ML003739202

Draft Regulatory Guide DG-1038 (Proposed Revision 2 to Regulatory Guide 1.82), Water Sources for Long-Term Recirculation Cooling Following a Loss-Of-Cooland Accident

ML003739202
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Issue date:	07/31/1995
From:	Office of Nuclear Regulatory Research
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DG-1038 RG-1.082, Rev 2
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• 0 o U.S. NUCLEAR REGULATORY COMMISSION July 1995 4 C, OFFICE OF NUCLEAR REGULATORY RESEARCH Division I Z #Draft DG-1038 DRAFT REGULATORY GUIDE

Contact:

A. Serkiz (301)415-6563 M. Marshall (301)415-5895 1 DRAFT REGULATORY GUIDE DG-1038 2 (Proposed Revision 2 to Regulatory Guide 1.82) 3 WATER SOURCES FOR LONG-TERM RECIRCULATION COOLING 4 FOLLOWING A LOSS-OF-COOLANT ACCIDENT 5 A. INTRODUCTION 6 General Design Criteria 35, "Emergency Core Cooling"; 36, "Inspection of 7 Emergency Core Cooling System"; 37, "Testing of Emergency Core Cooling System";

38, 8 "Containment Heat Removal"; 39, "Inspection of Containment Heat Removal System"; and 9 40, "Testing of Containment Heat Removal System," of Appendix A, "General Design 10 Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Domestic Licensing of 11 Production and Utilization Facilities," require that systems be provided to perform 12 specific functions, e.g., emergency core cooling, containment heat removal, and 13 containment atmosphere clean up following a postulated design basis accident.

These 14 systems must be designed to permit appropriate periodic inspection and testing to 15 ensure their integrity and operability. General Design Criterion 1, "Quality 16 Standards and Records," of Appendix A to 10 CFR Part 50 requires that structures, 17 systems, and components important to safety be designed, fabricated, erected, and 18 tested to quality standards commensurate with the importance of the safety functions 19 to be performed.

20 This guide describes methods acceptable to the NRC staff for implementing 21 these requirements with respect to the sumps and suppression pools performing the 22 functions of water sources for emergency core cooling, containment heat removal, or This regulatory guide is being issued in draft form to involve the public in the early stages of the development of a regulatory position in this area. It has not received complete staff review and does not represent an official NRC staff position.

Public comments are being solicited on the draft guide (including any implementation schedule) and its associated regulatory analysis or value/impact statement. Comments should be accompanied by appropriate supporting data. Written comments may be submitted to the Rules Review and Directives Branch, DFIPS, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555. Copies of comments received may be examined at the NRC Public Document Room, 2120 L Street NW., Washington, DC. Comments will be most helpful if received by October 2, 1995.

Requests for single copies of draft or final guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention:

Office of Administration, Distribution and Mail Services Section, or by fax to (301)415-2260.

1 containment atmosphere clean up. The guide also includes guidelines for 2 evaluating the adequacy of the availability of the sump and suppression pool 3 for long-term recirculation cooling following a loss-of-coolant accident 4 (LOCA). This guide applies to light-water-cooled reactors. Additional 5 information is provided in NRC Draft Bulletin, "Potential Plugging of 6 Emergency Core Cooling Suction Strainers by Debris in Boiling Water Reactors" 7 (Ref. 1); NRC Bulletin 93-02, "Debris Plugging of Emergency Core Cooling 8 Suction Strainers" (Ref. 2); Supplement 1 to NRC Bulletin 93-02, "Debris 9 Plugging of Emergency Core Cooling Suction Strainers" (Ref. 3); and Generic 10 Letter 85-22, "Potential for Loss of Post LOCA Recirculation Capability Due to 11 Insulation Debris Blockage" (Ref. 4).

12 Regulatory guides are issued to describe and make available to the 13 public such information as methods acceptable to the NRC staff for 14 implementing specific parts of the Commission's regulations, techniques used 15 by the staff in evaluating specific problems or postulated accidents, and 16 guidance to applicants. Regulatory guides are not substitutes for 17 regulations, and compliance with regulatory guides is not required.

18 Regulatory guides are issued in draft form for public comment to involve the 19 public in the early stages of developing the regulatory positions. Draft 2:0 regulatory guides have not received complete staff review and do not represent 21 official NRC staff positions.

22 The information collections mentioned in this draft regulatory guide are 23 covered by the requirements in 10 CFR Part 50, which were approved by the 24 Office of Management and Budget, approval number 3150-0011.

25 B. DISCUSSION 26 GENERAL 27 The primary safety concerns regarding long-term recirculation cooling 28 following a LOCA are (1) LOCA-generated and pre-LOCA debris materials 29 transported to the debris interceptors, resulting in adverse blockage effects, 30 (2) post-LOCA hydraulic effects, particularly air ingestion, and (3) the 31 combined effects of items (1) and (2) relative to long-term recirculation Change bars indicate substantive changes from Revision 1 of Regulatory Guide 1.82.

1 Debris resulting from a LOCA has the potential to block emergency core 2 cooling (ECC) debris interceptors (i.e., trash racks, debris screens, suction 3 strainers) and result in degradation or loss of NPSH margin. Such debris can 4 be divided into the following categories: (1) debris that is generated by the 5 LOCA and is transported by blowdown forces (e.g., insulation, paint), (2) 6 debris that is generated or transported by washdown, and (3) other debris that 7 existed prior to a LOCA (e.g., corrosion material, sludge in a BWR suppression 8 pool). Debris can be further subdivided into (1) debris that has a high 9 density and could sink but is still subject to fluid transport if local 10 recirculation flow velocities are high enough, (2) debris that has an 11 effective specific gravity of 1.0 and tends to be suspended or sink slowly but 12 will nonetheless be transported by very low velocities or local fluid 13 turbulence phenomena, and (3) debris that will float indefinitely by virtue of 14 low density and will be transported to and possibly through the debris 15 interceptors. Debris generation, early debris transport, long-term post-LOCA 16 transport, and attendant blockage of debris interceptors must be evaluated to 17 ensure that the ability of the ECCS to provide long-term post-LOCA core 18 cooling is not jeopardized. All possible debris sources should be evaluated, 19 including but not limited to insulation materials (e.g., fibrous, ceramic, and 20 metallic), filters, corrosion material, and paints or coatings. Relevant 21 information for such evaluations is provided in the Regulatory Position and in 22 Appendix A to this guide. References 5 through 17 provide additional 23 information relevant to the above concerns.

