ML13317A443
| ML13317A443 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/30/1982 |
| From: | Krieger R Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-04-02, TASK-4-2, TASK-RR NUDOCS 8212020250 | |
| Download: ML13317A443 (2) | |
Text
Southern California Edison Company P. 0.
BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 November 30, 1982 Director, Office of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 SEP Topic IV-2 San Onofre Nuclear Generating Station Unit 1 By letter dated September 14, 1982, the NRC forwarded their draft evaluation of SEP Topic IV-2, Reactivity Control Systems.
That letter requested that we inform you if our as-built facility differs from the licensing basis assumed in your assessment. The results of our review of your topic evaluation are provided as an enclosure to this letter.
If you have any questions regarding the enclosed information, please let us know.
Very truly yours, R. W. Krieger Supervising Engineer San Onofre Unit 1 Licensing Enclosure 8212020250 821130 PDR ADOCK 05000206 P
S Comments on SEP Topic IV-2 San Onofre Unit 1
- 1. In item 2 of the evaluation the NRC staff concludes that two groups of rods could move simultaneously instead of one group.
The basis for this conclusion is not apparent. There are failures in the bank overlap and master cycler circuitry which lead to rod groups within a bank being stepped out of sequence. However, groups are not stepped simultaneously.
- 2. In item 5 of the evaluation the NRC staff concludes that a group or bank of shutdown rods could move inadvertently. This conclusion does not appear entirely valid.
Only a group (and not a bank) of shutdown rods could move inadvertently.
Failure of shutdown cam switch while the bank selector switch is in position to move a shutdown rod group would cause this problem. Refer to Sheet 45 of Appendix A of SCE's April 30, 1982 letter.
- 3.
Item 6 of the evaluation should read:
"A group, bank or banks (out of overlap region) of control rods could move inadvertently."
- 4. In item 8 of the evaluation the NRC staff concludes that an individual control rod or cluster, clusters, group, bank or banks of control rods could fall into the core.
This conclusion does not appear entirely valid. Dropped rods occur singly, in groups, by bank or by banks but not in random clusters (rods) as implied by this conclusion.
- 5. In item 9 of the evaluation the NRC staff concludes that a cluster of rods would move opposite to the commanded direction. This conclusion requires clarification in that there are two types of failures related to the direction of rod motion. First, rod banks move in one direction only, regardless of which direction is commanded. This is caused by failure of cam switches or failure of directional relays.
Refer to Sheets 41 and 34-35 of Appendix A to SCE's April 30 letter. Second, rods move in wrong direction for a few steps when an immediate change in direction is called for. This is caused by failure of directional relays.
Refer to Sheets 37-38 of Appendix A to SCE's April 30 letter.
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