. In Reference 6 the rccommended value lof stagnation pressure for fibrous insulation panel failure was 20 psig. : Additional. experimental details are given in ~ Reference 6. I ~ Analytical studies (References 18, 19, and 24) of two-phase jets suggest that the extrapolation-of results'obtained from single-phase incompressible fluid studies to-two-phase LOCA (loss-of coolant accident) conditions may not be conservative, i This stems.from: (1) a potentially important' mechanism for debris generation by_ a LOCA jet may be stress to covering fibers resulting.from fluid flow tangential to the insulation surface at high velocities and'(2).the potential-for the area affected by two-phase jet expansion to extend to an: angle greater-than 90' (90' is assumed in the analytical treatment provided herein). Further discussion is provided in Appendix C. Buoyancy,-Transport, and Head loss of Fibrous Insulations t Buoynacy, transport, and head loss experiments 1were conducted with three types of as-fabricated and fragmented 3 ~ ' fibrous insulations the three types of as-fabricated insulation panels were: Type 1: 4" mineral wook or refractory mineral fiber core mineral. (6 lb. density) covered with Uniroyal #6555 asbestos cloth coated with 1/2 mil. Mylar. Type 2: 4" Burlglass 1200, or 4 layers of 1" thick Filomat'D (fiberglass) core material, inner covering of knitted stainless steel mesh, outer covering of Alpha Maritex silicone aluminum cloth,-product #2619. l I

Type 3:- Same insulation core materials as Type 2.

Inner and outer' covering of 18 ounce Alpha Maritex cloth, product

7371.

The Buoyancy Tests revealed that: a) 'In general, the time needed for both mineral wool and fiberglass insulation to sink was found to be less at higher water temperatures. b) Mineral wool does not readily absorb water and can remain afloat for several days. c) Fiberglass insulation-readily absorbs water, particularly hot' water, and sinks rapidly -(from 20 seconds to 30 seconds in-120*F water). d) Undamaged fiberglass pillows of type 3 (and possibly also of type 2) can trap air inside their covers and remain afloat for several days. 47

L 1 le ) Based on the observed sinking rates, it may be concluded that mineral wool pillows and some undamaged fiberglass pillows (those-that trap air inside their cover) will remain afloat after activation of the containment recir-culation system (approximately. twenty minuts after beginning of LOCA).- Those floating pillows will be readily transported to - the sink before activation ' of the recirculation system and will move only-if the water velocity exceeds the reported inci i nt trans ort velocities pe p j f) The reflective metallic insulation sample tested sank immediately and the closed cell (foam. glass) insulation sample floated indefinitely. ?. The Transportion Tests revealed that: a) Water velocities needed to initiate the motion of insulation are on the order of 0.2 ft/sec for individual shreds, 0.5 to'O.7 ft/sec for. individual small pieces (up to 4 inches on the side), and 0.9 to 1.5 ft/sec for individual large pieces (up to 2 ft on the side). b) Whole sunken pillows require flow velocities of 1.1 ft/sec for type 1 (mineral wool) and 1.6 to 24 f t/sec for type 2 and 3 (fiberglass) to flip vertically on to the sc reen. c) Whole floating pillows require a water velocity in excess of 2.3 ft/see to flip vertically against the sc reen. d). Insulation pillows broken up in finite size sunken fragments tend to congregate near the bottom of the screen if there is no turbulence generator, and depending on the water depth, unblocked space can remain near the top of the screens. ' With - turbulence generators (vertical posts 2 ft upstream of the I screen), some insulation fragments get lifted from the bottom and collect higher on the screen. A e) Insulation shreds, once in motion, tend to become suspended in the water column and collect over the entire screen area. f) The reflective metallic insulation sample tested required a flow velocity of 2.6 ft/see to start and keep moving. The Head Loss tests revealed that: l a) The measured head loss across a vertical screen in a flume due to blockage by insulation released upstream varies 2 from 7 to 10 times the approach velocity head, V /2g, for shole sunken pillows, from 13 to 36 times the approach velocity head for opened or broken up pillows and in excess of 240 times the approach velocity head for shredded pillows. These results correspond to a 50% screen blockage with the undamaged pillows. Opened pillows with separated, 48 mma - - - - - -. w- ,-.-%..-_.--m,, ,,,-+w -..v--, ._-,y. -,-,,,.-,ms-m .w-w-- e.-.mry ,--m ,,..,w-,-w e-m, ,4.-*-.m y

fragmented or shredded in'sulation layers, however, have - enough area to block the entire screen. _The screen was entirely (but not uniformly) covered only in the test with the shredded insulation. In the other tests, open apace remained-on the screen. For these conditions, the maximum measured head loss of 240 times the approach velocity head (for shredded pillows) would given screen head losses of 0.15 ft to 0.60 ft. for - approach velocities of 0.2 ft/see to 0.4 ft/sec. b) Measured head -losses through beds of accumulated fragments or shreds of mineral wool or fiberglass insulation were observed to vary nonlinearly with approach velocity and bed thickness. For mineral wool fragments the larger head losses were ' bserved for the larger fragmets tested (3 x 2 to 4 :x 1/8 o inch). For an insulation thickness of 1 inch, the maximum head loss was 0.4 ft at 0.2 ft/sec and 1.4 ft at 0.4 ft/sec. For fiberglass insulation fragments and shred s, the larger head losses were observed for the shreds..For an insulation thickness of 1 inch, the maximum head loss was 1.2 ft at 0.2 ft/sec and 6 ft at 0.4 ft/sec. f c) The head loss through as-fabricated insulation material i, is higher, by a factor of up to 10,. than that for accumulated fragments. For example, with water at 105 to 120*F and ~ an approach velocity of 0.2 ft/sec, the head loss through 2 inches of undisturbed mineral wool is about 3.5 ft and the head loss through 1 inch of undisturbed fiberglass is about 20 ft. These head losses are for insulation I samples sealed to the walls and 'the head loss would be less if leakage occurred around the sample, d) In addition to the varibles of insulation thickness and approach flow velocity, the actual head loss which may be expected across a sump screen is seen to depend critically on the manner of screen blockage. If some unblocked screen area remains, or if water can flow between pieces of insulation, the head loss would be small, whereas, if the entire screen area is uniformly ' covered with mats 'of undisturbed insulation or accumulated fibers, the head loss can be many feet. e) Best-fit expressions for the head loss through fibrous insulation were derived and reported in Reference 7. 3.4 Sump Hydraulic Performance To investigate the behavior of ECCS sumps under flow conditions that might occur during a LOCA, a test program was designed to cover a broad range of geometric features and flow variables representative of containment emergency sump designs. 49 _. -.. - - _. -., -, -. _... -. -. -. _ -...- -..- -.-~. -.. -.- -.. _.

Because some of the hydraulic phenomena of concern, particularly air ingestion, could involve scale effects if tested at reduced sc ale, a full-scale experimental facility was used. Three broad areas of interest for ECCS sump design were investigated: ' Fundamental behavior of the sump with' reasonably u~niform approach flow conditions ' Changes in the fundamental behavior of the sump as a result of potential accident conditions -- screen block-age, break and drain flow, ob structions, nonuniform approach flow, etc., -- that could cause degraded perform-ance in the recirculation system

Design and operational items of special concern in ECCS sumps.

The test program was designed to allow information from initial tests to be used to plan or redirect later tests; hence, ~ the tests were not necessarily conducted in the order listed below. Although the experimental program was modified, and tests were added on several occasions, tests used in the investigation may be divided into 7 series: Factorial Tests -- A fractional factorial matrix of tests was used to study primary sump flow and geometric variables. The factorial matrix provided a wide range of parameter variations and a method for effectively testing a large number of variables and determining their interdependencies. Secondary Geometric Variable Sensitivity Tests -- The effects on sump performance of secondary geometric vari-ables and design parameters of special concern in ECCS sumps were tested by holding all sump variables constant except one, for which several values were tested. Severe Flow Perturbations Tests -- The behaviors of selected sump geometries subjected to approach flow perturbations were investigated. Major flow disturbances considered were screen blockage (up to 75 percent), nonuniform approach velocity distribution, break-flow and drain-flow impinge-ment, start-up transients, and obstructions as illustrated I in Figures 3.9 and 3.10. Vortex Suppression Tests -- The effectiveness of several types of vortex suppressors and inlet configurations were evaluated. Scale Tests -- Scaling effects in geometrically scaled models using Froude number similitude and pipe velocity similitude were tested. Boiling Water Reactor (BWR) Suction Pipe Inlet Tests -- The hydraulic performance of BWR suction pipe geometries i typical of Mark I, II, and III designs was evaluated. 50

i l i NON-UNIFORM FLOW AND SCREEN BLOCKAGE SCHEMES i r:1 !1 n nn nr g { r NON-UNIFORM FLOW hj ((M& g i,NJ Dj 'g; u i (FLOW DISTRIBUTOR BLOCKAGE) L { g g } ) T W = M FT b_;f.( t = eo FT 3 j ) 3 _-s i y,? ? ? 3 g l (,,g d ffIlfI'll tit 0 -t t i nn nn n, nn r9% M4% ii :! .wti i k i To

SCREEN BLOCKAGE J

,u ~ u u u [t W = SUMP WIDTH ui g L = SUMP LENGTH .- % naJ 1.maJ lJ L.JI8'l 88 A 8' o e e e e nn ,o n, 4 silM l

!! l u si!!.! ::

E @ l".J ) l } ~ ,f aL 8 1 = i_ .o.n.om p w. = oc... n um. n .) O i Figure 3.9. Approach Flow Perturbations and Screen Blockage Schemes. 4 4 5

unta resulting -from the sump performance studies were analyzed using two approaches:- (1) functional correlations of the dependent variables in which the correlations were_ the i result of response-surface regression analysis or nondimensional empirical data fitting, and.(2) bounding envelope analyses in which boundary curves indicate the maximum response of the ~ data for each of the hydraulic. performance parameters as a function of the sump flow variables (the Froude number in. ) .particular). Due to the extremely small values of f the depen-i dent variables:and to the complex time-varying nature of the three-dimensional flows in the sump, the functional correla- -tions. approach showed no consistent,' generally applicable, correlation between the dependent and independent variables; hence,. the hydraulic performance of a particular sump under given flow and submergence conditions could not be reliably t predicted using this approach. However, the broad data base resulting from the sump studies made possible the use of envelope analyses.for reliably predicting the expected upper-bound for the hydraulic performance (void fraction, vortex type, swirl angle, and inlet loss coefficient) of any given sump whose essential features fall approximately within the flow and geometric ranges tested. The ability to describe the performance of ECCS sumps, with or without flow perturbations, using bounding envelope-curves is the most significant result of the test program. The application of an envelope analysis to test data resulting from all the sump performance tests is discussed in the follow-ing subsection of this report. Findings of the sump performance L tests are described in greater detail in subsequent sections. 3.4.1 Envelope Analysis The sump performance-test program generated a data base covering a broad range of ECCS~ geometric variables, flow condi-tions (including ' potential accident conditions), and design options (horizontal or vertical inlets, single or dual pipes, etc.). An envelope analysis applied to this broad range of 1 data resulted in boundary curves that describe the maximum expected air ingestion, surface vortex activity, swirl, and sump head loss as a function of key sump flow variables (Froude 4 number, velocity, etc.). Figures 3.11, 3.12, and 3.13 show typical envelope analysis curves for air ingestion, surface vortex activity, and swirl in' sumps with dual, horizontal outlets. Figures 3.14, 3.15, and 3.16.show typical envelope analysis curves for air ingestion, surface vortex activity, and swirl in sumps with dual, vertical outlets. 52 .~

12" SUPPLY LINE -P NOZZLE ( """ Cl l (I l i I l I f I t 0 y a. Break Flow Jet Impingement 79 L 12" DRAIN FLOW I NOZZLE DRAIN FLOW JET P TO E i }j SCREENS AND GRATINGS 'n$ ge-- = 1 FT i 1 = D}I! b } I l ll =O 0 l SUCTION PIPE 1 b. Drain Flow Jet Impingement Figure 3.10. Break and Drain Flow Impingement. 53

3&' . wesetuneso e6am vasts a eastumeno esom tests sum / / / \\ 8&E. I& E. u i... i EE. g e l s=,- =. .a ,%..t.0.,5. kN8 _O w E8 E2 ht

4. 8

1. s

3. s

3. 3

3. 3 gs PhouDe Istasesn, mA/"y-as e

u-i.ru..... mei E esatua88o ftem 71375 ta TEST 5: g_ [ Y El ss. / g

f. ss.

Y ss. I e [ as. o g g E'- . e .p ". g x " ~ 8 = =.e se sa ss ss se n.e s.a n.s s.e s

s. a m os a. o Figure 3.11.

Void Fraction (% by Volume) as a Function of Froude Number; Horizontal Outlet Configuration. Only data points indicating nonzero void fraction are plotted. 54 i f m-7 ,~ _ -ee.- g w,-ewv-,w -m ,m, m

a egefumet. 8 Lou 785T5 in 195754 I"~ s.!PTITM...F-E.'.,r i

u. g >.4.. o s...

I.. :. : s .a g.A,....,.. ..s. . v.

u...-

g

n.,.

i...-

J .m i .tize. m9.- 9 [....M%BKeiT' c. c. c. i. c. c. c. i. Figure 3.12. Surface Vortex Type as a Function of Froude Number; Horizontal Outlet Configuration. l..

