B17021, Forwards Response to 970915 RAI Re Tornado Missile Risk Analysis of Millstone,Unit 3,Emergency Generator Enclosure Openings. Commitments Made by Util,Encl

Forwards Response to 970915 RAI Re Tornado Missile Risk Analysis of Millstone,Unit 3,Emergency Generator Enclosure Openings. Commitments Made by Util,Encl

ML20203J726
Person / Time
Site:	Millstone
Issue date:	02/26/1998
From:	Bowling M NORTHEAST NUCLEAR ENERGY CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
B17021, TAC-M97508, NUDOCS 9803040255
Download: ML20203J726 (15)

Text

/ h[ Ikge Ferry Rd. (Route 156), %:erford, CT 06385 T Minstore Nuclear Power Station p

Nortlicaat Nurlear Energy Cornpany P.O. Box 12A Toterford, Cr 06385 0128 (860) 447-1791 Faz (860) 444 4277 j ne Northcet Utilitice System i

FEB 2 61998 Ddet No. 50423 B17021 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 '

Millstone Nuclear Power Station, Unit No. 3 I NRC Request for Additional information Regarding the Millstone Unit 3 Emeroency Diesel Generetor Exheuet Stack (TAC No. M97508)

On September 15, 1997,__ Nuclear Regulatory Commission (NRC) forwarded two questions to Norheast Nuclear Energy Company (NNECO) relating to the " Tornado Missile Risk Analysis of Millstone Unit 3 Emergency Generator Enclosure Openings,"

dated March 1985. This analysis had been provided to the NRC to address S!gnificant items List, item No. 75, NNECO provided a response to NRC_ Question 1 in a letter dated January 21,1998. Attachment 1 to this letter responds to NRC Question 2 and-completes NNECO's response to the NRC on this matter. Attachment 2 contains a listing of any NNECO commitments made in this response.

-Should you have any questions regarding this matter, please contact Mr. David A.

Smith at (860) 437-5840.

Very truly_yours, NORTHEAST NUCLEAR ENERGY COMPANY Martin L. Bowling, Jr. /

Millstone Unit No. 2 - Recovery Officer cc: H. J. Miller, Region I Administrator J. W. Andersen, NRC Project Manager, Millstone Unit No. 3 ^

/A;'.y i A. C. Corne, Senior Resident inspector, Millstone Unit No. 3 W. D. Travers, Ph.D., Director, Special Projects Office DWDM (uy40

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Docket No. 50-423 B17021 Attachment i Millstone Nuclear Power Station, Unit No. 3 NRC Request for Additional Information Regarding the Millstone Unit 3 Emeroency Diesel Generator Exhaust Stack (TAC No. M97508)

February 1998

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.. U.S' Nuclear Regulatory Commission B17021\ Attachment 1\Page 1 Request for Additionalinformation Concoming Emergency Diesel Generator Exhaust Stacks TAC NO. M97508 M4C Question

2. Your risk assessment for protection against tornado generated missiles only addresses the acceptance criteria for a single vulnerability, i.e., the EDG exhaust system. In order to rely on probabilistic arguments that tornado missile protection is not required, the risk assessment must also show that the overall risk from tornado generated missiles has not been increased (by not providing -

protection for the EDG exhaust system) beyond the acceptance riteria discussed in the guidance of Standard Review Plan (SRP) Section 2.2.3, which deals with identification of design basis events using probabilistic methods.

Therefore, the analysis should also consider all other Structurea, Systems, or Components (SSCs) not protected from tornado generated missiles that are required to prevent a release of radioactivity in excess of 10_CFR Part 100 that are not protected from tornado generated missiles. This guidance states that an expected rate of occurrence of potential exposures in excess of _the 10 CFR Part 100 guidelines of approximately 10-6 per year is acceptable if, when combined with reasonable qualitative arguments, the risk can be expected to be lower. ,

This-request for additional information need not be addressed if all other-safety-related SSCs (other than the EDG exhaust system) are adequately protected (by existing barriers / structures) from the effects of tornado generated missiles.

