MANGYSTAU, Kazakhstan — In a storage pool at a mothballed nuclear power plant on the shores of the Caspian Sea rests a key ingredient for anyone seeking to build a nuclear weapon: containers of spent atomic fuel with enough plutonium to make dozens of bombs.

Despite international concern about the waste at the Mangyshlak nuclear power plant, plans to transport it away from the Caspian shore have stalled in a dispute between Kazakhstan and the United States over just where and how it should be removed.

Kazakhstan has earned much international good will for unilaterally disarming after the 1991 Soviet collapse and handing over its nuclear arsenal to Russia under watch of the International Atomic Energy Agency (IAEA).

Still, the nation's atomic legacy as a testing ground for the Soviet nuclear program has left it with numerous waste sites as well as the remnants of an active atomic power program.

The Mangyshlak Atomic Energy Complex is one of those places, lying in a decrepit industrial area outside the city of Aktau in the moonlike desolation of western Kazakhstan. The reactor was shut down in 2003 for economic reasons, having worked a decade beyond its intended 20-year lifetime.

It lies behind two series of walls and radiation detectors, past a security checkpoint featuring metal detectors and X-ray machines, then gates opened by electronic badges and a numeric code. The sealed canisters of radioactive materials lie in a pool under metal floors welded together with seals from the IAEA. Video cameras with satellite feeds to the IAEA monitor the room, and IAEA experts visit once a month.

The 300 metric tons (330 short tons) of spent nuclear fuel contain nearly three metric tons (3.3 short tons) of plutonium enriched to more than 90 percent. That's better than usual weapons-grade but would require extensive processing to be made into bombs.

The fuel has been cooling for so long and was so lightly irradiated to begin with that it is no longer radioactive enough to be "self-protecting" against theft, according to the Washington-based Nuclear Threat Initiative (NTI), an antiproliferation organization.

"Thieves could load it into a boat and take it away without necessarily receiving radiation doses that would immediately be incapacitating," the NTI wrote on its Web site. Kazakhstan is one of five countries that share the Caspian Sea with Iran, which is suspected of seeking nuclear weapons. Iranian cargo ships sail by regularly, and the NTI notes that Tehran has shown interest in Aktau and has talked of opening a consulate there.

The United States has provided military assistance bolster Kazakhstan's shore defenses and plans to give some US$20 million (euro16.6 million) for new radars and intercept boats.

The Kazakhs want U.S. help in a US$40 million (euro33.3 million) project to move the spent fuel to a safer site, but those efforts are deadlocked. The Kazakhs want to take the fuel to Semipalatinsk, the former nuclear weapons test site in eastern Kazakhstan. The United States wants it shipped to Russia, where other radioactive materials were sent.

The Kazakhs planned to build single-use casks to transport the waste and then store it in reinforced underground bunkers. But the United States persuaded them to use dual-use casks in which the fuel can be both transported and stored.

However, work on the dual-use casks is on hold, and the Kazakhs continue to work on single-use casks.

"No work is being done on the dual-use casks because no funding is coming from the United States. And we cannot understand why," said Irina Tajibayeva, executive director of the Kazakhstan government's Center for the Safety of Nuclear Technologies. "This is not an example of good cooperation," she said.

The U.S. Embassy in Kazakhstan has declined several requests for comment made in recent weeks.

IAEA Spokeswoman Melissa Fleming said, "We are fully aware of the status of the discussion between Kazakhstan and the United States, and materials are currently properly under IAEA safeguards."

The plant's director, Gennady Pugachev, insists that "fears that our nuclear fuel could get into the wrong hands are groundless."

"We are not North Korea, where there is no government will to make (nuclear materials) safe," said Viktor Martyshkin, the reactor's information security chief. "Our government wants to make sure these materials do not get into some mad, criminal hands."

With the security at the plant, any potential theft would likely have to be at least partly an inside job. Pugachev notes employees' salaries are minuscule; he says he himself makes 20 times less than a guard at a U.S. nuclear facility would earn.

Pugachev is also well aware of the risks of loose nuclear materials, such as from a "dirty bomb" — a device that combines conventional explosives with radioactive material. "I know how to do it," he said.

A Western diplomat familiar with the IAEA said similar or larger quantities of spent fuel exist in dozens of countries and always represent a risk if they aren't secured.

Some Russian facilities are well-equipped, others aren't, the diplomat said, speaking on condition of anonymity. And negotiations about transferring such material can be difficult and lengthy because many parties are involved, each with its own legal and regulatory requirements, and all want to be protected against liability and compensated for what they are being asked to do, the diplomat said.