ML20207S515
| ML20207S515 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf, Clinton, 05000000 |
| Issue date: | 06/30/1986 |
| From: | Economos C BROOKHAVEN NATIONAL LABORATORY |
| To: | NRC |
| Shared Package | |
| ML20207S501 | List: |
| References | |
| CON-FIN-A-3346, CON-FIN-A-3396 NUDOCS 8703190591 | |
| Download: ML20207S515 (26) | |
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l Technical Evaluation Report (TER) for the Illinois Power Company's (IPC)
Clinton Power Station (CPS), Docket No. 50-461 on SER Outstanding Issue (8) -
Mark III Containment System Issues -
The Humphrey Safety Concerns (HSC) by C. Economos June 1986 I
Department of Nuclear Energy Brookhaven National Laboratory Upton,-New York 11973 Introduction e With three exceptions, this TER addresses only those HSC's that, by previous agreement with .the NRC staff, are considered BNL's responsibility. The three exceptions are the addition of the . issues related to HSC 4.4, 4.5 and 7.1. In 4
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earlier TER's (River Bend Station and Perry Nuclear Power Plant), these had been considered the responsibility of, the respective Technical Monitors. Notwith-standing these earlier decisions, we feel that BNL input in these areas is ap-
, propriate and have therefore included our evaluation here. Note that our con-clusion 'in each case is that the issues raised have been satisfactorily ' re-2: solved.
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, Humphrey Safety Concerns 1.1, 1.2, 1.4 and 1.5 1.1 Presence of local encroachments, such as the TIP platform, the drywell
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' personnel airlock and the equipment and floor drain sumps may increase the pool swell velocity by as much as 20 percent.
1.2 Local encroachments in the pool may cause the bubble breakthrough height to be higher than expected.
1.4 Piping impact loads may be revised as a result of the higher pool swell velocity.
1.5 Impact loads on HCU floor may be imparted and the HCU modules may fail, which could prevent successful scram if the bubble breakthrough height is raised appreciably by local encroachments.
Evaluation
- i The concern is that the presence of encroachments will tend to increa w non1 h-'
velocities and breakthrough height relative to the unencroached pool thereby causing increases in a variety of LOCA loads including bulk and froth impact and drag loads in regions above the initial pool surface.
As a result of the 1/10-scale simulations of pool swell conducted by the Containment Owners Group (CIOG) as reported in References 1.1.1, 1.1.2 and l 1.1.3, it has now been established that,.for the most part, the effect of encroachments is to decrease pool swell velocities relative to an unencroached -
or clean suppression pool. BNL has reviewed all of this information and has prepared a separate Technical Evaluation Report on its findings (Reference 1.1.4).
For those cases where pool swell velocities are reduced by the presence of
'. encroachments, this concern is considered to be resolved. For the CPS, however, one. instance of pool velocity increase was observed (Reference 1.1.2). This occurred directly adjacent to the containment wall with the so-called Clinton 11 encroachment in place. The excess in velocity was about 17%.
As discussed in Reference 1.1.4, the 1/10-scale tests can be shown to be overly conservative in terms of the way in which the pool swell was driven. This
, conservatism was quantified in Reference 1.1.4 by comparing the 1/10-scale clean pool tests with the 1/3 area scale PSTF tests (Reference 1.1.5) interpreted as '
i 1/3-scale geometric simulations by means of Moody's scaling laws. Note that the NRC specification of pool swell velocity is based on these latter tests. The i-conclusion based on this comparison is that the 1/10-scale tests overpredict peak pool velocity by about 80%. If it is assumed that this same correction applies to the encroached results, the peak measured velocity is found to be well below the peak value (50 fps) used for design basis loads.
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One additional concern that was identified in the CPS 1/10-scale tests was the j
' impact loading experienced by one of the encroachments that was examined (the Clinton II encroachment). This ledge, which extended three feet from the edge of the personnel and equipment hatch platforms, exceeded the established small i
structure criteria for bulk impact loads. The applicant addressed this concern
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in Reference 1.1.6 by developing an impact design load using the results of the 1/10-scale tests to determine a duration of impact (.019 secs) and combining this with procedures already approved by the NRC staff for this purpose. BNL has examined this proposed load methodology and concludes that it would represent an acceptable design load. The applicant has stated that the loads developed by :
this method are actually less than those used for the original design of the structure.
Conclusion BNL considers these issues closed for the CPS because the 1/10-scale tests have confirmed that encroachment effects on pool swell behaviour will not give rise to loading conditions that cannot be accommodated by the existing design basis.
References 1.1.1 Sets of slides provided by the CIOG to the NRC from the following 1/10-scale tests: (a) Clinton Tests F2R, ROS, and F5; (b) Grand Gulf Tests E3; (c) Perry Test 02; (d) an unidentified clean pool test (see lei.i.er of 19 March 1985 from J. E. forbeck to R. Pender, cc: J. Kudrick of NRC).
1.1.2 " Comparison of Velocities and Thicknesses of Water Column at Containment Wall for 1/10-Scale Pool Swell Tests", submitted by G. W. Smith of CIOG to H. R. Denton of NRC via letter of 15 May 1985.
1.1.3 Mintz, S. et al., "Clinton Plant Unique Encroachments Final Test Report",
General Electric Report MDE-36-0285, Attachment to IPC Letter No.
U-600006 dated April 29, 1985 from F. A. Spangenberg, (IPC) to A. Schwencer (NRC).
1.1.4 Sonin, A. and Economos, C., " Resolution of the Humphrey Issues Relating
' to Pool Swell in Mark III Plants", BNL Technical Evaluation Report, February 1985.
1.1.5 Ernst, R. J. et al., " Mark III Confirmatory Test Program-One-Third Scale Three-Vent Tests (Test Series 5801 through 5804)", General Electric Report No. NEDM-13407P, May 1975.
1.1.6 IPC Letter No. U-600020 dated May 16, 1985 from F. A. Spangenberg (IPC) to W. R. Butler (NRC).
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4 Humphrey Safety Concern 1.3
- Additional submerged structure loads may be applied to submerged structures near local encroachments.
