ML20010B505
| ML20010B505 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 08/11/1981 |
| From: | Lundvall A BALTIMORE GAS & ELECTRIC CO. |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM NUDOCS 8108170123 | |
| Download: ML20010B505 (33) | |
Text
.-
-~m BALT,M O RE
/- Y GAS AND 9
Ul$ f
-O ELECTRIC '
2
/4(jg 1 'l 1981w 3
/
G y,s%2f== e CHARLES CENTER.P.O. BOX 1475 BALTIMORE, MARYLAND 212
/
ARTHUR E. LUNDVALL, JR.
N
(([y" August 11, 1981 Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission
. Washington, D. C.
20555 Attn:
Mr. D. G. Eisenhut, Director Division of Licensing
Subject:
Calvert Cliffe Nuclear Power Plant Units Nos. 1 & 2, Dockets Nos. 50-317 & 50-318 Resnonse to NUREG-0737 Item II.B.1 Gentlemen:
Enclosed are the guidelines which are being used to develop operating instructions for use of the reactor coolant system gas vent system (RCSVS).
The vent system is scheduled to.be operational by January 1, 1982, by which time formal training vill be completed and operating instructions issued.
If any additional information is required, we vould be pleased to provide it to you.
Very truly yours, Oh)U-fora.E.Lundvall,Jy.,f Vice President-Supply -
cc:
J. A. Biddison, Esquire (w/o encl)
G. F. Trowbridge, Esquire (w/o encl)
Messrs. E. L. Conner, Jr. - NRC (w/ encl)
R. E. Architzel - NRC (w/o encl) l 0108170123 810811' S I[
PDR ADOCK 05000317 P
i
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a s
Procedural Guidelines For l,
Reactor Coolant Gas Vent System l
For l
Calvert Cliffs Units 1 & 2 l
I 1
1 1
i
t Table of Contents Pace 1.
Furpose T
Scope 3
3.
Refereaces 3
4.
System Status and Surveillance 4.1 RCGVS Standby Mode 3
4.2 Normal Plant Operations 4
4.3 Emergency Plant Operations 9
List of Ficures 1.
Response to System Valve Leakage 6
2.
Pressurizer Vent - aP vs Time (CCP on) 15 Pressurizer Vent - aP vs Time (CCP off) 16 3.
4.
Reactor Vessel Vent - aP vs Time (CCP on) 17 5.
Pressurizer Vent - Level vs Time (CCP on) 18 6.
Pressurizer Vect - Level vs Time (CCP off) 19 7.
Reactor Vessel lent - Pressurize-Level vs. Time 20 8.
Hydrogen Vent Duration vs Reactor Vessel Tempera *.ure 21 (2250 PSIA) 9..
Hydrogen Vent Duration vs Reactor Vessel Temperature 22 (1000 PSIA)
- 10. Hydrogen Vent Duration vs Reactor Vessel Temperature 23 (250 PSIA)
- 11. Vent Duration from Pressurizer at P = Psaturated 24
- 12. Steam Ficwrate (Pressurizer) 25 13.
Hydrogen Flowrate (Pressurizer) 26 14.
Steam Flowrate (Reactor Vessel) 27 15.
Hydrogen Flowrate (Reactor Vessel) 28
- 16. Pressurizer Pressure with a Non-Condensible Gas 29
- 17. Containment Hydrogen Pressure 30 18 RCGVS Accident Response 31 19.
RCGVS Schematic 33
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.a r
Procedural Guidelines 1.
Purpose:
To provide procedural guidelines for the Reactor Coolant Gas Vent System.
This document does not provide detailed operating piecedures, but is intended to be used as a guide when writing the detailed procedures.
2.
Scoce:
I
The procedures have been divided into three basic sections:
system status surveillance, normal operations, and emergency operation.
In addition to presentation of the operational g"idelines, the emergency operation includes a discussion of the plant r,%,,se to the use of the RCGVS.
3.
References:
3.1 Bechtel Drawing FSK-M-201 sheets 4-7 3.2 Bechtel Drawing FSK-MP-3137 3.3 Bechtel Drawing FSK-MP-3348 3.4 Bechtel Drawing FSK-MP-3410 3.5 ?achtel Drawing FSK-MP-4202 3.6 Bechtel Drawing FSK-MP-4459 3.7 Bechtel Drawing SK-J-67 sheets 1-2 3.8 Bechtel Drawing 62-460-E Note: A simplified sketch of this system is provided on Figure 19 for reference when using this document.
