ML20235A668
| ML20235A668 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/18/1987 |
| From: | Firlit J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Miraglia F Office of Nuclear Reactor Regulation |
| References | |
| AGM-NPP-87-230, GL-87-12, NUDOCS 8709230379 | |
| Download: ML20235A668 (30) | |
Text
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%SMUD SACRAMENTO MUNICIPAL UTILITY DISTRICT D P. O. Box 15830, Sacramento CA 95852-1830,(916) 452 3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA AGM-NPP 87-230 September 18, 1987 U. S. Nuclear Regulatory Commission Attn:
Frank J. Miraglia, Jr.
Associate Director for Projects Philips Building 7920 Norfolk Avenue Bethesda, MD 20014 DOCKET NO. 50-312 RANCHO SECO NUCLEAR GENERATING STATION LICENSE NO. DPR-54 GENERIC LETTER 87-12, LOSS OF RESIDUAL HEAT REMOVAL (RHR) HHILE THE REACTOR COOLANT SYSTEM (RCS) IS PARTIALLY FILLED
Dear Mr. Miraglia:
In accordance with 10 CFR 50.54(f), the Sacramento Municipal Utility District provides you with the enclosed description of the operation of Rancho Seco during the approach to a partially filled RCS condition and during operation with a partially filled RCS as der.cribed in Generic Letter 87-12.
If you have any questions please contact Jerry Delezenski of my staff.
Sincerely, b
Josep F. Firlit V Assistant General Manager.
Nuclear Power Production Sworn to and subscribed before me this
/M day of September,1987.
hxad lu/lq Notary Publ(c l
Attachment AME SHELBY i
NOTAMrPUWUC CALFORNIA SACf%hENTO COUNTY i
cc:
G. Kalman, NRC, bethesda (w/atch) jd"')
A. D'Angelo, NRC, Rancho Seco (
)
g IO
J.B. Martin, NRC. Region V
(
)
B'709230379 070918 i
ig PDR ADOCK 05000312 P
PDR RANCHO SECO NUCLEAR GENERATING STATloN C 1444o Twin Cities Road, Herald, CA 95638 9799;(209) 333 2935
NRC QUESTION 1.A Detailed description of circumstances and conditions under which Rancho Seco is entered into and brought through a draindown process and operated with RCS partially filled.
SMUD RESPONSE 1.A The Reactor Coolant System (RCS) is drained down for refueling preparation and anytime an inspection or repair to the following equipment is required:
- 1) Hot leg resistance temperature detector (RTD)
- 2) Pressurizer relief valve
- 3) Control rod drive mechanism removal
- 4) Pressurizer heater removal
- 5) Preparation for refueling - vessel head removal
- 6) Once through steam generator (OTSG) tube inspection / plugging / sleeving
- 7) OTSG primary side drain valve repair
- 8) Reactor coolant pump (RCP) removal / seal package repair or replacement
- 9) High pressure injection (HPI) nozzle or stopcheck valve inspection / repair / replacement
- 10) Core flood tank check valve repair
- 11) Cold leg RTD repair The latter six items listed require draindown to maintenance levels when vortexing cf the decay heat suction is of greater concern.
The RCS is initially cooled with heat removal by the OTSGs and depressuri-zation using normal pressurizer spray.
RCS boron concentration is increased and the RCS is degassed.
RCS temperature is reduced to 280*F and pressure to 250 psig. One train of the Decay Heat System is then placed in service. An RCP is run until RCS temperatures are less than 150*F. A steam bubble is maintained in the pressurizer to keep RCS pressure about 220 psig for RCP net positive suction head (NPSH) considerations.
When the RCS is sufficiently cooled, tha RCP is secured and forced flow through the core is provided by one train of the Decay Heat System. The RCS is depressurized by pressurizer auxiliary spray from the operating makeup pump.
Pressurizer water level is cycled to help cool the pressurizer metal. When RCS pressure is reduced to 30 psig, nitrogen is added to the pressurizer vapor space to maintain the higher hot legs in a water filled condition.
The pressurizer is allowed to cool to less than 200*F while maintaining a 30-50 psig nitrogen blanket.
Pressurizer water level is low in the operating band.
Filtered vent bottles are connected with high pressure hose to the hot leg l
1 inch high point vents.
The bottles continue to be isolated at this time.
The RCS vent header is isolated from the Haste Gas System.
The pressurizer vent and the hot leg vents to the vent header are then opened. Water from the hot legs drains to lower portions of the RCS, while coolant enters the pressurizer through the pressurizer surge line.
Nitrogen gas from the pressurizer gas space travels through the vent header to the top of the hot legs.
RCS pressure remains about 50 psig.
Pressurizer level indicators l
reflect loop and pressurizer level once equalization is complete.
l _ _ _ _ _ _ _ _ _.
i The RCS is then drained to the reactor coolant drain header from the bottom OTSG drains to a 30,000 gallon connection tank. As the RCS drains the RCS pressure decreases. Hhen pressurizer level is low in the indicated range, the reactor vessel level instrument is valved in and the remaining nitrogen pressure existing in the upper portions of the hot legs and pressurizer is passed to the Haste Gas System by opening the Reactor Building (RB) isolation valves on the reactor coolant vent header. A vent line between 1
the vent header and the center control rod drive (CRD) is then connected.
)
This vents the head area and allows communication between the pressurizer, hot legs, and head area, thereby allowing all RCS levels to equalize and drain down together.
When the P.CS pressure is at 0 psig, the reactor coolant vent header is again isolated from the Haste Gas System.
