ML18041A184

Forwards Description of Revised Design for Direct Torus Vent Sys,Per Util Safety Enhancement Program.Design Described Does Not Require Any Change to Tech Specs & Installation Can Begin W/O Prior NRC Approval

ML18041A184
Person / Time
Site:	Pilgrim
Issue date:	08/18/1988
From:	Bird R BOSTON EDISON CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
BECO-88-126, NUDOCS 8808240277
Download: ML18041A184 (24)

Text

Enclosure l piigrim "ri clear Power Station Rocky Hill Roao riirn c!r . Vassacnvsetts 02360 Ralph G. Bird Se~ or vice lies oe"'. 4u<<-ear BECo 88- 126 August k8, 1988 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 License OPR-35 Docket 50-293 REVISED INFORHATION REGARDING PILGRIM STATION AF TY NHAN H NT PR RAH

Dear Sir:

Enclosed is a description of a revised design for the Direct Torus Vent System (OTVS) that was described in the "Report on P1lgrim Station Safety Enhancements" dated July 1, 1987 and transmitted to the NRC with Mr. Bird' letter (BECo 87-ill) to Mr. Varga dated July 8, 1987. This revision supersedes in 1ts enti rety the Section 3.2 1ncluded in the July l, 1987 report.

On March 7, 1988 Boston Edison Company (BECo) personnel met with Or. Hurley, Hr. Russell, and Or. Thadani and prov1ded a tour of SEP modif1cations and an informal presentation of the quantification of competing r1sks associated with venting the containment and conclus1ons drawn from these results. Th1s presentation provided BECo the opportunity to respond to quest1ons posed under Item 1 Section 3,2 - "Installat1on of A 01rect Torus Vent System (OTVS)" in Hr.

Varga's letter to Hr. 81rd of August 2l, 1987 "Initial Assessment of Pilgrim Safety Enhancement Program". The material presented was made available to the resident inspector and was included as Attachment II in NRC Inspection Report 488-12, dated May 31, 1988.

As you are aware from plant inspections we have installed the DTVS p1ping and port1ons of related control wiring. Currently. the DTVS is isolated from the Standby Gas Treatment System (SBGTS) by bl1nd flanges installed in place of Valve AO-5025 and the DTVS rupture disk. This configuration was inspected by NRR 1n the performance of a technical review which focused on System, Hechan1cal Design and Structural Des1gn issues. The review took place on Harch 2-3, 1988 as documented in NRC Inspection Report 488-07, dated Hay 6, l988 and determined the installation configurat1on to be acceptable. We now plan to remove these blind flanges and proceed with installation of Valve AO-5025 and the DTVS rupture disk. We conclude the valve and rupture disk prov1de equivalent physical isolation of the DTVS p1ping from the SBGTS and appropriately ensure the operational integrity of the SBGTS under design basis accident conditions. Following completion of this work, we will perform a local leak rate test to verify that Valve AO-5025 is acceptably leak tight using the same method previously utilized in testing the bl1nd flange. We also plan to complete all remain1ng electrical work on the OTVS 1n accordance with

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BOSTON FOISON PANY August 1&, 1988 U.S. Nuclear Regulatory Commission Page 2 Qn the bas1s of the revised Section 3.2, we conclude that the DTVS design as described 1n the enclosure does not require any change to the Techr.'.cal Specifications and that we can proceed with installation without prior NRC approval.

Please feel free to contact me or Mr. 3. E. Howard, of my staff at (617) 849-8900 1f you have any questions pertaining to the design deta11s of the DTVS.

Attachment:

Section 3.2 Rev1s1on 1 "Installation Of A Direct Torus Vent System (DTVS)"

3EH/amm/2282 CC: Hr. 0. HcOonald, Pro)ect Hanager 01vision of Reactor Pro]ects I/II Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commiss1on Ha11 Stat1on Pl-137 Washington, D.C. 20555 U. S. Nuclear Regulatory Commiss1on Region I 475 Allendale Road King of Prussia, PA 19406 Senior NRC Resident Inspector Pilgrim Nuclear Power Stat1on

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Attachment to BECo Letter 88-126 Section 3.2 Revision 1 "Installat)on Of A Direct Torus Vent System (OTVS)"

page" 14, 15, 16, 17, 18, 19, 19A, 198

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32 NTA T N FA R TTR 3.2.1 iv f hn This design change provides the ability for direct venting of the torus to the main stack. Containment venting is one core damage prevention strategy utilized tn the BHR Owners Group Emergency Procedure Guidelines (EPGs} as previously approved by the NRC and fs required in plant-specific Emergency Operating Procedures (EOPs}.

