ML20005F878

LER 89-018-00:on 891219,determined That Three Pressurizer Pressure Safety Injection Instrumentation Channels May Not Have Adequate Margin Between Actuation Setpoint & Bottom of Instrument span.W/900111 Ltr

ML20005F878
Person / Time
Site:	North Anna
Issue date:	01/11/1990
From:	Kane G VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-018-01, LER-89-18-1, N-89-025, N-89-25, NUDOCS 9001170347
Download: ML20005F878 (5)

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{1 lf ., j :I VIRGINI A ELECTRIC AND PC'WER COMPANY 10 CFR 50.73. ]

l.Y ' NORTH ANN A POWER ST ATION

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, MINER AL, VIRGINI A 23117 E

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jL January 11, 1990 l I' - U. S. Nuclear Regulatory Commission Serial No. ' N-89-025 Attention: Document Control Desk NAPS /DEQ:deq .

Washington, D.C. 20555 Docket No. 50-338 License No. NPF-4 "

Dear Sirs:

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~ The Virginia Electric and Power Company hereby submits the following Licensee Event Report

- applicable to Nonh Anna Unit 1. - a Report No. LER 89-018-00 This Repon has been reviewed by the Station Nuclear and Operating Committee and will be

' forwarded to Safety Evaluation and Control for their review.

Very Truly Yours,

E. Kane Station Manager 1

Enclosure:

cx:: U.S. Nuclear Regulatory Commission 101 Marietta Street, N.W.

Suite 2900 Atlanta, Georgia 30323 Mr. J. L. Caldwell l NRC Senior Resident Inspector j f, North Anna Power Station i 9001170347 900111 9 PDR ADOCK 0500 S e 1

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~ NORTH ANNA POWER STATION, UNITS 1 AND 2 0 l5 l 0 l 0 l 0 l 3 l 318 1loFl014 E' f thE tal

-UNCERTAINTY ASSOCIATED WITH HARSH ENVIRONMENT BELOW ESF TRANSMITTER RANGE EVENT DATE tll LER NUMBER (6) REPORT DATE (?) OTHER F ACILITIES INVOLVED tel MONTH DAV YEAR YEAR 8

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NiME TELEPFONE NVM8tR ARE A CODE C. E. Kane, Station Manager 7 l0 l3 819 l 4 l -12 l 1 l 0l1 COMPLETE ONE LINE FOR E ACH COMPONENT F AILURE DESCRitED IN TH18 REPORT (13)

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I I I I I I I I I I I I I I IUPPLEMENT AL REPORT E xPECTED (141 MONTH DAY YEAR l i SUBMi&SION YE$ (19 yes, earnete,e LXPECTED SuGMISSION DATE) NO l l l ,

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L At 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br /> on December 19, 1989, with Unit 1 in cold shutdown (Mode 1 5) and Unit 2 at 100 percent power, engineering personnel determined that the three Pressurizer (Pzr) Pressure - Safety Injection (SI) instrumentation channels may not have adequate margin between the SI actuation setpoint and i the bottom of the instrument span to accomodate the errors associated with a L harsh containment environment. As a result, the Pzr low pressure SI actuation may not occur because of the potential for the transmitter to saturate below its g calibration span. Since all three channels could be affected if a harsh l containment condition exists, this event is reportable pursuant to 10CFR50.73(a)(2)(vii).

l l Failure to accomodate the errors associated with a harsh containment L environment following a small steam line bitak (SLB) inside containment is a

, result of -assuming a more conservative approach with respect to the l L environmental qualification assumptions for the transmitters. An l

engineering evaluation was performed to verify acceptable performance with the existing conditions. License Amendments wili be requested to incorporate j the respective analyses which justifies climination of the low pressure SI for  ;

small SLBs into the licensing bases. I This event posed minimal safety implications because the existing SBLOCA and the existing small SLB inside containment evaluations remained valid. The health and safety of the general public were not affected at any time during this event.

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0 'l0 -0l2 0F 0~j4 sexi tu mee =ar e au. no un ww nc remo .nu mm 1 1.0 _ Descriotion 'of the - Event ;j At 1430- hours 'on December 19,-19'89,- with Unit l' in ' cold shutdown (Mode )

5)- and Unit { 2. at c 100 a percent power, engineering personnel determined that j

, the three Pressurizer (Pzr) Pressure - Safety ~ 1njection '(SI) (Ells. System i Identifieri BQ)- instrumentation channels -(Ells System Identifier ' JE, I s LComponent Identifier CHA) may not have adequate margin between the SI l' actuation setpoint and . the-' bottom of the instrument ' span to accomodate the i

. crrors associated with' a harsh containment'. environment. As a result, the Pzr. -l low pressure St actuation may not ~ occur beettuse of the potential for the .

