05000443/FIN-2011003-03
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Finding | |
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| Title | Operability Evaluation for Degraded Concrete in ASR Affected Plant Structures. |
| Description | NextEra\\\'s analysis of the CEB samples found that the concrete has acceptable compressive strength and reduced but acceptable modulus of elasticity. To evaluate the effects of the reduced modulus, NextEra assessed the increase in strain for CEB building elements and found that the strain at the most limiting element remained less than the American Concrete Institute ACI-318 design stress limit and thus was acceptable. NextEra evaluated the impact on flexural capacity by reviewing the change in bending moment of structural elements. The reduced modulus causes the concrete to have increased flexure which has the effect of shifting the balance point in how load is transferred between the concrete and the imbedded steel (rebar). The reduced modulus causes a shift toward the reinforced steel in tension. The resultant change in bending moment was evaluated to show that the reduction in capacity was minimal and the stresses on the steel and concrete remain below the design stress limits with margin. NextEra\\\'s evaluation of the condition concluded that a change in the dynamic seismic response of the structure would be minor, and the CEB remains capable of performing its design function. The prompt operability determination for the CEB (ARs 1644074 and 1664399) evaluated how the reduced modulus would affect the structure by analysis of locally impacted sections. The evaluation did not address the effects of reduced modulus on the changes to the natural frequencies of the structure and the global response of the structurelo seismic loads. The inspectors requested further information on the effects of the reduced modulus on stresses and strain in the concrete and rebar system for which NextEra will complete additional analyses. The prompt operability determination (POD) for the Control Building (AR581434) as well as for other ASR impacted structures (AR1664399) evaluated the effects of reduced modulus on portions of the below grade structures and the components housed within them. The evaluations lacked details to explain the effects of the reduced modulus on structuralflexure as related to components attached to the structures, such as pipe supports and cable trays. Similarly, the evaluations lacked details with regard to the structure\\\'s response to seismic events as related to structure rigidity and changes in the natural frequency, and the bases to use the ground response spectra. Further, the evaluations lacked details to explain how the function of support anchor bolts would not be adversely impacted by reduced concrete compressive strength in the CBIET. This item is unresolved pending further NRC review of the above issues, action by NextEra to complete additional analysis of the CEB conditions and subsequent NRC Region I review of that analysis, and the completion of reviews by the NRC Office of Nuclear Reactor Regulation specified in the associated task interface agreement (ADAMS No. ML111610530). The result of these reviews will determine whether there is a performance deficiency associated with this item. |
| Site: | Seabrook  |
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| Report | IR 05000443/2011003 Section 1R15 |
| Date counted | Jun 30, 2011 (2011Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | J Johnson T Burns T Moslak W Raymond A Burritt A Turilin J Deboera Burritta Turilin J Deboer J Johnson T Burns T Moslak W Raymond |
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Finding - Seabrook - IR 05000443/2011003 | |||||||||||||||||||||||||||||||||||||||||||
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Finding List (Seabrook) @ 2011Q2
Self-Identified List (Seabrook)
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