ML13308B797
| ML13308B797 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/06/1980 |
| From: | Curran J, Morgan H Southern California Edison Co |
| To: | |
| Shared Package | |
| ML13308B793 | List: |
| References | |
| SO23-3-2.30, NUDOCS 8011250503 | |
| Download: ML13308B797 (11) | |
Text
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 NOV 6
DETERMINATION OF ADEQUATE CORE COOLING 1.0 OBJECTIVE 1.1 Inadequate core cooling (ICC) is a term that defines a reactor core condition that is degraded beyond that anticipated during normal plant operation. The ICC condition can result from operator error or from equipment failures. However, to induce ICC, operating procedures have to be improperly implemented or equipment failures beyond that considered credible in design must have occured. The ICC guidance provided herein addresses symptoms of ICC, corrective actions, and precautions, associated with equipment and procedures, that are closely related to preventing and mitigating ICC.
1.2 During normal plant operation a departure from nucleate boiling (DNB) left unattended may result in ICC. Guidance on this type of event is provided below. Accidents and anticipated operational occurances, improperly responded to, also can cause ICC.
Guidance on these types of events is provided. Recovery from an approach to ICC is also discussed.
2.0 REFERENCES
2.1 CE Operational Guidance for Inadequate Core Cooling.
IED 0 3.0 PREREQUISITES 3.1 Not Applicable.
I 4.0 PRECAUTIONS RECEIVED 4.1 Not Applicable.
Ngy 7198 5.0 CHECK-OFF LISTS 5.1 Check Off List 1 attached.
6.0 PROCEDURE 6.1 Determination of adequate core cooling.
6.1.1 The Check Off List should be used by the Shift Technical Advisor and/or Control Room Operators as an initial deter mination of adequate core cooling.
6.1.2 In examining these indications the STA and/or Control Room Operators should verify the instrument response is sufficient to indicate adequate core cooling. However, if an undesirable situation persists which has the potential for resulting in inadequate core cooling, then corrective action should be taken.
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SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 Page 2 6.0 PROCEDURE (Continued) 6.1.3 If indications reveal an approach to inadequate core cooling, notify the Watch Engineer immediately and ensure that corrective actions are taken. Continue to take readings at 10 min. intervals until conditions stabilize and adequate core cooling has been verified.
6.2 Inadequate Core Cooling due to Loss of Heat Sink Loss of feedwater to both steam generators during power operation has the potential of producing conditions which could lead to ICC due to loss of heat sink. Loss of feedwater may result from interruption of the feed system, or from the loss of offsite power. It may be the pri mary problem, or it may occur in conjunction with another accident such as a LOCA, MSLB, or FWLB. Of these, the FWLB is the most limiting as far as loss of heat sink is concerned, since it results in the quickest loss of steam generator liquid inventory, in addition to removing the faulted steam generator as a heat sink for the remainder of the accident.
6.2.1 With the loss of feedwater to the steam generators, the plant will exhibit the following symptoms as ICC is approached:
.1 The steam generator level drops to zero or to a constant value near zero as indicated on Steam Generator narrow range level instrumentation. One steam generator must have at least 50%
level, as indicated on wide range level instrumentation, to provide an adequate heat transfer surface area for heat removal.
E-089 Narrow range LI-1123-1 LI-1123-2 LI-1123-3 LI-1123-A4 Wide range LI-1125-1 LI-1125-2 E-089 Narrow range LI-1113-1 LI-1113-2 LI-1113-A3 LI-1113-4 Wide range LI-1115-1 LI-1115-2
.2 The steam generator secondary pressure rises to the steam bypass or relief valve setpoint, unless there is a break, in which case, the pressure in one steam generator drops to the containment pressure as indicated on steam generator pressure instru mentation for:
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 Page 3 6.0 PROCEDURE (Continued) 6.2.1.2 (Continued)
E-088 PI-1023A1/Bl PI-1023A2/B2 PI-1023A3/B3 PI-1023A4/B4 and E-089 PI-1013A1/Bl PI-101 3A2/B2 PI-1013A3/B3 P1-101 sA4/B4
.3 If the secondary pressure in one steam generator drops, as it does with a feedline break, the cooldown of the secondary side causes the primary to cooldown also. This in turn causes the primary pressurd to drop sharply at the beginning of the transient. The simultaneous decreases of the secondary pressure in one steam generator along with the primary pressure is an indication of a secondary break. A break on the primary side (LOCA) causes a decrease in primary pressure but does not cause a decrease in the secondary side pressure.
