ML19309A298
| ML19309A298 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 04/28/1976 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8003270719 | |
| Download: ML19309A298 (6) | |
Text
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NRC FORM 195 7g U.S. NUCLEAR REGULATCRY *~ ~ MISSION DOCKE l
50-312
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NRC DISTRIBUTION FcR PART 50 DDCKET MATERI AL TO:
FROM: SMUD DATE OF DOCUMEpiT MR R W REID....
SACRAMENTOy CALIF.......
4-28-76
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J J MATTIMOE.......
5-3-76
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ETTER O NOTORIZE D PROP INPUT FORM NUMBER OF COPIES RECEIVED
% ORIGIN AL U NC LASSIFIE D OCOeY 1 SIGNED......
DESCRIPTION EN CLOSU RE LTR RE THEIR 4-8-76 LTR...'.TRANS THE RANCHO SECo SURVEILLANCE HOLDER TUEE REPORT FOLLOWING...........
WITH RESULTS OF INSPECTION REPORT..........
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PLANr NAME: RAICHO SECO
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SAFETY FOR ACTION /INFORMATION ENVIRO 5-o-(U N X
ASSIGNED AD :
n E MocA(v ASSIGNED AD.
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KE1Th BRANCH CHIEF :
PROJECT MANAGER:
PROJECT MANAGER :
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INTERNAL DISTRIBUTION E RE W SYSTEMS SAFETY PT. ANT RYRTRMM vuvrvn w t'n X
NRC PDR HETNEMAN TFnRRcn ERNST X
I&E {M OELD ScunnFngn BENAROYA PALLARD LAINAS SPANGLER COSSICK & STAFF ENGINEERING IPPOLITO MTPC MAccAnY SITE TECH CASE KFIGHT OPERATING REACTORS GAMMILL HANAUER SIHWEIL X
STELLO STEPP HART.FSS PAWLICKI HUDIAN OPERATING TECH PROJECT MANAGEMENT RFACTOR SAFETY EISENHUr SITE ANALYSIS BOYD ROSS X
SHAO VOLLMER P. COLLINS NOVAK BAER BUNCH HOUSTON ROSZTOCZY SCHWENCER J. COLLINS PETERSON CHECK GRIMES KREGER MELTZ X 'X. Inad.EF HELTEMES AT & I SITE SAFETY & ENVIRC SKOVHCLT SALTZMAN ANALYSIS RUTBERG 1
DENTON & MULLER EXTEF.4AL DISTRIBUTION CONTROL NUMUER n
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REG. V-IE ULRIKSON(ORNL)
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g/ SACRAMENTO MUNICIPAL UTILITY DISTRICT O 620 SMU=
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44 April 28,1976 g
Director of Nuclear Reactor Regulabo$
Attention: Mr. Robert W. Reid, Chief Operating Reactors, Branch ~4 U.S. Nuclear Regulatory Comissign i
Washington, D.C.
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Docket No. 50-312
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Rancho Seco Nuclear Generating A.
Station, Unit No. 1 D-% *. %". g.
Dear Mr. Reid-On April 8,1976, The Sacramento Municipal Utility District requested an exemption from the requirements of 10 CFR 50, Appendix H, and requested changes to the Technical Specifications for Rancho Seco Unit. No. I relative to operation of Rancho Seco Unit No. I with reactor vessel surveillance specimens removed for the remainder of the first fuel cycle.
At the time of that request, inspections had not been completed and the corrective actions had not been decided upon for a fix to the surveillance specimen holding tubes.
The attached report describes the results of an inspection which has now been completed and provides the details of a corrective action which is proposed for the remainder of Fuel Cycle 1.
As noted in this report, no loose parts were generated as a result of the wearing action on the surveillance specimen holding tubes.
It should also be noted that the corrective action is identical to that taken at Oconee III with the exception that the surveillance holding tubes have been cut 100 inches below the top of the core support flange on all three tubes. This is lower than the cut made at Oconee III.
This places the mandrel, which is attached to the extension tube, inside the journal and therefore provides additional support in this area.
Rancho Seco Unit No. 1 utilizes an Atomics International loose parts and vibration monitor.
Loose parts detection is accomplished through eight channels on this monitoring system.
Two sensors are attached to the incore instrument guide tubes on the lower vessel head. Two additional sensors are attached to the service structure flange on the upper vessel head.
There are also two sensors at the upper tube sheet area of each steam generator.
These areas are the logical places for any loose parts to collect. Additional sensors are available on the primary system and may be connected to any of the eight channels on the loose parts monitor if necessary.
