ML20084N370
| ML20084N370 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 05/31/1983 |
| From: | Devincentis J PUBLIC SERVICE CO. OF NEW HAMPSHIRE, YANKEE ATOMIC ELECTRIC CO. |
| To: | Knighton G Office of Nuclear Reactor Regulation |
| References | |
| SBN-513, NUDOCS 8306030177 | |
| Download: ML20084N370 (11) | |
Text
.
SEARROOK STATION
% ONies:
1471 Worceew Rood Framinohem. Monochveetts 01701 m m og m g,
(417) 872 - 8100 May 31, 1983 SBN 513 T.F. B7.1.2 United States Nuclear Regulatory Commission Washington, D. C. 20555 Attention:
Mr. George W. Knighton, Chief Licensing Branch No. 3 Division of Licensing
References:
(a) Construction Permits CPPR-135 and CPPR-136, Docket Nos. 50-443 and 50-444
Subject:
Open Item Response (SER Section 7.3.2.8; Instrumentation and Controls Systems Branch)
Dear Sir:
In response to the Open Item included in the Safety Evaluation Report (Section 7.3.2.8) regarding "the effects of high temperatures on the reference legs of steam generator and pressurizer water level measuring instruments af ter high energy line breaks," we have enclosed a response to your Request for Additional Information (RAI 420.23).
The enclosed response will be included in a future OL Application l
Amendment upon completion of your review.
Very truly yours, YANKEE ATOMIC ELECTRIC COMPANY l
- w~
J. DeVincentis Project Manager ALL/bal Enclosure f
cc: Atomic Safety and Licensing Board Service List IC 5 4 8306030177 830531 PDR ADOCK 05000443 E
PDR 1000ElrnSt.,P.O. Box 330. Manchester,NH03105 Telephone (603)669-4000 TWX7102207595
]
420.23 Describe how the effects of high temperatures in reference legs of (7.2) steam generator and pressurizer water level measuring instruments i
subsequent to high energy breaks are evaluated and compensated for in determining setpoints.
Identify and describe any modifications planned or taken in response to IEB 79-21. Also, describe the level seasurement errors due to environmental temperature effects on other level instruments using reference legs.
RESPONSE: The error in dp level measurement systems due to changes in fluid 5/83 densities is:
R(ah-oh)~L pf~ep }
g g
E=
X 100 8N.calN, cal) where:
E
= Error in % span R
= Height of reference leg water level above the variable leg tap S
= Span (distance between taps) 1 L
= Water level above the variable tap heat
= Vapor calibration density cal
= Process fluid calibration density
~
^PR
= Chan.e in reference 1e. density from the caubrauon value Ofg
=Changeinvapordensityfron[g, cal i
Ohg
=Changeinprocessfluiddensityfron[g, cal Oh= feat-faccident Note:
l-This error determination assumes that the reference leg and variable leg below the variable tap are at the same temperature and produce counteracting errors.
A.
Effects of Post-Accident Conditions on Indicated Level 1.
Referen's Leg Heatup If the process conditions are not affected by the accident, the error due to reference leg heatap is:
Ra[R E=Spf.calPg.ca1)
A decrease in reference leg density will increase the indicated level.,, _ - - -.. -. - --- -.. - - _..
I 2.
Reference Leg Boiling j.
Depressurization to a pressure lower than the saturation pressure of a hot reference leg will eject water from the l,
reference leg. This will greatly reduce the reference leg l
average density and will result in a sudden, large increase l
in indicated level. The level error cannot be determined as there is no way of knowing the amount of water ejected.
l As reference leg boiling could only occur on a faulted l
component after a large steam line break inside containment or a LOCA, the operators will be instructed to disregard the level instruments on the faulted component if such a l
depressurization has occurred.
Reference leg flashing on l,
intact steam generators is prevented by the automatic closure of the Main Steam Isolation Valves (MSIV) after a main steam or feed line break that causes system depressurization.
l 3.
Process Density Changes If the containment conditions are not affected by the accident, the error due to process density changes is:
-ep, - tcap,-ap) X 100 E=
3Nfcal'hg. cal)
A decrease in system pressure and temperature will increase the indicated level.
B.
Effects on Safety-Related Level Setpoints l
1.
Steam Generator Low-Low Level Reactor Trip and Emergency l
Feedwater Initiation These functions are provided for protection in the event of a loss of feedwater. Those events due to problems outside of the containment will not result in a harsh environment l
that affects the level system. Feedwater line ruptures l:
l l
inside the containment will result in a harsh environment I
that will cause an error in indicated level.
l Reactor protection for feedwater line ruptures inside the containment is also provided by high pressurizer pressure, j
overtemperature AT reactor trips and safety injection on low steam line pressure, low pressurizer pressure and high containment pressure. The size of the break and the plant operating conditions determine which protective function will be applicable.
Main steam line breaks were not considered as steam l-l generator level is not relied on to provide protection.
l=
Analyses to determine the maximum level error due t.o I
reference leg heating were performed with the following I
considerations / assumptions:
, l I
a.
Containment response was analyzed with the CONTRAST-S computer program usind passive heat sink data given in FSAR Tables 6.2-3 and 6.2-4.