.4 Hot and cold leg primary coolant temperatures behave as follows for the different conditions with a loss of feedwater event:
.4.1 Initially, hot and cold leg temperatures are subcooled and decrease and then increase sharply. The magnitude of the decrease is greater and the duration is longer for a feed line break than for a loss of feed without a break.
.4.2 Hot and cold leg temperatures vary together for a loss of feed event. If the RCP's are on, the hot and cold leg temperatures are nearly equal throughout the transient.
If the RCP's are off, the hot leg temperature is about 100 to 40'F above the cold leg, and the curves are roughly parallel.
.4.3 For cold leg temperatures use TR-0115 and TR-0125 and/or CFMS.
.4.4 For hot leg temperatures use TR-0111 and TR-0121 and/or CFMS.
.5 Following a period of approximately constant temperature, the primary coolant temperatures increase well above the secondary saturation temperature, indicating the loss of the heat sink by dryout. This is an important indication of the approach to inadequate core cooling. If the RCP's are off, cold leg temperature will initially increase faster than hot leg tem perature, resulting in decreased core AT. Use TR-0115 and TR-0125 for cold leg temperatures and TR-0111 and TR-0121 for hot leg temperatures. Using the recorders will show a trend for easier determination of temperature trends.
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 Page 4 6.0 PROCEDURES (Continued) 6.2.1.6 If feedwater is still unavailable, the pressurizer relief valves will open, and quench tank temperature will rise. Quench tank instrumentation: temperature TI-0116, pressure PI-0116, and level LI-0116.
NOTE:
Whenever any break results in the release of high energy fluid to the containment, readings from non-qualified intruments must be used with caution and verified against readings from qualified instrumentation.
6.2.2 For recovery from a loss of heat sink, refer to Emergency Operating Instruction S023-3-5.30, "Loss of Feedwater or Steam Generator Level".
6.3 Inadequate Core Cooling Due to Loss of Primary Coolant 6.3.1 The significant symptoms at the start of a LOCA are provided in plant operating procedures, and in the LOCA Emergency Operating InstrUction. Additional symptoms of an approach to ICC due to loss of primary coolant are as follows, as the accident progresses:
.1 RCP motor current continuously decreases, if the pumps are still on, indicating the decreasing coolant density at the pump as inventory is lost and voiding occurs. Verify RCP motor amps.
(The following symptoms are the same with the RCP's off.)
NOTE:
If RCP motor amps are less than 600 amps or are decreasing with time, an approach to inadequate core cooling is indicated. Take action to increase heat removal from the reactor coolant system and in crease reactor coolant inventory if required.
.2 Steam generator primary side AP drops rapidly, even if RCP's are off, as indicated by steam generator AP indication.
.3 For a range of small break sizes greater than a minimum size which allows repressurization, reactor pressure decreases to, and levels off at approximately secondary pressure. Core inlet and exit temperatures are approximately equal at this time.
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 Page 5 6.0 PROCEDURES (Continued) 6.3.1.4 When the break is uncovered, RCS pressure might (if break is not very small) decrease abruptly accompanied by a decrease in hot and cold leg temperatures (saturated conditions).
.5 After core uncovery begins, the hot leg temperatures will increase (superheated conditions).
Verify this by checking incore thermocouple readings on the plant monitoring system.
