ML18038A246
| ML18038A246 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 03/31/1987 |
| From: | NIAGARA MOHAWK POWER CORP. |
| To: | |
| Shared Package | |
| ML17055C943 | List: |
| References | |
| NUDOCS 8704030387 | |
| Download: ML18038A246 (66) | |
Text
ASSESSMENT REPORT ON THE NEED FOR A LEAKAGE CONTROL SYSTEM FOR NINE MILE POINT UNIT 2
- March, 1987 8704030387 870331
- r PDR.
ADOCK 05000410 P
TITLE TABLE OF CONTENTS PAGE I.
INTRODUCTION AND
SUMMARY
II.
COMPARISON OF UNIT 2 ROCKWELL VALVES TO OTHER BWR PLANTS WITH ROCKWELL MSIV's A.
DEVELOPMENT OF PERTINENT MSIV FEATURES B.
EVALUATION OF UNIT 2 ROCKWELL FEATURES ON TABLE 1
C.
INDUSTRY EXPERIENCE ASSESSMENT III.
COMPARISON OF INDUSTRY LEAK RATE DATA A.
DESCRIPTION OF DATA BASES B.
ANALYSIS OF THE DATA IV.
RADIOLOGICAL CONSEQUENCE ASSESSMENT 12 V.
MAINTENANCE ASSESSMENT A.
INDUSTRY EXPERIENCE B.
TECHNICAL EVALUATION REVIEW OF BWR OWNERS GROUP RECOMMENDATIONS C
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MAINTENANCE CONCLUSIONS 14 14 15 23 VI.
CONCLUSIONS 23
0 I.
INTRODUCTION AND
SUMMARY
This report, provides Niagara Mohawk Power Corporation's evaluation of the necessity of installing a
leakage control system for the Nine Mile Point Unit 2
Main Steam Isolation Valves (MSIVs).
The results of our evaluation indicate that a
leakage control system is not required at Unit 2.
This assessment is based upon the following:
1.
Nine Mile Point Uni,t 2
Main Steam Isolation Valves are equivalent in design to BWR Rockwell Valves used at other nuclear power plants.
(See Section II) 2.
The industry,-leak rate test-data provides a basis to predict the leak rates at Unit 2 based upon the similarity of the Unit 2 valves to other Rockwell MSIVs used at BWRs.
(See Section III) 3, Based upon the leak rate data shown on Table 3,
the Unit 2 valves will meet the Technical Specification leak rate of 6
SCFH prior to initial critically
- and, maintain a
relatively low leak rate throughout each operating cycle.
About forty percent of all "as found" Type C leak data for the Rockwell type MSIV's were less than 6
SCFH.
Eighty-five percent of all Rockwell data obtained (representing 378 valves) were less than 38 SCFH.
An estimate for the "As Found" condition at the end of the first operating cycle for Unit 2,
based upon industry weighted
- averages, is 16 SCFH.
(See Section V) 0320K
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4.
The Niagara Mohawk evaluation of the allowable Main Steam Isolation Valve leakage was provided in a letter dated March 18, 1987.
That report demonstrated that MSIV leakage values as high as 38 SCFH/line did not result in unacceptable dose values when evaluated in accordance with NUREG 1169 (See Section IV).
5.
Evaluation of the maintenance record for Nine Mile Point Unit 1,
which uses Atwood Morrill Valves, demonstrates that it is one of the better plants for Main Steam Isolation Valve leak rate performance.
Additionally, a
maintenance assessment was performed for the Rockwell valves by Niagara Mohawk personnel.
Personnel from a
number of the domestic plants with the best leak rates were contacted, as well as General, Electric and the valve manufacturer.
In addition, a literature review was made (See Section V).
Based upon this assessment, a
number of methods will be utilized to improve the Main Steam Isolation Valve leakage characteristics at Unit 2 (See Section 5).
Section II provides a
comparison of Nine Mile Point Unit 2
to other plants using Rockwell valves.
Section III provides an analysis of industry leak rate test data.
Section IV provides a
radiological evaluation of the allowable leak rate values.
Section V discusses enhanced maintenance activities for the Hain Steam Isolation Valves.
Section VI provides an overall conclusion.
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II.
COMPARISON OF UNIT 2 ROCKWELL VALVES TO OTHER PLANTS WITH ROCKWELL VALVES A.
DEVELOPMENT OF PERTINENT MSIV FEATURES A list of pertinent valve features which could affect the leak tight integrity of the Rockwell valves was developed by General Electric for Unit 2
A list of the Boiling Water Reactors (BWRS) using Rockwell valves was also developed.
The list includes the domestic BWRs and Tokai 2,
a Japanese
- plant, using Rockwell MSIV's.
The data is compiled in Table l.
B.
EVALUATION OF UNIT 2 ROCKWELL FEATURES ON TABLE 1
Table 1
provides a comparison of the pertinent design features of Unit 2 (Y-Pattern)
MSIV's, and those of the same basic style.
The design features identified are those considered necessary to compare the equivalency of the NMP2 MSIV design to those which are currently in-service.
The following discussion describes the information on Table 1.
The organization of the discussion is the same format as Table l.
1.