The isolation valves to the hot
{
leg vent bottles are opened.
The hot legs, pressurizer, and head area are now cross connected to one another and vented to the RB atmosphere through the poly vent bottles.
The Reactor Vessel Level Indication (RVLI) now reads actual vessel level.
Draindown continues to the level required for the maintenance to be performed. Operators ensure decay heat pump vortexing will not occur by checking a minimum level curve, which takes into account decay heat flow rate and RCS temperature.
Reactor vessel level is placed on continuous computer readout while also displayed on a trend recorder. _ _ _ _ _
NRC OUESTION 1.8 Include any interlocks that could cause a disturbance to the system.
SMUD RESPONSE T0 1.B Several interlocks can interrupt the flow of decay heat cooling through the core.
- 1) RCS pressures in excess of 255 psig will automatically close the decay heat line isolation valve (s).
Th'e closing of either of the two series valves will cause an operating decay heat pump to trip.
The valves can oe riopened when pressure is reduced below 255 psig and the logic
{
reset.
The decay heat pumps cannot be started until a three minute timer times out.
This interlock actuation on a valid pressure signal is not a high priority concern when the RCS is in a drained-down condition, because a pressure generation event like Diablo Canyon's is relatively slow and attainment of 255 psig may not be possible if sufficient vent paths are opened (such as the electromatic operated valve (EMOV) which is required to be operable for RCS low temperature overpressure protection).
- 2) A core flood tank (CFT) discharge valve coming off its closed seat will send a signal to close one of the decay heat drop line isolation valves.
The closing of the drop line valve trips any operating decay heat pump. There is no timer or specifically designed bypass to defeat this interlock, but removing power from the Safety Features Actuation System (SFAS) analog cabinet will bypass the interlock after a few second time delay. The CFT discharge valves are closed and racked out for cold overpressure protection when the RCS is drained down; thus, the operator cannot open these valves from the control room.
- 3) Loss of power to either SFAS analog cabinet will result in closing of one of the decay heut drop line isolation valves.
These cabinets monitor wide range RCS pressure and provide the high pressure interlock.
The closing of either valve trips an operating decay heat pump.
The cabinets are powered from vital inverters. A modification under way during the current outage will retire the older inverter power supplies to vital loads.
The loads will be fed from new, more reliable inverters with vital power backup through a fast transfer static transfer switch that will decrease the likelihood of interrupting decay heat flow.
Several years ago a modification was made to allow the operator to re-establish decay heat flow even though an inverter had tripped. A circuit monitors power to the wide range pressure transmitter and allows the drop line valve to be reopened after a few seconds if the reason it closed was due to loss of pressure transmitter power.
This precludes a loss of decay heat flow for long periods of time.
Prior to this modification, an operator would be sent into the RB to manually open the valve.
j _ _ _ _ _ _ _ _ _ _ _ _ _. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
4)- Loss.of motive power to either decay heat drop line isolation valve
[.
results_in valve closure and decay heat pump trip when power is l
reapplied. The valve can be reopened following reset of protection I
circuitry. The pump can be restarted following the expiration of a three minute time delay.
To preclude inadvertent losses of decay heat flow when the RCS is open to the atmosphere (defined as hand holes, manways, or head removed) the decay heat drop line valves are racked out in their open position.
l 6
g - - - _ _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __
r NRC QUESTION 1.C Examples of type of information required:
NRC QUESTION 1.C.1 Time between full power operation and reaching partially filled condition (used to determine decay heat loads).
SMUD RESPONSE 1.C.1 Time to drain-downed conditions at Rancho Seco was estimated by selecting three shutdowns for OTSG tubeleaks in 1984.
Draindown for tube leak repair is a condition which requires the lowest RCS level which could result in decay heat vortexing.
Draindown is also on the critical path for tube repair and return to power operation and therefore a good measure of the shortest time to minimum RCS levels-with the maximum decay heat load.
The time between-reactor shutdown and hot leg / pressurizer level equalization was obtained.
Since draindown of the RCS to a holdup tank can commence after this step, this time represents the earliest a draindown could commence.
The average period for this evolution is 76 hours8.796296e-4 days <br />0.0211 hours <br />1.256614e-4 weeks <br />2.8918e-5 months <br />, with the minimum being 28 hours3.240741e-4 days <br />0.00778 hours <br />4.62963e-5 weeks <br />1.0654e-5 months <br />.
The time between reactor shutdown and actual draindown to minimal levels was then obtained.
The average period for this minimum level was 147 hours0.0017 days <br />0.0408 hours <br />2.430556e-4 weeks <br />5.59335e-5 months <br />, with the shortest time period being 76 hours8.796296e-4 days <br />0.0211 hours <br />1.256614e-4 weeks <br />2.8918e-5 months <br />.
NRC ()UESTION 1.C.2 Requirements for minimum steam generator levels.
SMUD RESPONSE 1.C.2 Rancho Seco operating procedures state that the steam generator level is to be maintained at 85% for outages estimated to last less than 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br /> and full wet layup for outages greater than 120 hours0.00139 days <br />0.0333 hours <br />1.984127e-4 weeks <br />4.566e-5 months <br />.
Secondary side OTSG 1evel ic dependent on the reason for the outage and any maintene.c.e that may be required to the OTSG or Main Steam System.
(Rancho Seco uoes not have main steam isolation valves between the OTSG and main turbine throttle valves.) For example, for OTSG tube leak outages the OTSG secondary level is raised and then drained several times to flush all radionuclides from the shell side.
