ML20041F063
| ML20041F063 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 03/09/1982 |
| From: | Mardis D FLORIDA POWER CORP. |
| To: | Stolz J Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM 3F-0382-03, 3F-382-3, NUDOCS 8203160152 | |
| Download: ML20041F063 (35) | |
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March 9.1982 d
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? NWQ Mr. John F. Stolz, Chief
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Operating Reactor Branch #4
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Division of Licensing y
j U.S. Nuclear Regulatory Commission Washington, D.C. 20555
Subject:
Crystal River Unit 3 Docket No. 50-302 Operating License No. DPR-72 NUREG-0737; Item II.B.1 Reactor Coolant System Vents AdditionalInformation
Dear Mr. Stolz:
By letter dated January 19, 1982, your staff requested additional information needed to continue your review of the Crystal River Unit 3 Reactor Coolaat System High Point Vents Operational Procedures submitted by letter dated July 1,1981.
Florida Power Corporation hereby provides responses to your fifteen questions per your request.
Very truly yours, 0
mk David G. Mardis Acting Manager Nuclear Licensing Enclosure RAW:mm okb Gs \\
0203160152 820309 PDR ADOCK 05000302 P
PDR General Office 32o1 TNrty-fourth street souin. P O Box 14042. st Petersburg. Florida 33733 813-866-5151
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l REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Question 1.
In addition to the operating guidelines for the high point vent system provided as part of your response to NUREG-0737 Item II.B.1, provide additional information regarding the following; a.
Criteria or pertinent information concerning a decision to terminate venting due to containment hydrogen concentration limits or allow-able pressurizer level limits (reference NUREG-0737 Item II.B.1 Clarification A.(2)).
b.
Methodology describing the determination of the location and size of a noncondensible gas bubble in the reactor coolant system (references NUREG-0737 Item II.B.1 Position (2) and Clarification A.(2)).
Operating guidelines for venting of the pressurizer in order to c.
maintain system pressure and volume control (reference NUREG-0737 Item II.B.1 Clarification C.(3)).
Response 1.a.
An evaluation is ongoing concerning the amount of hydrogen as a result of inadequate core cooling that will be released to the containment via the high point vent system.
This evaluation may determine whether the termination of venting is needed or not. The results of this evaluation will be forwarded on or about July 1,1982.
Response 1.b.
The determination of the location and size of a bubble can be made by monitoring plant process parameters, mainly primary and secondary system temperatures and pressures, during the transient. If a bubble develops in the hot leg of such a size as to decouple the primary and secondary systems, thereby initiating an interruption of heat removal via the steam generator, the operator is directed to bump the pumps or use the high point vents to remove the bubble and reestablish natural circulation. Decoupling of the steam generator is noted by the difference in temperature between the cold leg RTD and the steam generator saturation temperature. In addition, the steam generator pressure will decrease and, for small breaks wherein the steam generators play an active role, the primary side pressure will increase. The decoupling can be further confirmed by depressuring the steam generator and noting no accompanying change in the primary system.
Following the removal of the bubble in the hot leg and the establishment of natural circulation, the operator is expected to be able to recognize a reactor vessel head bubble by monitoring the effect on pressurizer level of opening the PORV. Methods for removal of a bubble in the reactor vessel head are provided in Section 3.2 and 3.3 of the CR-3 Operating Guidelines for High Point Vents.
The determination of whether a bubble in the primary system is mainly composed of noncondensable gas or of steam is not of particular significance. Either type of bubble can hinder the reestablishment of or interrupt natural circulation cooling if the bubble becomes too large.
i REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Page 2 Response 1.c.
The use of the PORY in conjunction with HPI (for depressurization and volume control for transients wherein the steam generator heat sink is not available) is bein into~ Abnormal Transient Operator Guidelines (ATOG) g incorporated (ref. Item I.C.1 of NUREG-0737). The high point vent system will not be utilized for this control.
.- Question 2.
The guidelines. state that the. operator will open the hot leg high point vents when the refill phase of the accident commences. In practice, the operator has no means to determine whether steam or saturated water is present in the hot legs, and will probably not notice a difference between natural circulation and steam condensing heat transfer modes. A transi-tion from one heat transfer mode to another may be obscured by temporary operation of the pressure vessel internal vent valves between the cold and hot legs. Discuss in detail how timely venting can be assured and present the necessary diagnostic and operational steps in explicit guideline form.
Response 2.
