ML17201K360

Safety Evaluation Supporting Util Request for Relief from Certain Pump & Valve Tests During Second 10-yr Interval Inservice Testing Program

ML17201K360
Person / Time
Site:	Dresden
Issue date:	09/01/1988
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML17201K308	List: ML17201K269 ML17201K360
References
NUDOCS 8809140275
Download: ML17201K360 (14)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING IST PROGRAM RELIEF REQUESTS COMMONWEALTH EDISON COMPANY.

. DRESDEN NUCLEAR POWER STATION, UNIT NOS. 2 AND 3 DOCKET NOS. 50-237 AND 50-249

• I.

INTRODUCTION The Code of Federal Regulations, 10 CFR 50.55a{g), requires that inservice testing {IST} of ASME Code Cla~s 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 specific

• _ written* relief bas been requested by the licensee and granted by the Commi*ssion pursuant to 10. CFR 50.55a{a){3){i), {a){3){ii), or {g)(6){i).

In requesting relief, the licensee must demonstrate that {1) the proposed alternatives provide an acceptable level of quality and safety, {2) compliance would result in hardship or unusual dlfficulties, or {3) conformance with certain requirements of the applicable Code edition and

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. addenda is impractical for its facility.

The Regulation, 10 CFR 50.55a{a){3){i), {a){3){ii), and {g){6}{i),

authorizes the Co0111ission to grant relief from these requirements upon*

making the necessary findings.

The NRC staff's findings with respect to granting or n9t granting the relief requested as part of the licensee's IS:r Program are contained in the Safety. Evaluation (SE) issued on the licensee's program *

. By 1 etter dated October 5, 1981, and December 10, 1982, Conunonwea 1th*

Edison Company submitted its second 10-year interval inservice testing

{IST) program for Dresden Nuclear Power Station, Units 2 and 3.

The Mechanical Engineering Branch with technical. assistance from EG&G, Idaho,

• Inc., completed a preliminary review on the IST program noted above, and interim Safety Evaluation Report {SER) was issued to the licensee on September 16, 1987.

In response, the licensee, by letter dated

. November 17, 1987, submitted program revisions proposing changes to certain relief requests that were denied in the staff interim SER.

By

• letter dated July 28, 1988 the licensee requested that relief request VR-16 concerning inservice testing of valve stroke times be withdrawn.

As a result the staff has not evaluated this relief request in its evaluation. The staff's evaluation of the remaining proposed relief request changes is provided below.

8809140275 880901 PDR ADOCK 05000237 P

PDC

2 II.

EVALUATION The requests for relief from the requirement of Section XI and the

• justification for testing certain valves during refueling outages have been reviewed by the staff with the assistance of its contractor, EG&G Idaho, Inc., (EG&G).

The Technical Evaluation Report (TER) provided in the Attachment is EG&G's evaluation of the licensee's relief request changes. Although EG&G evaluated relief request VR-16, since the licensee has withdrawn this request it has been removed from the TER.

The bases for relief requests identified as Attachments A through C to the TER are from the.licensees request dated November 17, 1988.

The staff conc~rs with and adopts, as part of this SE, the evaluations and conclusions contained in the TER. A sununary of the staff's determinations is presented in Table 1 of this SE.

The granting of relief is based upon the licensee* fulfilling the conunitments made in the basis for each relief request and the performance of the alternate proposed testing.

Request VR-22 requests relief from quart~rly testing during power for certain valves and requests that testing be performed during refueling outages. Although the staff agrees with the licensee that quarterly testing of these valves is impractical, it believes that in addition to testing during refueling outages, as requested by the licensee, these valves should be tested when the plant is in a cold shutdown if the

'conditions specified in Table 1 are satisfied. Subsections IWV-3412(a) and 3522 of Section XI of the ASME Code permit the relaxation of the valve exercising frequency to cold shutdowns if quarterly exercising is impractical. Since testing in cold shutdowns would be consistent with the code, the staff. considers this alternate testing as a relaxation of the ASME Code and relief is therefore not necessary provided the licensee performs this alternate testing.

