ML19254C582
| ML19254C582 | |
| Person / Time | |
|---|---|
| Site: | Millstone, Hatch, Monticello, Dresden, Peach Bottom, Browns Ferry, Nine Mile Point, Fermi, Oyster Creek, Hope Creek, Cooper, Pilgrim, Brunswick, Vermont Yankee, Duane Arnold, Quad Cities, FitzPatrick |
| Issue date: | 09/26/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Gilinsky V, Hendrie J, Kennedy R NRC COMMISSION (OCM) |
| References | |
| TASK-06-02.A, TASK-RR NUDOCS 7910170006 | |
| Download: ML19254C582 (2) | |
Text
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UNITED STATES 3.c, (/(,g NUCLEAR REGULATORY COMMISSION e
r, A. E WASHINGTON, D. C. 20555 o\\*..+,/
September 26, 1979 MEMORANDUM FOR: Chainnan Hendrie Commissioner Gilinsky Commissioner Kennedy Connissioner Bradford Commissioner Ahearne THRU:
Lee V. Gossick(signed) T A.Itehan Executive Director for Operations FROM:
Harold R. Denton, Director Office of Nuclear Reactor Regulation
SUBJECT:
RESOLUTION OF THE MARK I CONTAINMENT P0TENTIAL PROBLEM In our memorandua dated August 31, 1979, the staff identified a potentially significant concern relating to one of the blowdown loads (condensation loads) on the downcomers in Mark I containments. This concern involved the potential for overstressing of the downcomer-vent header connection which could lead to an overpressurization of the containment following a larga-break loss-of-w olant accident.
We have subsequently obtained additional information concerning the response characteristics of the downcomer-vent header system. Based on this information, we conclude that there is sufficient structural (fatigue) marr,1n in the existing plant configurations to preclude the need for any action at tnis time. A detailed description of the staff's evaluation is presented in the enclosure.
This issue will ultimately be resolvec ';y the detailed plant-unique analyses to be perfonned in conjunction with the Mark I Containment Long Tenn Program. The staff is presently finalizing the criteria that will initiate these plant-unique analyses.
Ob Harold R. Denton, Director N
Office of Nuclear Reactor Regualtion
Enclosure:
As stated
Contact:
D. Eisenhut, X27672 C. Grimes, X28204 cc: Secretary 1155 324 7010170 b%
s P
Enclosura CONDENSATION LOADS ON D0WNCOMERS IN MARK 4 CONTAINMENTS Following a review of data from the Mark I Full Scale Test Facility (FSTF), the staff indentified a potentially serious concern relating to condensation loads on the downcomers following a postulated large-break LOCA. The specific issue related to dynamic amplification of the downcomer condensation loads which could cause fatigue cracking in the downcomer-vent header intersection, which subsequently could lead to an overpressurization of the containment. The staff expected a significant dynamic amplification becaus a the condensation driving frequency observed n the test data was very close to the fundamental natural frequency (i.e., first or " swinging" mode response) of the downcomer-vent header system.
Subsequently, the staff determined Jat all operating plants have " tied" down-comers (i.e., a strap connects the ends of a pair of downcomers).
FSTF test data indicates that the loads on " tied" downcomers are lower than the loads on " untied" downcomers.
However, this finding did not completely alleviate the staff's concern regarding the potential for dynamic amplification of the condensation loads.
On September 5,1979, the staff met with representatives of the Mark I Owners Group to discuss this concern. The Mark I Owners Group presented structu al response analyses and additional FSTF data from which they concluded that the majority of the condensation load was exciting the second mode response (i.e., downcomer "spreaaing" or " wishbone" effect) for downcomers structurely tied together, because the highest loads result from a vertical thrust in the downcomer elbow. This finding was supported by strain and pressure measurement comparisons from the FSTF data. The Mark I Owners estimated the fraction of the load that could excite the first mode response and, assuming / lamic amplification of that fraction, concluded that only f
approximnely five percent of the ASME allowable fatigue usage would result for a design basis accident.
The staff agreed that this phemomenalogical description is adequately supported by strain and pressure measurement cumparisons, and that there is sufficient margin in the fatigue usage to accommodate the uncertaities in the assessment presented by the Mark I Owners Group. Based on this finding the staff concluded that there is not an immediate safety concern, and there is sufficient margin in the existing plant configurations to permit this issue to be finally resolved as previously scheduled as part of the Mark I Long Tenn Program plant-unique analyses.
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