For the small break LOCA cases wherein the steam generators play an active role in removing a portion of the core decay heat, the high point vents can be utilized, if the RC pumps are not available, to remove trapped gases in the hot leg and to return the primary system to subcooled natural circulation. In examining the usage of the vents, as documented in the CR-3 Operating Guidelines for High Point Vents, it was found that the period of the transient for which the utilization of the vents will be most effective is the refill period. As discussed in Section 3.1 of the CR-3 Operating Guidelines for High Point Vents, during the afill period of the transient, the level in the primary system will rise above the elevation of the emergency feedwater inlet nozzles. This will result in a cessation of the boiler-condensor (steam condensing) heat transfer mcde. Since the steam generator will cease to be an effective heat sink for the primary system, the RCS pressure will increase thereby indicating a "decoupling" of the primary and secondary systems. This will alert the operator that -
he is changing from one mode of cooling to the other.
Timely operation of the vents is assured in the following manner. First, vent operation is initiated only on a recognized need, i.e., lack of primary and secondary system coupling. Second, vent operation, once instigated, is continued until subcooled natural circulation is established. Subcooled natural circulation can be determined from system parameter displays and is measurably different from two phase natural circulation or - boiler-condensor heat transfer mode by the subcooled nature of the hot leg temperature. The slight discharge of inventory through the vents, caused
- by leaving the vents open until acceptable subcooling is reached, is necessary to assure full development of the desired cooling mode. This discharge does not pose significant adverse consequences as the discharge is less than the definition of a LOCA (see Response 6). In this situation, timely operation of the vents means positive assurance that, following the initiation of the refill mode, the transition to solid natural circulation is permanent.
REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Page 3 The operator, in fact, can't determine whether the plant is in the two-phase natural circulation cooling mode or the boiler-condensor mode of operation. However, as long as coupling is maintained, the operator can continue the cooldown with the steam generator. The operator will be able to determine if decoupling occurs as described earlier. The operator will then reestablish natural circulation by bumping the pumps as the pre-ferred method or using the high point vents if pumps are not available.
The detailed, explicit operator guidelines for utilizing the high point vents (HPV's) are being developed at this time. These guidelines will be created in the ATOG format for future inclusion into ATOG procedures.
Question 3.
Section 3.3 states that once natural circulation is established and temperatures in the hot and cold legs are between 500F and 1000F subcooled, the operator is to depressurize the plant with the PORV. We assume this applies to plants without vessel head vents. Mnreover, this depressurization rate is based on assuring that the rate of expanding steam from the vessel head into the hot legs is less than the relieving capability of the hot leg high point vents in order to preclude a net accumulation of steam at the top of the hot legs and interruption of natural circulation. The staff disagrees with this method of depressuri-zation for the following reason:
The depressurization rates provided in Figure 2 appear to be based on computer analyses.
B&W and their customars have yet to satisfactorily demonstrate to the staff the adequacy of their analy-sis models to properly predict the transport of steam in the vessel and primary coolant loops under transient and accident conditions, including post-LOCA. As such, we believe the uncertainties in the depressurization rates to be unquantified, and the consequences of incorrect depressurization significant.
We, therefore, request that you identify a method of depressurizing the primary system which does not rely on computer calculated curves and does not involve a risk of interruption of natural circulation.
Response 3.
Section 3.3 of the CR-3 Operating Guidelines for High Point Vents describes the removal of noncondensable gases or steam in the reactor vessel head for plants without reactor vessel head vents. The depressuri-zation rates shown in Figure 2 of the CR-3 Operating Guidelines for High Point Vents are not based on computer analyses.
The curves were developed using hand calculations as follows: It was assumed that the plant is in subcooled natural circulation with the reactor vessel head filled with hydrogen down to the outlet nozzles. At any given pressure the 3
volumetric capability (f t /sec) of the high point vents to remove the hydrogen gas can be calculated. This sets the allowed expansion rate of the hydrogen gas in the reactor vessel head to the hot leg. The ideal gas law was then utilized to translate the gas expansion rate into the maximum allowable depressurization rate which assures natural circula-
l REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Page 4 tion would not be interrupted. (The depressurization rates of the PORV and pressurizer vent, if installed, were calculated based upon.a steam discharge.) It should be noted that the expanding hydrogen gas bubble in the reactor vessel head is assumed to accumulate only in the hot leg high point vent region and none of the gas goes to the pressurizer. This leads to the worst case noncondensable gas accumulation rate in the high points of the hot leg. Thus, if the actual RCS depressurization rate is controlled within the maximum RCS depressurization rate then natural circulation should not be interrupted.
If natural circulation is interrupted during the venting of the vessel head, the operator is instructed to stop the depressurization and to re-vent the hot leg to reestablish natural circulation. Since core cooling would be maintained even with an interruption in natural circulation, the effect of losing natural circulation momentarily has little safety significance.
The hand calculations described above are for a noncondensable gas bubble in the reactor vessel head as opposed to a steam bubble. Since the hot legs will be significantly subcooled relative to the reactor vessel head
(~500F), any steam entering the hot leg from the reactor vessel head area would be condensed. In addition, if the subcooled margin is lost, the depressurization will be stopped until an adequate subcooled margin is restored. Thus, the above described procedure is equally effective for a steam bubble in the reactor vessel head.
