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Emergency Diesel Generators (EDGs)


Background: Nuclear Reactors need electricity to operate – without a supply their safety systems would be disabled. They do not generate their own electricity. Like all of us, they depend on the grid – offsite power. If offsite power fails, they depend on back up generators (EDGs). The generators are designed to supply electricity to keep coolant circulating to prevent the reactor core from heating and causing a meltdown; and to keep the spent fuel pool water cool to prevent the rods from melting and/ or catching fire. If the EDGs fail, the chance of an accident approaches certainty – the reactor can not be restarted without offsite power. Terrorist attacks, ice or wind storms – Nor’ Easters- can knock out transmission lines to nuclear reactors for extended periods. The industry has a history of problems with emergency diesel generators – in some cases all emergency diesel generators at a reactor were inoperable at the same time.


Pilgrim: The plant's electrical distribution system is described in Section 8 of the Final Safety Analysis Report (FSAR) and has redundant sources of power.  The preferred electrical power is supplied from offsite sources, which includes two independent lines from the 345KV system and a third line from the 23 KV system.  Should the offsite supplies become unavailable, either one of the two EDGs could provide adequate power to cool the reactor.  Should both EDGs become unavailable, the station blackout diesel generator (SBODG) could provide adequate power to cool the reactor.  As described in FSAR Section 2.3, the extreme maximum temperature for Plymouth is 102F, which is the highest temperature on record and was recorded in 1949 (source: the Weather Channel).  Plant design information shows the EDGs are operable at a temperature of 102F, and the SBODG is designed to operate at ambient conditions above the site extreme maximum temperature.  Finally, should the electrical systems not be operable as required by the plant technical specifications, Entergy would be required to shut down the plant. In summary, the EDGs have been operable for the ambient conditions experienced at the site, and margins exist between the EDG operability limits and the site average high temperature conditions.  Further, the EDGs would be operable for extreme ambient temperatures that could occur very infrequently.






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