3F0996-04, Provides Response to Request for Addl Info on GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves

Provides Response to Request for Addl Info on GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves

ML20117P151
Person / Time
Site:	Crystal River
Issue date:	09/14/1996
From:	Beard P FLORIDA POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
3F0996-04, 3F996-4, GL-95-07, GL-95-7, NUDOCS 9609200265
Download: ML20117P151 (6)

Text

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Florida Power CORPORATION

[kxsuit soazz September 14, 1996 3F0996-04 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555-0001

Subject:

Request for Additional Information on Generic Letter 95-07, " Pressure  !

Locking and Thermal Binding of Safety-Related Power-0perated Gate Valves"

Reference:

A. NRC to FPC letter, 3N0696-04, dated June 13, 1996 i B. FPC to NRC letter, 3F0796-ll, dated July 11, 1996 l

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Dear Sir:

In Reference A, the NRC requested additional information on the Florida Power  ;

Corporation (FPC) evaluation of pressure locking and thermal binding of safety-related j power-operated gate valves for Crystal River Unit 3 (CR-3). In Reference B, FPC i requested an extension until September 15, 1996 to respond to the NRC questions.

In order to provide additional assurance that these and all questions related to Generic Letter (GL) 95-07 had been adequately considered, FPC conducted an j independent, confirmatory review of safety-related power-operated gate valves at CR-3 i i for pressure loc *ging and thermal binding. Attachment A to this letter provides our l response to the specific NRC questions' contained in Reference A, and additional i insights on potential pressure locking identified during the confirmatory evaluation.

Please contact Brian Gutherman at (352) 563-4566 if you have any questions concerning this submittal.

Sincerely,-

b

. M. ard, Jr.

! Senior Vice President l Nuclear Operations PMB/SCP:ff Attachment jh ' ,

xc: Regional Administrator, Region II NRR Project Manager Senior Resident Inspector

[hS{M CRYSTAL FWER ENERGY COMPLEX: 15760 W. Power uno Street . Crystal River. Florida 344284708 . (352) 7954486

( 9609200265 960914 l PDR ADOCK 05000302 i P PDR

• U. S. Nuclear Regulatory Commission e 3F0996-04 Page 2 of 6 ATTACHMENT A FPC RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 95 07, " PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-0PERATED GATE VALVES" NRC Ouestion #1 Your submittal states that, if valve RCV-11, Pressurizer PORV Block Valve, is closed during power operation, thermal binding may occur during subsequent plant shutdown and cooldown, and that RCV-11 is required to be opened to mitigate low temperature over pressure (LTOP) events. Also, your submittal states that procedural controls exist in operating procedures to establish alternative means to protect against LTOP events if RCV-11 cannot be opened, and that these alternative means are considered sufficient to mitigate an LTOP event should RCV-11 become thermally bound.

Although redundance in system capability enhances plant safety, the NRC staff believes that each safety-related power-operated gate valve should have a deterministic basis for operability. Please address this issue.

FPC Response to Question #1 RCV-11, the pressurizer Pilot Operated Relief Valve (PORV) block valve, is safety-related for pressure boundary integrity only. The normal operational position is open. The valve operator is non-safety-related, and RCV-11 has no safety function in mitigation of accidents analyzed in Chapter 14 of the Crystal River FSAR. The conditions under which RCV-11 may become thermally bound would only occur as a result of the failure of RCV-10, the PORV. Normal expected operation would not result in potential for thermal binding of RCV-11. FPC considers that the measures established to compensate for possible thermal binding of RCV-11 are sufficient for its operating functions.

Improved Technic.a Specification LC0 3.4.10 requires the PORV and PORV block valve to be OPERABLE in MODES 1, 2, and 3. If the PORV is INOPERABLE, then ACTION ' A' requires that the block valve be closed and power removed. Plant operation may continue in this condition indefinitely. The function of the block valve in this case is to isolate a potential reactor coolant system (RCS) leak ,

pathway through the PORV. If the block valve were closed in accordance with this i ACTION, then it is possible that thermal binding may occur during plant shutdown y and cooldown. The LC0 does not require the block valve or PORV to be OPERABLE 1 in MODES 4, 5, or 6.

If the block valve was closed during power operation to compensate for an inoperable PORV and thermal binding occurred, during plant shutdown and cooldown, LTOP protection is provided by reducing and maintaining the Makeup Tank level less than or equal to 70 inches, and deactivating the Low-Low Level Makeup Tank interlock to the Borated Water Storage Tank suction valves.

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NRC Ouestion #2 In Attachment 1 to GL 95-07, the NRC staff requested that licensees include consideration of the potential for gate valves to undergo pressure locking or l thermal binding during surveillance testing. During workshops on GL 95-07 in '

each Region, the NRC staff stated that, if closing a safety-related power- ,

operated gate valve for test or surveillance defeats the capability of the safety '

system or train, licensees should perform the following within the scope of GL '

95-07:

a. Verify that the valve is not susceptible to pressure locking or thermal binding while closed,

b. Follow plant technical specifications for the train / system while the I valve is closed,

c. Demonstrate that the actuator has sufficient capacity to overcome these phenomena, or

d. Make appropriate hardware and/or procedural modifications to prevent pressure locking and thermal binding.

