ML15264A226
| ML15264A226 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse, Oconee, Arkansas Nuclear, Crystal River, Rancho Seco, 05000000 |
| Issue date: | 04/23/1984 |
| From: | Stolz J Office of Nuclear Reactor Regulation |
| To: | Hosler A BABCOCK & WILCOX OPERATING PLANTS OWNERS GROUP, WASHINGTON PUBLIC POWER SUPPLY SYSTEM |
| References | |
| GL-81-21, NUDOCS 8405140560 | |
| Download: ML15264A226 (10) | |
Text
Central File NRC PDR LPDR April 23, 1984 DEisenhut OELD EJordan JNGrace HOrnstein EBlackwood ACRS 10 Alan G. Hosler, Chairman PKadambi' BWOG Steering Committee Rlngram WPPSSRnga Richland, Washington, 99352 BSheron KHeitner
SUBJECT:
RESPONSE TO GENERIC LETTER 81-21, NATURAL CIRCULATION COOLDOWN
Dear Mr. Hosler:
Enclosed are requests for information oh.the subject of responses to Generic Letter 81-21-which were transmitted to certain Babcock & Wilcox reactor licensees. Enclosure 1 is applicable to ANO-1, the Oconee Units-and Rancho Seco; is applicable to Crystal River 3; and Enclosure 3 is applicable to Davis Besse. These requests for information have been separately sent to each of the licensees.
The purpose of this transmittal is to request the Babcock & Wilcox Owners Group to adopt a common approach in resolving this issue in a timely manner. The NRC staff is seeking assurance that the B&W plants can be cooled down using natural circulation while maintaining the primary coolant in the liquid phase at all times.
We have received an analysis from TMI-1 on this subject which substantially addresses our concerns, and we encourage you it6 uselthis to the extent appropriate.
Please contact Dr. Prasad Kadambi of my staff if you have any questions on this subject.
Sincere y yours, John F. tolz, Chief Operating Reactors Branch No. 4 Division of Licensing
Enclosure:
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ENCLOSURE 1 REQUEST FOR ADDITIONAL INFORMATION FROM RANCHO SECO, OCONEE 1, 2 AND 3, AND ANO-1 In response to Generic Letter 81-21, dated May 5, 1981, all PWR licensees were required to demonstrate, by analyses and/or test, that a controlled natural circulation cooldown from operating conditions to cold shutdown conditions, conducted in accordance with their procedures, should not result in reactor vessel voiding. Your responses, as given in References 1 and 2, to our request did not provide the required demonstration. Instead you stated that your natural circulation cooldown procedures have not been constructed to attempt to preclude reactor vessel head void formation, but rather to mitigate a void should one form.
The staff has concluded that upper head voiding is not a safety concern provided the operator is equipped with adequate training and procedures.
However, upper head voiding does make RCS pressure control more difficult during a natural circulation cooldown. Thus, it is the staff's position that the natural circulation cooldown procedure should be developed to prevent upper head voiding to the extent possible. The operator procedures must also address means of mitigating a reactor vessel head void should one form. We believe that the demonstration requested by the Generic Letter is required in order to develop these procedures.
We have also been examining the responses to the Generic Letter provided by other licensees with B&W plants.
We are concerned about the wide range of cooldown rates, ranging from lJoF/hr to 50aF/hr, utilized by B&W plants.
We believe that a coordinated Owner's Group response may be best in oroviding the requested demonstration.
We would like to note that we are aware of the calculations which have been performed to assess the reactor vessel upper head cooldown rate.
These calculations, References 3 and 4, show that the head cooldown rate is approximately 1 1/20F/hr.
We believe that the cooldown times implied by these calculations do not have sufficient technical justification and that they should not be used as the basis for operating procedures.
In summary, the staff requires that you provide the demonstration, via analysis and/or test data, requested in Generic Letter 81-21, to show that a natural circulation cooldown can be performed without formation of a reactor vessel head void. We believe this response can best be provided via the Owner's Group and are willing to discuss this with you at your earliest convenience.
REFERENCE Duke Power Company
- 1. Letter, W. 0. Parker, Duke Power Co, to H. R. Denton, NRC, 11/5/81.
- 2. Letter, H. B. Tucker, Duke Power Co., to H. R. Denton, NRC 2/19/83 SMUD
- 1. Letter, J. J. Mattimoe, SMUD, to J. F. Stolz, NRC, 11/16/81
- 2. Letter, W. K. Lathan, SMUD, to J. F. Stolz, NRC, 9/21/83 ANO 1
- 1. Letter, D. C. Trimble, AP&L, to D. G. Eisenhut, NRC, 11/13/81
- 2. Letter, J. R. Marshall, AP&L, to J. F. Stolz, NRC 7/13/83 All
- 3. Boman, B. L., "Reactor Vessel Head Cooldown During Natural Circulation Cooldown Prepared for Consumers Power Company,"
Babcock & Wilcox Utility Power Generation Division, February, 1983.
