ML18054A425
| ML18054A425 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 11/17/1988 |
| From: | Kuemin J CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8811220172 | |
| Download: ML18054A425 (4) | |
Text
consumers Power POW ERi Nii lllllCHlliAN'S PROliRESS General Offices: 1945 West Parnell Road, Jackson, Ml 49201 * (517) 788-0550 November 17, 1988 Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 DOCKET 50-255 - LICENSE DPR PALISADES PLANT -
STEAM GENERATOR TUBE INTEGRITY
- Telephone discussions with the NRC staff following an on-site review, of the Palisades Steam Generator inspection program resulted in requests for both short-term and long-term actions.
The requested actions are discus~ed below:
- 1)
Schedule and perform an analysis, during the next operating cycle, which will determine the maximum circumferential, thru-wall tube crack which can tolerate the vibration effects of the worst case plant transient (MSLB or LOCA) while maintaining tube integrity.
In addition, provide basis for operating the plant prior to plant startup.
- 2)
Describe the Palisades Steam Generator leak rate monitoring procedures and plant shut down requirements.
- 3)
Evaluate the need for tube stabilization at Palisades during the next operating cycle.
- 4)
Continue the Miz-18 qualification and inform the NRC of progress.
(Miz-18 is an eddy-current digital data acquisition system.
Palisades is currently using the Miz-12 analog system.)
- 5)
Discuss 1988 refueling outage Miz-18 ~esults including the results of the 8 X 1 probe.
TUBE INTEGRITY ANALYSIS Consumers Power Company met with Westinghouse on November 4, 1988 and with Combustion Engineering November 7, 1988 to discuss items 1 and 3 and to solicit proposals for performing the tube integrity evaluation.
These proposals are currently being evaluated.
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Nuclear Regulatory Commission Palisades Plant S/G Tube Integrity November 17, 1988 2
To address the question of what size circumferential crack can withstand the vibration effects of a MSB or LOCA, the following evaluations will be performed:
- 1)
An ATHOS or FLOW3 analysis to describe the steady state fluid flow properties (ie., fluid distribution, density and temperature) in the Palisades S/G's.
The conditions present during a MSLB or LOCA will then be estimated based on the ATHOS or FLOW3 results.
- 2)
Tube vibration analysis.
- 3)
Crack growth analysis based on the results of 1 and 2.
Once the vendor is selected and procurement arrangements are established, Consumers Power Company suggests that a meeting be held with the NRC to review the project scope.
Consumers Power Company presently intends to complete the tube integrity analysis and have the results submitted to the NRC by June 30, 1989.
The basis for operating the plant prior to the completion of the analysis is the following:
- 1)
The design of the antivibration bars at Palisades (batwings and scallop bars) prevents failure from the out-of-plane flow induced vibration associated with the North Anna failure.
Every tube passes through the diagonal batwing straps unlike that of the Westinghouse North Anna design.
- 2)
Palisades has never experienced a tube rupture or a shutdown due to an uncontrolled steam generator tube leak.
- 3)
The two most recent tube leaks, in December 1987 and August 1988, exhibited increases in primary to secondary leakage which is characteristic of stress corrosion cracking and, not high cycle fatigue.
- 4)
Primary to secondary tube leakage is measured via condenser off-gas sampling and analysis.
RIA-0631 the condenser off-gas monitor, also detects any increase in radioactive xenon.
In combination, these measures provide sufficient assurance that any tube leaks will be detected immediately.
- 5)
No CE plant has ever experienced a vibration induced steam generator tube failure.
In addition to the batwing design, CE steam generator tubing is considered by CE to have greater fracture toughness than that of many tubes in other plants due to an original specification require-ment of placing an upper bound on the yield strength of the material.
The tubing is therefore expected to be more resistant to crack-like failures.
OC1188-0206-NL02
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Nuclear Regulatory Commission Palisades Plant S/G Tube Integrity November 17, 1988
- 6)
The most likely cause of Palisades recent tube leaks is not vibration but one of the following:
A.
Support plate displacement causing tube ovalization and high bending stresses in the plane of the tubes.
B.
Hot-to-cold fatigue cycling of a locked tube, the driving force being the tube versus shroud delta T.
C, A combination of A and B above.
LEAK RATE MONITORING Consumers Power Company is required by Technical Specification 3.1.S to shut down the plant if primary to secondary leakage exceeds 0.3 gpm over a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period.
Administratively, however, a shu.t down is initiated if the leakage exceeds 0.1 gpm over a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period.
This requirement is contained in Palisades Standard Operating Procedure, SOP-1.
3 In the event of a primary to secondary tube leak, radioactive xenon gas enters the secondary system.
Per normal Chemistry Department procedures condenser off-gas samples are taken on a daily basis in order to measure the level of radioactivity present. Additionally, the primary to secondary leakrate calculation is performed a minimum of three times per week.
In the event excessive leakage is identified sampling is increased.
(Note: several modifi-cations were made to the off-gas sampling system during this outage to improve the integrity of the system and eliminate the possibility of air in-leakage).
In addition, if a tube leak occurs, leakage would also be detected on RIA-0631, the condenser off-gas monitor.
This device monitors the air ejector off-gas stream and was designed and installed as a radioactive effluent monitor for Radiologic~l Effluent Technical Specifications.
At this time RIA-0631 "alert" and "high" alarms are set at 5000 cpm and 10,000 cpm respectively. If either alarm is activated the chemistry department immediately takes the necessary samples and calculates the primary to secondary leakrate.
TUBE STABILIZATION The tube integrity analysis will also address the need for tube stabilization at Palisades.
If the analysis shows that vibration is not a valid mechanism for cracking, tube stabilization will not be required.
Further basis for not stabilizing is the assumption that once ~ tube is taken out of service, degradation stops or slows significantly. This a~sumption is supported at Palisades by eddy cu*rrent testing done on nine randomly located tubes in "B" S/G which were deplugged during the 1988 inspection.
All nine tubes were plugged in 1983 for volumetric degradation (IGA or wastage) or U-bend pitting.
A review of the 1983 ECT results against the 1988 results showed that none of the defects had grown.
OC1188-0206-NL02
Nuclear Regulatory Commission
.PaHsades Plant S/G Tube Integrity November 17, 1988 MIZ-18 QUALIFICATION AND 1988 MIZ-18 RESULTS 4
The Miz-18 qualification will continue immediately following plant start-up.
During the week of December 5, 1988 Consumers Power Company will be at Zetec evaluating Miz-18 parameters in order to determine the optimum methods for measuring tube degradation in the Palisades S/G's.
Following this evaluation Consumers Power Company will collect and evaluate data from many defect standards using several different ECT techniques.
Once the data has been evaluated the defect standards will be metallurgically analyzed to determine actual flaw depth.
A statistical comparison will then be performed to measure the accuracy of the ECT techniques.
The techniques demonstrating the best performance will be selected for future use at Palisades.
To support the qualification work a significant amount of Miz-18 data (approximately 600 tubes) was collected during the 1988 S/G inspection.
The following eddy current probes were included in this testing: 4C4F, 540 SF, 560 SF, 580 SF and the 8 X 1.
At this time most of the Miz-18 data has not yet been evaluated.
All of the data will be evaluated during the course of the qualification.
As the qualification progresses we will continue to update the NRC on project status including discussion on the results of the 1988 Miz-18 testing.
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f!:::::Kuemin Staff Licensing Engineer CC Administrator, Region III, NRC NRC Resident Inspector - Palisades OC1188-0206-NL02