NRC QUESTION 1.C.3 Changes in such operations while the RCS is partially filled.
SMUD RESPONSE 1.C.3 i
If the RCS is open to atmosphere through openings larger than the venting apparatus (manways, handholes, vessel head) the interlocks on the decay heat drop line valves can be defeated by removing the power supplies to the valves while they are in the open position.
l NRC QUESTION 1.C.4 Restrictions regarding testing, operations, and maintenance that could perturb the NSSS.
SMUD RESPONSE 1.C.4 The Operations Planning Section reviews maintenance and testing and assures it is properly coordinated, including operations which could affect the Nuclear Steam Supply System (NSSS). A senior licensed Unit Superintendent and two assistants (one currently senior licensed and one previously senior licensed) generate a detailed work plan for each shift in the areas of operations and testing. Any testing, operational evolutions, or mainten-ance which could adversely perturb inventory control of the RCS in a drained-down condition are not permitted. Shift Supervisors, Assistant-Shift Supervisors and licensed operators reviewing activities on their shift serve as a backup to the initini checks.
NRC QUESTION 1.C.5 Ability of the RCS to withstand pressurization if the reactor vessel head and Steam Generator manway are in place.
SMUD RESPONSE 1.C.5 In addition to pressurizer and CRD head vents available at Diablo Canyon, Rancho Seco has a 1 inch vent on top of each hot leg.
These vents are connected with high pressure hose to vented poly bottles.
The additional pressure relief capability of these vents would help to mitigate any RCS pressure increase, although their capacity is limited.
The burst pressure of the hose or poly bottle is unknown, but this vould be the first place of relief air or steam to the RB.
Tygon tubing is connected to the active leg of the RVLI as a local reference.
This tubing is vented to the RB atmosphere and would act as another small RCS pressure relief.
If RCS pressure were to increase more than a couple of pounds greater than RB atmosphere, this tubing would relieve small amounts of coolant to the RB floor.
The RVLI piping, instrument tubing, transmitter, and gauge glass are all rated at 2500 psig.
No pressure relief or loss of coolant is expected from the permanently installed level instrumentation.
The CRD venting apparatus consists of one quarter inch high pressure tubing and fittings.
The viewable swingcheck valve employed in one older style venting apparatus is rated at 50 psig. A more recently designed apparatus uses a rotometer rated at 450 psig.
The new style apparatus uses a 150 psig relief valve on the isolated vent header that lifts when the RCS pressure rises sufficiently to force significant steam flow through the CRD vent tubing.
I The Decay Heat System normally has a small portion of its flow routed through the RCS purification system.
Two large capacity relief valves (PSV-22012, nominal setpoint at 225 psig and PSV-22013, nominal setpoint at 150 psig) would lift prior to the automatic isolation of the Decay Heat System from the RCS at 255 psig.
The Rancho Seco Loss of Decay Heat Removal System Casualty Procedure instructs the control room operator to close the RCS to decay heat isolation valves when both trains of decay heat are lout and cannot be regained and the RCS is open to atmosphere.
This action will prevent an RCS pressure increase from being seen in the I
purification and Decay Heat Systems.
An' intact RCS, excluding small vents, is ultimately limited in pressuriza-tion by the EMOV.
Low temperature overpressure protection (LTOP) considerations require the EMOV block valve be open and the EMOV have its setpoint selector in the " low" position.
This setpoint corresponds to 450 psig and, when open, provides an equivalent 1.1 inch hole in the top of the pressurizer.
LTOP is required whenever the RCS is defined as not being open to the RB atmosphere, i.e., primary manway, handhole, or vessel head is not removed or similar size hole is not open.
The operator has several other means available to mitigate an RCS pressure increase.
The EMOV can be opened prior to the RCS reaching the 500 psig setpoint. An isolation valve can be opened from the control room which allows flow from the decay heat drop line through a 2 inch line to the RB floor. Operators could also be sent into the RB to open 1 inch manual drain valves on the bottom of each steam generator. Additionally, solenoid-operated 0TSG high point vents can be opened from the control rcom.
NRC QUESTION 1.C.6 Requirements pertaining to isolation of containment.
SMUD RESPONSE 1.C.6 Rancho Seco Technical Specifications and operating procedures do not require containment integrity for plant conditions such as those that existed at Diablo Canyon.
The Loss of Decay Heat Removal System Casualty Procedure instructs'the operators to close the major containment openings (equipment hatch, personnel hatch, RB purge inlet and outlet valves) prior to spill of reactor coolant to the RB floor.
NRC QUESTION 1.C.7 Time required to replace the equipment hatch should it be necessary.
SMUD RESPONSE 1.C.7 under optimum conditions the equipment hatch could be closed with the minimum number of bolts tightened in 45 minutes. Under adverse conditions, such as high airborne activity, the task could take 2 to 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.
(
l NRC QUESTION 1.C.8 Requirements pertinent to re-establishing RCS pressure boundary integrity.
SMUD RESPONSE 1.C.8 Requirements to re-establish RCS integrity are contained in one option of the Loss of Decay Heat Removal casualty procedure.
If the only " holes" in the RCS are the hot leg, pressurizer, and CRD vents, the RCS would be gravity filled from the borated water storage tank (BHST) to a level where the pressurizer is nearly filled. An RB entry would be made, the CRD vent closed, and nitrogen could be lined up to the pressurizer. Nitrogen pressure would be used to displace water from the pressurizer to fill the hot legs.