The torus vent line connecting the torus to the main stack wf 11 provide an alternate vent path for implementing EOP requirements and represents a significant improvement relative to exlstlng plant vent capability. For 56 psi saturated steam conditions ln the torus, apporoximately 1'l decay heat can be vented.

3,2.2 n h n This design change (Figure 3.2-1) provides a direct vent path from the torus to the main stack bypassing the Standby Gas Treatment System (SBGTS). The bypass ls an 8" line whose upstream end ls connected to the pipe between primary containment isolation valves AO-5042 A 5 B. The downstream end of the bypass is connected to the 20" main stack line downstream of SBGTS valves AON-108 and AON-112. An 8" butterfly valve (A0-5025), which can be remotely operated'rom the main control room, ls added downstream of 8" valve AO-50428. This valve acts as the primary containment outboard isolation valve for the direct torus vent line and will conform to NRC requirements for sealed closed isolation valves as defined in NUREG 0800 SRP 6.2.4. The new pipe is ASME III Class 2 up to and inclusive of valve AO-5025. Test connections are provided upstream and downstream of A0-5025.

The design change replaces the exlstlng AC solenoid valve for AO-5042B wfth a DC solenoid valve (powered from essential 125 volt DC) to ensure operability without dependence on AC power. The new isolation valve, AO-5025, ls also provided with a DC solenoid powered from the redundant 125 volt DC source. Both of these valves are normally closed and fall closed on loss of electrical and pneumatic power. One inch nitrogen lines are added to provide nitrogen to valves AO-5042B and AO-5025. New valve AO-5025 will be controlled by a remote manual key-locked control switch. During normal operation, power to the AO-5025 DC solenoid will also be disabled by removal of fuses ln the wlrlng to the solenoid valve.

This satisfies NUREG 0800 SRP 6.2.4, Containment Isolation System acceptance criteria for a sealed closed barrier. An additional fuse will be installed and remain in place to power valve status indication for AO-5025 ln the main control room.

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NUREG 0800, SRP 6.2.4, Item II.6.F allows the use of sealed closed barriers in place of automatic 1solation valves. Sealed closed barriers include bl1nd flanges and sealed closed 1solation valves which may be closed remote-manual valves. SRP 6.2.4 calls for administrative control to assure that sealed closed 1solat1on valves cannot be 1nadvertently opened. This 1ncludes mechanical devices to seal or 'iock the valve closed, or to prevent power from being supplied to the valve operator.

Consistent with SRP 6.2.4, valve AO-5025 will be a sealed closed remote manual valve under administrative control to assure that it cannot be inadvertently opened.

Administrat1ve control will be maintained by a key-locked remote manual control switch and a fuse removed to prevent power from being supplied to the valve operator.

In accordance with NUREG 0737, Item II.E.4.2.7 Position 6, AO-5025 will be sealed closed and verif1ed as such at least every 31 days.

A 20" pipe will replace the existing 20" d1ameter duct between SBGTS valves AON-108, AON-112'and the existing 20" pipe to the main stack. The existing 20" d1ameter duct downstream of AO-5042A 1s shortened to allow fitup of the new vent line branch connection.

A rupture disk will be included in the 8" pip1ng downstream of valve AO-5025. The rupture disk w111 provide a second leakage barr1er. The rupture disk is des1gned to open below containment design pressure, but will be intact up to pressures equal to or greater than those which cause an automat1c containment 1solation during any accident conditions.

The two Pr1mary Containment Isolation Valves (PCIVs)

AO-50428 and AO-5025 are placed in ser1es with the rupture disk. No s1ngle operator, error in valve operat1on can activate the DTVS. The rupture disk has a rupture pressure above the automatic conta1nment high pressure trip po1nt. Thus, the inboard PCIV (AO-50428) will receive an automatic 1solation pr1or to d1sk rupture. The inboard PCIV (AO-5042B) requires phys1cal electr1cal )umper 1nstallation to open at pr1mary conta1nment pressure above the automatic h1gh pressure trip po1nt.

Valve AO-5025 will be closed whenever primary conta1nment integrity 1s required and DC power to its solenoid control valve will be disconnected. Indication of valve position will be provided in the main control room even w1th the valve power removed. Use of the direct torus vent w1ll be in accordance w1th approved EPG requirements and controlled by EOPs in the same wanner as other ex1sting conta1nment vent paths. Pr1or to opening the vent valves the SBGT system will be shutdown and valves AON-108 and AON-ll2 (the outlet of SBGT) placed 1n a closed position.

