Regulatory Guide 1.82
| ML003740236 | |
| Person / Time | |
|---|---|
| Issue date: | 11/30/1985 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| MS 203-4, Reg Guide 1.82, Rev 1 | |
| Download: ML003740236 (22) | |
Revision 1V
November 1985 U.S. NUCLEAR REGULATORY COMMISSION
REGULATORY GUIDE
OFFICE OF NUCLEAR REGULATORY RESEARCH
REGULATORY GUIDE 1.82 (Task MS 2034)
WATER SOURCES FOR LONG-TERM RECIRCULATION COOLING
FOLLOWING A LOSS-OF-COOLANT ACCIDENT
A. INTRODUCTION
General Design Criteria 35, "Emergency Core Cool ing," 36, "Inspection of Emergency Core Cooling Sys tem," 37, "Testing of Emergency Core Cooling System,"
38, "Containment Heat Removal," 39, "Inspection of Containment Heat Removal System," and 40, "Testing of Containment Heat Removal System," of Appendix A,
"General Design Criteria for Nuclear Power Plants," to
10 CFR Part 50, "Domestic Licensing of Production and Utilization Facilities," require that systems be pro vided to perform specific functions, e.g., emergency core cooling, containment heat removal, and containment atmosphere clean up following a postulated design basis accident. These systems must be designed to permit appropriate periodic inspection and testing to ensure their integrity and operability. General Design Criterion I,
"Quality Standards and Records," of Appendix A to 10
CFR Part 50 requires that structures, systems, and com
..
ponents important to safety be designed,, fabricated, erected, and tested to quality standards commensurate with the importance of the safety function to be per formed. This guide describes a method acceptable to the NRC staff for implementing these requirements with respect to the sumps and pools performing the functions of water source for the emergency core cooling, con tainment heat removal, or containment atmosphere clean up. This guide applies to light-water-cooled reactors.
The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has conicurred in the regulatory position.
Any information collection activities mentioned in this'
regulatory guide are contained as requirements in 10 CFR
Part 50, which provides the regulatory basis for this guide. The information collection requirements in 10 CFR
Part 50 have been cleared under OMB Clearance No.
3150-0011.
- The substantial number of changes in this revision has made it impractical to indicate the changes with lines in the margin.
B. DISCUSSION
1. Pressurized Water Reactors In pressurized water reactors (PWRs), the contain ment emergency sumps provide for the collection of reactor coolant and chemically reactive spray solutions following a loss-of-coolant accident (LOCA); thus the sumps ierve as water sources to effect long-term recir culation for the functions of residual heat removal, emergency core cooling, and containment atmosphere cleanup. These water sources, the related pump inlets, and the piping between the sources and inlets are important safety components. The sumps servicing the emergency core cooling systems (ECCS) and the con tainment spray systems (CSS) are referred to in this guide as ECC
sumps. Features and relationships of the ECC sumps pertinent to this guide are shown in Figure 1.
The primary areas of safety concern regarding ECC
sumps and pump inlets are (1) post-LOCA hydraulic effects, particularly air ingestion, (2) blockage of debris interceptors resulting from LOCA destruction of insula tion and its transport, and (3) the combined effects of items (1)
and (2) relative to recirculation pumping operability (i.e., impact on net positive suction head (NPSH) available at the pump inlet).
Debris resulting from a LOCA has the potential to block ECC sump debris interceptors (i.e., trash racks, debris screens) and sump outlets resulting in degradation or loss of margin. Such debris can be divided into the following categories: (1) debris that is generated early in the LOCA period and is transported by blowdown forces (I.e., jet forces from the break), (2) debris that has a high density and will sink, but is still subject to fluid transport if local recirculation flow velocities are high enough, (3) debris that has an effective specific gravity near 1.0 and will float or sink slowly but will nonetheless be transported by very low velocities, and USNRC REGULATORY GUIDES
Written comments may be submitted to the Rules and Procedures Branch, DRR
ADM,
U.S.
Nuclear Regulatory Commission, Regulatory Guides are Issued to describe and make available to the Washington, DC 20555.
public methods acceptable to the NRC staff of Implementing specific parts of the Commission's regulations, to delineate tech- The guides are Issued in the following ten broad divisions:
n=ques USed by the staff In evaluating specific problems or postu lated accidents, or to provide guidance to applicant
s. Regulatory
1. Power Reactors
6. Products Guides are not substitutes for regulations, and compliance with
2. Research and Test Reactors
7. Transportation them Is not required. Methods and solutions different from those set
3. Fuels and Materials Facilities
8. Occupational Health out in the guides will be acceptable If they provide a basis for the
4. Environmental and Siting
9. Antitrust and Financial Review findings requisite to the issuance or contlnuance of a permit or
5. Materials and Plant Protection 10. General esebythe Commission.
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guides are encouraged at all times, and guides will be revised, as be obtained by writingthe Superintendent of Documents, U
appropriate, to accommodate comments and to reflect new Informa- Government Printing Office, Post Office Box 37082, Washington, ton or experience.