Conservatively high heat transfer coefficients have been used for the passive heat sinks to delay the containment pressure rise. This will purge more non-condensibles prior to the High I containment
)
pressure trip with a resulting temperature increase as saturation temperature is approached.
b.
Breaks are double-ended and the break effluents from both sides do not mix. This conservatively envelopes all types of breaks and maximizes containment temperature by maximizing the steam enthalpy.
c.
The mass and energy release rates are calculated assuming choked flow through the break.
d.
Containment initial conditions are 14.7 psia,1200F, 100% RH.
e.
High 1 and 2 operate at 6.8 psig (5.0 psig setpoint +
1.8 psig total allowance for instrumentation uncertainties). All functions actuated by High 1 or 2 occur.
f.
Pressure buildup is delayed by venting through the.
containment on-line purge system. A discharge coefficient of 1.0 was used. The pressure downstream of the purge valve is conservatively assumed to be 13.5 psia.
6 ft3 (5%
g.
Containment free volume is 2.84 x 10 higher than that used in the DBA analysis).
h.
The reference leg response is calculated following 2
guidelines prescribed in NUREG-0588 using the l
HESITET3 computer program. Figure 1 is the schematic of the reference leg model,
- i. Containment high pressure alarm is actuated at 1.0 psig.
J.
All events that reach the High 1 setpoint 10 or more minutes after the high pressure alarm are manually r
terminated at 10 minutes.
f Results of Analyses Figures 2 and 3 show containment temperature at the time the containment pressure reaches High 1 setpoint of 6.8 psig as a function of break size at 100% and 0% power levels, respectively. Smaller breaks result in higher containment temperature because of longer duration of containment venting through the containment on-line purge system. Also, the containment temperatures are higher at.-
i lower power levels because there is less flashing of the feedwater. The addition of low enthalpy steam from the flashed feedwater tends to reduce the containment temperature as it mixes with the high enthalpy steam coming from the steam generator.
The event is manually terminated by the operator 10 minutes after receipt of the high containment pressure alarm. This is considered sufficient time for the operator to evaluate his indication and take action using controls on the main control board. Depending on break size, power level and capabilities of the feedwater system, the feedwater control system may be able to maintain normal steam generator levels during the event.
Backup instrumentation / alarms available to alert the operator and assist in the.
evaluation'of the event-include containment drainage sump level, high leak rate alarm (Regulatory Guide 1.45),
containment temperature and humidity, steam generator and pressurizer level and pressure (differentiate between primary and secondary leaks), and steam and feedvater flow.
We have determined that the most severe event, i.e.,
highest reference leg temperature, occurs for a small break at low power when the High 1 setpoint is reached 10 minutes after the high containment pressure alarm is actuated.
Smaller breaks would result in higher reference leg temperatures after 10 minutes, but will be terminated by operator action..
The most severe event is a 0.04~DE break at 0% power level. Figures 4 and 5 are histories of the containment pressure and temperature and reference leg water temperature. The maximos reference leg water temperature is 1840F at 645 seconds after the break, the high pressure alarm is actuated at 45 seconds.
The increase in reference leg water temperature results in i
an error of 3.1%.
When added to the present setpoint of 15% results in a setpoint of 18.1%. The Technical Specification will be revised to increase the setpoint to 18.1%.
This setpoint is very conservative as the channel statistical error allowance includes a transmitter environmental allowance of 10%. This error is the result of summing the effects of the errors due to seismic events, radiation, temperature and pressure during a design basis event. Since the steam generator level system is not the primary trip function for large breaks inside the containment, the transmitter will not crperience the extreme conditions that result in the 10% allowance. We expect the actual error to be less than 10%. Testing has not been performed to determine a realistic environmental allowance for the steam generator level transmitters.
. _ _ ~ _ _. _, _._ _ _.__________.__ _._.
4 1
2.
Steam Generator High-High Level Trip The steam generator high-high level trip provides protection for excess feedwater flow events. These events do not cause a harsh environment; therefore, the trip setpoint will not be changed.
3.
Pressurizer High-High Level Trip The pressurizer high-high level trip provides protection for increase in reactor coolant inventory events. These events do not cause a harsh environment; therefore, the trip setpoints will not be changed.
C.
Effects on Accident Monitoring Instrumentation.
The Seabrook Emergency Operating Procedures will follow the guidance of the Westinghouse Owners Group Emergency Response Guidelines. These guidelines specifically require that the instrumentation errors-due to environmental effects and system pressure changes be considered. Appropriate error calculations
-(see Paragraph A.1 and A.3) will be performed and incorporated in the emergency operating procedures when the Buidelines are finalized and the as-built dimensions are obtained.
REFERENCES 1.
" Predictions of Containment Pressure-Temperature Transients Using CONTRAST-S MOD 1 - A Digital Computer Program", UEC-TR-006-SUP, June 1979.
l l
2.
NUREG-0588, " Interim Staff Position of Environmental Qualification of Safety-Related Equipment", 1979.
3.
"HESITET - A Digital Computer Program to Analyze Temperature Transients in Containment Passive Heat Sinks and Equipment", UEC-NU-509, October 1979.
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Figure 1 Schematic of Heat Transfer Model for Reference Leg Thermal Response O
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FIGURE 2 Containment Temperature At Time Of High 1 Trip vs. Break Size (100% Power Level)
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