VALVE RELATED PHYSICAL FEATURES The MSIV Information from Table 1 demonstrates that:
(a)
The NMP2 MSIV valve manufacturer and basic valve style is the same as for MSIV's used in at least 13 other BWR operating plants.
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(b)
The nominal valve sizes identified range from 18 to 26 inches.
Four other operating plants use the same 26 inch size valve as does NHP2.
(c)
The NMP2 MSIV design is in compliance with the ASME Section
- III, Class 1
design and manufacturing requirements.
The applicable codes and standards for the other plants are identified on Table l.
(d)
The NMP2 HSIV design pressure and temperature is 1375 psig at 586'F which is 10% higher than for the other plants identified because the NMP2 HSIV's were originally designed and manufactured for Black Fox Nuclear Power Plant requirements.
(e)
The minimum wall thickness identified is consistent with the minimum stress analysis
- criteria, corrosion allowance and valve supplier design.
(f)
Two NMP2 HSIV's located inside primary containment on the outboard main steam lines are rolled about 20'rom the vertical.
This rolled orientation is less than the 42',
35'nd 30 rolled positions used at other BWR's using the Rockwell MSIV's.
Based upon operating experience at other BWR plants, the NMP2 HSIV 20'olled position is not considered a significant factor for leak tightness.
For
- example, the Cooper Nuclear
- Plant, which has the best in-service leak tightness
- record, also has a
high (35')
rolled angle orientation.
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(g)
The latest Rockwell design (including NMP2) utilizes a 60/
valve stroke (of the main seat bore diameter).
This streamlines the flow past the main disc and thus minimize the effects of the flow induced vibration on the valve internals.
There have been no reported flow induced vibration problems on MSIV's having the same valve stroke to main seat bore ratio as NMP2 (which is 60%).
2.
VALVE RELATED DESIGN FEATURES FOR LEAK TIGHTNESS The MSIV information from Table 1 demonstrates that:
~f\\
The general configuration and valve related design features for leak tightness presented in Table 1
show that the Unit 2 valves are essentially a duplicate of'ther industry valves.
The basic seat configuration selected by the valve manufacturer, for this style of
- valve, is of the "Conical" geometry.
The conical geometry (a) provides a
mechanical load advantage which allows contact sealing stress to be developed with limited imposed
- forces, (b) resists lateral motion due to induced external vibration when
- seated, and (c) incorporates vendor past experience to assure adequate performance.
The other specific detail design features identified in Table 1
is consistent with the vendor's valve design practice for conical seat geometry.
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Sealin Force(s)/Load(s)
The MSIV design, uses all available sources of force (e.g.,
spring
- force, preumatic actuator
- force, and fluid media pressure loading) to maximize MSIV leak tightness capability.
Valve Stroke(s)
The stroke(s) selected by the valve vendor is provided to assure compliance with MSIV pressure drop requirements for the balanced disc design.
Recent vendor evaluations have indicated that the reduced main disc stroke (as used at NMP2) will streamline the flow, thus reduce
.the potential for flow induced vibration effects on the valve trim.
Valve closure speed is controlled by the adjustable hydraulic control valve.
There have been no reported flow induced vibration problems on MSIV's having the same MSIV valve stroke ratio as NMP2 (which is 60%).
Clearance/All nment The NMP2 MSIV disc-piston assembly clearance to the body-bore inside-diameter is consistent with all other BWR MSIV's having a
60% valve stroke to the main seat bore ratio.
The clearance was increased from some of the earlier manufactured MSIV's to enhance valve open/close function to reduce the potential for foreign material entrapment between the two surfaces.
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Materials
.The materials used for the main disc, stem-disc and the hardfaced seating areas are identified on Table 1.
The difference in main disc (carbon/alloy steel) and stem-disc (carbon/alloy steel) base materials is a
vendor-selected design based upon material availability and valve design.
The base material(s) are chosen such that they can be properly hardfaced with the Stellite 21 material.
The Stellited disc and seat
- surfaces, when properly mated and
- loaded, assure a
leak tight closure.
Stellite 21 hardfacing was selected by the valve vendor based upon its evaluation and successful experience in attaining a
leak tight valve for.steam service applications.
The wear surfaces (surfaces subject-to-relative motion) are also Stellite 21 hardsurfaced.
These sliding surface hardfaced areas minimize the potential for galling.
~Summar As discussed
- above, the Rockwell valves shown in Table 1
demonstrate the similarities between the Unit
¹2 valves and those in other BHRs.
The Unit 2 MSIV design is almost a duplicate of the LaSalle 1
5 2, Hanford 2,
Tokai 2
and Hatch MSIV's.
The characteristics of MSIV's on older plants are consistent with NMP2 MSIV's.
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C.
AN INDUSTRY EXPERIENCE ASSESSMENT ON THE ROCKHELL DESIGN MSIV's FOR BNR SERVICE Niagara Mohawk has performed an assessment of the industry's experience with the Rockwell designed MSIV's for BNR service.
This assessment was based upon information provided by other BHR operating
- plants, the valve supplier (Rockwell),
the General Electric
- Company, and evaluation of I.E.
Bulletins, Notices and Circulars applicable to NMP2 MSIV's.
Table 2
(attached) provides information on Rockwell MSIV changes that evolved with time and the Unit 2
MSIV implementation status.