24 PRESSURIZED WATER REACTORS 25 In pressurized water reactors (PWRs), the containment emergency sumps 26 provide for the collection of reactor coolant and chemically reactive spray 27 solutions following a LOCA; thus, the sumps serve as water sources to effect 28 long-term recirculation for the functions of residual heat removal, emergency 29 core cooling, and containment atmosphere cleanup. These water sources, the 30 related pump inlets, and the piping between the sources and inlets are 31 important safety components. The sumps servicing the emergency core cooling 32 systems (ECCS) and the containment spray systems (CSS) are referred to in this 3

I design guide as ECC sumps. Features and relationships of the ECC sumps 2 pertinent to this guide are shown in Figure 1.

3 The design of PWR sumps and their outlets includes consideration of the 4 avoidance of air ingestion and other undesirable hydraulic effects (e.g.,

5 circulatory flow patterns, outlets leading to high head losses). The location 6 and size of the sump outlets within ECC sumps is important in order to 7 minimize air ingestion since ingestion is a function of submergence level and 8 velocity in the outlet piping. It has been experimentally determined that air 9 ingestion for PWRs can be minimized or eliminated if the sump hydraulic design 10 considerations provided in Appendix A to this guide are followed. References 11 5, 7, 10, 11, and 12 provide additional technical information relevant to sump 12 ECC hydraulic performance and design guidelines.

13 Placement of the ECC sumps at the lowest level practical ensures maximum 14 use of available recirculation coolant. Since there may be places within the 15 containment where coolant could accumulate during the containment spray 16 period, these areas can be provided with drains or flow paths to the sumps to 17 prevent coolant holdup. This guide does not address the design of such drains 18 or paths. Because debris can migrate to the sump via these drains or paths, 19 they are best terminated in a manner that will prevent debris from being 20 transported to and accumulating on or within the ECC sumps.

21 Containment drainage sumps are used to collect and monitor normal 22 leakage flow for leakage detection systems within containments. They are 23 separated from the ECC sumps and are located at an elevation lower than the 24 ECC sumps to minimize inadvertent spillover into the ECC sumps from minor 25 leaks or spills within containment. The floor adjacent to the ECC sumps would 26 normally slope downward, away from the ECC sumps, toward the drainage 27 collection sumps. This downward slope away from the ECC sumps will minimize 28 the transport and collection of debris against the debris interceptors.

29 High-density debris may be swept along the floor by the flow toward the trash 30 rack. A debris curb upstream of and in close proximity to the rack will 31 decrease the amount of such debris reaching the rack.

32 It is necessary to protect sump outlets with debris interceptors of 33 sufficient strength to withstand the vibratory motion of seismic events, to 4

1 FIGURE 1. PWR WATER FROM SPRAY LOCA COVER PLATE 4 )EBRIS SCREEN I DEBRIS RACK INTERCEPTORS

'IT RECIRCULATION PUMP to (6) from (o)

(o) - SUMP OUTLET Ii) = PUMP INLET

" AS DETERMINED DURING SAFETY ANALYSIS CUBIC OR HORIZONTAL SUPPRESSOR MAY BE USED WITH EITHER SUMP OUTLET 5

1 loads imposed by the accumulation of debris. Considerations for selecting 2 materials for the debris interceptors include long periods of inactivity, 3 i.e., no submergence, and periods of operation involving partial or full 4 submergence in a fluid that may contain chemically reactive materials.

5 Isolation of the ECC sumps from high-energy pipe lines is an important 6 consideration in protection against missiles, and it is necessary to shield 7 the screens and racks adequately from impacts of ruptured high-energy piping 8 and associated jet loads from the break. When the screen and rack structures 9 are oriented vertically, the adverse effects from debris collecting on them 10 will be reduced. Redundant ECC sumps and sump outlets are separated to the 11 extent practical to reduce the possibility that an event causing the 12 interceptors or outlets of one sump to either be damaged by missiles or 13 partially clogged could adversely affect other pump circuits.

14 It is expected that the water surface will be above the top of the 15 debris interceptor structure after completion of the safety injection.

16 However, the uncertainties about the extent of water coverage on the 17 structure, the amount of floating debris that may accumulate, and the 18 potential for early clogging do not favor the use of a horizontal top 19 interceptor. Therefore, in computing available interceptor surface area, no 20 credit may be taken for any horizontal interceptor surface; preferably, the 21 top of the interceptor structure is a solid cover plate that will provide 22 additional protection from LOCA-generated loads and is designed to provide for 23 the venting of any trapped air.

24 Debris that is small enough to pass through the trash rack and that 25 could clog or block the debris screens or outlets needs to be analyzed for 26 head loss effects. Screen and sump outlet blockage will be a function of the 27 types and quantities of insulation debris that can be transported to these 28 components. A vertical inner debris screen would impede the deposition or 29 settling of debris on screen surfaces and thus help to ensure the greatest 30 possible free flow through the fine inner debris screen. Slowly settling 31 debris that is small enough to pass through the trash rack openings could 32 block the debris screens if the coolant flow velocity is too great to permit 33 the bulk of the debris to sink to the floor level during transport. If the 34 coolant flow velocity ahead of the screen is at or below approximately 5 35 cm/sec (0.2 ft/sec), debris with a specific gravity of 1.05 or more is likely 6

I to settle before reaching the screen surface and thus will help to prevent 2 undue clogging of the screen.

3 The size of openings in the screens is dependent on the physical 4 restrictions that may exist in the systems that are supplied with coolant from 5 the ECC sump. The size of the mesh of the fine debris screen is determined by 6 considering a number of factors, including the size of the openings in the 7 containment spray nozzles, coolant channel openings in the core fuel 8 assemblies, and such pump design characteristics as seals, bearings, and 9 impeller running clearances.

10 As noted above, degraded pumping can be caused by a number of factors, 11 including plant design and layout. In particular, debris blockage effects on 12 debris interceptor and sump outlet configurations and post-LOCA hydraulic 13 conditions (e.g., air ingestion) must be considered in a combined manner.

14 Small amounts of air ingestion, i.e., 2% or less, will not lead to severe 15 pumping degradation if the "required" NPSH from the pump manufacturer's curves 16 is increased based on the calculated air ingestion. Thus it is important to 17 use the combined results of all post-LOCA effects to estimate NPSH margin as 18 calculated for the pump inlet. Appendix A to this guide provides information 19 for estimating NPSH margins in PWR sump designs where estimated levels of air 20 ingestion are low (2% or less). References 5 and 12 provide additional 21 technical findings relevant to NPSH effects on pumps performing the functions 22 of residual heat removal, emergency core cooling, and containment atmosphere 23 cleanup. When air ingestion is 2% or less, compensation for its effects may 24 be achieved without redesign if the "available" NPSH is greater than the 25 "required" NPSH plus a margin based on the percentage of air ingestion.

