ML20054E140
| ML20054E140 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 04/21/1982 |
| From: | Dieterich R SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML20054E133 | List: |
| References | |
| NUDOCS 8204260178 | |
| Download: ML20054E140 (8) | |
Text
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L UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING APPEAL BOARD In the Matter of
)
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SACRAMENTO MUNICIPAL UTILITY DISTRICT
) Docket No. 50-312
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(Rancho Seco Nuclear Generating
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Station)
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AFFIDAVIT OF ROBERT A. DIETERICH City of Sacramento
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ss State of California
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ROBERT A. DIETERICH, being duly sworn according to law, deposes and states as follows:
1.
My professional qualifications are set forth in the evidentiary record of this proceeding in my testimony, following Tr. 1988. My position with the Sacramento Municipal Utility District, however, has changed since the hearing.
I am now Supervisor of Nuclear Licensing and Environmental Engineering in the Generation Engineering Department.
2.
The infounzion provided in SMUD's responses, dated Apr 21, 1982, to the Atomic Safety and Licensing Appeal Board's questions contained in an April 15, 1982 Memorandum and Order, was prepared by me and is true and accurate to the best of my knowledge and belief.
a h on Yo Robert A. Dieterich l
I ' * * * * * * * * * * * * *d[$$Id'$dk' * * * * *
- I Subscribed to and sworn before me this { # ay of April, 1982.
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LICENSEE'S ANSWERS TO APPEAL BOARD QUESTIONS POSED IN MEMORANDUM AND ORDER OF APRIL 15, 1982 m
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4 QUESTION NO. 1:
If the thermal sleeve has traveled to the bottom of the reactor vessel, what effect might this have on the instrumentation guide tubes?
SMUD RESPONSE:
The missing thermal sleeve is a cylinder approximately sixteen inches in length and two inches in diameter with a one-eighth inch thick wall.
(See attached figure. )
It weighs approximately three pounds.
A loose part of this size and weight could impact and damage the incore instrument guide tubes or other components in the reactor vessel lower head region.
However, a reactor coolant system loose parts monitoring system is installed and utilized at Rancho Seco.
There are several sensors located around the primary loop, two of which are mounted directly to incore instrument guide tubes below the reactor ves-sel lower head.
This instrumentation is set to alarm with less than one half foot pound impact.
Impacts in the lower head region of sufficient frequency or magnitude to cause damage would be detected by this loose parts monitoring equipment.
Significant, repetitive indications would occur substantially before any resulting damage could progress to a degree to be a safety concern.
That is, any loose parts impacts during operation which could potentially result in structural degradation in the lower head region can be detected and the plant promptly shut down.
To date, no such indications have been observed.
Also, consistent with and supportive of this loose parts monitoring experience, no losses of incore instrumentation indications have occurred.
(A loose part in the lower head
. impacting incore instrumentation components could result in severance of one or more of the 52 incore detector cable assemblies.
Even though technical specifications require the operability of 23 detectors above 80 percent power for calibration of out-of-core detectors, they do not serve a safety, protective, or accident mitigating function.
There-fore, such a reduction in monitoring capability is not a safety concern.
Losses of incore signals would, however, serve as a backup to the loose parts monitor to indicate damage in the lower head region.)
It should also be noted that damage to an incore guide tube inside the reactor vessel would not result in a breach of the pressure boundary since the tube extends a considerable distance outside the vessel to a pressure seal incorporating an electrical connection for the detector signal.
Based on the initial location, size and weight of the thermal sleeve; the direction and magnitude of reactor coolant flow; and the configuration of the Reactor Coolant System, t
the most probable final location is in the lower reactor head region.
This is consistent with the Appeal Board concern ex-pressed by the above question and responded to in the preceding j
paragraphs.
Possible other directions of travel, potential l
damage and final location have also been reviewed.
As with the lower head region, any such loose parts impacts could be detected and no safety concerns have been identified.
