ML20101E662

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Forwards Reactor Pressure Vessel Water Level Measurement Sys Evaluation Rept in Response to Generic Ltr 84-23, Reactor Vessel Water Level Instrumentation in Bwrs
ML20101E662
Person / Time
Site: Clinton Constellation icon.png
Issue date: 12/05/1984
From: Spangenberg F, Spengenberg F
ILLINOIS POWER CO.
To: Schwencer A
Office of Nuclear Reactor Regulation
Shared Package
ML20101E665 List:
References
GL-84-23, U-0766, U-766, NUDOCS 8412260331
Download: ML20101E662 (3)


Text

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~ lillNOlB POWER COMPANY CUNTON POWER STATION. P.o. Box 678 CLINTON, ILLINOts 61727 December 5, 1984

' Docket No. 50-461 Director of Nuclear Reactor Regulation Attention: Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U.'S. Nuclear Regulatory Commission

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Washington, D.C. 20555

Subject:

Clinton Power Station Unit #1 Response to Generic Letter 84-23 Reactor Vessel Water Level Instrumentation in BWRs

Dear Mr.'Schwencer:

This ' letter responds to NRC Generic Letter 84-23 dated October 26,

'1984 from D. G. Eisenhut addressing reactor vessel water level instrumentation. Due to our Atomic Safety Licensing Board hearing schedule. Illinois Power submitted, via letter U-0749, dated October 10, 1984, an Interim Closure Report regarding the Clinton Power Station compliance with proposed upgrades to the Reactor Vessel Water Level Measurement System (WLMS) design. Our final report, entitled " Reactor Pressure Vessel Water Level Measurement System Evaluation Report", has been completed and is attached. This report provides a plant-specific evaluation of the Clinton WLMS and represents our response to Generic

, Letter 84-23.

In general, Illinois Power has addressed the three potential-improvement categories listed in the' generic letter as follows:

Improvements have been made to the WLMS design to pr significantly reduce errors caused by high drywell temperatures and associated sensing line fluid flashing under low Reactor Pressure Vessel (RPV) pressure conditions. This was accomplished by reducing the vertical drop of selected sensing lines and-relocation of sensing'line flow restricting orifices in the drywell.

  • Level indication equipment for Clinton Power Station utilises analog instrumentation to improve reliability and accuracy.

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1A.120 i-Protection system logic was; reviewed to demonstrate compliance with the single' failure criteria.' Reviews were also performed

.to determine the consequences of a break in a reference les and a single failure in another protection system channel associated with an' intact reference les to assure that.

' operator action is not required to mitigate the consequences of the event.

' A detailed description of the modifications implemented in the Clinton WLMS design is contained in the' attached report. Illinois Power is currently proceeding with the installation of the modified system and will complete this effort prior to. fuel load.

The attached report was prepared utilizing the methodology for WLMS error analysis developed in the S. Levy. Inc. report SLI-8211. entitled

" Review of BWR Reactor Vessel Water Level Measurement Systems", dated July 1982,~ sponsored by the BWR Owners' Group. .The conclusions of our final report are consistent with the information provided in our Interim Closure Report except for a statement in Section IX of the Interim Report which concludes that automatic Emergency Core Cooling System

.'(ECCS) initiation is always provided by the modified WLMS. This statement'is.not accurate in that under worst case conditions (i.e..

drywell temperature greater-than 310*F and RPV pressure less than

' 63 psig) the WLMS will initiate those Reactor Pressure Vessel injection systems with a Level 2 setpoint (116 inches above Top of Active Fuel);

. i.e., High Pressure Core Spray and Reactor Core Isolation Cooling.

However, it will not initiate those systems with a Level 1 setpoint (17 inches above Top of Active Fuel); i.e.. Low Pressure Core Spray and Low Pressure Coolant Injection. This situation does not change the acceptability of the modified CPS WLMS since:

'- 1. Low pressure ECCS initiates automatically, based on WLMS input, early in the events postulated (i.e.. before the maximum flashing errors occur). The events postulated result in long-term conditions that are bounded by the worst case analysed conditions identified in Chapter 15 of the Clinton Final Safety Analysis Report;

2. Low pressure ECCS initiates automatically on a diverse signal, high drywell pressure, which can occur at anytime and will occur prior to the existence of flashing conditions
3. Low pressure ECCS does not trip on high water level inputs;
4. The operator has symptomatic Emergency Procedure Guidelines providing direction on the use of low pressure ECCS; and
5. The measurement errors under worst case conditions for our modified system are less than 20% of the error allowed in the generic letter.

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Our plant specific evaluation and modified WLMS design should provide the bases for closure of TMI Action Plan Item II.F.2 concerning detection of inadequate core cooling conditions.

Sincerely yours, b.

F. A. Spa gen erg Director - Nuclear Licensing Nuclear Station Engineering DLN/la Attachment cc: B. L. Siegel, NRC Clinton Licensing Project Manager NRC Resident Office Illinois Department of Nuclear Safety Regional Administrator Region III, USNRC

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