ML20207S510
| ML20207S510 | |
| Person / Time | |
|---|---|
| Site: | Perry, Grand Gulf, 05000000 |
| Issue date: | 11/30/1985 |
| From: | Economos C BROOKHAVEN NATIONAL LABORATORY |
| To: | NRC |
| Shared Package | |
| ML20207S501 | List: |
| References | |
| CON-FIN-A-3346, CON-FIN-A-3396 NUDOCS 8703190580 | |
| Download: ML20207S510 (16) | |
Text
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Technical Evaluation Report (TER) for the Cleveland Electric Illuminating Company's (CEI)
Perry Nuclear Power Plant (Perry), Docket Nos. 50-440/441 on SER Outstanding Issue (8) - Mark III Containment System Issues -
The Humphrey Safety Concerns (HSC) by C. Economos November 1985 Department of Nuclear Energy Brookhaven National Laboratory Upton, New York 11973 Introduction With one exception, this TER addresses only those HSC's that, by previous agree-ment with the Technical Monitor, are considered BNL's responsibility. The only exception involves the addition of the issue related to HSC 4.4 and HSC 7.1.
For the River Bend Stationi this issue was considered the responsibility of the NRC Technical Monitor. Notwithstanding this earlier decision, we feel that BNL input in this area is appropriate. We have therefore included an evaluation 7 here.
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 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 breakthr,ough height to be higher than expected.
1.4 Piping impact loads may be revised as a result of the higher pool swell ve-locity.
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 The concern is that the presence of encroachments will tend to increase pool ve-locities and breakthrough height relative to the unencroached pool thereby caus-ing 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 Con-tainment Owners Group (CIOG),2,3,<. it has now been established that, for the most part, the effect of encroachments is to decrease pool swell velocities rel-ative to an unencroached or clean suppression pool. A detailed report, 8703190580 870306 ~b
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t up.u).:4, J, Ss Technical Evaluation Report (TER) for the yktg 7 Ef Cleveland Electric Illuminating Company's (CEI) g Perry Nuclear Power Plant (Perry), Docket Nos. 50-440/441 on SER Outstanding Issue (8) - Mark III Contaiment System Issues -
The Humphrey Safety Concerns (HSC) by C. Economos October 1985 Department of Nuclear Energy Brookhaven National Laboratory Upton, New York 11973 Introduction With one exception, this TER addresses only those HSC's that, by previous agree-ment with the Technical Monitor, are considered.BNL's responsibility. The only exception involves the addition of the issue related to HSC 4.4 and HSC 7.1.
For the River Bend Station1 this issue was considered the responsibility of the NRC Technical Monitor. Notwithstanding this earlier decision, we feel that BNL input in this prea is appropriate. We have therefore included an evaluation here.
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 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 ve-locity.
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 The concern is that the presence of encroachments will tend to increase pool ve-locities and breakthrough height relative to the unencroached pool thereby caus-ing 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 simu,lations of pool swell conducted by the Con-tainment Owners Group (CIOG),2,3,< it has now been established that, for the most part, the effect of encroachments is to decrease pool swell velocities rel-ative to an unencroached or clean suppression pool. A detailed report,
4 i
i describing the basis for this conclusion has been prepared for the NRC by BNLs and is also included as Appendix A of this TER. For the Perry plant, in partic-ular, fluid velocities were consistently lower with prototypical encroachments in place. Accordingly, any changes to impact and drag loads that are caused by these encroachments will be favorable. That is, the loads will be less than those that will be experienced in a clean suppression pool.
Conclusion BNL considers these issues closed for the Perry plant because 1/10-scale simula-tions show that pool velocities are reduced by the presence of encroachments relative to those observed with a clean pool configuration.
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 (drywell wall, basemat, containment wall) and (2) loads on submerged structures proper, such as pipes and beams.
A two-dimensional 50LAV01 simulation was employed to determine the effect of Perry encroachments on these loads.6 About a 10%' increase in the containment wall load was predicted which is well within the design load specification. For submerged structure loads, even greater margins relative to design were ob-tained. For excmple, the pressure differential across a quencher arm was found to be 2.5 psid compared to a design load of over 15 psid.
Conclusion BNL con ~siders this concern to be resolved based on the demonstrated margin be-tween design and the loads estimated with a conservative (two dimensional) simu-lation of the encroachment effect.
