TXX-9924, Forwards Responses to Questions by NRC Re Application for Amends to Licenses NPF-87 & NPF-89,by Incorporating Changes Increasing RWST low-level Setpoint from Greater than But Equal to 40% to Greater than But Equal to 45% of Span
| ML20217P109 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 10/22/1999 |
| From: | Terry C, Walker R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-MA1769, TAC-MA1770, TXX-99244, NUDOCS 9910290215 | |
| Download: ML20217P109 (13) | |
Text
?c v.
p (e)TXU TXU Electric C.! erne Terry Comanche Peak
. SeniorVice President & Principal Nuclear oTicr Ste:m tiestric Station P.O Box 1002 Gen Rose,TX 76043 -
Tel:254 897 8920
. Fax:254 897 6652 herry1@txu.com Log # : TXX-99244 File # 10010 916 (3.3)
Ref. # 10CFR50.36 October 22,1999 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555
SUBJECT:
COMANCHE PEAK STEAM ELECTRIC STATION (CPSES)
DOCKET NOS. 50-445 AND 50-446 SUPPLEMENT TO LICENSE AMENDMENT REQUEST 98-001 RWST LEVEL SETPOINT CHANGE (TAC # MA1769 AND MA1770)
REF:
TXU Electric Letter, logged TXX-98033, from C. L. Terry to the NRC dated February 27,1998 Gentlemen:
Per the referenced letter, T.vU Electric submitted a request to amend the CPSES Unit 1 Operating License (NPF-87) and CPSES Unit 2 Operating License (NPF-89) by incorporating changes that would increase the RWST Low-Low level setpoint from "240%" to "245%" of span for CPSES Units 1 and 2. Provided herein are responses to questions asked by the NRC. Attachment 1 is the affidavit for this l
information supplementing License Amendment Request 98-001. Attachment 2 i
provides the requested information.
If you have any questions negarding the attached information, please contact
' Mr. J. D. Seawright at (254) 897-0140.
1
/
9910290215 991022 i
PDR ADOCK 0500044S 3 Cl P
\\
i
})O
(hTXU
- iXX-99244 Page 2 of 2 This communication contains no new licensing basis commitments regarding CPSES Units 1 and 2.
Sincerely,.
C. L. Terry By:
M
' RogerD. Walker
- Regulatory Affairs Manager JDS/js Attachments c-E. W. Merschoff, Region IV J. I. Tapia, Region IV D. H. Jaffe, NRR Resident Inspectors, CPSES Mr. Arthur C. Tate Bureau of Radiation Control Texas Department of Public Health 1100 West 49th Street Austin, Texas 78704
Attachment I to TXX-99244 Page.1 of1.
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION In the Matter of
)
)
TXU Electric
)
Docket Nos.
50-445
)
50-446 (Comanche Peak Steam Electric
)
License Nos.
NPF-87 Station, Units 1 & 2)
)
NTF-89 AFFIDAVIT Roger D. Walker being duly sworn, hereby deposes and says that he is the Regulatory Affairs Manager of TXU Electric, the licensee herein; that he is duly authorized to sign and file with the Nuclear Regulatory Commission this supplement regarding License Amendment Request 98-001; that he is familiar with the content thereof; and that the matters set forth therein are true and correct to the best of his knowledge, informa. tion and belief.
l off b/
i RogeM. Walker l
Regulatory Affairs Manager l
STATE OF TEXAS
)
)
COUNTY OF hh
)
ND Subscribed and swom to before me, on this Q2 day of OMw
,1999.
7 %% o e n wooman Notary Public 4
- q j nt??JPeg ;
. to TXX-99244 Page1 of10 QUESTIONS ON COMANCllE PEAK RWST SWITCHOVER LEVEL l
1.
Provide a table which contains the following information; (1)
Time ofinitiation and completion of each automatic or operator action relevant to switchover following a LOCA at time zero.
