ML20077H613
| ML20077H613 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 08/02/1983 |
| From: | Crouse R TOLEDO EDISON CO. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| 969, NUDOCS 8308110133 | |
| Download: ML20077H613 (4) | |
Text
1
.s o
- TOLEDO l
EDISON RCHAno P Cnoust V(e Prmw'nt Nucl*F (4191 PS9 5221 License No. NPF-3 Docket No. 50-346 Serial No. 969 August 2, 1983 Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Mr. Stolz:
This is in response to your letter dated June 1,1983, requesting for the additional information on natural circulation cooldown.
Attachment I provides Toledo Edison's response to your letter as relating to the Davis-Besse Nuclear Station Unit 1.
Very truly yours,
(( m u - -
RPC:FRM:llA cj a/10 cc:
DB-1 NRC Resident Inspector R o*'
yo THE TOLEOO EOISON COMPANY EOISON PLAZA 300 MAOISON AVENUE TOLEOO. OH10 43652 8308110133 830002 PDR ADOCK 05000346 P
[*
License No. NPF-3 Docket No. 50-346 Serial No. 969 August 2, 1983 Page 2 ATTACHMENT I TO TOLEDO EDISON LETTER TO THE NRC ON NATURAL CIRCULATION C00LDOWN j
Item 1:
Provide a detailed description of your natural circulation cooldown procedure and its basis (it should include guidance on i
possibility, prevention and mitigation of upper head voiding and natural circulation interruption due to hot leg voiding).
l Response: The present plant procedure (PP. 1102.10) for cooldown on natural circulation calls for a cooldown rate of the reactor coolant system (RCS) at approximately 20*F per hour. However, B&W has recently performed an analysis on reactor vessel (RV) head steam bubble formation on natural circulation cooldown with and without a continuous RV head vent (see B&W report sent to John F. Stolz on 4/15/83, serial No. 935). This analysis detecmined that the RCS could be cooled down at 1\\*F/hr. without any RV head void formation and no head vent. This number is
['
further backed up in Boman and Tally reports (referenced in your letter of June 1, 1983). However, the RCS can be cooled down at 22CF/hr. with the continuous RV head vent line proposed in our i
letter to John F. Stolz, dated 4/15/83.
Until the issue of the continuous head vent installation is resolved and except in the event of steam generator tube rupture, the maximum allowed cooldown rate during natural l
circulation in our procedure will be changed to less than 1 *F/hr. after the RCS has been depressurized to the saturation pressure that corresponds to the hot leg temperature prior to the tripping of reactor coolant pumps.
In the event of steam generator tube rupture, the RCS cooldown rate.(per existing emergency procedure EP. 1202.57) will be much higher (maximum 100*F/hr.) until the RCS has been depressurized to approximately 1000 psig. At this cooldown rate a steam bubble would form in the RV head.
In addition, this procedure also requires:
a) to maintain at least 50*F subcooling margin at core
- outlet, j
b) to periodically vent steam from the pressurizer as RCS temperature decreases to lower system pressure and c) to monitor pressurizer level and makeup tank level Further this procedure describes what operator actions are required if a steam void formation in the RV head occurs during natural circulation. These actions are:
1 1)
Stop depressurizing and cooldown.
+
2)
Increase makeup by starting the second makeup pump.
4
Licence No. NPF-3 Docket No. 50-346 Serial No. 969 August 2, 1983 Page 3-3)
Monitor core outlet thermocouples. A constant core outlet temperature shows natural circulation heat removal is effective. Monitor subcooling margin.
If subcooling margin is-less than 50'F, initiate high pressure injection (HPI) until 50*F subcooling is attained.
I 4)
Maintain pressurizer level constant between 100" and 200" as RCS pressure increases. Repressurization will compress the steam bubble in the head and decrease pressurizer level.
5)
Continue until an increase in RCS pressure does not decrease pressurizer level.
Toledo Edison feels that the existing procedure is sufficient to minimize void in the RV head and even if.a void situation does occur, there is enough procedural guidance given to the operators to take proper action to recognize its formation and to prevent it from interfering with natural circulation. We feel confident that the procedures used are adequate to safely cooldown on natural circulation at 1 to 1\\'F/hr. with proper recognition and corrective actions in case of a void formation.
Item 2:
Demonstrate that use of the procedure will not result in upper head voiding (demonstration based on analyses by Boman and Tally is acceptable).
~
Response: See response to Item 1.
1 Item 3:
Confirm and provide the basis for the conclusion that your procedures will not allow any voiding at the hot leg elevation.
I Response: See response to Item 1.
Item 4:
Provide an analysis that shows that there.is. sufficient condensate supply to support a conservative.est.imate of the time to reach the Decay Heat Removal System entry conditions.
Response: Toledo Edison has performed the analysis and concluded that the technical specification required condensate water capacity can support natural circulation cooldown for 34 hours3.935185e-4 days <br />0.00944 hours <br />5.621693e-5 weeks <br />1.2937e-5 months <br />. Both CSTs have high and low level alarms, and normal CST levels are kept above the' low level alarm set point. Assuming that the CSTs levels are at low level alarm set point, the condensate water cooling capacity is 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for natural circulation.
CSTs is not a safety grade system.
If water in CSTs is depleted, suction to'the auxiliary feed water pump can either be transferred manually to. fire protection system or automatically to-service water system. The water supply available from.the-service water system is infinite (from Lake Erie).
u
.=..
Licenze No. NPF-3 Docket No. 50-346 Serial No. 969 August 2, 1983 Page 4-At the cooldown rate of 1 *F/hr., the time required to bring the primary coolant to decay heat removal system entry condition is approximately.150-200 hours. Since service water supply is available indefinitely, sufficient cooling is available till off-site power is restored and reactor coolant pumps are restarted. This will restore RCS forced circulation to facilitate normal cooldown.
i cj.a/10 f
1 e
l l
4 4
4 i
.me-*.
7
-N,.-
4
-we 4 r a
w
-t
, rw r.-9 6
w-p yv-y.