ML20080G871
| ML20080G871 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/15/1983 |
| From: | Hukill H GENERAL PUBLIC UTILITIES CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 5211-83-258, NUDOCS 8309200376 | |
| Download: ML20080G871 (3) | |
Text
GPU Nuclear Corporation NggIg7 Post Office Box 480 Route 441 South Midoletown, Per.nsylvania 17057-0191 717 944 7621 TELEX 84-2386 Writer's Direct Dial Number:
September 15, 1983 5211-83-258 Office of Nuclear Reactor Regulation Attn:
J. F. Stolz, Chief Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Sir:
Three Mile Island Nuclear Station, Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-289 Mnke-Up/High Pressure Injection Nozzle /
Thermal Sleeve Integrity This letter provides additional information requested by the NRC Staff on the integrity of the TMI-l Make Up/High Pressure Injection (MU/HPI) nozzles and safe-ends. This information was requested in a meeting with B&W Licensees and B&W representatives on March 8, 1982.
As you are aware, the B&W Owners Group established a Task Force to addre s findings at several B&W Plants where instances of loose, cracked, or missing thermal sleeves were identified.
GPU Nuclear did not formally participate in the Task Force because the TMI-l safe-end design differs from the other B&W Plants (use of Inconel and no insulation) and NDE exams indicated no degrada-tion of thermal sleeves or safe-ends.
When the problem was first discovered at the other B&W Plants, TMI-l conducted a complete NDE exam with the following inspection results:
From site inspection reports:
A.
TMI-l Make-Up and HPI nozzles have been inspected by several NDE methods, depending on particular area, and in several instances, more than once.
1.
Radiographic o Safe-end to valve weld o Presence of weld beads o Location of thermal sleeve OO f o " Cap" between thermal sleeve and safe-end g
GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation 8309200376 B30915 PDR ADOCK 05000289 P
t
-Mr. J J. F. Stolz 5211-83-258 2.
- Liquid Penetrant Safe-end' from nozzle to valve, including welds o
- 3. - Ultrasound o - Safe-end from nozzle to valve, including welds
'The radiographic inspection aimed at detecting a " gap" between the thermal sleeve and safe-end was conducted twice.
An " intermittent line" appeared on the D-1 film.
Three additional views were taken-to determine that this was a nonrelevant indication.
The ultrasonic examination was capable of high sensitivity since the procedure benefited from methods developed from the~TMI-l work on IGA attack in stainless steel piping.
All sleeves are~in place. No cracking is in evidence in either nozzles or thermal sleeves.
5 B.
At TMI-1, the weld buttons are adequate protection against gross move--
ment of the. thennal sleeve.. There is no evidence of a problem of any kind at TMI-1.
Subsequent to the above inspections, the following reasons were identified by the B&W Owners Group Task-Force as a basis-for a scenario leading to the
~
degradation of the MU/HPI thermal sleeves and_ safe-ends at the other B&W plants:
1.
The thermal sleeve was-loose tolbegin with,:either from an inade-quate mechanical roll due to too little wall thinning, or from inadequate or nonexistent quality assurance of the fabrication p rocess.
2.
Loss of contact pressure precedes safe-end cracking.
- 3..High cycle, reverse direction make-up.line/ annulus flow causes crack initiation on the ID surface of the safe-end.
Pumping action as a result 'of the motion of the loosened thermal sleeve displaces fluid in the annulus between it and the safe-end due to turbulent buffeting.
4.
At' low flow, hot back flow occurs through the thermal sleeve.
Thermal stress cycles, by this mechanism,-propagates cracks ini-
.tiated:in Item 3 above.
Increasing the 3m flow reestablishes
- cooling flow in the design direction.
It_must be emphasized that there had been no fabrication quality assurance criteria on rolling: process: no minimum wall thinning, no radiography, no profilomet ry.
1:
By comparison, the factors inherent in the TMI-1 design that prevent the above scenario include:
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-...a Mr. J. F. Stolz. 5211-83-258 1.
TMI-1, unlike all other B&W plants, uses Inconel safe-ends.
For the same temperature the stainless steel thermal sleeve will bear more firmly on the safe-end since the coefficient of expansion of the stainless is considerably greater than for the Inconel.
2.
Also, unlike other B&W plants, the safe-end is not insulated. This fact will keep the average temperature of the safe-end at a lower value thereby causing the thermal sleeve to bear more firmly on the safe-end.
3.
IMI-1, unlike all plants experiencing problems, has seven impeller blades in each Reactor Coolant pump.
Other B&W Plants experiencing problems have five -impeller blades.
A five impeller blade pump causes pressure pulses in the RCS closer to the natural frequency of the thermal sleeve. Vibration has been identified as a possible mechanism to degrade the contact expansion residual pressure.
4.
TMI-1 maintains a normal continuous mcke-up flow from 3-5 gpm to prevent nozzle damage due to backflow.
5.
The TMI-l assembly is presently in a condition where all stress relaxation has already occurred.
The mechanical integrity of the attachment of the thermal sleeve to the safe-ends is goverened by stress relaxation of the Inconel safe-end. Tension in the safe-end o -
is the basis for the contact pressure that secures the sleeve in place.
If sigrificant stress relaxation occurs, the fit-up will degrade with time.
If stress relaxation is not significant then.
the sleeve will remain secure.
Data indicates that any stress relaxation occurs after a few hours.
Based on the above, our evaluation concludes that no potential for a safety concern exists at TMI-1.
There have not been any loose or cracked thermal sleeves found.
By inspection, the residual contact stress from fabrication is pre-sently adequate at TMI-1.
It can be shown from the creep stress relaxation
~
properties of Inconel, the safe-end material, that this contact pressure will not appreciably decline, either at the double duty nozzle (nozzle used for normal makeup and for HP1) or the HPI only nozzle.
The assembly is adequate
-as is *nd will reamin adequate indefinitely because creep stress relaxation will not reduce the residual contact pressure at the service conditions of 540 F.
Sincerely, L.
.D.Nbkill Director, TMI-l HDH :PGD:vj f.
cc:
J. Van Vliet R. Conte
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