If 26 air ingestion is not small, redesign of one or more of the recirculation loop 27 components may be required to achieve satisfactory design.

28 To ensure the operability and structural integrity of the racks and 29 screens, access openings are necessary to permit inspection of the ECC sump 30 structures and outlets. Inservice inspection of racks, screens, vortex 31 suppressors, and sump outlets, including visual examination for evidence of 32 structural degradation or corrosion, should be performed on a regular basis at 33 every refueling period downtime. Inspection of the ECC sump components late 34 in the refueling period will ensure the absence of construction trash in the 35 ECC sump area.

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1 BOILING WATER REACTORS 2 In boiling water reactors (BWRs), the suppression pool, in conjunction 3 with the primary containment, downcomers, and vents, serves as the water 4 source for effecting long-term recirculation cooling. This source, the 5 related pump suction inlets, and the piping between them are important safety 6 components. Features and relationships of the suppression pool pertinent to 7 this guide are shown in Figure 2. Concerns with the performance of the sup 8 pression pool hydraulics and ECC pump suction strainers include consideration 9 of air ingestion effects, blockage of suction strainers (by debris), and the 10 combined effects of these items on the operability of the ECC pumps (e.g., the 11 impact on NPSH available at the pump inlets). References 5 and 11 provide 12 data on the performance and air ingestion characteristics of BWR suction 13 strainer configurations.

14 It is desirable to consider the use of debris interceptors (i.e.,

15 suction strainers) in BWR designs to protect the pump inlets and NPSH margins.

16 The debris interceptor can be a passive suction strainer or an active suction 17 strainer or active strainer system. A passive suction strainer is a device 18 that prevents debris, which may block restrictions in the systems served by 19 the ECC pumps or damage components, from entering the ECC pump suction line by 20 accumulating debris on a porous surface. An example of a passive suction 21 strainer is a truncated cone-shaped perforated plate strainer. An active 22 suction strainer or an active strainer system is a device or system that will 23 take some action to prevent debris, which may block restrictions in the 24 systems served by the ECC pumps or damage components, from entering the ECC 25 pump suction lines, remove debris from the flow stream upstream of the ECC 26 pumps, or mitigate any detrimental effects of debris accumulation. Examples 27 of active mitigation systems are listed in Appendix B.

28 Suppression pool debris transport analysis should include the effects of 29 LOCA progression because LOCAs of different sizes will affect the duration of 30 LOCA-related hydrodynamic phenomena (e.g., chugging, condensation oscilla 31 tion). The LOCA-related hydrodynamic phenomena and long-term recirculation 32 hydrodynamic conditions will affect the transport of debris in the suppression 33 pool.

8

I FIGURE 2. BWR 9

1 Debris that is transported to the suppression pool during a LOCA, or 2 that is present in the suppression pool prior to a LOCA, could block or damage 3 the suction strainers and needs to be analyzed for head loss effects. This 4 head loss analysis should include filtering of particulate debris by the 5 accumulated debris bed. The head loss characteristics of a debris bed will be 6 a function of the types and quantities of the debris, suction strainer 7 approach velocities, and LOCA-related hydrodynamic phenomena in the 8 suppression pool.

9 C. REGULATORY POSITION 10 1. PRESSURIZED WATER REACTORS 11 Reactor building sumps that are designed to be a source of water for the 12 functions of emergency core cooling, containment heat removal, or containment 13 atmosphere cleanup following a LOCA should meet the following.

14 1.1 A minimum of two sumps should be provided, each with sufficient capacity 15 to service one of the redundant halves of the ECCS and CSS.

16 1.2 To the extent practical, the redundant sumps should be physically 17 separated by structural barriers from each other and from high-energy 18 piping systems to preclude damage to the sump components (e.g., racks, 19 screens, and sump outlets) by whipping pipes or high-velocity jets of 20 water or steam.

21 1.3 The sumps should be located on the lowest floor elevation in the 22 containment exclusive of the reactor vessel cavity. The sump outlets 23 should be protected by at least two vertical debris interceptors: (1) a 24 fine inner debris screen and (2) a coarse outer trash rack to prevent 25 large debris from reaching the debris screen. A curb should be provided 26 upstream of the trash racks to prevent high-density debris from being 27 swept along the floor into the sump.

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1 1.4 The floor in the vicinity of the ECC sump should slope gradually 2 downward away from the sump.

3 1.5 All drains from the upper regions of the reactor building should 4 terminate in such a manner that direct streams of water, which may 5 contain entrained debris, will not impinge on the debris interceptors.

6 1.6 The strength of the trash racks should be adequate to protect the debris 7 screens from missiles and other large debris. Debris interceptors 8 should be capable of withstanding the loads imposed by missiles, by the 9 accumulation of debris, and by pressure differentials caused by post 10 LOCA blockage.

11 1.7 The available interceptor surface area used in determining the design 12 coolant velocity should be calculated to conservatively account for 13 blockage that may result. Only the vertical interceptor area that is 14 below the design basis water level should be considered in determining 15 available surface area. Fibrous insulation debris should be considered 16 as uniformly distributed over the available debris screen area.

17 Blockage should be calculated based on estimated levels of destruction 18 (References 5 and 16).

19 1.8 Evaluation or confirmation of (1) sump hydraulic performance (e.g.,

20 geometric effects and air ingestion), (2) debris effects (e.g., debris 21 transport, interceptor blockage, and head loss), and (3) the combined 22 impact on NPSH available at the pump inlet should be performed to ensure 23 that long-term recirculation cooling can be accomplished. Such an 24 evaluation should arrive at a determination of NPSH margin calculated at 25 the pump inlet. An assessment of the susceptibility of the recircu 26 lation pump seal and bearing assembly design to failure from particulate 27 ingestion and abrasive effects should be made to protect against 28 degradation of long-term recirculation pumping capacity.

29 1.9 The top of the debris interceptor structures should be a solid cover 30 plate that is designed to be fully submerged after a LOCA and completion 11

I of the ECC injection. It should be designed to ensure the venting of 2 air trapped underneath the cover.

3 1.10 The debris interceptors should be designed to withstand the vibratory 4 motion of seismic events without loss of structural integrity.