NNECO Response A~ Tornado event Probabilistic Risk - Assessment (PRA) addressing all unprotected structures, systems and components required to prevent a release of radioactivity has not been prepared for Millstone Unit 3. NNECO's'dscision to evaluate the damage i probability associated with a potential Tornado missile impact to the Emergency Diesel-Generator (EDG) exhaust stacks was_ based on a review of the Millstone Unit No. 3 licensing basis requirements transmitted in NUREG-1031, " Safety Evaluation Report related to the operation of Millstone Nuclear Power Station, Unit No. 3," Supplement No.1, dated March 1985. In Section 3.5.2 of Supplement No.1 of_ the Safety-Evaluation Report (SER), the NRC identified several options available to NNECO for resolving the open issue relating to Tomado missile protection of the EDG exhaust stacks,- including the development of 3 limited PRA. It is NNECO's belief that the options identified in Section 3.5.2 of SER Supplement 1 continue .to represent acceptable analysis approaches under the Millstone Unit No. 3 licensing basis.

U.S'. Nuclear Regul: tory Commission I ' B170' 21\ Attachment 1\Page 2 A

in its January 21,1998 letter, NNECO stated that other unprotected targets had been identified and that an evaluation of safe shutdown capability assuming loss of the individual targets was underway. Enclosure 1 (8 pages) to this ietter provides the results of NNECO's evaluation. As discussed in Enclosure 1, all but one of the targets identified are either not required for safe shutdown, have been previously reviewed and accepted under the Millstone Unit No. 3 licensing basis, or have been shown through analysis to be able to support safe shutdown with degraded capability. The evaluation is based on the c~ollity of available systems, struc'ures and components to remove decay heat in support of achieving safe shutdown following a Tornado event with consequential Loss Of Offsite Power (LOOP) and coincident single failure and with no additional design basis events occurring simultaneously with the Tornado. This latter  ;

provision is consistant with the guidance provided in NRC Regulatory Guide 1.117, "

" Tornado Design Classification."

The single new target of concern is discussed in item 52 of Enclosure 1. Line 3-FWA-006-81-4 is a recirculation heating loop for the Demineralized Water Storage Tank.

The DWST is missile protected and provides the suction source for the Auxillary Feedwater System, The line is automatically isolated on a loss of power condition.

However, if power remains available throughout the event, tailure of this line due to a missile impact would result in a loss of DWST inventory. While this scenario is considered unlikely, corrective action will be taken to eliminate the potentici failure mode prior to entry into Mode 2. It is expected that administrative controls can be effectively implemented to require that the line be isolated upon receipt of a Tornado Warning.

U.S', Nuclear Regulatory Commission B17021%ttechment 1\Page 3 Docket No. 50-423 B17021 Enclosure 1 Millstone Nuclear Power Station, Unit No. 3 NRC Request for Additional information Regarding the Millstone Unit 3 Emeroency Diesel Generator Exhaust Stack (TAC No. M97508)

February 1998

I Attachment 4 Engineering Record Correspondence ,

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DATE: 02/19/98 25212-ER 98-0051 Rev. O TO: D. Dodson _m o FROM: J.D. Dakers [fhk t/liff6 INDEPENDENT M. Urick Y REVIEWER /[_ r] 8[/f!/f ,

APPROVED R.A. Andren h _e _ 2,/2. /)y

SUBJECT:

MP3 Tornado Missile Vulnerab'lities

REFERENCES:

Walkdown Resu!ts MP3-WLKDWN-98-097 DACKGRQUED Attachment A of this ERC, is a letter which was received tror.1 the NRC requesting additional information on items which are not protected from tornado missiles. Question 1 has previously been responded to, and this ERC will form the foundation for a response to question 2. Question 2 requests information on any additional potential tomado missile targets, specifically whether probabilistic methods have been used as the basis for not protecting certcin safety related items.