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1 New 8" vent pipe (8"-H88-44), nclud1ng valve AO-5025 is safety related. Vent pip1ng downstream of AO-5025, including S8GTS discharge piping to main stack, is also safety related. All safety related piping will be supported as Class I. Nitrogen piping 1s non-safety related and will be supported as Class II/I.

The interpretation of the Class II/I designation through this report is g1ven below:

All Class II items which have the potential to degrade the integrity of a Class I item are analyzed. Such Class II items do not require dependable mechanical or electr1cal funct1onality dur1ng SSE, only that all of the following conditions prevail:

l. The Class II items create no missiles wh1ch impact unprotected Class I items safety functions.

2. The Class II item does not deform in a way which would degrade a Class I item.

3. If the Class II item fails, then the Class I item is protected against the full impact of all m1ss1les generated by the assumed failure of Class II 1tems.

All electrical portions of this des1gn are safety related except for the ind1cating l1ghts on the MIMIC panel C904, the tie-ins to the annunciator, and interface with the plant computer.

1 n h n v 3.2.3.1 m/ m nn Af n inm n A h The torus purge exhaust line 1nboard isolation valve AO-50428 and the associated 8" pipe are the components of the CACS affected by the des1gn modificat1on. With incorporation of the sub)ect modification, the CACS will depend on both essent1al AC (for valve AO-5042A) and essent1al OC (for AO-50428) to perform 1ts purg1ng funct1on.

The new 8" torus vent line will be connected to exist1ng 8" CACS piping between valves AO-5042B and A0-5042A.

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The SBGTS fan outlet valves (AON-108 and AON-112>, ductwork from these valves to the 20" line leading to the main stack, and the 20" 11ne leading to the main stack are the components of this system affected by the proposed change.

Valve AON-108 is normally closed, fall-open.

Valve AON-112 1s normally closed, fail-closed, and these valves are provided with essent1al OC po~er and local safety related a1r supplies.

im r mn m P Valve AO-5042B is affected by the change from AC to OC power for the solenoid and by replacement of the ex1sting air supply with n1trogen. The add1tion of containment outboard isolation valve (AO-5025) will not affect the PCIS.

Valve AO-5025 acts as the pr1mary conta1nment outboard 1solation valve for the direct torus vent l1ne and will conform to NRC requirements for sealed closed isolat1on valves as defined in NUREG 0800 SRP 6.2.4.

f f ff m/ m nn This system has the safety function of reducing the possib111ty of an energy release within the pr1mary containment from a Hydrogen-Oxygen reaction follow1ng a postulated LOCA combined w1th degraded Core Standby Cooling System.

This system filters exhaust air from the reactor bui ld1ng and d1scharges the processed air to the main stack. The system f1lters particulates and iod1nes from the exhaust stream in order to reduce the level of a1rborne contam1nation released to the env1rons v1a the ma1n stack. The SBGTS can also f1lter exhaust air from the drywell and the suppression pool.

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This system provides timely protection against the onset and consequences of design basis accidents involving the gross release of radioactive materials from the primary containment by initiating automatic isolation of appropriate pipelines which penetrate the primary containment whenever monitored variables exceed pre-selected operational limits.

im n inm n m The primary containment system, in con3unction with other safeguard features, limits the release of fission products ln the event of a postulated design basis accident so that offsite doses do not exceed the guideline values of 10 CFR 100.

3,2.3.3 P 1 1 ff n f The improvements change the AO-5042B solenoid control from AC to OC enabling it to open (from its normally closed position) with no dependence on AC power availability. The existing air supply to-AO-5042B ls being replaced by nitrogen.

Ductwork at the outlet of the SBGTS ls replaced with pipe and the new vent line ls connected to the 20" line at the outlet of the SBGTS, Addition of a new 8" vent line with containment isolation valve AO-5025 off. the existing torus vent line could introduce a flow path under design basis cond>tlons that could vent the containment directly to the stack bypassing the SBGTS.

3.2.3.4 An analysis of the effects on the safety functions of CACS, SBGTS, PCIS and PCS for the lnstallatlon of the direct torus vent ls described as follows:

The change from AC to OC control and the replacements of air with nitrogen on AO-50428 does not adversely affect the ability to open AO-50428 when the containment ls being purged, or to isolate under accident conditions.

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The modt ftcattons the ductwork and 20" 1 inc leading to the main stack do not affect the design basis safety function of any of the safety related systems.

Dur1ng normal plant operattons, the CACS and the SBGTS da not use the torus 20" purge and vent line to perform the1r safety funct1ons.

The containment isolat1on valves are tn their normally closed position, thus matntatntng primary containment boundary 1ntegrtty.