DC 20013-7082.
WATER FROM
SPRAY
I
4 4 Go SCREEN I DEBRIS
RACK
INTERCEPTORS
RECIRCULATION
PUMP
(o) = SUMP OUTLET
(i) = PUMP INLET
- AS DETERMINED DURING SAFETY ANALYSIS
- CUBIC OR HORIZONTAL SUPPRESSOR MAY BE USED
WITH EITHER SUMP OUTLET
from (o)
FIGURE
1. PWR
C
__ ~C
_
C
(4) debris that will float indefinitely by virtue of low density and will be transported to and possibly through the debris screen. Thus, debris generation, early trans port due to blowdown loads, long-term transport, and attendant blockage of debris interceptors must be analyzed to determine head loss effect
s. Appendix A
provides relevant information for such evaluations;
References 1 through 12 provide additional information relevant to the above concerns.
The design of rumps and their outlets includes consideration of the avoidance of air ingestion and other undesirable hydraulic effects (e4g.,
circulatory flow patterns, outlet designs leading to high head losses). The location and size of the sump outlets within ECC Bumps is important in order to minimize air ingestion since ingestion is a function of submergence level and velocity in the outlet piping. It has been experimentally deter mined for PWRs that air ingestion can be minimized or eliminated if the sump hydraulic design considerations provided in Appendix A are followed. References 1, 3,
6, 7, and 8 provide additional technical information relevant to sump ECC hydraulic performance and design guidelines.
Placement of the ECC sumps at the lowest level practical ensures maximum use of available recirculation coolant. However, since there may be places within the containment where coolant could accumulate during the containment spray period, these areas can be provided with drains or flow paths to the sumps to prevent coolant holdup. This guide does not addrqss the design S>of such drains or paths. However, since debris can migrate to the sump via these drains or paths, they are best terminated, in a manner that will prevent debris from being transported to and accumulating on or within the ECC sumps.
Containment drainage sumps are used to collect and monitor normal leakage flow for leakage detection systems within containments. They are separated from the ECC sumps and are located at an elevation lower than the ECC sumps to minimize inadvertent spillover into the ECC sumps due to minor leaks or spills within containment. The floor adjacent to the ECC sumps would normally slope downward, away from the ECC
pumps, toward the drainage collection sumps. This"
downward slope away from the ECC sumps will minimize the transport and collection of debris against the debris interceptors. High-density debris may be swept along the floor by the flow toward the trash rack. A debris curb upstream of and in close proximity to the rack will decrease the amount of such debris reaching the rack.
It is necessary to protect sump outlets by debris interceptors of sufficient strength to withstand the v*ibratory motion of seismic events, to resist jet loads and impact loads that could be imposed by missiles that may be generated by the initial LOCA, and to withstand the differential pressure loads imposed by the
/ accumulation of debris.
Considerations in selecting materials for the debris interceptors include long periods of inactivity, i.e., no submergence, and periods of operation involving partial or full submergence in a fluid that may contain chemically reactive materials. Isolation of the ECC sumps from high-energy pipe lines is an important consideration in protection against missiles, and it is necessary to shield the screens and racks adequately from impacts of ruptured high-energy piping and associated jet loads from the break. When the screen and rack structures are oriented vertically, the adverse effects from debris collecting on them will be reduced. Redundant ECC pumps and sump outlets are separated to the extent practical to reduce the possibil ity that an event causing the interceptors or outlets of one sump to either be damaged by missiles or partially clogged could adversely affect other pump circuits.
It is expected that the water surface will be above the top of the debris interceptor structure after comple tion of the safety injection. However, the uncertainties about the extent of water coverage on the structure, the amount of floating debris that may accumulate, and the potential for early clogging do not favor the use of a horizontal top interceptor. Therefore, in computation of available interceptor surface area, no credit may be taken for any horizontal interceptor surface; the top of the interceptor structure is preferably a solid cover plate that will provide additional protection from LOCA
generated loads and that is designed to provide for the venting of any trapped air.
Debris that is small enough to pass through the trash rack and thus could clog or block the debris screens or outlets needs to be analyzed for head loss effects.
Screen and sump outlet blockage will be a function of the types and quantities of insulation debris that can be transported to these components. A vertical inner debris screen would impede the deposition or settling of debris on screen surfaces and thus help to ensure the greatest possible free flow through the fine inner debris screen. Slowly settling debris that is small enough to pass through the trash rack openings could block the debris screens if the coolant flow velocity is too great to permit the bulk of the debris to sink to the floor level during transport. If the coolant flow velocity ahead of the screen is at or below approximately S cm/sec
(0.2 ftl/sec), debris with a specific gravity of 1.05 or more is likely to settle before reaching the screen surface and thus will help to prevent undue clogging of the screen.