Evaluation The loads addressed under this item fall into two categories: (1) loads on sub-merged boundaries ( trywell wall, basemat, containment wall) and (2) loads on submerged structures proper, such as pipes and beams.
A two-dimensional SOLAV01 simulation was employed to determine the effect of Clinton encroachments on these loads (Reference 1.3.1). An increase in the con-tainment wall load was predicted which is within the design load specification.
. Eor _ submerged structure loads, margins were obtained for all but one or two structures (References 1.3.1 and 1.3.2). However, all structures are stated to be capable of accommodating the increased loads.
Conclusion BNL considers this concern to be resolved based on the stated margin between design and the loads estimated with a conservative (two dimensional) simulation of the encroachment effect.
References 1.3.1 IPC Letter No. U-0714 Dated May 25, 1984 from D. I. Herborn (IPC), to A. Schwencer (NRC).
1.3.2 Mark III Containment Issues Review Panel, " Assessment of Humphrey Concerns", CREARE R & D, Inc. Technical Memorandum TM-928, July 1984.
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Humphrey Safety Concern 1.6 Local encroachments on the steam tunnel may cause the pool swell froth to move horizontally and apply lateral loads to the gratings around the HCU floor.
Evaluation The utility has performed a potential flow analysis of the flow field through the HCU floor (Reference 1.6.1). This analysis assumed steady flow, i.e., the liquid droplets had velocities equal to air and all of the froth was allowed to pass through the openings in the HCU floor. The resulting lateral pressures were found to be 0.45 psid on the beams and 0.26 psid on the gratings. Floor and grating loads are stated to be well within design limits.
BNL concurs with the utility claim that the potential flow analysis is conserva-tive. In fact, independent calculations conducted by the NRC indicate that over 90% of the froth will continue in the vertical direction, impact on the HCU floor and lose all its velocity. As the froth begins to fall back toward the pool, the horizontal component of the flowing air will accelerate the froth to some extent 'out steady-state conditions are not expected to be attained. Con-sidering that the additional stresses are modest even with a conservative flow analysis, BNL does not feel that additional effort needs to be expended on this issue.
Conclusion BNL considers this issue to be closed.
References 1.6.1 IPC Letter No. P23-83(05-31)6 dated 5/31/83, G. E. Wuller (IPC) to A. Schwencer (NRC).
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l, Humphrey Safety Concern 1.7 GE suggests that at least 1500 square feet of open area should be maintained in the HCU floor. In order to avoid excessive pressure differentials, at least 1500 square feet of open area should be maintained .'t each containment eleva-tion.
Evaluation The applicant has indicated that the CPS design provides open areas on all floors above the HCU floor greater than the open area at the HCU floor (Refer- s ence 1.7.1). The latter, at 1824 square feet, is substantially greater than the required minimum.
Conclusion Based on the above response, BNL considers this issue to be closed.
References ,
IPC Letter No. U-0562 Dated November 23, 1002 fron G. E. Wuller (IFC) to 'k 1.7.1 . ,
C. G. Thomas (NRC).
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,r Humphrey. Safety Concern 2.1 The annular regions between the safety relief valve lines and the drywell wall penetration sleeves may produce condensation oscillation (C.O.) frequencies near the drywell and containment wall stractural resonance frequencies.
EvaluatioU "
As stated above, the concern is th3t additional and unaccounted for suppression pool boundary l loads may be produced by steam condensation at the exit of the sleeve annulus. However, the scope of this concern is expanded considerably by Humphrey in Reference 2.1.1. There it is speculated that, due to resonant cou-pling between the sleeve annulus C0 and the sleeve annulus acoustics, the pres-sure loads atlnigher frequencies could be amplified.
The~ applicant first addressed this concern using the generic approach described n in Reference 2.1.2. This methodology derives sleeve annulus C0 loads by conser-s vatively s'caling down the main vent C0 load data base. The potential for reso-nant amplification of these loads was not addressed.
.l The use of the main vent C0 data base for development of sleeve annulus loads
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cannot be rigorously defended because of substantial differences in geometry.
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However, based on the relative size of tne steam / water interface that would
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, exist at the sleeve annulus, BNL would judJe that any additional non-resonant loads that may occur will be second order relative to main vent loads. This judgement applies to both C0 and chugging loads.
The added sleeve C0 loads that were first proposed are substantial. For exam-ple, the peak-to-peak pressure amplitude (PPA) was about 20% of that used in the main wntlo'ad definition. -They are also applied uniformly in the circumferen-tial direc3 ion which represel.ts a sizable conservatism. This is because there are roughl'y twice as many main ve.its as drywell penetration sleeves. These mod-Sifications are clearly more L)arj second order. Thus, provided it could have been demonstrited that resona.it amplification does not occur, the C0 loads which
( were specifiec Mcsld have been considered adequate.
' In an attempt to demonstrate the absence of such'a 40upling, the applicant cited results from General Electric's 4TCC tests (Reference 2.1.3). A review of this material indicated that the contrary was the case; that is, the data implied that the type of resonant cot.pling suggested by Mr. Humphrey was not only possi-bh but apparently had actually occurred. In fact, it can be inferred from this i data that resonance causes about a two-fold increase in the basic C0 loads.
I e As a result of this finding,.the applicant proposed a completely new methodology for the C0 boundary loads (Rcference 2.1.43. This methodology has been devel-oped by General Electric utilizing the Mark I FSTF data base (2.1.5). This new
},, ' design To'1dinastasults in a substantial increase in the pressure loading at the y s higher end of'tne f requency spe'ctru.a'(20-50 Hz). For example, in terms of an
' x\, amplified rasponse spectrum (ARSJ, the load intensity is about double the one first proposed. H ihese new loads' are shown to be; bounded by other design basis loads. For exam-ple, on the drfwell wall the new sleeve CC load when added to the main vent C0 is bounded by the chugging load sptcification. On the containment wall, the
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bound is provided, with considerable margin, by the pool swell brundary load.