II I. CONCLUSION Based on the review of the licensees submittal, the staff concludes that the licensee's relief request changes are acceptable for implementation in accordance with the staff's modifications as indicated in Table 1 and the attached EG&G TER.

For the relief granted, the staff has determined that the requirements of the code are impractical, and that the changes to

.the.licensee's IST program will provide reasonable assurance of the operational readiness of safety related pumps and valves to perform their safety-related function, and that granting relief and accepting alternate*

testing methods pursuant to 10 CFR 50.55a(a)(3)(i) and {g)(6)(i) is authorized by law and will not endanger life or property, or the conunon defense and security. The staff has also concluded that granting relief is otherwise in the public interest considering the proposed alternative testing, or the hardships or the burden that could result if the requirements were imposed on the facility.

Principal Contributor:

H. Shaw Dated:

September 2, 1988

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Request No.

PR-1 PR-lA VR-22

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TABLE 1 REVIEW

SUMMARY

OF RELIEF REQUESTS DRESDEN UNITS 2 AND 3 Description of Relief Requests a) Request for relief from bearing temperature measurement for all centrifugal pumps except HPCI pumps b)

Propose alter~ative vibration measurement in lieu of Code required measurement for all centrifugal pumps except HPCI pumps Request for relief from bearing temperature meausrement for HPCI pumps Request for relief from quarterly testing.during power the valves 2(3)-305-115 NRC Evaluation

& Conclusion Relief granted under 10 CFR 55 {g){6}{i}

Relief granted, alternative acceptable.

under 10 CFR 55 {a){3){i}

Relief granted under 10 CFR 55 {g)(6){i)

Relaxation from ASME Code granted provided testing is perfonned when the reactor is in the cold shutdown mode for a suitable duration with the recirculation pumps stopped and the RHR systems in opera-tion, and at refueling outages

Attachment.I to SE LETTER REPORT, TECHNICAL EVALUATION OF PROGRAM CHANGES FOR PUMP AND VALVE INSERVICE TESTING PROGRAM, DRESDEN NUCLEAR POWER STATION, UNITS 2 & 3.

On September 16, 1987, an Interim Safety Evaluation Report (SER) was issued to Dresden Units 2 and 3.

In response, by letter dated November 17,1987, the licensee submitted program changes concerning the relief requests that were denied in the interim SER.

Changes to the licensee's IST program were revi.ewed utilizing the acceptance criteria and guidance contained in the following documents:

ASME Code Section XI, Code interpretations when applicable, the Code of Federal Regulations 10CFRSO, the Standard Review Plan; Section 3.9.6, and the Draft Regulatory Guide and.Value/Impact Statement titled, "Identification of Valves for.Inclusion in Inservice Testing Programs".

The four relief requests submitted, PR-1, PR-IA, VR-16*and VR-22 were evaluated to determine if testing the affected components in accordance with the Code requirements would be impractical, whether the licensee's proposed testing would provide a reasonable alternative to the Code requirements and whether it would place an unreasonable burden in the licensee if th~ tode requirements were imposed.

• -**"*Since licensee has withdrawn relief request VR'-16.it has been eliminated from>the reoort.

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1.

PUMP TESTING PROGRAM 1.1. Relief Request PR-1. lnservice Test Procedure. Vibration.

1.1.1. Relief Request.

The licensee has requested relief from the requirements of Section XI, Paragraphs IWP-3100, lnservice Test Procedure, bearing temperature measurement and IWP-4500, Vibration, pump vibration measurement in units of displacement amplitude, for all centrifugal pumps in the program with the exception of High Pressure Coolant Injection Main and Booster Pumps 2(3)-2302.

