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Bent Anchor Bolts in Boiling Water Reactor Torus Supports
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 January 24, 1989 Information Notice No. 89-06: BENT ANCHOR BOLTS IN BOILING WATER REACTOR TORUS SUPPORTS Addressees: All holders of operating licenses or construction permits for boiling water reactors (BWRs) with Mark I steel torus shells. Purpose: This information notice is being provided to alert addressees to the discovery of bent anchor bolts in BWR torus shell supports. It is expected that recipi- ents will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, sugges- tions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: During recent NRC inservice inspections (50-321/88-03 and 50-366/88-03) at E. I. Hatch Nuclear Plant, inspectors found a rock bolt anchoring a torus shell support bent about 3/4 inch. The NRC requested that the Georgia Power Company (GPC or licensee) perform a detailed survey of all torus anchor bolts in the E. I. Hatch Plant, Units 1 and 2, and determine the extent of bolt distortions. The licensee found 190 bolts in Unit 1 bent from 1/8 inch to 1 inch, with 45 of the bolts bent in excess of 1/2 inch. In Unit 2, the bolt distortions were not as severe. The subject rock anchor bolts were added to the torus supports to accommodate the vertical torus hydrodynamic loads that were identified in the 1970s during the Mark I containment systems review. The bolts were installed in slotted holes in the column support bases to allow for some lateral movement of the supports while resisting vertical hydrodynamic loads. However, the licensee believes that at the E. I. Hatch Plant the torus column supports experienced unexpected lateral displacements due to weld induced radial shrinkage of the torus as a result of the Mark I program modifications performed several years ago. These modifications consisted of welding T-stiffeners, saddle overlays, and conical web plates to the torus shell. The shrinkage of the welds resulted in excessive radial movement of the torus and the torus supports. The excessive radial displacement of the torus supports is believed to have caused the edges of the slotted holes in the column support bases to push against the anchor bolts and to eventually bend them. 8901170031 .. IN 89-06 January 24, 1989 Page 2 of 2 The licensee has performed an evaluation on the load capabilities of the bolts using 3/4 inch deflections as the criterion and found that their capacities have decreased from 310 kips to 230 kips. The licensee has not completed the evalu-ation on the bolt load carrying capacity using 1 inch deflections. On the basis of preliminary evaluations, the licensee concludes that the torus is adequately anchored to accommodate anticipated hydrodynamic loads. Discussion: Although rock anchor bolt distortions may not immediately affect plant operations, the NRC staff considers such distortions to be significant since the bolt load capabilities may be greatly reduced, and the bolts may crack and break if verti-cal hydrodynamic loads are applied. Anchor bolt distortions, if excessive and not corrected, may lead to the fracture of the torus and may jeopardize contain-ment integrity. There are a number of factors, ranging from temperature changes, methods and sequence of construction, design of the column base supports, and type and magnitude of loads applied, that can influence the movement of the torus supports. Depending on the allowances made for such movement in the design of the slotted holes in the support bases, the anchor bolts may be distorted by various means. In view of this fact, it is possible that varying degrees of anchor bolt distortions may exist at different nuclear power plants. Ac- cordingly, addressees may wish to inspect and evaluate the conditions of the torus supports at their plants to determine if any problems similar to those described above exist and to assure that the structural integrity of the torus shell is being maintained. No specific action or written response is required by this information notice. If you have any questions about this matter, please contact one of the techni- cal contacts listed below or the Regional Administrator of the appropriate regional office. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: Chen P. Tan, NRR (301) 492-0829 Jaime Guillen, NRR (301) 492-1170 Attachment: List of Recently Issued NRC Information Notices .. Attachment IN 89-06 January 24, 1989 Page 1 of 1 LIST OF RECENTLY ISSUED NRC INFORMATION NOTICES _____________________________________________________________________________ Information Date of Notice No._____Subject_______________________Issuance_______Issued to________ 89-05 Use of Deadly Force by 1/19/89 All holders of OLs Guards Protecting Nuclear for nuclear power Power Reactors Against reactors. Radiological Sabotage 89-04 Potential Problems from 1/17/89 All holders of OLs the Use of Space Heaters or CPs for nuclear power reactors and test and research reactors. 89-03 Potential Electrical 1/11/89 All fuel cycle and Equipment Problems major nuclear materials licensees. 89-02 Criminal Prosecution of 1/9/89 All holders of a Licensee's Former President U.S. NRC specific for Intentional Safety license. Violations 88-23, Potential for Gas Binding 1/5/89 All holders of OLs Supp. 1 of High-Pressure Safety or CPs for PWRs. Injection Pumps During a Loss-of-Coolant Accident 89-01 Valve Body Erosion 1/4/89 All holders of OLs or CPs for nuclear power reactors. 88-46, Licensee Report of Defective 12/30/88 All holders of OLs Supp. 2 Refurbished Circuit Breakers or CPs for nuclear power reactors. 88-101 Shipment of Contaminated 12/28/88 All holders of OLs Equipment between Nuclear or CPs for nuclear Power Stations power reactors. 88-100 Memorandum of Understanding 12/23/88 All major nuclear between NRC and OSHA materials licensees Relating to NRC-licensed and utilities Facilities (53 FR 43950, holding CPs and October 31, 1988) OLs. _____________________________________________________________________________ OL = Operating License CP = Construction Permit ..
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