ML19350C737
| ML19350C737 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 04/02/1981 |
| From: | Baynard P FLORIDA POWER CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 3-041-05, 3-41-5, NUDOCS 8104060646 | |
| Download: ML19350C737 (7) | |
Text
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- 3-041-05 J,
9 06 Ngg y h-N 5 ue #g" M Pr. John F. Stolz, Chief Operating Reactors Branch #4 Division of Licensing 1, M U.S. Nuclear Regulatory Camission OY Washington, D.C. 20555 13
Subject:
Crystal River Unit 3 Docket !b. 50-302 Operating License No. DPR-72 Missing Control Rod Upper Guide 7bbe '.t
Dear Mr. Stolz:
Florida Power Corporation identified a potential loose part in the "B" Chee-through Steam Generator (OTSG), at approximately 11 ~ a.m. on March 26, 1981. Crystal River Unit 3 shutdown was initiated for furler investigation as to the source of the indication. A small piece of stainless steel was discovered and removed from the "B" OTSG and forwarded to Babcock & nilcox Company for analysis. The appearance, con-figuration, weight, material and internal thread size, and evidence of zirco-nita on the threads give us high confidence that the part is a control rod upper guide tube nut. We have evaluated the effects of continued operation of Crystal River Unit 3 with a fuel assembly missing the upper nut from one of sixteen control rod guide tubes. Our analysis has included normal generating conditions, faulted conditions, and handling. Results of our analysis have shown the guide tube will be contained within the fuel assembly by the lower end fitting and the frictional restraint of the spacer grids. Analysis has also shown lateral positioning of guide tube in the upper sleeve region will be maintained by the close diametral fit with the upper end fitting. Our attached safety evalua-tions substantiates.these conclusions. Very truly yours, FLORIDA POWER CORPORATION W P. Y. Baynard 8 04060/ot'l/ S a Support Services General Office 3201 Tnutc ourtn street soutn. P O Box 14042. St Petersburg Ferda 33733 813-866-5151 r o
Safety Evaluation for Restart of Crystal River Unit 3 with Missing Control Rod Upper Guide hbe Nut he loose piece found in the "B" Once-through S,, am Generator has undergone detailed engineering analysis (See Enclosure 1) to determine Mth a high degree of probability that it is a fuel assembly control rod upper guide tube nut (See Figures 1, 2, and 3). Although the exterior surface of the loose piece is hignly distressed, the comparison between the data obtained in the analysis performed and the actual characteristics including threadsize and number of threads for the control rod upper guide tube nut provide information for identification; evidence of Zircalloy particles on the threading internal to the nut provides further confirmation of identification. Approximately 46,000 nuts of this design have been or are in service in IBW plants with no reported problems; it is a unique isolated occurrence. It is isolated to Crystal River Unit 3 Batches 4 and 5 fuel due to an alternate designed nut for pret lous batches. he 15x15 fuel assemblies which comprise the core consist of a square array of fuel rods, guide tubes and a center instrtraentation tube supported laterally at 8 locations by spacer grids and restrained from gross axial motion by the upper and lower end fittings. He 16 guide tubes within the assembly lattice are open at the tcp end to provide a channel for insertion of the control components. Each of the guide tubes has a threaded connection et both the upper and lower ends for attachment to the upper and lower end fittings. At assembly, a nut is threaded onto the guide tube at both the upper and lower ends and then welded to the fuel assembly end fittings. Figure 1 shaws the arrangement of the 16 upper guide tube nuts. he primary fbnction of the upper guide tube nut is to provide a structural attachment between the stainless steel, upper end fittings and the Zircalloy 4 guide tubes as shown in Figure 2. Ioads applied to the upper end fittings are transferred to the assembly structure through highly redundant load paths. Each of the 16 guide tubes provides a separate load path. In addition, the upper spacer grid has a skirted attachment to the upper end fitting that provides a redtridant load path to the fuel rods and guide tubes through a frictional interface. Continued operation with a fbel assembly with one upper guide tube nut missing has been analyzed for the following operational load conditions: 1. Normal operating loads (principally the loads imposed on the upper grid by the fbel assembly holddown spring) and the resulting stresses with the load dispersed over 15 guide tubes versus 16 guide tubes. Considerable margin was available to the fuel assembly load limits. 2. Handling loads for listing and mving the assembly by the upper end fitting were examined. Lift forces transmitted through only 15 guide tubes versus 16 guide tubes left considcroble margin to the fuel assembly's limits. L
3 LOCA loads and stresses associated with lifting and impacting the fbel assembly were analysed with only 15 guide tubes, and again there was considerable margin to the limits. Analysis shows that the guide tube assembly will be contained within the fuel assembly by the attachment at the lower end fitting and the frictional restraint of the spacer grids. Analysis fbrther shows that lateral positioning of the guide tube in the upper sleeve region will be maintained by the close diametral fit with the upper end fitting grillage. Finally, calculations were run on a guide tube without an upper nut. Flow lift forces acting against the weight of the guide tube and the friction provided by fully relaxed spacer grids (End-of-life relaxation) are not sufficient to lift the guide tube out of the fuel assembly. The calculational details to support the above analyses are on file in B&W's Calculational Package Files. Conclusion Based on the analyses performed as sumarized above, we have determined that the unit is safe to operate. PYB/jw (SER)
ENCLOSURE 1 i Preliminary Evaluat$on of Unidentified Crystal River Part Evaluation Unidentified Mk B Guide Tube Crystal River Part Upper Nut Radiation Reading 20R/hr @close to contact 13R (estimated) 4R/hr @ 8" to 10" 200mr @ 30" W'ight 36.25 gm 40.65 gm e Outside Dimensions Outside Diameter of full diameter 0.875" " cylinder" ranges from across machined flats 0.709" to 0 902" 0.75" length ranges from length = 1.0" 0.861" to 0.905" Inside Dimension length of threaded end length of threaded approx. 0.630" end approx. 23/32" (0.719") diameter of threaded threaded diameter = 5/8" end ranges from 0.546" to 0.631" diameter of unthreaded diameter of unthreaded end approx. 0.460" end = 0.500" Threads per inch 24 24 No. Active Threads 14 or 15 5/8" of active threads @ 25 threads / inch = 15 Material Stainless Steel 304 or 308 Stainless Steel l Energy Dispersive X-Ray Zirconium particle - Analysis of Plastic. identified ir one Replica of inside of nut location in threads L I l PYB/jw (SER)
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