(2)
Desenption of operator or automatic action and the reason for this action (3)
Water level and volume in the RWST and the containment sump at each specified time
RESPONSE
l The operator actions required for the RWST switchover phase described in the FS AR j
Section 6.3.2.8 (Manual Actions), Table 6.3-7 (Sequence of Switchover Operations) and Table 6.3-11 (RWST Outflow Large Break - Worst Single Failure) were updated in FSAR Amendment 96 to reflect the current procedures and analyses. Table 6.3-11 was also updated in Amendment 95. The RWST outflow in Amendment 95 for the ECCS pumps was based on input from single train pump nmout calculations. The current analysis of RWST outflow " : performed using input from a two train pump runout calculation consistent with the scenario of Table 6.3-11. Because the ECCS pumps discharge into a common header, each pump's nmout is reduced by the flow resistance.
The ECCS injection phase is described in the FSAR Section 6.3.2.8. The RHR j
Emergency Sump isolation valves automatically open on RWST Lo-Lo. T his is the only
{
automatic action in the switchover. No operator action is required prior to tHs automatic action.
)
The time ofinitiation and completion of each automatic or operator action relevant to switchover following a LOCA is broken down into two phases: 1) the ECCS injection phase in which the criteria is for a minimum of 9.5 minutes between the SI Signal and the earliest Lo-Lo alarm (Lo-Lo + uncertainty) and 2) the RWST switchover phase in which the criteria is for ECCS and Containment Spray switchover from injection to recirculation without stopping the pumps coincident with maximum drawdown and the worst single j
active failure.
j The following table provides the requested information by combining the ECCS Injection I
phase with the maximum RWST outflow analysis with worst single active failure (failure of one RWST to RHR suction isolation valve to close). The automatic action and the operator actions are in accordance with the FSAR Section 6.3.2.8 (Amendment 95) and Emergency Operating Procedures (EOPs) for this scenario. Alann and indication levels j
have been added to clarify the interface between the instrumentation and the operator. It is important to note that credit for the time (~1 min. 8 seconds) and RWST volume
(-25,724 gallons) between the Lo-Lo plus uncertainty and Lo-Lo minus uncertainty is 1
I l
. to TXX-99244 Page 2 of10 excluded from the criteria for each phase.
It should also be noted that the containment flood levels have been updated to reflect a recent re-analysis of minimum containment flood levels. The minimum flood level at receipt of the Lo-Lo alarm is 810.24 feet (approximately 27 inches above elevation 808'-
0" in lieu of the 21 inches presented in the previous submittal). TXX-98033, Attachment 2, page 3 is, therefore, revised as follows:
EFFECT ON CONTAINMENT FLOOD LEVELS Minimum Containment flood levels are impacted by the RWST setpoint changes.
The above described reduction ofinjection volume by raising the Low-Low setpoint reduces the minimum containment level at the time of RHR switchover to the sump by 4
about 6 inches. The minimum flood level at receipt of the Lo-Lo alarm is approximately 27 inches above elevation 808'-0". This is accqtable for RHR pump NPSH. NPSH analyses at a worst case pump runout f!ow of 4900 gpm show a margin of > 5 feet at an elevation of 808'-0" which is the containment floor elevation (i.e. a full sump). See the attached elevation sketch of the containment emergency sump.
l i
. to TXX-99244 Page 3 of 10 RWST OUTFLOW LARGE BREAK [9]
Duration Time RWST RWST RWST Sump (sec)
(min:sec)
Outflow Volume Levei Level Action / Event
[3,5,10]
[1]
(gpm) [2,6,7]
(gallons)
(El.)
( El..)
