ML20040B606
| ML20040B606 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 01/19/1982 |
| From: | Dale L MISSISSIPPI POWER & LIGHT CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| AECM-82-30, NUDOCS 8201260238 | |
| Download: ML20040B606 (5) | |
Text
_ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
MISSISSIPPI POWER & LIGHT COMPANY Helping Build Mississippi P. O.
B O X 16 4 0. JACKSON. MISSISSIP PI 39205 January 19, 1982 Nuctt An encouction oteAntME Ni y(,-
U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation
'M Washington, D.C.
20555
~~
m Attention:
ti r. Ilarold R. Denton, Director
Dear fir. Denton:
SUBJECT:
Grand Gulf Nuclear Station Units ! and 2 Docket Nos. 50-416 and 50-417 File 0260/L-334.0/5007/rl-001.0 Hydrodynamic LOCA Loading of IICU Floor AECtl-82/30 The attached report is provided by flississippi Power & Light (?!P&L) in response to concerns identified in the Safety Evaluation Report (SER) for Grand Gulf Nuclear Station NUREG-0831.
This information pertains '.o the loading of the hydraulic control unit (IICU) floor resulting from the design basis loss of coolant accident (LOCA). This aformation supplements that already submitted by flP&L via letter AECtl-81/-.01, dated October 9,1981, and by Bechtel Power in the letter VB-81/0577, dated November 10, 1981.
Please advise if clarification is required in regard to the attached information.
Yours truly,
?)
,/
/
L.
F. Dale flanager of Nuclear Services JGC/JDR:Im DO/
Attachment tir. N. L. Stampley (w/a)
I cc:
fir. G. B. Taylor (w/a) i tir. R. B. t!cGehee (w/a)
/ /
tir. T. B. Conner (w/a) f!r. Richard C. DeYoung, Director (w/a)
Office of Inspection & Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.
20555 8201260238 820119 PDR ADOCK OS000416 AESP1 A
PDR Member Middle South Utilities System
Page 1 Grand Gulf Containment Buildink HCU Floor Capability Evaluation I.
Background
d During the course of the generic review of Mark III containment LOCA loads, specified by General Electric Company in GESSAR II, Appendix 3B, the NRC raised cas.cerns regarding the methodology to be used for determ:ning drag loads on grating type structures and regarding the specified froth impact pressure derived from test data.
At a meeting in San Francisco, California on September 24, 1981, between the NRC, Bechtel, MP&L, and GE, NRC Staff requested that MP&L address several NRC questions regarding pool swell froth drad and froth impact loads applied to the Grand Gulf containment building IICU floor in order to resolve this issue, an open item identified in the Grand Gulf Safety Evaluation Report. MP&L provided the NRC with responses to all questions raised (AECM-81/401, dated October 9, 1981; VB-81/0577, dated November 10, 1981). Appropriate protions of those responses will be incorporated in the next available amendment to the Grand Gulf FSAR.
At a meeting between GE and the NRC held November 20, 1981, GE's presentation to the NRC provided further justification that the GESSAR II froth impact specification was bounding and conservative. The NRC indicated that this additional information still way prove to be insufficient and presented a "best estimate" alternate methodology for froth impact loads which correlates the froth impact pressure with the height of the impacted structure above the maximum suppression pool surface. The NRC also presented concerns that a single impulse duration may not be conservative due to structure natural frequency variations as well as test data interpretation.
To further assist in the resolution of f roth impact loads f or Grand Gulf, the NRC requested that MP&L perform further llCU capability evaluations using the NRC's "best estimate" methodology for froth impact loads and to consider variable froth impact pulse durations. At a meeting between the NRC, MP&L, and Bechtel on December 16, 1981, the NRC was given a status of the work completed as of that date.
Based upon discussions at that meeting, the NRC further clarified the criteria to be used in performing the HCU floor capability evaluation. The criteria are as follows:
1.
Due to the dynamic nature of the load, the capability of the structure may be evaluated using Elasto-Plastic Methods.
2.
