ML20100L543
| ML20100L543 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 12/05/1984 |
| From: | Koester G KANSAS GAS & ELECTRIC CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| KMLNRC-84-213, NUDOCS 8412110587 | |
| Download: ML20100L543 (2) | |
Text
. _ _ _ _ _
e KANSAS GAS AND ELECTRIC COMPANY THE ELECTftC COMPANY
@LENN L NOESTER WCE Peasetse? soucLane December 5,1984 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
20555 KMLNRC 84-213 Re:
Docket No. STN 50-482 Ref: 1) KMLNRC 84-196 dated 11/13/84 (attached)
- 2) KMLNRC 84-199 dated 11/19/84 (attached)
Subj: Testing of Pressurizer Power-Operated Relief Valves
Dear Mr. Denton:
The purpose of this letter is to request NRC approval of Kansas Gas and Electric Company's (KG&E) plan for testing the Wolf Creek pressurizer power-operated relief valves (PORV).
Reference 1, a report made pursuant to 10CFR50.55(e), described a test deficiency identified during the conduct of preoperational test SU3-BB13,
" Pressurizer Relief Valve and PRT Hot Preoperational Test".
The abstract for this test is in the SNUPPS FSAR Section 14.2.12.1.21.
Reference 1 also described the cause of the valve malfunction and the valve changes made by KG&E to assure proper valve operation. The valve modifications have been completed.
Reference 2 notified the NRC Office of Inspection and Enforcement, Wolf Creek Task Force, of KG&E's plan for resolution of the outstanding test deficiency associated with the PORVs. In summary, the PORVs will be tested by a surveillance test in accordance with the Wolf Creek Technical Specifications. Subsequently, with the plant in Hot Standby (Mode 3), the PORVs will be tested in accordance with a special procedure which will verify-that the preoperational deficiencies have been resolved.
The following points provide justification for post fuel load testing:
- 1) The special testing of the PORVs will be accomplished prior to initial criticality. Therefore, the potential for any radioactive contamination or exposure as a result of the testing is minimized.
- 2) KG&E is confident that the valve modifications have corrected the deficiency. However, in the unlikely event that the 0
8412110587 841205 1
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201 N. Market - W1chita, Kansas -Mad Address: RO. Box 208 I Wichita, Kansas 67201 - Teleptrote: Area Code (316) 261-6451
r Mr. Denton KMLNRC 84-213 December 5, 1984 problems persist, the fact that fuel has been loaded in the reactor vessel will not complicate additional corrective action on the valves.
- 3) The PORV block valves are operable and performed satisfactorily during preoperational tests.
- 4). Cold overpressure protection is afforded by the Residual Heat Removal Systems in accordance with Technical Specification 3.4.4.3.
- 5) Testing prior to fuel load would require an additional plant heatup and cooldown cycle.
KG&E believes the PORV deficiency identified during the preoperational hot functional testing has been resolved with the valve changes described in Reference 1.
Deferring the final testing until after fuel load, but before initial criticality, does not jeopardize the safe operation of the plant nor the health and safety of the public. No exemption to regulations and no changes to proposed plant Technical Specifications are required because of this matter.
It is requested that the NRC provide approval of KG&E's. plan for testing the pressurizer PORVs.
-Very truly yours, W$$
Y Glenn L. Koester Vice President - Nuclear GLK bb Attach: KMLNRC 84-196 KMLNRC 84-199 xc:RPDenise, Reg. IV PO'Connor (2)
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KANSAS GAS AND ELECTRIC COMPANY P. O. Box 208 Wochsta. Kansas 67201 n.e esacima ccwwwwr
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-November 13, 1984 T
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l Mr. R.P. Denise, Wolf Creek: Task Forca 4 Reactor Projaots Branch 2 U.S. Nuclear-Regulatory Consaission r
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Re Docket No. STN'50-482
.) n Subj Final 10CFR50.55(e) -Report - Pressurizer
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. Dear Mr. Denise l
-The attachment to this letter provides the final report submitted pursuant to 10CFR50.55(e) concerning the pressurizer power w
operated relief. valves (PORV) at Wolf Creek.. Generating Station (WCGS).
This matter was initially reported by Mr. H.K. Chernoff of Kansas. Gas < and. Electric Company (KGt2).to Mr. John Boardman of the Nuclear? Regulatory Conunission,~ Region'IV, on October 11, 1984.
a Kansas Gas.and Electric's plans. for resolution of -the -pressuriser PORV preoperational-test discrepancias will be provided to the NRC.under separate cover by November 19, 1984.
