ML20039B777
| ML20039B777 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/09/1981 |
| From: | Papay L SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8112230545 | |
| Download: ML20039B777 (5) | |
Text
Docket'No. 50-361
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50 55(e) Report.
Southern California Edison Company ~
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2244 WALNUT GROVE AVENUE ROSEMEAD, CAUFORNIA 91770
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December 9, 1981 t-m Mr. ' R.,H. Enge lke n, Director CJ Of fice of Inspection and Enforcement I?Ec IP S
U. S. Nuclear Re gulatory Commission =
SD 0
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-Region V
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1450 Maria' Lane, Suite 210 Y' A 57 Sic %
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Il Walnut Creek, California 94596-5368
Dear Mr. Engelken:
M di ;. -
- Subj ec t:
. Docke t No. 50-361 San Onofre Nuclear Generating Station, Unit 2 In a letter to youroffice dated November.12,.1981, we identified a condition which we consider. reportable in accordance
.with 10CFR50.5 5(e).
During operations performed in preparation for fuel loading, the Unit-2 -Core Support Barrel was removed for cleaning and' subsequently replaced.
Later, core. indexing verification data revetled a misorientation between the Core Support Barrel and
~ Reactor Pressure Vessel which was incompatible with design disclosure documents.
Enclosed in accordance with 10CFR50;55(e) are
- twenty-five.(25) copies of a Final Report; entitled, " FINAL REPORT
-ON MISORIENTATION' OF CORE SUPPORT BARREL,. SAN ONOFRE NUCLEAR
. GENERATING STATION, UNIT '2. "
If-you have any questions regarding this report, we would be pleased-to discuss this matter with you at your convenience.
Very truly yours,
/
0$f gS Enclosure s O
2
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cc:
Victor Stello (NRC, Director I&E)-
j' ![d A.L E. Chaffee (NRC, San -Onofre Units 2 &. 3)-
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FINAL REPORT ON MISORIENTATION OF CORE SUPPORT BARREL San Onofre Nuclear Generating Station, Unit 2 INTRODUCTION This report is submitted pursuant to 10CFR50.55(e).
It describes a condition discovered during preparation for fuel load involving misorientation of the core support barrel in Unit 2.
This report includes a description of the condition, an analysis of the safety implications and a summary of corrective actions taken.
By letter dated November 12,.1981 Southern California Edison confirmed notification to the NRC of this reportable condition.
BACKGROUND During operations performed in preparation for fuel loading, the Unit 2 core support barrel (CSB) was removed from the reactor vessel to allow -installation of surveillance capsules.
Removal of the CSB was performed by construction personnel in accordance with the construction procedure which had been used numerous times for fit-up of the reactor vessel internals.
Following installation of the surveillance capsules, contractor personnel performing this operation'for the first time lifted the CSB from its storage t
location in preparation for reinstallation into the reactor ve sse l.
an approved station gaintenance procedure, written specifically for removal and installation of the CSB, was utilized.
While suspended from the polar crane, the CSB was hydrocleaned to class B cleanliness requirements.
This evolution, which is not part of the CSB station maintenance procedure, was performed in accordance with a startup work permit and required that the CSB be rotated.
Upon completion of the 'hydrocleaning, the CSB was reinstalled into the reactor vessel using the station maintenance ~ procedure.
Fbilowing reinstallation of the core support barrel, the core indexing acceptance test detected a misorientation between the core support barrel and reactor pressure vessel which was incompatible with design disclosure do c umen t s.
The reactor pressure vessel and core support barrel both carry a 00 reference mark.
The Unit 2 reactor pressure vessel was installed with the 00 reference mark reversed relative to the original system design (i.e., the vessel 00 reference mark was installed f acing plant north).
Because of the symmetry of the vessel it was possible to retain this configuration while maintaining the original design orientation of the core support barrel, upper guide structure and reactor pressure vessel head r
(i.e., the internals and head were designed and fit-up with the 0
reference marks facing plant south).
The 00 marking on the reactor vessel was not changed because of its relationship to l
as-built data.
Installation and arrangement drawings as well as i
technical manuals for Unit 2 were revised with warning notes l
r i
Page 2 added to reflect the required relative positions of reactor pressure vessel and core support barrel.
The station procedure which was used for the most recent CSB installation used the wording of the technical manual but did not include the orientation warning notes, nor did it reference all applicable design disclosure documents.
DISCUSSION f
The following discussion is responsive to 10CFR50.55(e)(3).
~
Description of Deficiency During reinstallation following hydrocleaning, the core support barrel (CSB) was misoriented with respect to the reactor pressure vessel o f Unit 2 (i.e., the 00 reference mark on the CSB was oriented toward plant north).
This misorientation occurred when the maintenance procedure used for installation was interrupted and a cleaning procedure was interposed.
During the cleaning operation the CSB was rotated to facilitate cleaning.