The applicability of the FSTF data to the sleeve annulus loads involves consid-erable uncertainty because of the' great disparity in geometries betwean the two situations. This applies not only for the steam-water interface at the respec-tive pipe exits but, more importantly, for the acoustic path through which the mechanism tnat drives the C0 phenomenon is transmitted. In fact, it is not com-pletely apparent that for the FSTF case the system has actually achieved a con-dition of resonant coupling. This is because of the complexity of the FSTF vent system; i.e. the eight downcomers are connected to a vent header, which in turn is connected to a main vent which then connects to a simulated drywell. Because of this complexity, it is difficult to ascertain the effective relevant vent system natural frequency.with sufficient precision.
Despite the uncertainties cited above, there are several factors' that may be cited that compensate for any possible inadequacy. First, there is the qualita-
. tive' evidence from the 4TCO tests (Reference 2.1.3) that, even when resonant coupling clearly occurs, the load amplification is limited to less than a two-
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fold factor. Also, the generally conservative application of the available re-sults provides increased confidence in the adequacy of the load method. For ex-ample, the pressure results observed on 24" diameter downcomers are taken over directly and applied to the much smaller,14" diameter, SRVDL sleeves. Also, in developing the loads on the suppression pool boundaries, the effective source (steambubble)radiuswastakenequaltothatofthesleevewithouttakinginto account the actual presence of the SRVOL itself. As shown in a recent submittal by the applicant (Reference 2.1.6), this results in a margin of over 30% in the loads that were developed. BNL believes the margin would be even greater if the steam bubble were modeled more realistically (Reference 2.1.2). Additional con-servatism stems from the use of conventional acoustics for determination of pressure attenuation from the source to the pool boundaries. Dissipative mech-anisms that are present in the suppression pool and neglected in the analysis, would further reduce the loads.
Insofar as the chugging loads are concerned, BNL has not received a description of these, even though this information exists (Reference 2.1.7) and has been as-sessed by the Mark III Containment Issues Review Panel (Reference 2.1.8). The findings of this panel were that the proposed loads were only about 6% of main vent chugging and are easily bounded by design. BNL is satisfied that this is the case. Note that resonance effects are not expected to play any role in or influence the chugging phenomenon associated with the sleeve annulus.
_ Conclusions BNL considers this safety concern to have been satisf actorily resolved because the conservatively estimated new loads :tavt been demonstrated to be bounded by other design loads.
References 2.1.1 Humphrey Engineering, Inc., Letter dated June 17, 1982 from J. M. Humphrey (HEI) to A. Schwencer (NRC).
2.1.2 IPC Letter No. U-0714 dated May 25, 1984 from D. I. Herborn (IPC) to A. Schwencer (NRC).
2.1.3 Bird, P. F., et al., "4T Condensation Oscillation Test Program Final Test Report", General Electric Report NEDE-24811-P, May 1980.
2.1.4 IPC Letter No. U-600319 dated from F. A. Spangenberg (IPC) to W. R. Butler (NRC).
2.1.5 Fitzsimmons, G. W. et al., " Mark I Containment Program - Full-Scale Test Program Final Report", General Electric Report, NEDE-24539-P, April 1979.
2.1.6 IPC Letter No. U- dated from F. A. Spangenburg (IPC) to W. R. Butler (NRC).
2.1.7 Enercon Letter No. RWE-0G-060 dated May 25, 1983 from R. W. Evans (Enercon) to B. R. Patel (Creare R&D).
2.1.8 Mark III Containment Issues Review Panel, " Assessment of Humphrey Concerns", CREARE R&D, Inc., Technical Memorandum TM-928, July 1984.
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Humphrey Safety Concerns 2.2 and 2.3 2.2- .The potential condensation oscillation and chugging loads produced through the annular area between the SRVDL and sleeve may apply unaccounted for loads to the SRVDL. Since the SRVDL is unsupported from the quencher to the inside of the drywell wall, this may result in failure of the line.
2.3 The potential condensation oscillation and chugging loads produced through the annular area between the SRVDL and sleeve may apply unaccounted for loads to the penetration sleeve. The laods may also be at or near the nat-ural frequency of the sleeve.
Evaluation The concern here is that the steam condensation process (C0 + chugging) at the sleeve annulus exit will give rise to loads on the SRVDL and SRVDL sleeve analo-gous to the lateral loads experienced by Mark I and Mark II downcomers during postulated LOCA blowdowns and that these structures have not been designed to accommodate them. The applicant's specification for chugging loads is given in Reference 2.2.1 with additional clarification provided in Reference 2.2.2. The load has a half-sinusoidal time dependence with a duration of 3 mseconds and a peak amplitude of 28 Kips. It is stated that this load derives from the Mark 11 load methodology of Reference 2.2.3 as modified by the NRC Staff's Acceptance Criteria (Reference 2.2.4). The load is developed by scaling down the peak am-plitude to the outside diameter of the SRVDL sleeve and accounting for the fact that there are fewer chug sources created by flow through the SRVDL sleeve annu-lus than exist during DBA blowdowns through the Mark II pressure suppression system (i.e.: 16 SRV's for the CPS vs. about 100 downcomers in a typical Mark II plant) . Scaling down for pipe diameter is accomplished by assuming a 1.7 power dependence of the peak load amplitude on diameter. Load reduction for fewer chug sources utilizes the staff approved statistical representation for these loads (Reference 2.2.4). The region of application of the load is also scaled down using a first power dependence on diameter (Reference 2.2.2).
The applicability of the Mark II results for the present application is somewhat uncertain due to the substantial geometric differences (straight down vs. in-clined pipe and annular vs. circular cross section). Nevertheless, we find the approach reasonable and, in general, conservative. The use of a 1.7 power de-pendence of peak amplitude on pipe diameter is somewhat less conservative than we would have preferred since the available data (Reference 2.2.5) exhibit expo-nent values that range from 0.7 to 1.7. On the other hand, no credit is taken for the presence of the SRVDL in the steam bubble. This provides a substantial conservatism that BNL judges more than compensates for any possible non-conser-vatism in selecting this exponent.
