ML18066A625
| ML18066A625 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 08/26/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML18066A624 | List: |
| References | |
| NUDOCS 9909030129 | |
| Download: ML18066A625 (4) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555--0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE INSPECTION PROGRAM REQUEST FOR RELIEF PALISADES NUCLEAR PLANT DOCKET NO. 50-255
1.0 INTRODUCTION
Section 50.55a of Title 1 O of the Code of Federal Regulations (10 CFR 50.55a) requires that inservice inspection (ISi) of certain America:i Society of Mechanical Engineers (ASME) Code Class 1, 2, and 3 componentS be performed in accordance with Section XI of the ASME Boiler and Pressure Ve,ssel Code (the Code) applicable edition and addenda, except where specific relief has been requested by the licensee and granted by the Commission pursuant to paragraph 1 O CFR 50.55a(g)(6)(i), or alternatives approved pursuant to 1 O CFR 50.55a(a)(3).
In proposing alternatives, the licensee must demonstrate that (:I) the proposed alternatives provide an acceptable level of quality and safety; or (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety. In requesting relief, the licensee must demonstrate that the requirement is impractical for its facility. The regulation at 1 O CFR 50.55a allows the NRC staff to grant relief from ASME Code
- requirements upon making the necessary findings. The NRC staff's findings on whethe~ to grant the requested reliefs as part of the licensee's ISi program are contained.in this safety evaluation (SE).
Section XI, IWA-5250(a)(2), requires the removal and examination of all bolts when leakage is detected at a bolted connection. When minor leakage was detected at the casing flange of primary coolant pump (PCP) P-50A, Relief Request (RR) 13 was submitted to the NRC on December 20, 1998, to provide other means of addressing the integrity of the bolting. The staff provided written approval of RR-13 on Jahuary 28, 1999. Only 2 of the 16 PCP P-50A casing bolts were known to have any degradation from the known leak at that time. An additional.
adjacent bolt was recently determined to be slightly corroded, but remains within the Se.ction XI Code allowable limits.
2.0 EVALUATION 2.1 Request for Relief No. PR-06 In accordance with ASME Code,Section XI, if leakage occurs at a bolted connection, paragraph IWA-5250(a)(2) requires the removal of the bolting, a visual (VT-3) examination of the bolting for corrosion, and an evaluation in accordance with paragraph IWA-3100. Pursuant to 10 CFR 50.55a(a)(3)(i), Consumers Energy Company (the licensee) is requesting approval to use alternative requirements to those specified in ASME Section XI (1989 edition), IWA-5250(a)(2),
Enclosure
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as applied to the Palisades Plant Pressure Testing Program. If leakage is discovered at a bolted connection, the source of the leakage will be located and evaluated for corrective measures. If further evaluation is needed, the bolt nearest the source of leakage and any bolts that have degraded as a result of leakage will be removed and a VT-1 examination will be performed on the bolt(s).
2.2 Basis for Requested Relief (as stated by the licensee)
The ASME Section XI, 1989 Edition (the Code) imposes corrective action including the removal of all bolts at a bolted connection, for leakage detected during pressure test, regardless of the circumstances. The removal of all of the bolts may not be necessary to maintain piping, component and system integrity.
However, the Code does not allow the Owner to evaluate the effect of the leakage on the bolts in order to determine corrective action *::>r the acceptability of continued service without the removal of all of the bolting.
Leaking conditions at a bolted connection rnay be an important variable in the degradation of fasteners. However, leakage is not the only variable, and in some cases may not be the degradation mechanism. Other variables to be considered are: bolting materials, leaking medium, duration of the leak, and orientation of the leak (not all bolts may be wetted). These variables are important to consider before disassembling a bolted connection for a visual examination. Removal of bolting at a bolted connection may not be the most prudent decision and may cause undue hardship without a compensating increase in the level of quality or safety. The proposal by Consumers Energy to follow the requirements of ASME Code Case N-566-1 rather than the requirements of IWA-5250(a)(2) will provide
. an equivalent level of quality and safety at Class 1, 2, and 3 bolted connections.
