ML20049H451
| ML20049H451 | |
| Person / Time | |
|---|---|
| Site: | LaSalle  |
| Issue date: | 02/24/1982 |
| From: | Schroeder C COMMONWEALTH EDISON CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0519, RTR-NUREG-519 NUDOCS 8203030076 | |
| Download: ML20049H451 (15) | |
Text
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\\ ona First National Plaz2. ChicKgo. Illinois Commonwealth Edison J/
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O Address Reply to: Post Office Box 767 Chicago, lilinois 60690 February 24, 1982 k
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Mr. A. Schwencer, Chie f g
Licensing Branch #2 O_CEl'/03 t-Division o f Licensing
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- U. S. Nuclear Regulatory Commission Washington, DC 20555 pa ya
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Subject:
LaSalle County Station Units 4a'n'd-2GTV Fuel Lift Analysis
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NRC Doc _ket Nos. 50-373 and 50-374 Reference (a):
NUREG 0519, Supplement No. 2, Safety Evaluation Report Related to the Operation o f LaSalle County Station Units 1 and 2, Section 4.2.3.4, Seismic and Loss-o f-Coolant Accident i
Loadings.
Dear Mr. Schwencer:
The purpose of this letter is to provide LaSalle Unit 1 specific results o f the-Fuel Lif t Analysis.
Reference (a) s tates, in part,- that the NRC "...will j
condition the LaSalle License as follows:
(1)
By July 30, 1982, the applicant must submit to the NRC a j
complete description o f the analytical methods along with all analytical results necessary to show that the LaSalle Unit 1 fully meets the requirements of Appendix A to the Standard Review Plan, Section 4.2 (NUREG 0800) with regard to fuel bundle lif toff.
-(2)
Prior to approval to operate a second cycle at LaSalle Unit 1, the final assembly lif tof f issue mus t be reviewed by.
NRC, all questions arising from this review must be satisfactorily answered by the applicant, and the NRC must conclude that the lif tof f issue has been fully resolved."
i The analysis and results for BWR fuel assembly response to the ef fects of seismic and dynamic loadings during postulated accidents were previously covered via GE generic report NEDE-21175-P, 3oo/
l 8203030076 820224 PDR ADOCK 05000373 E
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A.~Schwencer February 24, 1982 "BWR 6 Fuel Assembly Evaluation-of' Combined Safe Shutdown Earthquake l
(SSE) and Loss-of-Coolant Accident (LOCA) Loadings", Novembe r 1976.
This earlier evaluation used a general methodology and mathematical model (Model I) characteristic of the then state-o f-art to calculate gap opening and associated impact loads.
For LaSalle, the early-results were initially accepted by the NRC-staf f (SSER 4.2.3.4);
i however, some model limitations became evident as a more comprehen-i sive methodology was developed in 1980.
The Upgraded Model (Model II) was used to reevaluate LaSalle Unit 1 fuel.
Again, the result met the gap criteria established to constrain disengagement of the lower tie plate from the fuel support casting, and the gap criteria relative to separation of the guide tube from the CR0 housing.
The fuel assemblies for LSCS Unit 1 were then evaluated for i
the maximum expected horizontal accelerations and vertical accele-rations under external event load combinations (the seven classical load cases -from the DAR) to demonstrate that the fuel assemblies can satisfactorily withstano these loads.
The results from this i
reevaluation show that the limiting load combinations fall wf. thin the allowable load envelope.
Attached herewith is a brief comparative report outlining both basic models and methods with LaSalle Unit 1 specific results.
Revision of NEDE-21175-P (Proprietary) is underway to upgrade the methodology and mathematical model.
That revision is expected to be provided to the NRC staf f about July 30, 1982 as the generic BWR reference for fuel lif t, applicable to LaSalle Units 1 and 2 among other recent BWR plants.
This information is provided to you as an interim report as requested during a telecon on January 12, 1982, between Messrs. A.
Bournia et al o f your'staf f and C. E. Sargent and G.
R. Crane o f
]
Commonwealth Edison Company.
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If there are any further questions in this regard, please contact this office.
Very truly yours, a-/15/9L-C.W. Schroeder Nuclear Licensing Administrator 4
1m Attachment
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Region III Inspector - LSCS t
1 3526N
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1.0 INTRODUCTION
The fuel bundles in the reactor core are supported horizontally by the fuel-support casting and core plate at their lower end and by the top guide at their upper end.
In the vertical downward direction, the fuel bundle weight is supported by a system composed of the fuel-support casting, control-rod guide tube, upper portion of control rod drive housing and reactor pressure vessel (RPV) bottom head.
