ML13331B074
| ML13331B074 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/17/1988 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8810190118 | |
| Download: ML13331B074 (3) | |
Text
Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 M. 0. MEDFORD TELEPHONE MANAGER OF NUCLEAR ENGINEERING (818) 302-1749 AND LICENSING October 17, 1988 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Additional Information Regarding Amendment Application No. 151 San Onofre Nuclear Generating Station Unit 1
Reference:
Letter, Charles M. Trammell, NRC, to Kenneth P. Baskin, SCE, Request for Additional Information - Amendment Application No. 151, July 26, 1988 The referenced letter provided Southern California Edison (SCE) with questions regarding SCE's Amendment Application No. 151 for San Onofre Unit 1.
Responsive to that request, the enclosed information is provided.
If you have any questions, please let me know.
Very truly yours, Enclosure cc:
J. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 2'DC
Enclosure NRC Question 1 Southern California Edison is requested to provide the original bases for allowing Control Group 1 to be inserted up to 10% into the core at power levels from 22% to 100% of full power.
SCE Response The Technical Specification Figure 3.5.2.1, prior to Proposed Change No. 169, shows a rod insertion limit for Control Group 1 at 10% insertion into the core from power levels from 22-100% power. The 10% insertion limit is a historic characteristic of this insertion limit curve which was generated for the SONGS Unit 1, Cycle 1 core operation. The core physics characteristics of the first loading of the San Onofre Nuclear Generating Station showed a potential for a low level of positive moderator coefficient at the initial operation of the core.
Discussions with personnel who were involved with the initial operation of Cycle 1 provided information that the operational consequences of the moderator coefficient were evaluated. Operations was concerned about the ability of the fixed movement speed of the rods relative to the need for reactivity control response in order to avoid actuation of the protective trip. Safety considerations were assured through the protection system function; however, reactor trips were undesirable for operation. The Group 1 control rods, if withdrawn fully from the core and needed to assist in reactivity control, would require time to move into the core resulting in a response time lag before their effect would be realized. It was recognized that allowing for the possible positioning of the rods, partially inserted into the core (less than or equal to 10%), would reduce the dead band movement time of Control Group 1 and provide faster reactivity control response if needed.
The need for this feature no longer exists because recent SONGS 1 cores do not exhibit a positive moderator coefficient at operating conditions. The discussion in Amendment Application No. 151 describes the updated insertion limit curve.
NRC Ouestion 2 Explain how the proposed change would increase the current margin of safety for the main steamline break and the ejected rod analyses.
SCE Response Currently, rodded depletions are carried out to EOL assuming Control Groups 1 and 2 inserted to their insertion limits. This results in higher calculated local peaking factors (FO) following a control rod ejection event. With Control Group 1 fully withdrawn, FO after rod ejection, will be less.
This results in lower peak clad and fueT temperatures. For main steamline breaks, no rod insertion allowance for Control Group 1 will result in a small increase in available shutdown margin.
-2 Primarily the proposed change will increase the margin to the FAH design limit, as the limiting FAH for a given loading pattern occurs with Control Groups 1 and 2 inserted to their insertion limits.
For future core load designs, with Control Group 1 fully withdrawn, a lower FAH is calculated which allows more flexibility in designing a low neutron leakage loading pattern with greater cycle length.