ML20238C650
| ML20238C650 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 02/05/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20238A944 | List:
|
| References | |
| FOIA-87-438 NUDOCS 8709100279 | |
| Download: ML20238C650 (38) | |
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SAFETY EVALUATION BY THE OFFICE OF' NUCLEAR REACTOR REGULATION CONCERNING MAIN STEAM ISOLATION VALVE OPERABILITY NIAGARA MOHAWK POWER CORPORATION NINE MILE POINT UNIT 2 DOCKET NO.: 50-410
1.0 INTRODUCTION
Two general problem areas were identified concerning the Nine Mile Point Unit 2 (NMP2) Main Steam Isolation Valves (MSIV). These problem areas can be cate-gorized into MSIV leakage rates which exceeded the 6 SCFH Technical Specifi-cation (TS) limit and the MSIV closure time operability which exceeded the 3 to 5 second TS range. This evaluation only addresses the closure time operability issue.
By letters dated October 21, November 17, December 8, and December 16, 1986, and January 27, 1987, the licensee has provided information on the MSIV mechanical design and closure time problems, including corrective action and technical justification, and a commitment to perform additional confirmatory testing.
The operability of each 24-inch reduced port, (21-inch) ball type NMP2 MSIV assembly depends ultimately on the ability of each MSIV actuator ball valve unit to demonstrate acceptable integrated MSIV system performance; i.e., each MSIV actuator must be operated with its associated 21-inch ball valve to i demonstrate that the assembly will function reliably by repeated valve closing l within 3 to 5 seconds, thereby preventing uncontrolled releases of radioactivity '
from the reactor vessel to the environment.
The October 21, 1986 submittal provided information pursuant to ".0CFR 50.55 (e) to NRC's Region I concerning MSIV closure time problems. TMs report !
I related to a cracked latching roller found on one MSIV actuator and excessive actuator trip times. A time-dependent phenomenon of increased latch tripping ;
force with increased open time was noted.
The report describes the original faulty mechanical actuator design features and associated problems, presents the design modifications teing implemented to resolve these problems, and discusses the testing performed to justify the resolution of the actuator problems. Justification for the corrective action is based on a design evaluation of the modified actuator together with the testing results to date and the additional planned confirmatory testing, i
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2.0 DISCUSSION In.the original mechanical . latch design, the hydraulic fluid was used.only to pressurize the hydraulic cyclinder, thereby moving the piston and compressing the springs to open the MSIV. . The fluid performed no function while the main steam isolation valve was in the open position as the hydraulic system was de-energized and the mechanical latch held the valve open. The modified actuator
' design removes the mechanical latch (actuator. device) assembly and modifies the existing actuator's hydraulic system to perform-the function of holding the-MSIV in the open position instead of the mechanical latch mechanism. Although the hydraulic fluid is now constantly under pressure when the valve is- open, the increased duty on the fluid will have no adverse effect on the actuator's ability to perform.
The MSIV actuator with the modified hydraulic system continues to use the canister assembly springs to provide the force for MSIV closure; it also uses the hydraulic system.to open the'MSIV. The two solenoid spring plungers as well as the mechanical latch mentioned above have been eliminated. The hydraulic system associated solenoid operated valves (SOVs) are retained. The SOVs in the original hydraulic design were closed (energized) only when the MSIV was being opened and then put in
'the normally open (deenergized) position. Their . function is revised in the modified design as they are maintained in the closed (energized) position during normal cperation with the MSIV open. .The hydraulic system being pressurized provides the force via the hydraulic cylinder to open the MSIV and hold it open against the closing force of the canister assembly springs. When the MSIVs are required to close, the SOVs are opened (deenergized), the hydraulic system is depressurized, and the fluid in the hydraulic cylinder which holds the MSIV apen is exhausted into the reservoir allowing the spring canister assembly to close the MSIV.
The new hydraulic system requires the following additional and/or redesigned equipment to enable the hydraulic system to perform the latching and tripping functions by depressurizing the system rapidly:
- new jockey hydraulic pump and hydraulic accumulator - to maintain hydraulic system pressure while reducing cycling times on the much larger main hydraulic pump; new pressure switch and controls - to maintain pressure by cycling the jockey pump;
- modified low leakage hydraulic cylinders - to minimize hydraulic fluid losses and associated system pressure decay via modification to existing cylinder design specifically adding a piston lip seal for minimizing jockey pump cycling, and a mechanical stop to establish MSIV full open position; change of hydraulic system related $1Vs' normal operating mode to one of being closed (energized) whihe the MSIV is open;
- modification of the SOVs - to rapidly open under hydraulic pressure by modification to existing SOV design via a spacer to increase the spring force and the combination of a graphite filled '
teflon backup ring added over the EP rubber 0-ring on the seat disc
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- modification.of both 2-inch diameter 50Vs' electrical supplies -
l to enhance reliability of both SOVs, supply will be .from either of U the Ltwo RPS uninterruptable power supplies through appropriate y 'auctioneering circuitry loss; a loss of either supply will not open (deenergize) either SOV;-
- new control room MSIV hydraulic system relateo instrumentation -
to allow detection of abnormal operation and alert the operator; and
- automatic stop by both hydraulic pumps on receipt of an emergency MSIV closure signal - to prevent an attempt to pressurize'the ;
hydraulic system which might deter or slow down MSIV closure. l
,- The proposed qualification of the redesigned and modified actuator consisted of three steps as follows:
During the first step, overall adequacy of the actuator assembly was attempted. -Data from the previous dynamic testing performed at Wyle Laboratories were submitted as applicable, since the modifications did not result in changing the previously defined seismic / dynamic requirements nor did-they appreciably affect the stiffness / mass characteristics of the operator / actuator. <
The second step consisted of evaluating the structural integrity of the added non safety related components, jockey pump and hydraulic accumulator. This was accomplished by analysis, demonstrating structural integrity during a seismic / dynamic event. The peak accelerations used in this analysis were derived from the required response spectra used for the actuator qualification.
The third step in the qualification of the actuator involved the 2-inch diameter hydraulic system SOVs which were part of the actuator dynamic testing performed at Wyle Labs in 1983. These SOVs were not required to function during the tests performed at Wyle.
In the modified actuator design, the additional function of the hydraulic system requires that the SOVs remain in a closed position and open upon demand to enable the MSIV to close within 3 to 5 seconds. Demonstration of operability of these hydraulic system SOVs during and after a seismic / dynamic event is required. To accomplish this, the acceleration levels and equivalent static loadings on the SOVs were developed based on a combination of the data available from the accelerometers that were mounted at the base of an 50V during the dynamic testing performed at Wyle Labs and a finite element analysis of the actuator assembly. The SOVs were !
then qualified for the required accelerations and loads resulting from seismic / hydrodynamic events. A combination of analysis, dynamic testing of a similar 50V and a static operability pull test 1 were performed on an identical SOV. The static operability testing l identified the need to install a spring spacer in the SOV assembly i to assure valve operability. This spacer has been installed in the l SOVs that are part of the actuator assemblies at NMP2 and in the SOVs used in the prototype test program.
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1 1
t Testing to demonstrate performance of the modified MSIV actuator was ,
conducted at Crosby Valve and Gage Company. This testing was done on the i same actuator which underwent seismic / dynamic operability testing on a 1 shake table at Wyle Labs. The following is a brief description of the testing performed:
On August 29, 1986, the hydraulic system was modified to perform )
the additional functions of holding the HSIV open and initiate MSIV j closure. A small accumulator tank, jockey pump, flow control valve ]
and pressure switch were added to the test actuator. The test j actuator was held in the open position for 3 days. During this time 1 it was noted that the hydraulic pressure dropped quickly, which required frequent cycling of the jockey pump.