Safety injection Signal (RWST Lo - uncertainty) 0:00 22,835 4V3,731 850.42'
<808 j
RWST Level Lo-Lo Alarm (+ uncer,ainty) 9:30 a
256794 832.14' 810.24' j
l RWST Level Lo-Lo Alarm (nominal) a 243,937 831.05' i
RWST Level Lo-Lo Alarm ( - uncertainty) 10:38 a
231,070 829.97' j
Auto-open emergency sump isolation valves, 30 11:08 22 610 829.02' Operator reset SI [4]
(>10:00)
Verify CCW Oow from RHR heat exchangers 30 22,362 828.07' j
21,993 827.14' Verify 8811 A&B open (emergency sump to 30 RilRPs)
Close 8812A&B (RWST to RilRPs) 50 21,623 825.62' Close 8814A&B,8813 (SIP mininow) 40 19,900 824.50' RWST level 24% (+ uncertainty) 157,726 823.79' 812.05 Close 8716A&B (RilRP crosstic) 45 19,551 823.26' 822.19' Close 8511 A&B,8512A&B (CCP Alt Miniflow) 40 19,136 137,431 822.08' RWST Level 24% (nominal)
Open 8807AtB (S1 to Charging Suction lleader 45 l 8,759 821 00' Crosstie)
RWST level 24% (- uncertainty) 117,197 820.34' Open 8804A&B (RHRP to SIP Suction)[8]
45 18,315 819.84' Check RWST level <24%
30 16,787 102,421 819.13' 812.76
)
Open llS-4782/4783 (emergency sump to CT 50 15,833 89,247 818 02' Pumps)
RWST Empty Alarm (+ uncertainty) 85,094 817.67' Stop ECCS pumps still taking suction from RWST 30 11,604 83,445 817.53
[12]
RV!ST Empty Alarm (nominal) 72,157 816.58'
~
Close 115-4758/4759 (RWST to CT Pumps) 120 20:23
[11]
61,505 815.68' RWST Empty Alarm (- uncertainty) 59,340 815.50'
]
i Sparger centerline
!8,751 812.08' Bottom of tank 0
810.50' 1
e
. to TXX-99244 Page 4 of10
(
NOTES:
i
[1]
Actions assume Safety injection Signal and Containment Spray Actuation Signai(conservatively) at time 0:00.
1
[2]
It is assumed that the RIIR, SI, charging and containment spray pumps operate at conservative flowrates. Pumped flowrates l
are assumed to be constant during each svep of switchover and the specified number of pumps of each type are operating:
RilRpump 2 pumps operating
=
CCHG pump 2 pumps operating
=
SIpump 2 pumps operating
=
CS pump 4 pumps operating
=
[3]
ECCS Valve operating times are maximum operating times from FSAR Table 6.3-1.
[4]
An allowance of time for valves 881 I A/B to automatically open occurs at RWST Level Lo-Lo.
[5]
Time required to complete the required action includes a conservative 30 seconds for operator response time for each manual procedure.
[6]
The flowrate in this column is assumed to occur during the entire time interval for its respective step. This is conservative since valve repositioning may reduce the flowrate during the time interval.
[7]
Flow out of the RWST during switchover includes allowances for both pumped flow to the RCS and containment and for backflow to the ;ontainment sump.
[8]
Following the completion of this step all ECCS pumps are aligned with suction flow from the containment sump with the exception of one RHR pump due to the single failure. The containment spray pumps continue to take suction from the RWST until the RWST level indication is less than or equal to 24% and the operator initiates switchover of the Containment Spray System.
[9]
Based on a Large Break LOCA in conjunction with a single failure of one of the RWST to RilR pump isolation valves (e.g.,
8812A or 8812D fails to close on demand).
[10]
Containment Spray valve operating times are maximum operating times of 20 seconds for liv-4782 and 11%4783 (sump isolation valves) and 90 seconds for IIV-4758 and 11%4759 (RWST isolation valves).
[11]
Total calculated outflow of 21,940 gallons during RWST to CT isolation is broken down into 30 seconds (11,275 gpm) for the operator response time and the valve 90 second stroke time. The valve stroke time is broken into 15 second (11,275 gpm) and 75 second (10,787 gpm) increments to reflect the decreasing flow rate as RWST level drops.
[12]
The minimum RWS*I transfer volume (146,030 gallons) and associated Empty Alarm could occur during the valve stroke time for the RWST to CT isolation. If this occurred, the operator would execute the ECCS pump protection caution and stop any ECCS pumps taking suction from the RWST while the CT isolation valves continued to stroke. A 30 second delay is conservatively assumed prior to this step for the operator to execute the ECCS pump protection caution. If the CT isolation does not occur 1 y 6% (i.e. RWST level continues to drop) the operator would execute a similar CT pump protection caution.
I 1
l I
4
, Attachment 2 to TXX-99244 Page 5 of 10 -
. 2.
Provide an elevation sketch of the containment emergency sump showing elevations at
. which pumps are switched off.-
RESPONSE
The design and licensing basis for the containment emergency sump does not include an elevation at which the ECCS or spray pumps would be shut off. The licensing and design basis ensures the ECCS and spray systems will operate continuously during RW ST switchover from injection to recirculation.