1 If you have any questions concerning this matter, please contact W
me or Mr. Otto Maynard of ray staff.
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-l Oridida$ signed-KENT R. BROWN (for)
Glenn L. Koester Vice President - Nuclear CLK jih
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o WOLF CREEK PRESSURIZER POWER OPERATED RELIEF VALVES (PORV)
Safety Evaluation Summary The ' Wolf Creek PORV's failed to close during a specific preoperational test.
This safety evaluation summary report is intended to define the
' conditions under which the valve malfunctioned; describe the reason for the failure to close; explain' the corrective action that was taken; and provide assurance of valve operability.
Introduction The Wolf. Creek pressurizer power operated relief valves (PORVs),
- manufactured by Garrett, are 3" x 6" and are solenoid operated.
They are intended to control pre ssurizer pressure to a value below the fixed hig h-pressure reactor. trip setpoint for a 401 load rejection assuming failure of the pressurizer spray system.
They also provide a safety grade means for reactor coolant system depressurization to achieve cold shutdown.
j Additionally, they serve as part of the cold overpressure mitigation system
( C0HS).
The PORVs are not required to open in order to prevent overpressurization of
.g the reactor coolant system for the loss of load event discussed in the f
Overpressure Protection Report.
The pressurizer safety valves perform this function assuming pressurizer spray and PORVs fail to operate.
The PORVs are electrically actuated valves which respond to a signal from the pressure sensing system or to manual control.
They are provided with Class 1E direct position indication in the main control room.
For each valve there are indication lights and alarms that are activated by stem-actuated limit switches.
Figure 1 shows the functional schenatic of the PORV.
The mode of operation of the valve is as follows:
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~ The valve is a line-pressure actuated, solenoid-controlled, relief valve of the caged-plug type.
The schematic diagram of _ Figure 1: sbows the unit with gt. ~ ~
the. solenoid. de-energized and the valve closed.
' Inlet pressure (either
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. vapor or water) flows into the valve inlet connection.and is ported through the solenoid seat to the actuator head chamber of the valve.
Inlet pressure
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is also ported underneath the piston and through the cage holes to surround m
the plug.
The fbrces tending to hold.the valve closed include the pressure
, - 2' in the actuator head chamber acting on the entire piston area and -the actuator spring load.
Inlet pressure also acts on.the annular area beneath the piston (and outside the seat diameter) in a direction to open the
-valve.
Since the annular area is less than the total piston area, the closing force predominates and the plug is held.down.against the seat with a force equal to the value of inlet pressure multiplied by the seat area.
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When the solenoid is energized, the magnetic force acts on the solenoid armature to move the ball from the vent seat (as shown) to the opposite seat, thus sealing off inlet pressure from the actuator head chamber.
At the same time,'the actuator head pressure is vented to discharge through the vent seat of the solenoid.
With the actuator head chamber now at discharge pressure,.
inlet pressure acting on the annular area is sufficient to overcome the actuator spring load.
The plug moves away frot.'the seat in the direction to open the valve.
As the valve opens, pressure inside the case builds up undbrneath that portion of the plug exposed to discharge pressure.
Because of the pressure drop through the cage flow holes, this pressure is less than inlet preisure but higher than the discharge pressure.
The large seating force that exits when the valve is closed is thus turned into an opening force, causing the plug to move to the full-lift position.
When the solenoid is de-energized, the ball moves back to the seat as shown, sealing off the path to discharge and repressurizing the actuator head chamber with inlet pressure.
With the plug in the' full-lift position, ' the opening force consists of inlet pressure acting on the annular area and cage pressure acting on the base of the plug.
The closing forces (consisting of inlet pressure in the actuator head chamber and the actuator: spring load) overcome the opening forces and cause the plug to move toward the seat.
Discharge pressure drops to a minimum as the valve reseats, and tbe valve is once more held' in the closed position by a force that is equal to inlet pressure multiplied by the seat area.
Discussion of Valve Malfunction It was in the closing mode, described above, in which the valves m al functioned. Specifically, the valves were being operated in the manual mode, discharging steam, and being held open for a period of approximately 32 seconds.
Prior to opening the valve,.the inlet piping (consisting of approximately fourteen feet of vertical downward run loop seal) was filled with cold water as were the valves themselves. The valves are located in a compartment which is below the top of-the pressurizer.