:==:'"- '-

,T 8... 1 i g 4,. c.,, ,",. 4 i-- .g b,%j.,,7?u,9a!%B".. vs. i... ci t. t ,,y:x. l.... t v. .d ... r 107 i ". s. Figure 3.13. Swirl as a Function Froude Number; Horizontal Outlet Configuration. 55 l

i i _E8 W g 1& a !& a - / X< E 14.s E 8 ~ M k 12.s-O g .a y .s O SE x 0 1

4. s X

x 0 u. x X X X y &s } O5 g h 0 xmie 40 m* E = 2 N a FE 'oeyed

s..

s. s

e. 2 E4

s. 6

s. s lo s

1. 2

1. 4

1. s

2. s FROUDE NUMBER, uA/g s Eog m.

s f Is.a. E o UNIFORM APPROACH FLOW TESTS (EXCEPT FOR c = 0 SUMPS) Is. s _ v UNIFORM APPROACH FLOW TESTS (FOR c = 0) .s_ ar PERTURBED APPROACH FLOW TESTS mC 14 N x 2 12.s S N /

s. s_

li O g e.a. T x E as, x h O 4.s o X < is x E y k g. ice d o5mr h ud.-=8 h

O.m*S Em 8o,e5 S$I

s. s

s. 2

s. 4

s. e

s. s

2. s

2. 2

2. 4

a. e

2. s

2. s FROUDE NUMBER, uGg s Figure 3.14.

Void Fraction Data for Various Froude Numbers, Vertical Outlet Configuration. Only data for nonzero void fraction plotted. 1 56 l

, :- e. 5 g...,, s t,,- f :.. g : : ~ >. t.- .+ g ,..,, f ; s <t .s a ; s... " A<. " . " : R,:. 1 ~,.:r./ "., >.>: y-- s

n. \\'{ u...

.I q,.# 9 ~ n Sr gu- ,g in, gp ,p .= I.s *, **. f,,a,s u 5 l ru. J,e fb ( = 4

1.

a'. J. Ja J. J. J. FRouDE Nues.ER. w/6 Figure 3.15. Surface Vortex Type as a Function of Froude number; Vertical Outlet Configuration. .= 7.0 U O WFo.es pp.o.CM, Lour Test 5 (tKctFT FO. e a.6 W. a x .,u. o C.. vim .g,, v< = <g g=u. j gn 2 *..".. ".

s. E. u

.84,.... ! =~ m l Sg , $ 6f I h ~ ?;b ' h },. W.f i d,*i

5: p.

ud, r! %..4~ ;L f.E... s : ".s ...o Figure 3.16. Swirl as a Function of Froude Number; Vertical Outlet Configuration. 57 ) . -. ~.

L L 3.4.2 G.eneral Sump Performance (All Tests) L: Free Surface Vortices -- Vortex size and type resulting from a given geometric flow condition are difficult to predict and are not reliable indicators of sump-perfor-i mance. Performance parameters -- void fractione pressure i loss coefficient, and swirl angle -- are not well corre-lated with observed vortex formations. - Air Ingestion -- Measured levels of air ingestion, even with air core vortices, were generally less than 2 percent. Maximum values of air ingestion with deliberately, induced swirl -and blockage conditions were less than 7 percent for j horizontal inlets and 12 percent for vertical inlets; these high levels always occurred for high flow and low submergence (F generally greater than 1.0). For submergences of 8 feet or higher, none of the configurations tested indicated air-drawing vortices ingesting more than 1 percent over the entire flow range even with severe' flow perturbations. Swirl (measured 14 diameters from suction inlet) -- Flow swirl within the intake pipes, with or without flow pertur-bations, was very low. In almost all cases, the swirl i angle was less than 4*, an acceptable value for RHR and CSS pumps. The maximum value for severely perturbed flows was about 8' and occurred during the screen blockage test series. i Sump Head Losses ---Suction pipe intake pressure loss coefficient for most of the tests, with and without flow perturbations, was in the range of 0.8+0.2 and agreed with recommended hydraulic handbook values. 3.4.3. Sump Performance During Accident Conditions (Perturbed Flow) i l Screen Blockage -- Screen blockages up to 75 percent of l the sump screen resulted in air ~1hgestion levels simitar to those noted under " Air Ingestion" above. Nonuniform Approach Flow Distributions -- Nonuniform approach flows, particularly streaming flow, generally increased surface vortexing and the associated void fraction. ( Drain and Break Flow -- Drain and breakflow effects were generally found not to cause any additional air-ingestion. They reduced vortexing ' severities by surface wave action. Obstructions -- Obstructions g2 ft or less in cross-section) had no influence on vortexing, air withdrawals, swirl, or inlet losses. 58

l 1 Transients -- Under transient, start-up conditions, momentary vortices were strong, but no air-core vortices giving withdrawals exceeding 5 percent void fraction (1 minute averags) were observed. 3.4.4-Geometric and Dasign Effects (Unperturbed Flow Tests) In general, no consistent trends applicabl'e for the entire range of tests were observed in the data between the hydraulic response of-the sump (air withdrawal, swirl, etc. ) and secondary j geometric parameters. However, for 'somte ranges of flow and submergences, the following observations are applicable: Greater depth from containment floor to the pipe center-line reduces surface vortexing and swirl. Lower approach flow depths with higher approach veloc-ities may cause increased turbulence levels serving to dissipate surface vortexing. 4 There is no advantage in extending the suction pipe beyond 1 pipe diameter from the wall. Suction pipe inlets located with less distance to the sump wall and greater pipe spacing reduces vortexing i and swirl. i 3.4.5 Design or Operational Items of Special Concern in ECCS j Sumps Vertical Outlets -- Comparison of vertical outlet data to corresponding horizontal outlet data showed some, but no major differences, in hydraulic performance of vertical outlet sumps'and horizontal outlet sumps of the same geometry and flow conditions: - average vortex types agreed within + 1; air withdrawals were somewhat higher for i vertical outlet sumps, usually within 1 percent (30 minute t averages) and 4 percent (1 and 5 minute averages);-swirl l angles differed only within + 1 degree. As in the case with horizontal outlets where sump performance was best with pipe projections close to the wall, vertical pipe outlets with perturbations performed best when placed close to the wall rather than at the center of the sump. Cover Plate -- A solid top cover plate-over the sump was effective in suppressing vortices as long as the cover plate was submergedJand proper venting of air from under-i neath was provided. No air-drawing vortices were observed for the submerged cover plate tests, and no significant changes in swirl or loss coefficients occurred. i l l 59 I

' Elevated Water Temperature --Changing water' temperature over the range from 40'F to 167'F had no significant ef fect on ' horizontal outlet sump performance' parameters. Vortex Suppressors p Cage shaped vortex suppressors made of floor grating to form cubes 3 and 4 ft on a side, and single layer horizontal floor grating over the entire sump area, were both found to be i effective in suppressing vortices and reducing air-ingestion to zero.- These suppressors were tested using 12-inch outlet ' pipes, and with-the water levels ranging from 0.5 to 6.5 ft above the top of the suppressors. Adverse screen blockages were used in - conjunction with sump configurations which produced considerable air-ingestion and strong vortexing without the suppressors; thus, suppressors' effectiveness were tested when hydraulic conditions were least desirable. The suppressors also reduced pipe swirl and did not cause any significant increase in inlet losses. Both the cage shaped grating suppressors as well as l the horizontal floor grates were made of standard 1.5 inch floor grates. r Tests on a cage shaped suppressor less than 3 ft on a side j indicated the existence of air-core vortices for certain ranges i of flows and-submergences, even though air-withdrawals were found reduced to insignificant levels. Either properly sized cage shaped suppressors made of floor grating, or' floor grating over the entire sump area, may therefore be used-to reduce air-ingestion to zero in cases where the sump design and/or approach flow creates otherwise undesirable vortexing and air-ingestion. Single Outlets Two. sump configurations (4 ft x 4 ft and 7 ft x 5. ft in plan, both 4.5 ft deep; 12 inch outlets) were tested under unperturbed (uniform) and perturbed approach flows with screen. blockages up to 75 percent of the screen area. For both the l configurations, unperturbed flow tests indicated air-withdrawals were always less than 1 percent by volume for the entire range of tested flows and submergences (F = 0.3 to 1.6). Even with perturbed flows, zero or near zero air-withdrawals were measured in both sumps for Froude numbers less than 0.8, suggesting insignificant vortexing-problems. For Froude numbers above 0.8, a few tests indicated significantly high air-withdrawal (up to 17.4' percent air by volumer 1 minute average) especially for the smaller sized sump. Measured swirl values in the pipes were insignificant for both the tested sumps, being in the range of 2 to 3 degrees even with flow perturbations. The inlet loss coefficients for both sump configurations were in the expected ranges for such protruding outlets, 0.8 + 0.2. l' 60

' Dual-Outlet Sumps With Solid Partition Walls Four dual-outlet sump configurations (one 20 ft x 10 ft sump with 24-inch-diameter outlets and three 8.ft x 10 ft sumps with

24. inch, 12 inch and 6 inch outlets,_respectively) were tested with solid partition walls in the sumps between the pipe outlets

+ ~and with only one outlet operational. None of the tests indicated.any significant increases in--vortexing, air-withdrawls, swirl, or inlet' losses compared to dual pipe operation without partition walls. :Thus, providing a partition wall in a~ sump should not cause any additional problems when only one pipe.is operating.- Bellmouths at Pipe Entrance p Limited tests on a sump configuration were conducted with and without a bellmouth attachment to the 12 inch outlets. Adding bellmouths at the ' pipe entrances did not show -any signi-ficant changes. in the vortex types, air-withdrawals,_and pipe swirl compared to those which otherwise existed under the same hydraulic conditions. Up to about 40 percent reduction in l inlet losses was noticed with the addition of a bellmouth. BWR Suction Pipe Inlets The hydraulic performance of three representative BWR -Residual Heat Removal System suction _ inlet configurations; namely, Mark I, Mark II, and Mark III designs, were investigated over j a Froude number range of from about 0.2 to 1.1 under both. unperturbed-(uniform) and perturbed approach flow conditions. ~ I Zero air-withdrawal was measured for both configurations at Froude numbers equal to or less than O.8 under all tests approach flows. At a Froude number above 0.8, under perturbed approach flows, the Mark I design (single inlet with conical strainer) allowed air-core vortices _ drawing up to 4 percent' air by volume (1 minute average), while-the Mark II"and Mark III design (which had a " tee" inlet with conical strainers on each end) showed air-withdrawls only up to 0.5 percent by volume (1 minute average). Swirl levels in the pipe were found to be about O to 3 degrees for the Mark I design and 2 to 7 degrees for Mark II and Mark III design. The inlet loss coefficient, including entrance and strainer losses (and " tee losses," if applicable), was determined to be about 1.0 for Mark I design and 1.7 for Mark II and Mark III designs, expressed in terms of suction pipe velocity head. Scale Model Tests To evaluate the use of reduced scale hydraulic models to determine the performance of containment emergency sumps and to investigate, in particular, possible scale effects in modeling the hydraulic phenomenon of concern, a test program involving 61 ~-

two reduced scale models (1:2 and 1:4) of a full size sump (1:1) was undertaken (Reference 22). The test results show that the hydraulic models predicted the hydraulic performance of the full-sized sump; namely, vortexing, air-ingestion from free surface vortices, pipe flow swirl, and the inlet' loss coefficient. No scale effects on vortexing or air-withdrawals were apparent within the. tested range for both model s. However, an accurate prediction of 2 pipe flow swirl and inlet loss coefficient was found to require that the approach flow Reynolds number and the pipe Reynolds' number be above certain limits. Based on these results, it is concluded that properly designed and operated reduced scale hydraulic models of geometric scales 1:4 or larger could be used to properly evaluate the hydraulic performance of a sump design. Evaluations of sump hydraulic model studies conducted in the past can be derived from this series of tests. Pump Overspeed Tests Two 8 x 10 x 4.5 ft. sumps (one with horizontal outlets; one with vertical outlets) were tested at higher flow rates to simulate pump overspeed or run-out (to Froude number = 1.6) conditions. No strong air-core vortices were observed with air-withdrawals greater than 1 percent (1 min or 30 min averages). ~ Maximum recorded pipe swirl angle was 0.9* (at 14.5 pipe diameters from entrance); inlet loss coefficients ~ averaged l 0.8 (Reference 23). l l 62 i

4.0 INDEPENDENT PROGRAM. REVIEWS Program reviews were. conducted before and during key ~ phases' ~ of the. work reported in Chapter 3. These reviews were performed for the purpose of soliciting comments'and technical concerns about the program's direction and goals from. experts. not con-nected with the, implementation and execution of TAP A-43. The o reviewers weret selected'from among the foremost authorities in - each of the areas reviewed. Two reviews were held; they were-sump hydraulic performance insulation debris calculational methods effects 4.1 Sump Performance Review The review consisted of two panel meetings.* The primary purpose of the first meeting, held March 17,.1981, was to intro-duce in detail the program plan and initial test results. The second' meeting, held June 4, 1981, was primarily for reviewer response and comment.i Additionally, at_both meetings the reviewers =were provided with preliminary program redirections, and were requested to comment on results to~date and give an -analysis of the proposed future program plan. overall,'the reviewers approved'of the program, the experimental test plan, its conduct, and data analysis. They concluded that the program and its directions were appropriate for resolving the sump performance issues. In direct response to reviewer comments, the temperature tests were performed immediately following the first 25 config-urations, and, therefore, earlier-in the' program than originally planned. l l L

Meetings were held on March 17, 1981, at Germantown, Maryland, and June 4, 1981, at Alden Research Laboratory of WPI, Holden, Mascachusetts. ' Review attendees and their affiliations were as given below:

P. Tullis/ Utah State University; D. Simons/ i Simons, Li and Associates; R. Gardiner/ Western Canada Hydraulic Laboratories; D. Canup/ Duke Power Company; W. Butler /U.S. Nuclear l Regulatory Commission; S.-Vigander/ Tennessee Valley Authority (TVA); i J.; Kennedy / University of Iowar R. Letendre/ Combustion Engineering, Inc. R. Letendre did not attend the meeting of June 4, 1981. i ormal written response and comments were requested at the close F of the second meeting. These responses are available through the office of Light Water Safety Research, Department of Energy, Washington,-DC. 63

L Divergent opinions emerged during the review concerning the .potentialsfor pump performance degradation when the fluid temperature;was near saturation. Some concerns were expressed-regarding the possibility of. degraded pump performance due to. cavitation or.the release of dissolved air into the water in the -cuction. lines leading to the pumps. Other opinions suggested that pump performance should be satisfactory at coolant temperatures near saturation,.because the' solubility-of. air in water-is low i near saturation.and, provided cavitation were not occurring in the pump,'any voids would collapse due to the static pressure increase t with-depth in the sump. These collapsing bubbles would then ~ form a_ turbulent environment and inhibit surface vortex activity. The pump issues raised by the reviewers, although not pertinent to the sump hydraulics program, are a part of~USI A-43 and have been addressed and resolved (see Section 3.2). The experimental research program did not examine the effects on sump systems of temperatures near saturation. Temper-ature effects were examined to the limits of.the capacity of the-experimental facility.(about 165*F)..However, up to that limit, no temperature effects on sump system performance were detected. 1 An area of general peer review group agreement was that sump system performance, with respect to air entrainment, could be improved in most sump configurations by the addition of a vortex suppression device (s). One reviewer, however, commented that such n a device (s) might be removed during some phase.of reactor opera-tions and not be replaced. _Such a possibility, in his judgnent, was sufficientijustification for an experimental research program that would allow the development of adequate sump design guidelines ) that were-based upon justifiable physical criteria (in the absence of vortex suppressors). The results of the studies provided in Section 3.4 confirm the usefulness of vortex suppressors in the improvement of sump system performance and, further, provide i hydraulic results for developing acceptable sump design' guidelines. ( The adequacy of recirculation sump pumps for performing reliably when air / water, mixtures are present and the long-term cooling function required of'the ECCS were matters of some concern to the review group. These' concerns have been resolved by the development of sump design guidelines which take into account pump performance specifications. 4.2 Insulation Debris Effects Review I The purpose of this review was to determine the adequacy of methods-(described in Section 3.2 and in detail in Reference 5) j' to conservatively estimate quantities of insulation debris that j might be produced in containment, its transport and its potential -for sump screen blockage. 4 i 64 i ) \\ . - - _ _ - -. _ - -. - - - _ _ _ - _ _ _, _ -. _. _ _.. - -, -.... _.,.. _,, - - _.,. -._ _.. -,-. _ _ - ~..... ~

+e-The-review was conducted in two phases. In the. initial -phase, a draft report describing the methods was provided to peer-panel and other. reviewers

to solicit their comments.

-Reviewers provided highly useful criticisms and comments with recommendations for improvements in the physical basis'and rigor of the development. ~ L As a consequence of the reviews,;the draft' document was i modified to accommodate the. comments of the reviewers. The modified. document was then transmitted to the reviewers who were l then requested to prepare comments for a formal peer panel review, the second phase of.the review process. Formal peer panel review took place at NRC Headquarters on March 31, 1982. Panelists Kennedy and Canup were unable to attend ~ Lthe meeting. 'A number of attendees, in' addition to; peer panel n9mbers, participated in the review.t Questions'that were raised-l - during the meeting and their. disposition are given below:

1.

It was observed that under some circumstances, the amount of i debris generated with the potential to migrate to the sump could be greater than that estimated in the draft report. It was-resolved by determining that the report would require the selection of those pipe break locations and jet targets that . ould generate the maximum of potentially transportable w debris without regard to initial blowdown and transport 1 direction. I 2. Questions were raised about a) the applicability,of the jet model used in the debris generation portion of the report, b) the assumption of uniform distribution of debris across the face of the jet and, c) the use of a 0.5 psi stagnation i ~ pressure cut-off for debris generation.. Resolution of 2.a) l l

Peer panel reviewers were:

R. Gardiner/ Western Canada Hydraulic Laboratories; D. Simons/Simons, Li & Associates, Inc. ; D. Canup/ I Duke Power Company; R. Mango / Combustion Engineering, Inc.; P. Tullis/ [ Utah State University; J. Kennedy / University of Iowa; W. Butler / l U.S. Nuclear Regulatory Commission; and S. Vigander/ Tennessee Valley Authority. Other reviewers included G. Weigand/Sandia and R. Bosnak, G. Mazetis, and T. Speis/U.S. Nuclear Regulatory L Commission.,Their written review comments are available through The Division of Safety Technology, U.S. Nuclear Regulatory Commission, Washington, DC. Tother attendees were S. Hanauer/NRC; K. Kniel/NRC; C. Liang/NRC; P. Norian/NRC; F. Orr/NRC; A. Serkiz/NRC; J. Shapaker/NRC; G. Hecker/Alden Research Laboratory; E. Gahan/ Burns and Roe; J. -Wysacki/ Burns and Roer W. Swift /Creare, Inc.; P. Strom/Sandia; and 0.'Weigand/Sandia. 65 i f'm

L e n. c; ,s was ' arrived at by. agreement that a modified Moody jet model - (Reference 17 ) ~ would be allowed to model the jet. It was~ agreed that the stripping of all insulation from(plant-and ' piping within>the crane wall and within the jet-represented a conservative treatment of insulation debris generation. / I Discussions'on Item 2.b) concluded that a definite"$robability existed - that debris distribution across the face of the jet would.not be uniform. It' was agreed that a distribution of debris across the jet-face;would be provided that would -represent the geometric di'stribution of insulation targeted by the jet in the contaisment. In addition, because of i uncertainties in jet transport to walls, itsnas agreed that the quantities of debris estimated to exit through crane' wall openings would be doubled ovbr,those quantities which would have been calculated in the; draf t report.. The use of a 0.5 psi stagnation pressure cut-of f -(Item 2.c)), for insulation damage was questioned by a number-of reviewers. Technical views were put forward by a Sandia staff member on the expected performance of jets under LOCA conditions. He stated that centerline stagnation pressures above'15 psig could be expected for at least five diameters downstream'of. high energy, high pressure breaks. An AEC. report (The Effects of Atomic Weapons, G. Glasstone, ed.) was' cited by Burns and Roe as the origin of the cut-of f estimate for debris genera-tion. Alden Research Laboratory reported on preliminary experiments at ARL that have shown that little insulation , damage occurred to fibrous insulation assemblies up to 6.5 ~ psi water jet pressures. It was agreed that the 0.5 psi stagnation pressure represented a conservative treatment for the' onset of insulation debris generation. It was further agreed that the assumption that all insulation within the jet cone would be transformed to insulation debris was conservative. The last assumption was chosen to represent-the volume within which insulation debris would be generated under'the treatment provided in Reference 5. The results'of work performed subsequently on the issues are provided in Section 5.3 of this report. i 3. Discussions were held on the physical accuracy of-the model in representing pipe whip, pipe impact, the directi6n of motion of dislodged insulation and its tra'jectory. 'It was first pointed out that the quantities of insulation generated by this mechanism would amount to 10 percent or less of that generated by jet forces. It was further pointed out that the ~ treatment in the report was designed to conservatively scope the problem, as opposed to providing detailed descriptions of system dynamics. It was agreed that the use of the treatment in the report would conservatively estimate the quantities of insulation debris produced by a minor contributor 'o debris t production and, as such, was satisfactory. 66

,A,_ 8 ~ p ,f ~ ^' s ./- r m. ,s C: 4.-l Questions wer raised on,the treatment of long term transport ,A~' following blowdown. These questions related to: .. + ~ c / Da) recirculation-flow velocities within containment, 7 b) hydraulic lift provided to sunken debris, c) drawdown of floating debris onto less than fully pubmerged sump screens'(ice-jam effect) and, ^ le d) transport me.chanisms of sunken debris, such as tumbling ^"and sliding.'. i In the-resolution' 6f 4. a), agreement was reached to account ^ for obstructions in flow paths and subsequent flow expansion. Agreement was reached:on Item 4. b) horizontally oriented if lift were to be approximated by drag for horizontal debris, .zero for vertically oriented. debris and. disregarded for tumbling debris.'- Item 4. c), was recognized as a potentially important mechanism for screen blockage. It. will be treated by established methods available in the literature. Tumbling 'and other transport mechanisms, as'noted under Item

4. d), could s,ignificantly affect the movement of. debris

,. towards screens. Panelists agreed to treatments which they considered to be_ conservative in dealing with debris movement via these nacha'nisms. 4 5. Argdments were raised that a period of debris transport intermediate to short to^em transport and long term transport l (as defined here) might exist. It was postulated that trane-port during such an interim period might seriously affect potential sump blocka,ge. Inasmuch as the report assumes . that all floating debris reaches the sump, such an interim ,,_ migration period would'not affect the consequences of such L l transport. With respect to debris of density equal to or greater than unity and its transport, discussions brought ,out that-the likelihood of a significant effect during such an interim period would be minor, flow patterns would show no preferential transport toward the sump and entrainment would be higher in the recirculation mode than in the interim id ,per o. 6. An issue,that failed to be resolved was the behavior of fibrous insulation in its migration toward a sump and the potential for-blockage by such material. As an issue, this problem has bean indicated to exist at only a few plants and is, consequently, plant specific. Nevertheless, it was an open issue at the time of the meetings. Following the meetings, 67

experimental studies were conducted at Alden Research Laboratory to estimate stagnation pressures required for the onset of debris-generation for nonencapsulated mineral wool and fiber-glass-insulations'(Reference 6), the transport characteristics of such debris and the pressure losses at sump screens caused by the accumulation of fibrous debris on screens (Reference 7). These findings are reflected in the findings provided in Section 5.3 of this report. All panelists, excepting S. Vigander of TVA, concluded that the use of the methods discussed would result in conservative estimates of sump screen blcckage. Vigander commented that while tue was of the opinion that the treatment would yield conservative, perhaps ultra-conservative, results, he could not with certainty arrive at that conclusion. He suggested that uncertainty analyses be conducted to establish the levels.of conservatism (if any) that are provided in the development. Other panelists agreed. that quantitative or qualitative error analyses would be desirable, although the~needs for such analyses were deemed not to be immediate or pressing. l l I l l l l l ~ l 68

5.0

SUMMARY

OF SUMP PERFORMANCE TECHNICAL FINDINGS 5.1 General Overview The containment emergency sump should be evaluated to determine design adequacy for providing a reliable water source to the ECCS and CSS pumps during a post-LOCA period. Both sump hydraulic performance under adverse conditions, and potential LOCA-induced insulation debris effects require adequate technical assessment to assure that long-term recirculation can be maintained. Typical technical considerations are shown in Figure 5.1. Each major area.of concern--pump performance, sump hydraulics, and_ debris generation potential--can be assessed separately, but the combined effects of all.three areas should then be assessed to determine the overall effect on the NPSH requirements-of the pumps. The sections below summarize technical findings and provide concise data sets. 5.2 Sump Hydraulic Performance ' Full scale tests show that adequate sump hydraulic performance is principally a function of depth of water (the submergence level of the suction pipe) and the rate of pumping (suction inlet water velocity). These variables can be combined to form a dimensionless quantity defined as the Froude number: 1 -Froude number = V// gs where t V = suction pipe mean velocity, s = submergence (water depth from surface to suction pipe centerline), and ~ g = acceleration due to gravity. The extent of air withdrawn from the sump by ingestion l is the principal parameter to be determined. Small amounts of air (i.e., j,2 percent by volume) can significantly degrade pumping capacity (References 11, 12, and and 13). Section 3.4 summarizes the results of full scale hydraulic tests. Figures 3.11 and 3.14 show typical void fraction data as a function of Froude number. References 9, 20, 21, 22 and 24, provide more detailed results from the test program at ARL. Generally, smnp design acceptability should be based upon j, 2 percent air ingestion to assure adequate pump performance. 69

Pumps Sump Design Debris j

Pump Design and,Oper.
Geometric Details
Types, Quantities, and Characteristics Location of Insulations
Incation in Plant kployed j
Bump and Suction Piping and Layout
Screens, Guards, etc.

' Containment Layout and i Break Locations

Air tngestion Effects
Hydraulic Characteristics I
- Air Ingestion
Estimating Quantities i
Cavitation Potential
- Swirl in Pipe of Debris l
Inlet Design
- Number of Inlets I
- Temperature Effects
Water Levels
Blowdown Effects
Temperature, e tc.

l

Particulate and Debris along-Tern Debris l

Ingestion Effects Migration

NPSH Requirements
Potential for Senp i

Screen Blockage i } i i l i i l

Air Ingestion Effects
Hydraulic Acceptability
Quantity and Type of l
NPSH Required
Need for Vortex Suppres-Debris i
Piping Layout sion?