The size of openings in the screens is dependent on the physical restrictions that may exist in the systems that are supplied with coolant from the ECC sump. The size of the mesh of the fine debris screen is determined based on consideration of a number of factors, including the size of openings in the containment spray nozzles, coolant channel openings in the core fuel assemblies, and such pump design characteristics as seals, bearings, and impeller running clearances.
As noted above, degraded pumping can be caused by a number of factors, including plant design and layout.
In particular, debris blockage effects or debris intercep tor and sump outlet configurations and post-LOCA
1.82-3
hydraulic conditions (e.g., air ingestion) must be consid ered in a combined manner. Small amounts of air ingestion, i.e., 2% or less, will not lead to severe pump ing degradation if the "required" NPSH from the pump manufacturer's curves is increased based on the calcu lated air ingestion. Thus the combined results of all post-LOCA effects need to be used to estimate NPSH
margin as calculated for the pump inle
t. Appendix A
provides information for estimating NPSH margins in PWR sump designs where estimated levels of air inges tion are low (2% or less). References I and 8 provide additional technical findings relevant to NPSH effects on pumps performing the functions of residual heat removal, emergency core cooling, and containment atmosphere cleanup. When air ingestion is 2% or less, compensation for its effects may be achieved without redesign if the
"available"
NPSH is greater than the "required" NPSH
plus a margin based on the percentage of air Ingestion.
If air ingestion is not small, redesign of one or more of the recirculation loop components may be required to achieve satisfactory design.
To ensure the operability and structural integrity of the racks and screens, access openings are necessary to permit inspection of the ECC sump structures and outlets.
Inservice inspection of racks, screens, vortex suppressors, and sump outlets, including visual examina tion for evidence of structural degradation or corrosion, can be performed on a regular basis at every refueling period downtime. Inspection of the ECC sump compo nents late in the refueling period will ensure the absence of construction trash in the ECC sump area.
2. Boiling Water Reactors In boiling water reactors (BWRs), the suppression pool, in conjunction with the drywell, downcomers, and vents, serves as the water source for effecting long-term recirculation cooling and for fission product removal.
This source, the related pump inlets, and the piping between them are important safety components. These components are referred to in this guide as the suppres sion pool Features and relationships of the suppression pool pertinent to this guide are shown in Figure 2.
There are concerns with the performance of the sup pression pool and pump inlets that are similar to those associated with the ECC sumps in PWRs, Le., post LOCA
hydraulic effects (particularly air ingestion),
blockage of debris interceptors resulting from LOCA
destruction of insulation and its transport (including suppression pool bulk velocity effects), and the com bined effects of these items relative to the operability of the recirculation pump (e.g., the impact on NPSH
available at the pump inlet). References 1 and 7 provide data on the performance and air'ingestion characteristics of BWR configurations.
As in the case of PWRs, it is desirable to include consideration of the use of debris interceptors in BWR
designs to protect the pump inlets. However, the loca tion of the debris interceptors need not be restricted to the pool itself. Debris interceptors or equivalent plant structures in the drywell in the vicinity of the down comers or vents could serve effectively in reduci,"
debris transport to the pump inlets.
Similarly, the smallest opening in the debris intercep tors is dependent on the physical restrictions that may exist in the systems served by the suppression pool For example, spray nozzle clearances, coolant channel open ings in the core fuel assemblies, and such pump design characteristics as seals, bearings, and impeller running clearances will need to be considered in the design.
C. REGULATORY POSITION
1. Pressurized Water Reactors Reactor building sumps that are designed to be a source of water for the functions of emergency core cooling, containment heat removal, or containment atmosphere cleanup following a LOCA should meet the following criteria:
1. A minimum of two sumps should be provided, each with sufficient capacity to service one of the redundant halves of the ECCS and CSS.
2. To the extent practical, the redundant sumps should be physically separated by structural barriers from each other and from high-energy piping systems to preclude damage to the sump components (e.g., rack'
screens, and sump outlets) by whipping pipes or hi, j
velocity jets of water or steam.
3. The sumps should be located on the lowest floor elevation In the containment exclusive of the reactor vessel cavity. The sump outlets should be protected by at least two vertical debris interceptors: (a) a fine inner debris screen and (b) a coarse outer trash rack to prevent large debris from reaching the debris screen. A
curb should be provided upstream of the trash racks to prevent high-density debris from being swept along the floor into the sump.
4. The floor in the vicinity of the ECC sump should slope gradually downward away from the sump.
5. All drains from the upper regions of the reactor building should terminate in such a manner that direct streams of water, which may contain entrained debris, will not impinge on the debris interceptors.
6. The strength of the trash racks should be adequate to protect the debris screens from missiles and other large debris. Each interceptor should be capable of withstanding the loads imposed by missiles, by the accumulation of debris, and by head differentials due to blockage.
