ML20059J459
| ML20059J459 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 01/25/1994 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20059J437 | List: |
| References | |
| NUDOCS 9402010031 | |
| Download: ML20059J459 (6) | |
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i UNITED STATES j ) JJ f j NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D.C. 20B66-0001 N...s../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE TESTING PROGRAM RE0 VESTS FOR RELIEF DETROIT EDIS0N COMPANY FERMI-2 DOCKET NO. 50-341
1.0 INTRODUCTION
The Code of Federal Regulations,10 CFR 50.55a, requires that inservice testing (IST) of certain ASME Code Class 1, 2, and 3 pumps and valves be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable addenda, except where alternatives have been authorized or relief has been requested by the licensee and granted by the Commission pursuant to Sections (a)(3)(i), (a)(3)(ii), or (f)(6)(i) of 10 CFR 50.55a.
In proposing alternatives or requesting relief, the licensee must demonstrate that: (1) the i
proposed alternatives provide an acceptable level 'of quality and safety; (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for its facility.
NRC guidance contained in Generic Letter (GL) 89-04,
" Guidance on Developing Acceptable Inservice Testing Programs," provides alternatives to the Code requirements determined acceptable to the staff without further NRC review.
Implementation of the GL 89-04 positions is subject-to inspection.
1 Section 10 CFR 50.55a authorizes the Commission to approve alternatives and to grant relief from ASME Code requirements upon making the necessary. findings.
The NRC staff's findings with respect to authorizing alternatives and granting or not granting the relief requested as part of the licensee's IST program are contained in this Safety Evaluation (SE).
Furthermore, in a revision of 10 CFR 50.55a effective September 8,1992 (see 2
57 FR 34666), the 1989 Edition of ASME Section XI was incorporated inL10 CFR 50.55a(b). The 1989 Edition provides that the rules for IST of pumps and valves-shall meet the requirements set forth in ASME Operations and Maintenance Standards Part 6 (OM-6), " Inservice Testing of_ Pumps in. Light-Water Reactor Power Plants," and Part 10 (OM-10), " Inservice Testing of Valves in Light-Water Reactor-Power Plants." Pursuant to 10 CFR 50.55a(f)(4)(iv), portions of, subsequent editions or addenda may be used provided that all related i
requirements of the respective editions or addenda are met, and subject to Commission approval.
Because the alternatives meet later editions.of the Code, relief is not required for those inservice tests that are conducted in accordance with OM-6 and OM-10, or portions therev.. provided all related requirements are met.
Whether all related requirements are met is subject to-NRC inspection.
9402010031 940125 PDR ADOCK 05000341 P
PDR l
1 The IST program evaluated in this SE applies to the first 10-year IST interval for the fermi 2 nuclear plant. The interval began January 23, 1988, and ends January 22, 1998. The first 10-year interval IST program is based on the requirements of the 1980 Edition, with addenda through Winter 1980 Addenda, of the ASME Section XI Code.
In Detroit Edison's (DE) letter of October 10, 1990, Relief Request PR-10-R3 was submitted.
DE requested approval of the relief request "to provide reasonable vibration limits for the acceptable, alert, and required action vibration ranges" of the high pressure core injection (HPCI) main and booster pumps. At the time of the submittal, the HPCI main and booster pumps were being tested every six weeks (versus once each quarter) based on the alert range acceptance criteria for the pump vibration. DE contends that the pump is operating acceptably and that the additional testing is unnecessary.
The relief request is evaluated below.
2.0 EVALUATION OF RELIEF RE0 VEST PR-10-R3 In the original safety evaluation for the Fermi 2 inservice testing program (NUREG-0798, Supplement No. 4), the NRC authorized the use of an alternative for monitoring vibration of pumps tested in accordance with ASME Section XI in the evaluation of Relief Request PR-1.
Rather than measuring vibration in units of displacement as specified in Section XI, IWP-2400(a) and Table IWP-3100-1, the licensee proposed to take measurements in units of velocity.
