ML20037A597
| ML20037A597 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 08/25/1978 |
| From: | Noonan V Office of Nuclear Reactor Regulation |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8003160038 | |
| Download: ML20037A597 (3) | |
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MEMORANDUM FOR:
P.. W. Reid, Chief, Operating Reactors 3 ranch *o. 41 Division of Operating Reactorc h
. 'V. S'. Noonan. Chief. Engineering.Branc.
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SUCJECT:
EVALUATION 0F CRYSTAL' RIVER UNIT 3 STEM GENERATOR ~
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DAMAGE RESULTIHG FROM BURNABLE POISON ROD ASSE!!3LY OREAX-UP The Engineering Branch, Diviston of Operating Reactors has ravicued Florida Power Corporation's submittals dated June 3 and August 22, 1973 regarding damage to steam generator B resulting frca the bresk-up of.a burnable poison red assembly at Crystal River Unit 3.
We have concluded that the licer.sce has conducted st:fficicat inspections and repairs and that the steam.gecrator integrity ha.s been vari fied.
Howevur, we have sho concludac tnat a visual or video inspectica of the primary side of the steati generator B upper tube shacc should be conducted during the ne.tt scheduled steam generator in,pection to veri fy tha... -. ~ica related degradation has occurred.
Uncent S. Necnan, Chief Engineering Branch.
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EVALUATION OF 46 CRYSTAL RIVER UNIT 3 STEAM GENERATOR DAMAGE RESULTING FROM BURNABLE POISON ROD ASSEMBLY BREAK-UP ENGINEERING BRANCH DIVISION OF OPERATING REACTORS By letters dated June 8 and August 22, 1978, Florida Power Corporation (the licensee) submitted a summary of the repairs of steam generator tube / tube sheet welds that were damaged as a result of the break-up of a burnable poison rod assembly at Crystal River Unit 3.
The licensee's repair program included video inspection and categorization of damaged tube stubs, leak testing, a 100% free path tube check, eddy current examinations (ECT), tube plugging, and dressing of the tube stubs.
In additiori a tube to tube sheet mock-up was prepared and tested at the Babcock and Wilcox fabrication facility to verify the structrual integrity of the damaged tube sheet area.
The tube stubs extend 0.3 inches above the upper tube sheet and the fillet seal welds extend about 0.1 inch ab;v: 'Sc tubeshect.
Using vide:
inspection the damage to the tube stubs and seal welds in ste n generator B was categorized as follows:
Class I (55% of the tubes)
Impact or roll over of tube ends may exist on the 0.D. Or I.D.
Deformed material does not include weld metal.
Class II (6% of the tubes)
Partially separated chip (silver); may exist with Class I, III, or IV damage.
Class III (26% of the tubes)
Minor weld damage extending into the upper 1/3 of weld metal.
Class IV (17% of the tubes)
Damage to the tube ends and weld metal in excess of Class III.
(Above percentages exceed 100% since Class II can exist with Class I, III, & IV).
Damage was in the form of cold working.
No cracks were observed.
Visual examination of steam generator A revealed no debris or. the upper tubesheet, no tube end damage and no tube-to-tubesheet weld damage.
The leuk tightness of the seal welds in both steam generators was verife oy pressurizing the partially filled secondary side of the steam generator with helium and inspecting each weld individually with a mass spectrometer capable of detectirig a 10-3 cc/sec leak.
No leaks were observed.
i gg 2 5 TBTS A 100% free path check of all tubes in steam generators A and B was performed.
Seven tubes in steam generator B which had debri lodged in them that could not be removed were plugged.
Eddy current inspections of 3% of the tubes plus the 19 tubes from which debri was removed was conducted in steam generator B.
Seven percent of the tubes in steam generator A were inspected, resulting in the plugging of one tube which had an ECT indication.
No significant ECT indications other than those described were observed.
4 Dressing of the damaged tube stubs consisted of the removal of any metal slivers with hand tools.
The licensee has performed flow calculations based on the reduced cross sections of the tube ends and has determined the effects to be negligible.
A ten tube mock-up of the tubesheet and damaged tube stubs was prepared by B&W.
Hardness traverses across the damaged tube ends, welds, and into the clad showed the effects of significant cold working.
Samples of the tube to tubesheet joints that were expanded, welded, and stress relieved per B&W fabrication procedures were tested with the welds completely t emoved.
Results of these tests showed a minimum strength of 2500 pounds axial tube load to initiate motion of the tube relative to the tubesheet
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and a minimum lead of 4520 pounds to completely free the tube from the tubesheet.
The maximum axial lead that the joint will experience during operation is 1100 pounds.
The 23 inch thick tubesheet attenuates any lateral leads and their resulting moments.
The licensee has conducted sufficient inspections of the damaged tube stubs, tutesheet, and steam generator tubes to discover any significart damage and adequate repairs have been completed.
The leak tightness of the seal welds has been verified and the mechanical integrity of the expanded joint has been demonstrated.
The mechanical joint integrity is not dependent on the seal welds.
The damace to the tube stubs and tubesheet was in the form of cold working which r ecuces the materials resistance to corrosion.
If corrosion occurs, the corrosion rate in the primary coolant environment would be very slow and would not effect the tube or tubesheet integrity during the remainder of the current cycle of operation.
However, during the next shutdown a visual or video inspection should be conducted to verify that no detrimental corrosion affects have occurred.
The Crystal River Unit 3 technical specifications currently impose a 1.0 gpm primary to secondary leak rate limit which will ensure integrity of the steam generator primary coolant boundary during operation.
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