3..
Please explain the statement on page 1 of Attachment 2. "there was insufficient instrumentation accuracy for a separate caution for the spray pumps after receiving an -
empty alarm on the RWST."
RESPONSE
l The analysis of the pump protection caution in EOPs 'showed that there was sufficient l
volume below the empty alarm (minus uncertainty), shown in the table above, to stop any l
pumps still taking suction from the RWST for pump protection. This is required if a h
single RWST isolation valve failed to close and for failures beyond the design basis. The analysis 'of RWST switchover using the empty alarm for initiation of spray pump switchover with a separate spray pump protection caution based on level indication'
]
showed that, although there was physically enough water, the indication uncertainty of
+/- 4% (+/- 20.5 inches,4 /- 20,il5 gallons) is too great to ensure both ftmetions could be performed. That is, if a RWST to spray pump isolation valve failed to close, spray pun:p protection might not occur before the RWST was empty.
i i
i i
1
)
i to TXX-99244 Page 6 of 10 s
4..
The February 27,1998 submittal stated that for the 1981 full scale model testing, the
" minimum specified level" was 810'-8", The submittal further stated that the " minimum tested level" that confirmed anti-vortex design was about 810'-3" at flow rates of up to 8858 gpm for a single suction line. Based on the above statements, it was asserted that vortexing would not be expected to occur at the full sump with water level of 21" above the full sump Please clarify the following items (1)
What are the meanings of the " minimum specified level" and " minimum tested level?"
(2)
Why the cited information of water levels for the 1981 full scale model testing are relevant and adequate to support the licensee's assenion that vortexing would not occur at the water level of 21" above a full sump.
RESPONSE
(1)
A minimum water depth above the sump floor of 8'-8" with maximum flow rates of 7,200 gpm for raray pump suction only,5,300 gpm for RHR pump only and 12,500 gpm for both P -fR and spray pumps was specified for the full scale model testing of the emergehy recirculation sumps for CPSES. The sump is six feet deep from floor elevation 808'-0". This meant that the testing was required to show adequate design for flood levels at or below Elevation 810'-8" with flows l
equal to or greater than those specified.
l The testing included levels which were lower than 8'-8" and flow rates which l
were greater than those specified. The testing data conservatively exceeded the l
specified parameters by testing lower levels with higher flow rates.
(2)
The previously calculated flood level of 21 inches above the 808'-0" floor was justified because, altbough the postulated level was below that tested, the flow rate to the suction was 180% of the maximum possible RHR suction. In addition, as shown in the table in the response to Question 1, the flood level will continue to rise relatively fast due to the spray pump injection.
As discussed in the response to Question 1 and shown in the table above, the RWST Lo-Lo setpoint change results in a newly calculated containment flood level of 810.24 feet (approximately 27 inches above the 808'-0" floor a id 8'-3" above the sump floor). (See attached sketch.) At this point, only one RHR pump (with a maximum runout flow of 4.900 gpm) takes suction from each sump.
Note that the statement in TXX-98033 that the " minimum tested level and flow for a single suction line that confirmed the anti-vortex design was approximately 810'-3" at up to 8858 gpm" should have read "..approximately 810.3' at up to 8858 gpm" which corresponds to 810'-3.6" (or 27.6 inches above the 808'-0" floor). This statement was drawn from two tests of the anti-vortex cage design.
1 l
l to TXX-99244 1
' Page 7 of 10 One test was performed with no blockage and the other was performed with 88%
blockage. The total flow rate for these two tests was 16,052 gpm with 7194 gpm to one pump suction and 8858 gpm to the other. The test with no screen b,ackage showed insignificant level change across the screens. This test conservatively represents the point of ECCS switchover when the screens would be essentially unblo;ked and the total flowrate thru the screens would be less than 31% of that in the test. The test with 88% screen blockage showed a 3.2" level drop across the screen; however, the level inside the screen was 27.6 inches above the 808'-0" floor. It was judged that this test data point conservatively represents the point of ECCS switchover when the flowrate thru the RHR suction line would be less than 56% of that in the test. Therefore, it is concluded that this data is both relevant and adequate to support the conclusion that vortexing will not occur at the minimum water level of 27 inches above the full sump.
