ML042960496
| ML042960496 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 10/18/2004 |
| From: | Arizona Public Service Co |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| FOIA/PA-2004-0307 | |
| Download: ML042960496 (2) | |
Text
- Palo Verde LOOP Risk Assessment Preliminary Assessment:
A loss of offsite power is a significant event at any nuclear facility, and more so for a Combustion Engineering plant without primary system power-operated relief valves, because of the inability to perform a reactor coolant system feed and bleed evolution.
To evaluate this event, the analyst used the Standardized Plant Analysis Risk Model for Palo Verde (SPAR), Revision 3 model, and modified appropriate basic events to include updated loss of offsite power curves published in NUREG CR-5496.
The risk associated with the Unit 2 reactor was analyzed because it represented the dominant risk of the event.
For the preliminary analysis, the following assumptions were made:
A loss of offsite power (LOOP) occurred The LOOP may have been recovered at a rate equivalent to that of the industry average.
Emergency Diesel Generator A failed and could not have been recovered prior to core damage Charging Pump E failed and could not have been recovered prior to core damage The conditional core damage probability was estimated to be 6.5 x 104 indicating that the event was of substantial risk significance and warranted an augmented inspection team.
The licensee's analysts provided a conditional core damage probability of 6.788 x 104.
Considering the error band in these calculations, this is exactly the same number that the SPAR provided.
Final Assessment:
Should not be confused with significance determination process. This evaluation does not impact action matrix The risk associated with the event will increase based on the following items:
Actual offsite power availability and recovery will be assessed. This will rule out early offsite power recovery.
- ( '- UP A site-wide CCDP will be assessed, so Units 1 and 3 risk will be additive.
I-Common equipment reductions will be made. Example, the Gas Turbine Generators can not provide all three units.
Other issues that may increase final risk:
Two 13.8 kV Magna-Blast Breakers failed IF TDAFW drains were not opened