ML20045C818

Forwards Ssar Markup Addressing Suppression Pool Strainer Issue 42.Info Will Be Included in Amend 30,scheduled for Transmittal to NRC on 930708

ML20045C818
Person / Time
Site:	05200001
Issue date:	06/18/1993
From:	Fox J GENERAL ELECTRIC CO.
To:	Poslusny C Office of Nuclear Reactor Regulation
References
NUDOCS 9306240426
Download: ML20045C818 (9)

Text

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' GENuclear Energy ' l

.w GeneralDectric Company

' 175 Curtner Annue. SanJose, CA 95125

.1 June 18,1993 Docket No. STN 52-001-3

?

Chet Poslusny, Senior Project Manager .i Standardization Project Directorate l i

Associate Directorate for Advanced Reactors' 1

and License Renewal Office of the Nuclear Reactor Regulation  ;

Subject:

Submittal Supporting Accelerated ABWR Schedule - Suppression Pool Strainer (New Issue #42)

Dear Chet:

Enclosed is a SSAR markup addressing the Suppression Pool Strainer Issue #42. This~

information will be included in Amendment 30, scheduled for transmittal to the NRC on July 8, . .

1993. .-

Please provide a copy of this transmittal to George Thomas.

Sincerely, W i i

ack Fox Advanced Reactor Programs cc: Alan Beard (GE) '

Norman Fletcher (DOE)

Frank Paradiso (GE)

Umesh Saxena (GE)-

BillTaft (GE)

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ABWR m6iman Standard Plant nev c of channels., recording of parameters, instrument pool. All water that leaves the suppression i rang,e and accuracy and post accident monitoring pool is cooled by the RHR heat exchangers during l equipment is discussed in Section 7.5. the three operational modes indicated above. I

--> lta sE M A For each of the three loops, water is drawn from l 6.2.2 Containment Heat Rernoval System the suppression pool, pumped through a RHR beat I exchanger and injected into the reactor vessel 6.2.2.1 Design Bases for the LPFL mode. Also, for each of the three loops for the suppression pool cooling mode, j The containment heat removal system, consist- water is drawn from the suppression pool, pumped I ing of the suppression pool cooling mode and the through a RHR heat exchanger and delivered to wetwell and drywell spray fectures are integral the suppression pool. On two of the loops I parts of the RHR system. The purpose of this (B&C), a portion of the water returned to the system is to prevent excessive containment tem- suppression pool may be passed through wetwell peratures and pressures, thus maintaining contain- spray headers. These two loops also have a ment integrity following a LOCA. To fulfill this manual feature for providing drywell spray.

purpose, the containment cooling system meets the Water from the RCWS is pumped through the heat  ;

following safety design bases: exchanger shell side to exchange heat with the l i processed water. Three cooling loops are pro- l l (1) The system limits the long-term bulk tem- vided, each being mechanically and electrically l

l perature of the suppression pool to 97.2 C separate from the other to achieve redundancy, when considering the energy additions to the A piping and instrumentation diagram (P&lD) is containment following a LOCA. These energy provided in Section 5.4. The process diagram, j additions, as a function of time, are pro- including the process data, is provided for all )

vided in the previous section, design operating modes and conditions. 1 1

(2) The single-failure criterion applies to the All portions of the containment cooling system. system mode are designed to withstand operating loads and loads resulting from natural phenom-(3) The system is designed to safety grade re- ena. All operating components can be tested quirements including the capability to per- during normal plant operation so that reliabil-form its function following a Safe Shutdown ity can be assured. Construction codes and  ;

Earthquake. standards are covered in Subsection 5.4.7.

(4) The system maintains operation during those The low pressure flooder (LPFL) mode is auto- i environmental conditions imposed by the matically initiated from ECCS signals orl LOCA. manually initiated. The suppression pooli cooling mode is started manually or automat-(5) Each active component of the system is test- ically. The RHR system must be realigned for able during normal operation of the nuclear suppression pool cooling by the plant operator power plant. after the reactor vessel water level has been recovered. The RHR pumps are already opera- 1 6.2.2.2 Containment Cooling System Design ting. Suppression pool cooling is initiated in any of the three loops by manually closing the The containment cooling system encompasses LPFL injection valve and opening the pool return several of the RHR operating modes, which are the valve. In the event that a single failure has low pressue flooder (LPFL) mode, the suppression occurred, and the action which the plant opera-pool cooling mode, and the containment spray tot is taking does not result in system initia-modes (drywell and wetwell). Containment cooling tion, then the operator will place the other starts as soon as the LPFL injection flow be- totally redundant system into operation by fol-gins. The suppression pool cooling mode cools lowing the same initiation procedure. If the the containment. The containment sprays cool the operator chooses to utilize the containment drywell and wetwell by condensing steam and the sprays, he must close the LPFL injection valves condensate running back into the suppression open spray valves. The drywell spray mode may I Amendment 29 6.2-16

l I N sG RT A Containment design features as related to debris formation have an important relationship to the ECCS's ability to provide containment cooling. A primary source of debris in containment is the thermal insulation. If insulation is dislodged and enters the wetwell, it can cause plugging of the ECCS suction strainers, which can impede ECCS performance and containment cooling.