On September 2, 1986, the actuator was tripped and a delay was noted )
between trip signal initiation and 50V opening. At this time the hydraulic cylinder and cap were replaced with one which included a ,
mechanical travel stop to control the MSIV open position. Further j 1
testing cuntineed which snowed delays in 50V opening and frequent jockey pump cycling.
On September 11, 1986, the 50V was disassembled and the cause of SOV trip opening delay was determined to be sticking of the 50V 0-ring.
On September 15, 1986, representatives of the 50V manufacturer (Target Rock corporation) examined the SOVs and testing with j alternate ring materials was initiated. j On September 17, 1986, the cause of the hydraulic system pressure drop and the resultant frequent jockey pump cycle times was identified as fluid leakage through the hydraulic cylinder. To alleviate this problem, a new piston with EP rubber lip seal was j ordered.
On September 23, 1986, actuator testing began with SOV disc seals equipped with the current EP rubber 0-ring / graphite filled teflon (TFE) backup ring combination.
On October 10, 1986, an enchanced piston lip seal was installed in the hydraulic cylinder on the test actuator, and on October 27, 1986 spring spacers were installed in the SOVs and testir.g continued.
According to the licensee, all of the tests at Crosby discussed in the preceding paragraphs were performed on a full size actuator. With the exception of the modified hydraulic cylinder and the previously discussed equipment which were added to facilitate the hydraulic latch, all of the equipment on the test actuator, including the SOVs are the same equipment which were seismically and dynamically qualified by shake table testing conducted at Wyle Labs in 1983, and reviewed by the NRC during the Pump and Valve Operability Review Team audit in 1985. The only changes from I
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l the previously qualified configuration were the elimination of the mechanical latch / spring components and expansion of the hydraulic system equipment and function.
The licensee's submittal dated December 16, 1986 provided additional actuator test results. These include twelve successful actuator trip tests since September 23, 1986, when the 50V disc seals were reported as being equipped with the EP ~ rubber 0-ring / graphite filled teflon (TFE) backup ring combination.
The last test was successfully completed on December 4, 1986 after the actuator had been held in the open position by the hydraulic latch system for a period of thirty eight days. During the test period, the jockey pump had cycled only four times.
3.0 EVALUATION From the October 21, 1986 submittal in plant testing revealed MSIV closure durations in excess of the 3 to 5 second TS requirements, and that the excessive closure time was related to the length of time the valve had been latched open.
During preoperational testing, cracked latching rollers were also discovered in those actuators.
The problem of MSIV closure operability should not be considered fully corrected until the complete modified MSIV assembly is capable of repeated closures within the 3 to 5 second TS range, first in Operational Conditions 4 and 5, then in Operational Condition 3 and finally in Operational Conditions 2 and 1.* The MSIV assembly includes a 24-inch reduced port (21-inch) ball valve with a modified seat spring configuration and a recoated tungsten carbide ball combined with a modified hydraulic actuator as described in Section 1.0.
A silicone base fluid was chosen for the hydraulic system because of its thermal stability and its good oxidative behavior under radiation exposure.
Dow Corning hydraulic fluid 510-100 was specified by the valve manufacture as being acceptable for use in the MSIV actuator.
The service life of the fluid in plant will be determined by periodic testing in accordance with Chemistry Maintenance Procedure N2-CSP-17. The shelf life of the fluid when kept at room temperature is indefinite. The effect of in-
- Tech Specs (Table 2.1)
Operational Condition Mode Switch Position Average Reactor Coolant Temp.
. 1. Power Operation Run Any temperature l 2. Startup Startup/ Hot Standby Any temperature
- 3. Hot Shutdown Shutdown > 200'F
- 4. Cold Shutdown Shutdown < 200*F
- 5. Refueling Shutdown or Refuel 5140F
i service operation will be monitored during refueling outages in accordance with procedures to detect significant changes in viscosity and accumulation of particulate. The licensee has committed to a sampling and testing schedule to occur once each refueling outage based upon the following facts:
- 1) the fluid is essentially in a static condition, 2) a filter is provided to remove particulate, 3) the valve is tested monthly to ensure operability, 4) the main steam tunnel and primary containment are a high radiation area during !
normal operation, and 5) the fluid is qualified for the application.
Although no changes over the service life are expected based on testing performed by Dow Chemical, the surveillance testing of the hydraulic fluid is considered to be added assurance for proper actuator performance. The staff According to the licensee the testing performed at Crosby has verified the capability of the hydraulic system SOVs to open as required. Since testing of the modified hydraulic system was initiated on August 29, 1986, in excess of 70 actuator trip tests were reported as being run. t j Eleven actuator trip tests were run using the EP rubber 0-ring /TFE -
backing ring material combination which has been installed in the SOVs on s the actuators at NMP2. The results of these eleven tests verified that every time this combination of 50V 0-ring material was tested the actuator successfully closed within the required 3 to 5 seconds. There were no unsuccessful test results reported using this combination of 0-ring materials.
Based on the above analysis and tests the modified MSIV hydraulic actuator appears to be qualified to operate reliably by itself. Operability of the redesigned MSIV assembly will be determined during the Pre-op testing program.
The October 21, 1986 submittal, Section 6 states that "when the modifications discussed in the report are completed and the valves have passed their pre- 3 operational tests, the MSIVs will be appropriate for normal operation of the I plant." The report refers to the prototype test program on a NMP2 MSIV assembly which will dbplicate the hardware and actual plant operating !
conditions to the extent possible. The initial prototype testing is scheduled i to be completed by April 1, 1987 with the test report provided to the NRC by 1 May 15, 1987. It is important to assess each closure time operability related
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test scheduled to be performed on each of the eight modified MSIVs installed I in NMP2. The insitu MSIV operability test assessments are important to be !
identified and satisfactorily passed, especially until the prototype test '
program has been successfully completed to confirm MSIV closure time operability.
The staff finds this acceptable.
A draft copy of Preoperational Test Procedure Number N2-P0T-1-2 entitled " Main Steam Isolation Valves" was included in the review. This cold shutdown test document is designed to prove that the NMP2 MSIVs will perform per their design logic during plant operation. The preop tests provide baseline data for future operations and testing, and to determines the operational readiness
! of the MSIVs. During the preop test procedure, each of the eight MSIVs will l be tested individually during fast closure with a 3-5 second requirement. Each MSIV will be tested four times with the results recorded. Note that the section entitled "MSIV Manual Isolation" of the Preop tests verifies several times that !
j all the MSIVs close simultaneously but there are no requirements for fast closure !
of all MSIV together required prior to criticality and prior to reactor system heatup to normal operating pressure and temperature (approximately 1000 psia and 550"F).
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J In lieu of the NMP2 Startup Test Procedure drafts, NMPC provided associated FSAR startup test descriptions. According to Table 14.2-227 describing main steam isolation valves functional tests [Startup Test (SUT-25A)], "At 5 percent and greater power levels individual fast closure of each MSIV will be performed to verify their functional performance and to determine closure times." Also full individual closures will be performed between 40 and 55 percent power and again between 60 and 85 percent power. These latter tests will ultimately be used to determine the maximum power test condition that has ample margin to scram. The stated test objectives of SVT-25A are to determine isolation valve closure time at rated conditions and to functionally check the HSIVs for proper operation at selected power levels.
According to FSAR Table 14.2-228 describing full reactor isolation [Startup Test (SUT-258)], " A test of the simultaneous full closure of all MSIVs is performed at greater than or equal to 95 percent of rated thermal power."
The test objective of SUT-25B is to determine the reactor transient behavior that results from the simultaneous full closure of all KSIVs. The recorded MSIV full closure times must meet the 3 to 5 second criteria.