Niagara Mohawk incorporates all design changes identified on Table 2
with a single exception as discussed below.
Information
- Notices, Bulletins and Circulars were reviewed for applicability.
Seventeen Information
- Notices, four Bulletins and one Circular were identified as potentially impacting the MSIV's.
Each of the documents was reviewed in detail for any necessary plant specific responses and actions.
Specific responses or actions on each recommendation have been developed for NMP2.
Two Information
- Notices, 81-28 and 84-48, describe a condition which may require a
modification package to be implemented for the attachment of the stem disc to the
- stem, and the main disc to the piston, This change was evaluated and is discussed further in the paragraphs below.
The applicable recommended actions in the other Information
- Notices, Bulletins and Circulars are being implemented.
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l V
N
Further evaluation and discussions with both the vendor and the General Electric Company regarding the potential for stem to disk separation indicate that the, potential for such an anomaly to occur on the NMP2 MSIV has been minimized for the following reasons:
(a)
The valve stroke as a percent of the mainseat bore diameter has been reduced to 60 percent.
This shorter stroke enables the MSIV's to (1) still meet its low pressure drop requirement and (2) streamline the flow past the main disc and thus minimize the potential for flow induced vibration problems.
(b)
No stem/disc separation problems have been experienced at four other operating plants (La Salle 1
5 2, Hanford 2
and Tokai-2) which incorporated the 60 percent valve stroke (to main seat diameter) ratio.
The MSIV's at these plants are almost the exact design duplicate as the NMP2 MSIV's.
Based upon items (a) and (b)
- above, Niagara Mohawk has concluded that the NMP2 MSIV's will not experience disc/stem separation anomalies which was previously experienced on earlier versions of the Rockwell MSIV design.
III. COMPARISON OF INDUSTRY LEAK RATE DATA A.
DESCRIPTION OF DATA BASES Niagara Mohawk Power Corporation obtained MSIV Type C
leakage test results from 9 out of 11 domestic BNR reactors having Rockwell 0320K
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manufactured valves (Brunswick 1
and 2
were in an outage and data could not be obtained).
As shown on Table 1, four of those plants have 26" valves as does NMP2.
The amount of data available varied from plant to plant due to the differences in the time they have been operating.
Some of the data goes back to 1973.
Various statistical analyses were made on "as found" and "as left" Type C
test results data.
Recent (1983 and later) upgraded maintenance and test procedures and tooling show improved "as left" leakage results;
- however, there is too little "as found" data reflecting equipment and procedural improvements to make a
positive assessment on subsequent "as found" leakage.
Consequently, as shown on Table 3,
the statistical analysis used all available "as found"
- data, a
conservative approach.
Most plants perform leakage tests on a
steam line or penetration and only test individual valves when excessive leakage is discovered.
The "as found" analysis uses these steam line totals.
There were 189 line tests (representing 378 valves) which yielded numeric data.
In 9
other instances, the person recording the data characterized the leakage as "excessive, gross, or high."
This fact is noted in the data summary but were not included in the plant or weighted averages.
A weighted overall plant average leakage of 27.14 SCFH per steam line was calculated which represents 189 leakage tests involving 378 valves.
A tally of individual tests indicates that 77 (39'/)
were 6.0 SCFH or below; an additional 92 (169 cumulative total) were 38 SCFH or under.
Cumulatively, 85%%u of all tests fall within 38 SCFH. 0320K
In conclusion, operating experience indicates that NMP2 has a high probability of meeting a
6 SCFH "as found" limit and an excellent likelihood of MSIV leakage not exceeding 38 SCFH per line throughout the operating cycle.
Adoption of the recent BNR Owners Group recommendations as to test
- method, procedures, and equipment will give additional assurance of reduced MSIV leakage.
B.
ANALYSIS OF THE DATA The leak rate data presented in Table 3
was impacted by three main factors that influence valve leakage performance:
1.
.Most data were obtained by testing with.pressure between the inboard and outboard
- seats, rather than through the valve in the direction of flow.
This increases the leakage rates because the pressure tends to unseat the inboard valve which reduces the valve seating force by a factor of two.
2.
Plants other than Unit 2
have a higher Technical Specification acceptance criterion (about 11.5 SCFH per valve versus 6
SCFH for Unit 2).
Presumably, a utility would not refurbish a valve with a
leakage rate between 6
and 11.5 SCFH;
.therefore, the average "as left" and subsequent
."as found" values in Table 3
are higher than they would have been if all plants had to meet 6
SCFH.
Some plants such as LaSalle have a limit of 100 SCFH for all four lines.
The "as left" value for such plants has been as high as 66 SCFH in a line.
These higher limits increase the weighted average. 0320K
3.
The effect of new maintenance practices, which will be implemented at Unit 2
as discussed in Section V,
and which are based upon the BHR Owner's Group recommendations, and the use of the new Rockwell lapping tool are just now affecting (improving) the results.
Therefore, future leakage rate data are expected to improve.
The effect of these three factors cannot be determined quantitatively, but it is expected that improved MSIV leakage rates will be achieved by implementing improved techniques, using the Rockwell lapping tools, and improving procedures to further reduce leakage.
Niagara Mohawk contacted some of the utilities with better leakage rate experience, and identified improved maintenance practices which are discussed in Section V.