The licensee has also noted that given the known condition of the PCP P-50A bolts, implementation of the proposed alternative would result in a significant reduction in risk to the plant and a reduction of plant staff dose if the remaining bolts would not require removal. A reduction of 12-16 hours of time at reduced inventory is expected by reducing the number of bolts removed to no more than four. The expected reduced inventory time with all bolts being removed is 164 hours0.0019 days <br />0.0456 hours <br />2.71164e-4 weeks <br />6.2402e-5 months <br />. A reduction of 740 to 990 mr is expected if only 2 to 4 of the 1~ bolts are removed.
2.3 Proposed Alternative (as stated by the licensee)
- Palisades shall implement the requirements of.ASME Boiler and Pressure Vessel Code Case N-566-1, "Corrective Action for Leakage Identified at Bolted Connections,Section XI, Division 1," when leakage is discovered at a bolted connecµon during a system pressure test. Code Case N-566-1 requires one of the following actions as an alterative to the requirements of IWA-5250(a)(2) when leakage is detected at a bolted connection:
(a)
The leakage shall be stopped, and the bolting and component material shall be evaluated for joint integrity as described in (c) below.
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(b)
(c) 3 If the leakage is not stopped, the joint shall be, evaluated in accordance with IWB-3142.4 for joint integrity. This evaluation shall include the considerations listed in (c) below.
The evaluation for (a) and (b) above is to determine the susceptibility of the bolting to corrosion and failure. This evaluation shall include the following:
(1) the number and service age of bolts; (2) bolt and component material; (3) corrosiveness of process fluid; (4) leakage location and system function; (5) leakage history at the connection or other system components; (6) visual evidence of corrosion at the assembled connection.
No immediate action is necessary when the evaluation required by Code Case N-566-1 determines that the leaking condition has not degraded the fasteners or.
the connection, or that the joint integrity will remain acceptable until corrective action for the leak is completed. However, reasonable attempts shall be made to stop the leakage as appropriate. If the acceptance of the component is by analytical evaluation, the evaluation analysis shall be submitted to the NRC in accordance with IWB-3144(b).
If the evaluation of the variables above indicates the joint integrity is indeterminat~ or that there is a need for further evaluation, the following actions shall be taken: -
- 1.
The bolt closest to the source of leakage and any bolts that have been
. degraded due to the leakage shall be removed;
- 2.
, The bolt(s) shall receive a* visual VT-1 examination;
- 3.
The visual VT-1 examination results shall be eva.luated and dispositioned in accordance with IWB-3517. If the removed bolting shows evidence of rejectable degradation, the bolts adjacent to the removed bolting shall be removed.and VT-1 examined and evaluated per IWB-3517.
The bolting removal and vlsual VT-1 examination(s) may be deferred to the next.
outage of sufficient duration if justified.
2.4 Evaluation In accordance with IWA-5250(a)(2), if a leak occurs at a bolted connection, the t;>olting must be removed, VT-~yisually examined for corrosion, and evaluated in accordance with IWA-3100.. In lieu of this reqliireme~t. the licensee has proposed to evaluate the bolting to determine its susceptibility to corrosion. The proposed evaluation will consider, as a minimum, bolting materials and visual evidence of corrosion at the assembled connection. The licensee has also proposed a VT-1 visual examination in lieu of a VT-3 visual examination on the removed bolt.
The VT-1 examination is more detailed than the VT-3 visual examination. The VT-1 examination
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also has a defined acceptance criterion, unlike the VT-3 visual examination, and provides greater assurance of quality and safety.
Based on the licensee's description, the staff has determined that the proposed evaluation represents a sound engineering approach and provides an acceptable level of quality and safety. In addition, if the initial evaluation indicates the need for a more detailed analysis, the bolt nearest to the source of leakage will be removed, VT-1 visually examined, and evaluated in accordance with IWB-3517. Therefore, the licensee's proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i) for the remainder of the.third 10-year ISi interval. *
3.0 CONCLUSION
The NRC staff has reviewed the licensee's submittal and concludes that the licensee's proposed
- alternative provides an acceptable level of quality and safety. Pursuant to 10 CFR 50.55a(a)(3)(i), the relief request is authorized for the Palisades lnservice lnspect!on Program for the the third 10-year interval, which ends in August 2005. Therefore, the licensee's proposed alternative is authorized pursuant to 10 CFR 50.55a(a)(3)(i).
Principal Contributor: R. Jolly Date: August 26, 1999