According to Regulatory Guide 1.68, Revision 2 entitled " Initial Test Programs for Water-Cooled Nuclear Power Plant," there is guidance in its Appendix A entitled " Initial Test Program" for MSIV fast closure testing as follows:
Following initial criticality, appropriate low-power tests (normally at less than 5% power) will be conducted including " Demonstration of the operability including stroke times of main steam line and branch steam line valves and bypass valves used for protective isolation functions at rated temperature and pressure conditions."
During power-ascension testing, verification of " operability and response i times of main steam isolation valves an'd branch steam line isolation valves" is included. This latter testing is recommended to be performed at approximately 25 percent power level.
There is reasonable consistency between the NMP2 preop and startup test i requirements and the guidance provided by Reg. Guide 1.66 regarding MSIV '
operability. While the Reg. Guide recommends low power MSIV fast closure "normally at less than 5% power," NMP2 Startup Test (SUT-25A) MSIV fast closure tests are scheduled per the FSAR to be performed "at 5% and greater power". However, in the letter dated December 16, 1986 the licensee has committed to perform the tests at less than or equal to 5% power. It is important that the first fast closure tests be conducted as soon as practicable q af ter the MSIVs reach normal operating temperature and pressure. The licensee !
has provided, and the staff finds it acceptable, the following schedule for f ast closure testing between the preop and 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> warranty run:
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Criticality- Power Description 10s < 5% Emergency (fast) close each MSIV. individually. {
'l for closure timing 47 10-20% Fast close MSIVs following initiation of shutdown from outside the control room
'111 50-55% Fast closure of each MSIV individual for closure timing i l
119 60-65% Fast close fastest MSIV for closure timing /
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-121 90% Fast close fastest MSIV for closcre timing /
scram avoidance 124 94% Fast close fastest MSIV for closure timing /
scram avoidance 136- 95-100% Initiate fast closure of.all MSIVs to initiate reactor scram
4.0 CONCLUSION
On the basis of modified actuator t'esting to date and contingent on successful completion of the preoperational tests, and the Prototype Testing Progra.a scheduled to be completed by April 1, 1987 (the test report to be provided by May 15, 1987), the staff concludes that the MSIVs are acceptable for plant operation up to the first refueling. The staff will evaluate the prototype program test results for the purpose of demonstrating long term operability prior to making a final decision on continued use of the modified MSIV 't assemblies beyond the first fuel reload.
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ENGINEERING BRANCH SALP Input For .
NIAGARA MOHAWK POWER CORPORATION i Plant: Nine' Mile Point, Unit 2 .
Licensing Activity: MAIN STEAM ISOLATION' VALVE OPERABILITY-MECHANICAL DESIGN MODIFICATION j
- 1. Management Involvement in Assuring Quality Overall rating for this attribute is category 2. The licensee exhibited ,
evidence of prior planning and assignment of prioritie's to. address the issue. -l
- 2. Approach to Resolution of Technical Issues Overall rating for this attribute is category 2. The licensee demonstrated understanding of the issues and provided a technically sound approach.for resolution.
- 3. Responsiveness to NRC Initiatives Overall rating for this attribute is category 2. The licensee was generally responsive.
- 4. Enforcement History - N/A
- 5. Reporting and Analysis of Reportable Events - N/A
- 6. Staffing - N/A
- 7. Training ~- N/A i
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i BRIEFING FOR COMMISSIONER ASSELSTINE ON NMP-2 MAIN STEAM ISOLATION VALVES FEBRUARY 27, 1987
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BALL VALVES VS, Y-PATTEPN GLOBE VALVES CllPPENT PROTOTYPE TEST PROGRAM STATUS F. WITT LEAKAGE PROBLEMS WITH Y-PATTERN GLOBE F. WITT VALVES l
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, MSIV LEAKAGE - DOSE CONSIDERATIONS DESIGN BASIS LOCA WITH TECHNICAL SPECIFICATI0F LEAKAGE j MEETS 10 CFP, PART 100 --0FFSITE MEETS GDC 19'- CONTROL ROOM OPERATORS MSIV PRE 0PERATIONAL TESTS MEET. TECHNICAL SPECIFICATIONS SHOULD LEAKAGE EXCEED TECHNICAL SPtclFICATIONS, VALVES WILL BE REFURBISHED TO MEET THE LIMIT IN UNLIKELY EVENT LEAKAGE EXCEEDS TECHNICAL SPECIFICATION LIMIT, NUREG 1169 INDICATES MAXIMUM LEAKAGE FOR NUMBER OF VALVE CLOSURES THROUGH FIRST FUEL CYCLE MEETS 10 CFR PART 100 - 0FFSITE MEETS GDC 19 - CONTROL ROOM OPERATORS 1
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EXCEEDED 300 SCFH THP0 UGH PACKING' 100 HOUP WARRANTY PUN LEAK TEST (REPEATED PEPACKED VALVE WITH PLANT PERSONNEL AND PROCEDURES)
FXCEEDED 300 SCFH THROUGH PACKING CURRENT DIRECTl") 0F PROGRAM DEVELOPMENT OF ACCEPTABLE PACKING DESIGN PROTOTYPE TESTING OF MSIV F0P TnTAL VALVE CLOSilRES DllRING PLANT FIRST FUFL CYCLE REPEAT PROTOTYPE TESTING WITH SECOND BALL AND SEAT LONG TERM TFSTING FDP DESIGN AND MATEPTAL IMPROVEMENTS l-1
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' COPY OF-LEIBSTADT REPORT TO NRC DATED MAY ?9, 1985 WAS MADE AVAll.ABLE TO NIAGARA M0HAVK LE1PSTADT BALL VALVF EXPERIENCE REPORTED BY GE ON REQUEST FROM NIArARA M0 HAWK (0CTOBER 1986) l l
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1 MSIV LICENSE EXEMPTION'
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vi) A schedular exemption to GDC 54 and GDC 55, Appendix A to 10 CFR Part 50 for the main steam isolation valves (MSIVs) until initial criticality and prior to operation in modes 1, 2, or 3. This exemption permits Niagara Mohawk Power Corporation to. load, fuel and to conduct startup tests up to criticality at Nine Mile Point Euclear Station, Unit 2 before completino the modifications reauired to. correct problems with the MSIV actuators and before completino installation and modifications to four of the valves (one in each linel to correct valve leakage problems (Section 6.2.4, SSER 5).
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'MSIV LICENSE CONDITION i i
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'(14) Main Steam isolation Valves (Section 6.2.4. SSE9. 51 l In accordance with their letter of October 20, 1986, Niagara I
Mohawk concerning Power Corporation the main shall meet steam isolation valvesthe following)comitments (MSIVs : )
(a) Confirmatory leak testing will be perfomed on all eight of the Nine Mile Point Nuclear Station Unit 2 tGIVs; in accord-ance with the test method for Type C tests discussed in 10 CFR Part 50, Appendix J, 111.C. during the first outage following the 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> warranty run or within 30 days follow-ing the 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> warranty run, whichever is earlier. This test is in addition to, not in place of, any required Appendix J testing.
(b)- A prototype test program shall be completed on the 19SIVs that will test the modified valve and actuator configuration similar to the MSIVs installed in Nine Mile Point Nuclear Station, Unit 2. The objectives of that program '
shall be as follows:
i) Verification of the mechanical integrity of the valve and the actuator for the expected operatino and test cycles.
ii) Demonstration of valve leak tightness for the expected valve duty cycles.
iii) Demonstration of the ability to close the valve within the Technical Specification limits under normal opera-
- ting pressure and temperature steam conditions.
iv) Verification of the conservatism of the between-the-seat leak test method as an alternative to across-the-valve seat leakage tests. ,
v) Provide baseline data for the evaluation of (1) the long term suitability of the valve and (2) potential design and material improvements.
(c) In addition, the prototype test report, which will address the confirmation of the valves' acceptability for the first operating cycle, shall be provided to the NRC by May 15, 1987.
).
