ML20128A068

Submits Addl Info Requested in 850214 Meeting Re Response to Generic Ltr 84-23, Reactor Vessel Water Level Instrumentation in Bwrs. Yarway Vs Gemac Level Indication Discrepancy in Monthly Operating Rept Discussed

ML20128A068
Person / Time
Site:	Oyster Creek
Issue date:	05/17/1985
From:	Fiedler P GENERAL PUBLIC UTILITIES CORP.
To:	Zwolinski J Office of Nuclear Reactor Regulation
References
GL-84-23, NUDOCS 8505240115
Download: ML20128A068 (8)

Text

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GPU Nuclear Corporation Nuclear

= s; r 888 Forked River, New Jersey 08731-0388 609 971-4000 Writer's Direct Dial Number:

May 17, 1985 Mr. John A. Zwolinski, Chief Operating Reactors Branch No. 5 Division of Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555

Subject:

Oyster Creek Nuclear Generating Station Docket No. 50-219 License No. DPR-16 Response to Generic Letter 84-23

" Reactor Yessel Water Level Instrumentation in BWRs" GPUN responded to the subject Generic Letter in a submittal dated December 18, 1984 and in a meeting with your staff on February 14, 1985. As a result of our discussion in February, it was agreed that additional information would be provided. Your requests for additional infonnation are addressed below:

1.

With regard to the Yarway vs. GEMAC level indication discrepancy as mentioned in the Monthly Operating Report: The currently initalled Yarway control room indicators require frequent calibration in ordu to remain in agreement with the local-rack mounted Yarways and control room GEMAC level indicators. This condition is attributed to the nature of the Yarway instrument and its associated transmitting device. The local Yarway indicator is an electro-mechanical device with wide range mechanical travel. Signal development is accomplished through a transformer and lever arm arrangement.

The combination of low differential voltage transmitted, the long distance to the control room amplifier / indicator, and the large amount of mechancial

" play" within the level sensor result in the need for frequent calibration.

Yarway Corporation recognizes the limitations of this equipment and no longer manufactures the model in use at Oyster Creek. Since recalibration brings the Yarway level indicators into satisfactory agreement with the GEMACs no further work is seen as necessary in the immediate future. Exact agreement between the Yarway and GEMAC indicators is not expected because each instrument employs a different type of differential pressure sensor and calibration is accomplished differently in each case. The Yarway system is scheduled to be replaced with modern analog transmitters and indicators during the outage scheduled for October 1985. Engineering and procurement associated with the installation of environmentally qualified Rosemount transmitters to replace the Yarways are in progress.

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06 b I I GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation

Mr. John Zwolinski.

U.S". Nuclear R2gulatsry Comission

=Page 2"

2. _-Piping configuration of the Fuel Zone Level System (FZL) and proximity of potential " hot spots": A detailed examination of the FZL reference leg runs has indicated that no'" hot spots" or tubing arrangement problems exist.

The reference. legs are not close to pump motors or relief / safety valve 7 outlets.

Isometric drawings of the FZL, Yarway, and GEMAC refererce legs and photographs of the affected areas reveal that a 24" main steam line and the

.10" reactor.feedwater lines come in close proximity to both reference legs.

Refer to the Attachments-3 and 4 for more detail.

It is expected that the

~feedwater lines would cool.down rapidly following an accident due to the loss of feedwater heating and it is not anticipated that the closeness of the

~feedwater lines would pose a threat to reliable indication. The feedwater lines are encased in insulation and will have minimal effect on the reference legs during normal operation. The proximity of the reference _ legs to the

-feedwater line (10 inch RF-2) is approximately 36 inches in one case and 18

. inches in the other.. The FZL_and GEMAC instruments share the same reference legs. The reference leg for FZL channel B comes within 18 inches of a main steam line due to the location of its reactor' vessel penetration and remains parallel for'a significant length. _The main steam line is encased in insulation and plant _ data indicates that tnis line has no effect upon reference leg temperature. Thermocouple measurements of reference leg temperature show that the channelLB FZL reference leg temperature agrees within four (4) degrees of the temperature of the other reference leg which is not near a steam line. Measurements also show that the reference leg temperature follows drywell ambient temperature which indicates no appreciable effect of the main steam line on reference leg temperature.