Screen Blockage l

NPSH Available
Sump Head Loss
Ioss of Available NPGH I

t I Is There Adequate NPSH Margin 1_ m ' (Under All Postulated Conditions?[ Figure 5.1. Technical Considerations Relevant to Containment Emergency Sump Performance i I l i

Sump hydraulic performance can, therefore, be assessed as follows: 1. Table 5.1 provides technical findings for sump designs where negligible (or zero) air ingestion would exist. 2. The adequacy of the sump geometric design and hydraulics performance based on air ingestion levels of < 2 percent l can be determined using Tables 5.2, 5.3, and 5.4. 3. Vortex suppressors provide a means to achieve zero air i ingestion. Vortex suppression devices such as those shown in Table 5.6 have been shown to reduce air ingestion levels to essentially zero. 4. Table 5.5 provides additional information pertinent to screens and grates that would affect hydraulic performance. 5. Elevated water temperature has been shown to have negligible effect on sump hydraulic performance in full scale tests conducted at temperatures up to 165'F. l l i I i 71

TABLE 5.1 Zero Air Ingestion Hydraulics Design Findings Item Horizontal Outlets Vertical Outlets Minimum Submergence, s (ft) 10 10 Maximum Froude Number, F O.25 0.25 Maximum Pipe Velocity, U(ft/s) 4 4 , cover PLAM l g g g... A A ted l l Geometric Findings

Item Horizontal Outlets **

Vertical Outlets ** Aspect Ratio 1 to 5 1 to 5 Elinimum Perimeter. dual: 36 ft; dual: 36 ft; single: 16 ft single: 16 ft (B-ey)/d >3 <1 c/d > 1.5 > 0; <1 ey/d > 0; < 1 > 1. 5 l Minimum Screen Area dual: 75 ft2; dual: 75 ft2; single: 35 ft2 single 35 ft2

See Table 5.3 for definitions.

The geometric findings were established using experimental results from References 9, 21, 22, and 23 and the variable ranges over which such data was taken. C* dual = dual outlet design, single = single outlet design. 72

TABLE 5.2 Hydraulics Design Findings Item Horizontal Outlets Vertical Outlets Dual l Single Dual l Single Minimum Submergence, s (ft) 7.0 8.0 8.0 10 Maximum Froude Number, F 0.53 0.40 0.41 0.33 1 l Maximum Pipe Velocity, U(ft/s) 8.0 6.5 7.0 6.0 Maximum Screen Face Velocity (Blocked and minimum subner-3.0 3.0 3.0 3.0 gence) (ft/s) Minimum Water Level suf ficient to cover 1.5 f t of (inside screens and grates) open screen Maximum Approach Flow Velocity 0.36 0.36 0.36 0.36 (ft/s) Sump Loss Coefficient, CL 1.2 1.2 1.2 1.2 -2.47 -4.75 -4.75 -9.35 Air Withdrawal, as, ao i as=ao + a1 x F al 9.38 18.04 18.69 35.95 (% air by Volume) l l F* " **E!'" ty gg Magytt W AMORATES l An h I 73 \\

i l TABLE 5.3 Geometric Desian Envelope rindinos l I l Size and Placement l Inlet Position ** Screens & Grates l l l l l l l l l Min. Screen Area l Aspect Ratio l Min. Perimeter l e /d l (B-e )/d l c/d l b/d l f/d l e /d ! (Plane face) y y x l i 1 I s { j ul Dual l 1 to 5 l 36 f t l>0 l l l l>4l 1.5*] 75 f t2 { o el l l 13 l > 1.5 l > 1 l l or l 4tl l l l l l l l l o8l Single l 1 to 5 l 16 ft l11 l l l l l > 1.5 l 35 ft2 a: ,.e l Dual l 1 to 5 l 36 ft l 1.5*l l>0 l l>4 l 1.5*l 75 f t2 i $jl l or l 11 l l>1 l l or l ~ ~ 53l l l l l l l l U# 1 to 5 l 16 ft l> 1 5 l l11 l l l > 1.5 l 35 ft2 >5l Single l 1 I l l l l I I L .. SCREENS 1 -J.--_____________=- ], . ["=* ,ll l = = = _ _ _______==_g l l ,l l l m, l, l. a. l j' I Definitions l

o. l l

3 jg -se-e n l P--- f 6 41 l I + l t= _- I 1 4 d : =). i_=======;

=== L

;=====

~==es l t1seneens ame : l scamens ase : ent.Tes l W onam l aspect navio, an-un l gy$c l l anemum punesatum p.an= se.+ se !g ,m i l I

- Preferred location.
Dimensions are always measured to pipe centerline.

1

I l TABLE 5.4 Additional Considerations Related To Sump Size and Placement

1.

Aspect Ratio, see Table'5.1. mi 2. Minimum Sump Perimeter, -,,a see Table 5.1. n 3. Sump clearance of 4 ft l between the screens / grates I and any wall or obstruction j of length Jt equal to or ,__.a <___-"JE6&EL 6;T-- greater than the adjacent screen / grates length (Bs g L. or Ls)+ 4. A solid wall or large obstruction may form the -- -----.__ = = = v f boundary of the sump on -{ f one side only, i.e., the .-sum m4 ) sump must have three (3) go $ f>g sides open to the approach '1 ~ i flow. l l l g-_-----w:=e.

n. -=

p mensmann age c. I-ana m L l 4 4" F l

These additional considerations are provided to ensure that the experimental data boundaries (upon which Tables 5.2 and 5.3 are baseB) resulting from the experimental studies at Alden Research Laboratory are noted.

75

TABLE 5.5 Screen, Grate, and Cover Plate Design Findings

1.

Minimum plane face screen area, see Table 5.2. 2. Minimum height of open screen should be 2 feet. 3. Distance from sump side to screens, 9st 9s may .-oous cena puva-be any reasonable value. p,- 4. Screens should be 1/4 Q . nyg inch mesh or finer.

=

q [;i q'g ammai H l f 5. Gratings should be ~ g: g r vertically oriented 1 to I p.- 1-1/2 inch standard i g-floor grate or equivalent. di j 6. The distance between the screens and grates shall be 6 inches or less. 7. A solid cover plate above the sump and extending to the screens and grates is required; the cover plate must be designed to ensure the release of air trapped below the plate (a cover plate located below the minimum water level is preferable). l

These additional details are pertinent to the Alden Research Laboratory's full scale tests and were found to yield satisfactory sump hydraulic performance.

i l l 76

TABLE 5.6 Findings For Selected Vortex Suppression Devices

1.

Cubic arrangement of essa vw co m - standard 1-1/2 inch I ,T or deeper floor I p:c,4j. #"T*# 7" grating (or its I equivalent) with a a.. uquql g characteristic ^ length, Ay, that is p__ ,.., 1,., m A > 3 pipe diameters; the top of the cube y must be submerged a minimum of 6 inches below the minimum water level. Non- , ___ _ __:=== _ _ _ _ o=_"il cubic designs, where I Av is J 3 pipe diameters er a m i for the horizontal h[!$ f, 1, h g_ j the depth and distances "'Y j upper grate, satisfying J:::4:k::_______q__ a to the water minimum water surface given =>ecomms m " W" for cubic designs are acceptable. 2. Standard 1-1/2 inch l soyP tw com-T" or deeper floor i.. Tif d m grating (or its f "AL equivalent) located d m horizontally over l ly%W n'" "^ ** the entire sump and containment floor p_; inside the screens and locatad between 3 inches and 12 inches below the minimum water level.

These types of vortex suppressors were tested at Alden Research Laboratory and have demonstrated the capability to reduce air ingestion to 0%, even under the most adverse conditions simulated.

77

l 5.3 Debris Assessments Debris assessments should consider the initiating mechanisms i (pipe break locations, orientations, and. break jet energy content), evaluation of the amount of debris that might be s generated, short-and long-term transport, the potential for. sump screen blockage, and head. loss that could degrade available NPSH. Table'5.7 outlines key considerations requiring evaluation. Evaluation of potential debris effects requires the following information: 1. Identification of major break locations (per SRP 3.5.2) and jet energy levels. 2. Types, quantities, methods of fabrication and installation, mechanical attachments, and hygroscopic characteristics of the-insulation employed on primary and secondary system piping, reactor pressure vessel, and major components (e.g., steam generators, reactor coolant pumps, pressurizer, tanks, etc.) that can become targets of expanding jet (s) identified under Item (1). 3. Containment plan and elevation drawings showing high energy line piping runs, system components, and piping that are sources of insulation debris, structures and. system equipment that become obstructions to debris transport, sump location (s), L and drawings showing sump design details, including trash j rack and screen details, as well as suction piping orientation. 4. Expected water levels during recirculation and RHR and CSS i pump NPSH requirements versus flow rate. t Generic findings regarding debris that might be generated, transported and lodged against sump screens (and the plant specific j dependence of these phenomena) are discussed in Section 3.3 ~- and presented in' detail in References 5, 6, and 7. The following-paragraphs summarize the findings: i 1. Break locations, type and size of breaks, and break jet targets are major factors to consider in the estimation of l potential quantities of debris generated. The break-jet is a high energy two-phase expansion that is capable of shredding insulation and insulation coverings into small pieces or fibers by producing high impingement pressures and large jet loads. 'A discussion comparing two-phase jet j phenomena with single-phase incompressible jet phenomena i is given in Appendix C. 2., Mirror (reflective metallic insulations) and totally encapsulated insulations do not appear to pose screen blockage problems. However, if the sump location can be directly targeted by an expanding break jet, a close examination should be made of possible jet load damage to such insulations and their possible prompt transport to the sump. 78 l l

r 1 TABLE 5.7 Debris Assess' ment Considerations

CONSIDERATION EVALUATE 1)

Debris Generator O Major Pipe Breaks & Location (Pipe Breaks & Location O Pipe Whip & ' Pipe Impact as identified in SRP O Break Jet Expansion Envelope 4 section 3.6.2) (This is the major debris-generator) 2) Expanding Jets O Jet Expansion Envelope O Piping &. Plant Components Targeted (i.e., steam generators) O Jet Forces on Insulation O Insulation Which Can Be Destroyed or. Dislodged by Blowdown Jets. O Sump Structure,(i.e., screen) Survivability 3) Short-Term Debris Under. Jet Loading Transport (transport O Jet / Equipment Interaction by blowdown jet O Jet / Crane Wall Interaction forces) O Sump Location Relative to Expanding Break Jet 4) Long-Term Debris Transport O Containment Layout & Sump Location (transport 1to the sump during O Heavy (or " Sinking") Debris the recirculation phase) O Floating Debris O Neutral Buoyancy Debris l 5) Screen Blockage Effects 0-Screen Design (impairment of flow. and/- O Sump Location or NPSH margin) O Water Level Under Post LOCA Conditions j 0 Flow Requirements Key Elements for O Estimated Amount of Debris Assessment of That Can Reach Sump Debris Effects ,O Screen Blockage O AP Across Blocked Screens l

per debris estimation methods described in Section 3.3 79

. ~

L '3. Low density insulations, such as calcium silicate and i unibestos, have closed cell. structures and. float. They 'are unlikely to impede flow through sump screens. Partially l. submerged screens should, however, be evaluated for pull-down of floating 1 debris. Low density hygroscopic insulations that, upon being wetted, have equilibrium densities greater 1 than water require plant specific determinations of screen blockage effects. 4. Nonencapsulated insulations (particularly mineral wool and fiberglass' materials) have been shown to present the possibility for high screen blockages or large screen blockage effects (References 5, 7, 14, and 15). These materials, even if deposited in relatively small thickness i layers onto sump screens (e.g., on the' order of an inch or less), can result in high pressure drops. For plants employing reflective metallic, nonhygroscopic, and/or l in particular fibrous, nonencapsulated insulations, the potential for screen blockage should be calculated using the methods provided in Appendix B, Estimating Debris Generation, Transport, and Sump Screen Blockage Potential. Appendix B, in Tables B.1 and'B.2, gives short quick methods for assessing the potential for sump screen blockage, and also gives, in Figure B.1, an involved procedure for calculating the effects of insulation debris from detailed i plant specific calculations. Both the short methods and j the more involved methods were developed from information l provided in References 5, 6, 7, 14, and 15. Where plant specific determinations of screen blockage effects are required, the methods provided in Reference 5 should be followed. l 5. <4 Pump Performance Under Adverse Conditions The pump industry historically has determined net positive suction head requirements for pumps on the basis of a percentage degradation in performance. The percentage is arbitrary, but j generally 1 percent-or 3 percent. A 2 percent limit on allowed air ingestion was selected here because data show that air ' ingestion levels' exceeding 2 percent has the potential to produce significant head degradation. Either the 2 percent limit in air ingestion or the NPSH requirement to limit cavita-tion may be used independently when the two effects act indepen-dently. However, air ingestion levels less than 2 percent will affect NPSH requirements. In determining these combined effects, the effects of air ingestion on NPSH required must be'taken into account. A calculational method for assessing pump inlet conditions is shown in Figure 5.2. For a given sump design, the following procedure can be followed: 80 _. _, -. _ _ ~, -,.... _, - _....,,.,,,,, - ..._.2.___..__,___._.-----

SUMP GEOMETRY,

SLOCKAGE, FLOW RATE

+ WATER LEVEL II AIR EST YES 88 0 m m, v oUAufv NR { PtPING w LD5st$ 2 PUMP ELEVATION w WATER TEMPERATURE CONTAINWENT 4 AIR PARTLAL I PRESSURE VELOC!TY d HEAT AT PUMP lf CALC PUMP MPSHR INLET STATIC + FROM PUMP PRESSURE curve lf CALC NPss AVAILABLE If CALC AIR DENSITY. l NR VOLUME FLOW RATE l i l I Figure 5.2. Flowchart for Calculation of Pump Inlet Conditions i 1 81

1 1. Determine the static water, pressure. at the sump suction pipe af ter debris blockage ef fects have been evaluated. (See .Section 5.3.) Note that the water level in the sump should not be so low that a limiting critical water depth occurs at the sump edge such that flow is restricted into the sump. 2. Assess potential level of sump air-ingestion using criteria set forth in Section'5.2. 3. Determine pressure losses between sump suction pipe inlet and pump inlet flange for the required RHR and CSS flows.. If the pump inlet is located less _ than 14 pipe diameters from suction. pipe inlet, the effect'of sump-induced swirl i should be evaluated. (See Section 3.2.3 and References 2 and 8 ).

