05000423/LER-1996-031-02, :on 960906,potential Failure of Safety Related Control Valves Due to Failure of non-qualified Air Regulators,Concluded.Caused by Failure to Consider Potential for Pressure Regulator Failure.Design Mod Being Developed

:on 960906,potential Failure of Safety Related Control Valves Due to Failure of non-qualified Air Regulators,Concluded.Caused by Failure to Consider Potential for Pressure Regulator Failure.Design Mod Being Developed

ML20141G474
Person / Time
Site:	Millstone
Issue date:	05/09/1997
From:	Peschel J NORTHEAST NUCLEAR ENERGY CO.
To:
Shared Package
ML20141G454	List: 05000423/LER-1996-031-01, Forwards LER 96-031-01 Per 10CFR50.73(a)(2)(v).Commitments Contained within Attachment 1 to Ltr 05000423/LER-1996-031-02, :on 960906,potential Failure of Safety Related Control Valves Due to Failure of non-qualified Air Regulators,Concluded.Caused by Failure to Consider Potential for Pressure Regulator Failure.Design Mod Being Developed
References
LER-96-031-02, LER-96-31-2, NUDOCS 9705220370
Download: ML20141G474 (4)

LER-1996-031, on 960906,potential Failure of Safety Related Control Valves Due to Failure of non-qualified Air Regulators,Concluded.Caused by Failure to Consider Potential for Pressure Regulator Failure.Design Mod Being Developed

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i) 10 CFR 50.73(a)(2) 10 CFR 50.73(a)(2)(x) 10 CFR 50.73(a)(2)(v), Loss of Safety Function 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
4231996031R02 - NRC Website

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e NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 315o 0104

(

l& 95)

EXPIRES 04/30/98 l

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FACluTY NAME 11)

DOCKET NUMBER (2)

PAGE (3)

Millstone Nuclear Power Station Unit 3 05000423 1 of 4 i

TITLE 14l Potential Failure of Safety Related Control Valves due to Failure of Non-qualified Air Regulators t

EVENT DATE (5)

LER NUMBER (6)

REPORT DATE (7)

OTHER FACILITIES INVOLVED (8)

MONTH DAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY YEAR FAc!LITY NAME DOCKET NUMBER NUMBER NUMBER 1

09 06 96 96 031 01 05 09 97 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(aH2)(viii)

I POWER 000 20.2203(a)(1) 20.2203(a)(3)D) 50.73(a)(2)pi) 50.73(a)(2)(x)

LEVEL (10) 20.2203(a)(2)D) 20.2203(a)(3)Di) 50.73(a)(2)Dii) 73.71 20.2203(a)(2)Di) 20.2203(a)(4) 50.73(a)(210v)

OTHER

~

20.2203(a)(2)Dii) 50.36(c41)

X 50.73(a)(2)(v) specify en Abstract below 20.2203(a)(2)0v) 50.36(cH2) 50.73(a)(2)(vii)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER linclude Area Code)

]

J.M. Peschel, MP3 Nuclear Licensing Manager (860)437-5840 d

COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DE SCRIBED IN THIS REPORT (13)

CAUSE

SYSTEM COMPONENT MANUFACTURER REPORTABLE

CAuSE

sY! TEM COMPONENT MANUFACTURER REPORTABLE To NPRDs To NPRoS i

SUPPLEMENTAL REPORT EXPECTED (14)

EXPECTED MONTH DAY YEAR NO SUBMISSION f

YES DATE (15)

Of yes, complete EXPECTED SUBMISSION DATE).

ABSTRACT (Limit to 1400 spaces,4.e., approximately15 single-spacedtypewritten knes) (16)

On September 6,1996, with the Unit in mode 5 of an extended cold shutdown, a design engineering review concluoed that I

specific safety related control valves could fail due to exceeding the manufacture's " maximum operating pressure differential pressure" (MOPD) rating of the Solenoid Operated Valves (SOVs) installed on the control valves. SOVs could fail to perform sifety related functions because of excessive operating pressure differentials. This can result from failures of non-qualified air rigulators installed in the Instrument Air (IA) system upstream of the SOVs. The failure of an air regulator would, in tum, result in full IA system pressure being applied to the SOV. The SOV can potentially fail to operate properly since they are not rated for full IA system pressure.