There are no other known 5 cations, which Millstone 3 has specifically used probabilistic methods to address targets unprotected from tornado missiles, but thera are other potential targe's which could contribute to risk during a tornado event. To provide an adequate response to the NRC question, it was decided a walkdown should be conducted to identify any potential targets which may be vulnerable to tornado missiles. Walkdown MP3-WLKDWN-98-097 was performed and documented. This walkdown ideritified 12 items which require formal review in preparation for the response to the NRC. The specific items are included in the scope section of this ERC. The identified items are reviewed and en assessment of the significance on plant shutdown capability made, which then can be used as input in response to the NRC request. It is expected that the PRA group will also review these items to address their significance from a probabilistic point of view.

s 25212-ER-98-0051 NGP 5.31 Rev.3 Page 1 of 6

t SCOP _E i The scope of this ERC covers the following items:

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Item No. Photo No. Desenption 3 5 MSV Bldg Roof: 43ets of ten main steam safety valve exhaust stacks.

17 6 MSV B!dg Roof: Typical of 4 main steam bypass valve exhaust y stacks.

18 7 MSV Bldg Roof: Typical of 4 main steam atmospheric dump stacks 19 8 MSV Bldg Roof: Unidentified candelabra shapod vent.

20 9 MSV Bldg Roof; Doorways on southwest and northwest corners of high roof have safety related items inside.. 3HW'JB5002,3HW'AOD5082 23 15 MSV Bldg South Outer Wall: Safety related conduit and junction box E 3JB'9834 inejde security door 371S at ground level.

25 18 ESF Bldg Roof: Y type vent to Teny Turbine.

26 19 ESF Bldg Roof: Elbow type vent to Terry Turbine.

32 22 Auxiliary Bldg Roof: Unidentified ducpork.

49 -

Large 10'x10' Duct (Overhead) Between TB and Secondary Containment: Unprotected. _

52 14,9 DWST: One overflow line, two backflow prevent lines and one unidentified line with a heat tracing wire all located on the outside.

61

_- Fall Pipe (Ground Leve:; Outside Southeast Corner EGE: Unprotected.

t REEERERCES i

1. MP3 FSAR Sections 3.8, 9.4.3, 9.f.4.2 and 10.3.3 2, Walkdown Report MP3-WLKDWN 98-097 I

3. Westinghouse Letter NS-OPLS OPL l 91 171, dated March 27,1391, Millstone 3 Better 1

, Estimate loss of Normal Feedwater / Station Blackout Analysis. (Presently being revised) 1 4. Regulatory Guide 1.117 Revision 1, April 1978 i

5. NRC Letter from J.W. Anderson to N.S. Carns, Request for Additional information Regarding i the Millstone Unit 3 Emergency Diesel Generator Exhaust Stack. (Attachment A)

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6. Drawing EM 117A (25212 26917 sh.1) revision 16 P&lD Emergency Generator Fuel Oil System i

7. Drawing EM 123A (25212 26923 sh.1), revision 30 P&lD Main Steam and Reheat

8. Drawing EM 123D (25212 26923 sh. 4), revision 10 P&lD Main Steam and Reheat

9. Drawing EM 123E (25212 26923 sh. 5), revision 17 P&lD Main Steam and Reheat

10. Drawing EM 130B (25212 26930 sh. 4), revision 31 Feedwater System i

11. Drawing EM 1528 (25212 26925 sh. 2), revision 11 ESF and MSV Buildings Ventilation t 12. Proto Power Calculation 96-067 Revision 0, up to Change 3 I

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25212 ER 98-0051 NGP 5 31 Rev. 3 Pace 2 of G

DODY The above list was developed after screening the items identified from the plant walkdown, considering safety related items which are exposed to toniadu missiles, or non safety related rtems which have the possibiltty of affecting the perf.ormance of safety related items. Accordingly this list conservattvely presents potantial targets, since av noted in Regulatory Guide 1.117

• lt is not necessary to maintain the function &l 6 apability of all Sr.lsmic Category I structures, systems

! and components because the probability of the joint occurrence of low probability events (loss-of

-coolant accident with DBT or smaller tornado, or earthquake with DBT or smaller tomado) is sufficiently small. However, equipment used to provide long-term core cooling following a LOCA l should be protectcd.' Considering this logic the specifics of each of above items is further I

reviewed and an assessment of the significance on plant shutdown capability, item 16 Mainsteam Safety relief valves 3 MSS *RV22A D,23A-D,24A-D,25A D and 26A-D are protected from tomado missiles, but the exhaust stacks from these valves protrude through the roof of the Mainsteam Vatve Building and are not protected from potential tomado missiles. The Mainsteam Safety relief valve exhaust stacks although safety related are not required for safe shutdown of 4

the plant. Cooldown by release of secondary side steam can be accomplished by the pressure i relieving or pressure relieving bypass valves.

i Item 17

} The pressure relieving bypass valves 3 MSS *MOV74A D are protected from tornado missiles, but the exhaust stacks from these valves extend through the roof of the Mainsteam Valve Building.