.In the same paragraph, fourth sentence, the staff stated:
All: ventilation system penetrations (except those of the SGTS [ standby gas treatment system]) are fitted with two fail-closed, air-operated butterfly dampers in series.
In Section 9.4.2.2.3 of FSAR Amendment 10, page 9.4-25, the applicent refers to " isolation dampers'." Not all of the dampers are of The
' the butterfly type.
underlined word should be deleted.
i In'Section 6.2.3 of'the SER, page 6-21, second paragraph, item 7, the staff stated:
.(7) The reactor building is assumed to limit inleakage to 100% of the reactor building and auxiliary bays volume per day under neutral wind loading conditions (3160 fta/ min).
In Section 6.2.3 of the SER, page 6-22, item 3 at top of page, the staff stated:
(3) The reactor building inleakage rate is not greater than
- 3,160 f t8/ min at a pressure equal to or below -0.25 in. WG -
[ water gauge]. ,
In Section 6.2.3.4 of FSAR Amendment 26, page 6.2-57d, the applicant increased the reactor building volume from 4,547,204 8ft to 4,593,600 ft 3 to., reflect the as-built plant configuration. Therefore the reactor building inleakage was increased from 3,160 fts/ min to 3,190 ft S/ min. The underlined numbers in both' sentences quoted above should be 3,190. The increased inleakage of
' 3,190 ft / min is included in the final draf t Technical Specifications issued 3 !
j to the applicant (Adensam to Mangan, letter dated June 26,1986).
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6.2.4 Containment Isolation System j In a letter dated August 28, 1986, amended by letters dated October 2 and October 10, 1986, the applicant requested a schedular exemption from the
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requirements of General Design Criteria (GDC) 54 and 55 of' Appendix A to 10 CFR 50 with regard to main steam isolation valve (MSIV) operability. The requested exemption is to permit fuel loading and performance of those startup tests that can be conducted in operational conditions 4 and 5 (cold shutdown and refueling) ;
before criticality. The applicant has reported that recent, testing of the MSIVs has shown that the valves are' unable to close consistently within the required time frame, and in some cases the valves have failed to close at all.
The proposed exemption will permit fuel loading and some limited precriticality
' testing to be performed in parallel with efforts to resolve the MSIV problems.
The exemption requested by the applicant would permit only those operations ,
that do not involve reactor criticality because it is restricted to cold shut- l down and refueling mode testing. Because the fuel had never been irradiated and criticality will be prohibited, virtually no fission products will be present. As a result, primary containment isolation for the protection of the public is not required; However, secondary containment integrity is required by the Technical Specifications for core alterations. This isolation will be provided by one refurbished leaktight MSIV in each main steamline (deactivated ,
and in the closed posit. ion). Likewise, because of the lack of fission products, j NHP-2 SSER 0 6-5
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the risk of undue exposure to those workers involved in MSh repair or codifi-cation is negligible. Because the radiological risk to both workers and the public is negligible for the requested exemption, the schedular exemption is acceptable.
The applice.nt's request for a schedular exemption from GDC 54 and 55 with re-gard to MSIV operability, to permit fuel loading and testing that can be per-formed in operational conditions 4 and 5, is acceptable because the fission product inventory in the fuel is negligible and criticality is prohibited dur-l ing this period and, therefore, there is negligible radiological risk to the l public and to workers. Secondary containment integrity will be provided by a closed and deactivated MSIV in each main steamline.
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l In accordance with 10 CfR 50.12(a), special circumstances exist that would warrant issuance of the requested exemption. The exemption would provide only l
l temporary relief from the applicable regulation, and the applicant has made l
good-faith efforts to comply with the regulation. The ability of the MSIVs to l
close within the required 3 to 5 see had been demonstrated by earlier tests.
I However, recent site testing revealed the inability of the valves to close.
l Furthermore, the staff finds that the proposed action is authorized by law, will not present an undue risk to the public health and safety, and is con-sistent with the commori defense and security.
In Section 6.2.4 of Supplement 3 to the SER, the staff indicated that the applicant had committed to lock closed the 3/4-in. solenoid valves on the drain lines of the main steamline penetrations. For clarification, the applicant's actual commitment was to remove the power supply fuses for these valves.
l 6.2.4.1 Containment Purge System In Section 6.2.4.1 of the SER, third paragraph, first sentence, the staff indi-cated that the applicant had committed to install debris screens on the 14-in.
i and the 2-in. purge / pressurization lines located inside the drywell. The sen-
! tence should be revised to read:
The applicant has committed to install quality assurance Category I debris screens on the inboard end of each 12-in. and 14-in. purge /
pressurization line located inside the primary containment.
6.2.4.2 NUREG-0737 Item II.E.4.2, Containment Isolation Dependability In Supplement 3 to the SER, Table 6.4 contained the containment isolation sig-nals and the paran.eters sensed to initiate each signal. In FSAR amendments through Amendment 26, the applicant included additional isolation signals.
Table 6.4 of this supplement contains a revised table of isolation signals.
6.2.4.3 Mafn Steam Isolation Valve Leakage Concerns The following two problems were recently uncovered concerning the main steam isolation valves (MSIVs): (1) defective actuators that affected valve closure time and latch disengagement and (2) leakage rates that exceeded the 6-scfh Technical Specification limit.
NHP-2 SSER 5 6-6
The excess leakage was attributed by the applicant to failure of the tungsten l carbide coating on the ball as a result of high localized stresses, and subse-l quent scratching of the stellite seat surfaces by the released tungsten carbide particles.
The resolution of the actuator problem will be addressed in a supplement to be issued before criticality.
The MSIV leakage concern and its interim resolution is covered in this supple-ment. The first issue to be addressed is the use of one MSIV in each main steamline, with a modified seat spring configuration and recoated tungsten carbide ball, to ensure secondary containment integrity to permit fuel loading and precriticality startup testing. The MSIVs will be deactivated in the closed position and Type C leak tested to verify leaktight integrity.
The second issue is the appropriateness of the use of all eight MSIVs, with modified seat spring configuration and recoated tungsten carbide balls, to
. ensure primary containment integrity and permit criticality and power operation through the initial fuel cycle. The applicant has provided information in letters dated October 8, 10, 17, and 20, 1986, concerning the MSIV leakage problem, its resolution, and a commitment to perform a modification verifica-tion test program during the first fuel cycle. As part of this program, the applicant has committed to perform a prototype test program to confirm the operability of the modified NMP-2 MSIVs. The tests will be conducted during the first few months of plant operation. The prototype valve configuration will duplicate the valve and actuator design used in the plant. The test objectives include (1) verification of the mechanical integrity of the valve and actuator for the expected operating and test cycles (2) demonstration of valve leaktightness for the expected valve duty cycles (3) demonstration of the ability to close the valve within Technical Specifi-cation limits under normal operating pressure and temperature steam conditions
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(4) verification of the conservatism of the between-the-seat leak test method as an alternative to across-the-valve seat leakage tests Other objectives of the prototype test program are to provide baseline data for evaluation of (1) the long-term suitability of the valve and (2) potential design and material improvements.
In March 1986 all eight MSIVs underwent Type C local leak rate tests (LLRTs) in accordance with the requirements of Appendix J to 10 CFR 50. The results of the i tests were acceptable. By August 1986 these valves were each cycled in excess of 100 times (75 valve cycles are estimated for 'the first fuel cycle) in an l attempt to correct actuator problems. Subsequent to these operations, leak testing in September 1986 indicated that all eight MSIVs had leakage rates above the limiting value of 6 scfh in the Technical Specifications. !
