ML19254C838
| ML19254C838 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 09/21/1979 |
| From: | COMMONWEALTH EDISON CO. |
| To: | |
| Shared Package | |
| ML19254C837 | List: |
| References | |
| NUDOCS 7910171063 | |
| Download: ML19254C838 (8) | |
Text
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Commonweaith Edison NRC Docket Nos. 50-295/304 ATTACHMENT A RESPONSE TO IE BULLETIN NO. 79-21
" TEMPERATURE EFFECTS ON LEVEL MEASUREMENTS" Item 1 Review the liquid level measuring systems within containment to determine if the signals are used to initiate safety actions or are used to provide post-accident monitoring information.
Provide a description of systems that are so employed; a description of the type of reference leg shall be
- included, i.e., open column or sealed reference leg.
Response
This review identified the t'ollowing systems:
Description System Steam Generator Level Open Column Pressurizer Level Sealed Reference Leg Containment Recirculation Float Type Level Switches Mounted at 5 Discreet Sump Elevations s
. Item 2 On those systems described in Item 1 above, evaluate the effect of post-accident ambient temperatures on the indicated water level to determine any change in indicated level relative to actual water level.
This evaluation must incl *rle other sources of error including the effects of varying fluid pressure and flashing of reference leg to steam on the water level measurements.
in tabular form The results of this evaluation should be presented similar to Tables 1 and 2 of Enclosure 1.
Response
As requested, the results of the requested evaluation are contained in the four tables listed below and included in this attachment.
Table No, 1:
Correction to indicated steam generator water level for Reference Leg Heatup effects due to post-accident containment temperature (before reactor trip).
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Commonwealth Edison NRC Docket Nos. 50-295/304 s '
Table No. 2:
Correcticn: to allcwdo~1e indicated steam generator water level for Reference Leg Heatup and Pressure changes following a high-energy line break, to assure that true level is between the level taps.
Table No. 3:
Correction to indicated pressurizer water level for Reference Leg Heatup effects due to post-accident containment temperature (before reactor trip).
Table No. 4:
Corrections to allowable indicated pressurizer water level for Reference Leg Heatup and Pressure changes following a high-energy line break, to assure that true level is between the level taps or above the pressurizer heater located below 17% level.
Item 3 Review all safety and control setpoints derived from level signals to verify that the setpoints will initiate the action required by the plant safety analyses throughout the range of ambient temperatures encountered by the instrumentation, including accident temperatures.
Provide a listing of these setpoints.
Response
The results of this review follow:
Former New Process Parameter Setpoint Setpoint Steam Generator Level 10%
15%
Pressurizer Level 5%
No longer functional The steam generator setpoint change was reviewed and approved by Commonwealth Edison Onsite Review on July 16, 1979.
A summary of this review fo I g6M.
In June 1979, Mi n'.oghouse informed Commonwealth Edison of a concern that hig',< *V line breaks inside the containment could result in heatta of. u'.e steam generator level measurement reference leg.
An inc;eated 24ference leg water column temperature wouldresultinadecreasfofthewatercolumndensitywitha l
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Commonwealth Edison NRL Docket Nos. 50-295/304 nsequent increase in the indicated steam generator water level.
u
}Lis bias could delay or prevent reactor trip and auxiliary feedwater initiation which are based on low-low steam generator water level.
Steamline breaks and LOCA's are protected by other reactor trips and safety injection signals.
The accident which does present a potential problem is the feedline rupture accident.
The loss of feedwater accident is protected by a reactor trip on low-low steam generator level, which has a nominal trip setpoint of 10% of the narrow range instrument span.
The analysis trip setpoint is conservatively assumed to be 0% of the narrow range instrument span.
A review of the potential inaccuracies in the steam generator narrow level instrumentation, exclusive of the reference leg heatup effect, was performed.
This review determined a maximum inaccuracy of 4.5%. Therefore, the steam generator narrow range level trip had been set with a 5.5% conservatism.
Westinghouse generically estimated the worst bias that might exist for the low-low steam generator level trip due to reference leg heatup effects to be 10% bias for temperatures up to 280 F.
Above 280 F, reactor trip and auxiliary feedwater actuation would occur on a high containment pressure signal.
Therefore, as an immediate corrective action to protect against a feedline rupture, the reactor trip and auxiliary feed-water actuation setpoint was raised to 15% of the narrow range level indication.
