05000528/FIN-2014003-03
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Finding | |
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| Title | Leakage on Reactor Vessel Bottom-Mounted Instrumentation Nozzle 3 |
| Description | On October 6, 2013, during an examination of the bottom mounted instrument (BMI) nozzles on the reactor vessel of Unit 3, white residue was discovered at the annulus region of Nozzle 3. The residue was collected for testing and identified as boron, lithium and trace amounts of primary water radionuclides, which was indicative of pressure boundary leakage during the operating cycle. Pressure boundary leakage is prohibited by Technical Specification 3.4.14. Non-destructive examination of Nozzle 3 identified axial cracking in the nozzle tube and a near-surface weld flaw in the J-groove weld that connects the nozzle to the reactor vessel. This allowed for a reactor coolant leak path in the pressure boundary. Corrective actions included completion of an American Society of Mechanical Engineering (ASME) Code approved half-nozzle repair and increasing the frequency of bottom mounted instrument visual examinations to every refueling outage. An extent of condition evaluation found no indication of unacceptable flaws or leakage in the remaining 60 BMI nozzle assemblies in Unit 3. Additionally, review of past inspections did not identify any evidence of leakage from bottom mounted instrument nozzles in Units 1 or 2. Destructive testing determined the cause of the event was primary water stress corrosion cracking of the bottom mounted instrument nozzle due to a weld defect that went undetected during fabrication. Inspectors reviewed all available causal information to assess if there was an opportunity to correct this condition prior to failure of the pressure boundary. Inspectors determined that initial installation and examinations of the affected weld were completed within the specifications used at the time of fabrication. Only surface examinations of the root weld pass, and inspections at every 0.5 in of weld thickness were required, and there was an allowance for cold straightening of nozzles, if required. As such, the defect associated with the weld during fabrication was not reasonably within the licensees ability to foresee, prevent, and correct. Therefore, the inspectors determined that no performance deficiency occurred. The issue is considered within the traditional enforcement process because there was no performance deficiency associated with the violation of NRC requirements. Inspection Manual Chapter 0612, Power Reactor Inspection Reports, Section 0612-09 states, in part, that such violations are dispositioned using traditional enforcement and may warrant enforcement discretion. The NRC Enforcement Policy, Section 6.1 (Reactor Operations), was reviewed to evaluate the significance of this violation. This violation was more than minor and best characterized at Severity Level IV (very low safety significance) because it is similar to Enforcement Policy Section 6.1.d.1. Additionally, a qualitative assessment of the observed RCS leakage condition concluded the risk was of very low safety significance (Green). The basis for this qualitative risk determination was that the leakage rate was very small with little boron residue accumulation on the lower reactor vessel head and no appreciable accumulation on the structures beneath the vessel. Any leakage was within the capability of RCS makeup systems. Additionally, detailed inspections did not reveal any loss of vessel material. The NRC decided to exercise enforcement discretion in accordance with Section 3.5 of the NRC Enforcement Policy and refrain from issuing enforcement action for the violation of Technical Specification 3.4.14.a (EA-13-232) for the following reasons: this issue is of very low safety significance (Green); it was determined that this issue was not within the licensees ability to foresee and correct; the licensee's actions did not contribute to the degraded condition; and the actions taken were reasonable to identify and address this matter. Further, because the licensees actions did not contribute to this violation, it will not be considered in the assessment process or the NRCs Action Matrix. Specific documents reviewed during this inspection are listed in the attachment. This licensee event report and its supplement are closed. |
| Site: | Palo Verde  |
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| Report | IR 05000528/2014003 Section 4OA3 |
| Date counted | Jun 30, 2014 (2014Q2) |
| Type: | Violation: Severity level Enforcement Discretion |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71153 |
| Inspectors (proximate) | B Parks D Reinert G George G Guerra J Drake M Baquera N Okonkwo T Brown T Skaggs Ryan W Sifre |
| Violation of: | Technical Specification |
| INPO aspect | |
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Finding - Palo Verde - IR 05000528/2014003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Palo Verde) @ 2014Q2
Self-Identified List (Palo Verde)
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