- Also, no plausible means have been identified for the thermal sleeve l
to cause thermal-hydraulic damage to the core from flow blockage.
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QUESTION NO. 2:
Do the intended repairs include location and perhaps removal of the missing thermal sleeve?
SMUD RESPONSE:
There are no plans at the present time to attem c to locate and remove the missing thermal sleeve.
Removal e
of the sleeve from its most likely location, the reactor lower head region, would require defueling the reactor and removal of the internals.
This would require a lengthy outage and cause unnecessary radiation exposure to maintenance personnel.
A shutdown is scheduled to begin in September of this year, during which a defueling and internals removal will occur for the purpose of performing an inservice inspection of the reactor coolant system as required every ten years.
Removal of the missing thermal sleeve will be attempted at that time.
QUESTION NO. 3:
In replacing the sleeve, will the original design of the sleeve retention buttons be changed?
If so, how?
It not, how will this problem be avoided in the future?
SMUD RESPONSE:
The design of the thermal sleeve retention buttons adjacent to the reactor coolant cold leg piping (see attached figure) are not being changed as part of the thermal sleeve replacement effort.
These buttons continue to serve only a secondary function.
Primary retention in the original design was by contact expanding the thermal sleeve into the diameter of the no2zle safe end.
The upstream end of the new thermal sleeve is now rolled and fitted into the nozzle safe q
end to assure retention of the sleeve.
New upstream retention buttons, that is, those in the nozzle safe-end, are being installed in conjunction with
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thermal sleeve and-safe-end replacement.
These buttons are similar to those in the original design and do not serve a retention function in the normal flow direction.
QUESTION NO. 4:
What is being done to prevent the loss of the thermal sleeves in the other nozzles?
If nothing is con-templated, why?
SMUD RESPONSE:
New thermal sleeves and safe ends are being-installed on two of the four high pressure injection nozzles --
the normal makeup nozzle with the missing thermal sleeve, and a second nozzle which had non-destructive examination indications of some thermal sleeve degradation.
These new sleeves are of the new design illustrated in the attached figure.
As can be seen the contact / support between the thermal sleeve and the nozzle and safe-end has been substantially increased versus the original design.
The new design is intended to prevent the degradation or loss of these thermal sleeves.
New thermal sleeves are not being installed on the other two nozzles.
These nozzles were inspected during the current l
outage by non-destructive examination techniques and no indica-l tions of degradation in the nozzle, safe-end or thermal sleeve l
were observed.
These nozzles are not used for system makeup i
I (a routine, continuous function) and have experienced approxi-mately six years of plant operation to date.
Therefore, it is l
l considered that the probability of the respective thermal sleeves l
l becoming loose prior to the next opportunity for inspection is extremely low and does not justify replacement at this time.
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QUESTION NO. 5:
How can we be assured of safe operation if the plant returns to full power after completion of these repairs?
SMUD RESPONSE:
At the time of the current shutdown, the high pressure injection nozzles had experienced approximately six years of plant operation and the safe operation of the unit continued to be assured.
Both the high pressure injection and makeup systems were fully functional.
Two of the high pressure injection nozzles were inspected with no indications of degradation being observed.
This combina-tion of experience to date and verification of current structural integrity supports a conclusion that the two unaffected nozzles are acceptable for continued plant operation.
The two nozzles which had indications of degradation are being replaced.
This replacement will restore the nozzles to a condition at least equivalent to the original.
The above actions provide adequate assurance that Rancho Seco can operate safely at full power until at least the end of the present fuel cycle.
Also, an ongoing evaluation and inspection program is being defined.
This activity will continue to evaluate the causes of the current problem to determine if further changes in design or operation are necessary.
Also, requirements for more frequent inspection of the nozzles may be determined.
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MAKE-UP/HPI N0ZZLE I
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.010" TO.015" THERMAL DIAMETRICAL CLEARANCE OLD THERMAL SLEEVE DESIGN SLEEVE BETWEEN THERMAL SLEEVE & N0ZZLE I.D.
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