. transmitter - to saturate below its calibration span. Since all three channels could ' be . affected :if a ; harsh containment condition exists, this event is reportable pursuant to 10CFR50.73(a)(2)(v). 1 The calibration span of the Pzr pressure SI instrumentation is between 1700 and. 2500 psig. The calibration procedure for the three Pzr low pressure 7 SI- instrument channels. specifies a setting of '1765 psig. This is consistent with . the ' Technical . Specifications which set forth a value of greater than or equal to 1765: psig with an allowable of greater than or equal to 1755 psig. The.

~ instrument ' loop ~ uncertainty is 157.7: psig (based on the limiting containment g

environmental conditions expected prior to SI actuation : following a steam

, line break ' inside containment equivalent to the UFSAR L credible steam line break). .The uncertainty of 157.7 psig subtracted from the 1765 psig setpoint

~o f the -instrument channels falls below the instrument span of 1700 psig.

Consequently, an SI may not be initiated, if a harsh containment condition ,

exists.

' Additionally, the minimum Si actuation setting of 1755 psig specified by the Technical Specifications rainus the uncertainty of 157.7 psig is equal to a value of 1597.3 psig. The safety analysis limit for the low Pzr pressure SI is 1595 psig. Since 1597.3 psig is above the safety analysis limit, full compliance with the Technical Specifications has been achieved and the safety analysis has been verified to adequately reflect the instrument uncertainties.

However, as discussed above, the current calibration span for the transmitters may not be wide enough to accomodate these uncertainties.

2.0 Significant S afety Consequences and Imolientions The small break Loss of Coolant Accident (SBLOCA) and the small steam line break (SLB) are the only two accident analyses in the current licensing li basis which rely on the low Pzr pressure SI and for which a harsh

. containment environment would exist.

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PACILITY f6ft9m H) DOCSET NUMBER (23 LER NUMOtR 161 PAGE131 E.I dI," " D 'NuaN s

, NORT11 ANNA' POWER' STATION, UNITS 1 AND 2 - o l5 l0 l0 l0 l3 l3 l8 8l9 -

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0 l0 0 l3 0F 0 'l 4 tai ta ==. . w. =w imie r assw Hn 4 Siculticant safety- Conscauences and Imnlications Cont'dc 2.0 u

, ThisL event posed min'i mal safety implications because results of 'a safety-F > evaluation; for the . Pzr low pressure Si channels ~ has determined the

, .following: .

. 1. For the SBLOCA it' has been concluded that a SI is initiated before the -

I containment = environment becomes harsh, and therefore. - the existing {

SBLOCA evaluation remains valid. 1

2. For. the small SLB inside containment, it was determined that a SI would X be initiated by a high : containment pressure at or before . the assumed .

SI . from, pressurizer low pressure. Additionally, even if no SI were to occur for any size SLB up to the equivalent of the credible SLB, the existing small , SLB- inside containment evaluation remains valid.

' ' The . health and safety ' of ' the general pub!!c were not affected at any

..l E time ' during this event.~

3.0 Cause of the Event Failure ; to accomodate the errors associated with a harsh containment  !

> environment . is a result of assuming a more conservative approach - for the environmental ' qualification assumptions of the transmitters, than was used i to establish the setpoint' sed calibration span.

4.0 Immediate correctivc_ Action As an immediate corrective action, an engineering evaluation was performed to verify acceptable performance with the existing conditions.

5.0 Additional ' Corrective Action License Amendments will be requested to incorporate the respective analyses which justifies climination of the low pressure SI for small SLDs into the licensing bases. Appropriate changes will be made to the UFSAR as part of the License amendments.

Additionally, the other Engineered Safety Features (ESF) and Reactor Protection System (RPS) instrumentation setpoints stated in the Technical Specifications will be verified to assure that uncertainties have been adequately accounted for. This includes uncertainties associated with a harsh environment, i-g ,

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' 6.0 Actions to Prevent Recurrence To prevent recurrence of similar events, the safety analysis limits for the ESF and RPS instrumentation stated in the Technical Specifications were verified to ' be within the range of the instrumentation.

7.0 Similar Events Previous events involving environmental qualification issues have t

occurred at North Anna Unit 1 on August 19,1987 (LER N1/87 018 00) and i September 11,1987 (LER N1/87 02100 and its supplement).

L h H.0 Additional Information

! f L lt has beet. recognized that the potential climination of the low '

pressure SI for small SLBs inside containment represents a change to the facility. Evaluation of this change in accordance with 10 CFR 50.59 has determined that an unreviewed safety question exists. However, the safety consequences are minimal, as described in section 2.0, and continued operation is justified. License Amendments will be requested to incorporate the respective analyses which justifies climination of the low pressure Si for small SLBs into the licensing bases. Appropriate changes will be made to the UFSAR as part of the License Amendments, l-l l-l NI POIM 346a 'c.5. CNa 19F8- 51b Afe' CN PO

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