United States Nuclear Regulatory Commission - Protecting People and the Environment

Bent Anchor Bolts in Boiling Water Reactor Torus Supports

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                January 24, 1989

Information Notice No. 89-06:  BENT ANCHOR BOLTS IN BOILING WATER 
                                   REACTOR TORUS SUPPORTS


All holders of operating licenses or construction permits for boiling water 
reactors (BWRs) with Mark I steel torus shells. 


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.

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                                                            January 24, 1989
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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.


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

89-03          Potential Electrical          1/11/89        All fuel cycle and
               Equipment Problems                           major nuclear 

89-02          Criminal Prosecution of       1/9/89         All holders of a
               Licensee's Former President                  U.S. NRC specific
               for Intentional Safety                       license.

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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