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.
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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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