ML20234D316
| ML20234D316 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Grand Gulf |
| Issue date: | 03/12/1974 |
| From: | Zudans Z FRANKLIN INSTITUTE |
| To: | Mckinley J Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20234A777 | List:
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| References | |
| FOIA-87-40 NUDOCS 8707070171 | |
| Download: ML20234D316 (15) | |
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ll THE FRANKLIN INSTITUTE RESEAHCH LABORATORIES iltfPH0nt (215) 44P 1000 i; 4 t t A D E L P H I A. P E. N N s T LV A N I A 19:45 i+ll (1 L t d J A M I N I N A N F t 194 PARFWAY a
S1H('li ANICAL AND N L ('lE All EN(.INICICILING IllCI' AICI'Sll'N'l' March 12, 1974 Mr. J. C. McKinley Senior Staff Assistant Advisory Committee on Reactor Safeguards United States Atomic Energy Commission Washington, D.C.
20545
Subject:
Grand Gulf Nuclear Station, Units I and 2 Subcommittee Meeting, San Jose, California, January 17 and 18, 1974.
Dear Mr. McKinley:
I have reviewed the working copy of the minutes of the subject meeting and have no comments to offer.
Very truly yours, Zen ZZ:ces Director
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i OFFACLAL Ube. Urtov ADVISORY COMMITTEE ON REACTOR SAFEGUARDS UNITED STATES ATOMIC ENERGY COMMISSION WASHINGTON. D.C. s0545 GRAND GULF NUCLEAR STAT _ ION, UNITS 1 AND 2 SUBCOMMITTEE MEETING WASHINGTON, D.C.
MARCH 6, 1974 Summary The Subcommittee met as announced in the Federal Register Notices dated February 11 and 22, 1974 to continue its review of the application 'oy the Mississip' i Power and Light Company for a permit p
to construct the Grand Gulf Nuclear Station, Units 1 and 2.
This was the fourth in a series of meetings on this application.
The Subcommittee discussed several items that had been reported as unresolved in the Regulatory Staff's Safety Evaluation Report and then took up the drywell design bases, suppression pool stratification, turbine missiles, suppression pool dynamics, guard pipes, pipe restraints, and hydrogen contre?.
The applicant was advised to be prepared to make a presentation on the guard pipe design for the 167th (March) ACRS meeting and to be prepared to discuss the hydrogen control problem and such other topics as may come up.
Attendees ACRS AEC D. Okrent, Chairman L. Slegers D. Moeller R. Tedesco L. Fox R. Cudlin
.W. Kerr G. Lainas J. C. McKinley, Staff G. Owsley W. Butler Aeroiet Nuclear M. D. Lynch C. F. Obenchain W. A. Paulson G. Niederauer C. Grimes J. A. Kudrick Southern Services, Inc.
L. B. Long Westinghouse NES C. L. Fredrickson Stone & Webster Engrg. Corp.
M. L. Boothby General Electric D. A. Rockwell J. Hench G. A. Esswein R. P. Barr L. J. Sobon ER1@TED.
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OFFICIAL USE ONLY Grand Gulf Meeting Date: 3/6/74 Attendees Continued Bechtel Power Corp.
Mississippi Power T. E. Johncon N. L. Stampley T. W. Haberma.
J. P. McGaughy, Jr.
V. A. Bert L. F. Dale J. K. Parikh A. S. McCurdy T. Mrozowski L. Nail M. A. Suavez A. J. Greere J. N. Awarez L. Pinzow R. A. Schnaible C. L. Reid F. C. Cheng M. C. Mauderly A. Conrad H. P. Marsh R. J. Peyton D. B. Heilig P. J. Garber N. Willowlby K. W. Stephene R. L. Ashley f
J. J. Tkacik Executive Sesssion (Closed).
Dr. Theofanous reported on the results of his visit to GE on February 27, 1974. He concluded that construction of the Mark III containment system could be allowed to begin at the applicant's risk with the understanding that the unresolved areas identified in the list dated February 12, 1974 (See Attachment A) would be resolved during construction.