7. The available interceptor surface area used determining the design coolant velocity should calculated to conservatively account for blockage that may result. Only the vertical interceptor area that is
1.824
DOWNCOMI
VENTS
FIGURE
2. BWR
1.82-5
below the design basis water level should be considered in determining available surface area. Fibrous insulation debris should be considered as uniformly distributed over the available debris screen area. Blockage should be calculated based on levels of destruction estimated (Refs. 1 and 12).
8. Evaluation or confirmation of (a) sump hydraulic performance (e.g., geometric effects and air ingestion),
(b) debris effects (e.g.,
debris transport, interceptor blockage, and head loss), and (c) the combined impact on NPSH available at the pump inlet should be per formed to ensure that long-term recirculation cooling can be accomplished. Such evaluation should arrive at a determination of NPSH margin calculated at the pump inlet. An assessment of the susceptibility of the recircu lation pump seal and bearing assembly design to failure due to particulate ingestion and abrasive effects should be made to protect against degradation of long-term recirculation pumping capacity.
9. The top of the debris interceptor structures should be a solid cover plate that is designed to be fully submerged after a LOCA and completion of the ECC
.injection. It should be designed to ensure the venting of air otherwise trapped underneath.
10.
The debris interceptors should be designed to withstand the vibratory motion of seismic events with out loss of structural integrity.
11.
The size of openings in the debris screens should be based on the minimum restriction found in systems served by the pumps performing the recircula tion function. The minimum restriction should take into account the requirements of the systems served.
12.
Sump outlets should be designed to prevent degradation of pump performance by air ingestion and other adverse hydraulic effects (e.g., circulatory flow patterns, high intake-head losses).
13.
Materials for debris interceptors should be selected to avoid degradation during periods of inactivity and operation and should have a low sensitivity to such adverse effects as stress-assisted corrosion that may be induced by the chemically reactive spray during LOCA
conditions.
14.
The debris interceptor structures should include access. openings to facilitate inspection of these struc tures, any vortex suppressors, and the sump outlets.
15.
Inservice inspection requirements for ECC sump components (i.e., debris interceptors, any vortex sup pressors, and sump outlets) should include:
a. Inspection during every refueling period down time, and b. A visual examination for evidence of structural distress or corrosion.
2. Boiling Water Reactors The suppression pool, which is the source of water for such functions as emergency core cooling, contah*)
ment heat removal, and containment atmosphere cleanup following a LOCA in conjunction with the vents and downcomers between the drywell and the wetwell, should contain the following features:
1. The inlet of pumps performing the above func tions should be protected by two debris interceptors:
a. A fine downstream debris screen and b. A coarse upstream trash rack to prevent large debris from reaching the debris screen.
It should be noted that certain design features of BWRs may perform a function equivalent to that of trash racks and debris screens. Design features such as deflectors and suction strainers may be considered equivalent to trash racks and debris screen
s. The terms
"trash rack"
and "debris screen" include equivalent plant features.
2. If it is demonstrated that significant amounts of debris will not be generated within the wetwell, the trash rack may be located in the drywell or the down comer system between the drywell and wetwell.
3. All drains from the upper regions of the reacte building should terminate in such a manner that dire',*
streams of water, which may contain entrained debris, will not impinge on the debris interceptors.
4. The strength of the trash rack should be adequate to protect. the debris screen from missiles and other large debris. Each interceptor should be capable of withstanding the loads imposed by missiles, by debris, and by head differentials due to blockage.
5. Bulk suppression pool velocity due to recirculation operation should be considered for both debris transport and coolant velocity computations.
6. The available interceptor area used in determining the design coolant velocity should conservatively account for blockage that may result. Fibrous debris should be assumed to be uniformly distributed over the available debris screen surface. Blockage should be calculated based on levels of destruction estimated. (See Refs. I
and 12.)
7. Evaluation or confirmation of (a) suppression pool hydraulic performance (e.g., geometric effects and air ingestion),
(b)
debris effects (e.g.,
debris transport, interceptor blockage and head loss, and clogging of pump seals by particulates), and- (c) the combined impact on NPSH available at the pump inlet should I
performed to ensure that long-term recirculation ooi.,*
can be accomplished. An assessment of the susceptibility of the recirculation pump seal and bearing assembly
1.82-6
design to failure due to particulate ingestion and abra sive effects should be made to protect against degrada tion of long-term recirculation pumping capacity.
k
8. The debris interceptors should be designed to withstand the vibratory motion of seismic events with out loss of structural integrity.
9. The size of openings in the screens should be based on the minimum restriction found in systems served by the suppression pool. The minimum restriction should take into account the operability of the systems served.
10.
The pool outlets to the recirculation pumps should be designed to prevent degradation of pump performance through air ingestion and other adverse hydraulic effects (e.g., circulatory flow patterns, high intake-head losses).
11.
Material for debris interceptors should be selected to avoid degradation during periods of inactivity and normal operations and should be compatible with the characteristics of the spray during LOCA events.
12.
