ML18153A730

Comment Supporting Proposed GL Re Pressure Locking & Thermal Binding of safety-related power-operated Gate Valves

ML18153A730
Person / Time
Site:	Surry
Issue date:	04/28/1995
From:	BOWLING M L VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF ADMINISTRATION (ADM)
References
FRN-60FR15799 60FR15799-00015, 60FR15799-15, GL-95-019, GL-95-19, NUDOCS 9508140035
Download: ML18153A730 (8)

Text

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J, .J'c v/ tfl }t,t 17 U/t 1 ~,j{9f'I( April 28. 1995 f\JLE S ;-*~C.. *;:: ,t :.~, * .-.. -** t. r~. USN;~:c Chief, Rules Review and Directives Branch U.S. NucJear Regulatory Commission Washington, DC 20555

Dear Sir:

PROPOSED GENERIC LEUER 6 (;7 //f /.F7f J J/..)7/ 75 *@ VIRSIIIIIA

,.DWEii Serial No. GL 95-019 NL&P/MAE R2 PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-BELATED POWER-OPERATED GATE VALVES In the March 27, , 995 Federal Register, the NRC announced that it is proposing to issue a generic letter regarding pressure locking and thermal binding of safety-related power-operated gate valves. This proposed generic letter is intended to ensure that addressees have performed or will perform evaluations, and as appropriate, analyses and/or corrective actions to ensure that related power-operated gate valves that may be susceptible to pressure locking or thermal binding are capable of performing their required safety functions.

Virginia Power encourages the NRC's efforts to solicit industry advice and recommendations in developing this proposed generic letter. Guidance for addressing pressure locking and thermal binding of power operated gate valves and the description of potential resolution options provided in Attachments 1 and 2, respectively, of the proposed generic letter are unnecessarily prescriptive and somewhat prejudicial.

Speciflcally, the guidance for addressing the valves discusses an acceptable approach for th~ . evaluations and states what will and will not be acceptable in the evaluation.

This appears to be very narrowly focused. This attachment also discusses*.

requirements for valve modifications such as a 10 CFR 50.59 analysis, adequate post-modification testing, and an evaluation of the effects of the

• modffication.

This is unnecessary guidance to Include in a generic letter. Regulations already exist to address the necessary considerations for modifications of safety-related equipment.

In addition, the description of potential resolution options in Attachment 2 discusses five potential resolutions.

Of those, only one (Option 4, to modify or replace valves) is not followed by statements that the option is considered by the staff to be either Inappropriate or difficult to justify for either pressure locking or thermal binding, or both. Potential resolutions should not be unduly prejudged or biased by the staff. Otherwise, a full backfit analysis in accordance with 1 O CFA 50.109 would appear to be warranted.

Finally, if Option 4 remains the only alternative acceptable to the -------------.---. -' 9508140035 950428 PDR PR MISC 60FR15799 PDR

' APR.'/28' 95 (FRI) 14: 26 VA PO,-NL&P NRC, then schedule completion times should be reevaluated as proposed by the Nuclear Energy Institute in their April 27, 1995 comments.*

In summary, we support the performance of evaluations, and as appropriate, analyses and/or corrective actions to ensure that safety-related power-operated gate valves that may be susceptible to pressure locking or thermal binding are capable of performing their requirect"safety functions.

However, the proposed generic letter does not provide adequate flexibility or take into account the increased reliability of these valves due to the completion of the Generic Letter 89-10 requirements nor does it recognize the recently completed technical assessment of this issue by the NRC Regional l~spectors.

We also endorse the comments submitted separately on this Issue by the Nuclear Energy Institute~

If you have any questions, please contact us. Very truly yours, ,#I. .i~ M, L. Bowling, Manager Nuclear Licensing and Programs cc: Mr. Clive Calloway.

Nuclear Energy Institute

• 1ns I Street, Suite 400 Washington, DC 20006-3708 P. 003 Southem Califomla Edison Company 23 .. ""ICEJIII STilll!!ET IIIIV1~ CAUFOANIA 92718 April 26 1 1995 Nuclear Regulatory Co11111ission Attention:

Chief, Rules Review and Directives Branch Washington, DC 20555 -Gentlemen:

Subject:

Southern Caltfornt1 Edfson*s (Edison) CD1111ents on Proposed Generic Letteri Prassure Locking and Therm1l lfndfng of Safety-Related Powar-Operat,d Gate Valves RefeTence:

Federal Register, *Proposed Generic Letter; Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves,* March 27, 1995 . In the referenced federal register, the NRC published the subject proposed Generic Letter for public connents.

