TXX-4400, Requests Approval for Use of ASME Code Case N-378 Re bottom-mounted Instrumentation Seal Tables.Application of Code Case N-378 Will Not Result in Significant Reduction in Plant Safety

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Requests Approval for Use of ASME Code Case N-378 Re bottom-mounted Instrumentation Seal Tables.Application of Code Case N-378 Will Not Result in Significant Reduction in Plant Safety
ML20114B574
Person / Time
Site: Comanche Peak  Luminant icon.png
Issue date: 01/21/1985
From: Beck J
TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To: Harold Denton
Office of Nuclear Reactor Regulation
References
TXX-4400, NUDOCS 8501290333
Download: ML20114B574 (2)


Text

._ _

Log # TXX-4400

, - File # 905.4 TEXAS UTILITIES GENERATING COMPANY MKYWAY TOWEH . 400 NORTH OLIVE MTHEET. L.H. MS

  • 13ALLAN.TEXAM 73201 January 21, 1985 2L"?d2" t

Mr. Harold R. Denton, Director Office of Nucle ar Reactor Regulation

U. S. Nuclear Regulatory Commission Washington, D.C. 20555

SUBJECT:

COMANCHE PEAX STEAM ELECTRIC STATION

, DOCKET NOS. 50-445 AND 50-446 3 CODE CASE USAGE

Dear Mr. Denton:

[

l In accordance with 10CFR50.55a(a)(3) NRC approval is requested for the usage of ASME Code Case N-378 for the CPSES Units 1 and 2 bottom mounted instr:: mentation (BMI) seal tables.

g The BMI seal table is one of the terminal points of the BMI flux thimble

[ guide tubing, anchoring the tubing to the containment structure. For both

Comanche Peak units, the seal table is located on the 2700 reactor vessel l axis, 38 feet 3 inches from the RV centerline at the elevation of the RV j mating surface.

b The seal table is a rectangular plate 8 feet 5 inches long by 2 feet 6 inches wide by 3/8 inch thick. The edges are slightly dished to contain

= any incidental spillage of prin.iry water when the incore flux thimbles are partially retracted as a normal part of refueling. The seal table material is SA240 TP304.

p The BMI thimble guide tubes pass through, and are welded to, the seal table . The seal table is in turn attached to the containment structure.

7 The tubing is an ASME Code Class 1 component. Thus the seal table is an L integral attachment to a Class 1 pressure boundary, and must meet the i applicable requirements of ASME Section III Subsection NB. It functions as

> a support to transfer loads from the tubes to the building. Code Case N-378 is invoked to exempt the seal table from the requirements of NB-2500 as required by NB-2121(a).

E

! 10CFR50.55a(a)(3)(ii) makes provisions to allow for alternate code

= requirements when "cotpliance...would result in hardships or unusual

. difficulties without a compensating increase in the level of quality and sa fe ty". With the seal tables installed and the BMI guide tubing welded to h- it, ultrasonic inspection of the tables (as required by NB-2500) would be extremely difficult, if not impossible. The presence of the guide tubes 7 (which pass through the seal table), collars for the flux thimble i

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insertien/ removal tosi suppsrt block, and drain spuds would not allow inspection of sufficient volume of material to provide meaningful results.

The manufacturing process for material of this type and thickness tends to produce excellent through-thickness properties. The major loading of the seal table is in the through-thickness direction. The load carrying capacity of the seal table is greater than that of the fillet welds joining the tubing to the seal table. The relatively low loads place both the weld ard the seal table well within the applicable stre-;s limits.

Applying code case N-378 to CPSES Unit 1 and 2 seal tables will not result in any significant reduction in the safety of the plant.

Should you have additional questions in this matter, please contact this o f fice.

Respec tfully,

%F oLL John W. Beck BSD/grr c- J. J. Stefano Distribution: 15: copies + original