ML20076L734

Forwards Draft FSAR Page Changes on TMI-2,Issue II.K.3.18 Re Mod to Automatic Depressurization Sys Logic,Per SER Confirmatory Issue 28 (NUREG-0853) & NUREG-0660 as Clarified by NUREG-0737.Info Will Be Included in FSAR Amend 27

ML20076L734
Person / Time
Site:	Clinton
Issue date:	09/12/1983
From:	Nelson R ILLINOIS POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
RTR-NUREG-0660, RTR-NUREG-0737, RTR-NUREG-0853, RTR-NUREG-660, RTR-NUREG-737, RTR-NUREG-853, TASK-2.K.3.18, TASK-TM 0982-L, 982-L, L30-83(09-12)-L, L30-83(9-12)-L, U-0665, U-665, NUDOCS 8309190062
Download: ML20076L734 (4)

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o U-0665 Illinois Power Company $E83(09-12)-L 500 SOUTH 27TH STREET, F. o. BOX 511. DECATUR, ILLINOIS 62525-1805 Docket No. 50-461 September 12, 1983 Director of Nuclear Reactor Regulation Attention: Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Clinton Power Station Unit 1 SER Confirmatory Issue #28 (NUREG-0853)

Modification of ADS Logic

Dear Mr. Schwencer:

Per our discussions on the resolution of SER issues with Dr. H. Abelson, NRC at the Clinton Site on August 10, attached is a draft copy of FSAR page changes on the subject TMI-2 issue II.K.3.18. This material describes the design option for modifi-cation of the automatic depressurization system (ADS) logic to be implemented for the Clinton Power Station.

Illinois Power is planning to include this information in FSAR Amendment 27 which is scheduled for issuance late this month. Attached for your early review are draft FSAR pages D-vi, D-89, D-90 and D-90a.

We trust that this information will resolve SER Confirmatory

. Issue #28 for closeout in the next SER Supplement. Please let us hear soon if you have any questions on this material.

Sincerely, i f R. . Nelson Director-Nuclear Licensing and Configuration Nuclear Station Engineering GEW/lt attachment cc: H. Abelson, NRC Clinton Licensing Project Manager R. A. Kendall, NRC ICSB H. H. Livermore, NRC Senior Resident Inspector

((ddf Illinois Department of Nuclear Safety /

8309190062 830912 PDR ADOCK 05000461 E PDR

CPS-PSAR AMENDMENT 27 Sze'8" ara 1983 FT DRAFT APPENDIX D REQUIREMENTS ~RESLLTING FROM TMI-2 ACCIDENT LIST OF FIGURES TITLE PAGE NUMBER A Typical RCIC Steamline Break Detection D-84 D-1 Logic Diagram Schematic Diagram of Time Delay Action to D-85 D-2 Preclude Spurious RCIC Isolation During System Start Sequence D-3 Postaccident Sampling Station Shielding D-35a D-4 Postaccident Radiation Zone Maps of Vital D-35c Areas ADS Initiation Logic Modification D-90a D-5 l

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- SEPTEMBER 1983 NRC ACTION PLAN (NUREG-0660 as clarified by NUREG-0737)

II.K.3.18 Modification of Automatic Depressurization System Logic - Feasibility for Increased Diversity for Some Event Sequences NRC Position The automatic depressurization system (ADS) actuation logic should be modified to eliminate the need for manual actuation to assure adequate core cooling. A feasibility and risk assessment study is required to determine the optimum approach. One possible scheme that should be considered is ADS actuation on low reactor-vessel water level provided no high-pressure coolant injection (HPCI) or high-pressure coolant system (HPCS) flow exists and a low-pressure emergency core cooling (ECC) system is running. This logic would complement, not replace, the existing ADS actuation logic.

CPS Response In response to this requirement, Illinois Power Company jointly sponsored through the BWR Owners' Group (BWROG) a program to evaluate feasible modifications to the ADS logic. The original study was submitted to the NRC via a letter from D. B. Waters (BWROG) to D. G. Eisenhut (NRR) , dated March 31, 1981. This study evaluated the feasibility of automating the vessel depressurization for isolation events with and without a stuck-open relief valve, and assessed the changes in overall plant risk. This study identified two preferred ADS logic design modifications but did not consider the effects of those modifications on proposed designs for ATWS mitigation _and on execution of procedures, developed from the BWR Emergency Procedure Guidelines (EPG's).

