ML20116A014

Responds to RAI Re GL 95-07, Pressure Locking & Thermal Binding of SR Power Operated Gate Valves

ML20116A014
Person / Time
Site:	Comanche Peak
Issue date:	07/18/1996
From:	Terry C TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20116A016	List: ML20116A014 ML20116A034
References
GL-95-07, GL-95-7, TAC-M93449, TAC-M93450, TXX-96413, NUDOCS 9607250258
Download: ML20116A014 (11)

Text

,

M Log # TXX-96413 +

l lllllll. = File # 10035 l

L. Ref. # 10CFR50.54(f) i F F GL 95 07 l 1UELECTRIC

c. tance Terry July 18, 1996 a,y w,,a,. ,

U. S. Nuclear Regulatory Commission Attn: Document Control Desk ,

Washington, DC 20555 0001

SUBJECT:

COMANCHE PEAK STEAM ELECTRIC STATION (CPSES) UNITS 1 AND 2 DOCKET NUMBERS 50 445 AND 50 446 -

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING GENERIC LETTER 95 07, " PRESSURE LOCKING AND THERMAL BINDING 0F I SAFETY RELATED POWER OPERATED GATE VALVES" (TAC NOS. M93449 AND M93450)

REF: 1. TU Electric letter logged TXX-95263 from Mr. C. L. Terry to NRC dated October 16, 1995 l

2. TU Electric letter logged TXX-95278 from Mr. C. L. Terry to NRC dated November 6, 1995

3. TU Electric letter logged TXX-96046 from Mr. C. L. Terry to NRC dated February 13, 1996 l

4. NRC Letter dated June 18, 1996 from Phillip M. Ray to Mr. l C. L. Terry Gentlemen:

l On August 17. 1995, the NRC issued Generic Letter 95 07, " Pressure Locking and Thermal Binding of Safety Related Power Operated Gate Valves."

Pursuant to Section 182a of the Atomic Energy Act of 1954, as amended, and l 10 CFR 50.54(f) TU Electric committed to implement the requested actions j in Generic Letter 95 07. Reference 1, 2 and 3 provided details of planned l corrective actions, as requested by the NRC.

l \

! Via this letter TU Electric is submitting response to additional i l information requested in Reference 4. Listed below are the NRC questions '

and TU Electric responses: 'V r

9 9607250258 960718 PDR I

ADOCK 05000445 '

P PDR \\

P.O. Box 1002 Glen Rose. Texas 76043

I I

TXX 96413 Page 2 of 5 ,

1. Regarding valves 8000A/B, Pressurizer Power 0perated Relief Valves (PORV) Block Valves., the licensee's submittal states that the valves may be closed to isolate a leaking PORV, and that during a steam '

generator tube rupture event, reactor coolant system (RCS) pressure a is less than the normal Operating pressure of 2235 psig. Has the l licensee evaluated this condition for potential depressurization- l induced pressure locking? Please discuss this issue. It appears l that the licensee has only considered the potential for thermally induced pressure locking.

TU Electric Response:

As part of the actions for Generic Letter 95 07. TU Electric has ,

reviewed these valves for the potential of thermally induced pressure '

locking and for potential depressurization induced pressure locking.

The result of this review is stated below.

The subject 8000A/B Valves are Pressurizer Power 0perated Relief Valves (PORV) Block Valves, and are located in the containment building, room 161. These valves are not subjected to high ambient temperature changes, e.g., active-function temperature of 120*F and maximum normal operating temperature of 120*F. Additionally, these valves are closed to isolate a leaking PORV and are required to be open during the steam generator tube rupture event, if pressurizer spray is not available for depressurizing the RCS.  ;

l In order to mitigate a steam generator tube rupture (SGTR) accident, '

the PORVs are used in the manual control mode to depressurize the RCS. The RCS depressurization and subsequent termination of the ECCS flow terminates the primary to secondary leak rate, preferably before the ruptured steam generator fills with liquid.

In the event that e PORV block valve is closed to isolate a leaking  !

PORV, it is assumed that this action takes place with RCS pressure at 2235 psig. This is a conservative high estimate for the pressure of the fluid potentially trapped in the valve bonnet.

