ML20199B446
| ML20199B446 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 06/10/1986 |
| From: | Andrews R OMAHA PUBLIC POWER DISTRICT |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| LIC-86-229, TAC-61724, TS-FC-86-363, NUDOCS 8606170151 | |
| Download: ML20199B446 (9) | |
Text
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9 Omaha Public Power District 1623 Harnt!y Orriaha. Nebraska 68102 2247 402:536 4000 June 10, 1986 TS-FC-86-363 LIC-86-229 Mr. Ashok C. Thadani, Project Director PWR Project Directorate #8 Division of PWR Licensing - B Office of fluclear Reactor Regulation U.S. Iluclear Regulatory Commission Washington, DC 20555
References:
(1)
Docket No. 50-285 (2)
Letter OPPD (W. C. Jones) to NRC (J. R. Miller) dated 9/26/83 (LIC-83-226)
Dear Mr. Thadani:
Relief Requests from ASME Boiler and Pressure Vessel Code,Section XI The Omaha Public Power District (0 PPD) submitted the Inservice Inspection Pro-gram for the Second Ten-Year Interval in Reference (2).
Since that time, OPPD has completed a review of the criteria of the winter 1980 Addenda to the ASME Boiler and Pressure Vessel Code (the Code) and has determined that certain re-quirements are impractical for the Fort Calhoun Station.
The attachment iden-tifies those code requirements determined to be impractical and provides infor-mation te support this determination.
Pursuant to 10 CFR 50.55a(g)(5)(iii),
OPPD, th :refore, requests approval of the attached relief requests for the Fort Calhoun Station.
The $150.00 application fee required by 10 CFR 170 is also enclosed.
Sincerely, 8606170151 860610 g
PDR ADOCK 05000285 G
PDR R. L. Andrews Division Manager Nuclear Production RLA/rh Attachment cc:
LeBoeuf, Lamb, Leiby & MacRae h
h 1333 New Hampshire Avenue, N.W.
Washington, DC 20036 l(f6 00
[O47 Mr. D. E. Sells, NRC Project Manager Mr. P. H. Harrell, NRC Senior Resident Inspector I
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Exceptions to Compliance with the Examination Requirements of the Winter 1980 Addenda to the ASME Boiler and Pressure Vessel Code,Section XI Rules for Inspection of Nuclear Power Plant Components Exceptions, Class 2 Examinations Item No. C5.20 The following are inaccessible piping welds:
Figure No.*
Line No.
Weld No.
B-4 28-MS-2001 12 through 16 12-BC-1,2 & 3 15-BC-1,2 B-6 28-MS-2002 12 through 16 12-BC-1,2 13-BC-1 15-BC-1,2 & 3 '
B-7 16-FW-2001 1,2, & 7 B-8 16-FW-2002 1,2,3,4 and 11 The welds listed above, with the exception of #7 on Figure B-7 and #11 on Fig-ure B-8, are inaccessible due to a cable wrapping which holds a system of heavy metal slats in place over the Main Steam and Feedwater Systems in Room 81 of the Fort Calhoun facility.
The Fort Calhoun Station Updated Safety Analysis Report (USAR), Appendix M, Section 3.5.8, has this to say about the protective enclosures around the main steam and feedwater lines in Room 81:
"A protective enclosure (has been) provided around the main steam and feedwater lines between the penetration sleeves and the first isola-tion valves, where a large rupture is postulated.
This enclosure, although designed primarily to limit the effects of jet impingement, also serves to minimize the reaction effects of a longitudinal rupture by containing the jet and preventing the form-ation of an unbalanced external force."
Also, a summary of the design criteria for the Main Steam and Feedwater pip-ing protective enclosuies is given in Attachment C to Appendix M of the USAR, a copy of which is attached with this exemption request.
These documents reflect the results of the " Fort Calhoun Unit 1 Pipe Rupture Analysis of Feedwater and Mainsteam Outside of Containment" by Nuclear Ser-vices Corporation (Campbell, California) done in 1973, and on file in the OPPD Nuclear QA/ Records Management System.
See copies of these figures from the 10 Year Inservice Examination Plan' by EBASCO Services, Inc., for the Fort Calhoun Station, Second Interval, supplied with this request.
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_-__-_-_--_-_-_--_-_a
Basically, the conclusion of this report is that the design of the protective enclosures is sufficient to assure the mitigation of a main steam line rup-ture or feedwater rupture in Room 81 so that all vital control capabilities will be maintained.
Updated Safety Analysis Report Section 14.12, " Main Steam Line Break" assures us that the radiological consequences of a Main Steam Line Break, concurrent with steam generator tube rupture will not exceed the exposure limits of 10 CFR Part 100.
