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

Saturday, February 9, 2013

Pilgrim LOOP / NOUE

Last evening (2/8) as a result of the blizzard burying the Northeast of the United States, Pilgrim Nuclear Power Station in Massachusetts suffered a LOOP event (Loss Of Offsite Power) and subsequent reactor trip (also popularly called a "scram") which is the as-designed event sequence for an LOOP event.  The NRC has made a press release this morning, the text of which follows:



The U.S. Nuclear Regulatory Commission Region I staff is monitoring the Pilgrim nuclear power plant after the site lost offsite power Friday evening. The plant is operated by Entergy Nuclear and is located in Plymouth, Mass.

Pilgrim automatically shut down after losing offsite power at 9:17 Friday night (2/8). The plant is stable and all plant safety systems responded as designed. The plant's diesel generators are currently supplying power to plant equipment. Plant operators declared an unusual event due to the loss of all off-site power. An Unusual Event is the lowest of four levels of the NRC’s emergency classification system.

There was no impact to plant workers or the public.


Pilgrim did not scram out from full power, as the plant had been operating at a reduced power level to negate
problems with a simmering relief valve.  The last data point shown by NRC for Pilgrim had the plant at 83% power.

If any updates are required, I'll make them here or on Twitter -- ' @atomicnews '.

(Data and reports from Entergy, NRC, Cape Cod Times, and others.)


UPDATE - Added link:

Click here for an excellent NEI piece on the history of US nuclear plants' response to severe weather.

11:00 AM Eastern 2/9/2013


  1. Was the loss of outside power really a loss of capability to deliver power to the grid? It's a shame such PWRs can not simply reduce power to meet reduced demand. Even if the grid is lost, the plant uses something like 10% of power for its own functions. Reactors such as PBMR or LFTR can load follow, not having to shut down and not having to have special cooling systems for fission product decay.

  2. LOOP means that the plant couldn't receive power from the grid -- and also had nowhere to send what it did generate. This plant (Pilgrim) is a BWR, and all BWR and PWR plants CAN and DO load follow to some extent. I do not know how many were built with the optional steam dump equipment to allow 100% load reject without scram, but I know that at least Westinghouse offered that on their PWR's.

    The concept that BWR / PWR plants can't load follow is being widely spread, and it's incorrect. While many commercial plants today have fuel that's not optimally designed for rapid load changes, there are design alterations that make very rapid load changes easily possible. (A number of early commercial plants could take what today would be considered as wild power transients in stride.)