4. -Calculate the static pressure at the pump inlet flange.

Static. pressure is equal to containment atmospheric pressure plus the hydrostatic pressure due to pump elevation relative to sump surface level less pressure losses and the dynamic pressure due to velocity. (See Section 3.2.3.) Note that no credit is allowed for containment overpressure per SRP j. Section 6.2. 5. Calculate the air density at the pump inlet, then calculate the air volu;ae flow rate at the pump inlet, incorporating the density difference from sump suction pipe to.the pump. 6. If the calculated air ingestion is found to be less than or equal to 2 percent,: proceed to Step 7. If the calculated air ingestion is greater than 2 percent, reassess the sump design and operation per Section 5.1. 7. Calculate the net positive suction head (NPSH) available. 8. If air ingestion is indicated, correct the NPSH requirement from the manufacturer's pump curves by the following relationship: NPSHrequired(air / water) = NPSHrequired(water) x$ l where p = 1 + 0.50 ap j and ap is the air ingestion rate (in percent by volume) at sthe pump inlet flange. 9. If NPSH available from Step 7 is greater'than the NPSH require-ment from Step 8, inlet considerations will be satisfied. ( 82

If the above review procedure leads to the conclusion that an inadequate NPSH margin exists, further plant specific discussions need to be undertaken with the applicant for resolution of differences, uncertainties in calculations, plant layout details, etc., for resolution of this finding. The lack of-credit for containment overpressure should be recognized as a conservatism which should be assessed on a plant specific basis. 5.5 Combined Effects The findings from Sections 5.2, 5.3 and 5.4 can be ccmbined in' the manner shown in Figure 5.3 to determine overall sump performance. l r 83 i

i i ECCS SUMP DESIGN SUMP DESIGN DEBRIS ANALYSIS T REDESIGN SUMP ATIO P AN e TYPES, OUANTITIES, AND LOCATION OF INSULATION l e HYDRAULICS eG OME N e INSULATION DEBRIS GENERATED e DEBRIS TRANSPORTED TO SUMP ( If l SCREENS & GRATES ARE l NO HYDRAULICS

SCREEN AND GRATE BLOCKAGE l

CORRECT DEFICIENCIES DESIGN CRITERIA AND LOSSES MET e USE VORTEX SUPPRESSORS f a SCALE MODEL TESTS 1r YES KEY SUMP PARAMETERS l e PROVE ADEQUACY OF ARE e SUMP LOSSES DESIGN, e.g., DATA NO GEOMETRIC YES i DESIGN CRITERIA e AIR WITHDRAWAL,as e IN-PLANT DEMONSTRATION i MET

MINIMUM SUBMERGENCE U

I 1

SCREEN AND GRATE LOSSES 3

I e SUCTION INLET CONDITIONS: NO A VES: YES - _ _I P.,T.,V,etc. DEFICIENCY s REMOVED PUMP PERFORMANCE DETERMINE NPSH PARAMETERS LOCATE PUMP AND DESIGN PIPING e CAVITATION AND PARTICULATE e MINIMUM WATER LEVEL e BETWEEN SUMP INGESTION BEHAVIOR AND PUMP e SCREEN AND GRATES LOSSES e PUMP PERFORMANCE CURVES

SUMP AND PIPING LOSSES e AIR INGESTION EFFECTS
PUMP INLET CONDITIONS; P,

p DEFINITIONS T,a,p, V, etc. p p p p " "~ e CONTAINMENT CONDITIONS NPSHA - NPSH AVAILABLE 3r NPSHR - NPSH REQUIRED a - VOID FRACTION (% BY VOLUME) 1 88 O AIR P ESENT = 1 *0 ap > 2% (ap > 0) /. NO j 1r CA TE -*- $ = 1.0 + 0.50a p V IS NO YES SATISFACTORY GRE TER HAN gxNPSHR DESIGN l Figure 5.3. Combined Technical Considerations for Sump Performance 84

] REFERENCES 1. Durgin, W. W., Padmanabhan, M., and Janik, C. R., "The Experimental Facility for Containment Sump Reliability i l Studies," (Generic Task A-43), ALO-132, Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, -1980. 2. Kamath,~P., Tantillo, T., and Swift, W., "An-Assessment of Residual Heat Removal and Containment Spray System Pumps Performance Under Air and Debris Ingesting Conditions," NUREG/CR-2792, Creare, Inc., Hanover, NH, September 1982. 3.

Reyer, R.,.et.

al., " Survey of Insulation Used in. Nuclear Pcwer Plants and the Potential for Debris Generation,"' ~ NUREG/CR-2403, Burns and Roe, Inc., Oradell, NJ, 1981. 3 4.

Kolbe, R. and Gahan, E.,

" Survey of Insulation Used in Nuclear Power Plants and the Potential for Debris Generation," NUREG/CR-2403, Supplement I,, Burns and Roe, Inc., Oradell, NJ, May, 1982. 5.- Wysocki, J. J., et. al., " Methodology for Evaluation of Insulation Debris Effects," NUREG/CR-2791, Burns and Roe, Inc., Oradell, NJ, (In revision). 6. Durgin, W. W. and Noreika, J., "The Susceptibility of Fibrous' Insulation Pillows to Debris Formation Under Exposure to Energetic Jet Flows," SAND 83-7008/NUREG/CR-3170, Alden Research Laboratory, Holden, MA, January 1983. .7. Brocard', D. N., " Buoyancy, Transport, and' Head' Loss of i Fibrous Reactor Insulation," SAND 82-7205/NUREG/CR-2982, Alden Research Laboratory, Holden, MA, November 1982. 8. Weigand, G. G..and Thompson, S. L., " Break Flow and Two-Phase Jet Load Model," Sandia National Laboratories, Albuquerque, NM, Presented at International Meeting on Thermal Reactor Safety, Chicago, IL, August, 1982. 9. Weigand, G. G., et. al., "A Parametric Study of Containment' i Emergency Sump Performance," SAND 82-0624/NUREG/CR-2758, Sandia National Laboratories, Albuquerque, NM, July 1982. lO Hydraulic Institute Standards for Centrifugal, Rotary and f Reciprocating Pumps, 13th Edition, Hydraulic Institute, Cleveland, OH, 1975. 85

11.

Merry, H.,

" Effects of Two-Phase Liquid / Gas Flow on the Performance of Centrifugal Pumps," NEL Cl30/76, 1976. 12. Murakami, M. and Minemura, K., " Flow of Air Bubbles in Centrifugal Impellers and Its Effect on Pump Performance," 6th Australian Hydraulics and Fluid Mechanics Conference, Adelaide, Australia, December 5-9, 1977. 13. Florjancic, D., " Influence of Gas and Air Admission on the Behavior of Single-and Multi-Stage Pumps," Sulzer Research Number 1970, 1970. 14. "Loviisa Emergency Cooling System Model Tests;" no author given, no publication date given; Translated from Finnish, Sandia National Laboratories, Report No. RS3140/81/191, printed December,1981. 15.

Tuokkola, Y.,

"Model Test of the Screen Meshes of the Emergency Cooling System," April 25, 1980; Translated from Finnish, Sandia National Laboratories, Report No. RS3140/81/192, printed December, 1981. 16. Niyogi, K. K. and Lunt, R., " Corrosion of Aluminum and Zinc in Containment Following a LOCA and Potential for Precipitation of Corrosion Products in the Sump," United Engineers and Constructors, Inc., Philadelphia, PA, September, 1981. i 17.

Moody, F.J.,

" Fluid Reaction and Impingement Loads," Specialty Conference on Structural Design of Nuclear Plant Facilities, Vol.1, Chicago, IL, December, 1973. 18. Weigand, G. G., Thompson, S. L., and Tomasko, D., "A Two-Phase Jet Model for Pipe Breaks," Proceedings of the Structural Mechanics in Reactor Technology (SMRT) Conference, Paris, France, August, 1981. 19. Thompson, S. L., " Thermal / Hydraulic Analysis Research Program Quarterly Report, January-March 1981," NUREG/CR-2338, Sandia National Laboratories, Albuquerque, NM, October 1981. 20. Padmanabhan, M., " Containment Sump Reliability Studies (Generic Task A-43) - Interim Report on Test Results," l . Alden Research Laboratory Report No. 59 "1, Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, , June 1981. 21. "Results of Vertical Outlet Sump Tests," Joint ARL/Sandia Report, ARL47-82/ SAND 82-1286/NUREG/CR-27 59, September 1982. i 86

22. Padmanabhan', M. and Hecker, G. E., " Assessment of Scale Effects on Vortexing, Swirl, and Inlet Losses in Large Scale Sump Models," NUREG/CR-2760, Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, June 1982. 23. Padmanabhan, M., "Results of Vortex Suppressor Tests, Single Outlet Sump Tests, and Miscellaneous Sensitivity Tests," (Generic Task A-43 ), Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, September 1982. l 24.

Weigand, G.

G.,

Thompson, S.

L., and Tomasko, D., Two-l Phase Jet Loads, NUREG/CR-2913, SAND 82-1435, prepared i for the U.S. Nuclear Regulatory Commission, prepared by Sandia National Laboratories, Albuquerque, NM, 1983. l t I 87

APPENDIX A PLANT SUMP DESIGNS AND CONTAINMENT LAYOUTS 9 f

d'/ u s g V4

26

./- ,/) r p p ) Nr . 4:. m / 0

n... y" ON

/glQ mn si i \\ / t r .a Shield taall Il .g ,7 g, 4. \\ . /.., /,i: sur sasu2stsee estris to sesah M. 33,,,... Figure A-1. ECCS Sump and Containment Building Layout, Crystal River Unit 3 A-1 l ,yw4 e'

99

4 s'

'* o'

d 4

r,. ,s. s %,,, \\ J$,@ 8 N, d i ?.. %. enmasa'*

p N

7 arr

f..,, ww c s

y i s 0,

.g s

1 } f 1 s \\ over yg gs y ;..h - h ),. n.- eg 1 frae ". - ~ gy,,

5

}' l. I mt*' lP .'. f \\ 5 $ cast \\ 3.%+.- - 815' " ",, n = I

L j

5

k. \\ ; %

%d } ' j\\ s' N' ~ s pt** % g,._.sewis **y,. A 7 p see. Figure A-2* ECCS Sump and Containment Building Layout, Oconee unit 3 A-2 i - ~ . ~ - - -. -.

l

O s' i.u.

4 86 / s/ p*~ o r ys i i ) J N l l \\'- l s ci. Duilding steam Generator (.,.;,, h<r ~ ', }N:s & . Jrassure d Reactnr '. g c p g vessel N / _f 'ewwf l.,- .V. s. + &p .. o 2 -,p l s. steam Generator l Notes hit 1 shows, Unit 2 is a mirror image. Arrows m gg, gg3e6" sateways fer insu3aties echris to reach sump Figure A-3. ECCS Sump and Containment *dnilding Layout, Midland Unit 2 A-3

gsW 1W +, l e b se*y$ ,e + e i .Wy

l '

_en, e n 45 x.= 8uw / . f s. 6' ,8 g,,, o. B"a 'd, Iida["Q) ,j v d '~ ./ l i E O 7 - .s.,' o .y 1 A,'"' It, ge y, r,'..,,_ w i Caela.t O 1 ,g y a.s es 1 g l i.= d Q / l-I / \\ ~,.,"1 J'ta"."'. h [ <,e aste Arrows sher pathumps for Sasalataan estria to remak '815 9 t 1 31.-3' e* l Figure A-4. ECCS Sump and Containment Building Layout, l Maine Yankee [ ( l A-4 l l t.

4' e f e 1 ~ N 4 N I ~. - .y ,/*, t l e. s \\ s l %s% r i / qp --. ann.se aan l 3 fA } I Cl -= l l ~ i l e, '4 / u u Bete: Arrows show pattways for gassistsas embris to sesek see. I Figure A-5. ECCS Sump and Containment Building Layout, Arkansas Unit 2 A-5 . -... -. ~... - - - - - - - -

s x I Ml PottsumE VESSEL STEEL CostTatssesEst? VESSEL PIPillt aPleet MEAK mREAK j LOCAT8001 L0c&T400s AREA AREA D#?WELL .,..a i ( '.*;. i . *. / g.*

SetATlesG AT

a.. e..-

..;.9 y,..; i '**4 acia t.. l unia .,4,,,,,,, [ M AK LOCATIOed ,. ', y GREAM LOCATaose ,L. Sol *-O' AREA AREA P... OmvwtL.L.FLoom JET BEFLECT0ft.' .e n. EL 499-4 PLATE s T m i v.-.- .-.we cs= m I -r=

Tv=u a

i ....... *,.,...p e0.sec0=En ..,.. : ~...; -00 ~e0wn VENTS VENTS a w. .ATER LEVEL 8* E L.464*= 0 /e t ui!r zy w-w: ; f.. 2qp e. *_ g.. e er cc a . E T.ut .1 .,E Ae,.,, '"a" '.:::,=,C. i ^ 6 to ReHt . f.a h EUCTeced SvCT10st r.:n..

c..r.