1.1.2. Basis For Relief. See attachment A 1.1.3. Evaluation.

When measuring the vibration of a pump using units of velocity, monitoring becomes more sensitive to small.

changes in pump performance which can be indicative of developing mechanical problems. Velocity measurements detect the high amplitude vibration that can indicate major mechanical problems such as unbalance or misalignment. Velocity measurements also detect the low amplitude, high frequency vibration caused by bearing wear that usually goes undetected using displacement measurements.

The licensee has proposed a system of testing based on ANSI/ASME OM-6 (Draft 8) which provides a reasonable alternative *to the requirements of the Code in both methodology and acceptance criteria.

Experience has shown that when serious.degradation of pump bearings occurs, bearing temperatures remain relatively constant until just prior to the actual bearing failure. With the bearing temperature measurement being taken on an annual basis, the likelihood of detecting a bearing failure during the test is minimal. Elimination of the requirement to measure bearing temperature would not impact the effectiveness of the pump

• monitoring program.

The accuracy of the bearfog temperature measurement is affected by variations in the temperature of the fluid passing through the pump *. This variation in fJuid temperature complicates the analysis of the trends of the bearing temperatures from yea~ to*

year.

In many cases, the licensee is burdened by the lengthy run time needed to achieve 3 successive bearing temperature measurements because of plant or system design limitations.

2

Based on the determination that the licensee's proposed vibration velocity monitoring program and limits provide a reasonable alternative to the Code requirements, and a more accurate means of monitoring pump performance, relief should be granted allowing the licensee to measure pump vibration in units of velocity.

Based on the determination that the measurement of bearing temperature provides little meaningful data, is a burden to the utility, and does not contribute significantly to the effectiveness of the pump monitoring program, relief from measuring bearing temperature should be granted.

1.2. Relief Request PR-IA.

lnservice Test Procedure. Temperature Measurement.

1.2.1. Relief Request. The licensee has requested relief from the requirements of Section XI, Paragraph IWP-3100, lnservice Test Procedure and IWP-4300, Temperature Measurement for the High Pressure Coolant Injection (HPCI} pumps, 2(3)-2302.

1.2.2. Basis. See Attachment B.

1.2.3. Evaluation. The licensee has addressed two issues in the relief request. The first issue addresses vibration testing which is in conformance with the Code requirements and need not be part of the relief request.

In the second part, the licensee has requested relief from the Code requirement to measure bearing temperature on an annual basis on the High Pressure Coolant Injection Pumps.

The HPCI pumps are steam driven turbine pumps which require the reactor to be in a steam producing mode of operation whenever the pumps are to be run. Operating these pumps will cause the suppression pool temperature and level to increase as this.is the exhaust point for the steam after it passes through the turbine pump.

This increase of temperature and level may challenge the Technical Specifications placed on the suppression pool.

Based on the determination that the Code requirements are impractical, and considering the burden placed on the licensee if the Code requireme'nts are imposed, relief should be granted from

• measuring the bearing temperature of the HPCI pumps.

In Section 1.1, the licensee developed a sound basis for measuring vibration using vibration ve~ocity rather than amplitude by proving that velocity me~surements are more indicative of pump degradation.

3

The Staff recognizes that the vibration of the HPCI and Booster pumps is above the vibration velocity limits adopted from OM-6

• and that the licensee has an action plan working to reduce the vibration to lower levels. However, the NRC Staff reconunends that the licensee take vibration velocity measurements in.

conjunction with the vibration amplitude and trend the results in order to increase the effectiveness of testing these pumps. Even with the readings above the limits adopted from OM-6, trending the velocity measurements could be valuable in detecting pump degradation.

The Staff further reconunends that, after the modification to the booster pump is.complete and the new vibration levels of the pumps are determined, the licensee take one* of two actions in the form of a relief request to the NRC:

1. If the new vibration levels are still above the limits adopted from OM-6, submit evidence establishing vibration velocity alert and action limits based on the actual pump vibration readings specific to these pumps.

These new limits, though higher than the those placed on the other pumps in the program, would need to be modeled similar to the other limits in the program and indicative of degradation for these particular pumps.