Question 4.
During conditions of inadequate core cooling, the operator is instructed to open the high point vents. Another instruction is to start the RCP's. If the pumps are started, can a slug of water impact the reactor vessel head or hot leg piping at the high point vent location? If so, is the vent system designed to withstand the dynamic loads associated with these water slugs?
If not, what precautionary measures are provided or will be provided to preclude pump start with the vents open?
Response 4.
The CR-3 specific operator guidelines instruct the operator to close the high point vent valves upon recovering from inadequate core cooling, i.e.,
the core exit thermocouples returning to saturation. This is prior to continuing with the normal small break guidelines for establishing natural circulation. Therefore, the valves will be closed prior to bumping the reactor coolant pumps to promote the initiation of natural circulation.
Question 5.
Recently, a number of plants with B&W-designed NSSS's have experienced bubble formation in the hot leg piping while in the shutdown cooling mode.
This has been caused by the flashing of stagnant hot water in the hot legs during depressurizing operations by the operator (the hot water was possib'y due to outsurges from the pressurizer).
What instructions are provided to the operator regarding the use of the vents to remove trapped steam under these conditions? In particular, should the vents be used or not? Consider that the containment may not
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O REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Page 5 be isolated and personnel may be in the containment. If vent operation under these conditions must be avoided, what provisions have been made to preclude vent operation?
Response 5.
In this case, wl.ere the plant is in the shutdown cooling mode and water has flashed to steam in the hot leg during depressurization, there is no problem of any safety significance. This condition would be noted by a rise in the pressurizer level and a subsequent loss of subcooling margin. If all other plant process instrumentation and incore instrumentation is normal relative to the shutdown cooling mode, the operator would limit the cooldown rate by procedures already in place until he demonstrates the pressurizer is the controlling pressure element in the primary system.
The operator is not directed to use the high poirit vents for the condition described above. Unless deteriorating conditions in the primary system were indicated, the use of HPVs during these circumstances is not needed.
In the unlikely event that deteriorating conditions in the primary system necessitated the use of the vents during the condition described above, the containment area would be cleared and appropriate actions taken to maintain containment integrity before venting. However, the clearing of containment and implementation of actions to maintain containment integrity would be prescribed by the deteriorating conditions, not the presence of a bubble in the hot leg during shutdown cooling mode.
Question 6.
Verify that the flow restriction orifice in each high point vent system path will limit reactor coolant leakage to less than the size corresponding to the definition of a loss-of-coolant accident (10 CFR Part 50 Appendix A) by providing the pertinent design parameters of the reactor coolant makeup system and a calculation of the maximum rate of loss of reactor coolant through a high point vent system flow restriction orifice (reference NUREG-0737 Item II.B.1 Clarification A.(4)).
Response 6.
The pertinent design parameters for the reactor coolant makeup system are discussed in Crystal River Unit No. 3 Final Safety Analysis Report Sections 6.1.2, 6.1.3, and 9.1.2. The calculation on the maximum rates of loss of reactor coolant through the high point vent system flow restriction orifice was performed using the JIP Computer Code (gal approved Topical Report GAI-TR-104, " Analysis of Thrust and 3et Impingement Forces Using the JIP Computer Program"). The flow restriction orifice was 3/8" internal diameter, and the code uses the Henry-Fauske Critical Flow Model for sub-cooled liquids to calculate critical flow. The results of the calculation show that at normal RCS operating pressure (2167.7 psia), a maximum reactor coolant leakage flow rate of 13.9 Lbm/sec through the orifice would be observed. This maximum leakage flow rate is less than the flow rate capability of the makeup pump and is, therefore, less than a LOCA per 10 CFR Part 50 Appendix A.
Question 7.
Verify that the portions of the high point vent system that are a part of the reactor coolant pressure boundary are classified Seismic Category 1.
REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Page 6 Response 7.
The Reactor Coolant High Point Vent System for the pressurizer and each hot leg has been classified as a Seismic Category I system.
Figure 1 identifies the seismic boundaries.
Question 8.
Describe the design features or administrative procedures, such as key locked closed valves or removal of power to valves during normal operation, that will be employed to prevent inadvertent actuation of the high point vent system (reference NUREG-0737 Item II.B.1 Clarification A.(7)).
Response 8.
Inadvertent actuation of the high point valves on the pressurizer and each hot leg during normal plant operation is prevented by the removal of power from these valves by opening selected breakers in the power circuit.
An open-closed status, as well as flow indication status, is available through the use of a separate power source.
Question 9.