The applicant in its submittal of October 20, 1985, and during the meeting with the staff on October 15, 1986, provided its evaluation describing the conditions NMP-2 SSER 5 6-7 l
. ,- l 1
that led to degradation of the tungsten carbide coating on the ball and of the seat that forms the seal. The applicant has provided the results of mechanical analyses showing that when the originally configured valve is opened from its closed position, the loads cause the seat to " rock," resulting in high local stresses on the ball. From the results of site frictional tests combined with the analytical results stated above, the applicant has hypothesized that the degradation occurs as follows:
(1) High local contact stresses when " rocking" occurs cause the softer stellite 6 seat material to be smeared onto the harder tungsten carbide ball surface when the valve is cycled open.
(2) When the stellite 6 material is present both on the ball surface and the seat, the high local contact stresses cause localized cold welding of j portions of the seat to the ball surface.
(3) Subsequent cycling of the valve causes local delamination of portions of -
the tungsten carb.ide coating when the local cold-welded areas are pulled apart. This premise is suppor.ted by the observations of the ball and simulated seat surfaces in the site friction test performed at about 55-ksi ball pressure. Pock marks were observed on both the seat and ball after 30 strokes of the valve during the test.
(4) The loose hard tungsten carbide flakes removed from the ball surface cut the softer seat surface when the valve is cycled, causing the seal between the seat and ball surfaces to be degraded.
The staff concurs that the above-stated failure mechanism appears plausible from the information obtained from the analytical and test data. Most as-suredly the data support the conclusion that the tungsten carbide coating degradation is the result of a faulty valve design, rather than related to a material problem with the coating itself.
To correct this design deficiency, the applicant decided to rearrange the seat springs. In this regard, four 115 pound springs were removed from the left side of the seal ring (facing the ball) and eight 57.5 pound springs were added on the right side of the seal ring to determine if rocking would be eliminated by the revised spring pack. The results of the analysis indicated that the modification should be effective in eliminating the rocking phenomenon. If the seat does not rock, the contact area of the seat on the ball is much larger.
The applicant states that the results of its calculations are that an order-of-magnitude reduction of stress is realized from the modification, and that the calculated bearing stress is reduced to approximately 2,700 psi.
The applicant has performed two tests to date for usessing the performance of the modified ball valve. One test consisted of straking a valve with a new ball and modified spring pack 75 times. This was followed by leak checking and subsequently examining the ball and seat surfaces for degradation. The appli-cant reported that the ball surface showed some evidence of wear similar to t
that observed in other tests where the contact pressure was low. No other degradation of the ball surface was reported. Inspection results reported for the seats are that the surface finish meets requirements and only some slight scratching and polishing were observed. The applicant reported the modified l
NMP-2 SSER 5 6-8
_ _ _ _ _ - . -_- -. s=a
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l valve passed the leakage test following 75 operating cycles. The results of simulated mock friction tests, in which a simulated stellite 6 seat was stroked across a tungsten carbide ball at a contact pressure of 3,500 psi, were reported to be similar to test results for the modified valve. Essentially the same wear observations were presented for 75 cycles for the ball and simulated seat in the mock friction test.
On the basis of the analytPal and test results presented by the applicant, the staff concludes there is reasonable assurance the modification will be effec-tive in reducing degradation of the ball / seat. However, the tests were per-formed on a new ball. The actual balls that will be used at NMP-2 will be recoated. To assess the difference between a recoated and a new ball, one must consider the fabrication process. The balls for the MSIV valves were initially fabricated as follows:
(1) The balls were cast using a 316 type austenitic stainless material.
The castings were extensively weld repaired to remove casting discon-tinuities (this is not unusual for this type casting). The casting then received a solution anneal heat treatment following weld repair.
(2) A Haynes 25 weld overlay was applied. The final coating thickness was between 0.080 and 0.100 in. The Haynes 25 coating was ground and then liquid penetrant tested.
(3) The Haynes 25 coating was grit blasted as a surface preparation before coating with a material rich in tungsten carbide. A minimum 0.010-in.
tungsten carbide coating was applied by Union Carbide Corporation using a detonation gun process. This process was used to obtain a low porosity coating with a minimum of distortion of the ball. The ball coating was ground and subsequently lapped to the seat.
Because the ball surface was damaged by stroking in the originally configured valves, it was necessary to refurbish their surf aces. The refurbishment consisted of mechanically removing the tungsten carbide coating, reapplying it, and refinishing the ball surface. Upon removal of the tungsten carbide coating, the Haynes 25 surface was liquid penetrant tested and any unacceptable dis-continuities were removed. In some cases the excavati." went into the casting material. The excavations were liquid penetrant testad to ensure no unac-ceptable discontinuities were present. The casting cnd Haynes 25 coating were locally weld repaired as necessary. Final Haynes 2f coating thicknesses ranged between 0.076 and 0.097 in. The Haynes 25 coating was ground and liquid penetrant tested. Application of the tungsten caroide rich coating and surface finishing was as previously described for the original ball.
The only difference between a new and refurbished ball is that a solution anneal heat treatment was applied to the ball following weld repair of the casting. The applicant stated that the repairs to the casting as part of the refurbishment were minor. Because the weld repairs to the ball were minor, the ball itself is a casting with a high ferrite number, and repaired areas were clad with Haynes 25 (which is highly corrosion resistant), the staff believes that the likelihood of susceptibility to stress corrosion has been mini-mized to an acceptable level without a second solution anneal heat treatment of the ball. Because the refurbished ball has been processed in a manner essentially the same as the original, with the exception described above, the staff concludes NMP-2 SSER S 6-9
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1 I
that the refurbished ball is. equivalent to a new ball and, therefore, the 75-cycle test that was performed with a new ball is appropriate for a iefur- j bished ball.
With respect to the use of one MSIV in each main steamline to provide secondary containment integrity before criticality, all four MSIVs will have the modified seat spring configuration.and recoated tungsten. carbide balls. However, the actuator modification will not be completed. Each valve will be cycled a few times to ensure proper seating before an LLRT is performed.in accordance with 10 CFR 50, Appendix J, Type C testing requirements. The MSIV_1eak rate must not exceed the limiting Technical Specification value of 6 scfh to be considered acceptable. The actuators will be deactivated in the closed position by opening the circuit breakers. The MSIVs will, therefore, be deactivated in the closed position during fuel load and startup testing that requires secondary integrity. Since the MSIVs'will_ meet Technical Specification limits for Type C 4 testing and the valves will not be operated after the leak testing, the staff finds it acceptable to use the modified MSIVs for secondary containment integ- 3 rity during operational conditions 4 and 5 (cold shutdown and refueling). )
1 The second issue pertains to the dse of the refurbished and modified inboard {
and outboard MSIVs for their intanded function of providing primary containment j isolation capability through the initial fuel load. While four MSIVs provide secondary containment integrity during fuel load and startup testing, the four remaining MSIVs (with modified actuators, recoated tungsten carbide balls, and modified seat spring configuration) will be installed in the main steamlines.
These four valves will then be placed in an operational status after successful j completion of Type ~ C leak tests with leakage not to exceed 6 scfh and valve i closure times of less than 5 sec required by the Technical Specifications. J The four valves used to provide secondary containment integrity will then be i upgraded in a similar fashion to operational status, f
The modified seat spring configuration was tested in conjunction with a new tungsten carbide ball for 75 valve cycles, which is an upper bound estimate of the number of cycles to the first refueling outage. After 75 valve cycles, ;
Type C leak testing indicated acceptable sealing integrity of less than 6 scfh. 4 Post-test inspection also indic:ted no evidence of ball coating degradation. .
On the basis of these results, the staff concludes there is reasonable assur- !
ance that the MSIVs with the modified seat spring configuration and recoated tungsten carbide balls will provide acceptable leaktight performance until the first refueling.
The staff also concludes that the tests perfomed to date indicate that the root causes of the high leakage have largely been corrected. However, it must be,noted that these same tests were not totally prototypical of in plant conditions. Because of these differences and recognition of the need for a more complete base, the staff concludes that confirmatory information is needed to verify continued acceptable MSIV performance during the first fuel cycle. This needed confirmatory information will be obtained from the MSIV prototype test program and during NMP-2 operation during the first fuel cycle.