2.

• If the. new vibration levels are within the limits*

adopted from OM-6, submit relief to place these pumps under the same vibration velocity limits as the rest of the *

. program and measure only vibration velocity.

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• 2.

VALVE PROGRAM 2.1. Relief Request VR-22. Tests For Check Valves.

2.1.1. Relief Request.

The licensee has requested relief from the requirements of Section XI, Paragraph IWV~3520, Tests For Check Valves, for the check valve in the charging line to the accumulator in the control rod drive system, 2(3)-305-115.

2.1.2. Basis.

In order to test this valve during operation, the CRD pump would have to be shut off. In doing this, a 250 F temperature limit recoimnended by General Electric could be.

exceeded causing* damage to the seals on the control rod drives.

Also, shutting off the CRD pump would stop seal.purge water flow

~o recirculation pump seals.

2.1.3. Evaluation. The Control Rod Drive (CRO) pump supplies the seal injection for the control rod drive units and the recirculation pumps.

With the unit at power, shutting off the.

CRo*pump ~ould threaten the 250 F temperature limit in the control rod drive units and would stop seal purge flow to the recirculation pumps.

The licensee has not provided any technical justification for not testing this valve in the cold shutdown mode.

With the reactor in cold shutdown, the recirculation pumps can be shut off if the RHR system is in operation and the CRD system stopped without threatening the temperature limit.

The licensee has demonstrated that the Code requirements are impractical with the unit at power but has not submitted adequate technical justification for not testing the valve when the unit is in cold shutdown. Therefore, relief should be granted providing that the licensee test the valve at cold shutdown when the recirculation pumps are stopped and at refueling outages.

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ATTACHMENT A TO TER RELIEF REQUEST NO. PR-1 PUMP NUMBER:

All centrifugal pumps in program except High Pressure coolant Injection Main and Booster Pumps 2(3)-2302 (see Relief Request PR-lA).

SECTION XI REQUIREMENTS:

IWP-3100 Inservice Test Procedure: IWP-4500 Vibration BASIS FOR RELIEF:

Pump vibration and bearing temperature are required to be measured to detect any changes in the mechanical characteristics of a pump.

This is to detect developing problems so repairs can be initiat.ed prior to a pump becoming inoperable (i.e., unable to perform its function).

• The ASHE Code minimum standards require measurement of the vibration amplitude displacement in mils (thousandths of an inch) every t.hree months and bearing temperatures once per year.

Dresden Station proposes an alternate program which is believed.to be more comprehensive than that required by Section XI.

This program consists of performing_ the. required vibration readings in velocity rather than mils displacement.

This technique is an industry-accepted method which is much more meaningful and.sensitive to small changes that are indicative* of.

developing mechani~alproblems.

T~ese velocity measurements detect not only

• high amplitude vibrations that indicate a. major* mechanical problem but also.

the equally harmful low amplitude - high f!;equency due to misalignment, im])alance, or bearing wear that usually go undetected by simple displacement measurements.

Iri addition, these readings go far beyond the capabilities of a bearing temperature monitoring program, which requires a bearing. to be seriously degraded prior to the detection of incre-ased heat at the bearing housing.

The vibration velocity readings on a*schedule of once every three months achieve a much higher probability of detecting developing problems than the once per year reading of bearing temperatures.

Data gathering on bearing temperatures also is not without its own problems.

The enforced thirty minute rt.in time, [i.e., IWP-3500{b) - three succe~sive readings taken at ten minute intervals that do not vary more.than 3\\], causes problems.with pumps

• having no recirculation/test loop.- Variations in the temperature of the

• pumped fluid also complicate analysis of bearing temperatures when attempting to trend any developing problems from year to year.

Improper interpretation of results could result*in unnecessary pump maintenanc~. *1n addition, it is impractical to measure bearing temperatures on many of the pumps in the program.