Weld #7 on B-7 and #11 on B-8 were examined during the 1985 outage. However, it was discovered that because these welds are located slightly inside of the bio-shield penetrations for the feedwater lines and only a limited examina-tion of the welds could be made using surface techniques.
These welds were examined to the extent practical (roughly 40% of the total weld length) during the 1985 ISI. The inttrference caused by their physical location does not prevent a 100% one sided Ultrasonic exam.
Because 100% of the weld volume can be covered with the UT exem, OPPD believes that the ultrasonic examinations will provide an adequate examination of the weld in the upcoming years. OPPD will, therefore, continue the surface exams to the extent possible, and do 100% of the required volumetric exams as scheduled in the normal ISI schedule.
Last, it should be noted that the required IWA-5000 system leakage test moni-tors the feedwater welds.
In conclusion, the OPPD believes that between the Ultrasonic Exams which are required by the code and can be performed, and the routine performance of the system leak checks that we have sufficient alternate exams to assure the integrity of weld 7 (Drawing B-7) and weld 11 (Drawing B-8) and can exempt these welds from the surface exam requirements of Section XI.
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ATTACHMENT C MAIN STEAM AND FEEDWATER PIPING PROTECTIVE ENCLOSURES Design Summary Those portions of the main steam and feedwater lines within Room 81 which are considered susceptible to a large break were provided with a protective enclosure designed to contain the steam or fluid to the extent that severe impinge-ment of jets on safety-related equipment or structures cannot occur.
The protective enclosures consist of a series of longitudinal flat steel bars placed around the outside of the pipe insulation and held in position by a series of independent loops of wire rope.
Design Assumptions - Main Steam Line Enclosu_es The critical break for the design of the enclosure is the longitudinal large break. In accordance with AEC criteria this is taken to be a slot break with a length equal to twice the pipe diameter and an area equal to the inside area of the pipe.
In the case of the main steam line the area of the break is 531 square inches. The maximum reactive force of the steam issuing through this break was obtained by means of a time-dependent dyna.c.ic analysis. The maximum calculated force is 559 kips.
Initially the steam jet is considered to impinge either on one or on
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two contiguous longitudinal bars. Under an assumed instantaneous application of load the bars would deform plastically at a load of 1.2 times the maximum jet force based on the minimum specified yield strength of the bars. Plastic defor-mation is limited to approximately twice the elastic deformation.
For this initial phase the wire rope was designed to resist a force equal to twice the jet force on the assumption that full reversal of the jet Based on the yield design of the bars this force is increased by a occurs.
factor of 1.2 and by an additional factor of 1.25 to account for variation in the yield strength of the bars. Any effect of the insulation in reducing the dynamic effect is conservatively disregarded.
Following this initial phase the entire annulus between the pipe and the enclosure is filled with steam.
In this case there will be leakage through the bars due to initial small gaps and widening of these gaps as the wire rope stretches under load. As a result, the pressure within the annulus will be less than the initial pressure within the pipe. Two cases are considered for design of the wire rope:
- 1) uniform pressure within the annulus and; 2) a combination of jet load on the bars directly in front of the assumed break and a uniform pressure within the remainder of the annulus.
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Within several hundredths of a second the jet load reduces to a rela-C tively steady state value. The load cases described above are considered for the appropriate reduced load and pressures. For these cases the wire rope is assumed to be at a temperature of 500*F and the reduced strength of the wire rope corresponding to this temperature is used.
At the main steam safety valves the spacing of the wire rope is increased to clear the valve nozzles and their reinforcing plates. At these locations the longitudinal enclosure bars are thickened and reinforced with stiffener plates to conform to the criteria given above. The wire rope size is increased and the spacing immediately adjacent to the nozzles is decreased to compensate for the increased spacing between wire rope loops in this area.
In order to maintain the configuration of the bars following pipe rupture, the individual bars are tightly fastened to the wire rope by means of wire rope clips. Each bar is fastened by clips at a spacing of approximately one foot.
The maximum gap that may form between individual bars during pressuri-zation is conservatively calculated by assuming that only one or two bars are loaded by the jet and that the wire rope slides freely through the clips fastening the wire rope to the individual bars so that the entire stretch of the wire rope is concentrated at two gaps. For this calculation, the yield strength of the bars is taken as 45 ksi and the modulus of elasticity of the wire rope as 11 x 6
10 psi. Assuming a 10% reduction for the effects of the clamping force of the clips and friction between the wire rope and the bars over its entire perimeter, a maximum gap of 0.62 inches results. Wherever such a gap could result in a
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possible jet impingement on a safety-related item a 1/8" thick batten plate is provided under the bars to cover this gap and prevent release of a jet.
Feedwater Line Enclosure The design assumptions for the protective enclosure around the feedwater lines are similar to those for the main steam line. The loads involved however, are far smaller.
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