Inservice inspection requirements should include:
(a)
inspection during every refueling period downtime, (b)
a visual examination for evidence of struc tural distress or corrosion, and (c)
an inspection, for evidence of debris or trash, of the wetwell air spaces and the drywell floor region, including the vents, downcomers, and deflectors.
D. IMPLEMENTATION
The purpose of this section is to provide information to applicants regarding the NRC staff's plans for using this regulatory guide. This regulatory guide has been developed from an extensive experimental and analytical data base. The applicant is free to select alternative calculation methods that are founded on substantiating experiments or limiting analytical considerations. Except in those cases in which the applicant proposes an alternative method for complying with the specified portions of the Commission's regulations, the methods described in this guide will be used by the NRC staff in its evaluation of all:
1. Construction permit applications and applications for preliminary design approval that are docketed after May 1986.
2. Applications for final design approval of standard ized designs that are intended for referencing In future construction permit applications and have not received approval by May 1986.
3. Applications for licenses to manufacture that are docketed after May 1986.
1.82-7
APPENDIX A
GUIDELINES FOR REVIEW OF SUMP DESIGN AND
K
WATER SOURCES FOR EMERGENCY CORE COOLING
The ECC sump performance should be evaluated under possible post-LOCA
conditions to determine design adequacy for providing long-term recirculation.
Technical evaluations can be subdivided into (1) sump hydraulic performance, (2) LOCA-induced debris effects, and (3)
pump performance under adverse conditions.
Specific considerations within these categories, and the combining thereof, are shown in Figure A-I. Determina tion that adequate NPSH margin exists at the pump inlet under all postulated post-LOCA conditions is the final requirement.
Sump Hydraulic Performance Sump hydraulic performance (with respect to air ingestion potential) can be evaluated on the basis of submergence level (or water depth above the sump outlets) and required pumping capacity (or pump inlet velocity). The water depth above the pipe centerline (s)
and the inlet pipe velocity (U) can be expressed non dimensionally as the Froude number:
Froude number = U//
where g is the acceleration due to gravity. Extensive experimental results have shown that the hydraulic performance of ECC sumps (particularly the potential for air ingestion) is a strong function of the Froude number. Other nondimensional parameters (e.g., Reynolds number and Weber number) are of secondary impor tance.
Sump hydraulic performance can be divided into three performance categories:
1. Zero air ingestion, which requires no vortex suppressors or increase of the "required" NPSH above that from the pump manufacturer's curves.
2. Air ingestion 2% or less, a conservative level at which degradation of pumping capability is not expected based on an increase of the "required" NPSH
(see Figure A-2),
3. Use of vortex suppressors to reduce air ingestion effects to zero.
For PWRs, zero air ingestion can be ensured by use of the design guidance set forth in Table A-I. Deter mination of those designs having air ingestion levels of
2% or less can be obtained using correlations given in Table A-2 and the attendant sump geometric envelope.
Geometric and screen guidelines for PWRs are contained in Tables A-3.1, A-3.2, A-4, and A-5. Table A-6 presents design guidelines for vortex suppressors that have shown the capability to reduce air ingestion to zero. These guidelines (Tables A-I through A-6) were developed from extensive hydraulic tests on full-scale sumps and provide a rapid means of assessing sump hydraulic performance. If the PWR sump design deviates signifi cantly from the design boundaries noted, similar per formance data should be obtained for verification of adequate sump hydraulic performance.
For BWRs, full-scale tests of pool outlet designs for recirculation pumps have shown that air ingestion is zero for Froude numbers less than 0.8 with a minimum submergence of 6 feet, and operation up to a Froude number 1.0 with the same minimum submergence may be possible before air ingestion levels of 2% may occur (Refs. I and 7).
LOCA-Induced Debris Effects Assessment of LOCA debris generation and determi nation of possible debris interceptor blockage is complex.
The evaluation of this safety question is dependent on the types and quantities of insulation employed, the location of such insulation materials within containment and with respect to the sump location, the estimation of quantities of debris generated by a pipe break, an, the migration of such debris to the interceptors. Thulj blockage estimates are specific to the insulation material and the plant design and require consideration of such effects as are outlined in Table A-7.
Since break jet forces are the dominant debris gener ator, the predicted jet envelope will determine the quantities and types of insulation debris. Figure A-3 provides a three-region model that has been developed from analytical and experimental considerations as identified in Reference 1. The destructive results of the break jet forces will be considerably different for differ ent types of insulation and must be individually addressed. The insulation type, how and whether it is encapsulated, and how it is fastened to the insulated surfaces all have significant influence on the maximum volume of insulation debris generated. Region I repre sents a total destruction zone; Region II a region where high levels of damage are possib~le depending on insula tion type, whether encapsulation is employed, methods of attachment, etc.; and Region HI, a region where dislodgement of insulation in whole, or as-fabricated, segments is likely occur. A more detailed discussion of these considerations is provided in Reference 1. Use of the outer boundary of Region II for estimating maxi mum volumes of total insulation destruction is consid ered a conservative bounding condition.
