ML19340F027
| ML19340F027 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 12/18/1980 |
| From: | Varga S Office of Nuclear Reactor Regulation |
| To: | Abel J COMMONWEALTH EDISON CO. |
| References | |
| NUDOCS 8101160523 | |
| Download: ML19340F027 (7) | |
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2 UNITED STATES
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NUCLEAR REGULATORY COMMISSION y
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December 18, 1980 h
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y Docket Nos. 50-295 and 50-304 Mr. J. S. Abel Director of Nuclear Licensing Commonwealth Edison Company Post Office Box 767 Chicago, Illinois 60690
Dear Mr. Abel:
In our Confirmaton Order dated February 29, 1980, we confirmed the Commonwealth Edison Company commitment to review the steady state steam generator operating level to detennine the optimum steady state level for the purpose of maximizing dryout time with due consideration for overfilling.
On April 28, 1980, CEC 0 submitted their evaluation for our review. We have completed our review and find there is appropriate justification for maintaining the current steam generator operating level and the low level trip setpoint. A copy of our evaluation is enclosed. We consider this issue to be complete.
Sincerely, I
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a.ga,.h Operating Reactor anch #1 Division of Licens1 g
Enclosure:
l As Stated cc: w/ enclosure See next page l
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Mr. J. S. Abel Commonwealth Edison Company E
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cc: Robert J. Vollen, Esquire 5
109 North Dearborn Street h
Chicago, Illinois 60602 Dr. Cecil Lue-Hing R
Director of Research and Development Metropolitan Sanitary District g:
of Greater Chicago 100 East Erie Street
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Chicago, Illinois 60611 s
Zion-Benton Public Library District E
2600 Emmaus Avenue j
Zion, Illinois 60099 5
3 Mr. Phillip P. Steptoe 5
Isham, Lincoln and Beale 2
Counselors at Law M
One First National Plaza 5
42nd Floor
=i Chicago, Illinois 60603 3
Susan N. Sekuler, Esquire s
Assistant Attorney General e
E Environmental Control Division 5
188 West Randolph Street, Suite 2315
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Chicago, Illinois 60601
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U. S. Nuclear Regulatory Commission E
Resident Inspectors Office
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5 105 Shiloh Blvd.
Ej Zion, Illinois 60099
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ENCLOSURE I.
INTRODUCTION Sy confirmatory orders dated February 11, 1980, and February 29, 1980 (Reference 1) the NRC requested the owners of Indian Point-2, Indian Point-3, and Zion Units 1 and 2, to review the steam generator operating level (SGOL) to determine whether the steady state values of these SG0Ls will provide the maximum dryout times for accidents and transients, with due consideration for overfilling. The owners of the above mentioned plants (Consolidated Edison Co. (CECO.), Power Authority of the State of New York (PASNY), and Commonwealth Edison (Comed) respectively) -hereafter "the licensees"- responded in references 2, 3, and 4 We have reviewed the licensees responses and conclude that the current steady state SG0Ls for the above mentioned plants will allow the operator adequate time (in excess of 30 minutes after reactor trip) to ensure continued supply of heat sink. We also concur with the licensees that increasing the SGOLs may in fact be counterproductive from the moisture carryover viewpoint and it's effect on the turbine blades.
II.
EVALUATION l
l In response to the NRC orders, CECO., PASNY, and Comed. reviewed the steady i
state SGOLs for their respective plants and concluded that no changes are warranted from the safety st ndpoint.
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For the Indian Point and Zion plants the SGOLs were optimized with respect j
to normal operation and operational transients, such as load swings and load rejection. Many other factors enter into the selection of this normal
., cperating leve?
These factors include mass available for discharge following a steam ine break, moisture carryover censiderations, and steam generator overfilling.
Probability of SG overfilling would increase, and mass discharge following a SLB would increase corresponding to any increase in SGOLs.
The licensees conducted sensitivity analyses to detemine the increase in steam gen.erator dryout time due to an increase in the steam generator level. The licensees also studied the effects of this level increase on core uncovery time and the moisture carryover in the steam lines.
These effects are discussed belcw:
A.
Steam Generator Dryout Tine An increase in nominal steam generator level is not the prime considera-tion in.he calculation of steam generator dryout time. One of the important quantities is post-trip mass at the low level setpoint. This is the steam generator mass that is used in dryout calculations. A steam generator dryout calculation entails the amount of time that is I
required to dissipate the liquid inventory in the steam generator below the low level setpoint due to decay heat generated in the core.
Increasing the low level setpoint will therefore increase the post-trip mass and hence, the steam generator dryout +
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Cryout time sensitivity analysis for the subject plants ans presented in the attached Table. This Table shows that each plant currently has at least 30 minutes after low level trip before the steam generator dryout is comoleted, thus allowing the operator adequate time to restore cooling water flow.
The dryout times listed in the attached table are based on best estimate decay heat curtes.
. Dryout Time Increase Sensitivity Zion-1,2 IP-2 IP-3 Liquid Inventory at Low Level Trip (lb) 82,360 69,400 70,870 (25i,NR)
(30".NR)
(30%NR)
SG dryout time for low Level Trio (min.)
40.0 40.3 34.2 Liquid Inventory Increase for an increase of Low Level Setpoint of 5% (lb) 3,000 2,900 2,950 Increase in Dryout Time for a setpoint increaseof5%(min.)
2.0 3.0 1.9 Low Level Setpoint Increase of NR 5%
5" 5 ",
Dryout Time Increase 5.0%
7.47, 5.6".
3.
Core Uncovery Time Steam generator dryout time is an important parameter, however, the total time to uncover the core is also of prime importance.
A generic Westinghouse analysis showed that the time required to begin core uncovery is about 30 minutes after the steam generators have dried out.
Thus, the total time available for the operator to ensure an adequate heat sink and prevent core uncovery ranges from 60 to 70 minutes (the sum of 30 and the dryout times listed in the Table above).
Therefore, as shown in the table above, an increase in dryout time of 2 to 3 minutes constitutes only 3 to 4% approximately of the total time to core uncovery.
C.
Moisture Carryover The steam generator operating water level has an 'r:,portant effect on -
moisture carryover to the turbine. Data obtained by Westinghouse from one of their operating plants indicates that a water level increase of approximately 5% of span results in a 15% to 25". increase in moisture
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carryover. Therefore, it is expected that an increase in SGCL will result in a corresponding increase in moisture carryover to the turbine. The increase in moisture content has a detrimental effect on the turbine blades.
III. CONCLUSION I
l The effect of increasing SG water levels (SGOLs or low level trip setpoints) have been shown to be insignificant with respect to increasing the time available for operater action. Furthermore, such a level increase would lead to potential turbine damage due to excessive moisture carryover.
Based on the above s aluation se conclude that t.he current SG0Ls and low level trip setpoints fcr the plants, the subject of this memo, provide adequate time for operator action to restore heat sink. Furthermore, we concur with the licensees in maintaining the current values of these two variables, namely SGOLs and low level trip setpoints.
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! References i
1.
Letter, H. R. Denton, ONRR, to D. L. Peoples, Feoruary 29, 1980.
2.
Letter, W. J. Cahill, Jr. (Ceco), to Director of tiRR, May 9,1980.
3.
Letter, P. J. Early (PASNY), to Director of NRR, April 11, 1980.
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Letter, D. L. Peoples (Comed), to Director of t4RR, April 28, 1980.
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