No C0 lateral loads are specified by the applicant. In Reference 2.2.2 it is argued that since the suppression pool end of the SRVDL sleeve is truncated per-pendicular to the discharge line axis, the potential for asymmetric dynamic pressure loads arising at that end is precluded. It is also argued (Reference 2.2.6) that at the drywell end of the sleeve where the truncation is at 45*
to the pipe axis, a constant pressure condition prevails during the C0 phase of the DBA blowdown. This would tend to suppress the development of unbalanced pressure loads across the SRVDL because only a very small section of the longer end of the pipe would experience the pressure reversal resulting from reflection off the annulus entrance. BNL believes that these arguments have sufficient merit to justify the absence of any explicit C0 lateral load specification on the SRVDL and SRVDL sleeve during postulated LOCA conditions.
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m Conclusion BNL considers this concern to be resolved because of the specification of a conservative chugging load for the SRVDL and SRVOL sleeve and because the CPS configuration for these structures does not permit development lof any significant unbalanced pressure loading during the C0 phase of the LOCA blowdown.
References 2.2.1 IPC Letter No. U-0714 Dated May 25, 1984 from D. I. Herborn (IPC) to A. Schwencer (NRC).
2.2.2 IPC Letter No. U-600319 Dated from F. A. Spangenberg (IPC) to W. R. Butler (NRC).
2.2.3 Davis, W. M., " Mark II Main Vent lateral Loads", GE Report NEDE-23806-P, October, 1978.
2.2.4 Anderson, C., " Mark 11 Containment Program Load Evaluation and Acceptance Criteria", NRC NUREG-0808, 2.2.5 General Electric Letter MFN-050-80 dated February 29,1980 from R. H. Buchholz (GE) to C. J. Anderson (NRC).
2.2.6 Informal Telephone Conference between BNL/NRC/IPC/GE/S&L, December 3, 1985.
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'Humphrey Safety Concerns 3.1 and 3.3 3.1 The design of the STRIDE did not consider vent clearing, condensation os--
cillation, and chugging. loads which might be produced by the actuation of
'the RHR heat exchanger relief valves.
3.3 Discharge from the RHR relief valves may produce bubble discharge or other submerged structure loads on equipment in the suppression pool.
Evaluation The concern is that, besides the main safety / relief valves (HSRV's), the RHR re-lief valves can also discharge fluids into the suppression pool during RHR oper-ation.in the steam condensing mode (SCM). As a result, loads could be produced analogous to those associated with MSRV discharges and/or LOCA blowdowns through downcomers. These loads have not been accounted for in-plant design.
The applicant states in Reference 3.1.1 that water and air clearing loads were developed by conservative application of conventional methods (i.e.: the main steam SRV load methodology). The applied loads are those that correspond to su-subsequent actuation at maximum reflood ' elevation; these are found to be " worst case" loads. The resulting containment boundary loads were assessed and found to be within design. Water clearing jets are found not to impinge on any struc-tures in the CPS suppression pool. Air clearing loads on submerged structures exceeded MSRV design loads in a few cases but all structures were found capable of accommodating these increases in applied loads.
For C0 and chugging loads on the pool boundaries, the applicant utilizes the ge-neric methods employed by all the Mark III utilities (Reference 3.1.2). No de-tailed description of the methodology is supplied by the applicant, but the gen-eral features can be discerned from the information supplied in References 3.1.3 and 3.1.4. Generally speaking, the method derives from a conservative applica-tion of the Mark II CO.and chugging methodologies. The specific application is to the GGNS RHR heat exchanger relief valve discharge line (RHRHXRVDL). Source terms are developed from selected chugs:and C0 pressure signatures from the Mark II data base. These are used to generate pressure loads on the GGNS pool bound-aries. They are shown to be bounded by the design main steam SRV loads by a wide margin.
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The conservatism in this load specification stems primarily from the use of the selected source strength directly without any reduction to account for the dif-
' ference in pipe diameter between the RHRHXRVDL (12 inches in the CPS) and that from which the data base derives (24 inches in the test facility).
l The adequacy of the C0 load also needs to be judged in the context of potential unstable steam condensation, i.e.: elevated suppression pool temperature.
BNL's evaluation of this aspect is presented under Humphrey Safety Concern 3.6.
A detailed description of lateral loads on the discharge line due to chugging is provided in References 3.1.5. The load is time dependent (half-sinusoid) with a peak amplitude of 32.5 Kips and 3 msecond duration. This load derives from the i Mark II load methodology of Reference 3.1.6 as modified by the NRC Staf f's Ac-ceptance Criteria (Reference 3.1.7) to account for the stochastic nature of the chugging phenomenon. This results in a peak design load amplitude that varies l
according to the number of chugs that would be expected during a particular ac-l cident scenario and the desired non-exceedance probability.
The peak amplitude selected by the applicant takes into account only the difference in diameter between the RHR discharge line (12 inches) and the standard Mark 11 downcomer (24 inches). This is accounted for by assuming that the peak amplitude scales with pipe diameter to the first power. It does not, for example, adjust the load for reduced submergence, which is also known to attenuate such loads. In particular, no modification for non-exceedance probability is employed so that the selected peak amplitude is to be associated with that used to derive the Mark II downcomer load. This is a very low value (10-5) and implies that many hours of chugging could occur before a serious exceedance of pipe structural capability would be expected.
Conclusion BNL judges that this issue has been satisfactorily resolved. This judgement is based on the generally conservative nature of the loads used for evaluation and the stated margins exhibited in existing structure capability.
References 3.1.1 IPC Letter No. U-0714 Dated May 25, 1984 from D. I. Herborn (IPC) to A. Schwencer (NRC).
3.1.2 Mark III Containment Issues Review Panel, " Assessment of Humphrey Concerns", CREARE R & D Inc., Technical Memorandum TM-928, July 1984.
3.1.3 Meeting Handouts from NRC/ Mark III/GE meeting of May 19, 20, 1983.
3.1.4 Ashley, G. K. and Leong, T. S., " Assessment of RHR Steam Discharge C0 in Mark III Containments", Bechtel Report, March 1984 3.1.5 IPC Letter No. U-600319 Dated from F. A. Spangenberg (IPC) to W. R. Butler (NRC).