The pressure relieving bypass valves are not the primary path for secondary side cooldown of the i plant. As discussed in item 18 below, FSAR Section 10.3.3 discusses possible tornado damage to I the steam relief system. Basad on this 'icensed position adequate redundancy is provided to

( l ensure plant shutdown capability, i

i Item 18 l

i The pressure relieving valves 3 MSS *PV20A-D are protected from tornado missiles, but the exhaust stacks from these valves extend thisugh the roof oi the Mainsteam Valve Building. FSAR Section 10 3.3 indicate:. *Four main steam pressure relieving bypt as valves are provided to ensure a secure path around the main steam pressure relieving valves in the event that the primary path is no longer available due to tornado missile o seismic damage to the discharge silencers. or loss of power or air to the main steam pressure relieving valves." Due to the I

reoundancy provided by the pressure relieving bypass valves, no specific quantitative probabilistic I arguments have been used to ensure that the safe shutdown of the plant can still be i accomplished after a tomado event. Based on this licensed position adequate redundancy is l provided to ensure plant shutdown capability.

25212 ER 95-0051 NGP 5.31 Rev. 3 Page 3 of 6

Item 19 This item is an atmospheric vent off line 3-MSS-006-210-4 from the Mainsteam System, on tho i

roof of the Mainsteam Valvo Building. This line relieves steam off the mainsteam isolation valves i solenoids, is not safety related, and is not required for safe shutdown of the plant.

! Item 20 On the roof of the Mainsteam Valvo Building inside of ths .,Clation enclosure are 3HVV'AOD50A2 and 3HVV'AOD5082 which are fully protected from potential tomado missiles.

Conduits 3CC9870K7 and 3CC987PT feeding these AOD's are exposed to tomado missiles.

These AOD's are for isolation of the Mainsteam Valve Building HVAC system for SLCRS purposes. The integnty of the Cantainment Enclosure Building is not maintained during a tomado as indicated in FSAR Section 3.8. Since the SLCRS function is lost there is no consequence to the failure of those dampers.

Item 23 Junction box 3JB'9836 and associated ductline 3DC986P09 as well as junction box 3JB'9834 and associated conduit 3CC986PR are inside of the Mainsteam Valve Building, but could be i exposed to potential tomado missiles through an adjacent denrway. Junction box 3JB*0836 and i associated ductline 3DC386P09 contain no cable, accordingly there is no tomado vulnerability.

I Junction box 3JB'9854 and associated conduit 3CC986PR service 3HW'TS27A, which is used to prevent overcooling of the Mainsteam Valve Building. This component is not required for safe shutdown of the plant under tomado conditions.

Item 25 and 26 i

I These items are associated with the steam drivsn auxiliary feedwater pump. One of the items is the primary steam exhaust path from the turbine via line 3-MSS-012-160 3, and the other is vent i

line 3-MSS-003111-4. Obviously with the lines exposed, the possibility of impact from a tomado missile cannot be produded. The possibility that a missile would damage this line such that i operation of the turbine driven pump would be affected is highly unlikely, but if an analogy similar to that of the diesel exhaust pipe is used, it could lead to the failure of the steam driven pump.

The unit s;>ecific Detter Estimate Loss of Normal Feedwater/ Station Blackout Analysis of the auxiliary feedwater system, from nominal full power conditions, shows the required decay heat can be removed by a minimum flow of 330 gpm delivered to two intact steam generators. This can be accomplished utilizing a single motor driven auxiliary feedwater pump,(assuming a single failure disables the other motor driven auxinary feedwater pump), as documented in Reference i

12. Reference 12 shows a single motor driven pump can deliver 354 gpm to 2 intact steam generators Accordingly, safe shutdown c'the niant can be achieved without the use of the

! steam driven auxiliary feedwater pump, from nominal full power conditions. In the unlikely event i of a loss of all feodwater EOP 35FR-H.1 would then be entered to mitigate the consequences of the loss of 'eedwater.

