ML19309F867
| ML19309F867 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 04/28/1980 |
| From: | Peoples D COMMONWEALTH EDISON CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8005010482 | |
| Download: ML19309F867 (10) | |
Text
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CN Commonwealth Edison I
) one First Nati:nal Plaza. Chicago. Illinois
'\\
7 j Address Reply to: Post Office Box 767 800501o W 2
/ Chicago, filinois 60690 j
April 28, 1980 Mr. Harold R. Denton, Director Of fice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Zion Station Units 1 and 2 Implementation of Sixty Day Items of Confirmatory Order NRC Docket Nos. 50-295 and 50-304 Reference (a):
February 29, 1980 letter from H.
R. Denton to D. L. Peoples
Dear Mr. Denton:
Reference (a) contained a Confirmatory Order dated February 29, 1980 for Zion Station Units 1 and 2.
That Order required Commonwealth Edison Company to perform certain actions within sixty (60) days of the date of the Order.
Attachment A to this letter provides Commonwealth Edison's response to those items.
Please address any questions that you might have concerning this matter to this office.
One (1) signed original and thirty-nine (39) copes of this transmittal are provided for your use.
Very truly yours, N
D. L.
Peop es Director of Nuclear Licensing DLP:WFN: rap Attachment 3384A
ATTACHMENT A Commonwealth Edison Company's responses to the NRC Staff's Sixty (60) Day items of Section C of Appendix A in Reference (a) follow.
C.1.
Review the steady state steam generator operating level to determine the optimum steady state level for the purpose of maximizing dryout time with due consideration for overfilling.
The results of this study shall be provided to the NRC.
Commonwealth Edison has performed the recommended review and has concluded that the current steady state steam generator operating level is at its optimum level.
A synopsis of this study follows.
The current steady state steam generator operating level was chosen based on analyses and setpoint studies.
This level was optimized in conjunction with FSAR 1
analyses and with respect to Class I transients, such as load swings and load rejections.
Many other factors enter into the selection of this normel operating level, such as mass available for discharge following a secondary pipe rupture, moisture carryover considerations, and steam generator overfilling.
Since all of these items were considered in the optimization of the steam generator normal water level, any increase in the normal water level will negate this optimization.
More detailed information, with regard to the effect of a' change in steam generator level on steam generatar dryout time, core uncovery time, and moisture carryover is provided below.
A. Steam Generator Dryout Time An increase in nominal steam generator level (i.e.,
j mass) is not the p' rime consideration in the calculation of steam generator dryout time.
One of the most 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 required to dissipate the liquid in'ventory in the steam generator below the low level setpoint dur to decay heat generated in the core.
Changing the low level setpoint will therefore increase the post-trip mass and hence, the steam generator dryout time.
. The current Zion low level setpoint results in a steam generator dryout time of approximately 40 minutes which allows considerable time for operator action, if required.
An increase in the low level setpoint by 5% of the narrow range span would increase the post-trip liquid mass by 3100 pounds, and the dryout time by about 2 minutes.
Table I provides Zion Steam Generator Dryout Calculational Results, which are based on best estimate decay heats.
In addition, if reactor trip were to occur at the normal operating level, an increase in the normal operating level would result in a similarly sm 11 increase in the dryout time.
8.
Core Uncovery Time Steam generator dryout time is a very important parameter, however, total time to uncovering the core should also be considered.
Analysis indicates that the time required to begin core uncovery, after dryout of the steam generators, is about 30 minutes for the Zion units.
Thus the total time available to ensure an adequate heat 1
sink is available, and prevent uncovering of the core, is about 70 minutes.
Therefore, a 5% increase in the narrow range steam generator level with its resultant 2 minute increase in steam generator dryout time does not appreciably increase the total available time for operator action.
C.
Moisture Carryover The steam generator operating water level has an important effect on moisture carryover margin, primarily because an increase in water level above the nominal valve tends to increase moisture carryover.
This trend has be_n observed at a Westinghouse plant operating at slightly below full power conditions.
Data obtained from this plant indicates that a water level increase of about 5% of span results in a 15% t'o 25% increase in moisture carryover.
Based on this information and recognizing that any increase in the quantity of moisture delivered to turbine blading can be detrimental, Commonwealth Edison has concluded that an increase in steady state steam generator operating level could result in an undesirable increase in moisture carryover to the turbine and therefore, the incisase should not be made.
- In conclusion, Commonwealth Edison has reviewed the present steam generator levels, both for normal operation and for low level trip, and concluded that the current levels are optimum.
The effects of increasing the levels i
at Zion Station have been shown to be negligible with respect to increasing available operator action time, but potentially detrimental with respect to increased moisture carryover which can lead to turbine blade damage.
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. Table I Zion Steam Generator Dryout Calculational Results Liquid Inventory.at 25% Narrow Range Level 82,360 lb Steam Generator Dryout Time for 25% Low Level Trip 40.0 min.
+
Liquid Inventory Increase for Increase In Low Level Setpoint by 5% (i.e. to 30%)
3,000 lb t
Steam Generator Dryout Time for 30% Low Level Trip 42.0 min.
Increase in Dryout Time for 5% Level Increase 2.0 min.
