ML19305D367

Responds to IE Bulletin 79-02 Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts. Torque Verification of All Expansion Anchors on Supports for 2.5- Inch Diameter & Larger Piping Completed Satisfactorily

ML19305D367
Person / Time
Site:	Cooper
Issue date:	02/05/1980
From:	Pilant J NEBRASKA PUBLIC POWER DISTRICT
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
IEB-79-02, IEB-79-2, NUDOCS 8004140479
Download: ML19305D367 (4)

Text

r .

• ~*

tcc CEMM QS p0R M t.POR 7 ocnc

%* .  ! Nebraska Public Power District ' " Ect'c'd@E Sc

.,l .J -

States C February 5,1980 Mr. Karl V. Seyfrit. Director U.S. Nuclear Regulatory Com.nission Office of Inspection and Enforcement Region IV 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011

Subject:

IE Bulletin No. 79-02 " Pipe Support Base Place Designs Using Concrete Expansion Anchor Bolts"

Reference:

1) Letter from J. P11 ant to K. Seyfrit Dated December 10, 1979, Same Subject

Dear Mr. Seyfrit:

Revision 2 to the subject bulletin required a factor of safety of five for shell type anchors when subjected to maximum support loadings including the SSE condition. As submitted in Reference 1, the original design cri-carion for Class IS pipe hangers and supports at Cooper Nuclear Station was a factor of safety of five for loading conditions including the OBE, which corresponds to a factor of safety of approximately 2.5 for the SSE. The impact of this major clarification in Revision 2 has been discussed at length with the staff, and as a result the following information is sub-mitted per the staff's request.

Requese Submit a schedule of the efforts to be accomplished in order to obtain a factor of safety of 5 for loading conditions including the effects of SSE.

Response

1. Torque verification of all expansion anchors on supports for 2-1/2" diameter and larger piping has been completed with satisfactory results (less than .4% defective in approximately 5600 anchor bolts cesced). All bolts reported as unacceptable were immediately re-placed with properly torqued wedge anchors as manufactured by ITT Phillips Drill Division.

2. All Class IS hangers and supports supporting lines 2-1/2" and larger are currently being further inspected for additional assurance of parameters added in Revision 1 of the subject bulletin. Further in-spection involves re= oval of each anchor bolt and a check for:

3004140 C)

Mr. Kcr1 V. S:;yfrit F2bruary 5,1980 Prgs 2 embedment depth, thread engagement, plate hole size, bolt spacing, edge of concrete member, and full expansion of the concrete anchor.

This inspection is approximately 95% complete and is being done in conjunction with hanger modifications identified to date. Anticipated completion is during the refueling outage commencing March 15, 1980.

3. Analytical work has been completed and recommended fixes for supports with factors of safety less than five for the loading conditions in-cluding the OBE have been proposed. (This amounted to approximately 134 of the 1642 hengers reviewed which fell into the subject bulletin catego ry.) Approximately 80% of those hangers identified as having a marginal factor of safety have now been modified. The remainder are expected to be completed during the outage commencing March 15, 1980.

4. During the March 15, 1980 outage all inaccessible supports found to be below a factor of safety of five for shell and/or 4 for wedge type anchors for loading conditions including the SSE will be reviewed and/

or modified as necessary.

5. After the upcoming refueling outage, review and/or modification will commence for accessible supports found to be below a factor of safety of five for loading conditions including the SSE.

Under this analytical review the architect-engineer for CNS has proposed to extend its evaluation to incorporate the following additional criteria:

A) Development of increased ultimate capacity of the expansion anchor's permissible loading due to actual concrete strength present (i.e.,

f'c = 3500 psi original vs. 5000 psi from statistical review of actual 90-day concrete cylinder breaks for various building areas) .

B) Utilization of the combination of spatial components for seismic loads as described in Reg. Guide 1.92, Dec. '74, Par. C.3, for loading conditions including the SSE. (Under the loading con-dition for OBE this approach was not used. Each spatial seismic component was applied simultaneously.)

C) Utilization of an elliptical tension shear interaction formula developed by fitting a curve to previously published test data.

This curve utilizes the tension and shear ratios raised to the 4/3 power and set equal to 1. -

The architect-engineer for CNS estimates that at least 90-95% of the supports will meet a factor of safety of five or greater when loading conditions including the SSE are established and after the required fixes for OBE loadings are completed. Of the 5 to 10% remaining, the minimum factor of safety is approximated to be 3.5 or greater for SSE loading conditions.

A minimum factor of safety of 3.5 is considered more than adequate to ensure the safe shutdown capability of CNS since all anchor bolt installation parameters will have been verified; however, these supports will be investigated and/or modified as necessary based upon combinations of the following considerations:

- Mr. Karl V. S:yfrit E brunry 5, 1980 Paga 3 A) Supports with the lowest factor of safety will be modified first.

B) At least one redundant loop of all essential systems will be initially modified to upgrade its factor of safety to an accept-able level.

C) The benefit gained in elevating the factor of safety versus the radiation dose incurred to personnel will be considered.

From a safety standpoint it is inadvisable to modify numerous supports on an operating system simultaneously; therefore, increasing the number of crews performing the modifications is not beneficial. There are, and have been since May 1979, 10 to 15 people performing piping support modifications at CNS on an overtime basis.

It must be recognized that because of confined pipe spacing, modifications to supports in an operating plant take a considerable number of iterations between the station staff and the architect-engineer performing the ana-lytical work. These interactions occur due to unforeseen interference problems, work space problems, temporary support conditions, etc. Modi-fications to one support may take on the order of weeks. This additional i time required is compounded by the finite number of stress analysts in the industry and the concurrent intensive analytical effort being per-formed under IE Bulletin 79-14.

Request Regarding the epoxy used for the installation of anchors at CNS:

a) what type epoxy was utilized b) where and how was it used c) did procedures govern the installation practices d) is any test data available on its use

Response

The Phillips "S" type anchors at CNS were installed with an epoxy adhesive; Colma-Dur Bonding Compound as manufactured by the Sika Chemical Corporation.

The installation was done in accordance with the contractor's procedure JP-1007 Rev. 2 (approved by the architect-engineer) which required the shell (with plug inserted) to be dipped into the adhesive prior to installation into the previously drilled hole. The adhesive was utilized specifically to reduce the possibility of loosening of the expansion anchors under cyclic or vibratory loadings. As an additional benefit, approximately 5% increase in ultimate strength (based on similar installations) is gained; however, no additional credit for this benefit was taken in the analytical calculations of the required factor of safety. No specific testing of the epoxy has been performed; however, several Phillips "S" type anchors have been replaced with larger wedge type anchors to comply with the required factors of safety and during the replacement process our field experience indicaces that the epoxy is of definite benefit.

c Mr. Karl V. Szyfrit February 5, 1980 Page 4 If you have any questions regarding this response, please contact me.

Sincerely,

. f -

Jay M. Pilant Director of Licensing and Quality Assurance JDW/cmk L