Two and a half years after a series of meltdowns, Japan’s effort to clean up what remains of the Fukushima Daiichi nuclear plant is turning into another kind of disaster.

The site now stores 90 million gallons of radioactive water, more than enough to fill Yankee Stadium to the brim. An additional 400 tons of toxic water is flowing daily into the Pacific Ocean, and almost every week, the plant operator acknowledges a new leak.

That operator, Tokyo Electric Power Co., known as Tepco, was put in charge of the cleanup process more than two years ago and subsequently given a government bailout as its debts soared. The job of dismantling the facility was supposed to give Tepco an opportunity to rebuild credibility.

But many lawmakers and nuclear industry specialists say that Tepco is perpetuating the kinds of mistakes that led to the March 2011 meltdowns: underestimating the plant’s vulnerabilities, ignoring warnings from outsiders and neglecting to draw up plans for things that might go wrong. Those failures, they say, have led to the massive buildup and leaking of toxic water.

“Tepco didn’t play enough of these what-if games,” said Dale Klein, a former chairman of the U.S. Nuclear Regulatory Commission, who recently joined a Tepco advisory panel. “They didn’t have enough of that questioning attitude” about their plans.

The leaks into the ocean are far less toxic than the radioactive plumes that emanated from the plant after the earthquake and tsunami, forcing 160,000 people to move out of the vicinity. Thanks to that quick evacuation, experts say, there are no expectations of a Chernobyl-style spike in cancer cases — although the government is conducting thyroid checks of thousands of children. But the flow of contaminated water amounts to a slow-burning environmental disaster with implications for Japan’s wildlife and its food chain.

The problems have prompted the central government to step in with about $500 million to fund new countermeasures, including a subterranean “ice wall” designed to keep groundwater from flowing into irradiated buildings.

The latest government-led actions are particularly galling for some, who say Tepco should have taken similar measures earlier. One lawmaker, Sumio Mabuchi, who was also an adviser to then-Prime Minister Naoto Kan, says Tepco, deep in debt, neglected to take important steps against the groundwater two years ago because of concerns about its bottom line. Tepco’s president, Naomi Hirose, testified in parliament last month that the company hasn’t “scrimped” on the cleanup, though he did say that Tepco is “majorly at fault” for its failure to manage the groundwater buildup.

The 40-year decommissioning is expected to cost 10 trillion yen, or about $100 billion — roughly two years’ worth of Tepco’s revenue — and the company says it is trying to save up and cut other costs. But for many Japanese, the company’s assurances inspire little confidence. Two members of Japan’s national legislature, speaking on the condition of anonymity to share what they describe as sensitive details, say Tepco continues to spend irresponsibly on lobbying politicians, offering them free trips to nuclear sites that include meals and lodging in hot springs resorts. A Tepco spokesman said the company does not offer such trips.