The ABWR design includes the necessary provisions to prevent debris from impairing the ability of the RCIC, HPCF, and RHR systems l to perform their required post-accident functions. Specifically, the ABWR does the following:

l The design is resistant to the transport of debris to the j suppression pool;

! l l The SPCU system will provide early indication of any potential l problem; The ECCS suction strainers meet the current regulatory requirements unlike the strainers at the incident plants.

The equipment installed in the drywell and wetwell minimize the potential for generation of debris.

In addition to the ABWR design features, the control of the suppression pool cleanliness is a significant element of minimizing the potential for strainer plugging. The COL applicant will review the issue of maintainin;; the suppression pool cleanliness and propose to the NRC staff an acceptable method for assuring that the suppression pool cleanliness is maintained. Methods shall be considered for removing, at periodic intervals, sedament and floating or sunk debris from the suppression pool that the SPCU does not remove. s ee s d sechan

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iw s.<,m a b v- on Refer to Appendix 6C for additionaly=r.; ion of ABWR design features.

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Standard Plant arv c i.

[ Included in the leak rate test summary report p will ^be, a report detailing the containment in-spection, a report detailing any repairs neces.

sary to pass the tests,'and the leak rate test l results.

i 6.2.6.5 SpecialTesting Requirements l The maximum allowable leakage rate into the j secondary containinent and the means to verify j that the inleakage rate has not been exceeded, as l well as the containment leakage rate to the j environment, are discussed in Subsections 6.2.3

and 6.5.1.3.

! 6.2.7 COL License Information t 6.2.7.1 Alternate Hydrogen Control

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! A comparison of costs and benefits will be i provided for alternate hydrogen control in j accordance with Subsection 6.2.5.

! 6.2.7.2 Administrative Control Maintaining i Containment isolation a

! The COL applicant will maintain the primary j ontainment boundary by administrative controls in 1 accordance with Subsection 6.2.6.3.1.

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l N S G.P~T 6 ld l 6.2.h.3 Suppression Pool Cleanliness The COL applicant v:ill propose for NRC staff review, acceptable methods to mairaain suppression pool cleanliness in support of preventing ECCS suction strainer plugging in accordance with l Subsection 6.2.1.8 and Appendix 6C. l l

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l Appendix 6C Containment. Debris Protection' for ECCS Strainers NRC Bulletin No. 93-02, " Debris Plugging: of Emergency Core Cooling -

Suction ' Strainers," references..NRC ' guidance 1and- highlights the need to adequately accommodated debris' in design by focusing on an '

incident .at -the Perry' Nuclear Plant.~ GE reviewed: the concerns' addressed by' NRC Bulletin (93-02'. and has' reviewed Jthe ~ design 'of ~ the -

ABWR for potential weaknesses:in. coping Lwith thelbulletin's GE has: determined ' that the' ABWR1 design;is more resistant L concerns.

to these problems for a number of reasons as : discussed in the -

following.

l l

The ultimate concern raised by1the- Perry incident wasL the ~

l deleterious effect of debris ;in -the. suppression pool- and how it-could-impact the ability to. draw water from the ' suppression pool during an l accident. The ABWR design has committed-to following. the guidance provided..in Reg- Guide 1.82, .Rev. I' (Water Sources for long-term Recirculation . Cooling following a L'oss of Coolant Accident)' and the ABWR.'is' designed to inhibit' debris generated during a LOCA' from i preventing operation of the' Residual: Heat Removal (RHR), Reactor Core Isolation Cooling-(RCIC) and High Pressure Core Flooder (HPCF) systems.

p The type of insulation material to be used has not Jyet been L ' determined. However, the newer insulating systems 1(NUKON) are.

packaged in large blanke'ts 'which are encased to prevent the' release of small particles.' Fine fibers of NUKON are created.only as the result

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~ Appendix 6C continued 1 of a LOCA's high pressures steam-water jet. If one of these blankets were to reach the wetwell it would prevent small particles from matting out on the ECCS suction strainers in an overall uniform manner that could plug the strainer. In addition, it should also be recognized that the ABWR has substantially reduced the amount of piping in the drywell relative to earlier designs and consequently the

, quantity of insulation required. Furthermore, there is no equipment in the wetwell spaces that requires insulation or other fibrous materials. The ABWR design conforms with the guidance provided by the NRC for maintaining the ability for long-term recirculation i cooling of the reactor and containment following a LOCA.

