Update morning May 11th:

A Nuclear Regulatory Commission spokesman tells the Associated Press that several thousand gallons of oil from the Indian Point nuclear power plant may have spilled into the Hudson River following Saturday's transformer explosion.

Update 4:25 pm May 10th:

The environmentalist group Riverkeeper reports spotting what appears to be a large oil sheen on the Hudson River this morning near the site of yesterday's transformer explosion at the Indian Point nuclear power plant. This morning, the sheen extended north and south of the plant, and all the way to the Rockland County side of the river, but it had not reached the Peekskill waterfront to the north, according to the group's patrol captain John Lipscomb. He said he didn't know what the rainbow sheen was for sure, but that it gave off an acrid, petroleum smell. "After two hours of floating around in it, I could feel it in my throat and my sinuses," Lipscomb said.

The activists reported spotting a breach in the boom state officials had deployed to contain the oil, but said that a second boom was being put in place this morning. Riverkeeper's Leah Rae shot this video:

IndianPointandSheen from Gothamist on Vimeo.

A spokesman for Entergy, the company that owns the plant, said it's not yet clear that transformer oil escaped through drains into the river, and that the sheen might be attributable to the foam used to fight the electrical fire, which contains an oily animal fat. The spokesman, Gerald Nappi, downplayed the risk transformer oil would play to the river if it did make it in, because it is a "light, clear, mineral-type oil." "Transformer oil would be of very little consequence to the environment locally," he said. "That being said we are very seriously taking every precaution to mitigate any potential release."

Gov. Cuomo, speaking to the media earlier today, said the oil in the river is definitely from the transformers:

There is no doubt but that oil did escape from the transformer, there is no doubt that oil did go into the holding tank and exceeded the capacity of the holding tank, and there is no doubt that oil was discharged into the Hudson River. Exactly how much, we don’t know.

Riverkeeper is advocating for the closure of the plant, citing safety concerns. Lipscomb noted that the explosion and oil sheen may be alarming for people, but that the plant pulls in and heats more than 2 billion gallons of river water per day, killing huge amounts of river life.

"[The plant] hurts the river every single day," he said. "And some days it hurts the river a little more."

We have reached out to the Department of Environmental Conservation for more information and will update if we hear back.

Original story:

A transformer blew up at the Indian Point nuclear power plant in Westchester County yesterday evening, shutting down one of the plant's two reactors and possibly sending oil into the Hudson River.

Gustavus Gricius was across the Hudson, driving home from hiking on Bear Mountain when he saw "a huge black ball of smoke" come up from the nuclear facility and sirens began going off. A public address system sounded, repeating "This is not a drill."

"There was an electrical, oily burning smell," Gricius told the Times. "Once we smelled that that's when we were like, 'Let's get out of here.'"

Good call.

Firefighters and plant workers extinguished the fire, and the Unit 3 reactor shut down automatically following the blast.

Management at Entergy, the utility company that owns the plant, declared the fire an "unusual event"—and they can say that again! The classification is the least serious of the four emergency-response categories, and no one was injured by the explosion and subsequent fire. The plant's transformers convert the energy generated by the nuclear reactors into electricity that can be handled by the grid.

Company spokesman Gerald Nappi said that an investigation into the failure is underway and that restarting Unit 3 is not a matter of days, but "on the order of a few weeks."

Gov. Cuomo visited the plant, which is 25 miles north of the Bronx, during the night.

“Luckily, this was not a major situation, but the emergency protocols are important," he told CBS2. "They’re important to me. I want to make sure that things work the way they’re supposed to work in this kind of emergency.

Cuomo said he is concerned that oil from the wrecked transformer and the foam used to fight the fire could travel through storm drains into the mighty Hudson. Federal and state environmental personnel are on site monitoring the situation.

This isn't the first time the city's freaky, energy-supplying neighbor has malfunctioned. As CBS2 notes:

In April 2007, there was a transformer fire at Indian Point 3, reportedly caused by a worn-out part.

In November 2010, a transformer exploded at Indian Point 2, cauing a fire and automoatic shutdown of the reactor.

Also:

Unit 3 had been shut down Thursday morning for an unrelated issue, a water leak on the non-nuclear side of the plant. It was repaired and there was no radioactive release, [a spokesman said.

That's reassuring. While we're all not freaking out, it's also worth remembering also that Indian Point sits within a mile or so of at least one seismic fault line and is considered one of the nation's 10 nuclear plants most at risk from earthquakes.

Update 11:42 am:

Indian Point is in Westchester County, not Rockland County. Gustavus Gricius witnessed the explosion from across the Hudson River in Rockland County.