ML20116B439

Special Rept 96-003:on 960617 Declared Reactor Vessel Level Indicating System B Train Inoperable.Determined Probable Cause to Be within Resistance Temp Detector (Rtd).Tagged RTD out-of-service & Performed Further Troubleshooting

ML20116B439
Person / Time
Site:	Wolf Creek
Issue date:	07/24/1996
From:	Warren C WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
96-003, 96-3, WO-96-0112, WO-96-112, NUDOCS 9607300036
Download: ML20116B439 (3)

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W@ NUCLEAR LF CREEK OPERATING C Clay C. Warren Vice Presdent Plant Operations July 24, 1996 WO 96-0112 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Station P1-1 37 Washington, D. C. 20555

Subject:

Docket No. 50-482: Special Report 96-003 Gentlemen:

Special Report 96-003 is being submitted in accordance with Wolf Creek Generating Station Technical Specification 3.3.3.6 Action Statement "A" l regarding inoperability of the "B" train Reactor Vessel Level Indicating System (RVLIS) for greater than thirty days.

If you should have any questions regarding this report, please contact me at (316) 364-8831, ext. 4450, or Mr. Terry M. Morrill at extension 8707.

Very truly yours, I

Cl C. Warren CCW/jad )

Attachment cc: L. J. Callan (NRC), w/a W. D. Johnson (NRC), w/a l J. F. Ringwald (NRC), w/a J. C. Stone (NRC), w/a 9607300036 960724 / 'l, PDR ADOCK 0S000482 ' '/ 4 S PDR /

/

300013 ,

PO. Box 411/ Jurhngton, KS 66839 / Phone: (316) 364-8831 An Equal Opportunity Employer M F'HCVET

1, u

, Attachmsnt to WO 96-0112 .

Page 1 of 2 a

Special Report l 96-03 Background Information The Reactor Vessel Level Indicating System (RVLIS) is provided for verificatica and long term surveillance of core cooling. It is also used for accident diagnosis and to determine Reactor Coolant System (RCS) inventory adequacy. Indication is provided in the main control room. RVLIS uses two trains of two differential pressure (d/p) cells to measure vessel level. Each train includes narrow and wide range level measurement to accommodate measurement with and without Reactor Coolant Pump operation. These d/p cells measure the pressure differential between the bottom and the top of the reactor vessel which indicates the level (or relative void content) of the fluid surrounding the core.

t To ensure an accurate level measurtment, RCS temperature (T m) is used for density compensation when the RCS is subcooled and wide-range RCS pressure measurements are used for density compensation when the RCS is saturated.

Strap-on Resistance Temperature Detector (RTDs) provide density compensation for the affect of ambient temperature change on the sensing fluid.

Technical Specification 3.3.3.6, Action Statement "A", requires that with the f number of operable accident monitoring instrumentation channels less than the total number of channels required, restore the inoperable channel to operable status within 30 days or submit a Special Report within 14 days.

f Descrintion of Events i

On June 17, 1996, at 1520 (CST) Wolf Creek Generating Station entered Technical Specification 3.3.3.6, Action Statement "A" due the inoperability of the RVLIS *B" train. Troubleshooting discovered the RTD for the ambient air j temperature output (BBTE1328) was providing undependable data. The ambient air temperature is used as part of the temperature compensation for the bottom of the vessel pressure input to RVLIS.

The subject RTD output is indicating low and sometimes falling outside the acceptable range of the input card. When this occurs a zero temperature indication is provided. The RTD is providing a lower than normal resistance, and therefore provides a final indicated level that is higher than actual This is non-conservative for a Loss of Coolant Accident (LOCA) event.

I Radiation levels at the location of the RTD within the bio-shield prevent '

further troubleshooting during power operations. The thirty days allowed by the action statement to correct the inoperability was exceeded on July 17, 1996, at 1521 CST.  !

, Attachment to WO 96-0112 Page 2 of 2 e

Asiditional Methods of Monitorina RCS parameters:

The "A" train RVLIS is operable and provides a level indication in the Control Room.

Additionally, RCS temperatures and pressures are provided through the RCS subcooling monitor which consists of redundant channels and output trains of thermocouple measurements, wide-range hot and cold-leg RTD temperatures, and reactor pressure signals. These parameters are used by the system to display thermocouple temperatures and to calculate saturation temperatures and margin of saturation. The data provided by the 46 core exit thermocouples and pressurizer level indication can also be used to determine adequate reactor core cooling.

The loss of RVLIS is accounted for in the Emergency Operating Procedures. The following Emergency Operating Procedures give guidance on the actions to be taken with RVLIS unavailable:

Critical Safety Function Status Trees EMG F-0 Response to Degraded Core Cooling EMG FR-C2 Response to Saturated Core Conditions EMG FR-C3 Response To Inadequate Core Cooling EMG FR-C1 Natural Circulation Cooldown With Steam EMG ES-05 Void in Vessel (Without RVLIS)

Cause of the Inonerability: I l

l Troubleshooting performed under Work Package 113414 determined the probable cause to be within the RTD which is located inside the Containment Building bio-shield. Radiation levels within the bio-shield prevent further troubleshooting during power operations. The RTD has been tagged out-of- '

service and logged into the Equipment Out-of-Service Log. Instrumentation and Controls personnel are continuing to monitor the RTD output for trending purposes.

Plans and schedule for restorina the channel to operable status:

Further troubleshooting and implementation of corrective actions will occur during the next outage of sufficient duration.