Natural convection core cooling would then evolve.
- 1
a NRC QUESTION 2.A A detailed description of instrumentation and alarms provided to the operators for controlling thermal and hydraulic aspects of the NSSS during operation with the RCS partially filled.
SMUD RESPONSE 2.A Temperature:
Decay heat suction temperature:
located in common suction line of both decay heat loops.
Range:
0*F to 300*F Readout:
Control Room Panel Meter Alarms:
None Incore Thermocouple:
located 6 inches above active fuel; not wired to vessel head area.
Range:
Class 1:
100 - 2200*F [36 T/Cs]
Class 2:
70 - 2200*F [16 T/Cs]
Readout:
Class 1:
SPDS (average of 5 highest)
Class 1:
IDADS computer system with CRT and alarm printer in control room [16 T/Cs]
Class 2:
Bailey computer system with continuous readout, alarm printer, and utility printer capabilities in control room [36 T/Cs]
IDADS [36 T/Cs]
Power Source:
Inverter backed, not affected by loss of offsite power Note:
Incore temperature maps of either al.1 Class 1 or Class 2 incore T/Cs can be illustrated on IDADS CRT Alarms:
Bailey computer: high:
635' IDADS computer:
high 635' The alarm setpoint can be changed through a software change request Decay Heat Loop Flow:
sensed downstream of decay heat cooler.
Range:
0 - 5000 gpm Readout:
Control room panel meter, SPDS, Bailey computer, IDADS computer Alarm:
Low flow annunciator:
2800 gpm Decay Heat Pump Current Range:
0 - 100 amps Readout:
Small edgewise meter on control room panel Alarm:
None 1
RVLI: pressure from 1 inch hurdpiped stainless steel pipe with high point at _ hot leg Gentille flow measuring tap and low point tap at centerline of lowest portion of cold leg downstream of RCP (4'-6" above top of actual fuel); piping constructed and sloped to eliminate air entrapment; instrument tubing from piping to instrument is approximately 4 feet long with constant downward slope to eliminate air entrapment; no Tygon tubing is used.
Range:
0 - 120 inches above cold leg centerline Accuracy:
0.2%
Reference:
RB atmosphere Power Supply offsite power Calibration Temperature:
190*F Readout:
Bailey computer, IDADS computer Alarms:
Bailey computer and IDADS computer:
high: 20 inches; low 10 inches The alarm setpoint can be changed through a software change request Hot leg level:
two safety grade instruments for each hot leg Bottom Tap:
Off decay heat dropline upstream of motor-operated isolation valves; zero level is 38 inches below the zero level of the RVLI Accuracy:
0.25%
Reference Tap:
Hot leg high point vent Range:
0 - 624 inches Power Supply:
Vital inverters; no loss on loss of offsite power Calibration
. Temperature:
140*F
' Readout:
IDADS computer, SPDS Alarms:
None (can be added through 3 so{tware change request)
Pressurizer Level:
Three temperature compensated transmitters, Bottom Tap:
47 inches above centerline of cold leg in pressurizer water space Reference Tap:
Pressurizer steam space Range:
0 - 320 inches (25 inches of level will remain in pressurizer unless surge line is drained)
Power Supply:
NNI; no loss on loss of offsite power
{
Calibration
)
Temperature:
Temperature compensated to pressurizer 1
Readout:
Control room console recorder, SPDS, Bailey computer Alarms:
Annunciator, low:
160 inches, low-low:
90 inches i
l 1 )
Local RVLI: a 14 inch level gauge sightglass is provided in the RB.
The gauge is flanged and can be located at either of two sets of level taps.
One tap covers the range 2 to 16 inches, the minimum level for component repair, and the other tap from 69 to 83 inches, the refueling level prior to floodup. Additionally, the level transmitter (RVLI) has a local indicator reading 0 - 100% corresponding to 0 - 120 inches.
A detailed comparison of the RCS level instrumentation in a draindown evolution follows. Operators rely on pressurizer level as an indica ion of RCS inventory when any pressure above ambient exists in the RCS.
ine RVLI cannot be used until the RCS is vented to the RB because the RVLI's reference is RB pressure. As the RCS drains and nitrogen pressure decreases, operators also observe hot leg level indications to check that the pressurizer and hot legs are draining together.
Both the pressurizer level instrument and the hot leg level instruments are now vented to the nitrogen space in their respective areas.
Since the vent header is open to the pressur1zer vapor space and to the hot leg high points, the pressure in these areas should be very nearly equal.
When pressurizer level has been reduced and nitrogen pressure has decreased to 5 psig, the center CR0 is tied to the vent header.
Draining continues to below pressurizer level indication and the vent header isolation to the Haste Gas System is opened. The combination of draining and venting the nitrogen to the Haste Gas System reduces the nitrogen pressure to 0 psig.
The vent header is then isolated from the Haste Gas System and the hot leg high point vents are opened to the RB atmosphere through filtered poly bottles.
The hot legs, pressurizer, and center CRD (reactor vessel head area) communicate through the vent header and all parts of the RCS are vented to the RB atmosphere through the poly bottles.
The RVLI will now give actual vessel level, because both the reference leg of the instrument and the RCS have RB atmospheric pressure as a reference.
It is noted that reliance on RB atmosphere as a reference for the RVLI will not indicate accurate reactor vessel level for intact coolant systems when the two high point vent bottles and their associated hoses and high efficiency particulate air (HEPA) filters cannot keep up with RCS pressure changes. A level decrease would result in drawing a partial RCS vacuum during RCS draindown.