Figure I shows the pressure time history of froth impact loads followed by froth drag loads. The froth impact loads on structures will vary with distance from the suppression pool surface as defined by Figure 4 of NRC (G. Maise) presentation of "Best Estimate Methodology for Froth Impact
Page 2
\\
l Loads." For further conservatism, as requested by the NRC, these pressures will be increased by 3 psi.
The revised figure will be provided by i
January 20, 1982.
2 3.
Froth drag is considered to be a constant at 11 psi.
4.
The dynamic nature of the load function (froth j
impact / froth drag) should be considered.
1 5.
Permissible ductivity ratios should be consistent with those accepted by the NRC for other similar 3
type loads, as defined by Regulatory Guide 1.142 (concrete) and SRP 3.5.3 (steel).
1 II.
Method of Analysis The 1c+d function as described in Figure 1 is considered an impulsive load.
Impulsive loads as defined in ACI 349-80 are time-dependent loads which are not associated with the collision of solid masses. Other loads classified as impulsive loads in the design of Grand Gulf Nuclear Station are:
a.
Jet impiegement b.
Blast pressure c.
Compartment pressurization d.
Pipe-whip restraint teactions.
When structural elements, concrete and steel, are subjected to these loads, the structural response is determined by one of the following methods:
For structural elements which respond elastica 11y, a.
the dynamic effects of the impulsive load is considered by calculating a dynamic load factor (DLF). The resistance available for the impulsive 1
load must be at least equal to the peak of the j
impulsive load transient multiplied by the DLF.
i b.
For structural elements which respond inelastically, the dynamic effects of impulsive loads are considered by performing a time-history dynamic l
analysis. Mass and inertial properties are ir-luded, as well as the nonlinear stif fness of i
s.ructural elements under consideration.
The
]
applicable permissible ductilities are as follows:
i.
Concrete Slabs Flexure
- 0. 05/ f-f ' fi 10 Shear 1.0 Dynamic Increase Factor 1.1 i
Steel Beams Flexure 10 Dynamic Increase Factor 1.1
Page 3 Ill.
Summary of Hesults The following results have been obtained to date regarding IICU floor capability:
1)
Maximum Dynamic Load Factor (DLF)
A study has been performed to determine the maximum dynamic load factor to be expected from the froth impact-froth drag loading specification.
Froth impact. duration (tg) was varied in 40 second increments f rom 0.020 seconds to 0.220 seconds to address the NRC concern regarding this parameter.
Froth impact peak pressure was varied from 11 psi to 16 psi to address the application of the NRC's "best estimate" methodology to froth impact pressure relative to the distance of the impacted surface above the maximum suppression pool surface.
Froth drag pressure was taken as 7.4 psi or 11 psi in combination with the aforementioned variables tc cddress the calculated Grand Gulf wetwell pressure and the GESSAR specified wetwell pressure following pool swell. This showed that the maximum dynamic load factor is insensitive to the relationship between the peak froth impact pressure and peak f roth drag pressure.
The maximum DLF is approximately equal to a constant (1.45) which occurs when the structural period is equal to td' Since the structural periods in question are in the range of 0.020 to 0.220 seconds, a DLF of 1.45 is used to multiply the maximum transient pressure for structural evaluations.
2)
Concrete Slabs The critical portions of the ecncrete slabs are located at Aximuths 90 (south) and 270 (north).
The maximum froth impact pressure applied at the bottom of the concrete slab is equal to 14.5 psi (11.5 + 3).
Using a DLF of 1.45 and concrete cylinder break test results, the shear stresses are within the code allowable as defined in Section 11.4 of ACI 318-71.
The bending of the slab is not critical and the stresses in the reinforcing steel are well within the code allowable.
3)
Steel lleams i
The steel beams at the same location as the critical concrete slab will be subjected to a froth impact pressure of 18.0 psi (15 + 3).
For steel beams in the grating areas, the critical beams are locai.d at azimuths 40 (south-east), 315*
(north-east) and 180 (west). The froth impact pressures as calculated for these beam; vary from 14.5 (11.5 +3) to 19.0 psi (16 + 3).
In all are :s, the ductility ratios are well within the permissible ductility of 10.
The hiehest ductility ratio needed is less than 3.0; the majority of tLt. ratios are less than 2.0.
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