APR: your source for nuclear news and analysis since April 16, 2010

Friday, April 29, 2011

Browns Ferry - LOOP

Relatively lost in the tragedy in the southern part of the USA is the fact that Browns Ferry experienced a total Loss Of Offsite Power, causing all three reactor plants to shut down.

No. 1 and No. 2 plants were operating at 75% power, while No. 3 was at 100% power when the tornado damage caused a complete LOOP that generated trip signals on all three plants. All shutdown immediate actions were normal except for No. 3 plant; one MSIV or Main Steam Isolation Valve is indicating intermediate... meaning it's neither on the open seat or on the closed seat.

All site diesels except one which was down for maintenance started and ran normally.

The LOOP caused valid RPS signals, PCIS actuation and the mentioned EDG start. RPS signals of course included full scram.

Although the plants were using RCIC, on No. 1 the water level did reach -45 inches causing the HPIC system to actuate to restore water level in the reactor pressure vessel.

All three plants are in hot shutdown at this time.

These events began at 5:01 PM on the 27th.

10:30 PM Eastern Friday 4/29


  1. Just don't understand why these plants can't continuously tap their own turbine generation to primarily run the facility, like most computer UPSes do by running off their own continuously charged batteries.

    James Greenidge

  2. @jimwg: There is a rule that without offsite power available, you can't have the reactors critical. This was determined many years back to be necessary for reactor safety. Even though in some plants the equipment is operating off the turbine generator, you still shut down if all offsite power is lost.

  3. it would be very interesting to see why that rule was developed, and perhaps a review of such things in extended SBO events..

    also how would that work with remote SMR instalations, where there is no offsite power to speak of?

    if some outside envolope event occured that caused loss of offsite power that was likely to run longer than stores of diesel would last, it would be nice to have some provisional rules, and switching equiptment for resuming limited power production to keep spent fuel pools cool....

    better to plan for such possibilites than to need to try to throw somthing toghether at the last minute....

  4. I think to run isolated you would need a smaller emergency turbine/generator system as the minimum power for the main system would be too low.