If the incore thermocouples indicate superheat, the core should be considered uncovered. Also, if still running, RCP motor current will be less than 50% of normal.
.6 If RCS pressure is less than secondary pressure, cold leg temperature will rise above primary saturation temperature even while hot leg temperature remains at saturation as heat transfer from the secondary to the primary side occurs, as indicated by RCS cold leg temperature recorders TR-0115 and TR-0125.
- 7 Pressurizer level indication may be erratic or off scale in either direction. It is not a reliable indicator while the RCS fluid is saturated.
.8 As voiding in the core occurs, the Ex-Core Nuclear Detector System may indicate a reading in excess of the shutdown neutron flux level.
This is due to decreased shielding provided as fluid density in the core decreases. However, void distribution in the core and/or downcomer cause the ex-core signals to be un certain and should not be relied on as the only indication of core level.
Use the CFMS for core level determination.
.9 As core uncovery proceeds, the rhodium Self-Powered Neutron Detectors (SPND) may indicate a reading in excess of the shutdown flux level.
This is a thermionic affect. The various axial levels of the Self-Powered Neutron Detectors may indicate the lowering of the two phase level in the core, if corrective action to refill the system is not accomplished. Consider able uncertainity currently exists in the known behavior of the SPND's following significant core uncovery. Hence, the SPND's are used to augment other indications.
.10 The core exit thermocouples might indicate superheat conditions at the core exit after the level drops below the top of the active core.
NOTE:
The above symptoms assume that the steam generators are available as a heat sink.
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 Page 6 6.0 PROCEDURES (Continued) 6.3.2 For recovery from a loss of primary coolant refer to Emergency Operating Instruction S023-3-5.6, "Loss of Coolant Accident".
6.4 Inadequate Core Cooling Due to Core DNB 6.4.1 A core anomaly, which is not included in the protection system setpoints might cause a lower DNBR than is being determined by the protection system. For example, a postulated flow blockage in the core support plate or fuel channels would result in a flow maldistribution in the core. This in turn would affect the temperature and power distribution in the core, and could cause local DNBR limits to be exceeded.- Depending on the magnitude of the effect, an alarm might occur on the in-core or ex-core nuclear instrumentation. Typical alarms indicating a core anomaly are the following:
SYSTEM ALARM
.1 Ex-Core Nuclear Detector.
. Nuclear Power Deviation Hi/Lo
.2 Core Protection Calculator.
. DNBR High Local Power Density
.3 CVCS..............
Letdown Process Radiation High
.4 Core Operating Limit...... Azimuthal Tilt Supervisory System Kw/ft Power Operating Limit Margin DNB Operating Limit Margin 6.4.2 For recovery from DNBR perform the following:
.1 If an alarm condition exists, and its cause cannot be quickly identified and corrected, reduce reactor power by an amount which will at least re-establish the required operating core margins. Obtain the necessary technical evaluation of the core anomaly from reactor engineering to determine if reactor shut down is required.
.2 Have chemistry sample the RCS for gross activity and/or Iodine.
.3 If the evaluation concludes that reactor shutdown is required, carry out an orderly plant shutdown, followed by a cooldown to refueling conditions as per Operating Instruction 5023 3-1.2, "Reactor Shutdown", S023-5-1.3, "Plant Shutdown from Minimum Load to Hot Standby" and S023-5-1.5, "Plant Shutdown from Hot Standby to Cold".
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 REVISION 1 Page 7 7.0 RECORDS 7.1 Check-Off List is to be given to Watch Engineer for review and disposition.
8.0 ATTACHMENTS 8.1 Check Off List 1 (4 pages)
H. E. MORGAN SUPERINTENDENT UNITS 2 AND 3 APPROVED:
.M. CURRAN PLANT MANAGER MT/sa
SAN ONOFRE NUCLEAR GENERATI*TATION OPERATING A UCTION S023-3-2.30 UNITS 2 AND 3 CHECK-OFF LIST 1 Page 1 REVISION 1.