IV.
RADIOLOGICAL CONSE UENCE ASSESSMENT OVERVIEN Niagara Mohawk has submitted a radiological analysis that demonstrates that a leakage control system is not required.
This conclusion is based on the results of a radiological
- analysis, comparison of the Unit 2
design features to those identified in NUREG
- 1169, and the conservatism of the Main Steam Isolation Valve leakage limits determined by the design basis accident radiological assessment. 0320K
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0 On January 14, 1987 and March 18, 1987 Niagara Mohawk submitted a
radiological analysis for Unit 2.
The analysis demonstrates that with up to 1000 scfh leakage per,line from the main steam
- system, using the methodology contained in NUREG
- 1169, the offsite doses remain within regulatory requirements, This conclusion is independent of the type of main steam isolation valve utilized.
Based on the NUREG 1169 comparison with
- NMP2, the isolated condenser path is the most probable scenario for calculation of radiological consequences.
The allowable MSIV leakage was determined based upon a simplified main condenser model for the beta skin and whole body III gamma
- doses, while a direct comparison ratio method was used to determine the 'thyroid doses.
The beta and gamma dose evaluation model utilized holdup of the MSIV leakage in the main condenser and subsequent release of radioactivity to the environment.
No credit was taken for the holdup of the noble gases in the main steam
- lines, drain lines or turbine building.
Additionally, the volume reduction due to steam condensing in the piping or components prior to being released was not considered.
The above conservative analysis provided results indicating that the most restrictive radiation limit was the Control Room beta dose.
The analysis demonstrates that a
MSIV leak rate of 150 scfh total for all steam lines (38 scfh/line) would not result in control room personnel doses in excess of regulatory limits.
The maximum leakage rate could be increased to 500 scfh from the main steam lines (125 scfh/line) and meet control room habitability guidelines with appropriate beta shielding (such as overalls).
A value as high as 1000 scfh/line would not produce offsite doses in excess of regulatory requirements. 0320K
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V.
MAINTENANCE ASSESSMENT Niagara Mohawk has reviewed recent Rockwell MSIV in service experiences with personnel from
- Cooper, FitzPatrick and Vermont Yankee Nuclear plants as well as industry literature on MSIV experience, such as NEDO : 25329, NUREG 1169, and the BHR owners group information.
Niagara Mohawk actively participates in the BNR Owners Group regarding the MSIVs.
This information, with the experience gained from Unit 1
MSIV testing and performance, provides valuable assistance in improving the leak testing of the Unit 2 MSIVs.
A.
Industr Ex erience Evaluation of the maintenance record for Nine Mile Point Unit 1
(which uses Atwood Morrill Valves) demonstrates that Niagara Mohawk is one of the better utilities for Main Steam Isolation Valve leak rate performances Additionally, a
maintenance assessment was performed by Niagara Mohawk personnel for the Unit 2
Rockwell valves.
A number of utilities with a history of low leak rates were contacted, as well as General Electric and the valve manufacturers Based upon this assessment, the following methods will be utilized to improve the Main Steam Isolation Valve leakage characteristics at Unit 2:
a.
The Hain Steam Isolation Valves wi 1 1
be tested in the direction of flow.
b.
The Main Steam Isolation Valves will be closed in a
"hot" condition (approximately 150 F) and tested as soon as practical.
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c.
The Main Steam Isolation Valves will be lapped in place, when necessary, with the Rockwell tool.
d.
The seat angle and the disc seat angle will be maintained by appropriate maintenance procedures.
e.
The actuator will be maintained with enhanced preventative maintenance procedures based upon industry experience.
The following discussion compares and establishes Niagara Mohawk's evaluation results regarding the NMP2 Rockwell designed MSIV's with the BWROG recommendations.
B.
Technical Evaluation Review of BWR Owners Grou Recommendations on MSIV Leaka e
The BWR Owners Group identified that improper maintenance is a
primary factor contributing to excessive MSIV leakage.
1.
Maintenance The BWR Owners Group indicated that care should be taken to ensure that maintenance equipment, procedures and personnel are effective in providing the services required to prevent latent detrimental effects on the valve.
For
- example, equipment planned for use should be checked out thoroughly prior to use, procedures should be
- proven, and personnel should be trained adequately.
NMPC Evaluation Results a.
NMPC is procuring vendor recommended maintenance
- boring, grinding, and lapping tools for use on the MSIV. 0320K
b.
NMPC is generating maintenance procedures based upon the MSIV instruction
- manual, vendor G.E.
engineering recommendations.
c.
NMPC m'aintenance practice is to utilize personnel who are trained and experienced in the preventative maintenance procedures.
In-house NMPC personnel, vendor technical representatives and other sub-contractors are utilized depending upon the task and services required.
d.
The existing MSIV's, recently procured from General Electric
- Company, were refurbished and upgraded by the
- vendor, (Rockwell),
inspected by G.E.
Quality Assurance prior to vendor
- shipment, and receipt inspected by NMPC Q.A.
personnel.
During the MSIV valve change-out, NMPC has obtained GE technical assistance.
Valve vendor participation will be obtained as required.
The BNR Owners Group also identified other factors that require maintenance attention:
1.
LLRT pressurization method 2.