This conservatively accounted for the existing 4.5%
inaccuracies and the 10% bias for reference leg heatup effects.
In additicn, backup trips to the low-low steam generator level trip are the steam /feedwater flow mismatch in coincidence with a low steam generator water level (nominal setpoint of 25%
of narrow range span), overtemperature delta T, high pressurizer pressure, and high containment pressure.
A safety injection signal from steamline differential pressure also provides backup protection.
Item 4 Review and revise, as necessary, emergency procedures to include specific information obtained from the review and evaluation of Items 1, 2 and 3 to ensure that the operators are instructed on the potential for and magnitude of erroneous level signals.
All tables, curves, or correction factors that would be applied to post-accident monitors should be readily available to the operator.
If revisions to procedures are required, provide a completion date for the revisions and a completion date for operator training on the revisions.
11C4 17n I iJO i>U
Commonwealth Edison NRC Docket Nos. 50-295/304
Response
The reactor operators have been advised of the containment temperature and pressure effects on level indication accuracy.
Emergency operating procedures have been revised to reflect the effect of containment temperature on steam generator level.
By December 15, 1979 the following tasks will be completed:
1.
Emergency Operating Procedures will be revised to reflect the effects on pressurizer level indication due to pressurizer pressure and containment temperature.
2.
Emergency Operating Procedures will be revised to reflect the effects on steam generator level due to steam generator pressure.
3.
Additional Operator Training as required by Items 1 and 2.
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TABLE 1 Correction to indicated steam generator water level for Reference Leg Heatup. effects due to post-accident containment temperature (before reactor trip)
Maximum containment temperature Correction to S/G Level, reached before reactor trin. OF
% of Span 90 0%
200 5%
0 280 10.5%
320 13.5%
0 4000 21%
BASIS:
Level Calibration Pressure =1000 psia Reference Leg Calibration Temperature = 90 F Height of Reference Leg I 1.1x Level Span True Level = Indicated Level - Correction 1 1 L-
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4 TABLE 2 Corrections to allowable indicated steam generator water level for Reference Leg Heatup and Pressure changes following a high-energy line-break, to assure that true level is between the level taps.
Correction To Corrections to Containment Minimum Allowed Maximum Allowed Temperature Indicated Level, Indicated Level, OF
% of Span
% of Span 90
+2
-4 0
200
+7
-4 0
2800
+12.5
-4 320
+15.5
-4 0
4000
+23
-4 BASIS:
Level Calibration Pressure = 1000 psia 0
Reference Leg Calibration Temperature = 90 F Height of Reference Leg n 1.1 x Level Span Pressure 2 50 psia Maximum Steam Generator Pressure = 200 psi + Calibration Pressure
= 1200 psia Boiling in the Reference Leg is not assumed.
1156 173
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t TABLE 3 Correction to indicated pressurizer water level for Reference Leg Heatup effects due to post-accident contain-ment temperature (before reactor trip)
Maximum containment temperature Correction to S/G Level, O
reached before reactor trip, F
% of Span 90 0%
0 200 7%
2800 14.5%
320 19.25%
400 29.5%
BASIS:
Level Calibration Pressure = 1000 psia Reference Leg Calibration Temperature = 90cp Height of Reference Leg = 1.1x Level Span 1156
4
TABLE 4 Corrections to allowable indicated pressurizer water level for Reference Leg Heatup and Pressure changes following a to assure that true level is between high-energy line break, the level taps or above the pressurizer heater located below 17% level.
Correction To Correction To Corrections To Containment Minimum Allowed Minimum Allowed Maximum Allowed Temperature Indicated Level, Indicated Level, Indicated Level OF
% of Span
% of Span
% of Span (Above Level Tap)
(Above Heater) 90
+6 4
-9 200
+13 11
-9 280
+20.5 18.5
-9 320
+24.25 22.5
-9 0
+35.5 33.5
-9 400 BASIS:
Level Calibration Pressure = 1000 psia Reference Leg Calibration Temperature =90 F Height of Reference Leg A 1.1x Level Span Pressure & 50 psia Pressure = 200 psi + Calibration Pressure = 2600 psia Allowable Level = Indicated + Correction Boiling in the Reference Leg $s not assumed.
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