In the vertically upward direction the bundle weight resists the upward forces caused by the flow of reactor coolant inside the vessel and any additional dynamic forces due to postulated accident loads which could potentially result in relative motion between the fuel bundle and its support. Under this dynamic condition, the bundle could theoretically unseat (herein defined as gap opening *) and, upon rescating in the fuel supports, produce impact forces on the vessel and internals. Analyses have been performed to determine the magnitude of the gap opening between the fuel assembly and its support casting and impact forces and to assure fuel design acceptability during the postulated accident conditions.
The dynamic analysis required to assess the amount of gap opening and associated impact forces is by nature a non-linear and complex process.
The nonlinearity is due to the hydrodynamic effects, frictional forces and the various gaps between the components. During a meeting at GE-San !ose March 28,1980 between GE, NRC and EG and G (NRC Staff Consultants), a mathematical model (Model I) and an analysis methodology consistent with the then current state-of-the-art used by GE to evaluate the gap opening and the associated impact forces were presented for NRC review. This was then determined to be consistent with the intent of the requirements of draft SRP 4.2, Appendix A.
The gap opening effects were evaluated for La Salle I using the methods and model type discussed with NRC and the results were submitted to NRC as a part of La Salle 1 FSAR. These results showed that gap opening was within acceptable lia::s.
Since that time, some of the limitations in this fuel lif t model and methodology reviewed by NRC on March 28, 1980 were recognized and steps were taken by GE to update and upgrade both the model and the methodology to eliminate these limitations consistent with the current state-of-the-art.
Since the 1980 La Salle I evaluation was performed before the i
updated model and methodology was available, these evaluations were repeated using the updated model and methodology. The results show the gap opening to be still within acceptable limits. However, for the gap opening evaluation of the other requisition plants, only the upgraded model (Model II) and the methodology is being used.
Details of both models and methodology and the associated La Salle results from both evaluations are summarized in the following sections.
- Fuel lift is defined as the amount of gap opening required to cause lateral disengagement of the fuel assembly lower tie plate from the fuel support casting such that the resulting loss of 'nel bundle lateral positioning could interfere with control rod insertions.
DETAILS OF MODEL I AND ASSOCIATED METHODOLOGY 2.0 This is a lamped mass model The mathematical model is shown in Figure 1.
made up of masses, springs, friction and gap elements representing the various components which include:
Fuel Assembly consisting of Upper and Lower Tie Plates, Tie Rods, Fuel a)
Rods and Expansion Springs, and Fuel Channel.
Vertical Fuel Support consisting of Fuel Support Castings, Control Rod b)
Control Rod Drive (CRD) Housings, Reactor Pressure Vessel Guide Tbbes, (RPV) Bottom Head, and RPV Support Skirt.
Horizontal Fuel Support consisting of Top Guide, Fuel Support c)
Castings, Core Plate, Shroud, and Shroud Support Plate.
d)
This is a one dimensional vertical dynamic model which includes nonlinear The model effects due to friction and gaps in the core assembly system.
mass and stiffness properties include structural and hydrodynamic effects, linear structural damping, and contains friction elements to simulate the vertical interaction between the fuel and the core plate and top guide and fuel channel and lower tie plate. The model also includes between the application of hydraulic uplift forces on the fuel assembly for the upset The three gaps, namely housing to guide tube, guide or faulted conditions.
tube to fuel support casting and fuel support casting to fuel assembly lower tie plate are modelled as one gap element and the calculated deflections could represent relative motion at any of these or a combination of these gaps.
The mathematical model is then subjected to loads from seismic (SSE) and This LOCA associated suppression pool dynamic loads and scram effects.
input consists of horizontal and vertical motions of the fuel support structure due to the dynamic loads, reactor coolant uplift forces on the fuel bundle due to the transient pressure differences caused by the flow of reactor coolant and scram uplif t forces on the fuel bundle due to control rod to fuel channel intersction.
The input dynamic loads were combined in such a manner that peaks of the the same instant of time. Then I
individual loads were aligned to occur at This l
the combined time history was applied to the mathematical model.
to the absolute sum method used in combining two or i
method is equivalent The time history analysis more dynamic responses from a linear analysis.
was performed using the component element method (Reference 1).
The faulted load combination cases considered for the gap opening evaluations The maximum gap opening resulting from the are shown in Table 1.
evaluation of these load combiration cases is 0.0288 inches which is to start the significantly less than the gap required (0.52 inches) disengagement of the lower tie plate from the fuel support casting.
