05000423/LER-1998-016, :on 980223,potential Air/Gas Intrusion in Chemical & Volume Control Sys Was Noted.Caused by Inadequate Initial Design.No Cause for Corrective Actions Because Both Flow Paths Were Operable

:on 980223,potential Air/Gas Intrusion in Chemical & Volume Control Sys Was Noted.Caused by Inadequate Initial Design.No Cause for Corrective Actions Because Both Flow Paths Were Operable

ML20247P389
Person / Time
Site:	Millstone
Issue date:	05/18/1998
From:	Danni Smith NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20247P381	List: 05000423/LER-1998-016, :on 980223,potential Air/Gas Intrusion in Chemical & Volume Control Sys Was Noted.Caused by Inadequate Initial Design.No Cause for Corrective Actions Because Both Flow Paths Were Operable 05000423/LER-1998-016-01, Forwards LER 98-016-01,determined Reportable at Millstone Unit 3 on 980223,per 10CFR50.73(a)(2)(vii).Commitments Made within Ltr,Encl
References
LER-98-016, LER-98-16, NUDOCS 9805270439
Download: ML20247P389 (6)

LER-1998-016, on 980223,potential Air/Gas Intrusion in Chemical & Volume Control Sys Was Noted.Caused by Inadequate Initial Design.No Cause for Corrective Actions Because Both Flow Paths Were Operable

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2)(viii) 10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(iii) 10 CFR 50.73(a)(2)(iv), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
4231998016R00 - NRC Website

text

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NRC f oRM 366 U.s. NUCLEAR REGULATORY Commission APPROVED BY OMB No. 3160 0104 EXPIRES 04/30/98 (4-95)

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LICENSEE EVENT REPORT (LER) iSt^u's ';'cW;,*,^,'a",^/otaio $,s",^o",^T!s"J,,=;?"fc o

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FAC1fTV NAME fil DOCKET NUMBER (2)

PAGE (3)

Millstone Nuclear Power Station Unit 3 05000423 1 of 6 TITLE I4)

Potential Air / Gas intrusion in Chemical and Volume Control Systam EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

~

MONTH DAY YEAR YEAR SEQUENTIAL REVISloN MONTH DAY YEAR FACIUTY NAME DOCKET NUMBER NUMBER NUMBER 01 05 18 98 02 23 98 98 016 OPERATING 5

THis REPORT is SUBMITTED PURSUANT To THE REQUIREMENTS OF 10 CFR 5: (Check one or more) (11)

MODE (9) 20.2201(b) 20.2203(a)(2)(v) 50.73(a)(2)(i) 50.73(a)(2)(viii)

POWER 000 20.2203(a)(1) 20.2203(a)t3)(i) 50.73(a)(2)(ii) 50.73(a)(2)(x)

LEVEL (10) 20.2203(a)(2)(i) 20.2203(a)(3)(ii) 50.73(a)(2)(iii) 73.71 20.2203(a)(2)(ii) 20.2203(a)l4) 50.73(a)(2)(iv) oTHER 20.2203(a)(2)(iii; 50.36(c)(1) 50.73(a)(2)(v)

Specify in Abstract below

~

20.2203(a)(2)(iv) 50.36(c)(2)

X so 73(a)(2)(vii)

LICENSEE CONTACT FoR THis LER (12)

NAME TELEPHONE NUMBER tinclude Area Codel David A. Smith, Manager, Unit 3 Regulatory Compliance (860)437-5840 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE TO NPRDS TO NPROS 9

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY YEAR X

YEs No submission 07 15 98 (If yes, complete EXPECTED submission DATE).