Closing Procedure 3.
Inadequate actuator loading 4.
Valve damage 0320K
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NMPC Evaluation Results a.
The Main Steam Isolation Valves will be tested in the direction of flow.
In this configuration, the pressure during this test tends to seat the valve.
Experience at Unit 1
indicates that testing between the inboard and outboard valves can cause unnecessary leak rate failures.
b.
The Hain Steam Isolation Valves will be closed in a
"hot" condition (about or above 150'F) and tested as soon as practicable.
Experience at Vermont Yankee indicates that test temperature and timing affect the test results.
c.
The Main Steam Isolation Valves will be subjected to the following tests and inspections in accordance with approved procedures.
(1) Initially, during each refueling outage at least two actuators (based upon actuator performance and experience) will be overhauled and preventative maintenance performed.
Based upon conversations with Cooper nuclear plant personnel, actuator maintenance is critical to low leak rates.
(2) Initially, during each refueling outage each actuator (based upon actuator performance and experience) will undergo a
leak test on the air/hydraulic systems in accordance with preventative maintenance procedures.
This procedure is also based upon conversations with Cooper nuclear plant personnel. 0320K
(3) During each refueling
- outage, any valve that needs to be refurbished, will be disassembled, inspected, reassembled and retested in accordance with mechanical maintenance procedures.
Inspections will include specific attributes such as seat angle and disk seat
- angle, excessive seat to guide surface alignment clearance, incorrect disc to seat
- contact, contamination, concentricity of seat bore-to body guide
- surface, and minimum/maximum apparent seat band width (seat to disc).
Further any lapping will be performed using the Rockwell tool, which results in superior leakage results.
Using the above practices,
- tools, and methods Niagara Mohawk estimates that the "as found" leakage value for each MSIV will be less than 16 scfh when tested at the first and subsequent refueling outages.
This prediction is based in part on the industry data search and evaluation.
As a part of that evaluation it was noted that new
- methods, procedures and lapping tools now being used will improve MSIV leak rates'ven though the Cooper valves are smaller than the Unit 2
- valves, Niagara Mohawk believes that the leakage values experienced at the Cooper Station are obtainable at NMP2.
2.
Valve Orientation:
The BWR Owners Group has recommended that in view of the increased risk of LLRT failure for rolled valves, care should be exercised to ensure correct poppet-to-seat alignment.
If this alignment proves problematic, then compensation (i.e.,
modification of dimensions) should be considered. 0320K
NMPC Evaluation Results:
NMPC has compared the NMP2 MSIV rolled angular position of 20'o the industry MSIV rolled angular position of 35'nd notes the following:'a)
The resultant (orientation) rolled angle of the NMP2 MSIV actuator and disc-piston assembly will be less than the resultant rolled angle existing on the Cooper MSIV's which have good leakage experience.
(b)
The NMP2 MSIV actuator/stem/disc-piston assembly resultant compound rolled angle centerline is approximately 50'.
When compared to the 45'enterline of a vertically installed
- MSIV, the differential of 5's considered insignificant.
(c)
The valve vendor has identified that the MSIV leak tightness capabilities will not be degraded provided the rolled angle does not exceed 35'.
(d) Review of Shoreham (35'olled angle) and Cooper (35'olled angle)
"as found" MSIV leakage test results (See Table 3) indicates that a rolled angle on this type of MSIV design, not exceeding 35', is capable of meeting leak tightness requirements.
3, Excessive Clearance/Seat-to-Guide Misali nment The BWR Owners Group has recommended that in the event conditions indicate that excessive clearances or misalignments
- exist, accurate measurements should be taken to determine the extent of these conditions.
Should it be determined from these measurements
- that, in fact such a problem exists, action should be considered to 0320K
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establish optimum conditions.
This should involve consultation with appropriate supplier or manufacturers'MPC Evaluation. Results (a)
NMPC has consulted with both G.E.
and the valve vendor to establish the minimum/maximum clearance required by the valve vendor as identified on Table l.
(Refer to valve related design features for leak tightness See item 2.4)
(b)
The vendor identified clearance range is considered adequate to assure proper seat-to-guide alignment as discussed previously in item 2.2.4.
(c)
NMPC plans to measure the body bore inside diameter and the outside diameter of the disc-piston assembly during scheduled MSIV refurbishment or if an MSIV consistently indicates excessive leakage characteristics.
4.
Lack of Concentricit Incorrect Seat Contact Excessive Co-Efficient of Friction/Corrosion:
The BNR Owners Group has made certain recommendations regarding the lack of concentricity, incorrect seat
- contact, and co-efficient of friction/corrosion.
Due to the close interaction of these three
- items, they are being combined in this discussion.
Due to the
- critical, indeed
- primary, nature of the interaction of these conditions, it is recommended that great care be taken in ensuring proper concentricity, providing correct seat contact and minimizing friction to the extent feasible. 0320K
NMPC Evaluation Results:
(a)
NMPC will assure that proper,concentricity of the seating features is maintained.
Some of these actions include the use of proper machining equipment, consultation with the valve vendor and dimensional inspection of those features which will affect concentricity, when necessary.
(b)
The inherent design of both the MSIV's, conical seat and balanced disc features optimizes self alignment and proper seat contact.