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.7 This analysis assumed steady flow, i.e., the liquid droplets had velocities equal to air and all of the froth was allowed to pass thorugh the openings in the HCU floor. The resulting lateral pressures were found to be 0.15 psid on the beams and 0.1 psid on the gratings. The additional stresses due to these lateral forces were found to be small fractions of the total stresses.6
BNL concurs with the utility claim that the potential flow analysis is conservative. 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 to-ward the pool, the horizontal component of the flowing air will accelerate the froth to some extent but steady-state conditions are not expected to be at-tained. Considering that the additional stresses are modest even with a conser-vative flow analysis, BNL does not feel that additional effort needs to be ex-pended on this issue.
Conclusion BNL considers this issue closed.
~~UMPHREY H 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 at each containment eleva-tion.
Evaluation The applicant has indicated that the Perry design provides open areas on all floors above the HCU floor greater than the open area at the HCU floor.6 The ,
latter, at 1900 square feet, is substantially greater than the required minimum.
Conclusion Based on the above response, BNL considers this issue to be closed.
HUMPHREY SAFETY CONCERNS 2.1, 2.2 and 2.3 2.1 The annular regions between the safety relief valve lines and the drywell wall penetration sleeves may produce condensation oscillation (C.O.) fre-quencies near the drywell and containment wall structural resonance fre-quencies.
- 2.2 The potential condensation oscillation and chugging loads produced through the annular area between the SRVDL and sleeve may apply unaccounted for l 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 SRVOL and sleeve may apply unaccounted for loads to the penetration sleeve. The loads may also be at or near the nat-ural frequency of the sleeve.
l Evaluation The concern is that additional and unaccounted for loads may be produced by the steam condensation that occurs at the exit of the sleeve annulus. The applicant
- has precluded the development of such loads by installing pressure seals to i eliminate the flow of steam from the drywell through the sleeve annulus. A i
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description of the seal assembly is provided in Reference 8. It is stated that the seal is designed for both normal and accident environmental conditions.
Conclusion ,
BNL considers this issue to be closed based on the assumption that the pressure seals described in Reference 8 will perform as claimed by the utility. BNL recommends that the appropriate entity (the NRC Mechanical Engineering Branch, perhaps) be requested to evaluate the adequacy of the seal design, if this has not already been done.
HUMPHREY SAFETY CONCERNS 3.1 and 3.3 3.1 The design of the STRIDE did not consider vent clearing, condensation oscillation, 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 (MSRV's), the RHR re-lief valves can also discharge fluids into the suppression pool. 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 has supplied a plant unique response for pipe clearing water jet loads and for air bubble loads in Reference 7. Using conventional methods (e.g. RELAPS/ MOD 1), conservatively applied, loads on pool boundaries and sub-merged structures were developed as well as the dynamic loads on the steam line piping itself. Some of the more obvious conservatisms included the use of a steam flow rate following valve actuation 17% greater than the rated capacity of the valve, the assumption that the initial submergence of the pipe correspond to that following upper pool dump, and the absence of any attenuation of the water jet to derive impingement loads on the basemat. The. applicant states that these
- loads have been evaluated and verified as bounded by original design or incorpo-rated as new design basis loads.26 For C0 loads on the pool boundaries, the applicant utilizes the generic methods i
employed by all the Mark III utilities.8 Generally speaking, the method derives l from a conservative application of the Mark II C0 methodology. The C0 source
! used in this scheme was developed from test observations and used to generate pressure loads on the pool boundaries, as well as submerged structure loads.
They are shown to be bounded by the design main steam SRV loads by a wide mar-gin.
! The adequacy of the C0 load also needs to be judged in the context of potential l unstable steam condensation, i.e.: elevated suppression pool temperature.
l BNL's evaluation of this aspect is presented under Hunphrey Safety Concern 3.6.
l l l
CEI does not examine their containment capability to accommodate chugging type loads either on the boundaries or the discharge pipe itself. The utility takes the position 'that there is no credible scenario, assuming only one failure, of low mass flux discharge through the RHR heat exchanger relief valve discharge line. Therefore, chugging and lateral tip loads are not addressed.
CEI's basis for this position derives from the fact that the bleedlire through which noncondensables are purged from the RHR heat exchanger is not routed into the SRV discharge line. Then, in the absence of SRV or PCV failure, steam dis-charges to the suppression pool at the low flow rates that cause chugging would not occur. Despite this position, the applicant indicates 2s that the lateral load capability of the discharge line is 11.5 kips static equivalent. This re-sults from application of the submerged structures load methodology for LOCA air bubbles.