4.0 System Status and Surveillance 4.1 RCGVS Standby Mcde
- 1. Description of Operatten Ouring normal plant operations, the Reactor Ccolant Gas Vent System is in a standby mode. All solenoid isolation valves (1-SV-103,104,105,402, 106) are closed with appropriate administrative controls in force to pre-vent inadvertent system operation.
.1.
i
\\
2.
Initial Conditions
- 1) RCS fluid bou.idaries are intact.
- 2) The plant is in any mode of operation except refueling.
- 3) The following interfacing systems are available for use with the RCGVS should the system be required:
Electrical Power for the Valves Quench Tank Containment Recembiners and H analyzers 2
- 4) The RCGVS temperature instrument (1-TI-101) is operational.
- 5) All RCGVS solenoid valves are closed with administrative controls imposed.
- 6) All manual valves in the vent path are locked open.
Ooerational Recuirements 1.
The leak tightness of the RCGVS isolation valves is verified by periodically monitoring the RCGVS temperature indicator (1-TI-101).
2.
The standby status of the system is verified by assuring that the administrative controls remain in ~ force.
4.2 Normal plant Ooerations 4.2.1 RCGVS response to valve leakage during normal operations.
1.
Description of Operation While in standby,1-TI-101 indicates that leakage has occurred past 4 Hub 1peo of the 4 solenoid valtas.
Operator response to the leakage includes verification that leakage is occurring, quantification of the leak rate, and eventual repair of the leaking valve. A flow chart to summarize operator response if provided as Figure 1.
2.
Initial Conditions
- 1. Same as Status and Surveillance 2.1-TI-101 indicates valve leakage by a temperature increase (and eventual alarm).
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- 3. ~ Ocerational Recuirements p/'1. Conduct a RCS leak rate determination'in accordance with estabinned plant procedures and ccmpare with a leak rate determination made prior to the temperature increase. No difference -indicates that either the temperature indicator is faulty or that the leakage has been contained by the seccnd isolation valve. An increase in the leak rate indicates that not only is leakage occuring, but it is also leaking past the second isolation valve.
2.
If there is no change in RCS leak rate, thennstrument mal-function is possible. No action is necessary other than to repair the instrument when plant conditions permit.
Periodic leak rate determinations should be made to verify that leakage does not occur while the instrument is out of service.
3.
If there is a change in RCS leak rate then one or both sets of isolation valves are leaking.
If the leak rate is less than technical specification limits, then operation can continue, but the RCS leak rate determination should be monitored to assure that the rate does not increase. The leaking valves should be repaired at the earliest opportunity' and if leakage reaches technical specification limits, the plant must be shutdown to repair the valves. Quench tank conditions should be monitored to assure proper temperature, pressure, and level are maintained in the tank.
The tank level will provide an independent check of the leak rate.
Temperature increase arid /
Jr_MnDiL(1 "I-10Z)
Perform RCS t.eak Rate
.v Compare with previous leak rate Increase?
o C eakaqc_iti IIll3Jmilid Y
'3.
Continue to monitor leak rate.
Shutdown and repair :
Probable instrument mal-honior QT conditions-
_]cdinq valves.
function.
Repair when plant con-Repair valves when plant ditions permit.
conditions perniit.
Continue RCS leak rate de termina tion..
Figure 'l Response to System Valve Leakage
1.2.2 RCGVS Use in RCS Ventino prior to Refueling BG&E refueling procedures were not available when these guidelines were written, but actual in plant use of the system should be compatib.le.
- 1. Descriotion of Ooeration The RCGVS may be used to vent.the RCS when the RCS is being pumped down to remove the reactor vessel head for refueling. This is done by aligning first the pressurizer vent and later the reactor vessel vent to the quench tank or atmosphere through the QT while the RCS fluid is being pumped out of the system.
- 2. Initial Conditions Same as Status and Surveillance except the reactor is in cold shutdown in preparation for head removal.