This would cause indicated level to be lower than actual, a conservative direction.
]
For an event similar to Diablo Canyon's in which steam generation exceeded the ability to relieve through the vents, the pressure in the RCS would result in an indicated level on RVLI higher than actual, or in a non-conservative direction. Hot leg level instruments would give a more accurate picture of actual level, but may also indicate slightly higher than actual because their reference leg is seeing a reduced pressure at their place of tap-in to the system due to flow out the hot leg vent path.
Pressuri7er level could also indicate higher than actual levels. Hater trapped in the loop seal of the surge line would be forced into the pressurizer by the differential pressure in the
'B' hot leg and the pressurizer gas space. _. _ _. _ _ _ _ _ _ _ _ _ _ _....
l Several differences in the RVLI methods between Westinghouse and Babcock I
and Hilcox.(B&H) plants provide for more reliable indication at plants such as Rancho Seco.
- 1) The level indication tap at B&W plants is from a stagnant cold leg.
Decay heat flow does not flow through this leg, eliminating most of the level error due to flow induced differential pressures.
- 2) The level indication tap is downstream of the RCP discharge, closer to the vessel than the Westinghouse level tap.
This eliminates any level error due to any vessel level lower than the RCP discharge lip.
- 3) The level indicator at Rancho Seco is hard piped with no Tygon tube reference leg. The piping run is short compared with Diablo Canyon's and there are no loop seals to trap air.
The level deviation between required level and the level where vortexing begins is much greater at.a B&W plant than at a Westinghouse plant. A 2 inch level range was required at Diablo Canyon. Minimum component repair levels at Rancho Seco are an indicated 18 i 2 inches.
Vortexing begins at 7 inches indicated at nominal decay heat flow rates.
The band is therefore at least a factor of 4.5 greater at Rancho Seco than at Diablo Canyon.
Decay heat flows are frequently reduced below the nominal 3000 gpm when vessel levels are at component repair values to give a greater factor between actual and vortexing levels.
, I
E NRC QUESTION 2.8 Should describe temporary connections, piping, and instrumentation used for this RCS condition.
SMODRESPONSE2.8 The hot leg high point vents and CRD vents were described previously.
There is no Tygon tubing employed in the connection of the remote RVLI to the RCS.
If the steam generators are to be drained, Tygon tubing is
-connected to the drain valve pip ng on the bottom of the OTSG and run up i
the D-ring next to the steam generator. This tubing is used.to monitor level in the OTSG when draining down individual OTSGs for tube repairs.
The OTSG's and RCS cold legs may be completely drained without reducing RCS level below the required level for decay heat removal (DHR) operation because there is an elevation drop in the cold leg piping between the RCP outlet and reactor vessel nozzle.
The level tap for the RVLI is located in this section of piping and is not affected by OTSG draining.
Tygon tubing may be connected to a tee off the active leg of the RVLI. A scale is mounted on the wall next to the tubing. A comparison between the tubing and the RVLI computer reading confirms that the RVLI is aligned and correctly calibrated. _-___-_____-_____a
NRC QUESTION 2.C Describe quality control process to ensure proper functioning of such connections, piping and instrumentation.
Include assurance that they do not contribute to loss of RCS inventory or otherwise lead to perturbation of the NSSS while the RCS is partially filled.
SMUD RESPONSE 2.C Since the Reactor Vessel Level System at Rancho Seco is "hard piped," no quality control beyond proper valving is required to place the system in l
service. RCS venting connections are well above the water level when the RCS is in a drained-down condition and will not result in a loss of RCS inventory.
Proper functioning of the RVLI is checked by operators as the draindown progresses by comparing the computer displayed value against pressurizer level indication and hot leg level indication. Any disparity would result in a work request to check the calibration of the RVLI. As noted above, complete draining of the OTSG/ cold leg via the RCS drain header will not interrupt DHR system operation.
NRC QUESTION 2.D Should also provide a description of ability to monitor RCS pressure, temperature and level after'the RHR function may be lost.
SMUD RESPONSE 2.D RCS wide range pressure (0-2500 psig) is available on console strip chart recorders, SPDS, and the Bailey and IDADS computer. A narrow range l
(0-400 psig) is also'available on a control room panel meter and on IDADS.
Incore temperatures will be available unless a refueling outage is under way.
Incore neutron detectors and T/Cs have been removed from the core area early in the refueling operation prior to refueling canal floodup.
Loss of residual heat removal (RHR) in itself will not result in loss of level indication.
Refer to previous paragraphs for an explanation of level indication anomalies should the RCS pressurize.
l 1
NRC QUESTION 3 Identify all pumps that can be used to control NSSS inventory, including:
(a) pumps you require to be operable or capable of operation (include information about such pumps that may be temporarily removed from service for testing or maintenance).
1 SMUD RESPONSE 3(a)
I Both decay heat trains are required to be operable when the RCS is in a
)
drained-down condition.
This includes the following for each train:
)
- 1) One decay heat pump with shutoff head of 190 psig.
]
- 2) One nuclear service cooling water pump which provides flow to the cooling w6ter side of the train's decay heat cooler (heat exchanger).
- 3) One nuclear service raw water pump which provides flow to the nuclear service water heat exchanger, cooling water to the trains emergency diesel generator, and flow to the bearing cooler of the decay heat pump.
The raw water system provides the ultimate heat sink for core decay heat when the RCS is in the drained-down condition by spraying water into the atmosphere where the decay heat is given up to ambient through evaporation.