3.1.6 Davis, W. M., " Mark II Main Vent lateral Loads", GE Report NEDE-23806-P, October 1978.
1 3.1.7 Anderson, C., " Hark II Containment Program Load Evaluation and Acceptance Criteria", NRC NUREG-0808, 4
4 Humphrey Safety Concern 3.2 The STRIDE design provided only 9 inches of submergence above the RHR heat ex-changer relief valve discharge lines at low suppression pool levels.
Evaluation The concern is that because of the relatively small submergence involved, steam condensation may not be complete leacing to steam bypass and failure of the pressure suppression system.
The applicant has addressed this concern using the generic approach common to all plants (Reference 3.2.1). The approach cites the full-scale data from the Humboldt Bay tests where it is shown that, over a wide range of steam flux rate, condensation was complete (i.e.: no steam bypass and containment pressuriza-tion), even with a clearance of 2 feet between the vertical vent pipe exit and the pool surface.
The applicant states (Reference 3.2.2) that the minimum submergence of the dis-charge line will be about 2 inches. This differs considerably from the four foot minimum suggested in Reference 3.2.3. Notwithstanding this discrepancy, in BNL's judgement either submergence, together with the degree of subcooling that would be expected during normal steam discharges through these lines (see dis-cussion of Humphrey Safety Concern 3.6) should preclude any potential for steam bypass.
Conclusion BNL considers this issue satisfactorily resolved for the CPS based on the large subcooling available during normal operations.
References 3.2.1 MPAL Letter No. AECM-82/1E3 dated August 19, 1982 from L. F. Dale, MPAL, to H. R. Denton, NRC.
i 3.2.2 IPC Letter No. U-0596 dated February 4,1983 from G. E. Wuller, IPC, to A. Schwencer, NRC.
3.2.3 Mark III Containment Issues Review Panel, " Assessment of Humphrey l
Concerns", CREARE R&D, Inc. , Technical M9morandum TM-928, July 1984.
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I Humphrey Safety Concern 3.4 The RHR heat exchanger relief valve discharge lines are provided with vacuum breakers to prevent negative pressure in the lines when discharging steam is condensed in the pool. If the valves experience repeated actuation, the vacuum breaker sizing may not be adequate to prevent drawing slugs of water back through the discharge piping. These slugs of water may apply impact loads to the relief valve or be discharged back into the pool at the next relief valve actuation and apply impact loads to submerged structures.
Evaluation The real issue here is that the various steam discharge lines may not have been equipped with properly sized vacuum breakers. This is a credible concern in view of the historical development of the same issue for the HSRV's. Because the potential for subsequent actuations was not fully appreciated in the early stages, the MSRV discharge lines were originally equipped with undersized vacuum breakers. When very high reflood elevations were encountered during tests with subsequent actuation, it became evident that this was so and much larger vacuum breakers were installed (from 1 inch to as much as 10 inch diameter or two 6 inch diameter).
The applicant indicates (Reference 3.4.1) that the CPS discharge lines are equipped with 2 inch vacuum breakers, a size we would consider marginally adequate for a 12-inch diameter discharge line. Their reflood analysis, performed with a standard GE computer model, reflects this. Their results show reflood elevation of about 13 feet, which is considerable hut still well below any crucial element of the system (the vacuum breakers are lowest and are located about 2-1/2 feet above maximum reflood). Water clearing loads were developed using this maximum reflood and all piping systems found capable of accommodating these loads.
Conclusion BNL considers this issue adequately addressed by the applicant and therefore closed.
References 3.4.1 IPC Letter No. U-0714 dated May 25 1984 from D. I. Herborn (IPC) to A. Schwencer (NRC).
Humphrey Safety' Concern 3.6 If the RHR heat exchanger relief valves discharge steam to the upper levels of the suppression pool following a design basis accident, they will significantly-aggravate suppression pool temperature stratification.
Evaluation Although the concern suggests that these discharges will occur following a DBA, the applicant has indicated (Reference 3.6.1) that during post-LOCA conditions the "RHR logic precludes the initiation of the steam condensing mode (SCM)".
Under these circumstances, steam discharges via the RHR heat exchanger relief valves cannot occur. On the other hand, continuous steaming for an extended period under normal conditions is possible and could not only result in excessive containment' pressurization via vertical thermal stratification but introduces the potential for unstable steam condensation leading to excessive dynamic loading on the pool boundaries.
The applicant's response to.this issue as given in Reference 3.6.2 is similar to the generic approach which was provided in the MP&L response (Reference 3.6.3).
A demonstrably conservative model'of thermal deposition, stratification and pool mixing was developed and applied using MP&L plant parameters. Based on this model, it was shown in Reference 3.6.4 that even after steaming at the very high flow rate assumed in the analysis for twenty minutes, the difference between the-average pool surface temperature (131*F) and bulk temperature (107*F) was only about 24*F. We note also that the peak temperatures reported are just barely approaching levels that might imply unstable steam condensation loads; e.g.:
about 130*F for a straight down pipe. Accordingly, BNL concludes that this scenario could safely proceed for as much as twenty minutes without the need for any mitigating action. The CPS applicant takes the position that because operation in the SCM is so operator intensive, detection of a failure and termination of the steam flow could be accomplished within two minutes. This appears to us somewhat optimistic, but BNL is satisfied that sufficient time is available to institute a number of actions which would effectively mitigate any adverse effects of this postulated failure.
Conclusion l
The issue raised by this concern is considered to be satisfactorily resolved for the CPS based on the assumption that post-LOCA operation of the RHR in a steam condensing mode will not occur.
References
! 3.6.1 IPC Letter No. U-600319 dated from F. A. Spangenberg (IPC) to W. R. Butler (NRC).
3.6.2 IPC Letter No. U-0596 dated February 4,1483 from G. E. Wuller (IPC) to
, A. Schwencer (hRC).
l r 3.6.3 MP&L Letter No. AECM-82/574 dated December 3,1983 from L. F. Dale (MP&L)
I to H. R. Denton (NRC).
