1CAN118604, Discusses Results of Volumetric Exam of Reactor Coolant Pump a Welds as Required by First 10-yr Inservice Insp Program. Analysis Shows Pump Casing to Be Structurally Sound W/Flaw Present.Calculation Repts Encl
| ML20213F461 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 11/11/1986 |
| From: | Enos J ARKANSAS POWER & LIGHT CO. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20213F464 | List: |
| References | |
| 1CAN118604, NUDOCS 8611140217 | |
| Download: ML20213F461 (3) | |
Text
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oA, o ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 UTTLE ROCK ARKANSAS 72203 [501)371-4000 November 11, 1986 1CAN118604 Mr. John F. Stolz, Director PWR Project Directorate No. 6 Division of PWR Licensing - B U. S. Nuclear Regulatory Commission Washington, DC 20555
SUBJECT:
Arkansas Nuclear One - Unit 1 Docket No. 50-313 License No. DPR-51 RCP Weld Flaw Indication
Dear Mr. Stolz:
Technical Specification 4.2.2 for Arkansas Nuclear One, Unit 1 (ANO-1),
states that post-operational inspections of components shall be made in accordance with the methods and intervals indicated in Section XI of the ASME Boiler and Pressure Vessel Code.
Applicable addenda as required by 10CFR50, Section 50.55a(g) shall be used, except where specific written relief has been granted by the NRC.
AP&L's Inservice Inspection (ISI)
Program is based on the requirements of the 1980 Edition through Winter 1981 Addenda of Section XI of the ASME Code, and remains in effect until December 19, 1994 (for ANO-1).
During the current refueling outage, we conducted a volumetric examination of the "A" Reactor Coolant Pump (RCP) welds as required by our first 10 year ISI Program, by performing a radiographic (RT) examination of the pump casing weld and a visual examination of the casing.
The RT indicated the presence of a flaw which exceeded the allowable indication standards of IWB-3000.
The indication is best described as a series of slag inclusions having an effective length (per ASME Section XI Criteria) of 5.66 inches.
It is located in the vertical weld which ties together the two scroll welds of the pump casing (see Figure 1).
Radiographic parallax techniques indicate that the top of the indication is at least 1.5 inches below the outside surface of the weld.
The weld is approximately 2.6 inches thick in this area.
It is believed that the flaw is small and does not continue very l
deep into the weld (as is typical of slag inclusions) although this cannot l
be established by RT techniques.
Application of special UT techniques (although unable to fully characterize the flaw) has shown rather conclusively that the flaw does not extend through the wall.
8611140217 861111 PDR ADOCK 05000313 G
PDR C)
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MEMBER MIDOLE SOUTH UTIUTIES SYSTEM J
a Mr. John F. Stolz Novembsr 11, 1986 Following identification of this flaw, the original preservice radiographs were reviewed to determine whether or not any flaw existed at this location preservice. Our review of the original RT shows a series of five small inclusions along a line approximately 5.66 inches long.
These inclusions were originally determined to be acceptable per the Code.
The new (current) radiograph shows clearly these same 5 flaws, but due to improved RT technology and films, it also identified 5 additional (and fainter) inclusions dispersed along the same line and between the original inclusions. What is now shown is a series of 10 unconnected flaws spread along a line approximately 5.66 inches long (see Figure 2).
Because of the quality of the preservice radiograph in the subject area, equipment was brought on site which could scan and perform computer enhancement of the film.
This technique worked very well and allowed us to characterize the flaw on the original film more clearly.
From this examination, we were able to determine conclusively that all parts of the flaw did indeed exist preservice and appeared essentially identical to the flaw identified in the current inservice RT and that no growth of the flaw has occurred during more than 12 years of pump service.
As such, we were also able to conclude that no inservice flaws exist.
Following this, a review of ASME Section XI was made to determine the proper course of action.
Section XI essentially addresses 2 types of flaws, preservice and inservice.
Preservice flaws discovered during construction and exceeding the acceptance criteria of IWB-3000 require the flaw to be repaired prior to placing the component in service.
For inservice flaws,Section XI requires a variety of actions, depending on the particular flaw, ranging from analysis and further inspection to repair and/or replacement.
Section XI does not specifically address the current ANO-1 situation, that is, a preservice flaw which was not detected and corrected prior to service but discovered later in time after the component was placed in service.
Given this, literal Code compliance is not possible, therefore, our course of action has been established to ensure that we meet the " intent" of Section XI.
In order to establish the " intent" of Section XI, the case of an inservice flaw discovered during operation was evaluated.
For example, if the existing flaw had been discovered at the end of the 1st operating cycle for "A" pump,Section XI would have required an evaluation (by analysis) to show acceptance with IWB-3600 and subsequent inspections at approximately 3, 7, and 10 years in accordance with IWB-2420(b).
These subsequent inspections would have been performed to ensure that the flaw was not propagating.
If the analytical evaluation and the 10 year inspection conclude that the flaw is acceptable and has not grown, the Code concledes the flaw is acceptable and no further special attention is necessary for that flaw and/or component.
Following this line of reasoning, several actions have been taken to demonstrate acceptability of the existing flaw.
Analyses were performed in accordance with IWB-3122.4.
The calculations were conservative in that the flaw depth was assumed to be 1.1 inches (the flaw starts 1.5 inches from the top of the weld and is assumed to continue to the inside surface of the weld).
It should be noted that we have strong indication from the UT
4 B
Mr. John F. Stolz Novembsr 11, 1986 measurement that no throughwall indication exists on the inside weld surface. The calculations also received an independent third party review to ensure Code compliance was met.
From these calculations (attached) it was shown that the flaw is acceptable in accordance with the acceptance criteria of IWB-3612.
Comparison of the enhanced original radiograph to the current (over 15 years later) radiograph shows conclusively that the flaw has not grown over the service period.'
Given the above, we have concluded that Code compliance has been achieved.
That is, the flaw is known to have existed for greater than 10 years and not to have grown over that period of time.
Analysis has shown the pump casing to be structurally sound with the flaw present.
Inspection of additional pumps is not believed to be required by the Code because the flaw actually found was not an inservice flaw but a preservice flaw.
However, a review of original radiographs for the other 3 RCPs was conducted to look for similar preservice flaws.
The computer enhancement process showed us that "C" RCP and "D" RCP had no indications of any unacceptable preservice flaw indications.
The original preservice radiograph of "B" RCP casing weld (in the general area of the inclusion on "A" RCP) indicated a very small and faint (as compared to the "A" RCP) inclusion about 0.625 inches long.
This flaw was identified preservice and determined to be acceptable per the Code.
Computer enhancement of the original radiograph indicates that the flaw may extend to a length of approximately 1.5 inches.
The results of "B" RCP evaluation and analysis will be reported in future correspondence.
This letter and attached calculations are submitted to you in accordance with IWB-3125(b) for your review and concurrence that Code compliance.has been achieved in that the " intent" of the Code has been met for a situation that is not specifically addressed by the Code.
Very truly yours, 2
g J. Ted Enos, Manager Nuclear Engineering and Licensing JTE/GWW/
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