The applicar.t also argues 26 that because operation of the RHR system in the steam condensing mode (SCM) is operator intensive, failure of the PCV or SRV would readily be detected and operation could be terminated rapidly (signifi-cantly less than 10 minutes). This would reduce both the probability of experi-encing chugging at all, and the number of chugs, should such a failure occur.
We do not concur with the applicant that chugging is not possible during SCM operation. A single failure corresponding to premature opening of the SRV dur-ing startup operation (when supply pressures are low), or simply a leaking SRV, could both produce the requisite low steam flux. Accordingly, the lateral load capability for the discharge line, as stated, requires evaluation. '
The methodology that has been employed by the rest of the Mark III Containment Issues 0wners Group for this load derives from the Mark II load methodology of Reference 27. This was modified by the NRC Staff's Acceptance Criteria 28 to ac-count for the stochastic nature of the chugging phenomenon. This results in a peak design load amplitude that varies according to the number of chugs that would be expected during a particular accident scenario and the desired non-exceedance probability. Since the load capability of the structure is already specified in the present case, this methodology has been used to estimate the number of chugs that the RHR discharge line can experience with only a single exceedance of the stated value of 11.5 kips. Taking into account the difference in pipe diameter (6 inch diameter RHR line versus 24 inch diameter Mark II down-comer), this number has been found to be about 4000. Even with a conservative interval of one second between chugs (a more realistic number would be closer to 2 secs), chugging could proceed for well over an hour before a single exceedance of structure capability would be expected. Thus, we would not expect serious exceedance of the available load capability to occur during the relatively small number of chugs that these structures will experience during the life of the Perry plant.
Insofar as boundary and submerged structure loads are concerned, these have been found to scale with chugging source intensity which varies with pipe area, all other things being equal. Accordingly, the excitation produced by chugging at the RHR discharge pipe exit can be expected to be only a small fraction of that associated, for example, with main vent chugging (1/20th or less). We judge '
that this type of excitation would only be a perturbation relative to the mar-gins provided by these other design loads (LOCA and MSRV).
Conclusion This issue is considered closed for water clearing, air bubble, and C0 loads.
This judgement is based on the conservatisms used for the development of design values for these loads, and/or the wide margins exhibited relative to other design -loads.
We also consider this issue closed for chugging type lateral loads based on the stated capability of the RHR discharge pipe.
BNL also considers this issue closed for chugging loads on pool boundaries and submerged structures because of the relatively small size of the discharge pipe compared with that of other more numerous chug sources that have been used for development of design loads.
HUMPHREY SAFETY CONCERN 3.2 The STRIDE design provided only 9 inches of submergence above the RHR heat exchanger 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 leading to steam bypass and failure of the pressure suppression system.
The applicant has addressed this concern using the generic approach common to all plants.ll 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 pressurization), even with a clearance of 2 feet between the vertical vent pipe exit and the pool surface.
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The applicant states that the minimum submergence of the discharge lines will be about 4 feet. With this kind of submergence and the level of subcooling that :
would be expected during steam discharges through these lines (see discussion of l concern 3.6), the potential for steam bypass is, in BNL's opinion, non-existent.
Conclusion BNL considers this issue satisfactorily resolved for the Perry plant based on the large minimum submergence that exists in this plant.
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 concern here is that the RHR 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 MSRV's. Because the potential for subsequent actuations was not fully appreciated in the early stages, the HSRV 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).
CEI first provided a description of their reflood analysis in Reference 7. In response to a number of questions raised by BNL, however, a revised version of this submittal has been developed.13 These revisions were needed to account for changes in the Perry discharge line system due to the installation of one additional 6" vacuum breaker (the original configuration employed one 1-1/2" vacuum breaker). The revised calculations indicated significant reductions in a number of loads including reflood elevation (from 25 feet to about 9 feet for the RHR-A system) and water jet loads on the basemat (from 31 to 9 psid).
The revised submittal also presented a benchmarking of the reflood analysis f against in-plant test results.16,17 These comparisons show that the model can I
generate conservative estimates of reflood behaviour provided empirical param-eters used in the analysis are properly selected.