25212 ERE::51 NGP 5 31 Rev. 3 Page 4 of 6

Item 32 The identified duct on the roof of the Auxiliary E>uilding is an exhaust duct from the Auxiliary Building Ventilation System (ABVS) and SLCRS system. As noted in FSAR Section 9.4.3, only certain portions of the ABVS are safety related. As noted in FEAR Section 3.8 the Containment Enclosure Building siding is lost during a tornado which ehminates the SLCRS system during tomado events. In addition any tornado missile damage to the ductwork would not result in a loss of the abihty 's exhaust from the safety related portions of the HVAC system, due to the i light gage of the material which would easily be penetrated by the tornado missiles. Collapse of I

the ductwork to preclude the ability to exhaust is not a credible failure mode for this system.

I Item 49 The 10 foot by 10 foot duct on the roof of the Auxiliary Building is an exhaust duct from the Auxiliary Building Ventilation System (ABVS) and SLCRS system. As noted in FSAR Section 9.4.3, only certain portions of the ABVS are safety related. As noted in FSAR Section 3.8 the containment enclosure building siding is lost during a tornado which eliminates the SLCRS system during tomado events, in addition any tornado missile damage to the ductwork would not result in a loss of the ability to exhaust from the safety related portions of the HVAC system, due to the light gage of the material which would easily be nenetrated by the tomado missiles.

Collapse of the ductwork to prevent exhaust is not a credible failure mode for this system.

Item $2 The lines identified entering missile protected DWST enclosure are non safety related 3-FWA-002129-4 for tank heat,3 FWA-006-81-4 for overflow,3 SGF 500 2v. for chemical addition, and 3 FWA 002145-4 for water treating. None of these lines are required for safe shutdown of the plant during a tomado event. 3 FWA 006-81-4,3-SGF 500-27-4 and 3-FWA 002-145-4 enter the tank at the top of the tarik, accordingly a failure of these lines would not lead to draining the tank. Line 3 FWA 006-81-4 is part of a loop which recirculates from the bottom of the tank to the top of the tank, through the DWST neater and associated pump. This line is isolated on a Loss of Power, which is the most probable case durir,g a tornado. A failure in this line prior to the Loss of Power could lead to some loss of tank inventory due to the pump continuing to run, or due the line draining. Condition Report MS 98-0955 has been initiated to identify the corrective actions to preclude the potentialloss of inventory from the DWST.

Item 61 The oil fill vent pipes 3 EGF-003 53-4 and 3-EGF-003 54-4 for the diesel generator fuel oil tanks protrude through the roof of the fuel oil vault. This line has previously been addressed by NRC Question 430.70. An update to FSAR Section 9.5.4.2, as a result of this question, indicates

'Should the filllines become damaged, the fuel oil storage tanks also can be filled from within

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their enclosure through a manhole on the top of the tanks.' '3ased on this, the filllines are not an issue during a tomado event.

l25212 ER4B-00Si NGP 5.31

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CONCLUSjQN The affect of damage to potential targets not protected from tornado missiles has been assessed in the ERC. Th., speofics for each target are addressed in the body of this ERC. This assessment provides the foundation for a response to the NRC addressing the request in referenco 5.

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i 25212 ER 98-0051 NGP 5.31 Rev. 3 Page 6 of 6

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• ggg .i Cart; Ie ce i ce F res 'ent AII^lN Mb'JI #'

-$ Chief Nuclear Of ficer PA6 t i Of# 2.