.e::. ....: r. s...., .. r:

n...e.1,

p..;

..'..:. ;;g.... :.. n. n.:L..... :. : *..***- E;:.

anTman, A,Eu,,e.e,,,,

sk eDi'. e mEAVT est7 STEEL a vuess erTw e esca esacans Figure A-6. Primary Containment Vessel, WPPSS Unit 2-t 1 A-6

APPENDIX B Estimating Debris Generation, Transport, and Sump Screen Blockage Potential ~ Generic evaluations regarding insulation debris generation (due-to LOCA effects), debris transport, sump screen in Section 3.3 of this report and detailed blockage potential and plant layout dependence are summarized in Reference B-1. Follow-up experimental studies which investigated debris buoyancy characteristics, transport, blocked screen head loss E-characteristics and jet load damage effects are reported in y 'Refe~rences B-2 and B-3. These later studies provide data which [ - can be used to bound some of the assumptions in Reference B-1, l -and also to develop a simplified set of screening evaluations to determine if sump screen blockage can occur. The purpose of this ~ appendix is to provide guidance in using results obtained from ~ i the above. The first step in assessing screen blockage is to determine if the types of insulations employed can: a) be transported to the screen (e.g., by recirculation velocities estimated within containment) and b) if such insulation can be deposited on the screen. Table B-1 presents a first round assessment.for screen blockage ~ potential and sets forth three criteria under which debris trahsport due to fluid velocities will be negligible, or non-existent. Use of Table B-1 thus permits a quick determination of lack of screen blockage. It also should be ' clearly noted that Table B-1 does not deal with fibrous insulation ~ effects. l l Tible B-l~ sets forth three criteria to assess debris t

transport potential fo'r the intermediate recirculation velocity ranges excluded in Table B-1, and performs a limiting blocked screen head loss calculation based on three key factors; those

-being: a) that the total volume of the respective insulations transports to the sump screen (if the recirculation flow velocities are high enough), b) that the head losses for the blocked sump screen are calculated from experimentally determined head loss characteristics, and c) that loss of 50% of the NPSH margin can be tolerated for the plant in question. In particular, Table B-2 provides a rapid means to calculate the equivalent volume of fibrous insulation (Vfb) which could be utilized (and assumed transported in total to the sump screen) and for which the screen blockage effects would not exceed 50% of l the NPSH margin required (AP )* m If Tables B-1 and B-2 do not result in acceptable,(or non-existent) sump blockage conditions, then the procedure p outlined in Figure B-1 (which is derived from the-methodology reported in Reference B-1) should be employed for the plant under review. f. B-1 \\

~ s ~ FigureJB-l outlines and provides guidance for following the methods reported in Reference B-1 for evaluating insulation . debris effects. The step-wise procedure described below provides

a. logical order for+ performing the calculational-methods in Reference B-1.

(It is recommended that References B-1, B-2, and. B-3 be' thoroughly read before attempting debris and screen loss calculations.) 1. Pipe break locations and orientations e'e determined for r possible LOCA's in containment.(Box l'of figure). 2.' Three mechanisms for debris generation are considered:- pipe whip-(Box 2), pipe impact (Box 3) and jet impingement-(Box 1 4). .Of these, the mechanism that produces the preponderance of debris -is jet impingement. 3. ,The containment volume intercepted by the jet is determined 1 (conical jet volume) (Box 5). l 4.- A large break jet can-shred insulation at p.ressures of-20 psig and above (Reference B-2). This is approximately equivalent to an. axial distance along-the jet centerline of .7-L/D's from the jet origin-(Reference B-4, based upon a stagnation pressure of 15 MPa and 35*C subcooled liquid). 'The volumes of insulation contained within this part of'the conical jet. volume are to be calculated (Box 6). 5. At points within the conical jet volume where the distance ~ measured along the centerline of the; jet is greater than 7~ L/D's but is less than the downstream point on the h centerline where theiaverage' stagnation pressure of the-jet-L is 0.5 psig, insulation is assumed to be dislodged'in an as-fabricated form..The outer boundary of the cone, corresponding to a stagnation' pressure of 0.5 psig, was established from information in Reference B-1 concerning a lower pressure limit for insulation damage. The volumes of insulation contained within this part of the conical jet volume are to be calculated (Box 7). Note: The results obtained from this calculation will be used to determine the volume of as-fabricated l ~ insulation dislodged; the calculational procedure ^ L then proceeds to Box 17. 6. Within the conical jet volume extending from the jet origin to 7 L/D's (% 20 psig) downstream, determine if encapsulated or nonencapsulated fibrous insulation is l l present (Box 8). 7. If the fibrous insulation described in 6 is present within the volume intercepted by the jet, determine its volume from the as-fabricated dimensions (Box 10). Fibrous ins'ulation located in the conical jet volume between the jet origin and 7 L/D's is shredded. B-2 ,_,_.,m.,_ _-..--_.-.,_.-.---,-..,.,m_

1 8. Determine the. volumes of insulation removed by pipe whip, o PW, pipeLimpact, PI and jet impingement (within 7 L/D boundary), JI. This fibrous portion is to be treated as . shredded fibrous debris.- Volumes are to be determined from as-fabricated dimensions (Box 9). 9. Determine those. volume fractions'of shredded fibrous debris that are.promptly transported by' pipe whip, apw, pipe impact, api, and by jet impingement, aJI, to the sump screen (Box 11). t l 10. Calculate-the maximum flow velocity that_ exists in containment under. recirculation conditions using the tethods provided in Reference B-1. Determin~e whether this flow velocity is sufficient to allow the sunken shredded fibrous debris to migrate to-the sump using the transport information given-in Table B-3 (Box 12). l 11. If the flow velocity calculated from 10, above, is sufficient to cause migration, all the shredded fibrous insulation generated (Vpw + VpI + VJI) is assumed to migrate to the sump screen (Box 13).

12. 'If..the flow velocity calculated from 10, above, is not large enough to-cause migration, prompt transport is the only mechanism for shredded insulation to reach the screen.

The volume of_this material at the screen is apw Vpw + V (Box 14).. V api pI'+ aJI JI 13. _ hen the volume of shredded debris that reaches the sump W screen (either 11 or 12 above apply), the equivalent thickness, t, of shredded debris forming a mat on the sump can be calculated: t = V/Ae, where V is the combined i debris volume and Ae is.the effective unblocked area of L the' sump screen (area available for flow) (Box 15). I Note: Before proceeding to the following step, calculations l provided in Boxes 17 through 22 are required. l l 14. After completing item 5 above, determine the total reflective metallic panel area, Am, contained within the . entire' conical jet volume out to an average stagnation . pressure of 0.5 psig on the jet centerline and determine the as-fabricated-panel area Af of fibrous or other sinkable insulation between L/D = 7 and an average stagnation pressure of 0.5 psig on the jet centerline (Box 17). 15. The maximum containment flow velocity calculated in item 10, above, is referred to, as are the flow requirements to allow debris migration (Table,B-1) (Box 12).. B-3 i i _. ~ - -. _.

16. If the maximum containment flow velocity is not large enough to allow debris to migrate, as-fabricated debris (either fibrous or. reflective metallic) does not reach the sump (Box 18). 17. If the maximum containment flow velocity is large enough to allow the migration of. fibrous as-fabricated insulation or both fibrous and reflective metallic insulations, it is assumed that such insulation (s) become aligned along the sump screen face to a height corresponding to the maximum as-fabricated insulation dimension, HI (see Reference B-3) (Box 19). 18. If only as-fabricated fibrous material migrates to the screen, determine if its equivalent length, A /HI, is f greater than the sump perimeter, P. If only as-fabricated reflective metallic can migrate to the screen, calculate the equivalent length, Am/HI. If both species can migrate, calculate the equivalent length of both, (Af+Am)/HI (Box 20). 19. If the equivalent lengths determined in item 18 above are less than the equivalent perimeter of the sump screen, P, the area not blocked by as-fabricated insulation is A - Ag, or A - Am, or A - (Af + Am), where A is the screen area of the sump (Box 21). 20. If the equivalent lengths calculated in 18 above are greater than the equivalent perimeter of the sump screen, P, the amount of screen blocked by as-fabricated debris can be no more than the area composed of the perimeter, P, multiplied of the insulation by the maximum as-fabricated height, HI, j (see Reference B-3). The area not blocked by as-fabricated l insulation is thus calculated to be A - HP, where A is the r screen area of the sump.(Box 22). 21. Using the equivalent shredded fibrous insulation thickness, t, obtained from 13 above, and the unblocked screen area, obtained from 19 or 20 above, determine the head loss through the debris mat using the head loss relations provided in Reference B-3 (Box 16). 22. The head loss calculated in Step 16 serves as debris analysis I input to the requirements for sump design, as shown in Figure 5.4 and discussed under Combined Effects in Section 5.5 of this report. l i B-4 l

References to Appendix B B-1 Wysocki,-J. J. et al., " Methodology for Evaluation'of Insulation Debris Effects," NUREG/CR-2791, U.S. Nuclear-Regulatory' Commission, prepared by Burns and Roe, Inc., Oradell, NJ, September 1982. B-2 Durgin, W. W. and Noreika, J. F., "The Susceptibility of Fibrous Insulation Blankets to Debris Formation Under Exposure to Energetic Jet Flows," NUREG/CR-3170, U. S. Nuclear Regulatory Commission, prepared by Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, 1983. B-3 Brocard, D. N., " Buoyancy, Transport and Head Loss of Fibrous Reactor Insulation," NUREG/CR-2982, U.S. Nuclear Regulatory Commission, prepared by Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, November 1982. B-4 Weigand, G. G., Thompson,.S. L., and Tomasko, D. "Two-Phase Je t Loads," NUREG/CR-2913, S AND8 2-1935, Sandia National Laboratories, Albuquerque, NM, January 1983. l l B-4a

l TABLE B-1. First Round Assessment of Screen Blockage Potential Criteria for "Zero" Potential for Screen Blockage Criteria Criteria Criteria 1 2 3 Vfb 0 0 >0 Vrm 0 >0 any value Vcc any value any value any value Vhg 0 0 0 Uf any value < 2.0 ft/sec < 0.15 ft/sec Hw > Hs 1 Hs 1 Hs i V b = volume of fibrous insulation employed i f Vrm = volume of reflective metallic insulation employed Vcc = volume of closed cell insulation with a specific gravity less than 1.0 (for Hw > Hs) this insulation will float on water surface above the sump. Vhg =_ volume of hygroscopic insulation employed Hw = water level'at sump screen I Hs = sump screen height Ug = flow velocity at the screen based upon the smaller of (1) the screen area that is shielded from prompt transport of insulation and below the minimum water level or (2) the smallest immediate, total approach-flow-area to the screens / grates below the minimum water level. B-5 ~,

TABLE C-2. Sh3rt F2r3 Precidure Fir Determining Lev 31s Of Acespttble Screen Blockage When Fluid Transport Of Insulation Debris Is Possible. Criteria for an Acceptable Potential for Screen alockage Criteria 1 Criteria 2 Criteria 3 Vfb=0 Vfb > 0 Vfb>0 Vrm>0 Vra > 0 Vrm"lanyvalue Vee

Vee = an value Vcc = any value Vg*O vhg = 0 Vg=0 h

h Ug > 2.0 Ug > 2.0 0.15 < Ug i 2.0 Ew > Hs Ew 1 Bs Ew 1 Hs Am = (La x Ps) 10.75 As Am

Ilm x Ps) 1 0.75 A" Am = 0 Ae = As - An A, = A "

Ue

O/Ae De = Q/A, AP = C,t* 0,E AP = C,t h,k 1

1

0. 5 AP " 3 0.5 AP a

m e fb = A, } Vib " A Y C, U, C, U, j t V ~<h V -ch ib fb fb fb V me Vcce Vhge Ewe Ise Of (see Table B-1) Vfbe r Am - screen area blocked by metallic insulation A, - effective unblocked screen area (area available to flow, Q) A's

screen area shielded from prompt transport of insulation and below the minimum water level j

f U. - effective flow velocity 1 Q - volume flow rate. L - largest linear dimension for reflective metallic insulation Ps - sump screen perimeter or its equivalent t - nominal thickness of shredded insulation on sump screen, t is the volume of as-fabricated fibrous insulation dislodged and shredded divided by the effective unblocked screen area AP - Net Positive Baction Bead stargin, difference between the net-positive p suction head available and the net positive suction head required Vib - volume of fibrous insulation that leads to a head loss of 0.5 APpm l AP - C,t*c," - head loss, (AP), equation for shredded insulation with nominal thickness t, AP = [ft), t = (ft), U, = [ft/sec) j fiberglass C, = 1080, a = 1.3, n = 2.3 sineral wool C, = 230, m = 1.4, n = 2.0 This head loss equation was suggested by the results of experiments reported in Beforence B-3. Other empressions developed from properly conducted esperiments can be used. B-6

4 s TABLE B-3 Transportation Tests Results l From Reference B-3 l AH V V V Pillow i s v SH ~7 y Condition Type [ft/sec) (ft/sec) (ft/sec) (ft)- Comments i 3g Floating whole ~ pillows ' 'l N/A N/A > 2.3 Never flipped 2 N/A N/A - N/A Sunk while against screen: - flipped vertical 3 N/A N/A N/A Sunk while against screens flipped vertical-Sunken 1 1.1 1.1 1.1 0.13 Only one pillow whole-tested pillows 0.9 1.1 1.1 0.07 Only one pillow tested folded in half on screen 2 1.2 1.8 2.0 0.44 7.1 1.4 1.6 2.4 3 1.5 1.7 2.0 0.60 9.4 1.1 1.6 1.6 0.33 8.3 Pillows on screens overlap by 2 inches l Sunken pillows 1 1.1 1.1 1.1 0.67 36.0 with covers 0.9 1.5 0.96 27.5 Not all pieces removed but vertical included and j separated-2 or 3 1.1 1.6 insulation 0.9 1.2 1.2 0.71 32.0 layers i i Sunken pillows 1 1.0 1.9 1.4 25.0 Not all pieces with covers 1.1 2.0 1.6 26.0 vertical and insulation i layers in 5~ 2 or 3 1.0 1.4 1.6 0.54 14.0 Significant l Pieces (see overlap of Figure 2.6) pieces on screen i I-B-7 l l

Table B-3 (continued) AH Y Y Pillow i s v M Comments Condition Type (ft/sec) (ft/sec) (ft/sec) (ft) sq7 sunken 1 0.4 1.4 1.6 1.35 34.0 Fragments collect on pillows in 4" x 4" x 1" bottom 1 ft of screen fragments. Covers not included. 0.6 1.3 1.4 2.45 80.0 with turbulence generators. Fragments collect on bottom 3 f t of screen 2 or 3 1.0 > 1. 6 Not all pieces reached the screen. Collected near screen bottom, Figure 4.6 1.0 > 1.6 0.72 18.1 with turbulence generators. Only about half the pieces on screen. Some pieces at mid-height. Sunken 2 or 3 0.4 > 1. 3 N/A 3.7 240 Not all pieces pillows in for on screen. shreds. 1.0 Screen entirely Covers not fps but not uniformly

included, covered.