In our judgement, the addition of six inch vacuum breakers to each of the RHR discharge lines provides a more than adequate capability to reduce reflood in-tensity and the loads associated with it. This is because the discharge line itself is only a six inch diameter pipe. This judgement is supported quantita-tively by the reflood analysis which has been performed. The conservatism of this analysis has been demonstrated by comparison with in-plant test results and is therefore a suitable tool for this application.
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Conclusion BNL considers this concern to have been satisfactorily resolved for the Perry p W t.
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 tempe'rature stratification.
Evaluation Although the concern suggests that these discharges will occur following a DBA, the staff does not consider such a scenario to be credible since the applicant has committed to refrain from use of the RHR system in a steam condensing mode following a LOCA. On the other hand, continuous steaming for an extended period under normal conditions is possible and could not only result in excessive con-tainment pressurization via vertical thermal stratification but introduces the potential for unstable steam condensation leading to excessive dynamic loading on the pool boundaries.
The applicant has addressed this concern via the generic approach which was pro-vided in the MP&L response.12. A demonstrably conservative model of thermal de-position, stratification and pool mixing was developed and applied using MP&L plant parameters. Based on this model, the applicant shows in Reference 13 that even after steaming at the very high flow rate assumed in the analysis for twen-ty minutes, the difference between the average pool surface temperature (126*F) and bulk temperature (102 F) was only about 24*F.. We note also that the peak temperatures reported are just barely approaching levels that might imply un-stable 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. BNL is also sat-isfied that sufficient time is available to institute a number of actions which would effectively mitigate any adverse effects of this postulated failure.
Conclusion The issue raised by this concern is considered to be satisfactorily resolved for the Perry plant based on the assumption that post-LOCA operation of the RHR in a steam condensing mode will not occur.
l l HUMPHREY SAFETY CONCERN 4.3 l
l All Mark III analyses presently assume a perfectly mixed uniform suppression l
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 tempera-ture in the lower part of the pool where the suction is located will be as much as 7-1/2 F 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."
l l
Humphrey's basis for expecting a temperature difference of up to 7-1/2 F is un-clear (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 stratifi-cation that will occur, together with knowledge of RHR suction elevation.
The first of these requirements was established to the staff's satisfaction dur-ing its evaluation of the GESSAR 11 containment loads.18 After a lengthy, de-tailed, and sometimes heated review process by the various interested parties,19 the worst case vertical temperature profile proposed by the General Electric Company for standard plant design (Fig. 381-3 of Ref. 20) was judged accept-able. The basis for this judgement is given in Reference 18. 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 indi-cates that the Perry RHR suction is located at an elevation 3'-9" above the basemat. Comparison with the temperature profile referred to above implies a temperature difference (Bulk-to-RHR suction) of about 8'F. This slightly ex-ceeds the value cited by Mr. Humphrey. On the other hand, for the GGNS with RHR suction elevation of 10'-6", a conservative temperature difference of about 6 F prevails; i.e.: RHR suction temperature is greater than bulk temperature.
Because of certain plant unique differences in the Perry suppression pool geom-etry, it can be argued that the above nonconservatism is actually less. Specif-ically, we note that the Perry pool depth is somewhat smaller than the GESSAR-II standard plant (18-1/2 feet versus 20 feet) and the bottom vent is substantially closer to the basemat (2 feet vs 4 feet). We would expect both of those to lead to a flatter vertical temperature profile; i.e: higher temperature at lower elevations. This is borne out by the Perry unique temperature profile that is included as Figure I-1 of the Perry FSAR. Comparison with this profile indi-cates a temperature differential between bulk and RHR suction less than 5 F.
Also, BNL is satisfied that RHR operation will be very effective in reducing vertical stratification at normal pool depth. This is based on the results ob-served during in-plant SRV tests in which RHR operation was involved.21,22 In fact, during the Kuosheng tests,22 it was found that RHR operation induces a fa-vorable radial temperature stratification. That is, higher temperature fluid is directed by the swirling motion toward the containment walls where the RHR suc-l tion strainers are typically located. For these reasons, as well a the margins
! thathavebeendemonstratedtoexistinheatexchangerperformance,g3 BNL con-cludes that the Perry analysis will provide conservative estimates of contain-ment response for normal pool depth despite the existence of vertical tempera-ture stratification induced by LOCA blowdowns.
Conclusion BNL considers this issue satisfactorily resolved for the Perry plant.