Attached are Edison 1 s connents on this proposed generic letter. If you have any questions or require additional infonnation.

please contact me. Sincerely, ;f~,9~ -Loo1ioo~ . st=Lo S6/LZ1to

.. e ATTACHMENT COM4£NT 1: The proposed Generic Letter should specify that sliding coefficients of friction for the-applicable materials, rather than valve factor, will be used in conjunction with a double disc drag condition when calculating an actuator's capability to overcome postulated pressure locking conditions for the long tenn. CCDIIENT Z: The proposed Generic Letter should state that in evaluating thennally induced pressure locking of a closed gate valve, if a distinct source of heat (other than nonnal cyclic changes in ambient temperature) cannot be identified, thermally induced pressure locking of that gate valve need not be considered credible.

COIIIM 3: The proposed Generic Letter should allow that actual motor and gear efficiencies, as determined from Matar Operated Valve Generic Letter 89-10 testing, will be considered suitable for determining capability of an actuator to overcome pressure locking I thermal binding for the long term. COIIIENT' 4: The proposed Gen~ric Letter should state that if a limit to bonnet pressure may be quantified.

in a pressure locking evaluation, then analytical methods demonstrating sufficient actuator capability will be satisfactory for the long term~ In addition, the proposed Generic Letter should state the methodology will be applicable ta both large and small gate valves, since the methodology and issues are identical to both groups. Examples where pressure may be quantified would be gate valves suppl;ed with internal relief valves with known setpoints, or gate valves susceptible to pressure locking due to some known pressure such as pump shutoff pressure or some other quantifiable system pressure.

• COffilENT 5: As stated in the proposed Generic Lett1r 1 thennal binding is applicable to solid wedge gate valves and possibly flex wedge gate valves with high temperature gradients.

Unless *high temperature gradient*

is defined by the proposed &eneric Letter, flex wedge gate valves would not be considered susceptible to thermal binding given the 1ack of supporting industry events documenting thermal binding of flex wedge gate valves. COIIIEJIT 6: Thennally induced pressure locking occurs due to an increase in the volume of water w;thin the valve bonnet as a result of increasing temperature.

When a water solid valve bonnet is assumed, the temperature increase results in a pressure increase of the water within the bonnet. No specific rate of

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• pressure increase due to temperature increases in a water solid valve. bonnet is ;dentified in the proposed Generic Letter. As stated in NUREG 1275, pressure will increase at a rate of 100 psi/Fat temperatures greater than 450

• F, and pressure will increase at a rate of 33 psi/fin the range of 100 F. Therefore the proposed Generic Letter should state that the thermally induced pressure increase rate for a water solid valve bonnet will be specified, in accordance with NUREG 1275, as: 33 psi/F for temperatures up to 450 f 100 psi/f for temperatures equal to or greater than 450 F. In addition the proposed Generic Letter should state. that if actuator capability can be shown ta be sufficient to open valves with these calculated pressures, then this evaluation will be acceptable for the long tenn. CotllENT 7: In addition to physical modification identified in NUREG 1275, procedural modifications which would eliminate the potential for pressure locking and thermal binding should be considered as suitable corrective actions and specifically endorsed by the proposed Generic Letter. CCNIENT 8: The proposed Generic Letter should state that gate valves. located in gas systems other than steam, should be considered exempt from pressure locking and thermal binding. COfiltENT 9: Based on lack of documented occurrences.

gate valves not in systems identified in AEOO/S92-07 should be considered exempt fTOm pressure locking and thennal binding. The proposed Generic Letter should clarify which systems are considered

• susceptible*

to pressure locking and thermal binding. CotllENT 10: Without specific screening criteria specified in the Generic Letter there exists a potential for inconsistencies, from plant to plant. in identifying the applicable pressure locking and thennal binding scope. The proposed Generic Letter should pTOvide specific screening criteria fn order to eliminate incon*istencies in implementation.