Quarterly surveillance testing of pumps required for the removal of decay heat continue throughout the draindown period.
This technically removes each pump from service for several hours for testing; however, should the in-service Decay Heat System be lost, the testing would be suspended and the alternate train would immediately be aligned for core heat removal.
NRC QUESTION 3(b)
Other pumps not included in item (a).
SMUD RESPONSE 3(b)
- 1) The high pressure (2900 psig shutoff head) makeup pump can supply as much as 525 gpm into the RCS cold leg or RCP seal inject lines.
- 2) The reactor coolant drain tank pumps (90 psig shutoff head) can supply water to the purification system and ultimately to the RCS through Decay Heat System piping.
- 3) The concentrated boric acid storage tank (CBAST) pumps (90 psig shutoff head) can provide flow to the suction of the makeup pump and can supply water to the RCS through the same piping as the makeup pump.
These pumps can also supply borated water through either decay heat train to the reactor vessel. _ _ _ _ _ _ _ _ _ _
i
- 4) The CBAST pumps and/or demineralized reactor coolant storage tank (DRCST) pumps could pump to the makeup tank, increasing its level and pressure until enough head was available to flow water through the makeup pump and its lines to the RCS and RCPs.
Note that the DRCST pumps are normally tagged out to prevent a boron dilution accident in this plant condition.
b 5)
Either HPI pump (analogous to makeup pump) could be used to inject water into the RCS through the normal RCS makeup line, HPI injection lines, or RCP seals.
- 6) The low pressure injection (LPI) warming pump can supply flow up to 100 gpm to the core through Decay Heat System piping with proper valve alignment.
Although they are not pumps, there are two borated sources of water available for gravity flow into the core should both decay heat pumps fail to function. The first is the BHST.
The BHST can be aligned to the Decay Heat System and provide gravity flow to the RCS as long as the RCS pressure remains less than 14 psig.
The second source is the spent fuel pool (SFP).
The SFP can also be aligned to the Decay Heat System and provide gravity flow to the RCS as long as RCS pressure remains less than 12 psig.
NRC QUESTION 3(c)
An evaluation of items (a) and (b) with respect to applicable TS requirements.
SHUD RESPONSE 3(c)
Technical Specifications require both decay heat trains remain operable when the OTSGs and RCPs are not available for service.
The action statement, should one train become inoperable, requires the plant be placed in cold shutdown within the next 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />.
For the draindown case, the plant is already in cold shutdown; therefore, the response is to repair the inoperable loop as expeditiously as possible and return the decay heat train to operable status.
The case of increasing level and pressurizing the makeup tank would conflict with the LTOP Technical Specification 3.2.2.3.
This Technical Specification limits the makeup tank level to 86 inches as an upper bound on the amount of water that could be injected into the RCS if the RCS level makeup valve were to fail open.
Level may have to be increased above 86 inches to provide sufficient pressure to inject water into the core using this method.
The use of any HPI pump except the designated makeup pump will require the removal of an operational clearance and the racking in of an HPI pump breaker. This is a violation of Technical Specification 3.2.2.6 (although the unrestricted makeup pump should provide sufficient RCS inventory restoration ability).
Similarily, HPI injection through an HPI injection valve would be a violatior, of Technical Specification 3.2.2.2, but injection through the normal makeup line should provide sufficient flow. --
l NRC QUESTION 4A A description of the containment closure condition you require for the conduct of operations while the RCS is partially filled.
NRC QUESTION 4B Examples of areas of consideration are:
I Equipment hatch e
Personnel hatches Containment purge valves SG secondary side condition upstream of the isolation valves (including the valves)
Piping penetrations e
Electrical-penetrations SMUD RESPONSE 4A & R Considerations for the equipment hatch and containment purge valves were discussed previously.
There is no distinction made in Rancho Seco Technical Specifications or procedures for drained-down conditions for the different types of penetrations listed.
If the RCS temperature at the decay heat suction is less than 140*F, containment integrity is not required.
If the temperature is greater than 140*F and the RCS is open to the RB atmosphere (defined as an opening of handhole size or larger),
containment integrity is required unless RCS boron concentration is greater than the required refueling boron concentration.
At least one operating RB purge fan is procedurally required (unless special controls are established on air sampling and activities allowed on the RCS are restricted, then the purge fan may be off with the hatch open).
This ensures maximum permissible concentrations (HPCs) are kept as low as possible for personnel in the RB and any traces of radionuclides do not leave by unmonitored pathways. The fans ensure a slight negative pressure in the RB and provide filtering for any release. Any leakage through RB penetrations would be internal.
It should also be noted that Technical Specifications require at least one purge valve with its automatic closure feature and associated RB purge fan trip be operable from either the purge exhaust radiation monitor or the RB accident radiation monitors. {
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NRC QUESTION 5.A Reference to and a summary description of procedures in the control room which describe operation while the RCS is partially filled, particularly:
NRC QUESTION 5.A.1 Draindown to the condition where the RCS is partially filled.
SMUD RESPONSE 5.A.1 The draindown process was detailed previously.
The specific operating i
procedures used are:
- 1) OP.B.4 - Plant Shutdown and Cooldown - provides general guidance in the draindown process and refers the operator to more specific operating instructions in other system-grouped procedures.
- 2) OP.A.1 - Reactor Coolant System - provides the details on equalizing levels in the RCS and draining the RCS to various component repair / refueling levels.
- 3) OP.A.3 - Pressurizer and Pressurizer Relief - provides detailed instruction on limits and precautions and instructions on press' rizer u
cooldown.