HUMPHREY SAFETY CONCERNS 4.4 and 7.1 l
4.4 The long term analysis of containment pressure / temperature response assumes l that the wetwell airspace is in thermal equilibrium with the suppression pool water at all times. The calculated bulk pool temperature is used to j 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 <
su'rface temperature of the pool. will be higher than the bulk pool
- temperature. This may produce higher than expected containment t, temperatures and pressures.
Evaluation The' concern is similar to that associated with HSC 4.3 above except here the issue is the difference between pool surface temperature and pool bulk temperature. Based on the GESSAR-II and Perry unique temperature profiles referred to previously, these differences are 8*F and 7*F, respectively, in
, 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 temperature difference.
The applicant's response to this concern is the generic one that was originally provided by MP&L for the GGNS. 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 .
l 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, i
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.
- HUMPHREY 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.
- l. 4.10 Justify that the current arrangement of the discharge and suction points of
- the pool cooling system maximizes pool mixing.
I -Evaluation
- . The concern here is that if the RHR system's geometric arrangement for the
! suction 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," a key element of which was the Perry one-tenth-scale tests. M In these tests, a number of concerns were addressed systematically. These included short circuiting, development of bulk i
(_ _ _ __ _ _. ,_. _ . _ ,, . _ . _ , _ _ _ _ _ _ . _ , , _ , . . . _ _ _ , _ _ _
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pool motion, ability to eliminate thermal 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 expected design conditions. Since the findings from these tests show that good mixing can be achieved, as well as the absence of short circuiting, we conclude that the Perry RHR system can be ex-pected to perform in a manner consistent with design assumptions.
Conclusion BNL considers the issues raised by these concerns to be satisfactorily resolved for the Perry plant. ,
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 effect chugging loads.
Evaluation The applicant's response to this concern is the generic one which was originally provided by MP&L for the GGNS.Il In this submittal, physical arguments and ana-lytical procedures are used to estimate the pressure field that would be gene-rated 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 submergence. The re-sults are compared with design on an ARS basis and shown to be bounded except for local loads in the frequency range 15 to 32 Hz. For these conditions an ex-ceedance 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-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 following: 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: application of i
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 address the staff concern relative to the combined effect of upper pool dump and encroachment on local chugging loads,2 + 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 Perry plant.
HUMPHREY CONCERN 19.2 The effect of local encroachments on chugging loads needs to be addressed.
E M ation The applicant's response to this concern is the generic one which was originally provided by MP&L for the GGNS.Il In this submittal, physical arguments and ana-lytir.a1 procedures are used to estimate the pressure field that would be gene-ratec 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 comnared 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 ex-ceedance of design amounting to 60% 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-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-lowing: the loads developed for GGNS are conservative for the Perry plant as indicated in their respective responses to Humphrey Concern 1.0; the GGNS TIP platform represents a much larger encroachment than any in the Perry plant: 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 con-vincingly by experimental results: application of the worst case chug to all vents below the encroachment also represents a very significant conservatism; in a recent submittal by CEI to address the staff concern relative to the combined effect of upper pool dump and encroachment on local chugging loads, 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 l 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 encroachment.
Conclusion BNL is satisfied that the issues related to this concern have been satisfactorily addressed by the applicant and are therefore considered closed.
I
Questions relating to three additional concerns were developed by BNL. Al though they have evolved from and are related to HSC 4.5 and HSC 19, they are not of-ficially recognized as Humphrey concerns. CEI has formally addressed these BNL questions in their June 24, 1985 submittal. To facilitate future reference, we will use the identifier BNL-1, BNL-2 and BNL-3 to denote these questions.
BNL-1 The effects of increased submergence and encroachment on local loads are addi-tive. ARS comparisons showing the combined effect should be provided.
Evaluation A generic response was developed for this concern and included in the July 11, 1984 submittal.24 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 de-sign.
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.
BNL-2 The presence of encroachments may result in an increase in the main steam SRV loads.
Evaluation Based on preliminary results observed during the GGNS in-plant SRV tests,2s BNL concludes that the effect of encroachment on SRV loads will be small.
Conclusion BNL considers this issue to be resolved subject to confirmation via a detailed review of the GGNS in-plant SRV test results.
BNL-3 Upper pool dump increases the length of the water column within the main steam i SRVDL. This will tend to increase pipe thrust loads during SRV actuation.
Provide an analysis of this effect.