5 1.11 The size of openings in the debris screens should be based on the 6 minimum restriction found in systems served by the pumps performing the 7 recirculation function. The minimum restriction should take into 8 account the requirements of the systems served.

9 1.12 Sump outlets should be designed to prevent degradation of pump 10 performance by air ingestion and other adverse hydraulic effects (e.g.,

11 circulatory flow patterns, high intake-head losses).

12 1.13 Materials for debris interceptors should be selected to avoid 13 degradation during periods of inactivity and operation and should have a 14 low sensitivity to such adverse effects as stress-assisted corrosion 15 that may be induced by the chemically reactive spray during LOCA 16 conditions.

17 1.14 The debris interceptor structures should include access openings to 18 facilitate inspection of these structures, any vortex suppressors, and 19 the sump outlets.

20 1.15 Inservice inspection requirements for ECC sump components (i.e., debris 21 interceptors, any vortex suppressors, and sump outlets) should include 22 (1) inspection during every refueling period downtime and (2) a visual 23 examination for evidence of structural distress or corrosion.

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1 2. BOILING WATER REACTORS 2 2.1 Features Needed To Minimize the Potential for Loss of NPSH 3 The suppression pool, which is the source of water for such functions as 4 emergency core cooling and containment heat removal following a LOCA, in 5 conjunction with the vents and downcomers between the drywell and the wetwell, 6 should contain an appropriate combination of the following features and 7 actions to ensure the availability of the suppression pool for long-term 8 cooling. The adequacy of the combinations of the features and actions taken 9 should be evaluated using the criteria and assumptions in Regulatory Position 10 2.2.

11 2.1.1 The inlet of pumps performing the above functions should be protected 12 by a suction strainer placed upstream of the pumps; this is to 13 prevent the ingestion of debris that may block restrictions in the 14 systems served by the ECC pumps or damage components. The following 15 items should be considered in the design and implementation of a 16 passive strainer.

17 (1) A suction strainer design (i.e., size and shape) should be 18 chosen that will avoid the loss of NPSH from debris blockage 19 during the period that the ECCS is required to operate in 20 order to maintain long-term cooling or maximize the time before loss 21 of NPSH caused by debris blockage when used with an active 22 mitigation system (see Regulatory Position 2.1.4).

23 (2) The size of openings in the suppression pool suction strainers 24 should be based on the minimum restrictions found in systems 25 served by the suppression pool. The minimum restriction should 26 take into account the operability of the systems served. For 27 example, spray nozzle clearances, coolant channel openings in 28 the core fuel assemblies, and such pump design characteristics 29 as seals, bearings, and impeller running clearances will need 30 to be considered in the design to ensure long-term pump 13

to determine 1 operability. An assessment should be performed from debris 2 the ECCS pumps' susceptibility to degradation should be taken to 3 ingestion and abrasive effects, and actions 4 minimize the potential for degradation of long-term 5 recirculation pumping capacity.

to prevent 6 (3) ECC pump suction inlets should be designed ingestion and other 7 degradation of pump performance through air flow patterns, 8 adverse hydraulic effects (e.g., circulatory 9 high intake head losses).

building 10 (4) All drains from the upper regions of the reactor streams of water, 11 should terminate in such a manner that direct impinge on the 12 which may contain entrained debris, will not 13 suppression pool suction strainers.

be adequate to 14 (5) The strength of the suction strainers should other large debris.

15 protect the debris screen from missiles and withstanding the 16 Each suction strainer should be capable of and LOCA 17 loads imposed by missiles, debris accumulation, 18 induced hydrodynamic loads.

the 19 (6) The suction strainers should be designed to withstand of structural 20 vibratory motion of seismic events without loss 21 integrity.

to avoid 22 (7) Material for suction strainers should be selected normal operations.

23 degradation during periods of inactivity and Position 2.2.1) that 24 2.1.2 The amount of potential debris (see Regulatory be minimized. This may 25 could clog the ECC suction strainers should 26 be accomplished by:

designed to clean 27 (1) Containment cleanliness programs should be plant procedures 28 the suppression pool on a regular basis and 14

1 should be designed for control and removal of foreign materials 2 from containment, or 3 (2) Debris interceptors in the drywell in the vicinity of the 4 downcomers or vents may serve effectively in reducing debris 5 transport to the suppression pool. In addition to meeting 6 Regulatory Position 2.1.1, debris interceptors between the 7 drywell and wetwell should not reduce the suppression 8 capability of the containment.

9 2.1.3 If relying on operator actions to prevent the accumulation of debris 10 on suction strainers or to mitigate the consequences of the 11 accumulation of debris on the suction strainers, safety-related 12 instrumentation that provides operators with an indication and 13 audible warning of impending loss of NPSH for ECCS pumps should be 14 available in the control room.

15 2.1.4 An active component or system (see Appendix B) should be provided to 16 prevent the accumulation of debris on a suction strainer or mitigate 17 the consequences of accumulation of debris on a suction strainer. An 18 active system should be able to prevent debris that may block 19 restrictions found in the systems served by the ECC pumps from 20 entering the system. The operation of the active component or system 21 should not adversely affect the operation of other ECC components or 22 systems.

23 2.1.5 Inservice inspection requirements should be established that include 24 (1) inspection during every refueling outage to ensure the 25 cleanliness of the suppression pool, (2) a visual examination for 26 evidence of structural degradation or corrosion of the suction 27 strainers and strainer system, and (3) an inspection of the wetwell 28 and the drywell, including the vents, downcomers, and deflectors, for 29 the identification and removal of debris or trash that could 30 contribute to the blockage of suppression pool suction strainers.

15

1 2.1.6 Procedures should be established to use alternative water sources.

to align the 2 Periodic inspection and maintenance of the valves needed 3 ECCS with an alternative water source should be performed.

and actions 4 In order to demonstrate that a combination of the features and that the five 5 listed above are adequate to ensure long-term cooling a LOCA, an evaluation using 6 criteria of 10 CFR 50.46(b) will be met following 2.2 should be conducted.

7 the criteria and assumptions in Regulatory Position the accumulation of 8 If a licensee is relying on operator actions to prevent of the 9 debris on suction strainers or to mitigate the consequences evaluation should be 10 accumulation of debris on the suction strainers, an indications, time, and 11 performed to ensure that the operator has adequate 12 system capabilities to perform the actions required.

13 2.2 Evaluation of Long-Term Recirculation Capability should be used in a 14 The following techniques, assumptions, and criteria of a combination of 15 deterministic evaluation to ensure that any implementation 2.1 are adequate to 16 the features and actions listed in Regulatory Position after a LOCA.