In Section 4.2, page 1 of Attachment I to your July 1,1981 submittal, a summary evaluation of the vent discharge area is provided but does not adequately address all of our concerns. Demonstrate, using engineering drawings and design descriptions as appropriate, that the high point vent paths to the containment atmosphere discharge into areas:
a.
That provide good mixing with containment air to prevent the accumulation or pocketing of high concentrations of hydrogen, and b.
In which any nearby structures, systecns, and components essential to safe reactor shutdown or mitigation of the consequences of a design basis accident are capable of withstanding the effects of the anticipated mixtures of steam, liquid, and noncondensibles discharg-ing from the vent system (reference NUREG-0737 Item II.B.1 Clarification A.(9)).
Response 9.a.
The reactor coolant high point vent systems are located in areas that have provisions for good mixing with containment air. There are missile shields above the pressurizer. However, there are no missile shields over the remainder of that compartment (or over the other steam generator compartment).
Therefore, the accumulation of hydrogen over the pressurizer is considered unlikely.
The reactor building ventilation system is designed such that an air supply duct system is located below the RCS high point vent system at elevation 110'-10" with the pressurizer and steam generator compartments. The designed vent systems are located approximately between elevations 160'-
0" and 180'-6". An additional air supply system is available at elevation 190'-0", just above the high point vent system. The air supplied from these lower elevations is returned and recirculated through an exhaust system located above the vent system at elevation 228'-0". See Figures 2, 3,4, and 5 for reference.
REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES Page 7 Response 9.b.
The reactor coolant high point vent piping is routed in such a manner that it avoids safety-related components essential to safe reactor shutdown or mitigation of the consequences of a design basis accident.
Question 10.
Verify that provisions to test the operability of the high point vent system are a part of the design and that the testing will be performed in accordance with Subsection IWV of Section XI of the ASME Code for Category B valves (reference NUREG-0737 Item II.B.1 Clarification A.(ll)).
Response 10.
The design of the reactor coolant high point vent system does consider the operability testing of the valves as part of the provisions in the design criteria. The manual and solenoid operated valves have been tentatively identified as Category B type valves per the definition discussed in Section XI, Subsection IWV-2000 of ASME Boiler and Pressure Vessel Code 1974 Edition and Addenda through Summer, 1975.
This classification will be verified and any appropriate testing specified by the CR-3 Inservice Inspection Specialist.
Question 11.
Verify that all displays (including alarms) and controls, added to the control room as a result of the TMI Action Plan requirement for reactor coolant system vents, have been or will be considered in the human factors analysis required by NUREG-0737 Item I.D.1, " Control-Room Design Reviews."
Response 11.
All displays (including alarms) and controls, added to the control room as a result of the TMI Action Plan requirement for reactor coolant system vents will be considered in the human factors analysis required by NUREG-0737, item I.D.1, " Control-Room Design Reviews".
Question 12.
Verify that the following high point vent system failures have been analyzed and found not to prevent the essential operation of safety-related systems required for safe reactor shutdown or mitigation of the consequences of a design basis accident:
a.
Seismic failure of high point vent system components that are not designed to withstand the safe shutdown earthquake.
1 b.
Postulated missiles generated by failure of high point vent system j
components.
c.
Dynamic effects associated with the postulated rupture of high l
point vent piping greater than one-inch nominal size.
l d.
Fluid sprays from high point vent system component failures.
Sprays from normally unpressurized portions of the high point vent system that are Seismic Category I and Safety Class 1, 2, or 3 and have instrumentation for detection of leakage from upstream isola-tion valves need not be considered.
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l REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION REQUESTS AND RESPONSES g
Page 8 Response 12.a. All components of the high point vent system are Seismic Class I.
Response 12.b. The design considerations for this system did not take into account g
postulating a missile generated by failure of the high vent system WI components, since piping and solenoid operated valves are secured by seismically qualified restraints.
- Response 12.c. All piping in the high point vent system is one-inch or less nominal size except for a short run of two-inch piping on the discharge end necessary to install a flow meter.
The dynamic effects associated. with the
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postulated rupture of this greater than one-inch nominal pipe size was not analyzed since:
the high point vent system components are Seismic Class I; the system is secured by seismically qualified restraints; and the piping is just a short run on the discharge end of the system.
Response 12.d. The reactor coolant high point vent discharge piping is routed in such a-manner that failures will avoid fluid sprays onto safety-related,
components.
- Question 13.
Describe the criteria used for sizing the high point vent system with "'
regard to its function of venting noncondensible gases from the reactor L coolant system (reference NUREG-0737 Item II.B.1 Clarification A.(3)).
Response 13.
Babcock and Wilcox document number 86-1107003-00 titled "High Point Vent Design Requirements and Design Inputs" was utilized for sizing the w
high point vent system. This was included in our letter to Mr. Denton on^ ^
April 11,1980, and is attached here for your convenience.
Question 14.