This location i away
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from the top of the pressurizer results in valves being substantially colder
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. than if they were at the top of the pressurizer.
Valve ambient temperature at Wolf Creek is approximately 90 degrees fahrenheit.
The preoperational test itself required approximately 32 seconds of e
continuous operation to achieve pressure relief of'200 psi.
The purpose of the test is to verify valve stroke time and leakage, after the valve has been opened for more than two seconds.
This test ' simulates certain conditions which may be encountered during plant operation such as loss of load.
The valve equipment specification contains requirements such as:
valve cycle time; discharge fluid rates; number of. design cycles; etc.
These design requirements are adequate to assure that the valve will perform its intended function.
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. addition to: assuring operability through equipment.~ specification t
requirements, considerable testing has been performed on these valves. Bis testing includes preoperational tests at other foreign and Gaestic plants and the following successful tests at Wolf Creek.
At. Wolf ~ Creek, tests perfermed in the automatic mode, during which the valve remained open for a s
period of approximately two seconds, were successful. Additionally all Wolf Creek. testing per formed without a
cold L loop seal was completed j
successfully. Further, a number of isothermal tests have been performed on the Garrett Power Operated Relier Valves.
These include.the EPRI Safety and Relief Valve Test Program, and Garrett operability tests.
In these tests, e
the valves closed as required.
When the valves: failed to close when signaled after the discharge period of approximately - 32 seconds,
the motor-operated block valv es,
which are.
installed upstream of the PORVs and whose function is s s preclude the loss of reactor coolant if a leak should develop in a PORV, were closed. Closing of.the PROVs was observed to occur simultaneously with block valve I
clo sure.
This occurred because the head actuator chamber (which was f
isolated) was at approximately 500 psis, the normal. discharge pressure.
j Closure of the block valve reduced-inlet pressure.
Since the active. area above the piston is three times greater than that below the piston,- the 500 i
psig was sufficient to overcome the falling inlet pressure.
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f Summary of Investigation he postulatect causes for the valve malfunction considered were:
solenoid j-failure, plug to cage binding,' and failure to get required fluid pressure to 4
l, actuator head chamber.
, Proper solenoid operation was verified.
We fact that the valve operated as designed in the automatic mode and inspection of the valve internals showed no evidence of. binding (i.e.,
gouging etc.),
eliminated the binding supposition. Therefore, there was strong indication -
I that the third postulated cause, that of failure to get required fluid pressure to the actuator head chamber, was the source of the malfunction.
By reviewing the valve design in conjunction with detailed manufacturing p'
drawings it was determined that differential thermal expansion between the 4
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. valve cage and the valve body bore in which the cage -is housed, would cause
! 4L the cage-to-body annulus to be reduced in size even to a point of ~ total k F-closure.
his annulus serves as a path for inlet fluid to travel to the
'g solenoid port and eventually to the actuator head - chamber as -defined
.i previously. To verify this supposition, a subsequent manual. test,-.similar p;;
to the tests in which malfunction occurred, was performed with the > valve -
[f 'g bod y heated to 228 degrees. fahrenheit.
De valve functioned as required l
providing strong support to the premise that differential thermal expansion
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was the cause of the malfunction.
It should*be noted that by heatin6 :the I_
valve body to 228 degrees fahrenheit the valve body bore was increEsed - by six mils which results in an additional annular clearance under the flow cond itions.
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i In' review of the valve nianufacturing drawings, it was determined that.the
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maxista and minista radial annular clearance at ambient temperature when.the
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parts (valve body and cage) are machined to within specified tolerances - are -
nine and six mils (0.009 - 0.006) respectively with diametral-clearance being eighteen to twelve mils (0.018 - 0.012).
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Page Four Based on the in formation from the testing described above and the small manufacturing tolerances, an analysis was performed to determine the effects of differential tenperature on the valve body and cage.
Figure 2 is a plot of the results and shows that for 100 degrees fahrenheit of temperature differential the annular gap is reduced by approximately three and one half mils (.0035).
This is based on the expansion of the cage with no' expansion of the valve bod y.
By heating the valve in the successful test, approximately six mils (0.006) annular clearance was added due to the thermal expansion of the valve body at its initial condition of 228 degrees fahrenheit.
This phenauenon was then analyzed to determine the effects of gap closure on fluid flow with a homogeneous flow model.