The body-to-disc-piston assembly clearance allows for minor misalignment in angularity just prior to disc-to-seat closure.
(c) Friction will be minimized by routine MSIV preventative maintenance inspection procedures as well as corrective maintenance.
5.
Secondar Factors Contributin to Excessive MSIV Leaka e:
~t:
h 6
p ddtht 1
dl taken to maintain the as-manufactured seat geometry.
Any contemplated changes should be carefully assessed and analyzed to ensure that the changes will not be detrimental,to valve performance.
NMPC Evaluation Results:
(a)
NMPC intends to maintain the "as designed" nominal seat geometry during any subsequent MSIV refurbishment activities. 0320K
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(b) Any future contemplated changes will be analyzed and will include consultation with the valve vendor and/or other knowledgeable entities.
Should any such change be implemented, MSIV performance will be monitored to verify acceptability.
6.
Leaka e
Sources Other Than Seat:
The BWR Owners Group recommended that care should be taken to correct or isolate any identifiable leak paths before LLRTs are performed.
NMPC Evaluation Results:
(a) Potential leak paths other than the seats for this type MSIV
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design are (1) the body-to-bonnet joint, (2) stem packing and (3)
LLRT equipment connections/joints attached to the valve/piping.
(b)
LLRT instructions and procedures require that all potential external leak path joints be checked with the "Soap Bubble/
Snoop" technique prior to commencing leak testing.
If joint leaks are noted they are to be fixed prior to commencing testing.
If leaks cannot be appropriately fixed, this fact will be recorded and brought to the attention of the responsible test engineer for resolution/disposition.
7, Po et Rotation:
The BWR Owners Group recommended that consideration should be given to preventing possible poppet rotation by installing an appropriate anti-rotational device to preclude possible guiding surface wear. 0320K
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NMPC Evaluation Results:
The NMP2 MSIV design has a minimal tendency to rotate for the following reasons:
(a)
The NMP2 MSIV disc stroke position is located in the flow path such that the tendency for disc rotation is minimized due to the stream-lining effects of the fluid forces.
(b) There have been no reported induced vibration problems, which would imply a propensity for disc rotation, at other operating BWR plants (LaSalle 1
5 2, Hanford 2
and Tokai-2) that also use the 26 inch MSIV's having a
60% percent valve stroke position ratio.
(c)
NMPC is evaluating the vendor's suggested new modified stem/stem-disc assembly design as a possible product improvement to further minimize any potential poppet rotation.
Maintenance Conclusions Niagara Mohawk has reviewed both industry experience and BWR Owners Group recommendations.
Nine Mile Point Unit 2 is implementing enhanced maintenance procedures and methods based upon this assessment which are expected to reduce MSIV leak rates.
VI. CONCLUSIONS Niagara Mohawk has demonstrated that a
leakage control system is not required.
The basis for this conclusion are summarized as follows: 0320K
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1.
The Unit 2 Rockwell valves are similar to other BWR Rockwell Valves; therefore the industry inservice experience and leakage data is applicable.
2.
The industry leakage data show that almost 40% of the "as found" data for Rockwell Valves were below 6 scfh, and 85%
were less than 38 scfh, which is consistent with and below the Nine Nile Point Unit 2
NUREG 1169 radiological analysis values evaluated.
3.
The NUREG 1169 analysis and design bases analysis show that the initial leak rate of 6 scfh and valve leakage status at the end of the operating cycle will be acceptable.
The leakage value for the "as found" condition at the end of the first operating cycle for Unit 2 is expected to be less than 16 scfh.
4.
The maintenance assessment shows that the Unit 2
implemented improvements in techniques, tools and procedures will provide assurance that industry average leak rates are
- met, and improved leakage values can be expected for Unit 2.
(0320K) 0320K
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e
TABLE 1 Page 1 of 4 COMPARISON OF NMP2 ROCKWELL MSIV FEATURES VS.