Section 6.3, page 4 of Attachment I to your July 1,1981 submittal, stat'es that all electrical portions of the high point vent system for the hot leg "two position" (on-off) valves will be Class. lE. ! Verify that the valves in
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the pressurizer portion of the high point vent system will also be Class 11E
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'A and that all high point vent system valves will be provided with Class IE, electrical power (reference NUREG-0737 Item II.B.1 Clarification A.(8)).
i Response 14.
The RC high point vent valves located on the pressurizer and each hot leg, m are designated as Class IE. Class IE,125VDC power is used to operate 3 each of the vent valves. The valves associated with the pressurizer and _
f Hot Leg A.are powered from DC system "A".
The remaining valves l
associated with Hot Leg B are powered from DC system "B".
y Three separate 125VDC Engineered Safeguard distribution panels are provided to power the valves (one for each vent location). The power cables ~are designated Class IE and are routed in accordance with the separation criteria stated in Crystal River Unit No. 3 Final Safety j
. Analysis Report Section 8.2.2.12.
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f Q$estion 15.
On page 5, of the Operating Guidelines, it states that when the RC pumps 3
s are not available; following a SBLOCA for removing trapped gases from the RCS.high pobts the hot leg vents can be utilized. Moreover, the first
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q sentence 4 astion 3.1 (page 6) states that operator ' action will be, i
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,t required to1op n the vents during small break transients.
It is our understanding that neither the RC pumps nor the high point vents are considered to be part of 'the engineered safety features (ECCS) and are
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?not ' required to be operaWe following a LOCA. Previous ECCS analyses 1y Mmitted on ligense-applications for plants with B&W NSSS's were not performed beyornfhe start of primary system inventory recovery and it g'
N was assumedy:bati h gle phase natural circidation would be reestablished s5 without'thesaid of either the RC pumps or the high point vents.
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E Please state whether or notvceration of the RC pumps and/or the high point. vents are necessyy in'c,rder to reestablish single phasc natural circulation following a sb'.iOC6,, If they are required, justify'why they are not considtred 93rt_of the engineered safety features, and required to i %
meet the de ign requirements oFESPs. If they are not required, provide i
the supporting analyses for SP8 OCA's which demonstrates that single phase natural circulation will tablished following recovery from a
, N SBLOCA. ; Discuss how steam j in the RCS high points (vessel bend, e
T' hot leg.'.* candy cane") will be condensed or removed and not inhibit natural
,', cirthi.ation or long-term cooling of the core, per the requirements 'of
' IUCIT 'i0.46(bX5).
, as Whhn cons.idering the need of the high point vents take into account also the possibility of an early break isolation which takes place during the peyiMetween interruption of natural circulation and start of steam cqea5mg heat transfer.
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The, long,,t[rm coo @g requirement of 10CFR50.46(b)(3) does not specify s
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the ;reestAfishment i of. single phase natural circulation as a design l
objective.$ather, 'It states that the..." core temperatures shall be I
maintained at an acceptable low value and decay heat shall be removed for_ the attended period of time required by the long-lived radioactivity l
remaining in the core." The long term cooling of the core, as required by 10CFR50.46(bX5), is provided by assuring that the core remains cov,ered
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(HP1 and LPI have been designed to take suction from the reactor building i
l sump, thereby assuring an indefinite supply of coolant. The SBLOCA
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, evaluations demonstrate that the ECC systems satisfy this requirement'.
., c $ ;It has never been assumed that single phase natural circulation would be i
reestablished following design basis SBLOCAs.
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Operation of the RC pumps and/or the high point vents is believed necessary in order to reestablish single phase natural circulation during catain small breaks. The range of break sizes, for which the reestablish-ment of single phase natural circulation would aid in bringing the plant to
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g REACTOR COOLANT SYSTEM VENTS ADDITIONAL INFORMATION '
REQUESTS AND RESPONSES Page 10 cold shutdown, is bounded by the largest break size for which natural
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circulation would not be lost (approx. 0.005 ft ) and the smallest break size for which the RCS pressure spontaneously depressurizes to the LPI 2
setpoint (approx. 0.05 ft ).
For breaks which are isolated during the period between the interruption of natural circulation and start of steam condensing heat transfer, the RC pumps or ' vents may be used to reestablish single phase natural circulation. However, if the steam bubble in the hog leg U-bend is small, it may be possible,to reestablish natural circulatior by pressurizing the system with the HPI system.
Alternatively, the plant would evolve to a high pressure and displace sufficient inventory through the PORY or code safety valves to establish a boiler-condensor mode of heat removal.