17 ensure a reliable water source for long-term recirculation and criteria listed below 18 Unless otherwise noted, the techniques, assumptions, strainers. The 19 are applicable to an evaluation of passive and active to develop test 20 assumptions and criteria listed below can also be used 21 conditions for suction strainers or strainer systems.

22 2.2.1 Debris Generation and Sources generation 23 2.2.1.1 Consistent with the requirements of 10 CFR 50.46, debris of different 24 should be calculated for a number of postulated LOCAs provide 25 sizes, locations, and other properties sufficient to calculated.

26 assurance that the most severe postulated LOCAs are zone of 27 2.2.1.2 An acceptable method for determining the shape of the 17). The 28 influence of a break is described in NUREG/CR-6224 (Ref.

be used to 29 volume contained within the zone of influence should 16

I estimate the amount of debris generated by a postulated break.

2 The distance of the zone of influence from the break should be supported 3 by analysis or experiments for the break and potential debris. The 4 shock wave generated during postulated pipe break and the subsequent 5 jet should be the basis for estimating the amount of debris generated 6 and the size or size distribution of the debris generated within the 7 zone of influence.

8 2.2.1.3 As a minimum, the following postulated break locations should be 9 considered.

10 (1) Breaks on the main steam, feedwater, and recirculation lines 11 with the largest amount of potential debris within the expected 12 zone of influence, 13 (2) Large breaks with two or more different types of debris within 14 the expected zone of influence, 15 (3) Breaks in areas with the most direct path between the drywell 16 and wetwell, and 17 (4) Medium and large breaks with the largest potential particulate 18 debris to insulation ratio by weight.

19 2.2.1.4 All insulation, painted surfaces, and fibrous, cloth, plastic, or 20 particulate materials within the zone of influence should be 21 considered debris sources. Analytical models or experiments should 22 be used to predict the size of the postulated debris.

23 2.2.1.5 The cleanliness of the suppression pool and containment during plant 24 operation should be considered when estimating the amount and type of 25 debris available to block the suction strainers. The potential for 26 such material (e.g., corrosion products) to impact head loss across 27 the suction strainer should also be considered.

28 2.2.1.6 The amount of particulates estimated to be in the pool prior to a 29 LOCA should be considered to be the maximum amount of corrosion 30 products (i.e., sludge) expected to be generated since the last time 17

and amount of 1 the pool was cleaned. The size distribution samples.

2 particulates should be based on plant 3 2.2.2 Debris Transport debris will be 4 2.2.2.1 It should be assumed that all the postulated For active strainers that 5 transported to the suppression pool.

should be assumed that all the 6 prevent the accumulation of debris, it pool by the end of the 7 debris is transported to the suppression should be 8 blowdown. For other strainers, an appropriate period to the suppression pool from 9 assumed for the transportion of debris 10 the drywell.

(i.e., pool swell, 11 2.2.2.2 It should be assumed that LOCA-induced phenomena suspend all the debris 12 chugging, condensation oscillations) will the onset of the LOCA.

13 assumed to be in the suppression pool at until LOCA-induced 14 2.2.2.3 Credit should not be taken for debris settling ceased. The debris settling 15 turbulence in the suppression pool has validated analytically or 16 rate for the postulated debris should be 17 experimentally.

operations, LOCA 18 2.2.2.4 Bulk suppression pool velocity from recirculation hydrodynamic forces (e.g.,

19 related hydrodynamic phenomena, and other should be considered for 20 local turbulence effects or pool mixing) velocity computations.

21 both debris transport and suction strainer 22 2.2.3 Strainer Blockage and Head Loss amount of debris estimated 23 2.2.3.1 Strainer blockage should be based on the in Regulatory Position 24 using the assumptions and criteria described the wetwell per Regulatory 25 2.2.1, and on the debris transported to as well as other materials 26 Position 2.2.2. This volume of debris, pool prior to a LOCA, should 27 that could be present in the suppression 18

1 be used to estimate the rate of accumulation of debris on the 2 strainer surface.

3 2.2.3.2 The flow rate through the strainer should be used to estimate the 4 rate of accumulation of debris on the strainer surface.

5 2.2.3.3 The suppression pool suction strainer area used in determining the 6 approach velocity should conservatively account for blockage that may 7 result. Unless otherwise shown analytically or experimentally, 8 debris should be assumed to be uniformly distributed over the 9 available suction strainer surface. Debris mass should be calculated 10 based on the amount of debris estimated to reach or to be in the 11 suppression pool. (See Refs. 5, 16, and 17.)

12 2.2.3.4 The NPSH available to the ECC pumps should be determined using the 13 conditions specified in the plant's licensing basis (e.g., Regulatory 14 Guide 1.1 (Ref. 18)).

15 2.2.3.5 Estimates of head loss caused by debris blockage should be developed 16 from empirical data based on the strainer design (e.g., surface area 17 and geometry), postulated debris (i.e., amount, size distribution, 18 type), and approach velocity. Any head loss correlation should 19 conservatively account for filtration of particulates by the debris 20 bed.

21 2.2.3.6 The performance characteristics of a passive or an active strainer 22 should be supported by appropriate test data.

23 D. IMPLEMENTATION 24 The purpose of this section is to provide information to licensees and 25 applicants regarding the NRC staff's plans for using this regulatory guide.

26 This proposed revision has been released to encourage public 27 participation in its development. Except in those cases in which an applicant 28 proposes an acceptable alternative method for complying with specified 19

1 portions of the Commission's regulations, the methods to be described in the 2 active guide reflecting public comments will be used in the evaluation of 3 applications for construction permits and operating licenses. The active 4 guide will also serve as guidance for the conduct of reviews under 10 CFR 5 50.59 that deal with plant modifications installed on primary coolant system 6 piping and components when such modifications may affect the availability of 7 water sources for long-term recirculation (e.g., altering potential sources of 8 debris). The active guide will also be used by the NRC staff to evaluate 9 licensees' compliance with 10 CFR 50.46.

20

1 REFERENCES 2 1. NRC Draft Bulletin, "Potential Plugging of Emergency 3 Suction Strainers by Debris in Boiling Water Reactors,"Core Cooling July 1995.'

4 2. U.S. Nuclear Regulatory Commission, "Debris Plugging of 5 Cooling Suction Strainers," NRC Bulletin No. 93-02, May Emergency Core 11, 1993.'