'3. Ooerational Reouirements
- 1) Obtain administrativ[ approval to operate the RCGVS valves.
- 2) Initiate RCS draining and line up the pressurizer vent to either the quench tank, waste gas system, or atmosphere. Assure sufficient N is supplied to the quench tank if the veqt path 2
containmerit i
does not include the waste gas system or atmosphere.
3 f
- 3) When the pressurizer empties, open the reactor vessel vent'to allow removal of fluid from the reactor vessel head.
4.2.3 RCGVS Use in RCS Venting Post-Refueling
- 1. Descriotion of Oceration
{
The RCGVS may be used to vent the RCS when the RCS is being refilled follow-ing refueling.
This is done by aligning the RCGVS to vent first tne reactor vessel head and then the pressurizer to the quench tank.
Vented gas is ultimately handled by the Waste Gas System.
- 2. Initial Conditions Sane as Status and Surveillance except the RCS is partially drained from refueling,with the system ready to be refilled. Administrative controls of the solenoid valves may not be in force.
l L
9
- 3) Ooerational Recuirements t
- 1. Obtain administrative approval (if required) to operate the RCGVS valves and repower the valves.
- 2. Align the system to vent the reactor vessel head to the quench tank ano waste gas systam ano commence system fill.
- 3. When quench tank level indicates liquid flow (or, alternately, a vent system drain may be monitored for flow) close the reactor vessel isolation valves and open the pressurizer isolation valves.
- 4. When the pressurizer is full, close all RCGVS solenoids and establish administrative controls in preparation for startup.
e 4
e
4.3 Emergency Plant Ocerations This section describes the operation of the RCGVS in response to a plant accident which has created a non-condensible gas bubble in the reactor coolant system.
The specific accident which csused the bubble to be formed will not be discussed; instead it will be assumed that a bubble exists regardless of the specific accident scenario.
It is also assumed that means to detect the presence of the bubble exists.
4.3.1 Determination of Venting Path and Duratien
- 1. Description of Operation The first step in the use of the RCGVS under post-accident conditions is the establishment of the need to vent, the determination of the vent-ing duration, and the choice of the venting path.
Detection of the gas bubble establishes the need to vent, and the venting duration and path are determin9d based upon the bubble size and RCS parameters'.
- 2. Initial Concitions
- 1) Same as Status and Surveillance except an accident has occurred which could lead to bubble formation.
- 2) The RCS fluid boundary may not be intact.
- 3. Operational Requirements 1.
Establi;hing the need to vent:
For the reactor vessel, if a gas bubble,no matter how small, a.
is detected in the reactor vassel by aP, heated-Junction thermocouple, or scme other suitable means, then there is a need to vent the reactor vessel.
b.
The presence of a non-condensible gas -in the pressurizer steam bubble can be' indirectly as;ertained by a departure frcm saturation _ conditions.
For a given pressurizer temperature, the pressure will be higher than sataration by an amount de-pendent upon the steam / bubble volume and amount of gas present in the steam space. The effect is illustrated in Figure l6.
9
This method, however, is only useful for large gas volumes and provides an indirect indication of the volume of gas and how long the pressurizer should be vented to remove j
the gas. Further, since gas is present in the space even during normal plant operations, the objective of vcating the pressurizer is not to remove all gas as is the case for the reactor vessel, but to remove enough of the gas so that ths pressurizer can continue to function efficiently
)
to maintain and control plant 7ressure. The procedural guidelines to accomplish this objective are as follows:
I 1.
If a bubble is detected in the reactor vessel, it vill be assumed that some hydrogen has collected in the i
pressurizer as well, even if the gas volume cannot be definitely measured in the pressurizer.
2.
In this case, or if hydrogen is identified in the pressurizer independent of its presence in the reactor vessel by departing from saturation, sluggish pressure control, or sa=oling; then there is a need to vent the pressurizer.
c.
For suspected volumes under 1000 SCF, to determine if the bubble is in the pressurizer:
1.
Vent one pressurizer steam space.
2.
Control all intut and outuut from RCS and charge
)
pressurizer with fluid. Observe level and pressure. If pressure increases and level does not, non-condensible gas is present.
2.
