ML20039C014
| ML20039C014 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 12/22/1981 |
| From: | Vincent R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-04-02, TASK-4-2, TASK-RR NUDOCS 8112280315 | |
| Download: ML20039C014 (3) | |
Text
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Consumers Power Company General offices: 212 West Mich6 gen Avenue, Jackson MI 49201 + (517) 788-o650 J
December 22, 1981 k' /'fo, d
e Dennis M Crutchfield, Chief g
M/G Operating Reactors Branch No 5 DEC J
I381ts fc Nuclear Reactor Regulation I
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US Nuclear Regulatory Commission
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Washington, DC 20555 re 18i " A DOCKET 50-155 - LICENSE DPR l@TTEs f
BIG ROCK POLNT PLANT - SEP TOPIC IV-2, REACTIVITY CONTROL SYSTEMS By letter dated December 7,.1981 the NRC transmitted a draft evaluation of SEP Topic IV-2 for the Big Rock Point Plant. This evaluation was based on previous Consumers Power Company submittals dated May.4, 1981 and September 28, 1981.
Consumers Power Company has reviewed the draft topic evaluation, and has determined that additional information is needed to place several items and the staff conclusions in proper perspective. Accordingly the attached comments are submitted for your consideration.
(
Robert A Vincent Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point f pages g
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Response to KRC letter of December 7, 1981 SEP Topic IV-2, Reactivity Control Systems 1.
Page 4,' Item No 6 With one exception that is explained below, continuous' motion of control rods is not allowed at operating conditions. For continuous simultaneous withdrawal of two rods at power operation, it would take a single failure.
in conjunction with an operator error.or two independent single failures.
With this in mind, two control rods moving simultaneously in continuous mode do not have to be analyzed to assure that specified acceptable fuel design limits are not exceeded, (at least for operating conditions) since more than just a single failure is required to initiate the incident.
The one exception mentioned above is of no real concern. As each rod reaches the bottom of the core.during normal rod withdrawal, it has a rod drive coupling integrity check performed on it.
This involves the appli-cation of a continuous withdrawal signal to the rod that just bottomed out of the core. Normally, no rod motion would result from this test.
However, a single failure of the system could cause another rod to move, resulting in an uncontrolled single rod withdrawal. An analysis of this.
event was provided as Appendix C of Consumers Power Company letter of May 4, 1981.
At cold shutdown conditions, continuous rod motion is allowed during some testing. These tests are the control rod drive coupling integrity test, control rod drive friction test (at reduced hydraulic pressure), and the control rod drive withdrawal timing tests. The shutdown margin test also allows continuous' motion, but only to insert rods, which is of no concern. None of the tests that use continuous withdrawal will have more than one rod that is not fally inserted at one time. Then the worst con-figuration for this failure would be two adjacent rods moving simultane-ously from full in to full out in continuous mode. Since shutdown margin must be maintained to compensate for full withdrawal of the highest worth single rod, there must be considerable rod motion before the reactor will go critical. This will give the operator soce amount of time to terminate rod motion. Since the operator has his hand on the' control switch while moving rods during these tests, and should be watching the position indication, it should take little time-for him to recognize the-problem and release the switch. Even if,the operator doesn't release the switch to stop rod motion, the short period trip or the high flux trip
. should stop rod motion and. insert the rods before any appreciable nuclear.
h heat is generated,.thus preventing any fuel damage.
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Page 4, Item No 7 Since there is no other means of altering the reactivity balance of the core to compensate for a rod insertion, the reactor power will merely decrease, which will conservatively increase the margin to fuel damage limits.
3.
Page 4, Item No 8 Alta gh rods have failed to withdraw in the past, a rod has never failed to scram. During power operations, if a stuck rod should occur, the altered core conditions are analyzed before any additional rods are withdrawn to insure that margin to fuel damage limits are not violated.
In cold conditions, a stuck rod will not adversely affect plant safety because there is sufficient shutdown margin to shut the reactor down with the highest worth stuck rod fully withdrawn from the core.
4.
Page 4, Item No 9 For a rod that moves slower than set speed, it may not insert in the normal notch mode, because it would not move to the next notch before the timed relays would shut off the hydraulic water supply. The drive would be scrammable, but it may not meet the scram time as required by the Big Rock Point Technical Specifications. This is inconsequential because it has a smaller safety impact than a rod that is stuck. The slow moving rod could be withdrawn in the normal notch mode, but the rod would take longer than normal to settle on to the locking collet.
A rod that moves faster than set speed could possible move 2 or possibly 3 notches instead of a single notch while in notch mode. For insert this is of no concern; for withdrawal this is in fact a subset of the uncontrolled rod withdrawal accident and thus is covered by the analysis presented in the May 4 1981 letter.
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