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AN ELECTRIC SYSTEM SFRVING M0RE THAN 600.0CG tN THf WfARI Ob CA!!IGON1A
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Mr. Robert W. Reid, Chief April 28,1975 Each channel has an alarm point presently set to alarm at 1/2 ft.-lb.
impact at the sensor location.
The alarm annunciat9e in the control room and also automatically turns on a 4-track tape rece m r to record the signal on the alarming channel and three other pre-selected channels.
This auto-matic tape start allows the operator to hear the signal immediately after an annunciation in the control room, even if he is not present at the loose parts monitor itself, to hear the sound.
Our evaluation indicates that there would be no safety problem even if a surveillance speimen holding tube were to fail. The loose parts monitor indication could be promptly investigated and an evaluation made to determine if the Rancho Seco unit should be shut down.
In our opinion continued operation of Rancho Seco with the surveillance specimen capsules removed and the surveillance specimen holder tubes restrained by the upper tube spring-loaded retaining device is acceptable for the remainder of Fuel Cycle 1.
Sincerely yours, bla$A L.'
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'J. J. Mattimoe Assistant General Manager and Chief Engineer attachment l
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RANCHO SECO SU"RVEILLANCE HOLDER TUBE REPORT INTRODUCTI0ff Y
The reactor vessel surveillance capsules and holder train at 4
Rancho Seco have been removed and the surveillance capsule holder tubes ins pected. Based on the results of these inspections, Rancho Seco will be operated for the remainder of Cycle 1 with the surveillance capsule holder tubes installed in the reactor vessel, but with the surveillance capsules and holder train removed. The surveillance specimen holder tubes (SSHT) will be secured from motion by spring-loaded retaining devices which will be loaded into the upper end of each holder tube. This report documents the inspection results and demonstrates the acceptability of these actions.
SURVEILLANCE CAPSULE HOLDER TUBE ARRANGEf1ENT:
The design of the reactor vessel capsu]e holder tubes is described in Section 2.5 of B&W Topical Report BAW-10100A.ll)
The surveillance capsules are attached to and secured within the holder tube by a spring-loaded push -
rod assembly holder train as shown in Figure 2-8 of Reference 1.
The plenum flange compresses the push rod assembly spring cartridge as the plenum is lowered into the core support shield.
The spring-loaded push rod assembly has four S-piece spacers (see Figure 2-10 of Reference 1) mounted along its axial length to provide lateral positioning of-the push rod. The top two of these. spacers are located in that portion of the axial length of the holder tube which is within the shroud tube. The third spacer is axially located in a portion of the holder tube with a thicker wall and within a journal bearing at the lower end of the shreud tube, mounted to the core support shield. The fourth spacer is approximately in the center of the ogee bend in the holder tube.
A female fitting on the lower end of the push rud mates with the top end fitting of the upper surveillance capsule as shown in Figure 2-11 of Refe ence 1.
The bottom end fitting of the lower surveillance capsule mates with a special fitting in the base of the holder. tube.which restrains the capsules from rotation.
The holder tubes themselves are contained within a shroud tube extending from the plenum flange to a location corresponding to the third push-rod spacer. The lower portion of the shroud tube is mounted on two pintles which allow rotation of the tube against the thermal shield for--
removal or insertion of the reactor internals.
Rotation of the holder tube during operation is prevented by the pin locking mechanism on each pintle and bearing, and the hold-down force applied by the capsule holder train.
SURVEILLANCE CAPSULE HOLDER TUBE INSPECTION:
All three SSHT's were inspected by remote video techniques for evidence of wear on the internal surface.
Evidence of wear. was noted at each of the push rod spacer axial locations, at the location of the hold-down spring, and at the surveillance capsule rings.
These wear sites are e
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1 attributed to contact and relative motion of the hold-down spring, spacer or surveillance capsule at their respective locations. _The wear indications are all very shallow with the e:;eption of some deep wear at the location of the spring cartridge on the upper ends of all three tubes.
Evidence of deep wear is also found at the fourth spacer location of one of the tubes. A small hole exists at this location on this tube.
External inspections were also conducted on all three tubes using the same video technique. The journal bearing area and the upper i
pintle were examined for evidence of wear. These inspection results j
confim the adequacy of the holder tube supports.
Ut examinations were conducted of each tube interior at the journal bearing area. These examinations showed some external tube wall thinning has occurred over a portion of the circumference.
b hhere were no loose. parts generated as a result of the above, described wearing.
l CORRECTIVE ACTION:
Evaluation based on the inspection results conclude that the Rancho Seco holder tubes retain sufficient integrity to remain in the reactor vessel.