This rotation resulted in the incorrect orientation of the CSB.
Upon resump tion o f the steps o f the -maintenance operation, reinstallation of the CSB proceeded from the rotated position.
The maintenance procedure was not adequate in that it did not include the caution notes of the design disclosure documents regarding orientation of the CSB relative to the reactor vessel.
In addition, the procedure did not require verification of CSB orientation immediately prior to installation into the vessel.
Analysis o f Safety Implication s An analysis of the safety implications, had the misorientation of the core support barrel remained uncorrected, indicates that it is physically possible to proceed with installation of the vessel internals and the vessel head.
There is no potential safety significance to the misorientation of the CSB since an analysis of the CSB stresses and core bypass flow indicates that the misorientation, if uncorrected, would not have compromised plant safety.
As shown by the initial discovery of the misorienttion, existing procedures are adequate to detect an improper CSB installation.
In addition, had the CSB misorientation not been detected, multiple procedural directives would have to be ignored in order for the plant to begin operation with additional or similar misorientations o f reactor components.
The following dicussion supports this position.
The correct installation configuration for the Unit 2 reactor system components are:
Reactor Pressure Vessel (RPV)' 00 reference mark oriented ~
o toward plant north Core Support Barrel (CSB) Oo reference mark oriented toward o
plant south
Page 3 o
Upper Guide Structure (UGS) 00 reference mark oriented toward plant south, o
Reactor Vessel Head (RVH) 00 reference mark oriented toward plant south The first component to be installed during reactor system assembly is the CSB.
As discussed earlier the CSB was installed with the incorrect orientation (i.e., CSB 00 reference mark oriented toward plant north).
This misorientation was detected during core indexin g.
If it is assumed that the results of the core indexing procedure were ignored and assembly of the reactor vessel internals continued, the core would be installed next.
Installation of the core is done with reference to plant north and not keyed to any particular orientation of the CSB.
Due to the symmetry of the core shroud, improper orientation of the CSB would not prevent proper loading of the core.
The next component to be installed is the UGS.
There are two potential ways of orienting this congonent.
1)
UGS 00 reference mark oriented toward plant north.
Orientation of the UGS in this manner assumes that the operator aligns the 00 reference mark on the UGS with the 00 key on the CSB which was installed with a north facing orier.tation.
This orientation would not be consistent with the correct installation configuration.
Assuming that this misorientation occurred, two RVH orientations must then be evaluated.
a)
This orientation reflects the correct RVH installation con fi guration.
The misorientation of the reactor system components would be discovered during fit-up of the in-core instrumentation package.
Since for this case the UGS is assumed to be misoriented (00 reference mark oriented toward plant north) and the RVH is installed correctly (00 reference mark oriented toward plant south) the in-core detector cables attached to the RVH would not match the correspondingly numbered in-core detector receptacles attached to the UGS.
Discovery of UGS misorientation would occur at this point.
Thus, further assembly of the RV components would not proceed beyond installation of the RVH.
b)
RVH 00 reference mark oriented toward plant north.
This would not be consistent with the correct installation configuration.
Misorientation of the RVH would be discovered by the inability to connect the head vent spool piece to the installed piping.
Even r
Page 4 if this error did not lead the operator to question the orientation of the UGS, correction of the RVH orientation to properly align the head vent would subsequently lead to the in-core detector cable mismatch discussed in a) above.
2)
UGS 00 reference mark oriented toward-plant south.
This UGS orientation would be consistent with the correct UGS installation configuration.
Again for this case there are two RVH orientations to be evaluated.
a)
RVH 00 reference' mark oriented towa' d plant north.
r As discussed earlier, the reactor system component misorientation would be discovered due to the head vent -
spool piece not matching with the installed piping.
b)
RBH 00. reference mark oriented toward plant south.
This installation reflects the correct RVH installation configuration.
For this case in which no-reactor conponents are misoriented other than the CSB, there are no other physical impediments that would alert plant personnel to the misoriented CSB.
For this case there is potential for the plant to go into operation.
Due to the physical symmetry of. the CSB, misorientation would have little if any effect on core thermal hydraulic behavior.
Analyses of core - bypass flow assume a combination of tolerances which would result in a larger CSB displacement than was actually measured as a result of the misorientation.
Scoping analyses have been. performed to evaluate the effect of ~ core loading and ultimate reactor vessel assembly based on a slightly distorted internal structure.
Calculated stresses have been reviewed by design engineers and all component load stresses remain within the elastic limit of the material.
There would be no permanent deformation to the structure as a result of the misalignment.
Based on these considerations, nothing has been found to suggest a significant impact either on normal operation or on plant safety.
Corrective Action The core support barrel was removed and an inspection ofithe barrel and reactor vescel' interior was conducted.
No damage was found. ~The core support barrel has been reinstalled with the proper orientation.
After reinstallation, inspection using optical instruments revealed no permanent distortion had occurred as a result of the misorientation.