ML061800084
| ML061800084 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 06/28/2006 |
| From: | Faulhaber H Omaha Public Power District |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-04-002, LIC-06-0070, TAC MC4686 | |
| Download: ML061800084 (2) | |
Text
Omaha Public Power District 444 South 16th Street Mall Omaha NE 68102-2247 June 28,2006 LIC-06-0070 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Reference:
- 1.
Docket No. 50-285 I
- 2.
Letter from Harry J. Faulhaber (OPPD) to Document Control Desk (NRC) dated June 9, 2005, Revised Request for an Extension to the Completion Date for Corrective Actions Taken in Response to Generic Letter 2004-02 (LIC-06-0067)
- 3.
Letter from Harry J. Faulhaber (OPPD) to Document Control Desk (NRC) dated June 12, 2005, Correction to Revised Request for an Extension to the Completion Date for Corrective Actions Taken in Response to Generic Letter 2004-02 (LIC-06-0069)
SUBJECT:
Supplement to Revised Request for an Extension to the Completion Date for Corrective Actions Taken in Response to Generic Letter 2004-02 (TAC#MC4686)
In Reference 2, the Omaha Public Power District (OPPD) requested an extension to the completion date for the corrective actions taken in response to Generic Letter 2004-02. In a phone call with the NRC on June 15,2006, the NRC requested clarification of the second bulleted item on Page 8 of Attachment 1 of Reference 2. This item describes how mitigative measures previously discussed will minimize the risk of degraded Emergency Core Cooling System and Containment Spray System functions. The following clarification of this item is provided:
i The current Fort Calhoun Station (FCS) Emergency Core Cooling System (ECCS) and Containment Spray System (CSS) net positive suction head (NPSH) design margin for the limiting loss of offsite power (L0OP)lLoss of Coolant Accident (LOCA) is 1.75 ft for the CS pumps and greater than 4.75 ft for the High Pressure Safety Injection System (HPSI) pumps. (Note that with LOOP, only one ECCSICSS train with suction from one sump strainer would be operable, because the worst single failure for this scenario is assumed to be one diesel-generator power source.) Head loss testing using the FCS post-2006 outage debris mix has been conducted for the replacement strainer modules. This testing determined a strainer head loss of less than 1 ft for a strainer surface area of 1500 ft2 for the limiting LOOPILOCA. Applying these test results to the current design margin, the resulting NPSH design margin would be approximately 0.75 fi for the CS pumps and greater than approximately 3.75 ft for the HPSI pumps.
The consequences of a number of small and medium break LOOPILOCA scenarios can be successfully mitigated with the installation of the interim strainers (550 ft2 of surface area each) since each strainer provides sufficient surface area to maintain the CS and HPSI pumps within their NPSH design margin.
This is because the debris loading for these cases would be less than that assumed for the limiting LOOPILOCA case. For large break LOOPILOCA scenarios with the worst case debris loading, Employment with Equal Opportunity
U. S. Nuclear Regulatory Commission LIC-06-0070 Page 2 securing the CS pump due to insufficient NPSH may be necessary. With no CS pump operating, containment pressure control and cooling would continue using the fully redundant containment cooling units. In these scenarios, strainer head loss is expected to be less than 3.75 ft, with sufficient HPSI system NPSH margin maintained to assure adequate flow is delivered to the core. In addition, HPSI pump flow may also be throttled which will result in significantly more NPSH margin.
The current FCS ECCS and CSS NPSH design margin for the limiting LOCA with offsite power available is 2.5 ft for the CS pumps and greater than 7 ft for the HPSI pumps. Since both ECCSICSS trains would be assumed operable in this scenario, the resulting debris load would be spread over a surface area of 1100 ft2 (both interim strainers). This amount of surface area is close to the tested case of 1500 ft2. Assuming strainer head loss is proportional to surface area, the estimated head loss for an 1100 ft2 screen is 1.5 ft. Using this estimate, the amount of available NPSH, estimated to be 1.0 ft for the CS pumps and greater than 5.5 A for the HPSI pumps, provides assurance that the CS pumps and HPSI pumps will be operable for LOCAs with offsite power available.
Additionally, the NRC requested that OPPD describe the materials that will be used to replace the calcium silicate (CalSil) insulation associated with the major components being replaced (steam generators and pressurizer) during the fall 2006 outage at FCS. OPPD plans to replace the CalSil insulation with reflective metal insulation (RMI) in areas where the exact dimensions are known (such as steam generator and pressurizer bodies), and with low density fiber glass (Thermalwrap) in areas where exact dimensions are not known (such as on the hot and cold leg welds to the replacement steam generators).
I declare under penalty of perjury that the foregoing is true and correct. (Executed on June 28, 2006.)
If you have additional questions, or require further information, please contact Thomas R. Byrne at (402) 533-7368.
Sincerely,
$?L$J 2&
Harry J.
ulhaber Division Manager Nuclear Engineering