3.6.4 Meeting Handout " Response to Question 9.2", NRC/ Mark III/GE Meeting, May 19-20, 1983.
Humphrey Safety Concern 4.3 All Mark III analyses presently assume a perfectly mixed uniform suppression pool. These analyses assume that the temperature of the suction to the RHR heat exchangers is the same as the bulk pool temperature. In actuality, the temperature in the lower part of the pool where the suction is located will be as much as 7-1/2 cooler than the bulk pool temperature. Thus, the heat transfer through the RHR heat exchanger will be less than expected.
Evaluation To complete the statement of this concern, the following should be added; ...
"and containment pressure and temperature greater than expected."
Humphrey's basis for expecting a temperature difference of up to 7-1/2*F is unclear (we assume here that Mr. Humphrey does intend Fahrenheit degrees). BNL agrees that in the event of a postulated LOCA, the reality will be a thermally stratified pool. However, to decide what the difference between bulk and RHR suction temperature is requires an estimate of the degree of vertical-stratification that will occur, together with knowledge of RHR suction elevation.
The first of these requirements was established to the NRC staff's satisfaction during its evaluation of the GESSAR II containment loads (Reference 4.3.1).
After a lengthy, detailed, and sometimes heated review process by the various interested parties (Reference 4.3.2), the worst case vertical temperature profile proposed by the General Electric Company for design (Fig. 3BI-3 of Reference 4.3.3) was-judged acceptable. The basis for this judgement is given in Reference 4.3.1. It implies that the profile is applicable only for a standard top vent submergence (-7.5 feet).
In responding to Humphrey concerns 4.7 and 4.10 (see later), the applicant indicates that the CPS RHR suction is located at an elevation 8'-0" above the basemat. Comparison with the temperature profile referred to above implies that the RHR suction temperature is greater than bulk temperature. Accordingly, this Humphrey concern is not relevant to the CPS.
Conclusion BNL considers this issue satisfactorily resolved for the CPS.
References 4.3.1 " Mark III LOCA-Related Hydrodynamic Load Definition", NUREG-0978, August 1984 4.3.2 Transcript of the ACRS Subcommittee on Fluid Hydraulic Dynamic Effec +;
Meeting of September 24, 25, 1981.
4.3.3 General Electric Co., 22A707, " General Electric Standard Safety Analysis Report", (GESSAR-II), Appendix 38 through Amendment 1, February 25, 1982.
Humphrey Safety Concerns 4.4 and 7.1 4.4 The long term analysis of containment pressure / temperature response assumes that the wetwell airspace is in thermal equilibrium with the suppression pool water at all times. The calculated bulk pool temperature is used to determine the airspace temperature. If pool thermal stratification were considered, the surface temperature, which is in direct contact with the airspace, would be higher. Therefore, the airspace temperature (and pressure) would be higher.
7.1 The containment is assumed to be in thermal equilibrium with a perfectly mixed, uniform temperature suppression pool. As noted under Topic 4, the surface temperature of the pool will be higher than the bulk pool temperature. This may produce higher than expected containment temperatures and pressures.
Evaluation The concern is similar to that associated with HSC 4.3 above except that here the issue is the difference between pool surface temperature and pool bulk temperature. Based on the GESSAR-II temperature profile referred to previously, this difference is 8*F, in rough agreement with the 7-1/2*F difference cited by Mr. Humphrey in HSC 4.3. Apparently, this was the AT he was referring to and it was mistakenly cited in connection with the Bulk-to-RHR suction tenperature di f ference.
The applicant's response to this concern is the generic one that was originally provided by MPAL for the GGNS (Reference 4.4.1). In this submittal, the issue is quantified by means of existing information and analyses. The results show that the effects of a 7 to 8 F difference between pool surface and bulk temperature would imply an increase in peak containment pressure and temperature of only 0.1 psi and 3*F, respectively. These modest differences are overwhelmed by the existing margins of 5 psi and 19 F that can be demonstrated to exist due to various conservatisms used in conventional containment response analysis. -
Conclusion Essentially, what this entire exercise has demonstrated once more is that the use of a mean or bulk pool temperature is an acceptable simplification which facilitates calculation of containment response. The result is not surprising.
BNL considers this issue to be closed.
References 4.4.1 Attachment to MP8L Letter No. AECM82/353 dated August 19, 1982, from L.
F. Dale (MP&L) to H. R. Denton (NRC).
Humphrey' Safety Concern'4.5
, A number of factors may-aggravate suppression pool thermal stratification. The chugging produced through the first row of horizontal vents will not produce any.
- . mixing- from the suppression pool layers below the vent row. An upper pool dump may contribute to additional suppression pool temperature stratification. The large volume of water from the upper pool further submerges RHR heat exchanger effluent discharge which will decrease mixing of the hotter, upper regions of i
the pool. Finally, operation of the containment. spray eliminates the heat
+ exchanger effluent discharge jet which contributes to mixing.
Evaluation A formal submittal by the applicant relating to this concern has not been made
~
available to BNL. However, based on our reading of the corresponding section of Reference 4.5.1, we conclude that the response for IPC would be identical to that provided via Reference 4.5.2; the generic response which corresponds to Action Plan 14 of the MPAL Submittal for the GGNS. This Action Plan'was to utilize the following " Program for Resolution".
3 1. Testing information will be s :bmitted to demonstrate the effectiveness of a chugging as a mixing mechanism in the suppression pool.
! 2. Analyses will be submitted to demonstrate that the suppression pool does not experience significant stratification during containment spray or following upper pool dump.