Evaluation The applicant has indicated in Attachment 3 of Reference 11 that these loads have been reevaluated and that the revised loads are within the capability of the existing SRVOL support configuraticn.
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Conclusion Based on the statement made by the applicant, BNL considers this concern to be resolved.
References
- 1. NRC Safety Evaluation Report for the River Bend Station on the Humphrey Safety Concerns.
- 2. 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 letter of 19 March 1985 from J. E. Torbeck to R. Pender, cc: J. Kudrick of NRC).
- 3. " Comparison of Velocities and Thicknesses of Water Column at Containment Wall for 1/M-Scale Pool Swell Tests", submitted by G. W. Smith of CIOG to H. R. Denton of NRC via letter of 15 May 1985.
- 4. Minty, S., et al., Perry Plant Unique Encroachments Final Test Report GE Report MDE-10-0185.
- 5. Sonin, A., "On the Resolution of the Humphrey Issues Relating to Pool Swell in the Clinton, Grand Gulf and Perry Plants", Enclosure to letter form C.
Economos, BNL, to J. A. Kudrick, NRC, dated July 16, 1985.
- 6. Attachment 1 to letter PY-CEI/NRR-0088L from M. R. Edelman, CEI to B. J.
Youngblood, NRC dated January 5,1984.
- 7. Attachment to letter PY-CEI/NRC-0007L from M. R. Edelman, CEI to B. J.
Youngblood NRC dated January 26, 1983.
- 8. Attachment 1 to letter PY-CEI/NRR-0281.L, from M. R. Edelman, CEI to B. J.
Youngblood, NRC, dated June 24, 1985.
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- 9. Ashley, G. K. and Leong, T. S., "An Approach to Chugging-Assessment of RHR Steam Discharge Condenstion Oscillation in Mark III Containments, Bechtel Report dated March 1984 and Attachment to letter AECM-84/0443 from L. F.
Date, MP&L, to H. R. Denton, NRC, dated September 7 1984.
- 10. Action Plan 6 of Attachment 1 to letter PY-CEI/NRR-0281L, from M. R.
Edelman, CEI, to B. J. Youngblood, NRC, dated June 24, 1985.
- 11. MP&L Letter No. AECM-82/353 dated August 19, 1982 from L. F. Dale, MP&L, to
- H. R. Denton, NRC.
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- 12. MP&L Letter No. AECM-82/574 dated December 3,1982 from L. F. Dale, MP&L, to H. R. Denton, NRC.
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- 13. Action Plan 9 of Attachment 1 to CEI Letter No. PY-CEI/NRR-0281L dated June 24, 1985 from M. R. Edelman, CEI, to B. J. Youngblood, NRC.
- 14. 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.
- 15. Gilbert Associates, Inc., "Model Study of Perry Nuclear Power Plant Suppression Pool - Final Report", November 1977.
- 16. NED0 21864P Mark I Containment Program, Final Report Monticello T-Quencher Test.
- 17. NEDE 23898P Mark I Containment Program Analytical Model for Computing Water Rise in a Safety / Relief Valve Discharge Line Following Valve Closure.
- 18. " Mark III LOCA-Related Hydrodynamic Load Definition", NUREG-0978, August 1984.
- 19. Transcript of the ACRS Subcommittee on Fluid Hydraulic Dynamic Effects Meeting of September 24, 25, 1981.
- 20. General Electric Co., 22A707, " General Electric Standard Safety Analysis Report", (GESSAR-II), Appendix 3B through Amendment 1, February 25, 1982.
- 21. Patterson, B. J., " Mark I Containment Program", Monticello T-Quenchers Thermal Mixing Test - Final Report", General Electric Co. Report NEDE-24542-P, April 1979.
- 22. NUTECH International " Final Test Report - Safety Relief Valve Discharge Test - Kuosheng Nuclear Power Station", Report ZTP-06-310, Rev. O, August 1982.
- 23. MP&L Letter No. AECM-82/353 dated August 19, 1982, from L. F. Dale, MP&L, to H. R. Denton, NRC. .
Youngblood, NRC.
- 26. Attachment to CEI Letter dated September 24, 1984 from Mr. R. Edelman, CEI, to B. J. Youngblood, NRC.
- 27. Davis, W. M., " Mark 11 Main Vent lateral Loads", GE Report NEDE-23806-P, October 1978.
- 28. Anderson, C., " Mark II Containment Program Load Evaluation and Acceptance Criteria", NRC NUREG-0808.
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