- 4. Tally, C. W., "Single Loop Natural Circulation Cooldown Prepared for Consumers Power Company," Babcock & Wilcox Nuclear Power Generation Division, August, 1982.
ENCLOSURE 2 REQUEST FOR ADDITIONAL INFORMATION FROM CRYSTAL RIVER 3 In response to Generic Letter 81-21, dated May 5, 1981, all PWR licensees were required to demonstrate, by analyses and/or test, that a controlled natural circulation cooldown from operating conditions to cold shutdown conditions, conducted in accordance with their procedures, should not result in reactor vessel voiding. Your responses, as given in References 1 and 2, to our request did not provide the required demonstration. Instead, you stated that your natural circulation cooldown procedures have not been constructed to attempt to preclude reactor vessel head void formation, but rather to mitigate a void should one form.
The staff has concluded that upper head voiding is not a safety concern provided the operator is equipped with adequate training an procedures.
However, upper head voiding does make RCS pressure control more difficult during a natural circulation cooldown. Thus, it is the staff's position that the natural circulation cooldown procedure should be developed to prevent upper head voiding to the extent possible. The operator procedures must also address means of mitigating a reactor vessel head void should one form. We believe that the demonstration requested by the Generic Letter is required in order to develop these procedures.
-2 We have also been examining the responses to the Generic Letter provided by other licensees with B&W plants.
We are concerned about the wide range of cooldown rates, ranging from 1JF/hr to 50"F/hr, utilized by B&W plants. We believe that a coordinated Owner's Group response may be best in providing the requested demonstration.
We would like to note that we are aware of the calculations which have been performed to assess the reactor vessel upper head cooldown rate.
These calculations, References 3 and 4, show that the head cooldown rate is approximately 1 1/20F/hr.
We believe that the cooldown times implied by these calculations do not have sufficient technical justification, and that they should not be used as the basis for operating procedures.
In addition to the concerns of cooldown rate, Generic Letter 81-21 required a demonstration that adequate condensate supplies exist to support your cooldown. An analysis demonstrating that you have sufficient condensate supplies has not been provided.
In addition, your response in Reference 2 indicates that if condensate supply is exhausted prior to reaching the Decay Heat Removal System entry conditions, you will utilize the HPI once through mode of cooling.
We believe that there may be other sources of water available to allow continued heat removal via the steam generator. Please evaluate your systems and identify other means of providino water to the steam generator durino a naturat circulation cooldown.
It is our position that reliance on the
3 HPI once through mode of cooling should not be required as a normal consequence of a natural circulation cooldown.
In summary, the staff requires that you provide the demonstration, via analysis and/or test data, as requested in Generic Letter 81-21, to show that a natural circulation cooldown can be performed without formation of a reactor vessel void. We believe this response can best be provided via the Owner's Group and are willing to discuss this with you at your earliest convenience. In addition, the staff requires a more complete assessment of your condensate supplies and a demonstration that it is adequate to support a natural circulation cooldown.
REFERENCES
- 1. Letter, W. A. Cross, FPC, to D. G. Eisenhut, NRC, "Generic Letter 81 Natural Circulation Cooldown," November 18, 1981.
- 2. Letter, G. R. Westafer, FPC, to J. F. Stolz, NRC, "Generic Letter 81 Natural Circulation Cooldown," July 28, 1983.
- 3. Boman, B. L., "Reactor Vessel Head Cooldown During Natural Circulation Cooldown Prepared for Consumers Power Company,"
Babcock & Wilcox Utility Power Generation Division, February, 1983.
- 4. Tally, C. W., "Single Loop Natural Circulation Cooldown Prepared for Consumers Power Company," Babcock & Wilcox Nuclear Power Generation Division, August, 1982.
ENCLOSURE 3 REOUEST FOR ADDITIONAL INFORMATION FROM DAVIS-BESSE 1 Your response (Reference 1) to Generic Letter 81-21 states that you have modified your natural circulation cooldown procedure to allow a cooldown of 1iF/hr. Based on Reference 2, it was demonstrated that the cooldown rate is sufficient to prevent void formation in the upper head.
With this cooldown rate, it is estimated that the time required to reach the decay heat removal system entry conditions is 150-200 hours.
We are concerned about the use of this analysis as the basis for your operating procedures. We believe that the 1 1/20F/hr cooldown rate does not have sufficient technical justification and should not be used as the basis for operating-procedures. In order for us to fully evaluate the results of the 8&W analysis, please provide justification for the computer model utilized. As part of that justification, identify all input assumptions, their basis and the impact of their uncertainties on the calculated results.
Also provide a description of any experimental or plant data, if any, you plan to utilize to verify the results.
REFERENCES
- 1. Letter, R. P. Crouse, Toledo Edison, to John F. Stolz, NRC, August 2, 1983.
- 2. Letter, R. P. Crouse, Toledo Edison, to Darrell G. Eisenhut, NRC, April 15, 1983.