Matters to be addressed are the following:
(1) Will the modified actuator affect the performance of the refurbished sealing surface? The successfully tested MSIV leakage corrective 4 action has not been tested in combination with the modified actuator. {
This is an objective of the prototype test program. {
NMP-2 SSER 5 6-10
_ _ _ _ _ ~. 6
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(2) Will modified MSIV performance be affected by steam flow and operating Tests temperature, pressure, and' steam conditions during valve closure? The proto-to date have been at ambient temperatures with no steam flow.Also, the in plant type test will. address this concern. tested after the MSIV full isolation test, in a shutdown, to provide in plant performance data after MSIV exposure to operating temperatures, pressures, and steam flow.
(3). Will the alternative between-the-heat leak test method be an acceptable test alternative to the~ conventional across-the-valve seat leak test after many cycles of valve operation? The actuator loads on the sealing surfaces may change with seat wear and affect the-leak test Verification results as valve of the closure cycles accumulate during plant operation.
between-the-seat leak test method as an alternative to across-the-valve seat test will be an objective of the prototype test.
Because of the importance of the above test data, the continued operability of the MSIVs will be conditioned on the successful performance of a concurrent.
prototype test program and in plant leak tests soon after the MSIV full isola-tion test. t Conclusion On the basis of testing to date and contingent on prototype test performa'nce, I the staff concludes that the refurbished MSIVs are acceptable for plant use up to the first refueling. The staff will evaluate the prototype test results in before making a determination on terms of demonstrating long-term operabilit) the continued use of the refurbished MSIVs beyond the first fuel reloading.
Specifically, the staff finds:
(1). The four MSIVs (one in each main steamline), with modified seat spring .
configuration and.recoated tungsten carbide balls, are acceptable for use to support secondary containment integrity for initial fuel loading and precriticality testing.
The inboard and outboard MSIVs, with modified actuators and refurbished (2) seat surfaces, are acceptable for providing primary containment isolation capability for the first fuel loading commencing with initial criticality.
This conclusion is contingent on verification of acceptable MSIV perform-ance by a special in plant test at NMP-2 and successful completion of a {a prototype testing program during the first fuel cycle to ensure the l achievement of the testing goals.
q The license will be conditioned as follows:
Nine Mile Point Unit 2 MSIVs:
A. Confirmatory leak tests using acceptance criteria that are the same as those outlined within the Technical Specifications for ,
the Appendix J LLRT program will be performed no later than the first outage (but within 30 days of) the 100-hour warranty run, l
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6-11 NMP 2 SSER 5 I
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'r .whichever is earlier. This' test is not intended to replace
- any Appendix J test requirement.
The. prototype-test program that will test the modified valve and B..
actuator configuration similar to the ones installed at Nine-Mile Point Unit 2 will include:
Verification of the mechanical integrity of the valve and actuator for the. expected operating and test cycles.
- Demonstration of valve leaktightness for the expected valve duty cycles.
- Demonstration of the ability to close the valve within Technical Specification limits under normal operating pres-sure and temperature steam conditions.
Verification of the conservatism of the between-the-seat leak test method as an al.ternative to across-the-valve seat leak-age tests.
- Other test objectives are to provide baseline data for evaluation of (1) the long-term suitability of the valve and (2) potential. design and material improvements.
C. The prototype test report that will address the confirmation of the valves' acceptability for the first operating cycle'shall be provided to NRC by May 15, 1937. This testing is scheduled to be completed by April 1, 1987.
6.2.5 Combustible Gas Control System In Section 6.2.5 of the SER, page 6-25, fifth paragraph, second and last sen-tences', the staff stated:
The applicant indicates that the reaction chamber is capable of processing 150 scfm of gas containing a maximum of 5 v% of hydrogen
' when the oxygen content is greater than 2_ v%....The recombiner is not designed to operate when hydrogen concentration exceeds 5 v%
with excess oxygen.
According to Section 6.2.5.2.2 of FSAR Amendment 15, page 6.2-76, the reaction chamber can process a maximum concentration of 5 v% of hydrogen.with excess oxygen. Excess oxygen is a concentration.of greater than 2.5 v%. The under-lined number should be changed to 2.5.
To clarify what is meant by excess oxygen, the second sentence should read:
The recombiner is not designed to operate when hydrogen concentra-tion exceeds 5 v% with excess oxygen (greater than 2.5 v% of oxygen).
By letter dated September 19, 1986, the applicant updated the zinc primer inventory within the primary containment which is a potential source of hydro-gen following a postulated loss-of-coolant accident because of zinc corrosion.
NMP-2 SSER 5 6-12
_ _ _ -CD 1
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he- - [tcp, q cg'og UNITED STATES
[ ' , . . , j NUCLEAR REGULATORY COMMISSION o a l WASHINGTON, D. C. 20555 l \-*a. f March 9, 1987 1
- DOCKET N0. 50-410 1
1 NOTE.T0: James McKnight, Document Control Branch
SUBJECT:
GENERAL ELECTRIC REPORT, "KKL IN-SERVICE EXPERIENCE WITH EPG-BALL VALVES (NIAGARA MOHAWK TASK NO. GE-1)"
OCTOBER 1986 The enclosed report entitled "KKL In-Service Experience with EPG-Pall Valves (Niagara Mohawk Task No. GE-1)" dated October 1986 was prepared for Niagara Mohawk Power Corporation (NMPC) by General Electric (GE). This report discusses the experience at Leibstadt Switzerland with the EPG-Ball Valves. The EPG-Ball i
V4.1ves design is used for the main steam isolation valves (MSIVsi at Nine Mile Point Unit 2 (NMP-?). This report was informally provided to the NPC by NMPC on February 25, 1987.
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Mary F. Haughey, Project #anager BWR Project Directorate No. 3 Division of BWR Licensing cc: PDR LPDR FWitt JKudrick . !
JLombardo RHermann JHulman Font 07- 438 8//6
-dWM*6%e. '
'l GENER AL kELECTRIC KKL IN-SERVICE EXPERIENCE WITH EPG - BALL VALVES (NIAGAPA M0 HAWK TASK NO. GE-1)
OCTOBER 1986 PREPARED BY: Gh M- #//5/fG -
gJ./J.B05EMAN,PRINCIPALENGINEER MECHANICAL EQUIPMENT / VALVE DESIGN PREPARED BY: b /#Nf'/f[
G. HANSON, SENIOR ENGINEER ~
"ATERIALS APPLICATION ENGINEERING NOTICE Neither the General Electric Company nor any of the contributors to this i document makes any warranty or representation (express or implied) with respect to the accuracy, completeness, or use#ulness of the information contained in this document, or that the use of such information may not infringe privately owned rights; nor do they assume any responsibility for liability or damage of erv kind which may result from the use of any of the <
information contained in this document. l
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L Purcose The purpose of this report is to document the in-service experience provided to GE by KKL on EPG designed ball valves used at Leibstadt. This report is in suceort nf the Niagara Mohawk Power Corporation task #0rce efforts regarding the current enncerns associated with the Main Steam Isolation Valves (MSIVs). f
Background
On Octnber 5, 1986, Mr. J. Boseman (Valve Design Engineering) and Mr. G.
Hanson (Materials Engineering) from General Electric Nuclear Engineering Business Operations were dispatched to meet with KKL personnel to obtain the Leibstadt experience with EPG. designed ball valves. GE and KKL personnel met on the 6th and 7th of October, 1986. for this purpose. The following KKL personnel were in attendance:
(*) Mr. Ulrich Frick; Mechanical Engineering Department Head Mr. Peter Buhlmann; Mechanical Engineering Group Leader Mr. Walter JAK; Mechanical Engineer Mr. Arthur Oberle, Consultant to KKL (retired BBC engineer - previously acquainted with Leibstadt ball valve efforts) ,
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(*) - Part Time The following information was provided by KKL regarding their experience (s) on this type of ball valve design.