COtltENT 11: Background~

Paragraph 3, Last sentence states: J.00/tOO~

• Pressure locking and thermal binding may occur in varying degrees but may not, in all cases. render a valve incapable of operating.

though a delay in valve stroke tiae or valve damage may occur.* et:J.o S6/4Z/t0 V

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• If open stroke time can be affected by the poss;bility of the motor going to locked rotor 1s spec;fied by the proposed Generic Letter, then credit for locked rotor aotor torque should also be permitted by the proposed Generic Letter. However. experience could support the assumption that for double disc gate valves, which-could be subjected to double disc drag under pTessure locking conditions, no measurable increase in Motor Operated Valve stroke time is considered to exist if the actuator can be shown to be capable of providing adequat* open thrust to overcome the pressure locked condition at rated motor output start torque. The proposed Generic Letter should either recognize that there is a possibility of an increase in stroke time. and allow use of locked rotor torque. or restrict analysis to the use of motor rated starting torque and assume no measurable increase in stroke time will occur. . CIIIIENT 12: Gate valves located in steam lines with the valve stem and bonnet oriented in a nonnal 1 upright. & vertical position should be excluded from the potential of condensate collection and subsequent thennal induced pressure locking. The proposed Generic Letter identifies valve orientation as a means for condensate*

collection in steam valves but does not specify what *orientation*

is. The proposed Generic Letter should clarify this item and pennit exclusion of Power Ope.rated Va 1 ves whose ori entati an is not a concern. COtllENT 13: The Generic Letter refers to Generic Letter 89-10, Supplement 6 as providing an acceptable approach to address pressure locking and thennal binding. Within Supplement 6 it is stated that Mexternal heat loads may be evaluated in a bounding manner*. Edison is unclear ~o how this would affect the pressure locking and thennal binding evaluation.

The proposed Generic Letter should clarify this statement.

COIIIENT 14: Retraction.of the valve stem during the open valve stroke will increase the available bonnet volume thereby decreasing the pressure of a water solid valve bonnet. Due to the clearances within a gate valve. the amount of stem travel prior to full disc IIOvement may significantly decrease the internal bonnet pressure.

Taking ~redit for known gate valve internal clearances as they relate to opening stem travel should be credited within the proposed Generic Letter as a suitable means of internal bonnet pressure reduction during stroking.

CCNIENT 15: ATTACHMENT

1. item 1. paragraph states: *Th* evaluation also should include review of generic studies for site-specific applicability, such as in the areas of thermal effects and design-basis depressurization.*

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• r e e The intended meaning of the above sentence is not clear. This concept should be clarified in the proposed Generic Letter. CCIMENT 1&: Although not ~onsistently stated in the draft Generic Letter, the pu-rpose of the Generic Letter, as initially stated in the first paragraph, is to ensure safety related gate valves uare capable of perfonning their required safety functions.*

Therefore, the evaluation of and corrective actions taken as a result of potential pressure locking or thermal binding of. safety related valves where safety function fs not impaired*

will be based on economic concerns at the utility.

• For example: a safety related gate with no safety function to open. COIIIENT 17: Although the susceptibility evaluation and further analysis as described in 50.54(f) Infonnation Request, l.a. 1.b, and 1.c, would be completed at the required time, analysis and evaluations at operating plants are living documents and as such are updated periodically as components are added or deleted from the plant. or <O

.. e e CONEfT 22: The Generic Letter should allow the possibility of pressure locking or thermal binding if plant recovery can be achieved by alternate means, such as local manual op1r1tion, ate., providing there is an insignificant increase in core melt probability.

CCNtEKT 23: The Generic Letter should allow for ignoring the affects of short term temperature changes that do not have enough time to cause bonnet water heatup. CGIH:HI' 24: The Generic Letter should allow for the use of motor inertia effects to overcome valve cracking load, for the long term. when the inertia can be quanti f; ed. COtll£NT 25: The Generic Letter should state there is no dissimilarity between justifiable envineering methods (excludi~g short term operability assessments) that are su1table for small or large valves, or between methods that are suitable for

• the short or for the long tenn. This should be stated unless reasoning can be stated, in the proposed Generic Letter. that the engineering methods acceptable for small valves are not acceptable for large valves. and that methods acceptable for the short tenw are not acceptable for long tenn. LOO/LOO~ et=Lo S6/LZ!t0