From: Mathew, Roy
Sent: Wednesday, March 23, 2011 9:10 AM
To: Nelson, Robert
Cc: Hiland, Patrick; Wilson, George; Skeen, David; Thomas, Eric
Subject: Electrical System Design for Japanese Plants
EEEB is preparing for a Commission meeting in April 28, 2011, to discuss the status of Japanese event and to provide an overview of the SBO rule.
Presently, we do not have any insights on the Japanese electrical power system design. If possible, we would like to get the following information through the NRC team in Japan.
1. How many offsite power circuits are provided to the safety buses? Are they independent and redundant and have sufficient capacity and capability to support cold shutdown capability for all postulated events at the plant?. How many of these sources are immediately available after a unit trip?. Are the offsite circuits shared with adjacent units?
2. How many loss of offsite power events have occurred in the last 20 years at each plant? What is the duration of loss of offsite power? How many loss of power events to one safety bus have occurred at the plant? In the last 20 years, has there been a station blackout event at any plants?
3. How many standby power sources (diesel generators or other power sources) are provided for each unit? How many are required as a minimum to support safe shutdown of the unit? What is the reliability of the standby power source?
4. Are standby power systems including the support systems (fuel oil, cooling water, switchgear, control power, raceways, cables etc.) protected from natural phenomena such as tsunami, flood, and earthquakes?
5. Are AC and DC power sources shared between units at a site?
6. DC System (Class 1 E)
o How many battery systems are provided per unit?
o Are they redundant and independent?
o What are the duty cycle (s) ? Provide manufacturer name and the types of batteries used (e.g., lead acid)
o How often is the battery capacity test performed?
o What is the amp-hour and nominal voltage rating of the batteries?
o Is there load shedding required if the DC system has to be used for loss of all AC events? If yes, what percentage of the loads are shed?
7. Are there any regulatory requirements to withstand and recover from a station blackout event? (loss of all offsite and onsite Class 1 E AC power sources with turbine trip).
9. If there are requirements, Is AC independent system used (DC) or Alternate AC power source used for coping with station blackout? Are these power sources protected from natural phenomena such as tsunami, flood, and earthquakes? Is there any specific analysis required by the licensees and do they have to update the analysis if assumptions change? What are the typical coping time(s)? How is the coping duration determined? Are there plant procedures and operator training provided for a station blackout scenario? Is station blackout assumed to occur in more than one unit at a multi-unit site?