5.
It appears that there is a possibility that the operator would have to tun, off the containment spray pumps because they could still be taking suction from the RWST when the EMPTY alarm is received, depending on the direction of the uncertainty on the level. In fact, isn't this what NOTE 12 is saying?
If so, then has the original problem of being required to turn off the containment spray pump been resolved?
RESPONSE
Note 12 is clarified as follows -
[12]
The minimum RWST transfer volume (146,000 gallons) and associated Emptv Alarm could occur during the valve stroke time for the RWST to CT isolation. If this occurred, the operator would execute the ECCS pump protection caution and stop any ECCS pumps taking suction from the RWST while the CT isolation valves continued to stroke. A 30 second delay is conservatively assumed prior to this step for the operator to execute the ECCS pump protection caution. If the CT isolation does not occur by 6% (i.e. RWST level continues to drop) the operator would execute a similar CT pump protection caution.
6.
To what step does NOTE 9 apply?
RESPONSE
j Note 9 describes the maximum RWST outilow scenario based on a failure of one valve to i
close in the step "Close 8812 A&B (RWST to RHRPs)".
, to TXX-99244 Page 8 of 10 7.
The original (2/27/98) submittal, on page 4/6, compares the 1981 testing with the flow rates and levels in the plant. The discussion is in terms of the RHR pumps. Verify that the flow rates used in the 1981 testing were higher than those predicted for the plant.
RESPONSE
The calculated single train RHR pump runout flow rate used in the minimum sump NPSH analysis is 4900 gpm. The minimum RHR pump flow rate specified for the 1981 testing was 5,300 gpm. Testing was performed at higher flow rates.
8.
The original (2/27/08) submittal (page 4 of 6) states that the 1981 full scale flow tests confirmed the antivortexing design of the RHR and the containment spray pumps.
However, the submittal does not discuss the adequacy of the calculated containment water level in terms of containment spray pump NPSH.
RESPONSE
[See Question 9 Below]
9.
Provide information justifying that the containment spray pumps will have adequate NPSH during both injection (down to the 6% RWST level) and recirculation.
RESPONSE
The spray pump protection caution at 6% ensures the spray pumps do not operate below the sparger centerline. The spray pump minimum NPSHa from the RWST at the centerline of the sparger is greater than NPSHr. The curve in FSAR figure 6.2.2-2 depicts the NPSHa for the Injection phase of the LOCA. The lowest possible elevation of the RWST corresponding to the centerline of the sparger (812.09 ft) is used for the Injection phase. Using this elevation, the NPSH available is greater than the NPSH required for the entire pump expected operting range.
The spray pumps have positive NPSHa > NPSHr in the sumps prior to the initiation of ECCS switchover which precedes spray switchover.
r
I
. to TXX-99244 Page 9 of10 RWST Elevation Sketch EL. 816'-10" Max. Flood Level name emme emme ammes assus emm amme ammes emme ammes emme emus ammme aus
- EL. 816' Trash Rack
- EL. 814 Fine Mesh Screen
.f EL. 812.05'
~
Min, flood level at 24% RWST level indicated (Cont. Spray Switchover) j L
EL. 810.24' Min.11000 level at 4b% MWs I level o-Lo Alarm (ECCS Switchover)
~27"
~48" l f NPSHa>NPSh.
- EL. 808 Containment Emergency Sump
[See FSAR Figure 6.2.2-3)
EL. 802'-0" Bottom of Sump h%N%N%%NNW
- to TXX-99244 Page 10 of10 6C
~
~
~
NPSH Available Injection P'we 20-O NPSH Available g
i b
Recirculation Phase 1,30-N.,
a.
- ,N
\\
z 20 -
'N
/<-
NPSH Req'd 1
'0-0 I
I e
0 000 2000 3000 4000 5000 Flow rate [gpm) l COMANCHE PEAK S.E.S FINAL SAFETY ANALYSIS REPORT f
i UNITS 1 AND 2 i
C O NTAINM EN SPR PUMPS f
Amendment 96 August 2,1999 FIO ORE 6.2.2 2 SHEETI