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l 1.n LE"BSTADT BALL VALVE SYSTEM APPLICATION (Si 1
l KKL uses large ball valves in two system acclications- as noted on_ Figure I dl,' attached. A 20-irch size ball valve was criainally used as .a shuto" l
valve in each of the twn feedwater lines located in the auxiliary build-inc. A 26-incb size ball valve is used as a turbine building shuto##
valve on each of the # cur mainsteam lines, These valves are also located in the auxiliary building.
L P.0 BALL VALVE MANUFAC'UDED ANC REFERENCE INFORMATION Manufacturer: . Gulf & Western Energy Products Group (EPG)
Warwick, Rhode Island l Typical Drawino: E20-1500-1 (Feedwater Valve)
Actuator Type: Efcomatic Assembly Series 600 (same size used on both feedwater and mainsteam shutoffvalves)
Installed Ball valve Stem / Bonnet Orientation: -
Feedwater-valve - mounted in the horizontal axis Mainsteam valve - mounted in the vertical axis 3.0 BALL VALVE RE0VIREMENTS 3.1 Feedwater Shutoff Valves The feedwater shu+.M' . valves are required to close automatically within 30 ' seconds a f ter raceiot of an RHR initiating signal. -The valves are recuired to open wehin 60 minutes after receiving an open signal. The maximum valve leakaga criteria is to be consistent with proper RHR system operation. The actual maximum criteria was not available during the meeting. The original criteria used for the production units was identi-fied as being 2cc par inch of valve size diameter.
3.2 Mainsteam Shutoff Valves KKL identified that the original opening, closing and leakage require-ments imposed on this valve #or procurement purposes was the same as those imposed for the inboard and outboard mainsteam isolation valves.
In actual practice % ever the valve need only be capable of being manually closed a'He mechanically er electrically within 20 minutos after the inboard =M outboard MSIV's have closed. The leakage criteria 1 aoolied need ceiv b- consistent with safe and prudent maintenance prac-tice when servicirc the turbine buildino equipment.
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d;O- INSTALLAT!0" AND OPED r 3G W STORY j
J.1 .u's*nev of Feedwater Shu'.V ' Valvas 1978-1980 - Design and manufacture of valves by EPG and subsecuen*
storage at the-site.lacproximately two years of storage).
1981-1982 Installation May-October 1982 - Pressure Test of Feedwater Lines - During the hydro-test of the .feedwater system it was found .that these valves leaked. so badly that they could not build up sufficient pressure to complete the test.
' November-December 198? - Disassembly of Valv's e - The major leakage was.
due to the spool / seals being frozen into the spool bore due to corrosion of the carbon steel spool bore and the subsequent buildup of corrosion product. This probably resulted in low seat to ball pressure.
It was-velieved that leakage through the packing area also contributed. KKL designed .a special' tool to apply enough pressure to remove the spool /
seals which were " frozen" in place from the corrosion. The pitting of the carbon steel in the packing area was approximately 10-20 mils deep.
There was also some scoring and removal of carbide from the surface of the ball in the same area as the scoring of the Nine Mile balls. KKL contacted Union Carbide regarding the damage to the carbide. Union Carbide stated that the Tungsten Carbide would stabilize. KKL locally ground the edge when the carbide was : palled. KKL cleaned up the corroded areas by grinding and reassembled the valves. They changed packing from Chesterton 1500 to Chesterton 1000 which was lower in chloride. The Chesterton 1500 had 16-46 ppm chloride. The subsequent January,1983, Pressure Test at 169 bars for'30 minutes was successful, KKL did not cycle the valves under pressure. KKL initiated a study of packing materials to detennine the effects on room temperature corrosion of carbon steel. They tuund that some packing performed better than others. One of the better performing ones was Graflex 6501, a graphite coated asbestos. A Swiss packing '(Titan) was ultimately chosen which also gave low corrosion.
February 1983 - Hydraulic actuator pump motor bus was found broken. The hydraulic cylinder was not properly centered resulting in seizure. The cylinder was replaced with a spare of the same s'ze and properly aligned.
July to November lof3 - Feedwater valve 52 was disassembled because of -
hign leakage. The sonnl/ seal seating surface, en the pressure side, was found to have P Wal cracks in the stellite everlay. The nther seats were not cracked. Naw seats were installed.
All of the small serires in the seats plus every 'ourth large spring was removed to reduce the spring load on the ball seating surface.
The corrosion was ground out on the spool / seals and the spool / seals were electroless Nickel plated to maintain the proper gap between the spool /-
seal and the spool bore (body).
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The. bonnets were modif h: on both valves to overccme a leakag'e probleai c
.and to resolve binding and scoring o' the bonnet to valve body surfaces en disassembly, The original design required re:ensioning of bolts after the first pressurization. This was not practical so the bonnet and seal
.Js redesigned to assure that the bolt preload was adeouate to remain sealed without.retorouing a#ter pressurization.
j Scored areas on the balls were locally blended.by grinding.
On one valve actuttor, the hydraulic fluid drained from the hydraulic cylinder to the reservoir. due to elevation of the reservoir being lower i than the cylinder. This resulted in a shock loading of the valve and i actuator structure and probably caused the bracket fracture previously observed. KKL relocated the fluid reservoir to prevent the draining potential.
The roller bearings were found to have more clearance than the packing lantern rings (0.Smm for bearings' versus 0.3 for lantern rings). KKL increased the clearance in the lantern ring to assure that the gearing would take the load.
November 1983 - Modifications Complete. Testing Resumed - Pro $lems !
wery \"
ene.ountered with the latch mechanism. The problem was scoring and KKL modified all solenoids by removing the f
'ing(of
/e Sealthe Ring trip No.solenoid.
28)~which caused the binding.
February 1984 - Problems with FW52 - Trip solenoid defective, needle valve damaged, filter repUced, pump coupling rubLing on sides. Mis-alignment of hydraulic cylinder bearings caused seizure of the cylinder and would not open the valve.
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May 1984 - Plant Startuo - Could not trip or close FW51 valve due to jacced solenoid. Could not open FW52 because of pump seals. KKL re . ,
placed the sea 4s and freed the solenoid.
June 1984 - Plant, Shutdown - Could not trip FW51. Latch rnechanism had to be reacjusted again.
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October loPa - External' leakace through the ' packing, pesolved by tight-ening the packing.
Sunree 19852-Fec%te" gate plus a notor operated valves wereinremoved valve each'line. and red 1 aced with check valve
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4.2 Historv of Main Steam Shutoff Valves Julv 1983 - All . inner soool/ seals springs were removed. The modified m-~
designeo bonnets were installed. Weld overlayed the bonnet sealing area with 13Cr 4Ni weld deposit. Reste111ted spool / seal seating surface (s).
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Steam valves were exposed to steam and temperature from an auxiliary boiler.
s tSpool/ seal bores were cleaned and ground to remove pitting Spool / seals .
were Kanigen Nickel plated to provide for proper clearance (packing)..
November 1983 - MSIV 22 - Wouldn't ~ close during functional test due to failure of the solenoid trip.
Pressure test at 1.1 bars. All valves leaked greater than 50 liters par -
minute. They couldn't tell how much higher. MSIV 22 was dismantled and lapped.
(0.9 cu ftThis perreduced hour). the leakage on this one valve to 30 liters per hour 1985 Overhaul and Test - New manual mechanical trip levers were supplied by BBC and installed for ease in tripping the valves. If the trip solenoid does not 90erate electrically when actuated, then the manual mechanical trip lever assures tripping.