DETAILS OF MODEL II AND ASSOCIA'ED MEH OD01hGY Subsequently, Model I was reviewed for updating in order to eliminste any model limitations that may have been present and also to incorporate recent state-of-the-art developments in modelling. Based on this critical evaluation of Model I, the following modifications were made to develop i
Model II.
Consideration of uplif t force on the guide tubes.
a)
A more detailed treatment of the hydrodynamic mass effects to account b) for the relative motion between the guide tubes and other components, Inclusion of core plate mass in the fuel lift model itself to provide c) a complete vertical dynamic model of the reactor core and core support structures.
d)
Use of two gap elements (as described below) rather than one.
The reactor internal structural response under the dynamic loads were frictional strongly affected by two non-linear phenomena, namely (i) effects between the core plate and fuel bundle and (ii) the various gap effects that exist in the core assembly. This would result in the system response being strongly dependent on the history of the input forcing function and the simple rule of aligning the maximum values (worst case phasing) of the input loads as was done using Model I may not produce Hence, a probabilistic consistently conservative system responses.
approach involving random phasing of the input forcing function was used for use with Model II.
The details of the mathematical model are shown in Figure 2 and Table 2.
This is also a lumped mass model of the same mechanical system considered in Model I but with (1) twosapelementsVandW(SeeFigure2)tosimulatethe g
potential uplif t of the fuel bundle with respect to fuel support and the guide tube with respect to CRD housing instead of one
- casting, gap element in Model I (See Figure 1).
(ii) a more detailed core plate modeling than in Model I.
a more detailed modeling of the hydrodynamics than in Model I to (iii) account for the relative motion between the guide tubes and the other components.
use of published test results for upper and lower bound friction (iv) coefficient values in the non-linear evaluation to bound the system responses.
--:--,~--
This model was subjected to loads from SSE and LOCA associated suppression However, in addition to the effects pool dynamic loads and scram effects.
of the hydraulic uplift forces on the fuel assembly, the hydraulic uplift effects on the guide tubes with respect to the CRD housing were also considered in evaluating the fuel lif t effects using this Nodel II.
Model II was then subjected to a series of non-linear dynamic analyses to evaluate the combined effects of the dynamic loads on the fuel assembly The method used to perform the non-linear analysis of Model II was system.
also the component element method.
Due to the transient and random nature of the dynamic loads and the complexity of the non-linear nature of the fuel mechanical system response under multiple excitation, a probabilistic approach involving random The random start times of phasing of the input time histories was used.
the different loads to be combined for each load combination were conservatively defined such that the strong motion portion of all loadings were forced to be simultaneously active at some time during the duration of the load combination.
A number of A statistical procedure was used to compute dynamic responses.
nonlinear analyses were performed with randomly selected time phasing of the input loads in the loading combination case under consideration based upon a conservatively biased interpretation of the NRC requirements for the combination of simultaneous loadings. Then using the mean and standard deviation of the responses from these analyses, response values (R) which have a nonexceedance probability (NEP) a and a confidence limit y were generated for design use.
For the La Salle I gap opening analysis, 5 nonlinear analyses were performed for each critical load case and an a value of 84% and a y value These values of a and y are of 50% was used to determine the gap opening.
consistent with the requirements of definition of input loadings. The basic the level of conservatism of the combined philosophy for this is that responses should be no less than that for the individual responses being This is consistent with the approach in Reference 2 for combined.
combining linear, elastic dynamic responses of a component when subjected to two or more dynamic loads.
The faulted loading combination cases considered for this analysis are the The maximum calculated gap opening from the same as given in Table 1.
evaluation of these combination cases is 0.186 inches. Again, this is less than the gap (0.52 inches) required to start the disengagement of the lower tie plate from the fuel support casting.
1 l
Hence, for La Salle I, it is concluded that the gap opening evaluated using both Models I and II is well within the allowable limit and that satisf actory fuel assembly alignment is maintained.
3.0 FUEL EVALUATION The feel assemblies for La Salle I were evaluated for the dynamic horizontal accelerations and vertical accelerations resulting from the 186 mil gap opening previously discussed. The results of this evaluation demonstrate that the fuel assembly can satisfactorily withstand this combined horizontal and vertical loading.
The method used for this evaluation was as follows:
Horizontal and vertical loading allowables (3.9 G horizontal and 1.6 G vertical) were previously established in NEDE-21175-P BWR/6 Fuel Assembly Evaluation of Combined SSE and LOCA Loadings (Amendment No. 2) for the A vertical only allowable (6.4 G vertical) was established fuel bundle.
based on the analyses shown in NEDE-23542-P Fuel Assembly Evaluation of
. Shipping and Handling Loadings.
