05000338/LER-1981-042-01, /01T-0:on 810522,Westinghouse Informed That Failure of One Vol Control Tank Level Transmitter Would Divert Letdown Flow,Causing Tank to Empty W/Suction Loss to Pumps.Caused by Design Error.Determined Reportable 810522

/01T-0:on 810522,Westinghouse Informed That Failure of One Vol Control Tank Level Transmitter Would Divert Letdown Flow,Causing Tank to Empty W/Suction Loss to Pumps.Caused by Design Error.Determined Reportable 810522

ML20004D495
Person / Time
Site:	North Anna
Issue date:	06/03/1981
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20004D490	List: 05000338/LER-1981-042, Forwards LER 81-042/01T-0 05000338/LER-1981-042-01, /01T-0:on 810522,Westinghouse Informed That Failure of One Vol Control Tank Level Transmitter Would Divert Letdown Flow,Causing Tank to Empty W/Suction Loss to Pumps.Caused by Design Error.Determined Reportable 810522
References
LER-81-042-01T, LER-81-42-1T, NUDOCS 8106090464
Download: ML20004D495 (3)

LER-1981-042, /01T-0:on 810522,Westinghouse Informed That Failure of One Vol Control Tank Level Transmitter Would Divert Letdown Flow,Causing Tank to Empty W/Suction Loss to Pumps.Caused by Design Error.Determined Reportable 810522

Event date:
Report date:
3381981042R01 - NRC Website

text

.

U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT CONTROL BLOCK / / / / / / / (1)

(PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

/0/1/

/V/A/N/A/S/1/ (2)

/0/0/-/0/0/0/0/0/-/0/0/ (3)

/4/1/1/1/1/ (4)

/ / / (5)

LICENSEE CODE LICENSE NUMBER LICENSE TYPE CAT g/ (6)

/0/5/0/0/0/3/3/8/ (7)

/0/5/2/2/8/1/ (8) / 0/ 6/ 0/ 3/ 8/1/ (9)

DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10)

/0/2/

/

On May 21, 1981, Westinghouse informed Vepco that a failure of one volume

/

/0/3/

/

control tank (VCT) level transmitter would divert VCT letdown flow, cause the _/

/0/4/

/

VCT to empty and result in a loss of suction to the charging /HHSI pumps if no /

-/0/5/

/

operator action was taken. This event was determined to be reportable pursuant /

/0/6/

/

to T.S. 6.9.1.8.i on May 22, 1981. Actions have been taken to insure operators /

/0/7/

/

respond appropriately to prevent this scenario. The public health and safety /

/0/8/

/

are not affected.

/

SYSTEM

CAUSE

CAUSE COMP.

VALVE CODE CODE SUBCODE COMPONENT CODE SUBCODE SUBCODE

/0/9/

/S/F/ (11) g/ (12) 1Ak13)/Z/Z/Z/Z/Z/Z/(14) [Z/ (15)

/Z/ (16)

SEQUENTIAL OCCURRENCE REPORT REVISION LER/R0 EVENT YEAR ' REPORT NO.

CODE TYPE NO.

(17) REPORT NUMBER

/8/1/

/-/ /0/4/2/

/\\/

/0/1/

g/

/-/

[0/

ACTION FUTURE EFFECT SHUTDOWN ATTACHMENT NPRD,

PRIME COMP. COMPONENT TAKEN ACTION ON PLANT METHOD HOURS SUBMITTED FORM SUB. GUPPLIER MANUFACTURER g/ (18) /_X/ (19) g/ (20) /_Z/ (21) /0/0/0/0/ (22) /Y/ (23) /N/ (24) /Z/ (25) /Z/9/9/9/ (26 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS (27)

/1/0/

/

The cause of this event is design error. Changes to circuitry and procedur_es /

/1/1/

/

are being evaluated. Operators have been informed of this design defect, are /

/1/2/

/

prepared to properly evaluate a VCT level transmitter failure, and are prepared /

/1/3/

/

to take appropriate action if a VCT level transmitter fails.