1.0 Indications for core cooling during loss of heat sink (Refer to Section 6.2).
1.1 Steam Generator Level 10 mins.
20 mins.
30 mins.
E-088 Narrow range LI-1123-1 LI-1123-2 LI-1123-3 LI-1123-A4 Wide range LI-1125-1 LI-1125-2 E-089 Narrow range LI-1113-1 LI-1113-2 LI-1113-A3 LI-1113-4 Wide range LI-1115-1 LI-1115-2 and CFMS NOTE:
One steam generator must have at least 50% wide range level to provide an adequate heat transfer sur face area for heat removal.
1.2 Steam Generator Pressure E-088 PI-1023A1/Bl PI-1023A2/B2 PI-1023A3/B3 PI-1023A4/B4 E-089 PI-1013A1/Bl PI-1013A2/B2 PI-1013A3/B3 PI-1013A4/84 and CFMS 1.3 Auxiliary Feedwater Flow (if applicable,, 700 gpm)
FI-4720-1 FI-4725-2
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 CHECK-OFF LIST 1 Page 2 REVISION 1 1.4 RCS cold leg temp.
10 mins.
20 mins.
30 mins.
TR-0115/CFMS TR-01 25/CFMS 1.5 RCS hot leg temp.
TR-01 11/CFMS TR-0121/CFMS 1.6 Quench Tank Temp.
TI-0116 Press. PI-0116 Level LI-0116
.1.7 Containment Pressure PI-0351-1 PI-0351-2 PI-0351-3 PI-0351-4 2.0 Indications for core cooling during a loss of primary coolant (Refer to Section 6.3) 2.1 Reactor Coolant Pump Motor Amps (CFMS)
Pool P002 P003 P004 NOTE:
If RCP motor amps are less than 600 amps or are decreasing with time, an approach to inadequate core cooling is indicated.
Take action to increase heat removal from the reactor coolant system and increase reactor coolant inventory is required.
2.2 Steam Generator AP E088 PDI 0978-1 PDI 0978-2 PDI 0978-3 PDI 0978-4 E089 POI-0979-1 PDI-0979-2 PDI-0979-3 PDI-0979-4
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 CHECK-OFF LIST Page 3 REVISION 1 2.0 (Continued) 2.3 Pressurizer Pressure 10 mins.
20 mins.
30 mins.
PR-010OA/CFMS PR-010OB/CFMS 2.4 RCA Cold Leg Temp TR-0115/CFMS TR-0125/CFMS 2.5 RCS Hot Leg Temp TR-0111/CFMS TR-0121/CFMS NOTE:
If Thot is not decreasing with time, inadequate core cooling is indicated. Verify no abnormal differences exist between hot leg (Th) RTDs and in-core thermocouples. Any abnormal differences are indicative of an approach to an inadequate core cooling condition. If in-core thermocouples indicate superheat, then the core should be considered uncovered.
2.6 Incore Thermocouples < super heated temps. Use Plant Monitoring System point I.D.'s (Later) 2.7 Subcooled Margin Monitor Press Temp 2.8 Reactor Vessel Level/CFMS Vessel Head Vessel Flange Hot Leg Elev.
Top of Fuel 2.9 HPSI Flow SE loop FI-0311-2/CFMS NE loop FI-0341-2/CFMS SW loop FI-0321-1/CFMS NW loop FI-0311-1/CFMS
SAN ONOFRE NUCLEAR GENERATING STATION OPERATING INSTRUCTION S023-3-2.30 UNITS 2 AND 3 CHECK-OFF LIST Page 4 REVISION 1 3.0 Indications of Core Anomaly 3.1 Azimuthal Tilt:
10 mins.
20 mins.
30 mins.
COLSS Power Operating Limits Yes/No Yes/No Yes/No Function Code N7, Report 1.
Circle One Circle One Circle One "Print" the report (Indicate report printed) 3.2 Local Power Density Margin JI-0003 3.3 DNBR Margin JI-0004