Although the RC pumps or high point vents may be required for the
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establishment of single phase natural circulation, the long term cooling 4
j requirement of 10CFR50.%(b)(3)is met without utilizing the RC pumps or Pe the high point vents. The present SBLOCA transients have been analyzed past the point at which the primary system pressure is controlled by the break, at pressures below the steam generator secondary pressure, or by the steam generator in a boiler-condensor mode of cooling; the core has been recooled; and the ECC injection exceeds the cere bolloff. Since the core decay heat continues to decrease thereafter, the ECC systems are thus assured of providing adequate makeup to keep the core covered l
provided that primary system pressure can be controlled.
Pressure control is pr.vided by the break, for the larger SBLOCAs, and by use of 4'
'.the steam generator for the smaller breaks. Since the condensing surface j
core, primary system pressure will be controlled at a value which assures
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in the steam generator is located at an elevation above the top of the that the HPI will keep the core covered for the long term. Additionally, i
J since the HPI and LPI systems can take suction from the containment sump, following the emptying of-the borated water storage tank, long y
term ECC injection is assured.
As seen from the foregoing discussions, long term cooling of the core for 7
a SBLOCA is maintained without the' need to establish single phase natural circulation. Thus, the RC pumps and the high point vents are not required to be a part of the engineered safety features. It is our belief '
that the use of available plant equipment, whether or not it is " safety grade", which aids the operator in managing the plant during a transient or accident,. should be identified in the operator guidelines. Thus, the operator guidelines. contain instructions for utilizing the RC pumps and the high ' point vents for the purpose of returning the plant to single phase natural circulation.
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CALCULATION DATA / TRANSMITTAL SHEET CALC.
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DOCUMENT IDENTIFIER TRu S. 86
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T1TLE_YlGil Pott /T~ VW DE.5/GM Rf001/26s fein/73 AND bE.s;tG/V /syyy~~
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DATE /2//f[7/ TITLE b e'
DATE/8/L*//f TITLE PURPOSE:
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SIDE!ARY OF RESULTS (INCLUDE DOC. ID'S OF PREVIOUS TRANSMITTALS & SOURCE CALCULATIONAL PACKAGES FOR TilIS TRANSMITTAL)
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BWNP-20211-1 (1-78)
!.ICENSING DOCITMFNT APPPOVAT, DOCtiMENTTLTLEhNO._YICA OIMT* Y6H1" hf.5/doV Nff)O/EA/*1fAf75, f/d/V //VR/7 LICENSING ENGINEER _ k[ UE/6/r 7~~
DATE Md /f, /97f I
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Oes^a 10etc^t Tecit serc-e^Gt -
& D0C. ID-SERIAL-REV NO.
CONTlW.T/ CUSTOMER / PLANT
/ 7[ OMY[M IF CllNiGE REQ'D. BY CI/A. LIST CI/A NO.
DOC./Cl! APT./ SECT./
PREPARER PREPARER'S MN ACER*
QUESTION NO.
NMIE, SIGNATURE 6 DATE S[NAJ1JPffr DATE j
8(p - //O 7 00 3 - co DJ ft/27N 0ll 8N /WZD/79 hbOA?MACN JG/20/79
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- Reviewed for technical accuracy including adequacy of calculational models or metbods and consideration of design requirements documents.
REVIEWER (See Matrix) - Document reviewed to ensure that system requirements and i
interfaces are consistent with overall plant design requirements.
SIGNATt!RE & DATE
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^! * * !M LICENSING - Documery[/evi~ued for organization and for compliance with SRC re<.irements, f o Mon t en t and for compatn ' It wi; "har 1tr.cr ing commitments.
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M4 LTE /dGNATURE & DATE IJtEfS N'G MANAGfE'S SIGNATURE & 6 ATE Cencurrence with the necessity tor a Research and Develooment program.
S IGN ATI m._ 'RE 6 DATE FOR TECll.
SPECS. ONLY RELEASED BY 6 DATE REVIE'RD BY a DAfE
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<,.,* c,s ENTING DESIGN CRITERIA l 6
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177 IIIGli POIrlT VEtlT OLSIGft CRITERIA A.
Summary Description Various postulated small breaks can lead to accident scenarios in which steam and/or non-condensible gases accummulate in the reactor vessel head, the upper portion of the hot legs and in the pressurizer. Following repressurization of the RCS by HPI,Phich will tend to collapse steam bubbles, remotely controlled vents on the upper hot legs and pressurizer can be used to vent non-condensible gases to aid in refilling the RCS and promoting natural circulation. flow for core cooling.
B.
Piping and Valving Considerations 1.
Vents shall be provided at the following reactor coolant system high points:
Top of each hot leg (2 vents total, one per hot leg) a.
b.
Top of pressurizer (1 vent)
Top of reactor vessel (2 vents - optional, not recommended by B&W) c.
2.
Vent piping and valving shall be designed and sized such that the failure to close off any one (1) of the vent points listed above could not cause a loss of coolant at a rate in excess of the normal makeup system capability at full design RCS pressure.