DATE (15)

ABSTRACT (Limit to 1400 spaces, Le., approximately 15 single-spaced typewntten tenes) (16)

On February 23,1998, with the unit in Mode 5, it was identified that there had been several Condition Reports (CRs) written since early 1997 describing Boric Acid pump air binding, or gas / air accumulation within the Boric Acid piping system. Gas / air accumulation within the system had resulted in the Boric Acid Pumps (3CHS*P2A and B) cavitating or becoming gas / air bound. Three primary pathways have been identified for gas / air intrusion: air introduced during batching operations, inadequate venting of connecting systems after maintenance, and hydrogen stripping. This gas / air binding pMnomenon has affected both trains of the Boric Acid Transfer (BAT) System. The Boric Acid system r: mains operable with the exception of the gravity boration pathway. The Reactor Water Storage Tank is operable as tn alternate boration path. These conditions are reportable pursuant to 10 CFR 50.73 (a)(2)(vii) as "any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to: (A) Shut down the r: actor and maintain it in a safe shutdown condition; [and] (D) Mitigate the consequences of an accident." This condition is historical. The cause for air intrusion into the Boric Acid Pumps is inadequate initial design of the Boric Acid system piping configuration. There were no adverse safety consequences from this condition. The unit has not l

experienced a reactivity event where operation of the BAT System has been needed, nor an event where emergency boration has been necessary.

The evaluation of hydrogen stripping / accumulation is ongoing, and the results of our investigation and corrective actions will be provided in a supplement to this report.

9805270439 980518

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PDR ADOCK 05000423 S

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.-U.S. NUCLEAR RESULAToRY Commission LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAoE (3)

YEAR SEQUENTIAL REVISION Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 2 of 6 98 016 01 TEXT (If rnore space is required, use additional copies of NRC forrn 366A) (17) 1.

Description of Event

On February 23,1998, with the unit in Mode 5, it was identified that there had been several Condition Reports (CRs) l written since early 1997 describing Bonc Acid pump air binding, or gas / air accumulation within the Boric Acid piping system. Gas / air accumulation within the system had resulted in the Boric Acid Pumps (3CHS*P2A and B) cavitating or becoming gas / air bound. Three primary pathways have been identified for gas / air intrusion: air introduced during Boric Acid batching operations, inadequate venting of connecting systems after maintenance, and hydrogen stripping. This g:s/ air binding phenomenon has affected both trains of the Boric Acid Transfer (BAT) System. The system remains operable with the exception of the gravity boration pathway. The Refueling Water Storage Tank (RWST) is operable as cn titemate boration path.

During the Nuclear Regulatory Commission (NRC) Inspection Manual Section 40500 Inspection, a question was raised regirding the adequacy of the root cause investigation associated with Condition Report (CR) M3-97-0954, dated May 14,1997, which attempted to determine the causes of the air binding problems with the Boric Acid Pumps. The root cause did not identify all the potential sources of air that could lead to air binding. CR M3-98-0975, dated February 19, 1998, was issued to re-evaluate the root cause.

(See attached figure for the following descriptions.)

Th3 boric acid batching process has led to air intrusion because the air filled space in the vertical section of piping belowl ths Boric Acid Batch Tank is swept into either the "A" or "B" Train when the batch tank drain valve is opened for filling End the respective train's pump is running for mixing during batching operations. Air binding of the Boric Acid Pumps could prevent the flow of boric acid from the system when called upon. Also, both pumps tie into a common header to the charging pumps. Sufficient air within the system could lead to air binding of one or more charging pumps as they tika suction from a common header. These conditions are reportable pursuant to 10 CFR 50.73 (a)(2)(vii) as "any event whIre a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system designed to: (A) Shut down the rtactor and maintain it in a safe shutdown condition; [and] (D) Mitigate the consequences of an accident." This condition is being dispositioned in accordance with the Millstone Corrective Action Program.

Tha Boric Acid Transfer System consists of two separate trains, each containing a Boric Acid Storage Tank (BAST),

Boric Acid Pump (to transfer borated water from the storage tank to either the Volume Control Tank (VCT), the RWST, or the suction of the charging pumps), a Boric Acid Batch Tank and associated piping and valves. The Boric Acid Batch Tcnk is located on the floor level abova the two trains. There is a long vertical drop in the piping from the batch tank to a connection with each system. During a batching operation a slug of air is trapped in this line and is swept into the operating Boric Acid Pump as it circulates the boric acid solution for mixing. A vent valve was installed on this section of piping during this outage.