OTHER BWR (ROCKWELL) MSIVS FEATURES NMP2 LaSALLE LaSALLE HANFORD TOKAI 1
2 2
2 HATCH 2
FITZ-VERMONT DUANE BRUNSNICK BRUNSNICK COOPER PATRICK SHOREHAM YANKEE ARNOLD 1
2 1.0 (GENL MSIV INFO) 1.1 VALVE MFGR 1.2 BASIC SYTLE/FIG NO (Uni-Directional/
Bal Disc/Stop Vlv)
Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell Rockwell JMMNTY JMMNTY JMMNTY JMMNTY 3MMNTY JMMNTY JMMNTY JMMNTY 3MMNTY 3MMNTY JMMNTY JMMNTY Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Fig 1612 Rockwell
'MMNTY Fig 1612 1.3 NOM VALVE SIZE (IN) 1.4 APPLICABLE CODE(S)
(ASME SEC III-CLl:
Y/N) 26 Yes 26 Yes 26 Yes 26 Yes 26 Yes 24 Yes 24 20 ANSI ANSI B16.5 B16.5 24 Yes 18 20 24 ANSI ANSI ANSI 816. 5 B16. 5 B16. 5 24 ANSI 816.5 1.5 DESIGN PRESSURE/
TEMP (PSIG/'F) 1.6 MIN HALL THICKNESS (INCHES) 1375/
586 1.74" 1
~ 58 1.58 1250/
1250/
575 575 1250/
1250/
575 575 1.58 1
~ 58 1
~ 48 1.74 1250/
1250/
575 575 1.74 1.74 1250/
1250/
575 575 1.468 1.468 1.74 1250/
1250/
1250/
575 575 575 1250/
575 1.74 1.7 INSTALLED VALVE ORI ENTATION(S)
(VERTICAL/ROLLED)
(QTY) (DEGREES)
V-(6) 20'-(2)
Inboard/
Outside V-(6)
V-(6) 35'-(2) 35'-(2) 30'+42'nboard/
Inboard/
Inboard/
Outside Outside Outside V-(Al1 )
V-(Al1 )
V-(Al1 )
V-(Al1 )
V-(6)
V-(4) 17'(2) 35'-(2)
Inboard/
Outside V-(6)
V-(4)
V-(6) 30'-(2) 30'-(4) 30'-(2)
Inboard/
Inboard/
Inboard/
Outside Outside Outside V-(4) 30'(4)
Inboard/
Outside 1.8 VALVE STROKE AS '/
OF MAIN SEAT BORE DIAMETER (0384C) 60 60 60 60 60 85 85 85 85 74 85 85
~,
~
4 c
.a C
TABLE 1 Page 2 of 4 NMP2 LaSALLE 1
LaSALLE HANFORD TOKAI 2
2 2
HATCH 2
FITZ-VERMONT DUANE COOPER PATRICK SHOREHAM YANKEE ARNOLD BRUNSHICK BRUNSHICK 1
2 2.0 VALVE RELATED DESIGN FEATURES FOR LEAK TIGHTNESS 2.
1 CONFIGURATION 2.1.1 CONICAL/FLAT/
SPHERICAL (MAIN DISC/SEAT)
Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1
', Coni ca 1 Coni cal Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 2.1.2 MAIN SEAT BORE DIA (INCHES) 23.52 23.50 23.50 23.50 23.50 18.21 18.21 18.21 18.21 15.25 15.25 18.21 18.21 2.1.3 MAIN SEAT/DISC INCLUDED ANGLE-NOMINAL (DEGREES) 90'0'0'0'0'0'0'0'0'0'0'0'0'.1.4 (MAIN SEAT)-SEAT BAND HIDTH (INCHES) 2.1.5 FLEXIBLE MAIN DISC DESIGN (YES/NO)
.136/
.130 Yes
.143/
.136 Yes
.143/
.136 Yes
.143/
.136 Yes
.143/
.136 Yes Yes Yes
.116/
.116/
.111
.111
.116/
.111 Yes
.116/
~ 111 Yes-
.118/
.110 Yes
. 118/
.110 Yes
.116/
.111 Yes
.116/
.111 Yes 2.1.6 STEM-DISC & SEAT CONF IG (CONICAL/
FLAT/SPHERICAL)
Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1 Coni ca 1
- 2. 1. 7 STEM-DISC/MAIN DISC
- 4. 56/
SEAT BORE DIA (IN) 4.55 4.56/
4.56/
4.56/
4.56/
4.56/
4.56/
4.56/
4.56/
2.505/
2.505/
4.56/
4.55 4.55 4.55 4.55 4.55 4.55 4.55 4.55 2.500 2.500 4.55 4.56/
4.55 2.1.8 STEM-DISC SEAT NOMINAL INCLUDED ANGLE (DEGRESS) 90'00 90'0'0'0'0'0'0'0'0'0'0'.1.9 STEM-DISC'S SEAT-SEAT BAND HIDTH (INCHES)
.203/
.183
.203/
.203/
.183
.183
.203/
.203/
.183
.183
.203/
.183
.203/
.183
.203/
.183
.203/
.183
.138/
.120
.138/
.120
.203/
.183
.203/
.183
ae
/
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\\*
P r
'I sr=,
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TABLE 1 Page 3 of 4 NMP2 LaSALLE LaSALLE HANFORD TOKAI HATCH 1
2 2
2 2
FITZ-VERMONT DUANE COOPER PATRICK SHOREHAM YANKEE ARNOLD BRUNSWICK BRUNSWICK 1
2 2.2 SEALING FORCE(S)/
LOAD(S) (APPARENT) 2.2.
1 DIRECTION OF APPLIED MEDIA (OVER DISC/
UNDER DISC)
Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc Over Disc 2.2.2 SPRING FORCE AT CLOSURE (LBS.)
8,050 8,050 8;050 8,050 8,050 7,100 7,100 7,,100 7,100 3,200 4,200 7,100 7,1'00 2.2.3 PRESSURE FORCE ASSIST TO SEAL (YES/NO) 2.2.4 ACTUATOR MIN
'OADING (PSIG) 2.3 VALVE STROKE(S)
Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 Yes 90 2.3.1 VALVE MAIN DISC 14.12 STROKE (IN)(NOMINAL) 14.12 14.12 14.12 14.12 15.44 15.44 15.44 15.44 11.25 13.00 15.44 15.44 I
2.3.2 STEM-DISC STROKE 1.00 (INCHES) (NOMINAL)
(Free Lift) 2.3.3 CONTROLLED CLOSURE Yes SPEED (YES/NO) 1.00 Yes 1.00 Yes 1.00 Yes 1.00 Yes
.62 Yes
.62 Yes
.62 Yes
.62 Yes
.50 Yes
.62 Yes
.62 Yes
.62 Yes (0384C)
li C
l 4
NMP2 LaSALLE LaSALLE HANFORD TOKAI 1
2 2
2 TABLE i Page 4 of 4 HATCH 2
V r
FIT2-
~
VERMONT DUANE BRUNSNICK BRUNSNICK COOPER PATRICK SHOREHAM YANKEE ARNOLD 1
2 2.4 CLEARANCES/ALIGNMENT 2.4.1 CLEARANCES BETNEEN
.035/
DISC-PISTON ASSY
.050 RIBS (O.D.)