To respond to these additional concerns the BWROG provided a report to the NRC, via a letter from T. J. Dente (BWROG) to D. G. Eisenhut (NRR) , dated October 28, 1982, which supplemented the previous feasibility study. This study developed and compared eight different ADS modifications which would extend ADS operation to transient events which do not result in a release of steam to the drywell but which may require depressurization of the reactor pressure vessel _(RPV) to maintain adequate core cooling. In addition, these ADS modification options conformed the ADS initiation logic to that employed in the EPG's and that currently proposed for certain ATWS modifications.

As a result of their review of these BWROG reports, the NRC has indicated that two of the proposed ADS modification options are acceptable as means of resolving TMI Action Plan Item II.K.3.18.

The two acceptable ADS modifications are as follows:

DRAFT D-89 MAPI

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• CPS-FSAR -., AMENDMENT 27

([ SEPTEMBER 1983 (1) the addition of a bypass timer to the high drywell pressure trip if reactor water level remains below the low pressure ECCS initiation setpoint for a sustained period; or (2) elimination of the high drywell pressure trip.

Of the two acceptable ADS modifications, Illinois Power Company will implement Option #1, as described above, at the Clinton Power Station.

The option chosen for CPS bypasses the high drywell pressure portion of the current ADS logic after a specific time interval and adds a manual switch which allows the operator to inhibit automatic ADS initiation during postulated ATWS scenarios if required.

Figure D-5 shows the CPS logic design for this alternative. The high drywell pressure signal (2 psig) is oypassed by installing a second (" bypass") timer that is actuated on low RPV water level (Level 1). When this timer times out, the high drywell pressure trip is bypassed and the ADS initiates on the low RPV water level signal alone. The additional logic would not affect the high drywell pressure--low RPV level initiation sequence insofar as it responds to pipe breaks inside the drywell.

A time delay of approximately eight minutes for the high drywell pressure bypass logic has been chosen for preliminary evaluations.

Calculation of an exact delay setting for the bypass timer will require that a detailed analysis be conducted. This analysis will be based on (1) avoidance of excessive fuel cladding heatup using 10CFR50 Appendix K models and (2) providing sufficient time to allow recovery of RPV water level above Level 1 during an ATWS event. Once the bypass timer times out, the bypassing of the high drywell pressure is sealed-in, and the bypass timer does not automatically reset. Because of the lower RPV water level trip setpoint utilized in the CPS BWR/6 design, thc logic scheme described (i.e. timer does not auto-reset if RPV level restored above Level 1) reduces the possibility of repeated partial core uncovery.

The advantage of adding the manual ADS inhibit switch is that it simplifies the execution of those steps in the EPG's related to ATWS mitigation. Thus the ability of the control room operator to inhibit the ADS when desired is enhanced. The other modification to the ADS initiation logic, i.e. incorporation of the high drywell pressure bypass, does not significantly impact the simplicity or probability of accomplishment of the operator actions specified in the EPG's.

NUREG-0737 requires that a proposed modification be submitted for NRC approval by April 1, 1982 or four months prior to expected Illinois issuance of an operating license, whichevar is later.

Power Company will submit these details in an amendment to the CPS FSAR by February, 1984 and will implement the ADS logic modification prior to fuel loading.'

DRAFT D-90 pp-

. CPS-FSAR AMENDMENT 27

,'4 SEPTEMBER 1983 High Drywell Pressure (2 psig)

Seal -:

s in

• RPV Low Water RPV Low Water 1 Level (Level 1) - Level (Level 1)

ECCS Actuation - Low Pressure ECCS Actuation Seal 1 d In v v RPV Confirmatory High Drywell 1, 2 Low Water Level Pressure Bypass (Level 3) - Timer (Nominal Scram Level Setting 8 min.)

L 105 Second ADS 3 Actuation Timer u

Low Pressure ECCS Pumps Running ( > 145 psig at pump discharge) a Manual Inhibit 1 i Switch Not Activated 1

ADS Actuation Notes: 1. These blocks represent the changes that are being made to the existing ADS logic.

f 2. The exact delay time setting for the High Drywell l

Pressure Bypass Timer will be determined by detailed analysis and submitted via an-FSAR revision. This timer cannot be reset.

3. The 105 second actuation timer resets if reactor water level recovers above trip elevation before it times out. The timer restarts if the low RPV j

water level signal occurs again.

FIGURE D-5: ADS INITIATION LOGIC MODIFICATION DRAFT )RA E

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