05000315/FIN-2012004-03
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Finding | |
|---|---|
| Title | Design Basis of Seismic Category I Structures and Equipment |
| Description | The plant UFSAR states that the auxiliary building seismic Category 1 structure was designed to the Specification for the Design, Fabrication and Erection of Structural Steel for Buildings; adopted in 1963 by the American Institute of Steel Construction (AISC). In various sections of the UFSAR, certain structures have allowable stresses that are specified for both the Operating Basis Earthquake (OBE) and the Safe Shutdown Earthquake (SSE). Where specified, these allowable stresses are not increased above normal allowable stresses for the OBE load condition. However, in discussion of the auxiliary building requirements, the UFSAR simply states for the OBE, all stresses in the steel superstructure are within allowable as specified by the 1963 code... (AISC). This AISC specification defined the structural steel allowable design stresses for normal load cases and, under a separate subsection, allowed a one third increase over normal stresses for seismic and wind loads. The AISC specification is used as a design code in the building industry where structures are not designed to OBE or SSE loads, but to earthquake levels specified in the building codes. The licensee maintained that the one third increase over normal stresses was acceptable for use in design under the OBE load conditions for the auxiliary building even though the one third increase was not used in the OBE analysis in other sections of the UFSAR. The NRC Safety Evaluation Report, dated September 10, 1973, stated that the acceptance criteria were consistent with the other plants licensed at the time. The inspectors cannot determine if the NRC ever accepted the use of the additional margin, for the OBE load condition, at D.C. Cook. The inspectors are not aware of any other plants that have a Safety Evaluation Report documenting approval to utilize the one third increase. D.C. Cook is a pre-standard review plan (NUREG-0800) plant; however, the inspectors have noted for context, that NUREG-0800 as well as the AISC Specification for Safety-related Steel Structures for Nuclear Facilities, N690, has always specified use of normal allowable stresses without the one third increase. The plant UFSAR states that the auxiliary building seismic Category 1 structure was designed to the Specification for the Design, Fabrication and Erection of Structural Steel for Buildings; adopted in 1963 by the American Institute of Steel Construction (AISC). In various sections of the UFSAR, certain structures have allowable stresses that are specified for both the Operating Basis Earthquake (OBE) and the Safe Shutdown Earthquake (SSE). Where specified, these allowable stresses are not increased above normal allowable stresses for the OBE load condition. However, in discussion of the auxiliary building requirements, the UFSAR simply states for the OBE, all stresses in the steel superstructure are within allowable as specified by the 1963 code... (AISC). This AISC specification defined the structural steel allowable design stresses for normal load cases and, under a separate subsection, allowed a one third increase over normal stresses for seismic and wind loads. The AISC specification is used as a design code in the building industry where structures are not designed to OBE or SSE loads, but to earthquake levels specified in the building codes. The licensee maintained that the one third increase over normal stresses was acceptable for use in design under the OBE load conditions for the auxiliary building even though the one third increase was not used in the OBE analysis in other sections of the UFSAR. The NRC Safety Evaluation Report, dated September 10, 1973, stated that the acceptance criteria were consistent with the other plants licensed at the time. The inspectors cannot determine if the NRC ever accepted the use of the additional margin, for the OBE load condition, at D.C. Cook. The inspectors are not aware of any other plants that have a Safety Evaluation Report documenting approval to utilize the one third increase. D.C. Cook is a pre-standard review plan (NUREG-0800) plant; however, the inspectors have noted for context, that NUREG-0800 as well as the AISC Specification for Safety-related Steel Structures for Nuclear Facilities, N690, has always specified use of normal allowable stresses without the one third increase. For the SSE load condition, the inspectors noted that the calculated stresses in both the crane and the auxiliary building structure were less than the allowable stresses and the SSE load condition was consistent with the licensing basis per the UFSAR. Since the SSE load condition was satisfied, for lesser seismic events, such as the OBE event, the inspectors concluded that the crane would retain its ability to safely hold and lower the load. The use of higher allowable stresses for the OBE load condition is a design margin concern used to justify continuing plant operations following seismic events less severe than the OBE. Therefore, the inspectors concluded that there was no immediate safety concern with the conduct of dry cask operations. Whether the one third increase for the OBE load condition was permitted by D.C. Cooks licensing basis, and if the change was correctly applied using 10 CFR 50.59, will be categorized as a URI (URI 05000315/2012004-03; 05000316/2012004-03; 07200072/2012001-01, Design Basis of Seismic Category I Structures and Equipment). Further review of the sites design and licensing basis was needed with assistance from the Office of Nuclear Reactor Regulation through a Task Interface Agreement. |
| Site: | Cook  |
|---|---|
| Report | IR 05000315/2012004 Section 4OA5 |
| Date counted | Sep 30, 2012 (2012Q3) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | M Mitchell J Lennartz J Neurauter J Ellegood V Meghani R Temps P Laflamme M Learn C Morrell R Edwards J Parrotv Meganij Ellegood J Mancuso K Riemer M Mitchell R Edwards T Taylor |
| INPO aspect | |
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Finding - Cook - IR 05000315/2012004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Cook) @ 2012Q3
Self-Identified List (Cook)
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