There are no adverse affects an the primary containment system by the addition of the OTVS. Valve AO-5025 will conform to NRC criteria for sealed closed tsolatton valves as defined tn NURfG 0800 SRP 6.2.4 and will not affect design basis accidents. Use of the OTVS will be in accordance wtth the containment venting provisions of EPGs as approved by the NRC and controlled by EOPs tn the same manner as other existing containment vent paths. The effects on the torus of the new 8" piping and AO-5025 have been evaluated for Hark I program loadtngs, using ASHE BPVC Section III criteria. The remaining p1ptng including the rupture dtsk was evaluated using ANSI B31.1 requ1rements.

Our1ng plant startup and shutdown (non-emergency condttton) when the purge and vent line is 1n use, valve AO-5025 remains closed. In addition, the rupture d1sk downstream af valve AO-5025 will provtde a second positive means of preventing leakage and prevent direct release up to the stack during conta1nment purge and vent at plant startup ar shutdown.

Ouring conta1nment high pressure cond1ttons, the torus ma1n exhaust 11ne is autoeattcally 1solated by the PCIS. There is no change to the existing primary containment 1solatton system function for AO-5042A or AO-50428. The sealed closed position of valve AO-5025 and the addtttanal assurance added by the rupture disk downstream will prevent any inadvertent discharge up the stack for all design basis accident conditions.

Installation of the OTVS does not adversely affect the safety functtans of the CACS, SBGTS, PCIS or the integrity of primary containment or any other safety related systems. ~

Rev. 1 (7/25/88)

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Use of the DTVS w11 1n accordance v1th the conta1nment vent1ng prov1s1ons of KPGs as approved by the NRC and controlled by KOPs 1n the same manner as other ex1st1ng conta1nment, vent paths. The OTVS prov1des an 1mproved conta1nment vent1ng capab111ty for decay heat removal wh1ch reduces potent1al ons1te and offs1te 1mpacts relative to the ex1st1ng conta1nment vent1ng capab111ty.

Rev. 1 (7/25/88)

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Enc1osure 2 LIST OF RECENTLY ISSUED GENERIC LETTERS Generic Date of Letter No. Sub 'ect Issuance Issued To 89-16 INSTALLATION OF A HARDENED 09/01/89 ALL GE PLANTS WETWELL VENT (GENERIC LETTER 89-16) 88-20 GENERIC LETTER 88-20 08/29/89 ALL LICENSEES SUPPLEMENT 1 SUPPLEMENT NO. 1 HOLDING OPERATING

( INITIATION OF THE INDIVIDUAL LICENSES AND PLANT EXAMINATION FOR SEVERE CONSTRUCTION VULNERABILITIES 10 CFR 50.54(f)) PERMITS FOR NUCLEAR POWER REACTOR FACILITIES 89-15 EMERGENCY RESPONSE DATA 08/21/89 ALL HOLDERS OF SYSTEM GENERIC LETTER NO. OPERATING LICENSES 89-15 OR CONSTRUCTION PERMITS FOR NUCLEAR POWER PLANTS CORRECT ACCESSION NUMBER IS 8908220423 89-07 SUPPLEMENT 1 TO GENERIC 08/21/89 ALL LICENSEES OF LETTER 89-07, "POWER REACTOR OPERATING PLANTS, SAFEGUARDS CONTINGENCY APPLICANTS FOR PLANNING FOR SURFACE OPERATING LICENSES, VEHICLE BOMBS" AND HOLDERS OF CONSTRUCTION PERMITS 89-14 LINE-ITEMS TECHNICAL SPEC IF I- 08/21/89 ALL LICENSEES OF CATION IMPROVEMENT - REMOVAL OPERATING PLANTS, OF 3.25 LIMIT ON EXTENDING APPLICANTS FOR SURVEILLANCE INTERVALS OPERATING LICENSES, (GENERIC LETTER 89-14) AND HOLDERS OF CONSTRUCTION PERMITS 89-13 GENERIC LETTER 89-13 7/18/89 LICENSEES TO ALL SERVICE WATER SYSTEMS POWER REACTORS PROBLEMS AFFECTING BWRS, PWRS, AND SAFETY-RELATED EQUIPMENT VENDORS IN ADDITION TO GENERAL CODES APPLICABLE TO GENERIC LETTERS 89-12 GENERIC LETTER 89-12: 7/6/89 LICENSEES TO ALL OPERATOR LICENSING POWER REACTORS EXAMINATIONS BWRS, PWRS, AND VENDORS IN ADDITION TO GENERAL CODES APPLICABLE TO GENERIC LETTERS

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