He reported that an ECCS analysir had been made for Grind Gulf using the GETAB code. This analysis indicated only a 3% margin to critical power ratio. He noted that GETAB is a "best estimate" approach and questioned if 3% was an adequate margin. He also noted that the upper core reached the critical heat flux in tuo or three seconds while the l
middle core takes about eight seconds to reach the same point.
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urric1AL Udc unor Grand Gulf Heeting Date: 3/6/74 Dr. Theofanous reported that GE has done some work with jet pumps operating with quality at the suction. A proprietary topical report, NEDO-13239, is to be issued on this topic in the next several weeks.
Dr. Theofanous said that GE claims and has promised to document, that if no water flow is assumed to enter the downcomer region of the core, the reflooding time is changed by only half a second.
Further, if all of the water in the lower plenum is assumed to be lost the long term cooling model predicts that core reflooding would be changed by only one or two seconds.
Dr. Theofanous had been concerned that there might not be enough dissolved gases in the reactor water in the lower plenum to provide suf ficient nucleation sites for adequate lower plenum flashing. He has now been convinced that there is enough dissolved gas to assure lower plenum flashing.
GE is continuing to work on the refinement of blowdown forces on reactor internals and the effects of acoustic decompression.
Dr. Theofanous thought that he would have to wait to see the results.
During his visit, Dr. Theofar.ous received a hand written document supporting the noding and umss assumptions used in the vent clearing model. He thought that both the GE and Aerojet models were rather crude and he concluded that the addition of 30% margin was simply a matter of judgment to cover uncertainties.
Dr. Zaloudek did not share Dr. Theofanous' concern for the vent clearing model.
Dr. Theofanous asked GE to make a presentation to the Subcommittee on bubble formation and fluid flow in the suppression pool. He thought that the information provided in the quarterly reports on the confirmatory test program for the Mark III Containment was rather sketchy and should be more complete.
With regard to the quantification of splashing forces, GE is obtaining some data in the large scale test facility, but is waiting for the Swedish data that has been given to the AEC.
Dr. Theofanous is having some crouble accepting GE's claims for uniform temperature distribution in the suppression pool. He thinks that the surging effect of steam bubble collapse in the vents is limited to low flow conditions. GE has agreed to provide additional information regarding the flow regimes around the vents and relief valve discharges.
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OFFICIAL USE'ONLY Grand Gulf Meeting Date: 3/6/74 Dr. Theofanous expressed his continuing concern with GE's LOCA analysis which assumes discharge from the broken pipe according to the Moody model. He believes that the initial flow will be a subcooled liquid and that flow coefficients of one or greater can exist. If this is the case then the loss of fluid from the reactor system will be more rapid and the pressure reached in the drywell will be greater than currently predicted.
Dr. Zaloudek agreed with the potential for a brief period of subcooled flow but could not propose an improvement to the model. He thought that any improvement would be small. He believes that results from the blowdown heat transfer tests are needed in order to suggest further improvements in the analytical model.
Dr. Zaloudek continued to be concerned with suppression pool surface dynamics and the potential for uncovering the top row of vents. He noted GE'o claim that the containment could tolerate having the top row of vents uncovered for ten seconds or full LOCA flow for three seconds.
He also noted that there was no indication of GE investigations into water oscillations or wave action in the suppression pool. He also felt there were no valid data regarding potential stratification in the pool, however, GE is planning to perform some tests to obtain data in this area.
Meeting With Mississippi Power and Light Company (Open)
Regulatory Staff Items Mr. Owsley (AEC Regulatory Staff) reported on the status of the items that remained outstanding in the Staff's Safety Evaluation Report. The first of these items was the reliability of the cooling water supply to the recirculation pump bearings. Failure of this water supply could cause a simultaneous failure of both recirculation pumps, an unreviewed accident. The Staff position was that the cooling water supply had to be upgraded to safety grade. The applicant has proposed to provide a pump trip on loss of bearing cooling water and to evaluate the consequences of a loss of bearing cooling water. The Staff is currently evaluating these proposals.
Dr. Butler (L) indicated that if the trip circuit was designed to meet IEEE-279 requirements that proposal would be acceptable.
Mr. Owsley (L) noted that the applicant has proposed manual actuation of the containment spray syatem and the Staff had asked for automatic actuation. The applicant does not agree with the need for automatic actuation but has agreed to provide it.