6 3. USNRC, "Debris Plugging of Emergency Core Cooling Suction Strainers,"

7 NRC Bulletin No. 93-02, Supplement 1, February 18, 1994.'

8 4. Generic Letter 85-22, "Potential for Loss of Post-LOCA Recirculation 9 Capability due to Insulation Debris Blockage," December 3, 1985.1 10 5. A.W. Serkiz, "Containment Emergency Sump Performance (Technical Findings 11 Related to Unresolved Safety Issue A-43)," NUREG-0897, Revision 1, 12 USNRC, October 1985.2 13 6. J. Wysocki and R. Kolbe, "Methodology for Evaluation 14 Debris Effects," NUREG/CR-2791 (SAND82-7067), USNRC, of Insulation September 1982.2 15 7. G.G. Weigand et al., "A Parametric Study of Containment 16 Performance," NUREG/CR-2758 (SAND82-0624), USNRC, July Emerency Sump 1982.

17 8. M.S. Krein et al., "A Parametric Study of Containment 18 Emergency Sump Performance: Results of Vertical Outlet Sump Tests,"

NUREG/CR-2759 19 (SAND82-7062), USNRC, October 1982.2 20 9. M. Padmanabhan and G.E. Hecker, "Assessment of Scale 21 Effects on Vortexing, Swirl, and Inlet Losses in Large Scale Sump 22 Models,"

NUREG/CR-2760 (ARL-48-82), USNRC, June 1982.2 23 10. M. Padmanabhan, "Results of Vortex Suppressor Tests, Single 24 Tests, and Miscellaneous Sensitivity Tests," NUREG/CR-2761 Outlet Sump 25 (SAND82-7065), USNRC, September 1982.2

'Copies are available for inspection or copying for a fee from the NRC Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax (202)634-3343.

'Copies of these documents are available for inspection fee from the NRC Public Document Room at 2120 L Street or copying for a 20555; telephone (202)634-3273; fax (202)634-3343. NW., Washington, DC documents may be purchased at current rates from the Copies of NUREG-series U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone or from the National Technical Information Service by (202)512-2249);

writing NTIS at 5282 Port Royal Road, Springfield, VA 22161.

21

for 1 11. M. Padmanabhan, "Hydraulic Performance of Pump Suction Inlets NUREG/CR-2772 Emergency Core Cooling Systems in Boiling Water Reactors,"

2 3 (ARL-398A), USNRC, June 1982.2 of Residual Heat 4 12. P.S. Kammath, T.J. Tantillo, W.L. Swift, "An Assessment and Debris 5 Removal and Containment Spray Pump Performance Under Air September 6 Ingesting Conditions," NUREG/CR-2792 (CREARE TM-825), USNRC, 7 1982.2 Reactor 8 13. D.N. Brocard, "Buoyancy, Transport, and Head Loss of Fibrous July 1983.2 9 Insulation," NUREG/CR-2982 (SAND82-7205), Revision 1, USNRC, Insulation 10 14. W.W. Durgin and J. Noreika, "The Susceptibility of Fibrous Jet Flows,"

11 Pillows to Debris Formation Under Exposure to Energetic 12 NUREG/CR-3170 (SAND83-7008), USNRC, March 1983.2 Sump Blockage 13 15. J.J. Wysocki, "Probabilistic Assessment of Recirculation 1 and 2 14 Due to Loss-of-Coolant Accidents," NUREG/CR-3394, Volumes 15 (SAND83-7116), USNRC, July 1983.2 of 16 16. D.N. Brocard, "Transport and Screen Blockage Characteristics (SAND83-7471),

17 Reflective Metallic Insulation Materials," NUREG/CR-3616 18 USNRC, January 1984.2 BWR ECCS 19 17. G. Zigler et al., "Parametric Study of the Potential for (Draft Strainer Blockage Due to LOCA Generated Debris," NUREG/CR-6224 20 August 1994.'

21 for Public Comment) (SEA No. 93-554-06-A:I),

Core 22 18. Regulatory Guide 1.1, "Net Positive Suction Head for Emergency2, 1970.

Cooling and Containment Heat Removal System Pumps," November 23 3Requests for single copies should be made in writing to the U.S. Nuclear and Mail Regulatory Commission, Washington, DC 20555, Attention: Distribution Requests for Services Section; requests may also be faxed to (301)415-2260. documents are drafts will be filled as long as supplies last. Copies of NRC NRC Public also available for inspection or copying for a fee from the (202)634 Washington, DC 20555; telephone Document Room at 2120 L Street NW.,

3273; fax (202)634-3343.

22

I APPENDIX A 2 GUIDELINES FOR REVIEW OF 3 WATER SOURCES FOR EMERGENCY CORE COOLING 4 Water sources for long-term recirculation should be evaluated under 5 possible post-LOCA conditions to determine the adequacy of their design for 6 providing long-term recirculation. Technical evaluations can be subdivided 7 into (1) sump hydraulic performance, (2) LOCA-induced debris effects, and (3) 8 pump performance under adverse conditions. Specific considerations within 9 these categories, and the combination thereof, is shown in Figure A-i.

10 Determination that adequate NPSH margin exists at the pump inlet under all 11 postulated post-LOCA conditions is the final criterion.

12 SUMP HYDRAULIC PERFORMANCE 13 Sump hydraulic performance (with respect to air ingestion potential) can 14 be evaluated on the basis of submergence level (or water depth above the PWR 15 sump or BWR suction strainer outlets) and required pumping capacity (or pump 16 inlet velocity). The water depth above the pipe centerline (s) and the inlet 17 pipe velocity (U) can be expressed nondimensionally as the Froude number:

18 Froude number u 19 where g is the acceleration due to gravity. Extensive experimental results 20 have shown that the hydraulic performance of ECC sumps (particularly the 21 potential for air ingestion) is a strong function of the Froude number. Other 22 nondimensional parameters (e.g., Reynolds number and Weber number) are of 23 secondary importance.

24 Sump hydraulic performance can be divided into three performance 25 categories:

A-1

1 1. Zero air ingestion, which requires no vortex suppressors or increase of 2 the "required" NPSH above that from the pump manufacturer's curves.

3 2. Air ingestion of 2% or less, a conservative level at which degradation 4 of pumping capability is not expected based on an increase of the 5 "required" NPSH (see Figure A-2).

6 3. Use of vortex suppressors to reduce air ingestion effects to zero.

