ML20003A274
| ML20003A274 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 06/24/1974 |
| From: | Reid R, James Shea US ATOMIC ENERGY COMMISSION (AEC) |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8102030384 | |
| Download: ML20003A274 (2) | |
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ATOMIC ENERGY COMMISSION WASHWGTON, D.C. 20545 JUN 2 4 is74
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Files (Docket No. 50-155)
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/d. L ) icmann, Chief, ORB #2, L w ne INVERTED CONTRO. R0D P01 SON PINS - BIG ROCK POIhT (CONSUMERS POWER COMPANY)
An evaluation has been made of the information availabic concerning the status of control rods at the Big Rock Reactor as part of the review of the nutber of inverted poison pins existing in all boiling water reactors.
Inversion of the poison pins could, depending upon the constructi)n, allow movement of the steel balls within the pin which may, if the boron carbide compacts, allow the boron carbide to migrate from the tip of the poison pin, thereby reducing ef fective length of the control rod.
Because of the construction of the rods and the lack of af firmative test data to determine the number of inverted poisoa ains, larger BWRs have been required to perform eddy current testing and additional evaluation of the currently installed control rod.
In the case of the Big Rock Point reactor, it was concluded that the outer 16 rods were of a construction which would not cause a problem if the poison pins were inverted. The other inner 16 rods were partially x-rayed before installation and the data was reviewed to determine whether eddy current testing of the control rods would be necessary.
i Consumers Power Company submitted the results of the review of x-ray data in a letter dated April 18, 1974.
J The inner 16 control rods were installed in 1971. X rays obtained at the procurement stage were available on 14 of these rods. The X rays were readable for 11 of the 14 control rods. All poison pins were examined in one control rod and 50 percent of the poison pins were examined in ten rods. Only 1 inverted pin was discovered out of 384 pins examined. For a 144-inch core, CE has shown that the maximum effect of total loss of boron carbide from one pin of a control blade is about one percent of the reactivity worth of the control blade; i.e.,
a control blade worth 3.0 percent could change to 2.97 percent. Because of the shorter rods in the Big Rock reactor which reduce the length of the poison pin from which poison would be removed upon compaction, the effect of boron carbide compaction in a single inverted poison tube in the Big Rock reactor control blades would be less than for the larger s
3 cores and is not considered significant.
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Files JUN 2 41974 Based on (1) the low frequency of inverted pins found (1 cI 384 -
0.26%), and (2) the low number of rods subject to possible inverted
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tubes for which no data is available (5 of 32), it is concluded that the likelihood of a sufficient number of inverted poison tubes existing in the Big Rock Point reactor is sufficiently low that there if is reasonable assurance that the health and safety of the public will not be jeopardized by operation of the reactor without eddy current testing of the control rods.
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%Y Robert W. Reid Operating Reactors Branch #2 Directorate of Licensing
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I\\.bt James J.
'a Operating Reactors Branch #2 Directorate of Licensing cc: Consumers Power Company AEC PDR K. R. Coller, L:0R T. J. Carter, L:0R D. L. Ziemann, L:0RB #2 R. W. Reid, L:0RB #2 J. J. Shea, L:0RB #2 R. M. Diggs, L: ORB #2 OCC i
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