The Indian Point Energy Center, a controversial and ageing nuclear plant near New York City, has split the Democratic presidential candidates .

As campaigning continued before the New York primary on 19 April, Bernie Sanders called the facility “a catastrophe waiting to happen”. Hillary Clinton said only that it needed more oversight.

A senior member of the Union of Concerned Scientists told the Guardian “the whole New York metropolitan area is potentially imperiled by an accident at Indian Point”.

Last week, the company that runs Indian Point revealed that 227 bolts holding the interior of a nuclear reactor at the site have “degraded” or gone missing. In February, the plant reported that a radioactive material, tritium, had leaked into groundwater.

The plant, about 40 miles north of midtown Manhattan on the eastern bank of the Hudson river, has a 40-year history of accidents, fires and complaints. Governor Andrew Cuomo ordered an investigation into February’s “unacceptable” leak. He has called for the plant to close.

“In my view, we cannot sit idly by and hope that the unthinkable will never happen,” Sanders said in a statement. “It makes no sense to me to continue to operate a decaying nuclear reactor within 25 miles of New York City where nearly 10 million people live.”

The Vermont senator elaborated on his stance, calling for the US to phase out nuclear plants along with more polluting resources such as fossil fuels.

“Nuclear power is and always has been a dangerous idea because there is no good way to store nuclear waste,” he said.

Clinton, a former New York senator, accused Sanders of tardiness in his attention to the controversial plant.

“I’m glad he discovered Indian Point,” she told a local talkshow, Capital Tonight. “We also have to be realistic and say, ‘You get 25% of the electricity in the greater New York City area from Indian Point.’

“I don’t want middle-class taxpayers to see a huge rate increase. So this needs to be done in a careful, thoughtful way.”

The former secretary of state said the plant needed greater regulation, and cited a continuing review by the Nuclear Regulatory Commission. Indian Point is in the midst of a license renewal process that will last at least through September.

Edwin Lyman, a senior nuclear scientist with the Union of Concerned Scientists, said that while the non-partisan group did not have “a general position on nuclear power per se, we believe that every nuclear plant has to be operated to a very high level of safety and security”.

“Some plants deserve greater scrutiny and protection than others based on the potential consequences of a catastrophic accident or terrorist attack,” he said.

Indian Point, Lyman told the Guardian, “should be a top candidate” for such scrutiny, given that 16 million people live within 50 miles of the facility.

Referring to events caused by a tsunami in Japan in 2011, Lyman said a “Fukushima-type accident could cause either the melting of the reactor core or severe damage to the spent fuel pool that would cause a fire and large release” of radioactive material.

In the case of Fukushima, radiation traveled as far as 25 miles into populated areas where people were not immediately evacuated.

“The whole New York metropolitan area is potentially imperiled by an accident at Indian Point,” Lyman said.

The plant is one of the few employers in the small town of Buchanan, but it is also the target of local protests. Nuclear scientists and pipeline experts have warned that the risks of running the plant are high, especially given the large amount of waste that is stored at the site.

The office of the governor did not immediately reply to a query about whether Cuomo, who has endorsed Clinton, would urge her to change her position.

According to Entergy, the company that runs Indian Point, the February leak which caused a nearly 65,000% increase in radiation levels in affected groundwater “has not migrated off site and as such does not pose an immediate threat to public health”.

Jerry Nappi, a spokesman for the company, told New York public radio the plant was “reliable” and “verified as safe by inspectors who come to the plant each day from the federal government”.

“Indian Point, when it’s online, emits virtually zero greenhouse gases so it’s an important component to New York state trying to meet its clean energy and clean air goals,” Nappi said.

The disagreement between Sanders and Clinton mirrors their stances on fracking for natural gas. The senator has called for a ban, citing growing evidence that drilling causes earthquakes. The former secretary of state has called for intense regulation of the industry.

“I want the federal government to regulate much more toughly than we have in the past,” she said on Monday.

In 2014 Cuomo signed a law that banned fracking in New York.