Th2 physical configuration of the "A" Boric Acid Transfer System Gravity Boration lines contains a high point segment of piping which is at a much higher elevation (51 feet - 6 inches) than the elevation of the line running from the "A" Boric Acid Storage Tank to the suction of the "A" Boric Acid Pump (45 feet - 0 inches). This section of piping is a dead leg (only opened if gravity boration is needed) and provides a large volume to trap gas / air once i titroduced into the system. Our investigations have identified that some of the gas collected in these high points is hydrogen, The evaluation of hydrogen stripping / accumulation is ongoing, and the results of our investigation will be provided in a supplement to this report. It is presently believed that hydrogen is stripped in the miniflow lines on the Ch;rging pump discharge at the miniflow orifices, and the Reactor Coolant Pump number 1 seal leakoff. The hydrogen is then transported to the Charging pump suction header via the seal water retum path. Due to the piping configurations, N4C FORM 306A 495)

.-U.s. NUCLEAR REoVLAToRY Commission LICENSEE EVENT REPORT (LER) l TEXT CONTINUATION FdCILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) f YEAR SEQUENTIAL Revision Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 3 of 6 98 016 01 TEXT 01more space is required, use additionalcopies of NRC Form 366A) (17}

l cny gas accumulation would migrate to the high points. A vent valve is installed on this section of piping.

l On the *B" Boric Acid Transfer System suction piping the vertical line from the Boric Acid Batch Tank contains a short horizontal segment at an elevation of 47 feet - 10 inches, which connects a short vertical segment that leads down to the horizontal suction line between the "B" Boric Acid Storage Tank and the suction of the *B* Boric Acid Pump (elevation of j

45 feet - 0 inches). This short horizontal section of piping at elevation 47 feet - 10 inches can also trap air during j

bitching operations.

II.

Cause of Event

This condition is historical. The cause for air intrusion into the Boric Acid Pumps is inadequate initial design of the Boric Acid system piping configuration. Inadequacies in the design of the piping layouts and the lack of vents in some locations resulted in trapped air in the system. Contributing factors were inadequate batching and venting procedures.

Th3 boric acid batching process used introduced air into the BAT System. The large amount of maintenance performed during this outage on portions of the Chemical and Volume Control and the Boric Acid Transfer Systems could have introduced air pockets into the Boric Acid Transfer System which may not have been adequately vented.

l It is presently believed that hydrogon is stripped in the miniflow lines on the Charging pump discharge at the miniflow orifices, and the Reactor Coolant Pump number i sealleakoff. The hydrogen is then transported to the Charging pump suction header via the seal water return path. Due to the piping configurations, any gas accumulation would migrate to th3 high points.

Ill. Analvsis of Event Th3 operability of the boric acid transfer portion of the Chemical and Volume Control System (Boron injection System) cnsures that sufficient negative reactivity controlis available during each mode of operation. Failure to maintain the Boric Acid Transfer System lines full of borated water could result in portions of the piping containing voids and/or cntriined gas pockets which could adversely affect the ability of the boric acid or charging pumps to function properly.

Th3 Boric Acid Transfer System and the Gravity Boration lines to the charging pumps are redundant to the Refueling Witir Storage Tank, which is the primary source of boration. This condition is significant in that if these trains were inoperable when the RWST was inoperable this could have resulted in the unit operating in a condition that was outside th3 units design basis.

There were no adverse safety consequences from this condition, in that the unit has not experienced a reactivity event where operation of the Boric Acid Transfer System has failed, nor a Design Basis Event where operation of the emergency boration function has been necessary.

IV. Corrective Action

There was no immediate impact on equipmerit operability and immediate corrective actions were not required because the unit was in full compliance with Technical Specification 3.1.2.1, "Boration Systems Flow Path - Shutdown," as both flow paths from the Refueling Water Storage Tank were OPERABLE.-__

NRC FORM 336A U.s. NUCLEAR REGULATORY CoMMtssK)N (4 95)

UCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEQUENTIAL Revision Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 4 of g 98 016 01 TEXT Uf more space is required, use additionalcopies of NRC Form 366A) (17)

Tha following corrective actions have been completed:

1.