References 1, 9, 10, 11, and 12 provide more detaile&._
information relevant to assessment of debris generation and transport.
1.82-8
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 pumping capacity.
The percentage has been at times arbitrary, but gener ally in the range of 1% to 3%. A 2% limit on allowed air ingestion is recommended since higher levels have been shown to initiate degradation of pumping capacity.
The 2% by volume limit on sump air ingestion and the NPSH requirements act independently. However, air ingestion levels less than 2% can also affect NPSH
requirements. If air ingestion is indicated, correct the NPSH requirement from the pump curves by the rela tionship:
NPSHrequired(atp <2%) = NPSHrequired(liquid) x where 0 = 1 I+ O.SOcp and ctp is the air ingestion rate (in percent by volume) at the pump inlet flange.
Combined Effects As shown in Figure A-I, three interdependent effects (i.e., sump hydraulic performance, debris effects, and pump operation under adverse conditions) require evalu ation for determining long-term recirculation capability.
Figure A-2 provides a logic diagram for combining these considerations to evaluate the ECC sump design and expected performance. The same logic applies to BWR
design evaluations of suppression pools and the outlets to recirculation pumps.
1.82-9
TABLE A-I
HYDRAULIC DESIGN GUIDELINES* FOR ZERO AIR INGESTION
Item Horizontal Outlets Vertical Outlets Minimum Submergence, s (ft)
9
9 (m)
2.7
2.7 Maximum Froude Number, Fr
0.25
0.25 Maximum Pipe Velocity, U (ft/s)
4
4 (m/s)
1.2
1.2
- These guidelines were established using experimental results from References 3.4, and 5 and are based on sumps having a right rectan gular shape.
Cover Plate Trash Rack
_____
__
/
and S...
Minimu Wte:Debris Screen V!
Minimum Water H I
I
-
-
Fr =
U
1.82-10
TABLE A-2 HYDRAULIC DESIGN GUIDELINES FOR AIR INGESTION - 2%
Air ingestion (ot) is empirically calculated as Ct= a. +(a,1 xFr)
where ao0 and axl are coefficients derived from test results as given in the table below.
Horizontal Outlets Vertical Outlets Item Dual Single Dual Single Coefficient a,
-2.47
-4.75
-4.75
-9.14 Coefficient a,
9.38
18.04
18.69
35.95 Minimum Submergence, s (ft)
7.5
8.0
7.5
10.0
(W)
2.3
2.4
2.3
3.1 Maximum Froude Number, Fr
0.5
0.4
0.4
0.3 Maximum Pipe Velocity, U (ft/s)
7.0
6.5
6.0
5.5 (m/s)
2.1
2.0
1.8
1.7 Maximum Screen Face Velocity (blocked and minimum submergence) (ft/s)
3.0
3.0
3.0
3.0
(m/s)
0.9
0.9
0.9.
0.9 Maximum Approach Flow Velocity (ft/a)
0.36
0.36
0.36
0.36 (rn/S)
0.11
0.11
0.11
0.11 Maximum Sump Outlet Coefficient, CL
1.2
1.2
1.2
1.2 Cover Plate Trash Rack
- /b and
--
M
u We Debris Screen N7*
Minimum Water!,
II
II
Level as Determined During Design Fr =
U
1.82-11 i
il
TABLE A-3.1 GEOMETRIC DESIGN ENVELOPE GUIDELINES FOR HORIZONTAL SUCTION OUTLETS*
Size Sump Outlet Position"
Screen Sump Outlet Aspect Min. Perimeter Min. Area Ratio (ft)
(in)
ey/d (B - ey)/d c/d b/d f/d ex/d (ft2)
(M2)
Dual I to 5
36
11
>m4
75
7
1
- o3
> 1.5
> I>
1.5 Single
1 to 5
16
4.9
35
3.3
- Dimnanlons are always measured to pipe centexilhn.
0prefetrod location.
Trash Rack
-
and Debrs Screeni Aspect Ratio = L/B
Minimum Perimeter = 2(L + B)
C.
II
II
C,
t.J
C-
C
C
Size Sump Outlet Position**
Screen Sump Outlet Aspect Min. Perimeter Min. Area Ratio (ft)
(m)
ey/d (B - ey)/d c/d bid f/d ex/d (ft 2 )
(M2 )
Dual I to S
36
11
>0
>4
75
7
>. I1
> I
I
> 1.s Single I to 5
16
4.9
<1.5
-
35
3.3
- Dimensions are always meesured to pipe centerline.
"Preferred location.
Trash Rack and Debris Screen II
Aspect Ratio - L/B
Minimum Perimeter - 2(L + 9)
C
TABLE A-3.2 GEOMETRIC DESIGN ENVELOPE GUIDELINES FOR VERTICAL SUCTION OUTLETS*
- OQ
TABLE A-4 ADDITIONAL GUIDELINES RELATED TO SUMP SIZE AND PLACEMENT
1.