Sunken Tests conducted single in 1 ft wide fragments fiume with 7 4"x4*x1" 1 0.6 inch water depth 2 or 3 0.7 4"xl"xl" 1 0.3 2 or 3 0.5 Shreds 1 0.3 2 or 3 0.2 Metallic N/A 2.6 2.6 reflective 2.0 2.3 sample NOTATIONS: Vi = velocity needed to initiate motion of at least one piece of insulation (not including covers when separated from pillows) vs = velocity needed to bring all material on screen Vy = velocity needed to flip all pieces vertically on screen AB = head loss at Vy (or Vs if Vy not given) B-8 _----_-------_------_______________________________J

4 (1)lSREAM LOCATIOceS AND ORIENTATIONS l (2) (S) (4) . l Pet wMer (Pw)l l PIPE ItePACT (PQ l l JET IMPmGEMENT (JI)l (S) t DETERMME CONTAlleMENT VOLUME INTERCEPTED SY JET 7Nm (.> DETERMcNE JET VOLUME DETERMINE JET VOLUME SEGMENT SEGMENT OUT TO CONE AMIS FROM CONE ANIS DSTANCE OF DISTANCE OF T L/D* F L/D* TO D.5 pol. (8) I' [ IS INSULATION EleCAPSULATED l OR NONENCAPSULATED FSROUST DETEmessE AREAS AND VOLUMES OF IBISULATION REMOVED AS YES NO 2 SMREDDED FSROUS DESRIS. IseSULATION DISLODGED BY JET. Vpg. V,. V, (SUBSCRIPTS (10)

=AMAW SROUS.

f p jg REFER TO FORMATION DETERMINE VOLUME OF FSROUS MECMA900SMS). MSULATION REMOVED BY A7 1r (,g) DETERMmE VOLUME FRACTIO 988 OF SMREDDED FSROUS DEBRIS PROtsPTLY TRANSPORTED TO SUMP, CALCULATE MAXIMUM FLOW VELOCITY AS-FASRICATED DESmts DOES poo epw,*pg,*J FC3 FLOW PATMS WITHIN CONTAB0 MENT NOT M10 RATE TO SUMP DURWG REC 8RCULATION MODE. DOES (SS) MAXtMUM FLOW VELOCtTY EQUAL OR E EXCEED DESRIS TRAteSPORT VELOCITY I VILUME OF SMREDDED FSROUS REQUmEDT ASSUME DEBRIS SECOMES ALIGNED DESRIS AT GUMP W VERTICALLY ON SUMP SCREEN TO Y 4Ypg

Va"V MEIGHT OF AS-FABRICATED pw MAXIMUM DRAENSION. Hg (14)

I' (21) VOLUME OF SHREDDED FSROUS AREA NOT SLOCMEJ BY AS-(2M I DESRIS AT SUMP 18 FABRICATED IIISUs.AT'ON IS IS Ag/M. Am/M OR (A + Am)/M LESS g pg pg+ egg gg = V A-As. A-Am OR A-(Ag+ Am) TMAN TME SUMP PER6 METER, P7 op,%+ e V Y o (iS) v CALCULATED TM8CKNESS OF gggy 3 SMREDDED FSROUS DESRss AT (22) <r SUMP. t = VIA,' CALCULATE 6EAD LOSS THROUGH UesBLOCKED SUMP AREA FOR AREA NOT BLOCMED SY AS-DESRIS TMICKNESS.g FASRICATED II63ULATION W A-Mg (23) DEBR68 ANALYSIS INPUT TO SUMP DES 80N (SEE FIGURE 6.4) Ypy - VOLUME OF SMREDDED FSROUS INSULATION REMOVED SY PPE WHIP. (FT ) S Ypg - VOLUME OF SMREDDED FSROUS INSULATION REMOVED SY PIPE IMPACT. (FT ) S V - VOLUME OF SMREDDED FSROUS INSULATION REMOVED BY JET SIPipe0EMENT.(FT ) jg 3 opy-FRACTf000 OF VOLUME OF SMREDDED 1888ULATION CAUSED BY Pet WHIP PROMPTLY TRANSPORTED TO SUMP. j opg - FRACTIO 8d OF VOLUME OF SMREDDED NeSULATION CAUSED BY PIPE RfPACT PROMPTLY TRANSPORTED TO SUMP. egg - FRACTION OF WOLUME OF SMREDDED SISULATION CAUSED SY JET GMP8NGEMENT PROMPTLY TRANSPORTED TO SUMP. L/D - RAtlO OF PIPE LEleGTH TO PPE DIAMETER. V - TOTAL WOLUME OF SHREDDED DESRIS TRANSPORTED TO SUMP SCREEN-(FT )8 A, - AREA OF AS-FASRICATED FSRoUS OsSULATION DISLODGED BY JET. (FT ) 8 Am - AREA OF AS-FABR8CATED REFLECTIVE METALLIC SsSULATW88 DISLOOGED BY JET. (FT ) S A - EFFECTIVE AREA OF Sub8P SCREEN.(FT8) A, s-EFFECTIVE UNBLOCKED SUts' SCREEse AREA (AREA AVALASLE FOft FLOW) (FT2) Ng - MAMasuu LINEAR DIMENS80N OF AS-FASRICATED 8880LAT80N (FT) P - PEmanaETER OF EFFECTIVE SubdP SCREEnd (FT) 9 - CALC 41ATED THICMIESS OF SBGEDDED DEBRIS NAT Oss SUMP SCf4EN.(les) Figure B-1 Flowchart for the Determination of Insulation l Debris Effects B-9 l _., - ~,,. - , ~ _ _ _ - - _. _ _. - - - - - - - -. - ~ -.. - -

APPENDIX-C Insulation Debris Formation as a Result of Two-Phase Jet Impingement Experiments have been carried out to determine the onset of ' failure of as-fabricated fibrous; insulation due to jet impingement. These experiments were conducted using water jets at ambient temperature, at various stagnation pressures, and at l two angles of jet-impingement: normal to the insulation surface and'-45' to the insulation surface (Reference C-1). 4 Table C-1 shows the key experimental results from the tests conducted in Reference C-1; the table presents the camage and failure pressure data. The insulation that was the most susceptible to failure was the Type 1 insulating pillows. Visable damage occurred at stagnation pressures of about 10 psig (90' impact) and 15 psig (45' impact); failure of the pillow occurred at stagnation pressures of about 35 psig (90

impact) and 30 psig (4 5* impact).

Visable damage was defined as the pressure-at which the first signs of structural failure occurred, e.g., fraying of the fibers in the covering, etc. Failure of the insulation pillow was defined as the pressure where there was a release of fibrous insulation from the as-fabricated insulation panel. In both instances the insulation panel was subjected for a period of five minutes to an impact from a two inch diameter, i incompressible water jet at a constant stagnation pressure, Po. The stagnation pressure for fibrous insulation panel - failure, referred to-in this appendix as the failure pressure, will be set at 20 psig. This is the recommended value for incipient failure given in Reference C-1. Two Phase Jets The flow field for two-phase jets impinging on targets is extremely complicated. Reference C-5 has reported the centerline behavior of two-phase jets and has reported the radial loading l for axisymmetric impinging two-phase jets. In the jet flow field there are three natural divisions of the field. There is a nozzle (or break) region where the flow chokes. In this region there is a core at choked flow thermodynamic properties that projects a distance downstream of the nozzle depending upon the degree of subcooling. Downstream o{ this region there is the free jet region. Here the-jet expands almost as a free, isentropic expansion. The flow is sugersonic throughout this entire region. The free jet region terminates at a stationary shock wave near the target. This shock wave arises.because of the need for the target to propagate pressure waves upstream and, thus produce a pressure gradient that will direct the fluid around the target. Downstream of the L C-1 ) t ........ ~. . ~. -. ~ ~

Table C-1 Experimental Results from' Reference C-1 for the Stagnation Pressure for Incipient Damage and Failure

Insulating' 90* Impingement. Angle 45' Impingement Angle Pillow

'(Pressure, psig) (Pressure, psig) i Type Damage / Failure Damage / Failure 1 10/35 15/30 2 40/>65 30/>65 3 60/65 45/50 l' i Type 1: 4" mineral wool or refractory mineral fiber core material (6 lb. dens.ity) covered with Uniroyal #6555 asbestos cloth coated with 1/2 mil. Mylar. Type 2: 4" Bur 1 glass 1200,.or 4 layers of 1" thick Filomat D (fiberglass) core material, inner covering of knitted stainless steel mesh, outer covering of Alpha Maritex silicone aluminum cloth, product #2619. i Type 3: Same insulation core materials as Type 2. Inner and outer covering of 18 ounce Alpha Maritex cloth, ' product

7371.

i i 4

For comments about failure modes during the experiments see Reference C-1.

f C-2

shock is the target region where the local flow field imposes a pressure loading on the target. Depending upon the upstream flow conditions and the L/D of the target there may be a substantial total pressure loss across the shock wave. This loss arises because of the irreversible physics that characterize the shock. As indicated above, methods for calculating the centerline behavior of impinging.two phase jets were developed in Reference C-5. Figures C-1 and C-2 have been taken from Peference C-5 and show the centerline total pressure behavior for vessel (break) stagnation conditions of 15 MPa and 8 MPa at various saturated and subcooled states and for various L/D's. Radial j target-pressure distributions were also given in Reference C-5. i Figures C-3 and C-4 show-target pressure contours. These figures l display, in an approximate fashion, the radial target pressure distribution as a function of the axial position of the target and the vessel (or break)' stagnation conditions. Figure C-3 is for stagnation conditions of Po = 150 bars (15.0 MPa) and ATo = 35'C, where Po is the stagnation pressure and ATo denotes the degrees of subcooling. Figure C-4 is for Po = 80 bars (8.0 MPa) and ATo = 0*C. Both of these figures show that the region targeted by an impinging two-phase jet is highly dependent upon the thermodynamic conditions at the break. ' Fibrous' Insulation Debris Model Test data have indicated that there can be substantial differences in the pressure loss between shredded and as-fabricated insulations for equal volumes blocking a flow I stream; the shredded insulations lead to larger losses. Currently, methods do not exist, other than statistical, for evaluating the amount of fibrous insulation that is removed in an accident and becomes shredded as a result of hydrodynamic forces. There is a clear need for such a model because of the large impact sump screen pressure loss can have on the net positive suction head (NPSH) available. At the same time there exist very little data or analyses upon which to base modeling. The next few paragraphs show a model for evaluating the fractions, by volume, of shredded and as-fabricated panels that result; the model is based principally upon two studies recently funded by the NRC. They are provided in References C-1 and C-5. It should be understood that the approach used in developing this model was to make assumptions that always resulted in substantial conservatism in arriving at the amount of shredded fibrous insulation; this was done because shredded fibrous insulation poses the greatest potential threat to NPSH available. The model consists of defining two regions within the two-phase jet volume defined in Reference C-6. The first region is a circular cone with total included angle of 90' extending from the jet origin to 7 L/D's downstream (see Figure C-5); all of the fibrous insulation within this volume is assumed-to be shredded. The second region is the frustum of a circular cone C-3

P = 150 BARS 1.1 .n 70 AT, = 50 AT, = 35 AT, =

90

^'o = 0 AT, x, = 0.333 80

o

.70 .60 o Q. N .50 N Q_ .40 .30 \\ .20

10 I

l 0.0 O.0 2.0 4.0 6.0 8.0 10. L/D i Figure C-1 Centerline target pressure as a function of axial target position (L/D) for break stagnation conditions of 150 bars and various subcoolings and qualities. L is the target position, D is the pipe diameter P is the centerline pressure, and Po z is the stagnation pressure at the break. C-4

P = 80 BARS 1.1 ^T 70 1.0 e ~ AT, = 50 AT, 35 r ^T = 15 .90 AT, o ~ 0 = 0.333 x, = 0 750 x = .80 o .70 .60 c a. .50 N o. .40 .30 .20 .10 0.0 ( 0.0 2.0 4.0 6.0 8.0 10. L/D l l L Figure C-2 Centerline target pressure as a function of axial position (L/D)for break stagnation conditions of 80 bars and various subcoolings and qualities. L is the target position, D is the pipe diameter, Pz is the centerline pressure, and Po is the stagnation pressure at the break. l C-5 ,n-,. - - ~ -.,,a -.,-e

