ML20056F680
| ML20056F680 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/19/1993 |
| From: | Marsh W SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML19310D647 | List: |
| References | |
| NUDOCS 9308300254 | |
| Download: ML20056F680 (2) | |
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m' Southem Califomia Edison Company 23 PARKEH STREE1 f
IRveNE. CA1.sFORNIA 92718 i
July 19, 1993
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WAGEH C MAHSH MANAGLM OF M.eC44.AM ME Ot.pLATOMY AP F AIMS (714) 4&e 4403 r
U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket Nos. 50-361 and 50-362 Root Cause Evaluation for CPC Axial Shape Anomaly San Onofre Nuclear Generating Station Units 2 and 3 r
Reference:
NRC Inspection Report 93-05; NRC Open Item 361/93-05-03 This letter provides for your information a copy of our root cause evaluation of the Core Protection Calculator (CPC) axial shape anomaly at San Onofre Nuclear Generating Station, Units 2 and 3.
In February 1993, Southern California Edison (SCE) Engineering expanded its l
core follow activities at San Onofre Units 2 and 3.
As a result of this i
effort, an anomaly was discovered in the CPC synthesized axial power shapes.
Specifically, the CPC channels were generating " cosine type" axial shapes while incore instrument measured and predicted shapes had changed to " saddle type." The unexpected CPC axial power shapas were believed to be inconsistent with those assumed for the CPC uncertainty analysis.
It was concluded that the CPC channel dependent shape annealing matrix was responsible for the unexpected axial power shapes from the CPC channels.
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At the time of this discovery in February, immediate action was taken on both units to increase the DNBR penalty by 15%, to reduce power to below 85%, and to remeasure the shape annealing matrix for each CPC channel.
Following generation and installation into the CPCs of a new shape annealing matrix, the plants were returned to full power. This discovery and SCE's actions were i
discussed with the NRC during a number of telephone conversations.
l' SCE, with input fraa ABB Combustion Engineering, initiated an evaluation to 5
l determine the root cause of the CPC synthesized anomalous shape. The enclosed l
report (Enclosure 1) describes the symptoms of the anomaly, the potential root causes investigated, the conclusion as to the root cause, and the corrective actions that will be implemented for the next operating cycle of Unit 2 (Cycle i
7).
l The root cause of the CPC synthesized anomalous axial power shape is concluded to be insufficient perturbation of normalized core axial power shape relative N
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Document Control Desk to non-signal effects in the normalized middle excore detector level during the measurement of the shape annealing matrix at Beginning of Cycle (80C).
The breakdown in the coherent relationship is concluded by SCE to be caused either individually or by a combination of the plant computer incore detector deadband, manual collection of data, or fuel management effects.
It is noted that ABB Combustion Engineering does not believe that fuel management effects were a root cause, but rather, that these effects were contributory factors that may have exacerbated the impact of the root causes. contains information proprietary to ABB Combustion Engineering.
Also enclosed in the same binder as Enclosure 1 is Enclosure 2, which is an Application for Withholding and an affidavit from ABB Combustion Engineering, the owner of the information, which sets forth the basis on which the information may be withheld from public disclosure by the NRC in accordance with 10CFR2.790.
In addition, a non-proprietary version of this report is provided as Enclosure 3.
Accordingly, it is requested that the information which is proprietary to ABB Combustion Engineering be withheld from public disclosure in accordance with 10CFR2.790. Correspondence with respect to the proprietary aspects of the Application for Withholding or the supporting affidavit should be addressed to Mr. R. J. Land of ABB Combustion Engineering.
Copies of this letter and the non-proprietary version of this report are being forwarded to cognizant personnel at other COLSS/CPC plants.
If you have any questions regarding the enclosed report or if you would like additional information, please let us know.
Sincerely, Enclosures cc:
B. H. Faulkenberry, Regional Administrator, NRC Region V C. W. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2&3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3