Dc. Okrent noted that the Regulatory Staff position on the containment spray system had shifted between November 27,1973 (D. M. Crutchfield memo dated December 13, 1973 on GESSAR, SDN 50-447) and the present. At that time hk. Crutchfield indicated that the Staff would require a containment spray system completely separate from the ECC systems but OFFICIAL USE ORLY
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Grand Gulf Meeting Date: 3/6/74 now the containment spray is part of the RHR system.
Dr. Okrent asked the Staff to be prepared to discuss the reasons for this change in position at the next Subcommittee meeting.
Drywell Design Bases
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Mr, Cudlin (L) described the Regulatory Staff's BWR blowdown model used to calculate the peak drywell pressure. He used Slide 1 to illustrate the location of the various breaks that are assumed to occur in the various systems. For the Grand Gulf application the assumed rupture of one main steam line produces the highest calculated peak drywell pressure. A break in the recirculation line produces a calculated peak pressure slightly less than that calculated for a steam line.
m Mr. Cudlin useo Slide 2 to illustrate the GE models used to calculate the blowdcen frem a recirculation line break. Volume 1 represents
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the reactor vessel and intact recirculation loop while Volume 2 represents the balance of the ruptured recirculation loop. The break is assumed to have occurred at the suction of the recirculation pump. Flow from the suction pipe is based on its full cross sectional area while long term flow from the other side of the break is controlled by the cross sectional area of the jet pump nozzles. For the short term model, GE uses a factor of 0.5 on the Moody flow from the loop side of the break; the Regulatory position is that this factor has not been adequately justified and a factor of 1.0 would be acceptable to the Staff. Currently CE calculates it would take approximately 1.9 seconds to deplete volume 2 using the 0.5 multiplier; it would take less time than that using a multiplier of 1.0 and that would result in a higher drywell pressure. The applicant and GE have been asked to calculate the blowdown of the loop side of the break as a function of pressure in the loop. The applicant has agreed to do this. Based on the results of these calculations the Staff will establish a drywell design pressure.
Mr. Niederauer (ANC) described the Aerojet vent clearing model which utilizes seven nodes as shown on Slide 5.
This model is slightly different from the GE model. The Aerojet model assumes the water to be an incompressible fluid, the system is isothermal and undergoes branched single dimension flow. Slide 6 tabulates the rationale for using a seven node model.
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l Grand Gulf Meeting Date: 3/6/74 The Subcommittee had some difficulty in understanding why this model was adequate or better than the GE model, and why it should not give results closely approximating the experimental values since it used empirical coefficients derived from experimental data and adjusted to give the right retults. There was some question as to whether this model, adjusted to give test rig results, could accuarately predict actual containment performance.
Mr. Niederauer showed a sensitivity study in which the irreversible loss coefficients were doubled in one case and haived in another, the results are depicted on Slide 7.
Dr. Zudans pointed out that these are already in existance codes that depict three dimensional fluid flow and he wonderd why Aerojet did not utilize these.
He was told that this model was intended to predict vent clearing time only.
Mr. Rockwell (CE) said that the GE model is conservative (predicts longer i
time to vent clearing) compared to test facility results and although it uses few aodes, it is adequate. He believes the loss coefficients used by CE are appropriate.
Mr. Niederauer said that the Aerojet results agreed well with the GE results; GE predicted the top vent would clear in 0.9 see while Aerojet calculated 0.87 sec.
Mr. Tedesco (L) affirmed that the Regulatory Staff intended to preserve a 30% margin between the calculated peak drywell pressure and the design pressure but ongoing studies may result in a margin at the OL stage either more or less than 30%. He also confirmed the Staff's intent to require a 30% margin based on the best knowledge available at the time an application is reviewed for future plants.
Suppression Pool Stratification Mr. Cudlin (L) reported that the Regulatory Staff had not identified any stratification problems with this design but the potential will be investigated in the test program.
Mr. Rockwell (GE) thought that low flow rate tests were approximated near the end of every blowdown. At this point " chugging" occurs', this is the alternate action of vent clearing and condensation with water being pumped in and out of the vents. This pumping or surging action tends to cause mixing of.the pool. The first confirmatory tests starting with low steam flow rates are scheduled for the first quarter of 1975.