Determination of Venting Duration a) For the reactor vessel, the vent duration is selected to be i
long enough to remove the entire gas bubble from the vessel l
head. By reviewing the RCS temperature and pressure conditions, the venting duration is determined bv referring i
to Figures 14 and 15 b) For the pressurizer, the vent duration is selected as long enough to remove a sufficient amount of the gas from the pressurizer steam bubble to prevent the gas from interferring with RCS pressure control. This is done by venting the pressurizer long enough to remove the mass equivalent of the steam bubble. Steam bubble size is given by pressurizer level instrumentation and with this and the RCS temperature and pressure, the venting duration is determined by referring
to Figure 9.
This vent duration is illso sufficient to remove on equivalent volume of hydrogen, should the bubble ce pure hydrogen.
The centing times are based upon system vent flow rates illustrated in Figures 12 and 13.
c) The venting process will result in a pressure d.rease within the RCS, the extent of which is influenced by the venting lo-cation, charging pump availability, and tha initial pressure, level and temperature conditions. F'gures 2 through 7 present the impact of a timed vent upon system pressure and pressurizer level for the venting process.
Dependent upon initial conditions and the duration of venting required, it may be necessary to temporarily secure the venting process before the selected venting duration has elapsed to restore pressurizer level and plant pressure. However, as illustrated on the figures, the pressurizer pressure and level changes are slow enough to be controllable. Care must be taken during venting that the vent process is not allowed to proceed long enough to produce steam bubbles in the main RCS due to reduction of pressure to saturation.
Prior to venting, the operator must determine the minimum RCS pressure allowable (based upong RCS temperatures) and terminate venting prior to reaching that pressure.
Similarily, when venting the reactor vessel or pressurizer, pressurizer level must not be alloweu eo decrease to below the heaters.
The effect of this venting process-on pressurizer pressure and level stability was determined by performing heat and mass balances upon the pressurizer. An f attial.pressurimlevel of 3
800 ft was assumed for these calculations.
Although cres,ure
[
and level changes will result from venting, the vent rate is slow enough that the changes are controllable.
3.
Selection of Venting Path The RCGVS removes gas from the RCS by venting the RCS to the quench -
tank.-
The quench ' tank may be vented either to the waste gas system or to containment.
The choice of which path to use is based upon the following guidelines:
- 1) With pcwer and the quench tank rupture disc bicwn, vent to the quench tank.
Then with water in the tank,it will provide cooling.
With l
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no water in the tank, vent to atmosphere' as this location should provide more complete mixing with the containment atmosphere and quicker access to the hydrogen reccmbiners.
- 2) With the quench tank rupture disc intact, small quantities e
of the gas may be vented to the waste gas system or remain in the QT and thus not enter the containment atr 1 sphere.
Larger quantities of gas are vented to containment from the quench tank.
3)
Venting of hydrogen to containment will cause an increase of containment hydrogen concentration.
Figure 17 illustrates the impact of the venting with and without hydrogen recombiners in operation.
It is cbvious that if large quantities of hydrogen must be vented, the recombiners must be in operattan and even then hydrogen may approach combustible levels.
If the concentration approaches combustible levels, the operator will have to make a decision to continue venting or to secure vent-ing until containment hydrogen levels decrease.
The decision should be based upon the following:
1.
Venting the reactor vessel should take orfority over et-tainment hydrogen limits due to tne potential for interruption of core cooling with hydrogen in the vessel.
2.
Venting the pressuri:er should not take priority over contain-ment hydrogen limits unless the pressurizer bubble is inter-
]
ferring with the ability t$ maintain present pressure control.
4.3.2 Venting the Reactor Vessel to the Containment This section and the following sections describe operator actions to vent the RCS via the various vent paths in the event of an accident.
A summary flew path for the venting process is provided in F igure 18.
- 1. Description o'f Operation The RCGVS is initially in standby and the need to operate the system to remove a gas bubble from the reactor vessel has been identified.
After obtaining administrative approval to operate the system, the reactor vessel is vented to containment for a time period determined by system pressure, temperatures, and bubble size.