7 For PWRs, zero air ingestion can be ensured by use of the design 8 guidance set forth in Table A-l. Determination of those designs having 9 ingestion levels of 2% or less can be obtained using correlations given in 10 Table A-2 and the attendant sump geometric envelope. Geometric and screen 11 guidelines for PWRs are contained in Tables A-3.1, A-3.2, A-4, and A-5. Table 12 A-6 presents design guidelines for vortex suppressors that have shown the 13 capability to reduce air ingestion to zero. These guidelines (Tables A-l 14 through A-6) were developed from extensive hydraulic tests on full-scale sumps 15 and provide a rapid means of assessing sump hydraulic performance. If the PWR 16 sump design deviates significantly from the design boundaries noted, similar 17 performance data should be obtained for verification of adequate sump 18 hydraulic performance.

19 For BWRs, full-scale tests of suppression pool suction strainer screen 20 outlet designs for recirculation pumps have shown that air ingestion is zero 21 for Froude numbers less than 0.8 with a minimum submergence of 6 feet, and 22 operation up to a Froude number 1.0 with the same minimum submergence may be 23 possible before air ingestion levels of 2% may occur (Refs. A-i and A-5).

24 LOCA-INDUCED DEBRIS EFFECTS 25 Assessment of LOCA debris generation and the determination of possible 26 debris interceptor blockage is complex. The evaluation of this safety 27 question is dependent on the types and quantities of insulation employed, the 28 location of such insulation materials within containment and with respect to 29 the sump or suppression pool strainer location, the estimation of quantities 30 of debris generated by a pipe break, and the migration of such debris to the 31 interceptors. Thus blockage estimates (i.e., generation, transport, and head 32 loss) are specific to the insulation material, piping layout, and the plant A-2

I design.

2 Since break jet forces are the dominant debris generator, the predicted 3 jet envelope will determine the quantities and types of insulation debris.

4 Figures A-2 provides a three-region model that has been developed from 5 analytical and experimental considerations as identified in References 6 A-i and A-6. The destructive results (e.g., volume of insulation and other 7 debris generated, size of debris) of the break jet forces will be considerably 8 different for different types of insulation, different types of installation 9 methods, and distance from the break. Region I represents a total destruction 10 zone; Region II represents a region where high levels of damage are possible 11 depending on insulation type, whether encapsulation is employed, methods of 12 attachment, etc.; and Region III represents a region where dislodgement of 13 insulation in whole, or as-fabricated, segments is likely occur. References 14 A-i and A-6 provide a more detailed discussion of these considerations.

15 References A-i and A-6 through A-10 provide more detailed information relevant 16 to assessing debris generation and transport.

17 PUMP PERFORMANCE UNDER ADVERSE CONDITIONS 18 The pump industry historically has determined NPSH requirements for 19 pumps on the basis of a percentage degradation in pumping capacity. The 20 percentage has at times been arbitrary, but generally is in the range of 1% to 21 3%. A 2% limit on allowed air ingestion is recommended since higher levels 22 have been shown to initiate degradation of pumping capacity.

23 The 2% by volume limit on sump air ingestion and the NPSH requirements 24 act independently. However, air ingestion levels less than 2% can also affect 25 NPSH requirements. If air ingestion is indicated, correct the NPSH 26 requirement from the pump curves by the relationship:

27 NPSHrequired(ap <21.) = NPSHrquired(liquid) X 9 28 where 9 = 1 + 0.50cp and cp is the air ingestion rate (in percent by volume) 29 at the pump inlet flange.

30 COMBINED EFFECTS A-3

I As shown in Figure A-l, three interdependent effects (i.e., sump or 2 suction strainer performance, debris generation and transport, and pump 3 operation under adverse conditions) require evaluation for determining 4 long-term recirculation capability (i.e., loss of NPSH margin).

A-4

I APPENDIX A REFERENCES 2 A-i A.W. Serkiz, "Containment Emergency Sump Performance (Technical Findings 3 Related to Unresolved Safety Issue A-43)," NUREG-0897, Revision 1, 4 USNRC, October 1985.1 5 A-2 G.G. Weigand et al., "A Parametric Study of Containment Emerency Sump 6 Performance," NUREG/CR-2758 (SAND82-0624), USNRC, July 1982.

7 A-3 M.S. Krein et al., "A Parametric Study of Containment Emergency Sump 8 Performance: Results of Vertical Outlet Sump Tests," NUREG/CR-2759 9 (SAND82-7062), USNRC, October 1982.'

10 A-4 M. Padmanabhan and G.E. Hecker, "Assessment of Scale Effects on 11 Vortexing, Swirl, and Inlet Losses in Large Scale Sump Models,"

12 NUREG/CR-2760 (SAND82-7063), USNRC, June 1982.'

13 A-5 M. Padmanabhan, "Hydraulic Performance of Pump Suction Inlets for 14 Emergency Core Cooling Systems in Boiling Water Reactors," NUREG/CR-2772 15 (SAND82-7064), USNRC, June 1982.'

16 A-6 U.S. Nuclear Regulatory Commission, "Parametric Study of the Potential 17 for BWR ECCS Strainer Blockage Due to LOCA Generated Debris," NUREG/CR 18 6224 (Draft for Public Comment) (SEA No. 93-554-06-A:1), August 1994.2 19 A-7 D.N. Brocard, "Buoyancy, Transport, and Head Loss of Fibrous Reactor 20 Insulation," NUREG/CR-2982 (SAND82-7205), Revision 1, USNRC, July 1983.'

21 A-8 W.W. Durgin and J.Noreika, "The Susceptibility of Fibrous Insulation 22 Pillows to Debris Formation Under Exposure to Energetic Jet Flows,"

23 NUREG/CR-3170 (SAND83-7008), USNRC, March 1983.'

'Copies of these documents are available for inspection or copying for a fee from the NRC Public Document Room at 2120 L Street NW., Washington, DC 20555; telephone (202) 634-3273; fax (202) 634-3343. Copies of NUREG-series documents may be purchased at current rates from the U.S. Government Printing Office, Mail Stop SSOP, Washington, DC 20402-9328 (telephone (202) 512-2249 or (202) 512-2171); or from the National Technical Information Service by writing NTIS at 5282 Port Royal Road, Springfield, VA 22161.

2Requests for single copies of drafts should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention:

Distribution and Mail Services Section. Requests for drafts will be filled as long as supplies last. Copies of drafts are also available for inspection or copying for a fee from the NRC Public Document Room at 2120 L Street NW.,

Washington, DC 20555; telephone (202) 634-3273; fax (202) 634-3343.

A-5

I A-9 J.J. Wysocki, "Probabilistic Assessment of Recirculation Sump Blockage 2 Due to Loss-of-Coolant Accidents," NUREG/CR-3394, Volumes 1 and 2 3 (SAND83-7116), USNRC, July 1983.'