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OFFICIAL USE ONLY Grand Gulf Meeting Date: 3/6/74 In the unlikely event that severe stratification did occur in a real containment and the pool surface temperature rose to the point where the vapor pressure became a problem, the containment spray system could be actuated to cool and mix the pool surface. There may be other practical means to sasure adequate mixing.
Dr. Okrent recalled that rather severe damage occurred in the suppression pool at a foreign reactor when a relief valve was allowed to discharge for a prolonged period and the suppression pool temperature allowed to rise above normal limits. He asked if a similar condition could develop if there was severe stratification in the Mark III suppression pool and a small steam break were to occur.
Mr. Rockwell replied that two conditions were necessary to obtain the I
damage observed at the foreign reactor; one was to have a high pool temperature and the other was to have a high mass velocity of steam flow. Although high water temperatures could be postulated for Mark III the mass velocity through the vents is rather low. He referred to some German experimental work in this area.
Dr. Theofanous suggested that other phenomena may be at work in condensing steam flow that can produce high frequency acoustic energy and some rather severe pulsations. He does not believe all l
of the phenomena are completely understood. He does not believe GE has pressure transducers with the proper frequency response installed in test facilities. He thought that transducers with a frequency response of up to 20,000 bz were needed. He noted that rather simple experiments have shown that low steam flow rates can give very high acoustic pulses.
Dr. Okrent asked if the Regulatory Staff had access to the German experimental work, and, if it did, had the data been analyzed and what were the Staff's conclusions.
From the fact that Mr. Slegers spoke from his prior association with the German organization that performed the experiments, it was apparent that the Staff did not have the German data. The Staff is currently reviewing the data developed in Sweden at the Marviken reactor on low mass flow rate injection of steam into a suppression pool. In addition, some high mass flow rate (relief valve discharge) tests have been made at the Quad Cities, Unit 2 reactor.
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Grand Gulf Meeting Date: 3/6/74 l
In order to avoid possible damage from pressure pulses of steam discharging into hot suppression pool water, the applicant has agreed to place a Technical Specification limit on the maximum suppression pool water temperature at which reactor operation would be allowed. This limit is such that even after a reactor blowdown, the pool water temperature will not be high enough to cause severe pulsations.
Dr. Okrent asked the Regulatory Staff to be prepared to discuss what are acceptable maximum pool temperatures for various reactor operating conditions, at some future Subcommittee meeting.
Turbine Missiles Dr. Schauer (L) reported that the proposed containment meets the Staff's current requirements with respect to its ability to resist the penetration of turbine missiles. The Staff's tentative criteria are contained in something referred to as " Document A."
Dr. Schauer said that the references in the Safety Analysis Report and Bechtel's topical report B-TOP-9 describe design methods that will provide a containment that will conform to the Staf f requirements for missile penetration.
The Staff is currently having a study performed at the Naval Ordnance Laboratory regarding the missile impact resistance of structures.
Another program is performing a series of missile impact tests.
Dr. Schauer suggested that further discussion of these programs be deferred to a later meeting in order that the proper Staff personnel could make the presentations.
The Staff had not confirmed that the 4.5 f t shields adjacent to the low pressure turbine would prevent low angle missiles from striking the containment, but agreed that if the applicant calculated no penetration based on the methods of B-TOP-9 the Staff would accept that conclusion.
Mr.
Tedesco noted that the Staff is preparing a Regulatory Guide on Turbine missiles and is still trying to decide on an appropriate turbine overspeed condition for the generation of the missile, Grand Gulf has assumed the missile is released at 180%
of normal turbine speed.
Su_p.pression Pool Dynamics Mr. Rockwell (GE) described GE's concept of the air sweeping portion of vent clearing and the associated pool dynamics.