Our investigation of actual piping configurations 'is based on existing Eas-built drawings and photographs of the affected areas.. Detailed-isometrics will be developed during the next outage of sufficient duration to verify our understanding of.the layouts.

-3.

Operator-training to deal with ambiguous level indication: In 1983 and 1984 licensed personnel were trained on the Symptom Based Emergency Operating _ Procedures (E0Ps) which included simulator training at the GE.

Simulator in Morris, Illinois.

This training was provided to licensed operators and shift technical advisors (STAS) and included dealing with the various conditions associated with reference leg flashing. A complete description of the phenomenon was presented along with an analytical treatment of the effects of reactor conditions. Discussion of the various types of

detectors and their inputs to ESF systems was also dealt with. To summarize, our present and future simulator training includes the following: level instrument operation and temperature effects on the various types of instrumentation, level monitoring under changing reactor conditions, drywell

'_ temperature effects on reactor level indication, differences between hot and cold leg sinstrument' response, Yarway instrument response, cold leg instrumentation, and various level flashing events.

In addition, failure of individual instrumentation was also included during simulator training.

~

? Mr.EJohn 'Zwolinski

'U.S. Nucitar Rigulatory Commission'

-Page 3 i~

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4. -Scenarios leading to high contaimeent. temperature causing flashing in reference legs and errors in water level instrumentation which may confuse the operators: The logic diagram shown in Attachment 1 depicts the conditions necessary to reach-a state of inadequate core cooling without the operator's knowledge. As can;be seen from the figure, there are many failures which must-occur in order to reach an inadequate core cooling (ICC) condition without.the operator's knowledge. These failures include:

(1)'. Reactor Pressure-Vessel (RPV) inventory reduction event which

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requires Emergency Core Cooling System (ECCS) injection but ECCS injection fails (2) Undetected loss or degradation of drywell cooling for at least nine days at rated conditions prior to the inventory reduction in (1)

(3)(' All RPV. level instruments give incorrect indications of actual RPV inventory-(4) The operator takes no actions based on multiple alarms to enter the Emergency Operating Procedures (E0PS)

In light of multiple system failures and operator errors which must occur, it is highly unlikely that a condition of ICC without the operator's knowledge and without his taking actions to restore and assure adequate core cooling could exist.'

4 In the event that any comments or questions arise, please contact Mr.

Drew Holland of imy staff at (609)971-4643.

Very truly yours, t 0 f,}

vne t

iedler Vice President and Director Oyster Creek

- P8F/DH/ dam Attachments cc: Dr. Thomas E. Murley, Administrator

. Region I U.S. Nuclear Regulatory Commission

' 631 Park Avenue

- King of Prussia, PA 19406

' NRC Resident Inspector 1-Oyster Creek Nuclear Generating Station Forked River, NJ 08731 4

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ATTACHMENT 2 Notes:

1.

A complete loss'of feedwater is _ required.

If only a partial loss of feedwater occurred, the remaining feedwater would reflood the RPV and remove core decay heat after a scram on low RPV. level.. A low level scram will occur at any drywell temperature.

2 2.-

Indicated level must be above L0.

If level drops below this value, Core Spray pumps-start, FZL instrument turns on, Isolation

~ Condensers start, and with a coincident high drywell pressure, Contaimaent Spray starts and will reduce drywell stemperature.

3. - - A drywell. temperature of greater than 3500F is required so that indicated level will remain above-LO2 so that no ECCS starts occur.

- 4.

A-drywell temperature of greater than 4500F is required for an on-scale level reading when the actual level is below the low instrument tap. A LOCA or MSLB will not result in such temperatures.

5.

The FZL instrument is density compensated for drywell temperature up to saturation conditions. When~ saturation is detected in the reference leg, the instrument turns itself off. The only potential way that the Fuel Zone can give misleading information is when the -

reference leg oscillates in and out of saturation.

6.-

The Containment Control section of the E0Ps requires the operator to monitor indicated RPV water level and temperatures on the level instrument reft.rence. legs in order to assure that he is receiving valid level indication.

If all of the RPV level instruments have

.been invalidated by this criteria or, saturation is detected in the GEMAC reference leg or, the operator is unsure of the actual level in the RPV, he is. directed to flood the RPV.

7.

Given any confusion regarding level status, the operator would initiate FZL indication by manually tripping the recirculation pumps.

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