~~
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- 2. Initial Conditions
,j, Same as Status and Surveillance except
- the RCS fluid boundary may not be intact
- an accident has occurred which has created a bubble in the reactor vessel
- the bubble size has been determined and the containment vent path chosen
- 3. Operational Requirements
- 1. Permission to use the RCGVS is obtained, and power restored to the system (if applicable).
- 2. Using the bubble size and RCS temperature and pressure, determine the vent duration to remove the bubble.
- 3. Assure that there is sufficient water in the pressurizer to conduct the vent without uncovering pressurizer heaters.
It may be necessary b raise pressurizer level prior to venting or to secure venting temporarily and reestzblish level if large bubbles are to be re-moved.
Charging should be in operation during the vent to minimize pressurizer level changes.
Pressure will also drop during the vent-ing process.
The effect of the vent on pressurizer pressure and level is illustrated in Figures 4 and 7 Pressurizer heaters should be energized during the vent to minimize the pressure drop.
- 4. Place the hydrogen recombiner(s) in operation and monitor containment H2 concentrations if not already acccmplished.
- 5. Vent to containment by opening the containment isolation valve and then one of the two reactor vessel isolation valves.
- 6. Secure venting after the predetermined time has elapsed by closing the reactor vessel isolation valve and then the containment isolation valve.
- 7. Evaluate the effectiveness of the vent on bubble removal and repeat if necessary after returning RCS pressure and pressurizer level to desired levels.
a.3.3 Venting the Reactor Vessel to the Quench Tank
- 1. Descriotion of Operation This operation is identical to the previous section except the vented gas is directed from the quench tank to the containment atmosphere or waste gas system.
This path is used primarily for small bucole volumes unless the containment path is unavailable or the rupture disc has already been ruptured.
- 2. Initial Conditions Same as vent to containment except for the vent path.
- 3. Operational Requirements
- 1. Same as the vent to containment except for the vent path.
- 2. During. venting to'the quench tank, monitor vent tank instrumen-tation.and (assuming the containment vent path is available and with the rupture disc already ruptured) terminate venting to the quench tank by redirecting vent flow to containment if tack water level decreases to the point where it is no longer providing ecoling for the vented gas.
4.3.4 Venting the Pressurizer to the Containment or Quench Tank Description of Operation This operation is identical to the previous operations except that the pressurizer is the source of vented gas.
4.3.5 Non-Condensible Gases in the Steam Generator Another place in the RCS where non-condensible gases can collect is in the steam generator U-tubes.
Since there are thousands of tubes in which the gases could collect, it would ce impractical to install a vent on each tube.
Non-condensible ses collecting in the tubes could affect natural circulation.
Guidelines for starting and maintaining natural circulation for emergency conditions are presented in CEN-128, Vol.1, " Response of Combustion Engineer-ing Nuclear Steam Supply System to Transients and Accidents", April 1980.
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fionitor for Bubble formation f_RecheckBubbleStatu Necessary b
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Y No
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Determine bubble siz(e and, Eithe;r non-condensibles in pressurizer or previous j
vent duration vent of RV7 l-Determine vent sink Yes No Energize p}ressurizer heaters, establish Determine ve$nt duration No need to vent charging flow, verify pressurizer level 1
1 j.
Determine vent size
}
Obtain administrative approval Energize pressurizer heaters, verify pressurizer level, to vent charge if necessary
}
Energize 112 recombiner Obtain administrative approval to vent 7
1 j.
Proceed with vent Energize il recombiner and monitor 11 concentra tion 2
(ner.t page)
At explosive limi ts?.
!!N Ncs Proceed tNth Vent 1.
Wi th adequate RCS pressure control, (next pa00)
Do not vent until ll concentration 2
is accepable, or;
~
i 2.
with inadequate RCS pressure control or if vent path is to intact QT, proceed with vent.
(nextpage) n a *O e -
Vent to QT,for tired interval Vent to containnent for tined interval t-tbnitor QT Conditions
. e.
I f* ear ruptu7re disc setpoint?
. r '.I Ye\\(Operator Option) 1:a Conti,/nue Vent
- 1. Switch to containment vent,
)
waste gas vent, or 2.
Continue vent through I
ruptured rupture disc.(a e v m c o...- ~. ~... m.. 3 c._
d-Secu"re' vent af ter tined interval l
Bubble Status as necessary
(
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e t
It I