ML20212B427
| ML20212B427 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 02/24/1987 |
| From: | Julie Ward SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Miraglia F Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20212B431 | List: |
| References | |
| JEW-87-237, NUDOCS 8703030556 | |
| Download: ML20212B427 (7) | |
Text
$SMUD SACRAMENTO MUNICIPAL UTILITY DISTRICT G P. O. Box 15830, Sacramento CA 95852 1830,(916) 452-3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA JEW 87-237 February 24, 1987 Director of Nuclear Reactor Regulation Attention: Frank J. Miraglia, Jr.
Division of PWR Licensing-B U S Nuclear Regulatory Commission Washington D C 20555 Docket 50-312 Rancho Seco Nuclear Generating Station Unit #1 PRESSURIZER HEATER FAILURES
Dear Mr. Miraglia:
Your letter dated December 31, 1986 requested additional information in order to complete your review of the pressurizer heater failures at Rancho Seco.
The District's January 22, 1987 submittal provided a partial response to your req ue s t. provides the District's response to the remaining questions from your December letter.
On February 20, 1987, a meeting was held with the staff on the pressurizer heaters. As a result of this meeting the staff requested further clarification on several items. Attachment 2 contains a list of these six items one of which, item 4, has been addressed in the B&W analysis included as.
The remaining items, as agreed to by the NRC staff, will be addressed prior to restart of the plant.
- is the B&W analysis and report on the presurizer event. The report provides a conservative evaluation of the estimated maximum temperature and locations as well as addressing the metallurgical and functional condition of the pressurizer components. Attachment 4 contains B&W supporting calculations used in the evaluation.
Based upon the analysis conducted by B&W and upon the inspections and repairs performed by Rancho Seco personnel, the District concludes the pressurizer and RCS are operable.
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DISTRICT HEADQUARTERS O 6201 S Street, Sacramento CA 95817-1899
Frank J. Miraglia, Jr. February 24.1987 If you have any questions contact Ray Ashley of my staff at extension 4475.
Sincerely, f
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E. Ward eputy General Manager, Nuclear Attachment cc: Syd Miner, NRC - Bethesda T. D'Angelo, NRC - Rancho Seco d
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ATTACHMENT 1 RESPONSES TO NRC'S QUESTIONS REGARDING PRESSURIZER HEATER FAILURES QUESTION 1.
Describe the measured and analyzed temperature transient in the pressurizer metal and the steam water space during the event. What was the maximum temperature reached and describe its location? Were any component's design temperature reached or exceeded? What was the temperature transient on the pressurizer PORVs and SVa? Describe how any overheating of the pressurizer or its components would affect its operation including the integrity of the pressurizer itself. Describe the relevant ASME requirements and compliance with these requirements in light of exceeding the design temperature or other aspect associated with the event.
RESPONSE
B&W has evaluated the pressurizer heater incident and provided a summary report. This report (Attachment 3) and its associated calculations (Attachment 4) are provided for your review. As requested, the report provides a review of the incident and analyses of the conditions which existed inside the pressurizer. This evaluation includes conservative estimates of maximum temperatures and locations as well as addressing the metallurgical and functional condition of the pressurizer components.
The B&W assessment shows that the temperature transient did not affect the short term (prior to startup) operability of the pressurizer and its components.
Both the EMOV, and the safety valves were removed, inspected, and reinstalled. The safety valves were refurbished prior to reinstalla tion. The B&W analysis also shows that no significant temperatures were reached in the upper head.
A fatigue analysis will be performed prior to Restart to determine the potential long term impact of this incident on the fatigue life of the pressurizer.
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s QUESTION 2.
Based on your evaluation of the damage to the heater bundle, describe the damage, extent of deformation, the maximum temperature reached by the tubes and the maximum temperature reached by the pressurizer.
RESPONSE
Several elements in the upper bundle and the top-most element in the middle bundle were permanently bowed due to buckling and/or uneven heating and cooling. Other than the bowing, the sheaths appeared to be intact. Ten of 39 upper bundle elements had open-circuit failures.
Three of the 13 heater groups in the upper bundle had zero resistance to 8round. The maximum temperature of the heater elements was on the order of 20000F - 25000F. The maximum temperature reached in the pressurizer is addressed in the B&W report (Attachment 3).
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QUESTION 13.
Were the supply cables to the heaters found to be overstressed? Have they been evaluated for their capabilities along with the fault current effect on other cables sharing the same cable tray?
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RESPONSE
The District has calculated a maximum temperature of 235 degrees C for the cable after two successive fault trip cycles. This is less than the 250 degrees C limit established for cable used at Rancho Seco. Based on this, the District concludes that t'he insulation of the cables on the faulted circuits has not been damaged, therefore, there is no effect on cables sharing the same cable tray.
ATTACIDENT 2 FEBRUARY 20, 1987 MEETING CIARIFICATIONS REQUESTED 1.
Provide a table which compares the available pressurizer conditions and the assumptions made in the analysis. This will include a discussion of the degree of conservatism in the assumptions.
2.
Provide further clarifications on the maximum wall temperature and location.
3.
Provide information as to the composition of the pressurizer wall cladding and base material.
4.
Provide information on the effect, if any, to the cable connectors.
Provide clarification on the repeated open/close of the breakers.
5.
How many times were the breakers operated?
Provide information on the possibility / impact of cladding cracking 6.
as a result of wetting of the hot pressurizer surface.
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ATTAQDENT 3 B&W REPORT ON RANCHO SECO PRESSURIZER HFATER INCIDENT l
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