- 4) OP.A.6 - OTSG Secondary Side - provides detailed instructions on layup conditions for OTSGs for cold shutdown.
- 5) OP.A.8 - Decay Heat System - provides a vortexing curve for decay heat flow versus RCS level for the drained-down condition.
NRC QUESTION 5.A.2 Treatment of minor variations for expected behavior such as caused by air entrainment and doentrainment.
SHUD RESPONSE 5.A.2 Operating Procedure A.8, Decay Heat System, contains an operating curve for avoidance of an entrainment and assurance of adequate NPSH to the decay heat pumps based on decay heat flowrate, RCS temperature, and reactor vessel level.
If air is entrained in the decay heat flow, an Operations Department special order provides direction to re-establish required reactor vessel level prior to starting the standby DHR pump to avoin an entrainment in both DHR pumps.
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NRC QUESTION 5.A.3 i
Treatment of boiling in the core with and without RCS pressure boundary integrity.
SHUD RESPONSE 5.A.3
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Rancho Seco Casualty Procedures address boiling in the core when the RCS t
is filled and vented with a steam bubble in the pressurizer.
Boiling conditions are not specifically addressed when the RCS is drained down.
1 NRC QUESTION 5.A.4 Approximate time from loss of RHR to core damage.
SHUD RESPONSE 5.A.4 Approximate times from loss of RHR to core damage are not provided in operating procedure <.
NRC QUESTION 5.A.5 Level differences in the RCS and the effect upon instrumentation indications.
SHUD RESPONSE 5.A.5 It is possible for the level on the cold leg side to be slightly higher than the hot leg side if the RCS is not vented.
Level differences will also occur if the RCS should boil, the hot leg loop seal is established by water levels in excess of the top of the hot leg piping, and the CRD vent cannot relieve the RCS pressure. A small volume of water would be forced from the area above the core into the cold legs.
This level difference between cold and hot legs is limited to a few inches by reactor vessel internal vent valves.
Level indicated to control room operators would increase due to the increased cold leg level and increased RCS pressure.
Rancho Seco procedures do not address these anomalies.
The procedures address proper venting of the RCS during drained-down conditions and the avoidance of coolant boiling to prevent the situation leading to the level I
anomalies. _ _ _ _ _
NRC QUESTION 5.A.6 Treatment of air in the RCS/RHR. system, including the impact of air upon NSSS and instrumentation response.
SMUD RESPONSE 5.A.6 There are several areas in the Rancho Seco Decay Heat System in which vortexed air could be trapped before it was returned to the RCS.
The displaced water would result in a vessel level increase.
This increase would be seen on the RVLI.
If the entrapped air was returned to the RCS, the air could accumulate in the cold leg reactor vessel annulus if sufficient' volumes of air were entrained to overwhelm the venting capability of the mechanical seal between the cold and hot legs.
The accumulated air would displace water in the annulus and result in a higher vessel and hot leg water level.
This increase in level would be indicated on the RVLI.
Rancho Seco procedures do not specifically address the impact of air on the NSSS and on instrument response.
Prevention of vortexing and air entrain-ment with specifications of minimum vessel level in relation to Decay Heat System flow and temperature are employed to avoid this problem.
NRC QUESTION 5.A.7 l
Treatment of vortexing at the connection of the RHR suction line to RCS.
SMUD RESPONSE 5.A.7 Operating Procedure A.8, Decay Heat System, instructs the operator to maintain RCS level above a certain point based on flow and temperature with reference to a graph.
Similarily, the Loss of Decay Heat Removal System Casualty Procedure, C.12, lists the response to a low flow condition. L
l NRC QUESTION 5.B l
Include the analytic basis used for above procedure development.
SMUD RESPONSE 5.B An analytic basis used for procedure development for concerns other than vortexing has not been prepared; however, the methodology developed I
through operating experience provides a high level of confidence in the DHR System procedures.
A test procedure was conducted during the Rancho Seco hot functional test program in 1974 to empirically find the level at which vortexing occurred when one or two decay heat pumps were run at nominal flowrates. -__
4 NRC QUESTION 5.C.a Procedural guidance pertinent to timing of operations, required instrumentation, cautions and critical parameters.
i SMUD RESPONSE 5.C.a Procedural guidance pertinent to timing of operations while in the DHR mode have not been factored into the procedural development.
Instrumentation available to the operators while in the DHR mode is described in SHUD Response 2.A.
Cautions and critical parameters were included during the procedure
. development stage.
NRC QUESTION 5.C.b Operations control and communications requirements regarding operations that may porturb the NSSS.
Include restrictions on testing, maintenance j
and coordination of operations that could upset the condition of the NSSS.
SMUD RESPONSE 5.C.b No written basis is used for these controls.
See SHUD Response 1.C.4 for controls on testing and maintenance.
NRC QUESTION 5.C.c Response to loss of DHR, including:
I 1.
Regaining control of RCS heat removal.
2.
Operations involving the NSSS if DHR cannot be restored.
3.
Control of effluent from the containment if containment was not in an isolated condition at the time of loss of DHR.
SMUD RESPONSE 5.C.c Operations Casualty Procedure C.12, Loss of Decay Heat Removal System, and Operating Procedure A.8, Decay Heat System, address losses of DHR.
Restoration of DHR flow following loss due to an interlock actuation are included in the operating procedure.
Losses from other causes are addressed by the casualty procedure.