3.
The effluent flow from all vent points shall be route / " ectly to the containment atmosphere. The region into which the disc.." ge is diverted shall enhance mixing and dilution so as to minimize the potential for local regions from reaching flammable concentrations of gases.
Discharge needs to be routed and directed so that liquid effluent can not discharge on or fall on electrical equipment or mechanical operating equipment.
4.
The piping and valving for the venting system shall be routed, oriented and protected so that damage from pipe whip, jet impingement and missiles
~.
will not occur.
5.
Pipe routing, orientation and elevation shall assure that all remotely
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operable valves are (a) located well above the maximum level of water in C
the containment expected for the worst case DBA and (b) protected from the containment spray and relief discharges. Each vent shall be designed to remain functional after all design basis events except large LOCA's, evacuation of the Main Control Room and loss of all AC power.
6.
Vent piping and valving shall be designed for 2500 psig and 670 F and any gaskets or seals shall be compatible with all anticipated effluent fluids.
This includes water, saturated steam, steam wa'.er mixture, superheated steam, fission product gases, helium, nitrogen and hydrogen. Provisions for venting hydrogen shall include the necessity for spark free valves.
7.
Each venting point shall be individually operable independent of any other point vent. Operator guidelines shall be provided to reduce the possibility of venting from more than one vent point at a time and to minimize the possibility of excessive RC system depressurization.Ref.
k Section B2.
8.
All piping and valving shall be connected to the RCS and supported in such a manner so that any stress due to weight, thermal transients, internal piping conditions and external environment will be within the maximum allowable stresses at the existing vent nozzles. Piping shall be designed to prevent the formation of traps and minimize the possibility of water and/or steam hammer.
9.
Existing nozzles in the RC System shall be used for the venting system.
i No new nozzles shall be added exclusively for venting.
If it is desired j
to incorporate the optional reactor vessel vent, one of two (2) locations shall be used:
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A vent line may be connected to a blind flange covering a CRDM mounting a.
nozzle if there are any without a rod drive mechanism in place.
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b.
Otherwise, a vent line may be connected to the venting port of a rod drive mechanism closure.
- 10. General RV Vent Requirements a.
If either of the above options are implemented, the RV head vent valve shall be located on the upper working platform of the service support structure. The valve and connections shall be protected from damage by personnel working on the service structure platfom. Vent tubing to the valve shall be routed under the support structure work platfom to avoid damage by personnel with access to that area. Con-sideration shall be given to preventing the vent line from being damaged at the point where it passes under the work platform.
b.
The discharge line from the vent valve shall be routed away from the
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service structure in a fashion to preclude vented liquid effluent from wetting the CRDM's, or any other nearby electrical device or cable.
- 11. RV Venting from a CRDM Closure a.
rio more than two APSR drives shall be used for the RV vent.
Each vent line shall be connected to a closure venting assembly which has been modified for this purpose. The vent line shall not be attached to any of the shim or safety rod drives without appropriate considerathn of ejecting a control rod during the venting process.
b.
The remotely vented closure (s) shall be modified to 1) accommodate the fitting for the threaded vent line connection, 2) remove the vent valve assembly.
c.
Except in an emergency, the APSR drive shall not be vented with the RCS temperature over 300 F.
If vented at temperatures in excess of
(
300 F, the plant shall be shut down and the closure assembly o-rings replaced unless it can be detennined that the closure assembly had not - - - -
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exceeded 300 F.
d.
Unless the venting of the APSR drive aoove 300 F is considered C
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a Faulted Condition, the CRDM Code Stress Report shall be revised to implement the thermal transients due to hot RCS water flowing through the drive mechanism.
Tests or analysis shall confirm that the pressure boundary design e.
temperature of the vented APSR(s) shall not be exceeded during the venting operation.
- 12. RV venting from a drive mounting nozzle If the RV vent is incorporated into a blind flange covering a vacant a.
CRDM mounting nozzle, the vent hole shall be small enough to limit outflow to less than nomal makeup system capability at full design RCS pressure.
- 13. Two remotely operated isolation valves mounted in series shall be provided to control the vent flow. The two CROM vent lines shall be tied together and controlled by the same two valves.
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- 14. All remote operable "two position" (on-off) valves shall be of the fail closed type, with power required to open and power requircd to maintain open. Valves shall have proven fail " closed" action on loss of power.
No packings are pemissible.
C.
Control and Instrumentation Considerations 1.
All valves for any one vent nozzle shall be powered from a supply separate i
l from that which powers the valves for any other vent nozzle so' that any single power supply failure cannot cause a failure to vent at more than one vent nozzle. Vital power supplies shall be provided for all of the I
vent isolation valves. Complete vent shutoff of any one vent nozzle shall be assured on loss of all power to its venting system.
(.. _ _... _ _.
i__
2.