- . The first of these items addresses the concern that chugging does not provide any mixing below the top vent. The test information that was supplied indicates
. that this is not correct. . Measurements obtained from so-called drag disks that
! had been installed in-the PSTF facility indicated that flow reversals occur
! periodically in both the middle and bottom vents during the chugging phase of the steam blowdown. Although this is a qualitatively useful finding, the
- attempt to quantify pool turnover time from this information cannot be taken i seriously. This is because the drag disk device requires careful calibration under even the best of circumstances (steady, uniform flow). Under the i unsteady, highly non-uniform flow conditions that prevail within the vents
! during chugging, the notion that quantitatively correct values of flow
- velocities can be obtained using this procedure is not credible. Furthermore,
! even if 'one were to accept these quantitative estimates, their applicability for ,
the case involving upper pool dump, which can increase top vent submergence from 7-1/2 to as much as 12 feet, would be highly suspect.
l As for the second item, none of the Mark III applicants have provided any
- information. The CPS applicant suggested informally that some relevant
. information could be developed from a reading of their FSAR. BNL has done this and has determined, among other things, that the CPS upper pool volume increases
- i the pool depth by only two feet, that the upper pool water at the time of dump is 120 F and that the suppression pool bulk temperature at the time of pool dump
, is in the range 136*F to 147*F. We have also been able to establish that the
- dump is accomplished by two 24-inch diameter, gravity fed drain lines that
! terminate with a vertical orientation about 19-feet above the suppression pool 1 surface. These drain lines are located at azimuth 53* and 325* which places
, them in close proximity to the RHR suction lines (Azimith 37* and 323*).
Finally, we have -been informed (Reference 4.5.3) that the dump is accomplished ,
over a period of time of about 8 minutes.
f L
9 If during this time interval no other mass or energy addition to the suppression pool occurs, the combined suppression bulk pool temperature would be reduced by 2 to 3 F. Thermal stratification between bulk and pool surface temperatures would increase to the same extent but this bounding value can easily be accommo-dated, in our judgement, by other conservatisms (see discussion for HSC 4.4).
The effect of pool dump on thermal stratification as it relates to RHR suction is more difficult to estimate but as a limiting case we can speculate that the upper pool water, because of its downward velocity (10-20 fps) and greater den-sity, preferentially sinks to the bottom and displaces the hotter stratified layers of pool water. Except for the possibility of short circuiting which we judge to be unlikely because of the high elevation of the CPS RHR suction, this
" cold-water-sinks-to-bottom" scenario represents a worst case in terms of the RHR suction temperature differential from bulk pool temperature. That is, by displacing the hotter layers of water upward, the RHR suction temperature is re-duced to the maximum degree possible. Our attached Figure 4.5.1 demonstrates this effect. Note especially that although the local temperature at the RHR suction elevation decreases, it still remains higher than bulk pool tempera-ture. This represents an important conservatism as was pointed out during eval-uation of HSC 4.3 above. Thus, upper pool dump also does not impact negatively on the RHR suction to bulk temperature difference in the CPS.
The remaining concerns implied in the statement of this Humphrey concern are al-so taken account of in our evaluation here. This is because our arguments have used the worst case thermal stratification; i.e.: the temperature profile was developed without assuming RHR operation. Thus, any RHR operation, however in-efficient, will further improve the situation as we have characterized it here.
Conclusion BNL judges that upper pool dump in the CPS will not seriously increase pool thermal stratification. This is because the increase in pool depth is relative-ly small (only 2 feet) and because the RHR suction in the CPS is located at a high elevation (8 feet above the basemat) relative to the worst case temperature profile, References 4.5.1 Mark III Containment Issues Review Panel " Assessment of Humphrey Concerns", CREARE R&D, Inc., Technical Memorandum TM-928, July 1984.
4.5.2 MP&L Letter No. AECM 82/353 dated August 19, 1982, from L. F. Dale, (MP&L) to H. R. Denton, (NRC).
4.5.3 IPC Informal " Response to Request for Information via Phone Call on August 6, 1985", August 1985.
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Humphrey Safety Concerns 4.7 and 4.10 4.7 All analyses completed for the Mark III are generic in nature and do not consider plant specific interactions of the RHR suppression pool suction and discharge.
4.10 Justify that the current arrangement of the discharge and suction points of the pool cooling system maximizes pool mixing.
Evaluation The concern here is that if the RHR system's geometric arrangement for the suc-tion and return lines is not properly designed, the capability of the system to induce bulk mixing and remove thermal energy will be degraded.
The applicant has addressed these concerns via the generic approach developed for the Mark III Containment Issues Group (Reference 4.7.1). The key element of this study was the Perry one-tenth-scale tests (Reference 4.7.2). In these tests, a number of related concerns were addressed systematically. These in-cluded short circuiting, development of bulk pool motion, ability to eliminate thernal stratification and the presence of isolated recirculation zones.
BNL has reviewed this information in detail and has concluded that the Perry one-tenth-scale tests correctly simulate design conditions in Mark III plants, and, along with the other test information provided, include a sufficient range of parameters to encompass the CPS plant unique features, and are therefore applicable. Since the findings from these tests show that good mixing can be achieved, as well as the absence of short circuiting, the staff concludes that the CPS RHR system can be expected to perform in a manner consistent with design assumptions.
Conclusion BNL considers the issues raised by these concerns to be satisfactorily resolved .
for the RBS.
References 4.7.1 Quadrex Corp., "A Survey of Tests and Analyses on the Effectiveness of the RHR System in the Pool Cooling Mode", Report No. QUAD-1-82-245, Rev. A, November 1982.
4.7.2 Gilbert Associates, Inc., "Model Study of Perry Nuclear Power Plant Suppression Pool - Final Report", November 1977.
i
l
_Humphrey Safety Concern 19.1 The chugging loads were originally defined on the basis of 7.5 feet of submer-gence over the drywell to suppression pool vents. Following an upper pool dump, the submergence will actually be 12 feet which may affect chugging loads.
Evaluation The applicant's response to this concern is the generic one which was originally provided by MPAL for the GGNS via Reference 19.1.1. In this submittal, physical arguments and analytical procedures are used to estimate the pressure field that would be generated on the suppression pool boundaries if the worst case chug from the Mark III data base were to occur with the top vent at a 12-foot submer-gence. The results are compared with design on an ARS basis and shown to be bounded expect for local loads in the frequency range 12 to 32 Hz. For these conditions an exceedance of design amounting to 35% occurs on the basemat.