PR-1 included specific ranges, in inches per second (ips), for acceptable, alert, and required action as follows:
Acceptable Range:
< 0.236 ips Alert Range:
2 0.236 ips to < 0.314 ips Required Action Range: 2 0.314 ips Because the licensee began experiencing vibration levels in the alert range of PR-1 for the HPCI main and booster pumps (pump numbers E4101C001A/B), an increase in the alert limit above the values specified in PR-1 was requested.
2.1 Licensee's Basis for Relief The licensee states:
During preoperational testing of the HPCI system, vibration of the HPCI main and booster pump were measured and determined to fall within the required action range of Relief Request PR-1.
This high apparent vibration was caused by induced vane-passing frequency from the 4 vane booster pump impeller.
Pursuant to this high apparent vibration, Relief Request PR-9-R2 and PR R2 were written requesting relief from the requirements of Relief Request PR-1 until refueling outage 1 (RF01) at which time the HPCI booster pump impeller would be changed from a 4 to a 5 vane impeller, reducing the induced vane-passing frequency caused by the 4 vane impeller design.
- During RF01, the HPCI booster pump impeller was changed from a 4 to a 5 vane impel l er.
This eliminated the induced vane-passing vibration emanating from the booster pump. As part of the post-modification testing, vibration data were taken to provide baseline vibration signatures. While vibration levels were reduced significantly, both pumps are still exhibiting vibration levels approaching or exceeding the IST program alert level of 0.236 in/sec of Relief Request PR-1.
The following table demonstrates the large reduction in vibration achieved when the HPCI booster pump impeller was changed from a 4-to a 5-vane impeller:
HPCI Vibration Reference Values Main Pump Vertical Horizontal Vibration (in/sec)
Vibration (in/sec)
Before Impeller 0.176 0.598 Ch_a ngeou t After Impeller 0.185 0.230 Changeout Booster Pump Vertical Horizontal Vibration (in/sec)
Vibration (in/sec)
Before Impeller 0.264 0.549 Chanaecut After Impeller 0.120 0.145 Chanopout Vertical and horizontal vibration velocities are frequency dependent with readings being higher for machines operating at higher speeds. HPCI [ pumps]
operate at approximately 4000 RPM which is significantly higher than most rotating machinery (typical machinery operates at 1800 RPM).
The HPCI main and booster pump design is such that the vibration in the horizontal direction is resonant with the normal pump operating speed (approximately 4000 RPM) resulting in higher vibration levels. Vibration levels for the vertical direction will be less than the horizontal direction as pump design provides for a more rigid restraint in the vertical direction.
These higher levels of vibration are not detrimental to the long-term operability of the machine and will not prevent early detection of pump degradation as intended by the ASME Section Code and the DE [ Fermi 2] IST program.
a i
1 In support of this conclusion it should be noted that if current HPCI vibration levels were taken in mils (as allowed by the ASME Section XI Code), the highest reading would be less than 1.4 mils overall which is well below the upper end of the acceptance range of 2.8 mils as provided by the Code for the specific HPCI pump.
Given that the pump is operating acceptably at vibration velocities at or approaching the IST program lower alert level, a new set of vibration velocity ranges have been developed.
These new vibration velocity ranges will allow for early detection of pump degradation prior to component failure.
2.2 Alternative Testina The licensee proposes:
Pump vibration measurement will be taken in vibration velocities (in/sec) with the acceptable, alert, and required action ranges as follows:
Using the guidelines contained in ASME/ ANSI OMa-1988, Part 6, Table 3,
" Ranges for Test Parameters":
Where V, = reference vibration velocity (in/sec) peak Acceptable Range s 2.5 V, Alert Range
> 2.5 V, to 6 V, or > 0.325 in/sec Required Action Range
> 6 V, or > 0.70 in/sec Where main pump V, = 0.21 in/sec Where booster pump V, = 0.13 in/sec By applying the foregoing guidelines, the new HPCI main and booster pump vibration acceptance criteria are:
NEW PUMP VIBRATION ACCEPTABLE RANGES MAIN PUMP Acceptable Ranae Alert Ranae Reouired Action Ranae s 0.325 in/sec 0.326 in/sec
> 0.700 in/sec to 0.700 in/sec
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B0OSTER PUMP t
Acceptable Ranae Alert Ranae Recuired Action Ranae 5 0.325 in/sec 0.326 in/sec
> 0.700 in/sec to O.700 in/sec 2.3 Evaluation i
The licensee has requested what is essentially a change to an existing relief t
request, which allows the use of velocity measurements rather than displacement measurements, for monitoring the vibration of the HPCI main and booster pumps.