Control of vent valves shall be remote manual and operable from the control room only. There is no requirement for operation from any
(
auxiliary location. Direct indication of valve positions shall be provided in the control room.
3.
Control of valves for any one vent point shall be independent of the control for valves for any other vent point.
4.
Both vent valves at a vent point shall be powered by the same power source, but controlled by two (2) independent switches. An alarm shall indicate both valves are energized.
5.
The vent valve operating switches shall be such that the vent valve will not open when power is applied to the switch.
It must take an independent action to operate the switch.
D.
Operating Guidelines and Modes 1.
The venting system may be used to vent the RCS during RCS filling operations if no venting system functional requirements are violated.
~
2.
Priorities of system design shall be as follows:
a.
RC system integrity b.
Capability to vent to containment atmosphere 3.
Special precautions shall be taken to prevent any unauthorized venting.
Such precautions shall be in addition to normal administrative controls.
Particular restrictions shall be applied to the optional CRDM venting point,.,so that venting from this point is limited to emergency conditions only. Ref, B11 above.
E.
Testability 1.
Provisions shall be made for testing all portions of the venting system at any time during startup of the plant. Testing shall consist of the b
following:
b.
r, a.
Confimation of free flow passage from each vent point. This will include exercising of all valves and checking the flow.
J Flow indication need only indicate that flow is present, and quantification is not required. Such testing shall normally be done during initial fill.
b.
Confirmation of vent shutoff capability shall be established by initially filling the vent lines during pre service hydro and establishing effluent flow into the containment with the vent valves open. The vent valves in each vent system will then be closed till effluent flow is observed to cease.
If it does not cease after a few minutes and continues at some observable rate this should be quantified by timing flow into a. vessel of known volume. A leakage rate in excess of 10cc per hour from a vent" system at pre service hydro pressures shall be considered unacceptable No ex;ernal leakage is. permissible.
c.
Flow indications which have been previously tested shall be monitored to assure that gross inadvertent venting is not occurring during normal reactor operation. Ref. Section Ela above.
F.
Thermal Stress and Insulation Considerations 1.
When practical, effluent piping from the high point vent nozzles to the vent valves shall be themally insulated to:
a.
Provide piping protection b.
Reduce heat losses c.
Min:imize piping stresses i
d.
Provide personnel protection 2.
Provisions shall be made to minimize thermal stresses due to venting, b
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so that intermittent venting can be tolerated..
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d.
Refueling Considerations
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The optional venting system for the RV head shall be designed for convenient h
dismantling during refueling with a minimum o. perturbation to valving and electrical connections.
11. Environmental Qualifications 1.
The high point vent system shall be designed to maintain its integrity and function for the lifetime of the plant, assuming periodic replacement of consummables.
2.
All components located inside primary containment shall be qualified to the maximum LOCA or main steam line break (MSLB) environmental conditions and to the process conditions stated in Section B6.
I.
Safety Classification 1.
All fluid portions of the. venting systems from the vent nozzles up
(
to and including all vent valves are part of the reactor coolant pressure boundary and as such are seismically qualified and classified per Reg. Guide 1.26 as safety class A or B, depending upon piping size.
2.
The valves shall be classed as active, subject to the requirements of Reg. Guide 1.48.
3.
As a minimum, all electrical portions of the system for hot leg "two position" (on-off) valves shall be class IE.
.e..
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A study was p2rformed to determine the flow rate of water, saturated steam, super heat steam and non-condensible gases throughHighPointVentValves(HPV). The v
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Ps P; = System Pressure at Vent P2 = Pressure at End of Vent Pipe P3 = Receiver Pressure K) = Flow Resistance k-factor of Vent Pipe X2 = Flow Resistance k-factor of All Down Stream Piping, Valves, Turns, etc.
V The venting rates will be a function of P, P, P ' E, X and type of fluid being j
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l 2
I vented. Since venting rates are a function of so many variables, the following restrictions were put on the calculations:
i
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(1) Minimum vent area is at the system exit (A) on figure).
(2) P,A,y,andP3 2 is always less than critical pressure are such that P j
2 for sonic flow rates.
(3) Non condensible gas temperatures equal temperature of saturated steam.
1 I
Minimum flow rates (with sonic velocities) of saturated steam and non condensible gas
~
as a function of K) and Pj are shown on Figures 1 and 2.
Superheated steam will have approximately the same Cp/Cv ratio as saturated steam and the flow rates will therefore be equal to the flow rates on Figure 1 times a correction factor.
This correction factor is equal to the square root of the density ratio of superheated to saturated steam.
Figure 3 shows ventino rates of. water as a function of the whole systern v
l k-factor and pressure per one square inch of vent area..Two phase flow will be assumed I
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as the linear ratio of saturated steam and water weighed by the psrcent quality j
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