Terrorists may be able to slip lethal nuclear materials undetected by U.S. detection resources because the Department of Homeland Security isn't making certain its $350 million in research grants are aimed at closing technological gaps.

The department's Domestic Nuclear Detection Office selects research projects that are supposed to strengthen Homeland Security's technology to detect nuclear smugglers, but "doesn't document the rationale for how its immediate funding priorities are intended to fill gaps," according to the Government Accountability Office.

Homeland Security officials claimed "they discuss" each project's rationale, but the accountability office said "because these discussions are not documented, it is unclear to what extent these projects and research challenges align with gaps."

The detection office spent $350 million on 189 research projects from 2008-13 but didn't document how they would broaden Homeland Security's detection capabilities to fill gaps that would allow terrorists to smuggle nuclear materials into the country. Consequently, Homeland Security is pouring money into projects that may not protect the nation as intended.

Also, agencies that use the resulting technology don't always know the role of the devices. For example, U.S. Customs and Border Protection officials weren't certain if prototype devices they received from one project were designed for actual use or as a theoretical concept.

Investigators reported that 20 percent of the research projects were conceptual or were found to be unfeasible, while 9 percent were discontinued or were completed but have "no use for resulting knowledge, technology or device," the report said.

Also, Border Protection officials said they are given hundreds of pages of documents that provide scientific details, but do not explicitly state how projects fill nuclear detection gaps.

The report also found that the detection office can't effectively analyze how well completed projects address research goals.

"DHS is right to invest in preventing nuclear material smuggling, but it has to focus on the outcomes of that spending and not just shoveling money out the door," said Scott Amey, general counsel at the watchdog group Project on Government Oversight. "Bad investments won't just lead to another story about government waste, it might lead to a story about how immature, overstated or misapplied technologies made us less safe and secure."

Leslie Paige, spokesman for Citizens Against Government Waste, another watchdog group, was even more emphatic, saying, "It is absurd that the GAO should have to actually expend valuable oversight resources in order to instruct federal officials on such basic, commonsense management practices."

Others said the detection office must communicate with the agencies that will use their research.

"It seems like the research groups are going off in their own direction and not integrating with the end users," said Chris Edwards, a budget expert at the libertarian Cato Institute think tank. "They need more outside input. They should get critical input before they go spending a lot of money."

There are also doubts in some quarters that the nation can be secured with nuclear detectors.

"Combating nuclear smuggling through screening is like looking for a needle in a haystack," said James Carafano, a homeland security expert at the conservative Heritage Foundation. "I was always skeptical if that investment was worth it. It's a questionable mission, poorly implemented."

Cato Homeland Security Research Fellow Benjamin Friedman said taxpayers, Congress and the president give Homeland Security the difficult task of protecting the borders with nonexistent technology.

"Here is an example where political demand and scientific reality come into conflict," Friedman said. "That objective is obviously not particularly feasible."

Americans may not be threatened by nuclear attack, but that's not because of secure borders.

"People tend to think we have a mature sense of technology that protects our borders, but we don't," Friedman said. "I don't think the threat is as big as it's made out to be because of the difficulties to develop a nuclear device."

Regardless, Homeland Security — formed in 2002 by combining 22 existing agencies — struggled to do what it was designed to accomplish.

Edwards pointed out, for example, that Homeland Security's Transportation Security Administration spent millions of dollars on full body scanners at U.S. airports that were ultimately withdrawn.

"DHS has a record of spending a lot of money without proper controls and without knowing what they're doing," Edwards said. "They don't plan and do proper analysis of projects before they end up spending tens and hundreds of millions of dollars."

"That means that Americans aren't as protected as they could be if DHS did a better job of allocating their investments," he said.

Carafano agreed, saying "We're beyond the point where we have to excuse this behavior because it's a new start up. It's not a new start-up anymore."

"We should blame [Homeland Security] for not doing better cost-benefit analysis for their whole budget," Friedman said.