AND BODY BORE I.D.
( IN)
- 2. 5 MATERIALS
.035/
.050
.035
.050
.035/
.050
.035/
.050
.018/
.018/
.028
.028
.018/
.018/
.028
.028
. 018/
.028
.018/
.028
.018/
.028
.018/
.028 2.5;2 2.5.3 STEM-DISC BASE MATERIAL r
MAIN DISC/SEAT STELLITE MATERIAL 2.5.1 MAIN DISC BASE MATERIAL SA-350 (GR.LF2)
SA-350 (GR.LF2)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-105 SA-182 (F-11)
SA-182 (F-11)
SA-182 (F-11)
SA-105 ASTM A-182 (F-11)
SA-105 SA-350 SA-182 SA-182 (GRLF-2)
(F-11)
(F-11)
Stel 1 i te Stel 1 i te Stel 1 ite Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 ite Stel 1 i te
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21 SA-185 (F-11)
SA-182 (F-11)
¹21 SA-182 (F-11)
'SA-182
'(F-11)
¹21 2.5.4 STEM-DISC/SEAT STELLITE MATERIAL 2.5.5 SLIDING SURFACE MATERIALS STELLITED (YES/NO)
Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 ite Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te Stel 1 i te
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21
¹21 Stel 1 i te
¹21 Yes (0384C)
i
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TABLE 2 Page 1 of 2
SUMMARY
OF CURRENT ROCKWELL (BWR) MSIV DESIGN CHANGE EVOLUTION STATUS DESCR I PT I ON PURPOSE NMP2 MSIV STATUS (1) Disc-piston connection configuration changed from a spherical backseat to either a conical or flat backseat configuration.
Resolve disc to piston separa-tion failure potential exper-ienced at Nucleanor.
INCORPORATED (2) Numatics air valves Resolve sticking air valve replaced with Norgren air spools at Nucleanor valves.
Vermont Yankee.
INCORPORATED (3) Improved stem/stem-disk and main disk/piston connection (joints).
Resolve stem/stem-disc and main disc to piston separa-tion potential as exper-ienced at Brunswick Hatch-2.
INCORPORATED (4)
New modified stem/
stem-disc assembly design.
Resolve potential stem/stem-disk cracking and separation as experienced at Confrentes
& Kuo Sheng.
(Due to flow induced vibra-tion noted on designs with greater than 60%
stroke lengths)
NMP2 MSIVs do not contain this new modified change suggested by the valve vendor as a product improve-ment.
The NMP2 MSIVs have a
60% (percent) valve stroke position as an integral part of the design and manufacture which minimizes the tendency for disc rotation as a result of the streamlining effects of fluid forces.
NMPC, however is in the process of evalu-ating the suggested product improvement.
1p 4'
o
~
TABLE 2 Page 2 of 2
SUMMARY
OF CURRENT ROCKWELL (BWR) MSIV DESIGN CHANGE EVOLUTION STATUS DESCRIPTION Spring flange bronze bushings PURPOSE Reduce propensity for galling/friction between yoke guide 5 tubes NMP2 MSIV STATUS INCORPORATED NEH Spring Divider material Reduce propensity for scoring/galling of the yoke guide tubes INCORPORATED Modified packing chamber design To replace asbestos packing/enhance pack-ing/stem leak tight-ness capability with graphite rings INCORPORATED NEH Limit switch trip arm design For plants modifying original MSIV valve stroke to a shorter stroke (e.g.
60%)
NOT APPLICABLE TO NMP2 MSIV
c,l+
I) 4
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TABLE 3 Page 1 of 1
NSIV TYPE C "AS FOUND" LEAKAGE DATA PLANT Cooper LEAK RATE
'O.
OF AVERAGE (3)
HI (3)
LO (3) LINE TESTS YEARS 8.4 20.0 0.8 48 1973-1986 LaSalle 2
9.9 44.8 0.8 12 1983-1987 Vt Yankee 11.7 46.0 1.0 44 1973-1985 WPPSS 2
13.4 29.9 0.7 1985-1986 FitzPatrick 14.4 Gross 16 1978-1985 Hatch 21.8 Gross 29 1980-1986 Duane Arnold (1) 80.2 318 16 1983-1985 LaSalle 1
225.8 854.3 5.5 1984-1985 Shoreham (2) 4.1 10.1 0.5 1985-1986 All Plant Weighed X = 27.14 for 189 Line Tests (1) Valve Averages rather than line averages (2) Valves have not seen steam loads (3) Leak rate values in SCFH
7-
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