An immediate notification was made at 2140 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.1427e-4 months <br /> on September 6,1996, pursuant to 10CFR50.72(b)(2)(iii)(C) and 10CFR50.72(b)(2)(iii)(D) as a condition that alone could have prevented the fulfillment of the safety function of a system or i

structure needed to control the release of radioactise material or to mitigate the consequences of an accident.

l The cause of this condition was the failure to consider the potential for pressure regulator failure in the original design and selection of SOVs.

No immediate corrective actions were required since the components affected were either not required for operation in mode 5, er compensatory measures had previously been taken, or no immediate corrective action was required. A detailed review, i

including walkdowns of each safety related SOV interfacing with the instrument air system has been completed. A cesign modification is being developed, and will be installed, which will prevent over pressurization of the SOVs. The plant will be maintained in Mode 5 or lower until such time as the modifications have been completed and the issues resolved.

l 9705220370 970509 7

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PDR ADOCK 05000423 S

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• NRC FORM 366A U.s. NUCLEAR REGULATORY Commission i

01-9 5)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME (1)

DOCKET NUMBER (2)

LER NUMBER (6)

PAGE (3) i YEAR SEQUENTIAL REVISloN Millstone Nuclear Power Station Unit 3 05000423 NUMBER NUMBER 2 of 4 1

96 031 01 TEXT (If more space is required use additionalcopies of NRC form 366A) (17) i 1.

Description of Event

l-On September 6,1996, with the Unit in mode 5 of an extended cold shutdown, a design engineering review of NRC G:neric Letter 91-15. " Operating Experience Feedback Report - Solenoid Operated Valve Problems at US Reactors, December 1991," was completed. The review concluded that the unit is susceptible to failures of safety related control valves due to the potential application of full Instrument Air (IA) system pressure. This in tum, would result in exceeding tha " maximum operating pressure differential (MOPD)" rating of the Solenoid Operated Valves (SOVs). As identified within NUREG 1275, Volume 6, " Operating Experience Feedback Report - Solenoid Operated Valve Problems", SOVs hive failed or could have failed to perform safety related functions because of excessive operating pressure dif'erentials. These events can result from the failures of non-qualified air regulators in the Instrument Air lines upstream of the SOVs. The failure of an air regulator would, in tum, result in full lA system pressure being applied to l

ths SOV.

i An immediate notification was made at 2140 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.1427e-4 months <br /> on September 6,1996, pursuant to 10CFR50.72(b)(2)(iii)(C) and 10CFR50.72(b)(2)(iii)(D) as a condition that alone could have prevented the fulfillment of the safety function of a system or structure needed to control the release of radioactive material or to mitigate the consequences of an accident.

A total of 48 SOVs which perform safety related applications had been originally identified in various systems which would be susceptible to such a failure. A subsequent design engineering review examined the safety function and failure mode of each SOV. Seven (7) of the 48 identified SOVs (three valves in the CHS System and four valves in HVG System) provide no active safety function and are not required to operate in the event of an accident. The seven SOVs meet the electrical separation requirements of Regulatory Guide 1.75, " Physical independence of Electric Systems." As a result of the subsequent engineering review, forty-one (41) ASCO SOVs have been identified which provide an active safety function. The systems affected and the rernaining number of SOVs affected include:

1.

High Pressure Safety injection System (SlH)- 3 2..

Low pressure Safety injection (SIL)- 2 3.

Chemical and Volume Control System (CHS) - 2 l

l 4.

Auxiliary Feedwater System (FWA)- 2 1

5.

Reactor Plant Gaseous Drains (DGS) - 2

6. Auxiliary Steam (ASS)- 2 7.

Charging Pump Cooling (CCE)- 2 8.

Nitrogen System (GSN)- 1 9.