7-- (BARS) A= 1.0 B= 2.5 .C= 5.0 D= 10.0 6-E= 15.0 F= 20.0 G= 25.0 H= 30.O != 35.0 5-- = = a= 40.0 K= 45.0 L= 50.0 M: 55.0 N= 60.0 4-- 0= 65.0 P= 70.0 0= 75.0 e C R= B0.0 3-- = = = s _1 2-- = = = = 1- - ' * '.. '. = - a c \\P o=150 AT o= 35 L c/D= 1.07 0-l l l l l l l l l l l .,,,,,,I 1 2 3 4 5 6 l RADIUS / D l Figure C-3 Composite target pressure contours as a function of target L/D and target RADIUS /D for stagnation I conditions of Po = 150 bars and 35 degrees of subcooling. Smooth lines connecting like alphabetic letters form an approximate pressure i contour corresponding, in bars, to the pressure versus alphabetic letter key. This contour is approximate and is only informational. ( l C-6

i 7-- (BARS) A= 1.0 B= 2.5 C= 5.0 D= 10.0 6-- E= 15.0 F= 20.0 G= 25.0 H= 30.0 != 35.0 5-- J= 40.0 e K= 45.0 L= 50.0 M= 55.0 N= 60.0 4-- o= ss.O P= 70.0 0= 75.0 O R= 80.0 3-- = s y 2 1_ _..... P o= 80 AT o= 0 L c/D= .50 l 0-l l l l l l l l l l l l 3 1 2 3 4 5 6 RADIUS / D l ( Figure C-4 Composite target pressure contours as a function of target L/D and RADIUS /D for stagnation conditions of Po = 80 bars and saturated liquid. Smooth lines connecting like alphabetic letters form an approximate pressure contour corresponding, in bars, to the pressure versus alphabetic letter key. This contour is approximate and is only informational. C-7 ... -.. -, _ - - - _.. ~. - - _ - -. - -.,. - - -

BOUNDARY OF RIGHT CIRCULAR CONE REGION II ORIGIhATING ) AT PIFE BREAK REGION I I I I 90 l I I I I I I i 7 I'/D's l BOUNDARY I I I I l Po=0 5 PSIG BOUNDARY FIGURE C-5 ILLUSTRATI.ON SHOWING THE IWO REGIONS FOR THE INSULATION DEBRIS MODEL l C-8 ... ~ - -

_ __.- ~ l with total included angle of 90* that extends from 7 L/D's to the point where the average stagnation pressure becomes 0.5 psig; in this region all of the fibrous insulation is assumed to be dislodged as as-fabricated pane s. The size of the first volume was established using insulation ' integrity-data from Reference C-1 and'using two-phase jet expansion models from Reference C-5. In Reference C-1, as noted above, data indicated that the onset of insulation failure damage can occurfat stagnation pressures as low as'20 psig. The assumption that is made'for-the purposes of this model is that fibrous-insulation shreds at stagnation pressures greater than or equal to the failure pressure, 20 psig. Referring to Figures C-1 and C-2 the value of 20 psig occurs approximately 7 L/D's downstream of the jet origin along the centerline of the jet. l ' psig requires the extrapolation of data taken using a two inch Choosing the failure threshold for fibrous insulations as 20 diameter, incompressible water jet to a loss-of-coolant accident (LOCA) situation that may involve large,-high_ energy, and compressible two-phase jets. The uncertainties present in such an extrapolation must, therefore, be recognized. The principal area of concern is the implicit assumption that a two-phase LOCA I jet is analogous to a 2 inch diameter. incompressible water jet. This concern stems from (1) differences in loading mechanisms and I (2) the region affected by the jet (cone-of-influence). Damage to insulation from a two-phase jet could result from normal surface loading, loading resulting from shear forces acting tangential to the surface and from loading that could result from pressure imbalances due to distortions of the insulation surface. Although this extrapolation is disturbing, every effort has been made to mitigate'any effects due to scale or different phenomena by choosing conservative failure criteria and affected volume. The size of the second volume was established using the Moody jet analysis as modified in Reference C-6..This volume begins at L/D = 7 and extends to a plane in the jet where the jet thrust (as calculated by Moody) divided by the jet area is equal to 0.5 psi. This is the plane where the average distributed pressure (force per unit area) on a flat agisymmetric target would be equal to 0.5 psig. (The outer boundary for dislodging insulation by jet forces, 0.5 psig boundary, was established in Reference C-6.) The Moody type jet model was selected for establishing the outer boundary of region II because it always resulted in a larger L/D value for the boundary than the two-phase jet analysis l in Reference C-5, thus assuring that the effects of modeling -uncertainties are mitigated'by a conservative boundary selection. Moreover, the above boundary does not' change the jet volume defined in Reference C-6. Finally, note that all other forms of insulation (reflective metallic, closed cell, etc.) that are in the jet volume (volumes I and II above) are assumed to be dislodged by the jet in as-fabricated panels. C-9 L.

5 Other Discussion The experiments' referenced here (Reference C-1) were conducted with a single phase fluid (water)' at ambient temperature..Under these conditions, the principal mode of failure that was observed (i.e., rips.or tears occurring in the insulation covering near the periphery of the area' impacted by the jet) supports the above modeling, which assumes that the damage to the insulation is due principally to stress occurring under normal pressure loadings. However, under two-phase jet flow conditions, other phenomena can become important in influencing the mode of failure of l insulation coverings. A significant effect of the impact of a -two-phase jet onto a surface normal to the jet axis is the migration of fluid at high velocities parallel to the surface. The forces associated with such flow could result in shear stresses in the fabric sufficient to fail the covering. Were such a failure mechanism to become the principal failure mode, the above failure-pressure criterion for insulation failure may not remain valid. An additional consideration to.take into account is the effect of temperature on the strength of materials'used for insulation coverings. Under LOCA conditions, insulation coverings would be subject to higher temperatures than the l temperatures that existed in the incompressible water jet L experiments. For those insulation covers, however, made up of j fiberglass or similar refractory material, no significant change in strength of the materials will occur as a result of such temperature differences. In fact, as long as fiberglass remains solid, its strength increases with increasing temperature (Reference C-2). Furthermore, the types of fiberglass used for insulation covers, e.g., lime-aluminum borosilicate glass, can be used for continuous duty up to about 600*F (Reference C-3) and has a softening temperature range of between 1350*F and 1560*F (Reference C-4). Finally, within several pipe diameters of the pipe break, l [ analysis (Reference C-5) indicates that the angle subtended by the exiting jet may be significantly greater than 90'. In that volume, a greater amount of insulation debris (e.g., shredded insulation debris) would be generated than under the 90' included angle assumption used here and in Reference C-6. It is expected, however, that the assumption that insulation disintegration occurs (i.e., insulation shreds or fibers form the resultant debris) within an included angle of 90* from the jet origin to a distance at which the stagnation pressure reduces to 20 psig is sufficiently conservative to provide an overall conservative result. C-10 l 1 _,..,...m,___ _m., ,,_,___..,m -______.,__m

The assumption is made that a' stagnation pressure of 0.5 psig represents the lower limit to which insulation damage (intact insulation dislodged) can occur. The value of 0.5 psig was given in Reference C-6 and is considered to'lue conservative. A number of the assumptions presented regarding fibrous debris generation have evolved from analytical studies (References C-5 and C-6) and experimental work (Reference C-1) and are considered to be conservative for the following reasons: 'l. . Complete insulation disintegration (i.e., the rendering of as-fabricated insulation into shreds or fibers) is assumed within jet volumes where stagnation pressures equal or exceed 20 psig. Such stagnation pressures (20 psig) have been observed to tue those for-.the threshold of damage to the covers of the most damage susceptible as-fabricated insulations. Inasmuch as no detailed study has been made on the disintegration or dislodgement of insulations, the most severe damage (compatible with existing knowledge) to insulation from the standpoint of potential sump blockage has-been assumed. 2. The duration of jet impingement during jet damage experiments lasted approximately twice that required for large LOCA blowdown (i.e., 5 min. versus approximately 2 min.). '3. The outer boundary of volume I where the fibrous insulation is shredded was fixed on the basis of the occurrence of a stagnation pressure of 20 psig along the centerline of the jet. 'The pressure, in fact, falls off in a radial direction from the jet axis. [ 4. Insulation, in as-fabricated form, is assumed to be dislodged at. stagnation pressures between 20 psig (7 L/Ds) and 0.5 psig. I i Consideration must be given, however, to other phenomena l related to two phase jet flow. These could result in insulation [ covering failure under conditions less rigorous than those l. assumed in this development. They include: L 1. A major failure mechanism, under two-phase jet conditions, may be shear force failure or imbalanced pressure force failure as opposed to normal pressure force loading. 2. For some target situations (subcooled flows on close-in targets) the 90' cone of influence assumption may not be sufficient to target all affected insulation. i C-ll L.

References to Appendix C C-1 Durgin, W. W. and Noreika~, J. F., "The Susceptibility of Fibrous Insulation Pillows to Debris Formation Under-Exposure to Energetic Jet Flows," NUREG/CR-3170, U.S. Nuclear Regulatory Commission, Prepared by Alden Research Laboratory, Worcester Polytechnic Institute, Holden, MA, 1983. C-2 Handbook of Tables for Applied Engineering Science; Second Edition; Bolz, R.E.,

Tuve, G.L.,

editors; CRC Press; Cleveland, OH, 1983. C-3 The Encyclopedia of Engineering Materials and Processes; Clauser, H.R. editor-in-chief; Reinhard Publishing Corporation; New York, NY, 1963. C-4 Handbook of Plastics and Elastomers; Harper, C.A., editor-in-chief; McGraw-Hill Book Company; New York, NY, 1975. C-5 Weigand, G. G. and Thompson, S. L. " Break Flow and Two-Phase Jet Load Model," Sandia National Laboratories, Albuquerque, NM. Presented at International Meeting on Thermal Reactor Safety, Chicago, IL August 1982. C-6 Wysocki, J. J., et al., " Methodology for Evaluation of Insulation Debris," tlUREG/CR-2791, Burns and Roe, Inc., Oradell, NJ, September 1982. i l l C-12 l l

NRC roRu 335

1. REPORT NUMBE R IAssiemed by DOC /

U.S. NUCLEAR KEGULATORY COMMISSION (7 77, BIBLIOGRAPHIC DATA SHEET Fo C ent"

4. TITLE AND SUSTsTLE (Add Vohme No., sf sprer,sar/

2. (Leave blank /

Containment Emergency Sump Performance

3. RECIPIENT'S ACCESSION NO.

Tcchnical Findings Related to Unresolved Safety Issue A-43

7. AUTHOR (S)

5. DATE REPORT COMPLETED M ON TH l YEAR A. W. Serkiz March 1983 9.. PERFORMING ORGANIZATION N AME AND MAILING ADDRESS (Include 2,p Codel DATE REPORT ISSUED I

^" Division of Safety Technology April 1983 Office of Nuclear Reactor Regulation ,L,,,,,,,,, L U.S. Nuclear Regulatory Consnission Washington, DC 20555

8. (te. e u.nni

12. SPONSORING ORGANIZATION NAME Af4D MAILING ADDRESS (Include 2,p codel p

USI A-43 Same as 9, above.

11. CONTR ACT NO.

13. TYPE OF REPORT PE RIOD COVE RE D (Inclusive d.fes) 4 Final Staff Report

15. SUPPLEMENTARY NOTES

14. (teave afa>Al

16. ABSTRACT (200 words or less)

This report summarizes key technical findings related to the Unresolved Safety Issue (USI) A-43, Containment Emergency Sump Performance. The technical issues can be subdivided into: sump hydraulic performance, LOCA generated debris effects and recirculation pump performance under post-LOCA conditions. The technical findings presented in this report provide a means to address these sump design and performance aspects and provide the technical basis for-the proposed changes to NRC's Standard Review Plan, Section 6.2.2 and Regulatory Guide 1.82. l l [

17. KEY WORDS AND DOCUMENT ANALYSIS 17.. DESCRIPTORS Containment Emergency Sump Performance USI A-43 l

17b. IDENTIFIERS /OPEN-ENDED TERMS 18 AVAILABILITY STATEMENT UR TY LA S IThis report /

21. NO. OF PAGES Unlimiited Availability

20. SECURITY CLASS (Thes page) 22 PRICE l

unc1=ce4f4ma S N tic F O R M335 67 77)

~_ ~ UfetTE3 STATE 3 sitsi cuuan NUCLEAR ftEZULI. TORY COAMNSSION ,osisst 6 *tts mo IY'." Su WASHINGly. D.C. 20586

3. 3 c OFFCAL BUSINESS PENALTY FOR PRIVATE USE,6300 F

i s 120555078877 1 C00796 US NRC ADM DIV 0F TIDC POLICY & PUB MGT BR-POR NUREG W-501 WASHINGTON DC 20555 i s k ) f ~.-,. ..... _, _ _. _. -, -. _ _ _ _ -. _}}

ML20074A975

Contents

Text

1.0 INTRODUCTION

SUMMARY

1.0 INTRODUCTION

1.2 Background

SUMMARY

SUMMARY

Navigation menu

ML20074A975

Text

1.0 INTRODUCTION

SUMMARY

1.0 INTRODUCTION

1.2 Background

SUMMARY

SUMMARY

Navigation menu

Search