',: Meast Nuclear Energy Cn!

c.; Ms. Patricle t. Loftus Director . Regulatory /f fatri P.O. Box !?8 daterford, C106335 SLE)[CT: RE0 JEST FOR AD0li:'JAL liFORMil0N REGARDING Till MILLSTONE UN!13 EMERGENCY Di[SEL GENERATOR En%UST STACK (TAC NO. H97508)

Dear Hr. Carns:

Dy letter dated July 22. 1997, the staff provided you an update of the NRC's Hillstone Restart Assessment Plan ' Plan). Encl:sure 3 to the Plan contained the Significant items List (Sil) for Hillstone Unit 3. Sil (75 fc Hills cne Unit 3 addressed two inspector follow up items; one concerning the emergency diescl generatc* exhaust stack, The NRC staff has reviewed the closure package for this item and in order to support further NRC evaluation, you are requested to provide the NRC with answers to the enclosed questions. Fiease respond to this request for additional infonnation expeditiously in order for the staff to complete its review in a timely manner.

Sincerely, James W. Andersen, Project Manager Special Projects Office Licensing Office of Nuclear Reactor Regulation Oxlet No. 50 423

Enclosure:

As stateri cc w/ enc 1: Ses next-page l

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1. Based on o probabilistic rip uses! ent (PRA) described in the final sunwry report. *iornado H15511e Risk Analysis of HWstone vit 3 [mergency Generator Enclosure Openings,* dated March 1985, Northeast Nuclear Energ Comp!*y O!NECO) concluded that the probability of significant damage to an errergency diesei genera:or (EDG) exhaust piping from tornado generated missiles is l 1ess than ! x 10 6 per year. Accor:1ngly, a change was implemented in the last amendment (dated roarch 1996) to the firial Saft:y Analysis Report (fSAR) to delete the licensing comitment, which required NNECO to open the [M exha>.st piping access hatches during a tornado alert. The staff finds that the above cited RA was col,, pe-forced to demonstrate the risk of tornado generated missiles, which could enter ry of Pe openings in the exhaust plenums to cause damage to the

[0G exhaust system. It does not adress the probability of the EDG exhaust stacts located outside the building teing M: by 1;'nado generated missiles. Therefore, provide a PRA to demonstrate the risk of torr!;o gercated missiles, which could cause damage to any portion of the [0G cxhaust stacts. Th11 FRA s* >uld consider all potential modes of tornado missile damage to the exhaust stacks, not Nst the orobability that missiles will enter one of the openings of the exhaust plenum

2. Your risk assessment for prc.f:tior gainst tornado generated missiles only addresses the acceptance criteria for a sv;te vOerability, i.e., the EDG exhaust system. In order to rely on probabilistic arguents Pat to-ado missile protection is not required, the risk assessment must also show that the overall rip from tornado generated missiles has not been increased (by not providing protection fo* the LM exhaust system) beyond the acceptance criteria discussed in the guidance of Standard Re,*es Plr (SRP) Section 2.2.3, which deals with identification of ,

design basis events using r*;:3bW tic methods. Therefore, the analysis should also consider all other structures. syste !. or c:nponents (SSCs) not protected from tornado generated missiles that are re::;1 red - prevr a release of radioactivity in excess of 10 CFR Part 100 that are not protected fro- :rna0: generated missiles. This guidance states that an expected rate of occurrence of poterc 9.1 W:sures in excess of the 10 CFR Port 100 guidelines of approximately 10 6 pr year s accciabic if, when combined with reasonable qualitative arguments, the risk can be Mecte: to be lower. This request for additional information need not be addressed if til otm safe -related SSCs (other than the EDG exhaust system) are adequately protectec {bj ec.:1ng :vriers/ structures) from the effects of tornado generated missiles.

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Attachment 2 Millstone Nuclear Power Station, Unit No. 3 NRC Request for Additional Information Regarding the Millstone Unit 3 Emeroency Diesel Generator Exhaust Stack (TAC No. M97508)

Commitments February 1990 N

o U. 8., Nuclear Regulatory Commission B17021%ttachment 2\Page 2 List of Regulatory Commitments The following table identifies those actions committed to by NNECO in this document. i Please notify the Manager - Regulatory Compliance at the Millstone Nuclear Power Station, Unit No. 3 of any questions regarding this document or any associated i regulatory commitments.  ;

i Commitment Committed l Date j Implement corrective actions to eliminate Prior to entry potential loss of DWST inventory due to a into Mode 2 tornado missile impact to line 3 FWA-006-81-4 (Ref:M3-98-0955).

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