"The clearance between the trash rack and any wall or obstruction of length 9. equal to or greater than the length of the adjacent screen/grate (B. or L.) should be at least 4 ft (1.2 m).
2.
A solid wall or large obstruction may form the boundary of the sump on one side only, ie., the sump must have three sides open to the approach flow.
3.
These additional guidelines should be followed to ensure the validity of the data in Tables A-I, A-2, A-3.1, and A-3.2.
Trash Rack and Debris Screen
1.82-14
TABLE A-5 DESIGN GUIDELINES* FOR INTERCEPTORS AND COVER PLATE
1. Screen area should be obtained from Table A-3.1 and A-3.2.
2.
Minimum height of interceptors should be 2 feet (0.61 m).
3.
Distance from sump side to screens, gs, may be any reasonable value.
4.
Screen mesh should be V4 inch (6.4 mm) or finer.
5.
Trash racks should be vertically oriented 1-to lb-inch (25- to 38-mm) standard floor grate or equivalent.
6.
The distance between the debris screens and trash racks should be 6 inches (15.2 cm) or less.
7.
A solid cover plate should be mounted above the sump and should fully cover the trash rack. The cover plate should be designed to ensure the release of air trapped below the plate (a plate located below the minimum water level is preferable).
- See Reference 1.
Solid Cover Plate
-.. ,.,Tr sh Rack
- 'Debrls Screen
%" Mesh (max)
1.82-15
TABLE A-6 GUIDELINES FOR SELECTED VORTEX SUPPRESSORS*
1.
Cubic arrangement of standard l%-inch (30-mm) deep or deeper floor grating (or its equivalent) with a charac-"-ý
teristic length, £4, that is at least 3 pipe diameters and with the top of the cube submerged at least 6 inches
(15.2 cm) below the minimum water level. Noncubic designs with 9. > 3 pipe diameters for the horizontal upper grate and satisfying the depth and distances to the minimum water level given for cubic designs are acceptable.
2.
Standard 1l-inch (38-mm) or deeper floor grating (or its equivalent) located horizontally over the entire sump and containment floor inside the screens and located below the lip of the sump pit.
- Tests on these types of vortex suppressors at Alden Research Laboratory have demonstrated their capability to reduce air ingestion to zero even under the most adverse conditions simulated.
Design #1:
Trash Rack and Solid Top Cover Debris Screen
5 ----------
- - --
Floor Grtins Floor Grating Trash Rack and Dabri: Scraen Trash, Rack and SolidTop overDebris Scraen Design #2.
o-~poa
1.82-16
TABLE A-7 DEBRIS ASSESSMENT
CONSIDERATION
1. Debris generator (pipe breaks and location as identified in SRP Section 3.6.2)
2. Expanding jets a
S
0
Major pipe breaks and location Pipe whip and pipe impact Break jet expansion envelope (This is the malor debris generator)
"* Jet expansion envelope
"* Piping and plant components targeted (i.e., steam generators)
"* Jet forces on insulation
"* Insulation that can be destroyed or dislodged by blowdown jets
"* Survivability under jet loading
3. Short-term debris transport (transport jet forces)
4. Long-term debris transport (transport during the recirculation phase)
by blowdown to the sump a
0
0
0
0
0
S
0
S
0
U
a S
S
5. Screen or sump outlet blockage effects (impairment of flow and/or NPSH margin)
6. Downstream blockage (effects of debris deposition and recirculation)
Key elements for assessment of debris effects Jet/equipment interaction Jet/crane wall interaction Sump location relative to expanding break jet Containment layout and sump (or. suction) locations Debris physical characteristics Recirculation velocity Debris transport velocity Screen or outlet area Water level under post-LOCA conditions Recirculation flow requirements Head loss across blocked screen or outlet Core coolant channels Spray nozzles Pump clearances
"* 3stimated amount and types of debris that can reach sump
"* Predicted screen or outlet blockage
"* AP across blocked screens or outlets
"" NPSH required vs NPSH available
1.82-17 EVALUATE
PUMPS
SUMPS
"* Location. In Plant;
Redundancy
"* Geometric Parameters Interceptors (Racks. Screens),
Cover. etc.
I
"* Short-Term Transport by Blowdown Jet
"* Long-Term Transpoit by Recirculation Velocities
" Potential for Interceptor Blockage
" Head Loss Across Interceptors i
I
"* Pump Design and Operating Characteristics
"* NPSH Requirements (No Air)
" Sump and Suction Piping - Losses
"* Effects of Air Ingestion on NPSH Required
"* Cavitation Potential
- Inlet Design
- Temperature Effects
"* Effects of Particulate and Debris Ingestion Is There Adequate NPSH Margin Under All Post-LOCA Conditions?
FIGURE A-i. Technical Consideration Relevant to ECC Sump Performance
"* Types. Quantities, and Location of Insulation
"* Containment Layout and Break Locations
"* Estimated Quantity of Debris Generated
00
oo3
_
_C
C
!