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. C.2 Evaluate possible co-impregnation of-the charcoal in the plant's air e f fluent filtration systems with KI and 12 and an amine such as TEDA (triethylene-diamine) to improve the lodine removal capability of these systems.
The results of this review shall be submitted to the NRC.
Commonwealth Edison has performed the recommended review.
The results of this review including analyses indicate that it is technically feasible to utilize co-impregnated charcoal in the air effluent filtration systems at Zion Station.
- However, a
at this time the desired co-impregnants will not be added to the presently installed charcoal.
Instead, when the existing charcoal is to be discarded, it will be replaced with new filtration cells containing co-impregnated charcoal.
The basis for this follows.
With the exception of the miscellaneous vents system, all of the Zion station air effluent charcoal filtration systems were sampled and tested in April.'980.
The charcoal samples for all the filters passed the technic al specification requirements for I2 adsorption from the gas stream.
These test results indicate that the presently instailed charcoal is still adequate to perform the design function of the air filtration system.
The charcoal in these filters is riot the co-impregnated type.
Therefore, the presently installed charcoal will remain in place in the air effluent systems.
Sampling and testing will i
continue to be performed in accordance with the Zion technical
]
specifications.
At such time as any filtration system's charcoal fails to meet the technical specification requirements, the charcoal in that filtration system will be replaced with new co-impregnated charcoal.
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. C.3 Evaluate effects on plant systems stability if power is reduced as much as 50%, treating power as a parameter.
(For example, the ef fects on the feedwater flow automatic control).
During the'intitial start-up testing program the Zion units were operated at various part power levels, including 50% power, for extended periods.
Since startup, operation at reduced loads has occurred on numerous occasions as result of equipment outages, testing, etc.
A review of these conditions indicates that the Zion units can operate for extended periods in a stable condition at 50% powe. with the feedwater flow control in the automatic control made.
However, as expected under these conditions, plant therma; afficiency decreases as power decreasec.
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. C.4 Submit a schedule to implement the ATWS instrument modification justified in accordance with the Westinghouse analytical results contained in the letter from T. M.
Anderson to S. H.
Hanauer in NS-TMA-2182 dated December 30, 1979.
Commonwealth Edison has reviewed the subject letter.
The analytical results contained in the December 30, 1979 Westinghouse letter indicate that the Zion units can withstand the consequences of the postulated ATWS events.
There are only two functions that are needed to mitigate the consequences of the most severe ATWS events prior to proceeding to long term shutdown conditions.
These functions are the actuation of the auxiliary feedwater system and the tripping of the main turbine for those events that result in a potential loss of heat sink, such as the loss of load or the loss of main feedwater.
Normally, these functions are obtained via the reactor scram signal and through the reactor protection system.
Since these are postulated to be unavailable during an ATWS, another method of guaranteeing auxiliary feedwater initiation and main turbine trip will be inctalled.
The new meth3d will be independent of the scram system and unaffected by a common mode fault in the reactor protection system.
It will meet to the extent practicable the design bases for the Alternate Mitigating Systems Actuation Circuitry (AMSAC) described in Sectj on 9.2 of the December 30, 1979 Westinghouse letter.
Currently, it is Commonwealth Edison Company's understandir.g that the Westinghouse AMSAC concept has not received NRC concurrence.
Once the NRC Staff has concurred or approved this concept, Commonwealth Edison has determined that approximately 6-8 months will be necessary to provide adequate front end lead time to develop the scope of the required ATWS instrument modification including the necessary interactions with Commonwealth Edison's architect engineer, the Westinghouse ATWS Owner's Group and Westinghouse, and to receive NRC Staff concurrence.
Once the scope of work has been defined, an additional 5-6 months are necessary to develop and review the bid specification, let and evaluate the bids, and purchase the equipment.
Finally, an additional 12-13 months are r.ecessary for the vendor to design, procure, proto-type test and deliver the equipment.
Upon del.very, the equipment will be installed during the next schedule j - refueling outage for each unit.
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The preliminary schedule for the Zion units is:
January 1981 Scope of Work Defined and Conceptual Engineering Complete June 1981 Completion of Purchasing Activities June 1982 Delivery of Equipment Complete Fall 1982 Installation of Unit 2 Equipment During Presently Scheduled Refueling Outage (Begins September)
Spring 1983 Installation of Unit 1 Equipment During Presently Scheduled Refueling Outage (Begins February)
Both sytems will be made operational after installation of the second system.
This will eliminate the temporary need for separate sets of operating procedures for each unit as well as separate operator training.
As previously indicated, the above schedule is based on the analytical results contained in the Westinghouse letter of December 30, 1979.
Should the scope of the ATWS instrument modification as finally approved by the NRC Staff change significantly, this schedule may be modified.
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. C.5 Establish an on-site group whose function shall be to examine plant operating characteristics, NRC bulletins, licensing information service advisories and other appropriate sources which may indicate areas for improving plant safety.
Where useful improvements can be achieved, the group shall also develop and report detailed recommendations for revised procedures, equipment modifications or other improvements to offsite management.
Commonwealth Edison has established a Plant Nuclear Safety Review Committee at the Zion site.
This committee which consists of six (6) members including a chairman was established to perform the funcians indicated above.
A Zion Station administrative procedure has been reviewed and approved establishing this committee as well as specifying the purpose, participants and their qualificationg and scope of review.
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