B&W has concluded that the cause of the observed tube wear is flow induced relative motion of the surveillance capsyle train and the holder tube.
To minimize the possibility of unacceptable wear occurring during the remainder of Cycle 1, the following step are to be taken:
1.
Surveillance capsules and push rod assembly are to.be removed during the remainder of Cycle 1 operation.
2.
The holder tubes will be. secured from motion by a spring-loaded retaining device which will be loaded into the upper end of each holder tube. All three tubes will be-cut near the top of the journal, and an extended spring-loaded retaining (fevice will be installed which expands inside the journalind provides structural continuity of the tube.
Due to the indications of wea~ noted above at the journal bearing area of the holder tube, this area will be expanded by rolling to restore adequate journal bearing support.
This action will allow time for the engineering of the holder tube design modifications and material procurement prior to the resumption of the surveillance capsule irradiation program.
SAFETY EVALUATION:
Reactor Vessel:
The request for an exemption to the requirements of 10 CFR 50, Appendix H in Reference 2 provides the justification for operation with the
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_y reactor vessel surveillance specimens removed.
Removal of the specimens
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from the reactor vessel for the remainder of Cycle 1 will not adversely affect the results of future testing of these specimens or the overall results of the surveillance program.
Surveillance Capsule Holder Tube:
The present condition of the Rancho Seco surveillance holder tubes has been evaluated.
The loads on the tubes measured during hot functional testing are very low compared to the allowable loads A comparison of these loads is provided in B&W Topical Report BAW-10039.(3) A fatigue evaluation has been performed using the as-measured strains and appropriately conservative factors for the reduction in cross-sectional area and notch effects associated with the wear sites.
The results of this evaluation have concluded that the maxinum alternating stress levels during continued operation are well below the high-cycle endurance limit for the 304 stainless steel material.
Based on the large margins in the design, the corrective action taken as described above-and the results of the evaluation, the tubes are considered acceptable in their present condition for the remainder of Cycle 1 operation with the surveillance capsules and push rod assembly removed and the spring-loaded retaining devices installed to provide proper holder tube restraint.
Based on the considerations discussed above, the holder tubes are considered structurally adequate for 1 cycle of operation.
Even though structurally adequate, failures in the areas of wear, as described above, have been considered.
Complete severance at the wear locations within the shroud tube would have no immediate effect since these portions are contained by the shroud tube.
Severance at the 4th spacer location would allow the lower portion of the holder tube to oscillate on the hinged mounting brackets (pintles).
This motion would be expected to wear the anti-rotation portion of the mounting bracket at the dowel pin.
This wear would allow larger oscillations until eventually the upper portion of the holder tube.and sprina-loaded retaining device would be free and would drop into the annulus vetween the thermal shield and the reactor vessel wall.
Dependii.g on the motion and condition of the upper portion of the tube, it may be in one or more s'ections severed at the wear locations.
These sections, depending on their length, would either wedge in the annulus between the therma: shield and the vessel wall, or for shorter pieces, may wedge in the lower reactor vessel head.
The spring-loaded retaining devices would prchably wedge in the lower head.
Damage from these loose parts could occur to the reactor vessel clad, incore instrument guide tubes and the lower reactor internals.
This damage would not represent an inminent threat to public health and safety but could require extensive evaluation of repair to assure these structures remain serviceable for the life of the plant. The Rancho Seco Unit No.1 loose parts monitor i. capable of detecting a failute of this magnitude and an orderly shutdown couW bc made before any signmcant damage would result..
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v CONCLUSION:
. It is casicluded that operation of Rancho Seco with the surveillance specimen capsules removed and the surveillance specimen capsule holder tubes restrained by the upper tube spring-loaded retaining device is acceptable during the balance of Cycle 1.
This change will not be inimical to the health and safety of the public.
REFERENCES:
(1) Reactor Vessel Material Curveillance Program -
Compliance with 10 CFR 50, Appendix H, for Oconee Class Reactors, BAW-10100 A, Babcock & Wilcox, February 1975 (2) Letter, Mr. J. J. Mattimoe, SMUD, to Mr. R. W. Reid, NRC, Docket No. 50-312, Proposed Amendment No. 42, April 8,1976.
(3)
Prototype Vibration Measurement Results for B&W's 177 - Fuel Assembly, Two-Loop Plant, BAW-10039, Babcock & Wilcox, April 1973.
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