Other combinations of horizontal and vertical allowables were established based on a linear combination rule.
If the predicted horizontal and vertical loadings fall within the area bounded by the linear combination rnie, then the fuel bundle has been demonstrated capable of withstanding the predicted loadings.
If the predicted horizontsi and vertical loadings fall outside of this then an analysis is performed specifically addressing these loads.
- area, Resulting component loads are then compared to a110wables previously established by NEDE-21175-P or additional stress analyses and/or tests are performed to assure component acceptability.
The most limiting combinations for La Salle I fell within the area determined by the linear combination rule. These limiting load combinations were:
Vertical (Gs)
Horizontal (Gs) 5 0
4.1 1.5 F
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4.0 REFERENCES
1.
Samuel Levy and John P. D. Wilkinson,
' Component Element Method in Dynamics ,1976, McGraw Hill.
' ' Methodology for Combining Dynamic Response s , R. K. 7/at tu, U.S.
2.
NRC, Nures-0484, Rev. 1, May 1980.
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TABLE 1:
LOAD C0KBINATION CASES Faulted:
N+AP,+SSE+SRVg+ S3 Case 1 Fanited:
N+AP,+SRVg 3+SSE+ CHUG Case 2 Case 3 Faulted:
N+AP,+SSE+SRVADS+ 1 Case 4 Faulted:
N+AP,+SSE+SRVLSPA 2
Case 5 Faulted:
N+AP +SSE+AP+S f
3 Case 6 Faulted:
N+AP +SSE+V, g
Faulted:
N+AP +SSE+P, Case 7 f
where including the is the acceleration due to annulus pressurization, AP action of jet impingement and jet reaction forces on the RFV.
CHUG is the acceleration due to chugging of the pressure-suppression fluid following a LOCA.
is the acceleration due to condensation oscillation CO and CO ) of the pressure-suppression fluid following a LOCA.
(CD is the peat core pressure drop during a LOCA.
AP g
is the peak core pressure drop during the bounding upset event.
f AP normal full power, full flow operating i'orces.
N 1
l S
uplift forces on the fuel due to scram.
3 acceleration due to pool swell following a LOCA.
is the P,
is e ac e era n ne t discharge of the safety-relief SRVADS valves (SRV) by the automatic depressurization system (ADS).
- 8' SRV
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ALL is the acceleration due to discharge of I or 2 SRVs (SRV 3p SRY r2 is a special case of this).
is the acceleration due to the safe shutdown earthquake.
SSE V
is the acceleration due to vent clearing following a LOCA.
SRV is the acceleration due to the worst case of MAI SRV SRV and SRV gg 1 or 2.
TABLE 2:
FUEL LIFT MODEL II MASS REPRESENTED STIFFNESS REPRESENTED COMPONENT BY NODE BY ELEMENT 1
11 Channel EPV Botton, CRD, CED Hga.
7 13 Y1 f
Top Guide Neglected 8
14 Core Plate 2
11 Upper Tie Plate Fuel (inner rows) 3 W4 Fuel (onter rows) 4 W5 2
W1 Tie Rods W6 5
Lower Tie Plate 6
W7 and W8 Guide Tubes, Fuel Support Casting Expansion Springs Neglected W2 (inner rows)
W3 (onter rows)
Hydrodynamic Model 10 thru 39 IS * "" 34 Spring Element NOTE:
Il
=
Friction Element Yi
=
Stop Element W1
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FIGURE 1 - LA SALLE 1 FUEL LIFT (MopELT) l
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F XI I6 CR W1 W3,#
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FW9 - -u Y1 Y2 W4 W5 tsi V__
W6 FW9 - --- u I*
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1 VERTICAL DYMAMIC HONLINEA FIGURE 2a
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q Continued in Fip re 2 30 I
.T 30 17 i
X14 X26 16 29 X25 X13 X24 X12 14 27 X23 X11 26 13 X10 X22 25 X21 X9 e
11 X20 XB 10 X19 X7 X6 l
VERTICAL DYNAMIC NONLINEA FIGURE 2b:
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38 X34 37 X33 36 X32 35 X31 34 X30 21 X18j
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A X5 $
j r
X17 X29 h
32 19 X28 X16 31 18 X27 X25 0
s7 YERTICAL DYNAMIC NONLINEA FIGURE 2C:
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