4 A-1O D.N. Brocard, "Transport and Screen Blockage Characteristics of 5 Reflective Metallic Insulation Materials," NUREG/CR-3616 (SAND83-7471),

6 USNRC, January 1984.'

A-6

FIGURE A-I. Technical Considerations Relevant to PWR ECC Sump Performance PUMPS

• Pump Design and Operating Characteristics

• NPSH Requirements No Airl

• Sump and Suction Piping - Losses A-7

FIGURE A-2. Multiple Region Insulation Debris Model for PWRs 4/ Boundary of a Right Circular Cylinder Originating at the Postulated Pipe Break REGION I - REGION II R EGION Ill Total High Levels of Di slodging in Destruction Damage Possible. I "As -Fabricated" Materials and Pieces or Segments L/D e-- Dependent I I No te:

Pre ssure Isobars Shq own Are Calculated Tar get Pressures for Bre ak Conditions of 150 Bars and 35*K Sul bcooling RID R - Radius of Circular Flat Plate Target SBar L Distance From Break LD 7I% to Target D - Diameter of Broken Pipe Pstag 0.5 psi or Major Wall Boundary I A-8

TABLE A-I PWR 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 NOTE: These guidelines were established using experimental results from References A-2, A-3, and A-4 and are based on sumps having a right rectangular shape.

, Cover Plate Fr =

1F.

U A-9

TABLE A-2 I-PWR HYDRAULIC DESIGN GUIDELINES FOR AIR INGESTION <2%

Air ingestion (a) is empirically calculated as

(=(xo + (W, x Fr) where Cio and a, are coefficients derived from test results as given in the table below Horizontal Outlets Vertical Outlets Item Dual Single Dual Single Coefficient c, -2.47 -4.75 -4.75 -9.14 Coefficient o, 9.38 18.04 18.69 35.95 Minimum Submergence, s (ft) 7.5 8.0 7.5 10.0 Wm) 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/s) 0.36 0.36 0.36 0.36 (m/s) 0.11 0.11 0.11 0.11 Maximum Sump Outlet Coefficient, C, 1.2 1.2 1.2 1.2 Fr = U v---

A-10

TABLE A-3.1 PWR GEOMETRIC DESIGN ENVELOPE GUIDELINES FOR HORIZONTAL SUCTION OUTLETS Size Sump Outlet Position' Screen Sump Outlet Aspect Min. Perimeter Min. Area Ratio (ft) (m) e,/d (B-e,)/d c/d b/d f/d e./d 2

(ft ) (m2)

Dual 1 to 5 36 11 >4 75 7

>1 >3 >1.5 >1 >1.5 Single I to 5 16 4.9 - 35 3.3 NOTE: Dimensions are always measured to pipe centerline.

"* Preferred location.

A-11

TABLE A-3.2 PWR GEOMETRIC DESIGN ENVELOPE GUIDELINES FOR VERTICAL SUCTION OUTLETS Size Sump Outlet Position' Screen Sump Outlet Aspect Min. Perimeter Min. Area Ratio (ft) (m) e,/d (B-e ,)/d c/d b/d f/d

______(ft e ./d 2) (in 2 )

Dual 1 to 5 36 11 >0 >4 75 7

>1 > >1 >1.5 Single 1 to 5 16 4.9 1 1 1 <1.5 - 35 3.3 NOTE: Dimensions are always measured to pipe centerline.

SPreferred location.

A-12

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 P equal to or greater than the length of the adjacent screen/grate (B, or L.) should be at least 4 feet (1.2 meters).

2. A solid wall or large obstruction may form the boundary of the sump on one side only, i.e., 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.

4 ft (minl I

-~

--r,.--------

L oii B, Sump Pit I Trash Rack and Debris Screen A-13

TABLE A-5 PWR DESIGN GUIDELINES FOR INTERCEPTORS AND COVER PLATE

1. Screen area should be obtained from Tables A-3.1 and A-3.2.

2. Minimum height of interceptors should be 2 feet (0.61 meters).

3. Distance from sump side to screens, g-, may be any reasonable value.

4. Screen mesh should be 1/4 inch (6.4 mm) or finer.

1

5. Trash racks should be vertically oriented 1- to 1 /-inch (25- to 38-rmn) 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).

NOTE: See Reference A-1.

Solid Cover Plate t~ 3~ _,,.,Trash Rack

\Debris Screen

'I," Mesh (max)

A-14

TABLE A-6 PWR GUIDELINES FOR SELECTED VORTEX SUPPRESSORS

1. Cubic arrangement of standard 11/2-inch (30-mm) deep or deeper floor grating (or its equivalent) with a characteristic length, QP, 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 0, > 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 11/2-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.

NOTE: 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: T:h Rdtk Solid Top Cooo ---- r Dobrir Sr,-

I IMs,,ndard Ig'WaI' Tt Leo" Rak TrTrash

-dn mwn p Cc o s o(ltFlop Sterflrashrrr e D esig n #2: S o lid Fhll~lr c

[S d hl--d ;

A-15

I APPENDIX B 2 EXAMPLES OF ACTIVE MITIGATION SYSTEMS 3 In-Line (or Pipeline) Strainer 4 A strainer installed in the piping system, upstream of equipment, that will 5 remove harmful objects and particulates from the fluid stream by a backwashing 6 action.

7 Self-Cleaning Strainer 8 A strainer that is used upstream of equipment to filter out harmful objects 9 and particulates and is designed to clean itself without the aid of external 10 help.

11 Strainer Backwashing System 12 A system designed to dislodge objects and particulates from the surface of a 13 strainer by directing a fluid stream in the opposite direction of the flow 14 through the strainer.

B-i

I REGULATORY ANALYSIS 2 A separate regulatory analysis was not prepared for this proposed 3 Revision 2 to Regulatory Guide 1.82 since the guidance for pressurized water 4 reactors has not been changed; the guide is being revised to better clarify 5 the type of analysis applicable to boiling water reactors. Therefore a new 6 regulatory analysis is not needed. The regulatory analysis (NUREG-0869, 7 Revision 1, "USI A-43 Regulatory Analysis," October 1985) that was prepared 8 for the resolution of USI A-43, "Containment Emergency Sump Performance," is 9 available for inspection or copying for a fee in the Commission's Public 10 Document Room at 2120 L Street NW., Washington, DC 20555 (telephone (202)634 11 3273, fax (202)634-3343).

RA- 1

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