Responses to loss of both-Decay Heat Systems with the RCS open to the RB atmosphere apply to the Generic Letter concerns.
Two RCS conditions are addressed: one in which a large RCS drain path is already available and one in which only the RCS vents are open. _ - __.
'The initial steps of both responses are the same.
The RB is evacuated and Health. Physics is advised of an imminent spill.
The equipment hatch and personnel hatch are closed, the RB exhaust and supply fans are stopped, and the RB purge inlet and outlet valves are closed. The normal RB sump discharge pathway is closed.
For situations where a large drain path already exists, water from the I
450,000 gallon BHST is gravity flowed through the Decay Heat System to the point of overflow to the RB floor. Water accumulates on the RB floor until sufficient NPSH is available for an RB spray pump to recirculate the spilled water back to the BHST.
Heat removal can be sustained indefinitely in this manner.
There are two options for situations in which only RCS vents are open.
If the required secondary systems are operable and the condenser or atmospheric dump valves (ADVs) are available, the RCS can be filled to the level of the CRD vents, an RB entry made, the CRD vents and pressurizer vents closed, and a nitrogen bubble established in the pressurizer. This action would force water into the hot legs and allow natural circulation to the OTSGs for heat removal.
I The second option uses gravity flow from the BHST to increase RCS inventory
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until pressurizer level is high in the indicating range.
The BHST is then J
isolated from the RCS and the RCS drained to the RB floor through a 2 inch, motor-operated drain valve located downstream of the RCS to decay heat isolation valves.
Draining continues until pressurizer level is low in the indicating range.
The batch feed and bleed process.is continued by repeating the gravity fill process from the BHST and drain to the RB floor.
The accumulation of coolant on the RB floor is circulated back to the BHST with an RB spray pump.
1 - _ - _
NRC QUESTION 6 Brief description of training provided to operators and other affected personnel that is specific to partially filled operation.
SHUD RESPONSE 6 Both Nuclear Training and Nuclear Operations provide training to operations personnel for the RCS in this configuration as follows:
- 1) Classroom training is conducted during initial license training for Hot License candidates on the DHR System.
This training includes lessons on operator response to alarms relating to the DHR System.
The lesson plan teaches the student to refer to Operations Procedure A.8, Decay Heat System, which has operational curves relating RCS level control versus temperature, thus ensuring adequate NPSH while in the partially filled conditions.
2) 10 CFR 55/Denton requirements specify that a loss of shutdown cooling scenario be simulated for licensed operators as part of their requali-fication training and this is included in our training.
The SMUD lesson plan for " Loss of Shutdown Cooling" provides the student an opportunity to train on the use of Casualty Procedure C.12, Loss of Decay Heat Removal.
- 3) Training on Procedure C.12, Loss of Decay Heat Removal System, is included in the Licensed Operator training program.
Procedure C.12 includes responses to loss of DHR for various RCS conditions.
- 4) Operations provides training to crew members in the form of crew briefings.
Prior to entering an unusual plant condition, the operators are briefed on the hazards of that particular unusual plant condition.
5)
If the plant is in the partially filled condition for refueling purposes, a dedicated Senior Reactor Operator (SRO) is assigned to the control room as " Refueling SRO." His sole duty is to monitor RCS and fuel conditions.
Prior to this special assignment, the SRO is briefed on the potential consequences of a loss of DHR capabilities and ensures that the requirements of OP A.8, Decay Heat System (specifically, RCS level versus Decay Heat System flow) are maintained.
i --
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NRC QUESTION 6.A Maintenance personnel training regarding avoidance of perturbing the NSSS.
SMUD RESPONSE 6.A All maintenance training programs include lessons designed to train
- personnel on fundamental Rancho Seco systems and their interrelationships.
These lessons include training personnel on strict adherence to work and clearance procedures where variations in plant or work conditions may impact the scope of a planned work package.
Maintenance training programs also include material designed to train" personnel on the possible effects on a plant system or component while working on a component of a system. The Maintenance Training Program does not specifically address the NSSS in the partially filled condition. - ____ _ _______
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MC QUESTION 7
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Identification.of additional resources provided to operators while the RCS
- Al is partia11y' filled,hwch as assignment of additional personnel with
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Shift Technical Advisors (STAS) are maintained on shift until the RCS is provideJ'a sufficient vent path following draindown after power operation.
This is tht, most critical period for loss of DHR-function due to the higher
. decay heat load.
Loss.of DHR function and RCS' temp 9r?.ture incretse to greater than 160*F r
w:,ald cause an Alert and full manning of the Te:hnical Support Center (TSC), which would provide all available resourtes to the shift.
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NRC QUESTION 8 Comparison of requirements implemented while the RCS is partially filled and requirements for other Mode 5 operations, e.g., reduced flowrate.
SMUD RESPONSE 8' There are no differing requirements between partially filled and other i
Mode 5 operations at Rancho Seco. Minimum flowrates are not specified in Technical Specifications or operating procedures.
Normal flowrate is 3000 gpm.
This is also the lowest flowrate specified on the hot leg vortexing curve and corresponds to a level of 7 inches above the hot leg centerline.
Should the decay heat load be low and it is desired to operate low in the draindown band, the decay heat flow is throttled.
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NRC QUESTION 9 Describe any changes made as a result of this letter along with
-implementation, schedule.
SRJD RESPONSE 9 l'
During the course of preparing this response, the DHR System procedures and operation methodology were reviewed in detail. As of the transmittal date of this letter, no changes in either procedures or physical design of the DHR System have been identified.