Some specific examples are.as follows:.

A)

. CORE SPRAY I, -A, B 1401 These pumps are lubricated by the pumped medium.

The temperature of the pumped liquid could have an adverse affect on the accuracy of any yearly trending.

B)

LPCI 2(3) - A, B, C, D 1502 Same as A) above.

C)

CCSW 2(3) - A, B, C, D - 1501-44 These bearings are contained in an oil-filled reservoir. The ambient temperature of the pump space is changeable, thereby varying the start temperature of the data. Results would be extremely difficult to trend fran test to test.

D)

DIESEL GENERATOR COOLING WATER PUMP - 2, 2/3*, 3-39038 The bearings on these pumps are internal to the unit because the pump and motor are directly attached to each other and at no point is a bearing accessible for tem~erature readings.

The foregoing reasons demonstrate that the proposed program of vibration measurements is a more practical method of testing which exceeds the requirements of the ASHE COde.

ALTERNATIVE TESTING:

The alternative testing described herein for pump vibration monitoring was developed using ANSI/ASME OM-6 (Draft 8) as a gliideline, with the intent ~f incorporating into the program any additional requirements of OM-6 to those found in ASHE Section XI.

Pump vibration measurements will be obtained and recorded in velocity Cinches per second), and are broadband (unfiltered) peak readings. All inonitored locations are clearly marked to identify the specific point at which the transducer is to be placed while taking vibration measurements.

using portable equipment.

The readout system and transducers used to take vibration measurements are capable of frequency response in the range of one-third minimum pump speed to at least one-thousand hertz, and they have a minimum accuracy over that range of +/-5\\.

All centrifugal pumps in the program will have vibration measurements taken in a plane approximately perpendicular to the rotating shaft in two orthogonal directions on each accessible.pump bearing housing. Measurement will also be taken in the axial direction on all bearing housings when accessible. Reciprocating pumps will have vibration measurements taken approximately perpendicular to the crankshaft and the line of plunger

• travel, including the axial direction when accessible on each pump bearing housing.

The Acceptable, Alert, and Required Action Ranges of OM-6, Table 6100-1 will be used in lieu of Table IWP 3100-2 of Section XI as shown below.

Corrective actions will be taken in accordance with Article IWP-3230.

Vibration Ranges PwnE TvDe Acce2table Range Alert Range Required Action Range Centrifuga1C3) o~s2.5VREF (1) 2.5VRgp<VS6VREF V>6VREF But Not > 0.325 in/secC2)

But not >.7 Reciprocating o~s2.5VREF 2.5VRgp<VS6VREF V>6VREF

'Notes:

(1)

VRBF is the reference velocity determined when the pump is known to be running acceptable.

_(2)

All upper limits are listed in inches/second (peak).

(3)

All centrifugal pumps in the IST Program operate at a speed greater than 600 rpm.

1n/secC2)

ATTACHMENT B TO TER RELIEF REQUEST NO. PR-lA PUMP NUMBER:

2(3)-2302 - High Pressure COOlant Injection (HPCI).

§_ECTION XI REQUIREMENTS:

IWP-3100 Inservice Test Procedure; IWP 4500 Vibration BASIS FOR RELIEF:

As stated in PR-1, the measurement of vibration velocity in lieu of vibration displacement and bearing temperature is the pr~ferred method of detectirig mechanical change 1h pumps.

However, vibrations have been observed on the Dresden HPCI pumps, as well as other similar units throughout the country, which are greater than the maximum values specified in the ANSI/ASKE oM-6 (Draft 8) document.

The pump manufacturer attributes the high vibration to a vane passing frequency vibration created by the booster pump and transmitted hydraulically to the main pump where the high vibrations are observed.

As. a corrective action, Dresden plans to replace the present booster pump impeller with a staggered-vane impeller which, as seen at other plants in the country, will reduce the vibration.to an acceptable level.

This work is planned on Unit 3 during the Spring, 1988 refueling outage and on Unit 2 during the Fall, 1988 refuel_ing outage.