The analysis was qualitative, without much theoretical or empirical support. The initial condition of the drywell, suppression pool and containment is illustrated 0FFICIAL USE ONLY w_-__-______________
f 0FFICIAL USE ONLY Grand Gulf Meeting Date: 3/6/74 in Slide 10, the water level on both cides of the vents is equal and quiescent. About 0.8 see after the LOCA the water level in the drywell has been depressed far enough to uncover the top vent (See Slide 11) and air beings to enter the suppression pool, the surface of the pool near the drywell wal beings to bulge upwards. As the volume of the bubble increases the surface of the pool rises in a curved shape. At about 1.0 see much of the drywell air has been injected into the pool and the bubble is shown in Slide 12 about to break the surface due to bouyant forces. To break through the surface the bubble does not have to push the water completely away but only to make channels through the remaining layer of water. When the bubble approaches within one or two feet of the surface it becomes unstable and the surface breaks up allowing the air to vent into the containment as illustrated by Slide 13. This venting at about 1.1 see is accompanied by a great deal of water entrainment. What is thrown up is a frothy mixture of air and water. Once the bubble has broken through the surface there is a head of water on the containment wall side of the pool tending to push water back against the vents. After the air bubble is passed the pool settles down to a quasi-steady steady state with steam being condensed and a small amount of air bubbling through.
i GE's large scale test facility has a series of resistance probes on j
two foot centers in the vicinity of the vents that can give a three dimensional indication of the shape of the air bubble injected into the pool.
The applicant's preliminary calculations for platform loadings were more conservative than the model shown at this time. Initially the applicant assumed that the air bubble extended across the pool from the vents to the containment wall and accelerated the water above it as a solid mass, upward with increasing velocity. Based on this model the applicant calcula ted impact pressures of about 1800 pounds per square foot on a platform ten feet above the normal water surface and 2200 pounds per square foot for platforms twenty four feet above the normal surface (See MSP&L Co. letter dated February 6,1974). The applicant hav refined the model somewhat more in Amendment No.18 l
and intends to obtain load vs height data from the larga scale test facility. He contends that the current design is adequate but that it can be strengthened if later information shows this to be necessary.
Dr. Okrent noted that this was an area in which the analysis was changing rapidly and suggested that further discussion be put off to a future Subcommittee meeting.
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OFFICIAL USE ONLY t-Grand Gulf Meeting Date: 3/6/74 Dr. Zaloudek inquired into the effects of the test facility side walls on the pool dynamics and was told GE that the forces ascociated with pool dynamics were quite large compared to the sidewall effects.
Dr. Zaloudek explained that the sidewalls prevent the appearance of any circumferential effects.
Mr. Rockwell thought that there would be waves on the pooi surface and perhaps in a circumferential direction but he did not believe their amplitude would be great enough to interfere with the functioning of the vents. There was also some discussion of the forces on various pool structures as a result of surging of the pool water following vent clearing. The applicant had directed his attention to both vent clearing and seismic excitation of the pool but had not calculated the natural frequency of waves in this particular shape of pool.
There was also a discussion of the consequences of non-uniform steam-air mixing in the drywell as the vents cleared and the potential for some vents passing a high percentage of air while other vents were receiving I
a high concentration of steam at the same time. GE believes that the LOCA will cause turbulence and good mixing in the drywell and even poor mixing will not seriously alter the performance of the suppression pool.
Dr. Okrent did not feel assured that the Staff had independently confirmed that no unexpected phenomena would occur as a result of the three dimensional effects in the suppression pool.
Dr. Hench (GE) noted that when GE designed the large scale test facility it recognized that it would not represent circumferential effect.4 This fact was not overlooked but was recognized. GE recognized three areas that might be affected by circumferential effects. One was the peak drywell pressure; which is controlled by the time it takes to uncover the vents which would take place before serious surface disturbance occurred on the pool. The second is peak containment t
pressure which could be affected by vents being uncovered.
Dr. Hench pointed out that all of the air from the drywell is vented in the first two or three seconds which would be the exciting force for any oscillations.
Because of the size of the pool he would expect the natural frequency of ar.y oscillations to be greater than two or three seconds and would not be sustained. This would preclude significant bypassing of the pool.
The third affect would be wave impact forces on platforms.
These result from the air passing into the pool and had already been discussed.
Dr. Okrent expressed his hope that the applicant and the Staff could resolve these questions on three dimensional effects by the next Subcommittee meeting.
