05000327/FIN-2017008-04
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Finding | |
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Title | Potential Inadequate Determination of Failure Modes for Qualified Life for Foxboro/Weed Instrument |
Description | Introduction: The inspectors identified a URI to review the adequacy of the licensees justification for failure modes and the degradation leading to them in the determination of the qualified life for the Foxboro/Weed Instrument transmitters documented in the licensees EQ Binder IPT-002. Description: The inspectors reviewed EQ Binder IPT-002 for Foxboro/Weed Instrument flow transmitter qualification. In reviewing qualification test report QOAACIO, Rev. A, the inspectors identified two concerns with the qualification. a. The inspectors noted that the qualification test report identified that polysulfone had the most limiting activation energy, 0.72 eV, for the Weed instrument assembly. However, the 0.72 eV was not being used by the licensee to determine the qualified life in the Arrhenius calculations in accordance with NUREG-0588 Section 4(6) and RG 1.89, Rev. 1, C.5.c. When inspectors questioned the licensees use of a less limiting activation energy (0.78 eV for resistors), the licensee determined that the 0.72 eV was based on the degradation and failure modes associated with the tensile strength material property for polysulfone. The licensee consulted the component manufacturer, and determined that creep was the correct material property to be evaluated for end of life. The activation energy for polysulfone creep was identified as 3.81 eV. The inspectors have challenged the licensees determination that creep is the only material property that can produce a failure of the sealing function for polysulfone. The inspectors noted that the requirements in IEEE Std. 323-1974, Section 5 require, in part, that assurance be provided that any extrapolation or inference be justified by allowances for known potential failure modes (i.e. loss of sealing function) and the mechanisms leading to them (i.e. the degradation in various material properties). If the degradation associated with creep is not the only degradation mechanism that could lead to a loss of sealing function over time, inspectors question if the degradation of other material properties would have more limiting activation energies than the licensees current activation energy for the Foxboro/Weed Instrument transmitter (0.78 eV). b. The 0.78 eV activation energy used by the licensee for qualified life was derived from an academic white paper that documented experiments performed in the early space program. The white paper specified that its experimental methods were not validated. The vendor that qualified the transmitter subsequently used this experimental information to determine the qualified life of the transmitters. This activation energy appeared not to be valid in the range of service temperatures that the transmitters are expected to age in prior to a DBA. The inspectors identified that these experimental tests did not follow any identifiable quality standard. The tests were conducted as early as 1963, the white paper was published in 1968, and the inspectors could not identify any subsequent verification of these experimental methods. Although no failure modes and effects analysis was evident, the table of
11 components in the qualification appeared to identify other components that could have much more limiting activation energies that were identified by qualification, as low as 0.5 eV. The licensee has captured these concerns in their corrective action program as CR1366039, CR 1363427. The inspectors need further information from the licensee and NRC technical staff to evaluate the concerns. This URI is opened to determine if a performance deficiency exists. (URI 05000327/2017008-04, 05000328/2017008-04, Potential Inadequate Determination of Failure Modes for Qualified Life for Foxboro/Weed Instrument) |
Site: | Sequoyah ![]() |
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Report | IR 05000327/2017008 Section 1R21 |
Date counted | Dec 31, 2017 (2017Q4) |
Type: | URI: |
cornerstone | No Cornerstone |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.21N |
Inspectors (proximate) | T Fanelli M Greenleaf C Franklin S Walker |
Violation of: | Pending |
INPO aspect | |
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Finding - Sequoyah - IR 05000327/2017008 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Sequoyah) @ 2017Q4
Self-Identified List (Sequoyah)
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