Troubleshooting of the Boric Acid Transfer System to determine the source (s) of air intrusion into the system and corrective actions have been identified.

2.

Procedures have been revised to incorporate lessons learned from the troubleshooting effort to avoid air l

entrainment during Boric Acid Transfer System operation to address deficiencies in the design of the system.

3.

Vent valves have been added to the high points in the gravity boration pathways.

l Tha following corrective actions remain to be completed:

1.

Validate effectiveness of the revised batching procedure and revise as necessary. (Prior to Mode 2) 2.

Evaluate potential system modifications to minimize hydrogen stripping and eliminate locations which promote gas accumulation. (Prior to Refueling Outage 6) 3.

Investigate potential sources of hydrogen and recommend corrective actions to reduce or eliminate the gas buildup.

(Prior to Mode 2) 4.

Develop a surveillance program to periodically monitor the affected piping, to establish a gas accumulation rate and periodicity for venting gas to ensure charging pump operability (Prior to Mode 2) 5.

Establish a maximum allowed volume of gas in the boric acid gravity boration piping, to ensure pump operability and establish an allowable venting frequency. (Prior to Mode 2)

V.

Additional Information

None

Similar Events

Listed below are other historical LERs which reported conditions resulting from inadequate design. A majority of these sv;:nts were identified as a result of the Configuration Management Review Process.

LER 96-007-00 Containment Recirculation Spray, Quench Spray, and Safety injection System Outside Design Basis l

Due to Design Errors LER 96-009-02 Inoperable Shutdown Margin Monitors from Low Count Rate, Due to inadequate Design Control LER 96-013-00 Residual Heat Removal System Design Deficiency Due to Non-conservative Original Design Assumption LER 96-026-02 Non-Conservative Primary Grade Water Flow Rates Used in Boron Dilution Safety Analysis LER 97-003-00 Potential For Recirculation Spray System (RSS) Piping Failure Due To RSS Pump Stopping And j

Restarting During Accident Conditions LER 97-015-00 Potential Vortexing of Recirculation Spray System Pumps LER 97-021-00 Defective Design of RSS Expansion Joint Tie Rod Assembly LER 97-02840 Potential Loss of Net Positive Suction Head for Recirculation Spray System Pumps LER 97-029-00 Design Basis Concem on SGTR Analysis for MSPRBV k

r-NAC FORM 366A (4-951

,.-U.S. NUCLEAR REGULATORY COMMISSION (4 9 0 LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACUTY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3)

YEAR SEOuENTIAL REVISloN Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 5 of 6 98 016 01 TEXT tif more space is required, use additional copies of NRC Form 366A) (17)

LER 97-031-00 RHR Valve Low Pressure Open Permissive Bistable Setting Set Non-Conservatively LER 97-035-00 Potential Nonconservatism for Steam Generator Water Level Low-Low Trip Setpoint Due to PMA Term Uncertainties l

LER 97-041-00 Voluntary Report: Operation of Service Water System With Only One Pump Operable LER 97-046-00 Containment Recirculation Spray System Cubicle Flood Potential LER 97-048-00 Oversized PGS Impeller Could Poten+.ially Result in Non-Conservative Boron Dilution Event LER 97-051-00 Design Deficiency for 4.16kV Feeder Fault Clearing Times Manufacturer Data Ells System Code Rnctor Coolant System..

..AB Chimical and Volume Control System...

..CB Ells Comoonent Code Pump..

..P Tank..

..TK Velve..

..V e

W FORM 366A U.S. NUCLEAR REGULATORY COMMISSION 14-9 3)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMSER (6) -

PAGE (3)

YEAR SEQUENTIAL REVISION Millstone Nuclear Power Station Unit 3-05000423 NUMBER NUMBER 6 Of 6 98 016 01 TEXT fit more space is required, use additional copies of NRC form 36GA) (17)

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