As stated in PR-1, measurement of bearing temperatures has many inherent problems and can produce very misleading results. In the case of HPCI, the pumps are driven by a steam turbine which exhausts to the suppression pool.

Extended run times to stabilize bearing temperatures would create problems in maintaining the suppression pool temperature below the Technical Specification limit of 95°F and the suppression pool level within its limits.

ALTERNATIVE TESTING:

For the HPCI pumps only, vibration amplitude will be measured in units of displacement.

Dresden will continue to use ASME Section XI, Table IWP 3100-2 as the basis for establishing vibration limits. Bearing temperatures will not b~ measured for reasons stated above *. After the booster pump impellers are replaced and data is obtained regarding the vibration characteristics of the HPCI pumps, Dresden will consider monitoring HPCI vibration amplitude in units of velocity and, if possible, establish the vibration limits based on ANSI/ASME OK-6 (Draft 8).

ATTACHMENT C TO TER RELIEF REQUEST NO. VR-22 SYSTEM:

control Rod Drive (CRD)

COMPONENT:

2(3)-305-115

• CATEGORY:

C FUNCTION:

Located in the charging water line to the CRD accumulator TEST REQUIREMENTS:

CT-1 exercise valve every 3 months.

BASIS FOR RELIEF:

In order to test this valve during operation, the CRD pump would need to be shutoff.

In doing this, a 250°F temperature limit recormnended by General Electric could be exceeded causing damage to the seals on the control rod drives. "Also, shutting off the CRD pump would stop seal purge water flow to recirculation pump seals.

ALTERNATE TESTING:

Bach refueling outage, the CRD pump will be shutoff to.test the integrity of the valves.

The integrity.of the valves will be verified by the ability of each CRD accumulator to hold its pressure above the low pressure alarm*

setpoint. A time limit will be selected (based on vendor recommendations, operating/maintenance experience, and technical input from other sources) for which the accumulators must maintain their pressure above the low pressure setpoint.

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.... *~ I Attachment o RELIEF REQUEST NO. VR-16 SYSTEM:

operated valves requiring full stroke CATEGORY:

FUNCTION:

TEST REQUIREMENTS:

Stroke time evaluation per BASIS FOR RELIEF:

Paragraph IWV-3413(c) re uires that valve stroke time be evaluated against the previous stroke time o determine if corrective ction is required.

To establish consistency in e luating stroke times a make program implementation more practic, Dresden Station pr. poses to establish a reference stroke time for eac valve which will e used for evaluating performance.

This reference v lue will be de rmined by averaging stroke times.

This actually results a tighter b d of acceptable stroke times but is much easier to administer.

The lim ing value of full stroke time for each valve will remain. as lis d in IST Program tables.

In addition, it is impractical to ap 1 the requirements of IWV-3413(c) to

• valves with very short stroke times (.e., < 2 seconds), particular.ly solenoid valves which typically hav f 1 stroke times under one second.

For these short stroke time valves vari nces of 50 percent or more can occur in the measured times for r asons t at are in. no way related to valve performance, for example, opera r reactio times.

In these specific cases, verifying that the valve strok times do not exceed 2 seconds would be sufficient to evaluate valve erformance.

ALTERNATE TESTING:

Bach stroke time will Time will be establi compared to as follows:

The Alert Stroke

1.

with *refere~ce stroke times grea

~ime will ~e 25 percent greater r than 10 seconds, the han the reference

2.

3.

4.

alves with reference stroke times ds, the Alert Stroke Time will be the reference time.

valves with reference stroke times Alert Stroke Time will be set at 3 seconds.

For valves with reference stroke times less 1.5 Stroke Time will be set at 2 seconds.

and 10 greater

seconds, Alert If a measured stroke exceeds the Alert Stroke Time, the test frequency shall be increased to once each month until corrective action is taken, at which time the original test frequency shall be resumed.

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