The staff stated that normally open, safety-related power-operated gate valves I which are closed for test or surveillance but must return to the open position  !

should be evaluated within the scope of GL 95-07. Please discuss if valves which meet this criterion were included in your review, and how potential pressure  !

locking or thermal binding concerns were addressed.

i FPC Response to Question #2 Surveillance Testing FPC has completed a second, confirmatory review of valves susceptible to pressure locking and thermal binding (PL/TB) utilizing a lead engineer who performed this review for another licensee. The confirnatory review was performed independently of personnel who performed the initial review. Powr-operated gate valves which are closed during surveillance testing, and are required to open to fulfill a safety function were evaluated for susceptibilit." to PL/TB. Neither the initial nor the confirmatory review identified any safety-related power-operated gate valves that are susceptible to pressure locking or thermal binding as a result of surveillance testing.

Normal Operating Conditions The confirmatory review was not limited to susceptibility during surveillance testing, but also evaluated susceptibility during normal operating conditions.

The confirmatory review identified the following normal operating conditions that could potentially create pressure locking or thermal binding:

ASV-5 & ASV-204 Emeraency Feedwater Pump Turbine Steam Inlet Valve ASV-5 & ASV-204 can potentially experience boiler effect pressure locking during and following startup. The valves are located in vertical piping runs and the

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, U. S. Nuclear Regulatory Commission

- 3F0996-04 Page 4 of 6 stems are horizontal. A steam bypass is installed around each valve and connects 10" above (downstream of) the centerline of the valve (Figure 1). The bypass connection is to allow a small amount of steam flow during normal operation to keep the piping and the turbine warm. During normal operation, the main steam has about 40 F of super heat on the bottom disc face (upstream). The steam )

bypasses around the valve, and due to the reduced pressure downstream of the valve, the steam will then have more than 100 F of super heat. During normal operation no condensate will remain in the line.

During shutdown, the main steam will be lower in pressure and temperature. Some condensate may form in the downstream line and drain to the top of the valve.

The condensate can be drawn into the bonnet of the valve as it cools during shutdown when the steam inside the bonnet condenses creating a vacuum. It is very unlikely for the bonnet to become . water solid. However, it was conservatively assumed that the bonnet would become completely water solid, and then pressure locking could potentially occur. As the plant is heated up, the steam bypassing the valve causes the valve to heat up and the trapped fluid tries to expand. Since the fluid is trapped, it cannot expand and pressure in the bonnet can increase sufficiently to lock the disc.

A procedure change will be made for startup operations to assure this potential pressure locking condition is prevented. The present plan is to open the valves in MODE 5 or 6 prior to startup to drain any condensate, and then close them for

. continuing normal startup. Condensate will not collect in the bonnet during startup since the high pressure side of the valve is on the bottom, and the >

pressure will prevent condensate from entering the bonnet from the top. The procedure change necessary to prevent pressure locking will be made prior to startup from the next outage.

NRC Ouestion #3 .

Through review of operational experience feedback, the staff is aware of ,

instances where licensees have completed design or procedural modifications to preclude pressure locking or thermal binding which may have had an adverse impact on plant safety due to incomplete or incorrect evaluation of the potential effects of these modifications. Please describe evaluations and training for plant personnel that have been conducted for each design or procedural '

modification completed to address potential pressure locking or thermal binding I concerns.

FPC Response to Question # 3 Modifications were performed on valves DHV-3,-4, 5, & 6 to address PL/TB. The modifications consisted of drilling a 1/8" hole through the high pressure-side disc of each valve's flexible wedge. This is a common modification described in NUREG-1275 performed to eliminate pressure locking. The modifications were evaluated and approved in accordance with CR-3 Nuclear Engineering Procedures, which include multi-department reviews, ASME Code required evaluations, 10CFR50.59 safety impact assessments,. and Plant (Onsite) Review Committee approval. The valve vendors were contacted to solicit and include their approval for the modifications. Field work was performed in accordance with approved work instructions and procedures, by qualified personnel, and was inspected by Nuclear

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Page 5 of 6 i Quality Control inspectors. Specific inspections were performed to verify that the approved design was correctly translated into the physical modification.

Inspections included hole size and hole location verification, and valve disc orientation inspection on reassembly to verify the drilled disc faced the high pressure source. The modified wedge was installed in DHV-4 in May 1992, and in the remaining valves in May 1994. No problems have been experienced with the operation of these valves due to the installation of these modifications.

Controls have been established to assure that future maintenance activities preserve the modifications to these valves. First, the specific component drawings for the valves contain notes which show the size and position of the drilled holes in the valve wedges, and provide reference to the controlling j modification numbers. Second, the computerized inventory management system contains notes in the part description of spare wedges for these valves describing the modification and referencing the modification documents. The inventory management system also contains controls which restrict the use of the spare wedges until authorized by the Procurement Engineering group.

These modifications eliminated a potential failure mechanism due to pressure locking. However, they were essentially " invisible" to plant operators in that the pre-modification operation of the valves remained unchanged. Accordingly, there was no necessity for pre-turnover operator training on these modifications.

Although no training was given on the specific modifications, operator training on the general subject of valves includes instruction on the phenomena of PL/TB of gate valves.

Only one operating procedure change has been made to date to address PL/TB. It was added to identify that thermal binding could occur if the PORV block valve was closed hot. This problem was identified during the initial PL/TB evaluation, therefore, the identified problem was validated by engineering prior to inclusion in the procedure. This procedure change was evaluated for impact on FPC's accredited operator training program through the same documented processes that all operating procedure changes receive. Subsequent procedure changes to either operating or surveillance procedures addressing PL/TB are expected to originate from similar engineering reviews, and be added to procedures and the operator training program through the same process. No special processes have been used for procedure changes addressing PL/TB, and none are considered necessary.

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! U. :S. Nuclear Regulatory Commission

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