The size of the tube rupture has a large influence on the time the l reactor operators are likely to open the PORV block valve, if closed, and on the RCS pressure. For the scenario in which a steam generator  !

atmospheric relief valve (ARV) opens and fails to close, the RCS will j cool and depressurize to approximately 1200 psi before the ARV is  !

assumed to be closed. TU Electric believes that, the reactor  !

operators will not attempt to open a closed PORV block valve at this i point, it is however procedurally permissible. It is more likely,

that the block valve will be opened just prior to initiating the RCS l

l 1

l l

! TXX 96413 Page 3 of 5 i

depressurization. At this point, the RCS pressure will be between l 1600 and 1800 psia. However, 1200 psi will be used as a l conservatively low assumption for RCS pressure when the block valve is opened,

! An analysis was performed to address this postulated I

depressurization induced pressure locking during steam generator tube l rupture event. This analysis assumes that initially the bonnet l cavity is filled with liquid (condensed steam at 2235 psig) and the l worst case RCS pressure is decreased to about 1200 psi. With con:.ideration given to the factors that affect margin, e.g., 0.67 valve factor, derated motor torque, degraded available voltage at the motor terminals, pullout efficiency, and upper bound stem factor, the stem thrust required to open the valve, with 2235 psig presumed to be trapped in the bonnet and 1200 psi differential pressure across the disc is determined to be about 11000 lbs. Using GL 89-10 method to l

calculate operator output, the least motor margin of these operators is 116%, refer to attachment 1 (Table 1). Therefore, with the ,

current operator switch settings, it is concluded that the PORV block ,

valve is acceptable, and no further actions are warranted.

2. Regarding valves 8716A/B, the licensee's submittal states that, since these valves are located downstream of the residual heat removal (RHR) heat exchanger, where the sump fluid has been cooled, and that since they are in a stagnant leg, not directly in contact with the fluid to the cold leg, then thermally induced pressure locking is not a concern. However, during the initial states of the recirculation phase of accident mitigation, water flowing in the RHR system may be significantly higher in temperature and may transfer heat to these valves. Please discuss this issue. Also, please provide any analysis completed, if applicable, for our review.

TU Electric Response:

The subject valves 8716A and 8716B are located in the piping crosstie downstream of the residual heat exchanger and are normally open j during normal plant operation and residual heat removal (RHR) ,

operation. The aforementioned valves are in safeguard building, room  ;

66 and 67, and are not subjected to significant ambient temperature l changes, e.g., active function temperature of 133*F and maximum i normal operating temperature of 122*F.

During the post LOCA ECCS injection phase, water from the refueling

water storage tank (RWST) is delivered to the cold legs via normally open valves 8809A and 8809B. The injection continues until the RWST low low water level alarm is actuated, or if the containment sump

s l l

l

~

l

^

TXX 96413 Page 4 of 5 ,

level is high enough to provide the required net positive suction head (NOSH) to the RHR pumps and then cold leg recirculation is started.

At the initial stages of cold leg recirculation, the reactor operator is instructed to align and establish ECCS to deliver water from the containment sump, through a heat exchanger cooled by component cooling water, to the cold legs before 8716A & B are closed, refer to attachment 2, (Figures 1, 2, and 3 from CPSES Emergency Response Guideline EOS 1.3A, " Transfer to Cold Leg Recirculation"). For 1 thermal induced pressure locking evaluation on valves 8716A and '

8716B, the worst case initial condition at the valve is the realistic lowest temperature of the water in the valve bonnet when the valves are closed. This temperature is assumed to be 70*F, and is based on actual surveillances performed during each shift of room temperatures and/or average RWST water temperature (CPSES Tech. Spec. 3/4.5.4 specified 40'F as a minimum temperature). Regardless of any assumed single failure or difference in RHR pumps performance, 70*F is considered a credible temperature in the valve bonnet before and after closure. Thermal analysis has been performed to show that the amount of heat transfer by conduction from high temperature fluid to these valves, when they are called upon to open to initiate hot leg recirculation, is small, refer to attachment 3 (Calculation ME CA-  !

0260-4077, Rev. 0). As a result, thermal induced pressure locking is unlikely because small temperature changes during valve operating '

sequences will not cause the pressure of the fluid in the bonnet, if  ;

trapped, to be higher than the pressure on the upstream and downstream sides of the disc assembly. Additionally, based on the static test results and existing operators output capability determined by GL 89 10 program, these operators have substantial motor margins, i .e. , 123%, 172%, 493%, and 265% for 1-8716A, 1 8716B, 2 8716A and 2 8716B respectively, refer to attachment 1 (Table 1).

