Feb

11

Pilgrim Nuclear Power Plant, near Plymouth, Massachusetts was forced into a cold shutdown, due to a loss of offsite power (LOOP). This is not a big deal, but I'm sure some of the FUD folks will make hay out of Pilgrim's situation.

First, the need for power in New England is diminished. Current load is off by the equivalent of three nuclear plants right now. Projected load at New England's hub was supposed to be 16,980 megawatts and the actual load is 14,240 megawatts. So the temporary loss of the nuclear plant affects price, but not supply.

Second, when a nuclear plant loses offsite power, it is supposed to shut down. Usually, it shuts down without operator assistance.

Offsite power is used to power the plant's internal lights and equipment. Station service power comes from the grid, into the local switchyard, to the station service transformers and into the plant's power distribution systems. I'm guessing the LOOP problem is in the nearby switchyard, which is a huge substation and the origin of major transmission line(s). If there is a problem in the switchyard or in the transmission lines, then there is no transportation available for plant's produced power.

When there is a LOOP, diesel generators automatically activate. In US nuclear plants, there are three diesel generators, any one of which can handle the station's full load. One generator feeds the "Train A Circuit," which serves all critical loads, including battery chargers. Another generator feeds the "Train B Circuit" which feeds the redundant system of vital loads. The third generator is the swing - it can switch between Train A and Train B circuits. The Train A and B circuits are color coded, physically isolated, electrically isolated and the swing generator is a "break-before-make" swing (to maintain integrity of electrical separation).

Generators are frequently tested and test results are reported to the NRC. There is adequate amount of fuel available on site to power the generators for days (I forgot how many days are required under 10 CFR).

Currently, Pilgrim's diesel generators are operating as planned. As the nuclear plant finalizes its cold shutdown procedures, the load on the diesel generators becomes less critical. Depending on the design, vital systems needed to cool the primary system and to assure cold shutdown.

In the unlikely case where all three diesel generators fail, there are at least two banks of redundant batteries. These are massive lead acid batteries, which are hard wired into the redundant systems. Diesel generator failure will cause the batteries to supply energy without even a second of delay. Batteries are downstream and they feed four redundant vital circuits. Vital circuits are designed for instrumentation and control and they are color coded, physically isolated and electrically isolated.

Now the FUD folks (Fear, Uncertainty and Doubt) will argue that Pilgrim is a lot like Fukushima. There is enough truth to the statement to make the comparison seem valid. But the comparison is completely bogus and fear is unwarranted.

Like Fukushima, Pilgrim:

   1. Was designed by General Electric
   2. Is a Boiling Water Reactor (BWR) Mark I design.
   3. Is 40+ years old
   4. Has an ocean-facing site.
   5. Had a LOOP incident

Unlike Fukusima, Pilgrim:

   1. Has an upgraded BWR design
   2. Is designed to manage LOOPs
   3. Has access to unlimited amounts of fuel oil
   4. Didn't experience an historic earthquake
   5. Didn't experience a historic tsunami
   6. Didn't experience a historic earthquake, THEN a subsequent tsunami,
   AND a LOOP, THEN a loss of fuel oil
   7. Didn't incur any physical damage to any part of the facility

If you can keep objective distance from the Fukushima incident, you might appreciate that their plant's design. Their 1960-era design withstood an historic earthquake and it kept on tickin'. It withstood a subsequent tsunami of historic proportions and it kept on tickin'. It withstood a subsequent LOOP, and it kept on tickin'. Later, and only after the subsequent loss of fuel oil, did some units at Fukushima fail. It took four simultaneous failures before some units became crippled.

Keep in mind; some other units at Fukushima remain largely undamaged. Those undamaged reactors could technically return to service and provide electric power to the region. For policy and practical reasons, it isn't going to happen, but from an engineering perspective, it is technically possible.

Before memories fade and fear media takes over, it should remain clear that Fukushima did not cause the original earthquake, or the tsunami or the LOOP. There was a massive earthquake and massive tsunami, which damaged an entire coastal region, including local nuclear, coal and gas power plants.

Don't let the FUD folks make you go loopy over Pilgrim. While the station experienced a LOOP, a far more serious incident happened nearby. There was a 17-car pileup on one of Boston's highways. Pilgrim's LOOP will be reported nationally. The pileup will be relegated to page four of the local paper.


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