MS21 httch roller tearing was found to have a crack.
Valves results: were tested for closing with no pressure with tne following-s- MS21 - Closed within 2 days (not sure when)
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MS22 - Closed af ter ? hours, would not close on hand trip (prior to
% insalling the new mechanical manual trip).
MS23 - Closed properly (less than twn minutesi MS24 - Closed only after-manually tripping via the solenoid.
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[" a Aucust 1986 - Valves were actuated with no pressure and only MS22 failed to close. The trio solenoid was frozen in place due to the lubricant Lg m which had hardened, Va.lve was disassembled end examined.
Some scoring and carbide was missing on the ball in high pressure Surface areas. Also some upstream edge corrosion /spalling.
relapped and valve reassembled with new packino, Ball and seat s
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a 5.0. vA!NSTEAM SHUT 0FF VALVE *0DiFICAT'ONS The KKL mainsteam ball valve design was modified as described belnw:
5.1 All of the small inrer sorings were removed from the nested springs located in the spool / seal assembly. Demoval of these springs was recom-mended by the manufacturer to minimize scoring and thereby the leakage potential by reducing the imposed spring load from 600 lbs to approxi-mately 400 lbs or approximately 40%.
5.2 The ball is coated with Nickel NEVER-SEEZ after maintenance and relapping in order to minimi:e friction and thus the potential for ball scoring.
The vendor recommended this practice to enhance operability.
5.3 The bonnet- pressure seal was redesigned / modified to minimize the poten-tial for scoring the bonnet sealing surface during bonnet removal. This modification was recommended by BBC.
5.4 The body and bonnet guide surfaces were hardfaced with a 13 Cr 4Ni alloy to minimize corrosion between those surfaces and thus the scoring poten-tial of the sealing surfaces for use with the pressure seal. This modification was a BBC recommendation. -
5.5 The originally supplied Chesterton Packing 1500 was replaced with a 3/8 inch square Titan (Swiss supplier) packing set. This modification was incorporated due to the concern for corrosion of the bore surfaces and the quality control of the original type packing for chlorides, flourides and contaminants which could act as a catalyst for corrosion.
5.6. The spring retairer bore diameter was increased in order to assure that the spring (s) woulc not bind-up when compressed.
5.7 The lantern ring diameter was changed to assure that the roller bearing would be the effective load bearing member and to minimize eccentric rotation. .
5.8 All trip solenoids were modified by removing the sleeve (PC #2R) which had been the cause for malfunction on the feedwater-valve.
5.9 The manual operator (actuator) trip lever was modified to permit manual mechanical tripping from the above flooring. In addition, the modified trip lever design incorporated a greater mechanical edvantage to assure mechanical trippinc o' the actuator.
5.10 In addition to tne above, KKL uses a specially (BBC) desigred ore loed fixture for boltinc up the body to bonnet closure. This fixture was designed to minimi te the potential for leakage through that joirt and tn minimize axial rnverer.t n' the ball due to stud relaxation after the !
valve is pressurd Zed.
5.11 Attachment 1 (dertifies the originally provided materials list for the various spare parts items which can be used to compare to the NMP-? MSIV i ball valves.
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I 5.12 KKL nted tha+ La'ter 'f rding the radial cracks on the. feedwater velve the spool / seal on all of the valves wer ire-hard' aced with ste!!ite to assure a quality iccol/ seal sear.
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l 6.1 KKL identified that the two feedwa ter st?s valves were resved lfrom the l systrS andtr9placed with a thirc swingt check valve (inside the auxiliarv
building) pc 'a motor 4 operated gate valvei / n the turbir,e building. The decision to rcmove these valves was based primarily upon the inability of the valve to close ' eiiably within the 3Cisecond requirement for comp'iti-bility with operation 07 the RHR system. '
i, 6.2 Pl.th regard to tre ' main steam shutoff ball valves, KXL identified *. hat l
' the modified svalves' are.still installed in the system. Since the valvst are not recuired to perform a safety-related function, there are no immediate pla n to replace those steam valves.
7.0 CTHERITEMSDISCUSSEDlNOTED s i
l 7.1 KKL identified that numerou:, problems were experienced with the EFCOMATIC Series 600 actuator. The problem areas experience are highlighted on,the attached figures 2 and 3. . The types of problems ranged from ,leaung j seals, broken brackety cracked roller bearinf to misalignment of pa.rh.
Due to the short time ' schedule for the visiti; specific details were. not, discussed for each p'roblem area. Essentially; KKL replaced or repaired parts or re-aligned Natures deoending upon the cause.
- Modification ;
efforts were limited tu beefing up the bracket and changing the mechan- ' l ical menual trip laver. '
v.2 KKL fndicated tha* they have not specifically noted chattering of the
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ball valve (s) per se.
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7.3 With regard to scoring of the thrust washers, KKL did not observe any
- evidence of en1 tact nf the thrust washer on the feedwater shutoff valves but did noto s]me light scoring en the main steam shutoff valves.
7.4 KKL identifie that thould Niagara Mohawk Power Corporation have need fnr an engineering test v6ve, that the removed feedwater valves are avail-able for their use. 'XKL also identif t+d that Sultzer Y-pattern MSIV's are available From *t/J SwentendoM cancelled power olant should Niagara Mohawk be interestsd. If inte9sted KKL suggested contacting the U.S.
besed KSB acent, Fr. Bradford L. Rebinson, who is located at the (KSB Inc.) Commerce r ev,175 Comercu Drive, Haupeauge, N.Y. *11~88 (Tel:
pi6 '31-0303, E W - en 06).
- 7.5 'Since Dr. Varg) *-, #5C Als on vacatien and not available, Mr. A. Oberla f retired) 'wrap 'm t,he SEC Engineering Departrent and a cortuitant 1
tn V.KL, was askM 'n rot with us since he was kMwledgeable witiL10me of 1' 'he history and problem areas concerning this ball type vahe desiga.
During the cis ussine, it was noted that some in'ormal seat load calcu-
!ations (not aWWlable at the meeting) had been cer#ormed and that h46 srating stressts wera 'roted when a static differen-fal oressure was j applied across the bal' en seat contacting surfaces. Recol?ection by Mr.
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Oberle, indicated that he highest stress condition occurred d ust cri m to valve closure assuming concentric valve rotation.
Fich contact stress could also be expec+ed when closing the valve should eccentric bal!
.rotat on cccur which.was evidenced by the ball scoring loca'tions.
7.6 During the meetjaa it 'was noted that alignment and tolerance stack-uos of the ball to secol/ seal is considered important to improve valve operation /per#ormance.
7.7 Both of the balls from the feedwater valves were visually examined. Both of the balls were covered with a high temperature red oxide on the inside diameter of the ball. One of them was also coated with red oxide on the outside surface of' the ball indicating that some. water had been present on the outside sur' ace of this ball. There were heavy burnish marks on the Tungsten Carbide starting from the bore and eminating 8 or 10 inches towPd the seat. These burnish marks were present in a band approximate-ly 8 inches wide. There were only small amounts of carbide removed )less than 1 inch diameter spots) inthe same high stress area as the Nine Mile Point valves.
Visual examination nf the photographs of the balls from the steam valves showed similar wear marks and spalling on the carbide surfaces except that the wear pattern was not as wide as the wear pattern oc the feedwater valves.
Another difference noted was the steam valve had what appeared to be corrosion of the carbide coating at the leading edge of the hole in the ball on the upstream side of the valve (pressure side).
All of the Leibstadt balls (both steam and feedwater valves) showed much less spalling of the carbide than the Nine Mile balls examined by GE.
General Electric, on behal' of Niagara Mohuk Corporation, thanked the KKL personnel and Mr. Oberle for their time and cooperation in assisting us, on such a short meeting notice, with their experiences and information.
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