Therefore, it is concluded that these valves are acceptable, and no further actions are warranted.

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 l l may have had an adverse impact on plant safety due to incomplete or incorrect evaluation of the potential effects of these modifications.

l 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.  !

i

TXX 96413 Page 5 of 5 TU Electric response:

Engineering and plant personnel evaluation of operational experience feedback including Significant Operational Experiences Report 84 07.

" Pressure Locking and Thermal Binding of Gate Valves," NUREG 1275, NUREG/CR 5807 IN 95-14 and IN 96 08 has led to the modification of several valves in units 1 and 2. Specifically, modifications were made to the containment sump to residual heat removal pump suction valves (18811A,18811B, 2 8811A, 2-8811B) and the containment sump to containment spray pump suction valves (1HV 4782,1HV-4783, 2HV-4782, 2HV-4783) to address the potential for pressure locking. The modifications consisted of installing a pressure relief valve in the bonnet of each affected valve to mitigate pressure locking and/or valve over pressurization. The potential effects of these modifications were addressed in a Safety Evaluation which concluded that no unreviewed safety issue exists.

These modi ications were assessed to have no direct impact on the training of plant personnel. The concepts of pressure locking and thermal binding and the associated operational experience feedback has been integrated into plant personnel training programs.

Specifically, lesson material for Auxiliary Operators, Licensed Operators, and mechanical maintenance personnel includes information on this subject. Attachment 4 to this letter is an excerpt from one of the lesson notes which provides an example of the depth to which the concepts of thermal binding and pressure locking effects are taught to plant personnel. Maintenance personnel were originally trained in the 1989 and 1990 time frame. The topic was also taught to Hechanical Haintenance personnel as a continuing training topic in 1995. Operations personnel have been initially trained on this topic. Continuing training for operations personnel is currently scheduled for this year.

l If you have any questions, please contact Obaid Bhatty at (817) 897 5839. l l

s'

') - l N

C. L. Ter y i

OB/ob l i

cc: Mr. L. J. Callan, Region IV

, Ms. L. J. Smith, Region IV Hr. P. H. Ray, NRR Resident Inspectors, CPSES l 4

1

aa.-~ a.- a-,.a..w. . - , . . . .u.,,2w n, _, _ _ , , _ , _ , _ _ , _ _ , _ .

i

\

l l

ATTACHMENT 1 TO TXX-96413 TABLE 1-0PERATOR MOTOR MARGIN I

i l

i k

j

Table 1: Operator Motor Margin

-Tag No. DMTQ OKR POn l AF Vr SFunseat MTR CapeMNty Tdhp Tun Tpd Tvert TeeniTeetti MTR lastgin, %

1-8000A 14.8 52.5 0.4 0.9 0.8 0.0077 :23249 4868 3472 2743 3286 8883 162 1-80008 14.8 52.5 0.4 0.9 0.8 0.0077 123249 4868 5209 2743 3286 -10820 119 2-8000A 14.8 52.5 0.4 0.9 0.8 0.0077 -23249 4868 3642 2743 32_86 -

J9053 157 2-8000B 14.8 52.5 0.4 0.9 0.8 0.0077 e (23249 4868 5331 2743 3286 '

s10742. 116 1-8716A 58.9 l 27.2' O.45 0.9 0.8 0.011543 35975 0 16164 0 0 -

"16164; 123 -

2f2

'i8716B 58 9 035 0?9 05 0TOIIST3 . 1. ; t35975 0 13246 0 0 113246 172 N 716A 58.9 27.2 0.45 0.9 0.8 0.011543 - - 35975 0 6069 0 0 '

-6069 493

~ T9 2is

~ ~

'2-8756B 58 9 2f~2 0 45 0 0.8 0.011543 35975 0 9847 0 0 ; 19847, Notes. DMTQ = Darsted Motor Tertius Rating Due to Elevated Temperattre. Fth [Attadimert X of ME4A40001093]

OAR = Actuator Overas Gear Rate [Attachmert J)

POE = PuE Out Efficiency [Attamment J of ME4A61093[.

AF = Asphcahon Factor [Atts& ment J of ME4A@001093].