However, the Perry incident was not the result of a LOCA but rather debris entering the Suppression Pool during normal operation. The arrangement of the drywell and wetwell/wetwell airspace on a Mark III containment (Perry) is significantly different from that utilized in the ABWR design. In the Mark III containment, the areas above the suppression pool water surface (wetwell airspace) are substantially

covered by grating with significant quantities of equiprnent installed in these areas. In these areas are no real barriers to prevent small quantities of debris from falling into the suppression pool from the spaces located above the pool surface. This arrangement contributes t

to a much greater potential for debris to enter the suppression pool 4

during outage activities as well as activities in the containment during power operation. Furthermore, access to the wetwell airspace (containment) of a Mark III is allowed during power operations. In contrast, on the ABWR the only connections to the suppression pool are 10 drywell connecting vents (DCVs) and access to the wetwell ,

during power operations is prohibited. The DCVs will have horizontal

steel plates located above the openings that will prevent any material falling in the drywell from directly entering the vertical leg of the DCVs. This arrangement is similar to that used with the Mark II connecting vent piper. Vertically oriented trash rack construction will be installed around the periphery of the horizontal steel plate to intercept debris. The trash rack design shall allow for adequate flow from the drywell to wetwell. In order for debris to enter the DCV it

. would have to travel horizontally through the trash rack prior to falling into the vertical leg of the connecting vents. Thus the ABWR is resistant to the transport of debris from the drywell to the wetwell.

Appendix 6C continued In the Perry incident, the insulation material acted as a sepia to filter suspended solids from the suppression pool water. The Mark I. II, and III containment's have all used carbon steel in their suppression pool liners. This results in the buildup of corrosion products in the l suppression pool which settle out at the bottom of the pool until they I are stirred up and resuspended in the water following some event j (SRV lifting). In contrast the ABWR liner of the suppression pool is fabricated from stainless steel which significantly lowers the amount I of corrosion products which can accumulate at the bottom of the pool. l Since the debris in the Perry incident was created by roughing filters on the containment cooling units a comparison of the key design features of the ABWR is necessary. In the Mark III design more l than 1/2 of the containment cooling units are effectively located in -!

the wetwell airspace. For the ABWR there are no cooling fan units m  ;

the wetwell air space. Furthermore the design of the ABWR Drywell  !

Cooling Systems does not utilize roughing filters on the intake of the containment cooling units.

In the event that small quantities of debris enter the suppression pool, the Suppression Pool Cleanup System (SPCU) will remove the debris during normal operation. The SPCU is described in Section i 9.5.9 and shown in Figure 9.5.1 of the ABWR 'SSAR. The SPCU is  !

3 designed to provide a continuous cleanup flow of 250 m / hour )

(1100 gpm). This flow rate is sufficiently large to effectively j maintain the suppression pool water at the required purity. The SPCU system is intended for continuous operation and the suction  :

pressure of the pump is monitored and provides an alarm on low j pressure. Early indication of any deterioration of the suppression l l pool water quality will be provided if significant quantities of debris were to enter the suppression pool and cause the strainer to become plugged resulting in a low suction pressure alarm.

l The ECCS pump suction pool strainers for the ABWR will meet the l requirements of Reg Guide 1.82, Rev.1. The suction strainers at l Perry did not meet the current regulatory requirements. The ABWR ECCS suction strainers will utilize a "T" arrangement with conical strainers on the 2 free legs of the "T". This design separates the

! strainers so that it minimizes the potential for a contiguous mass to block the flow to an ECCS pump. The ABWR design also has additional features not utilized in earlier designs that could be used l

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I a Appendix 6C continued in the highly improbable event that all suppression - pool suction strainers were to become plugged. The alternate ' AC (Alternating Current) independent water addition mode of RHR allows water from >

the Fire Protection System to be' pumped to the vessel and sprayed in the wetwell and drywell from diverse water sources to maintain  ;

cooling of the fuel and containment. The wetwell can also be vented at low pressures to assist in cooling the containment.

In summary the ABWR design includes the necessary provisions to prevent debris from impairing the ability of the RCIC, HPCF, and RHR systems to perform their required post-accident functions.

Specifically, the ABWR does the following:

The design is resistant to the transport of debris to the suppression pool; The SPCU system will provide early indication of any potential problem; The ECCS suction strainers meet the current regulatory requirements unlike the strainers at the incident plants.

The equipment installed in the drywell and wetwell minimize the potential for generation of debris.

In addition to the ABWR design features,.the control of 'he t suppression pool cleanliness is a significant element of ' minimizing the potential for strainer plugging.

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