The applicant argues that this exceedance is not important because this is a lo-cal load affecting only the basemat liner and that because of the hydrostatic head to which the liner is subjected, it will not experience a " negative pres-i sure in the frequency range of exceedance". Also, "since the liner is backed by concrete everywhere, no natural modes in this range are excitable".
Without passing judgement on the merits of these arguments, BNL notes the fol-
. 1owing: the increase in submergence due to upper pool dump for the CPS is only t
about 2 feet (Reference 19.1.2) compared to 4-1/2 feet for GGNS; chug loads
- would be correspondingly reduced
- the use of an acoustic model in the analysis represents a significant conservatism; dissipative mechanisms not accounted for in such an analysis result in pressure attenuation which is much greater than predicted; this has been borne out convincingly by experimental results: appli-cation of the worst case chug to all vents, which is done for local loads, also represents a very significant conservatism; in a recent submittal by CEI to ad-dress the staff concern relative to the combined effect of upper pool dissp and encroachment on local chugging loads (Reference 19.1.3), it was shown that by .
postulating a maximum strength chug at the central vent and average strength chug at adjacent vents, the design loads were capable of bounding the combined
- effect.
In summary, the margins inherent in the design load for chugging are very large. They can more than accommodate any increment in loading caused by off-design effects such as increased submergence due to upper pool dump.
Conclusion BNL considers this issue satisfactorily resolved for the CPS.
References 19.1.1 MP8L Letter No. AECM-82/353 dated August 19, 1982 from L. F. Dale, MP&L, to H. R. Denton, NRC.
l 19.1.2 IPC Letter No. U-600319 dated from F. A. Spangenberg, IPC, to W. R. Butler, NRC.
19.1.3 CEI Letter dated July 11, 1984 from M. R. Edelman, CEI, to B. J. Youngblood, NRC.
I
__.2._..__._______--______________~_. ___ _
. - - - -_ .-_ - ~ - - .-
4
- .- ^
- Humphrey Safety Concern 19.2
' The effect of local encroachments on chugging loads needs to be addressed.-
Evaluation The applicant's response to this concern is the generic one which was originally
, .provided by MP&L for the GGNS via Reference 19.2.1. In this submittal, physical arguments and analytical procedures are used to estimate the pressure field that -
! would be generated on the suppression pool boundaries if the worst case chug
- from the Mark III data base were to occur at vents located below the GGNS TIP platform. The results are compared with design on an ARS basis and shown to be bounded except for local loads in the frequency range 12 to 30 Hz. For these-conditions an exceedance of design amounting to 60% occurs on the basemat.
4
- The applicant argues that this exceedance is not important because this is a lo-cal load affecting only the basemat liner and that because of the hydrostatic head to which the liner is ' subjected, it will not experience a " negative pres-sure in the frequency range of exceedance". Also, "since the liner is backed by concrete everywhere, no natural modes in this range are excitable".
Without passing judgement on the merits of these arguments, the staff notes the
, following: the loads developed for GGNS are conservative for the CPS; as indi-
' cated in their respective responses to Humphrey Concern 1.0, the GGNS TIP plat-form represents a much. larger encroachment than any in the CPS: the use of an acoustic model in the analysis represents a significant conservatism; dissipa-
- tive mechanisms not accounted for in such an analysis result in pressure attenu-
- i. .
ation which is much. greater than predicted; ~this has been borne out convincingly by experimental results: application of the worst case chug to all vents below
, the encroachment also represents a very significant conservatism; in a recent i submittal.by CEI to address the staff concern relative to the combined effect of upper ' pool dump and encroachment on local chugging loads (Reference 19.2.2), it
- was shown that by postulating a maximum strength chug at the central vent and l average strength chug at adjacent vents, the design loads were ' capable .of bound-
- ing the combined effect.
! In summary, the margins inherent in the design load for chugging are very
- large. They can more than accommodate any increment in loading caused by off-L design effects such as encroachment.
4 Conclusion BNL is satisfied that the issues related to this concern have been satis-factorily addressed by the applicant and are therefore considered closed.
References 19.2.1 MP&L Letter No. AECM-82/574 dated December 3,1983, from L. F. Dale (MP&L) to H. R. Denton (NRC).
19.2.2 CEI Letter dated July 11, 1984 from M. R. Edelman (CEI) to l B. J. Youngblood (NRC).
Additional Safety Concern BNLl*
The effects of increased submergence and encroachment on local -loads are additive. ARS comparisons showing the combined effect should be provided.
Evaluation A generic response was developed for this concern and included in an earlier CEI submittal (Reference B.1.1). As indicated in.the evaluation provided for HSC-19.1 and 19.2 above, by postulating the very reasonable assumption that a maximum strength chug occurred only at a central vent with average strength chugs at surrounding vents, local loads were reduced to levels which were adequately bounded by design.
Conclusion The utilities have provided an adequate demonstration that the design load for chugging has sufficient margin to accommodate the increment in loading caused by the combined effects of encroachment and increased submergence. BNL considers this issue to be closed.
References B.1.1 CEl Letter No. PY-CEI/NRR-0123L dated July 11, 1984 from M. R. Edelman (CEI) to B. J. Youngblood (NRC).
- This additional concern, which evolved from HSC19 and was developed by BNL, is not formally recognized as a Humphrey concern. It is therefore denoted by this special notation.
a e
Additional Safety Concern BNL3*
Upper pool dump increases the length of the water column within the main steam SRVDL. This will tend to increase pipe thrust loads during SRV actuation.
Provide an analysis of this effect.
Evaluation The applicant states in Reference B.3.1 that the SRVDL's have been designed to accommodate a subsequent actuatior, level which is six feet above the normal suppression pool level. Accordingly, the increase due to upper pool dump is "within design consideration for the SRV lines".
Conclusion Based on the statement made by the applicant, BNL considers this concern to be resolved.
References B.3.1 IPC Letter No. U-600319 dated from F. A. Spangenberg (IPC) to W. R. Butler (NRC).
- This additional concern, which evolved from HSC19 and was developed by BNL, is not formally recognized as a Humphrey concern. It is therefore denoted by this special notation.
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