- Hydraulic Characteristics
'
- Water Level Above Sump Outlet
- Sump Outlet Velocity
-Air Ingestion
-Inlet Losexo
"* NPSH Required
"* NPSH Available Id
l LI
l
DEBRIS
DEFINITIONS
NPSH - Net Positive Suction Head NPSHA - NPSH Available NPSHR - NPSH Required a - Void Fraction I% by Volume)
P - Pressure T - Temperature U - Velocity In Pipe FIGURE A-2. Combined Technical Considerations for Sump Performance
1.82-19
,' REGION 1I
High Levels of I
D
lamage Possible.'I"
Materials and I
Attachment Dependent
4
,
BID'
/
REGION III
islodging in a-Fabricated"
Pieces or Segments
2.5 SBoundary of a Right Circular Cylinder Originating at the Postulated Pipe Break Note:
Pressure Isobars Shown Are Calculated Target Pressures for Break Conditions of
150 Bars and 35K
Subcooiing R = Radius of Circular Flat Plate Target L = Distance From Break to Target D - Diameter of Broken Pipe
- O~~
7-
1Bar P s
0.5 psi or Major Wall Boundary N
FIGURE A-3. Multiple Region Insulation Debris Model (A discussion of the model is provided in Ref. 1)
1.82-20
REGION I
Total Destruction D
R/D
I
m m
m
REFERENCES
1.
U.S. Nuclear Regulatory Commission, "Containment Emergency Sump Performance (Technical Findings Related to Unresolved Safety Issue A-43)," NUREG 0897, Revision 1, October 1985.
2.
U.S. Nuclear Regulatory Commission, "Methodology for Evaluation of Insulation Debris Effects,"
NUREG/CR-2791 (SAND82-7067), September 1982.
3.
U.S.
Nuclear Regulatory Commission,
"A
Para metric Study of Containment Emergency Sump Performance,"
NUREG/CR-2758 (SAND82-0624),
July 1982.
4.
U.S. Nuclear Regulatory Commission,
"A
Para metric Study of Containment Emergency Sump Per formance: Results of Vertical Outlet Sump Tests,"
NUREG/CR-2759 (SAND82-7062),
October 1982.
5.
U.S. Nuclear Regulatory Commission, "Assessment of Scale Effects on Vortexing, Swirl and Inlet Losses in Large Scale Sump Models,"
(SAND82-7063), June 1982.
6.
U.S.
Nuclear Regulatory Commission,
"Results of Vortex Suppressor Tests, Single Outlet Sump Tests and Miscellaneous Sensitivity Tests,"
NUREG/CR-2761 (SAND82-7065), September 1982.
7.
U.S. Nuclear Regulatory Commission, "Hydraulic Performance of Pump Suction Inlets for Emergency Core Cooling Systems in Boiling Water Reactors,"
NUREG/CR-2772 (SAND82-7064), June 1982.
8.
U.S. Nuclear Regulatory Commission, "An Assess ment of Residual Heat Removal and Containment Spray Pump Performance Under Air and Debris Ingesting Conditions," NUREG/CR-2792 (CREARE
TM-825), September 1982.
9.
U.S. Nuclear Regulatory Commission, "Buoyancy, Transport, and Head Loss of Fibrous Reactor Insulation," NUREG/CR-2982 (SAND82-7205), Revi sion 1, July 1983.
10. U.S. Nuclear Regulatory Commission, "The Suscep tibility of Fibrous Insulation Pillows to Debris Formation Under Exposure to Energetic Jet Flows,"
NUREG/CR-3170 (SAND83-7008), March 1983.
11. U.S. Nuclear Regulatory Commission, "Probabilistic Assessment of Recirculation Sump Blockage Due to Loss-of-Coolant Accidents," NUREG/CR-3394, Vol umes I and 2 (SAND83-7116), July 1983.
12. U.S. Nuclear Regulatory Commission, "Transport and Screen Blockage Characteristics of Reflective Metallic Insulation Materials,"
NUREG/CR-3616 (SAND83-7471), January 1984.
NOTE: NUREG-series documents are available from the Superintendent of Documents, U.S.
Govern ment Printing Office, P.O. Box 37082, Wash ington, D.C. 20013-7982. Information on order ing may be obtained by calling (202) 275-2060
or 2171.
1.82-21
REGULATORY ANALYSIS
A separate regulatory analysis has not been prepared for the revision to this regulatory guide. The changes were made as a result of the resolution of unresolved safety issue (USI) A-43, "Containment Emergency Sump Performance."
A regulatory analysis (NUREG 0869, Revision 1, October 1985) prepared for the resolution of USI A-43 was made available in the Commission's Public Document Room, 1717 H Street NW., Washing ton, D.C., at the time of its publication. This analysis is appropriate for Revision 1 to Regulatory Guide 1.82.
1.82-22