W = Rate of Available Voltage and Narreplate Voltage [Attadimet Wof ME4AN1093[

SFuneemt = Average Unseating Srem Factor oblasied from Test Results . .M [From Test Data or Attammert T of ME4A4000'10931 MTR Capab4ty = (DMTQXOARXPOEXAFXW)*2/SFunseat Tbdp = Thrust requred to overcome borniet pressurtesten using Ccm Ed. method.

Tun

• Thrust requred to tsteedge the valve obtained from the last static test results. either measured using strasi geges or denve from spnng podt dew b Tpd = Stem repection loed, b Tvert = Reverse peton effed, b Total Trog'd = Tdbp + Tun + Tvert .Tpd MTR Margri. % = ((MTR Capabsty - Total Troq'd)/(Total Treq'd))100 07/02/96

l ATTACHMENT 2 TO TXX-96413 Emergency Core Cooling System Valve Configurations Figures 1, 2, and 3 I

1 t

l. .,

( OP51.SYS.RH1 , 2E85100 l 4 E8510A 8512A 8511B [

RWST ML

< J _k_R B5128 8511 A 8801A

1. A N'

LCV-112D CCPs COLD LEGS 8804A 8801B (ALL)

LCV-112D m:

8812A

' E 8809A CONT.  ;[ > PASS 8716A i SUMP #1 -, HOT 8811A

LEGS '

8924 8840 (2, 3)

CONT. ,7, 87168 ,

SUMP #2  :

COLD RHRP LEGS l RHR Hx g

N (3, 4)

' n

' 88048 8809B 8807A - 8812B HOT gI y, ; ; l 8802B LEGS J L  ;; (1, 4) 1r 8806 8821B 8835 COLD J L LEGS s

(

8821A 8802A HOT LEGS 88148 (2, 3)

M 8814A

- 8813aM ,

86 Figure 1 EMERGENCY CORE COOLING SYSTEM (INJECTION ' PHASE)

W 1

8 DS )

2

)

3 D 4 T S )4 DS TS LG L OG LG OG OE E i ,

2 O 3 HL E (1 OE H LE CL L( ( C CL B

2 5 0 3 8 8 8 8 M= w, M

)

^ A N B

8 g 9 0

8 8

1 2

8 8

=

A 4

1 8

O TI A

L 8 U I

M C 7 R I

C A

1 0

8 8

M B

1 0

8 8

d

^ B y

B '

I E

R G

8 7

6 1

7 N E L

8 8 B 4

1 D

B 8 L 4

0 M 8 O A

8 8 [(C 4 S 0

8 S I '

3 7M 8 ^ 1 E e X 8 T

1. H 8 S w R Y

S H

I R

=G B

1 1

5 8

y,~,

r 9:: I '

T N S

WL I

B RO O 0

1 5

A 2 y, w

, Q) C 8

1 5 A E

G- D 1

8 g

1 5 R

$ 8 O l C B

s Y C

N A 2 1 E 0

g 5 G 1

5 8 E R E

M E

D 2

E 2 N 2 o

=1 1 C1 1 ,

VCL

' ,C V

n;, T NP N N' 2 L

A 2  : =,, OM CU e

r u

' S 1

r 8 8

8 2 1

= h8 iF g

' 8 8 ' 8 T

S W A R 7 0

8

' 8 M M B

7 0

8 4 8 2

9 _

1 8 _

H _

R.

S V

S.

I S

P O

OP51.SYS.RH1 85100

[ ] 8510A b 3( 8512A 8511B

RWST ML gg L A L A 85128 8511A l 8801A t

1

N LCV-112D CCPs COLD g LEGS mT, _ ,

8804A 88018 (ALL)

Lb132E i

8812A I I COLD RHR HX N LEGS N QA 8809A (1, 2)

CONT.

M 1Ch 4 PASS 8716A M SUMP #1 = M HOT

'^ LEGS 8924 M (2, 3) 8840 N- 8716B M

=

SUMP #2 8811B COLD RHRP LEGS g

RHR HX l N'

' (3' 4) 8807A N G '

' 8804B M

8809B HOT 1 4) 88078  ::

0 N rg 7 8835 COLD M

SIPS J L h[

LEGS (ALL) 8N g 8802A HOT '

LEGS (2, 3) 88148 8814A

- 8813

-= == 8-16-94

. Figure 3 EMERGENCY CORE COOLING SYSTEM (HOT LEG RECIRCULATION)

___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . . - , - - . - .._ _.