/

/1/4/

/

/

FACILITY METHOD OF STATUS

% POWER OTHER STATUS DISCOVERY DESCRIPTION (32)

/ (30) DISCOVERY [1f,5_[

g/ (28)

/1/0/0/ (29) /

NA g/ (31)

/

Notification from NSSS /

ACTIVITY CONTENT RELEASED OF RELEASE AMOUNT OF ACTIVI'lY (35)

LOCATION OF RELEASE (36)

/1/6/

/Z/ (33)

/Z/ (34) /

NA

/

/

NA

/

l PERSONNEL EXPOSURES l

NUMBER TYPE DESCRIPTION (39) j

/1/7/ /0/0/0/ (37) LZL (38) /

NA

/

PERSONNEL INJURIES l

NUMBER DESCRIPTION (41)

/1/8/ /0/0/0/ (40) /

NA

/

LOSS OF OR DAMAGE TO FACILITY (43)

TYPE

DESCRIPTION

l

/1/9/

/Z/ (42) /

NA

/

l PUBLICITY l

ISSUED DESCRIPTION (45)

NRC USE ONLY

/2/0/

/N/ (44) /

NA

/////////////

gEOFPREPARER W. R. CARTWRIGHT PHONE (703) 894-5151 1

l

$106090

Virginia Electric and Power Company North Anna Power Station, Unit #1

Attachment:

Page 1 of 2 Docket No. 50-338 Report No. LER 81-042/01T-0

Description of Event

On May 21, 1981, Westinghouse Electric Corpotation informed Vepco that a failure of one volume control tank level transmitter could cause the charging /high head SI pumps to lose suction. After reviewing electrical and instrument drawings on May 22, 1981, Vepco engineers determined that this event was possible at North Anna Units 1 and 2 and is reportable pursuant to T.S. 6.9.1.8.i.

The volume control tank (VCT) level instrumentation control system has two independent level transmitters. If either level transmitter fails high, letdown which is normally aligned to the VCT would be automatically diverted to the gas stripper. Without operator action, the VCT would empty causing the operating charging /HHSI pump to be damaged from loss of suction. Due to breaker coincidence or low charging pump discharge header pressure, the remaining charging pumps would receive an automatic start signal and could also fail due to loss of suction.

In the case described above, automatic charging pump suction realignment upon a low VCT level signal does not occur because the VCT to RWST swap over control contact sets from each transmitter are wired in series. A single transmitter failure in the high direction defeats the swap over action. This control circuitry arrangement is a violation of the Nuclear Regulatory Commission regulations related to separation of protection and control systems and single failure criteria as delineated in GDC-24 and IEEE-279.

Probable Consequences of Occurrence Since all direct control room VCT level indication (including alarm functions) are based on one transmitter (LT-115), most of the indication available to the operator would be consistent with a high VCT level if this transmitter failed high. A failed level channel could be detected from the control room by indirect indications such as RCS make up rate, RCS letdown rate, pressurizer level, VCT pressure, primary flow rate to the gas stripper, position indication of divert valve LCV-115A, and demand output from auto / manual divert valve controller LC-112C, which uses input from the other level transmitter (LT-112). Direct confirmation of a suspected failure of LT-115 could be confirmed by a check of a local level indicator in the auxiliary building which receives its signal from level transmitter LT-112. Failure of LT-112 in the high direction would be easier to evaluate since most control room indications in this case would be inconsistent with a high VCT level.

Discussions with Control Room Operators, Senior Reactor Operators, and Shift Supervisors indicates that most have experienced a failure of a single VCT level transmitter during training at the Surry Power Station simulator; however, many were unaware that auto charging /high head safety injection pump VCT to RWST suction swap over could be defeated by single level channel failure. All CRO's, SRO's, and STA's currently operating North Anna Units 1 and 2 have been informed of this design defect and are prepared to properly evaluate this event.

Attachment: Page 2 of 2 Probable Consequences of Occurrence (cont)

A standing order has been issued which delineates specific actions to be taken in the event that a VCT level transmitter fails. The actiens described in the standing order maximize operator time to evaluate VCT conditions when a VCT level transmitter fails and insures that in the unlikely event that charging /high head safety injection pump suction is lost, only one pump will be damaged. The actions insure that at least one pump will be available for safety injection. The actions have been reviewed and are consistent with the Basis section of the Technical Specifications.

The actions described in the standing order significantly reduce any consequences or this event. No adverse consequences are expected. The public health and safety are not affected.

Cause of Event

The cause of this event is design error. The system was built as described in the FSAR (see Sec. 9.3.4 page 25)._. ~

~

Immediate Corrective Action

The standing order described above was issued. Operators were informed of the design defect.

Scheduled Corrective Action Changes to circuitry and procedures are being evaluated.

Actions Taken to Prevent Recurrence Actions to prevent recurrence are not required.

l Generic Implications l

This problem is generic to several Westinghouse plants. Westinghouse has notified affected units.

l l

l t

l l