05000285/FIN-2015007-11
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Finding | |
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| Title | Raw Water Strainer Analysis and Commercial Dedication |
| Description | The following issues were discussed during the inspection, but the licensee was unable to provide the required information to be able to disposition the issue in accordance with Inspection Manual Chapter 0612 as either minor or more than minor. Additionally, parts of the aforementioned calculation were performed by third-party vendors, so the licensee staff did not have specific knowledge of the calculation because they did not prepare them. To close the unresolved item the NRC needs additional information to be able to address the following concerns: Material Properties: Calculation FC07716 performed a chemical analysis to conclude the strainer was a cast iron material because there was no specific receipt paperwork on the design or construction. The chemical analysis concluded that the strainer body was cast iron but the test equipment used was unable to measure carbon. The team questioned the validity of using equipment unable to detect carbon as carbon is a major component of steel and its content has a significant impact on its properties. Especially with steel being a major component in a power plant. In addition, the calculation used a hardness test to correlate the strength of the cast iron. The calculation used average hardness values, rather than minimum values as is required by ASME codes, to correlate a strength value. The team questioned why the average value was used instead of the minimum specified. Analysis methodology and results: The calculation used ANSYS simulation software to compute the stress levels within the equipment. However, the results of the computer model were not verified or validated. Specifically, the team was not provided with evidence that parametric or sensitivity studies were performed particularly for the model mesh. The ANSYS model had a coarse mesh size, with less than eight elements through the thickness. Typically a mesh this coarse will not accurately predict the stress levels. Additionally, the ANSYS results showed some areas with stress levels that exceeded the acceptance criteria established with the calculation (another issue of concern), but the high stress was averaged across the thickness. The ANSYS model has several assumptions that the licensee could not provide a basis for; therefore the team questioned the validity of the models results for commercial dedication. Acceptance criteria: The purpose of Calculation FC07716 is to convert the non-safety related commercial equipment into safety related by commercial dedication. However, the analysis uses the ASME design code as the acceptable stress limits because the raw water strainers are part of the raw water piping system. The final safety analysis report states that the raw water system piping code of record is United States of America Standards USAS B31.1. The team questioned why ASME allowable stresses were used instead of United States of America Standard USAS B31.1 allowable stress limits. No code reconciliation was provided during the inspection to address the issue. Loading conditions: Calculation FC07716 does not address a barge impact loading condition. As stated in URI 05000285/2015007-09 (see Section 1R21.2.12.3), a barge impact is a required loading condition for the intake structure. The barge impact is a large loading and will produce large accelerations within the intake structure. In turn, these accelerations will affect the strainer system, which is assumed to be made from cast iron which is a brittle material. The effects of the barge impact on the raw water strainer system do not appear to be analyzed. |
| Site: | Fort Calhoun  |
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| Report | IR 05000285/2015007 Section 1R21 |
| Date counted | Mar 31, 2015 (2015Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21 |
| Inspectors (proximate) | J Dixon M Schneider P Elkmann R Kellarb Correllc Smith G Gardner J Bozga J Braisted J Dixon M Yeminy T Farnholtz |
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Finding List (Fort Calhoun) @ 2015Q1
Self-Identified List (Fort Calhoun)
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