The results substantiate the heated test results and the differential expansion premise.
Specifically, for all relief conditions, the minimum annular diametral gap between the body and the cage necessary for the PORV to function properly is 1.12 mils.
With the valve starting cold (90 degrees fahrenheit) and suddenly exposed to high pressure steam (650 degrees fahrenheit) it will take 5.75 seconds for the annular orifice gap to be reduced from 15 mils to 1.12 mils.
In 7.47 seconds, the annular orifice is conpletely closed off.
If the annular orifice gap started out at 18 mils, it would take approximately 9 seconds for the gap to be reduced to 1.12 mils. By 11 seconds, the 18 mil gap would be completely closed.
In this analysis the cage expands as a function of time and temperature and the thermal expansion of' the valve body during these time intervals is negligible.
Corrective Action Taken The valves under discussion were disassembled and dimensions of the body bore I.D. and cage 0.D. were taken.
This showed that the disnetral annular clearances at ambient temperature were nominally 15 mils and 18 mils for the two _. valves.
A field change notice (FCN) was prepared to machine the cages to an O.D.
of.4.55 to 4.57 inches, thereby providing a final diametral annular clearance of 114 mils and 111 mils respectively.
This action was taken with full cognizance and technical support / assurance by the. valve designer / manufacturer (Garrett) and Westinghouse.
In designing the valve to meet the specification requirements, the-designer kept the annular clearance anall so that it.would. serve as a filter to prevent any debris that may be entrained.in the fluid from fouling the _
three-way ball valve of the solenoid.
Ho wever, -
the valve manufacturer (Garrett) has detennined that the clearance provided by this design need not be this sna11.
Garrett has also confirmed that the machining to resize the cage is a product improvement.
Summary and Conclusion The Wolf Creek pressurizer PROVs failed to close PC-'r 4
discharge of water T
follo wed by steam which was conducted manue' :- < er extended period of i
time. The cause of this mal function was determL.r i
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> differential
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Page Five
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thermal. expansion (valve bod y to cage) resulting in a restriction of an essential - fluid flow path to the valve actuator head assembly.
Identification of the cause of the malfunction is supported by testing in other operating modes, successfully repeating the failed test with reduced differential temperatures, and a detailed engineering analysis.
A valve, modification, specified by - Westinghouse and concurred with by Garrett (the valve designer / manufacturer) has been made which corrects the malfunction without having any deleterious effects on valve function.
l Based on-the information contained herein and supporting doctmentation, it is concluded that the Garrett pressurizer power-operated relief valves will function under all design conditions.
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November 19, 1984 Mr. R.P. Denise, Director Wolf Creek Task Force s
U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaz'1 Drive, Suite 1000 3
Arlington, Texas 76011
'Rei Docket No. STN 50-482 Ref Final 10CFR50.55(e) Report KMLNRC 84-196 dated 11/13/84 from GLKoester, KC&E, to RPDenise, NRC
.Subj Resolution of Pressurizer PORV Test Discrepancies v
Dear fir. Denise:
The purpose of this letter is to provide, as wa5 indicated in the Reference, Kansas Gas and Electric Company's plans for resolution of the pressurizer power operated relief valves (PORVs) preoperational l
test discrepancies.
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I The failure of the pressurizer PORVs to close as required during L
' performance of a portion of their preoperational test is an outstanding l
test discrepancy. 'The pressurizer preoperational test (SU3-BB13) will be closed with outstanding test discrepancies which will be resolved after fuel load but prior to initial criticality through the use of an Operations Special Procedure written for testing of the PORVs.
After fuel load the valve surveillance required by the Wolf Creek Generating Station- (WCCS) Technical Specifications will be perfomed.
Upon successful completion of this surveillance test, the plant will be brought to the appropriate temperature and pressure, at which time the Special Procedure for testing can be completed. This Special Procedure will entail all steps of the preopcrational test necessary l
to resolve the existing test discrepancies. This will include a test of the automatic actuation function and the extended blowdown function of these valves.
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Mr. Denise KHLNRC 84-199 November 19, 1984 Technical justification for this course of action was provided in the Reference and copies of the Special Procedure for testing the PORVs will be made available for your review.
If you have any questions concerning this subject, please contact me or Mr. Otto Maynard of my staff.
Yours very truly, Original Signed GLENN L. KOESTER Glenn L. Koester Vice President - Nuclear GLKabb xc RCDeYoung PO'Connor (2)
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