The main and booster pump combination are horizontal centrifugal' pumps.
Because of the mounting of the pumps, frequency response effects, such as vane-passing frequencies, experienced by one pump will impact the other. Thus, the replacement of the impeller on the booster pump reduced the overall vibration levels for the main pump following refueling outage 1.
Even with the reduction in the vibration levels, the pumps operate at a normal level that, with periodic spikes, result in measurements above the alert action range specified in Relief Request PR-1.
1 The proposed ranges for the HPCI main and booster pumps vibration acceptance criteria are consistent with the ranges in Part 6 of the ASME/ ANSI Operations
~'
and Maintenance Codes and Standards (DM-6).
Using the above stated reference values of 0.21 ips for the main pump and 0.13 ips for the booster pump, the absolute limits are as conservative as values applying the multipliers (2.5 to 6 times reference value) for relative changes (i.e., 0.13 ips x 2.5 0.325 ips, 0.21 ips x 2.5 =.525 ips). Therefore, the alert and required action limits specified are the more conservative of the two values of absolute or relative limits.
The licensee does not indicate that the requirements of OM-6 will be adopted for the fermi 2 inservice testing program.
Rather, they have used'the limits specified in OM-6 to determine the acceptability of the vibration levels currently being experienced on the HPCI main and. booster pumps and the proposed levels for monitoring the pumps.
Rather than a. change to the current IST program which was developed to the 1980 Edition, addenda through Winter 1980, of Section XI, with relief requests approved in the. original safety evaluation, the.
request is more appropriately viewed as a revision 'to the alternative in PR-1 l
and is evaluated as such.
The current limits for the other pumps included in PR-1 will remain at the lower levels and are not affected by this evaluation
- \\
The proposed limits are higher than the previous limits, but are not j
inconsistent with industry standards such as OH-6 (discussed above), Vibra-
]
Metrics, IRD Mechanalysis, and others for assessing pump condition. The levels.
i are not indicative of a " smooth-running pump," though.a number of pumps ' operate-within the proposed limits and are considered to'be operating "normally" for the particular installation.
Continuing to impose the lower limits-for alert and required action would result in testing more often than necessary to ensure operatioral readiness or in declaring the pumps inoperable when in an acceptable operating condition.
Therefore, it would be a hardship on the licensee to
oa. t continue using the lower limits for the HPCI pumps until the end of the first IST 10-year interval when the entire IST program will be updated to a later 4
edition of the Code, including raising the limits for the remaining pumps in PR-1.
The increase in the level of quality and safety provided by the continued imposition of the lower limits, resulting in testing at twice the normal frequency, does not compensate for the hardship concerns. Based on the hardship i
without a compensating increase in the level of quality and safety, the proposed alternative is acceptable for the remainder of the first 10-year interval.
PR-1 is applicable to all pumps in the inservice testing program other than the residual heat removal pumps which have limits specified in Relief Request PR-8.
The licensee's proposal for PR-10 will also take exception to PR-1 for the HPCI main and booster pumps and PR-1 should be revised to note the change upon approval of PR-10.
The alternative to raise the limits for vibration acceptance criteria for the HPCI pumps above those specified in currently approved Relief Request PR-1 is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) based on the hardship without a compensating increase in the level of quality and safety if the previous requirements were continued to be imposed.
3.0 CONCLUSION
The staff concludes that the relief request evaluated in this SE will provide reasonable assurance of the operational readiness of the HPCI pumps to perform their safety-related functions.
The staff has determined that authorizing the alternative pursuant to 10 CFR 50.55a(a)(3)(ii) is authorized by law and will not endanger life or property, or the common defense and security and is otherwise in the public interest.
In making this determination, the staff has considered the burden on the licensee if the previous requirements were imposed.
Principal Contributor:
P. Campbell, DE/EMEB Date: Osnuse" 25. 1594 a
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