Reactor Plant Ventilation (HVR)- 12

10. Main Steam System (MSS)- 3 l

11. Primary Grade Water (PGS)- 1

12. Turbine Plant Misc. Drains (DTM) - 8

13. Quench Spray System (OSS)- 1 11.

Cause of Event

Ths cause of this condition was the failure to consider the potential for pressure regulator failure in the original design and selection of SOVs.

e

'*U.s. NUCLEAR REGULATORY COMMisslON (4-95)

LICENSEE 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 3 of 4 96 031 01 TEXT lif more spaceis required. use additionalcopies of NRC Form 366A) (17) til. Analysis of Event

)

An immediate notification was made at 2140 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.1427e-4 months <br /> on September 6,1996, pursuant to 10CFR50.72(b)(2)(iii)(C) and 10CFR50.72(b)(2)(iii)(D) as a condition that alone could have prevented the fulfillment of the safety function of a system or structure needed to control the release of radioactive material or to mitigate the consequences of an accident.

The potential for over-pressurizing SOVs was first identified in NRC Information Notice (lN) 88-24, entitled " Failures of i

Air Operated Valves Affecting Safety Related Systems". The IN identified that air regulators could fail in a way that cpplies full air system pressure to downstream solenoid valves. If the affected SOVs are not rated for a sufficient MOPD, then the solenoid valves could fail to operate correctly if full air system pressure were applied.

l The air regulators located in the Instrument Air system supply lines to safety related SOVs were neither installed nor i

maintained as safety related qualified components. The instrument Air system is a non-safety related system. As a rtsult, the safety related equipment (valves, dampers, etc.) whose operation requires the availability of Instrument Air era designed to fail safe on a loss of air. The SOVs will vent air from the equipment. The failure of a non-qualified pr:ssure regulator could result in the full Instrument Air system pressure (nominally 110 psig) being applied to the SOV.

if the full air system pressure were applied to the existing SOV proper operation of the SOV is not guaranteed.

in the energized position, the SOV core assembly is raised to block the exhaust port. However, an excess pressure would act to retard or prevent the valve core assembly from dropping down (shifting) when de-energized. As a result, ds-energizing the valve solenoid would not ensure that the valve would achieved its cc rect de-energized position (block off the supply port). In this case, air pressure is applied to the control valve. This is n)n-conservative with r: gard to performing the safety function of the identified control valve.

I

IV. Corrective Action

I No immediate corrective actions were required. The components affected were not required for operation in mode 5 I

with the exception of Charging Pump Cooling (CCE) temperature control valves. The CCE valves were determined to be available but inoperable and therefore required no immediate compensatory action. A detailed review including walkdowns of each safety related SOV interfacing with the lA system was completed.

I A design modification is being developed, and will be installed, which will prevent over pressurization of the SOVs. This modification will include, but not be limited to, air regulator qualification, air regulator replacement, and/or SOV l

replacement. The plant will be maintained in Mode 5 or lower until such time as modifications have been completed to correct the potential over pressure condition on the 41 SOVs that perform an active safety function.

l

' V.

Additional Information

None l

i i

NT.C FORM 366A (4-95)

=

e i

r

• U.s. NUCLEAR REGULATORY COMMisslON (4-95)

LICENSEE EVENT REPORT (LER) l 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 4 96 031

.01 i

TEXT tif more space is required, use additionalcopies of NRC Form 366A) (11) t

Similar Events

None Manufacturer Data

[

Ells System Code High Pressure Safety injection System _.

..BQ Low Pressure Safety injection..

..BP Chemical and Volume Control System..

..CB Auxiliary Feedwater System..

..BA R: actor Plant Gaseous Drains.....

..VE Auxiliary Steam..

..SA Charging Pump Cooling..

..CC Nitrogen System..

..LK Rractor Plant Ventilation..

..VA Hot Water Pre-heating..

...LV Main Steam System...

..SB Primary Grade Water...

.. KC

' Turbine Plant Misc. Drains..

..TF Quench Spray System..

...BE Ells Component Code Valve, Sole noid, Flo w............................................. F SV l

ASCO SOV Model # NPK8320A173E ASCO SOV Model # NPK8320A186E 1-.