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,d 0FFICIAL USE ONLY Grand Gulf Meeting Date: 3/6/74 Cuard Pipes Mr. Habermas (Bechtel) identified ten high energy process pipes that originate in the drywell and pass through the containment. A failure of one of these pipca between the drywell wall and the containment wall could result in overpressurizing the containment. To minimize this possibility these pipes will be provided with guard pipes capable of containing a double-ended rupture of the enciesed process pipe and l
venting the fluid back into the drywell. The ten lines provided with this protection are; four main steam lines, two feedwater lines, one main steam drain line, one RRR shutdown line, one RCIC steam line, and one RCIC water line. All ten lines are brought through a common tunnel from the drywell to the containment wall.
An illustration of the conceptual design for the guard pipes is shown in Slide 8.
The guard pipe is anchored in the containment wall and thermal expansion movements are accommodated by sliding through the drywell wall. A testable bellows seal is provided al the drywell wall. This seal is arranged so that it experiences only drywell pressure and not guard pipe design pressure. The guard pipes are designed to provide access to the process pipe welds for inservice inspection (See Slide 8). Bechtel claims there is nothing new in this design since it has been used in other nuclear applications.
The Subcommittee discussed various aspects of the proposed design, including seismic requirements, the potential for bellows leakage, the desirability of carrying portions of the drywell outside of containment (the flued head), and the clearance and friction characteristics of the various pipe guides.
Dr. Okrent asked if the containment could tolerate the failure of both a process line and, its guard pipe and was told that was considered to be a double failure and was not considered. He also asked if there was any potential for the failure of one process line and its guard pipe to propogate to other lines in the pipe tunnel. He was told that there was some separation of the pipes but the matter was not explored in depth. Failure of any of the process lines does not af fect the capability to provide emergency cooling to the core.
Dr. Okrent advised the applicant that the subject of protection of these process lines would be taken up again at another Subcommittee meeting. He asked the Staff to be prepared to discuss its acceptance criteria at the next Subcommittee meeting.
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Crand Gulf Meeting Date: 3/6/74 Pipe Reatraints Dr. Zudans reiterated his concern for designing pipe restraints to use up 50% of their ultimate strain.
Mr. Esswein described the restraints and pointed out that their sole function was to inhibit pipe motion in the event of a rupture, to do this they need to absorb energy by plastic strain. After a great deal of discussion, it turned out that there are a sufficient number of restraints close enough together so that a failure in one would not result in unacceptable consequences.
Dr. Zudans appeared to be satisfied.
Dr. Okrent asked the Staff to be prepared to discuss its reasoning on the design of this restraint system at the next Subcommittee meeting.
Hydrogen Control Dr. Okrent asked if the applicant or any of his consultants had made a study of the reliability of the proposed hydrogen mixing system. He wanted to know both the probability of the valves opening prematurely and of the system failing to start.
l Mr. McGaughy stated that the systems were seismic category I and designed to IEEE-279 standards and therefore he felt that they were as reliable as any of the safety systems. He said that extensive tests had been performed on the valves proposed for this system but they had not brought the data with them.
Dr. Okrent asked for a probabilistic estimate for proper functioning of the proposed system for the next Subcommittee meeting.
Dr. Hench l
(GE) said that this study had not yet b en done but would be before the 9
I design is completed.
Dr. Okrent asked for GE's reliability objective in designing such a system.
Dr. Hench indicated it should be in the range of about 10-4 to 10~3 and he thought it could be achieved.
Dr. Okrent asked, what would be the consequences of a failure of the vacuum breaker function of the air circulation system valves. He was told that this could result in water overflowing the weir wall and flooding the lower portion of the drywell. No safety related equipment would be affected. In fact in a large LOCA this area fills will water which eventually spills back over the weir wall into the suppression pool.
Dr. Okrent was also told that if hydrogen was generated and released during the first 10 to 60 see of a LOCA it would be carried into the air depleted drywell and then over into the suppression pool and finally 0FFICIAL USE ONLY 1L
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' Meeting Date: 3/6/74 into containment where it would be adequately diluted. All va.ve actions associated with ECCS functioning and system isolation will have taken place before conditions favorable to hydrogen burning occur. Thus if the hydrogen did burn it would not affect any of the safety related components. The Staff had not evaluated this argument.
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