WASHINGTON – As the Pentagon seeks to modernize the nuclear enterprise, the majority of the focus has been on the creation of new delivery systems like the B-21 Raider bomber, the replacement for the Ohio-class ballistic missile submarine, and the next ICBM design.

But undergirding all that is an aging nuclear infrastructure, one that those in charge of handling America's nuclear arsenal worry is not getting the attention it deserves.

Over the last few budget cycles, military construction and facility maintenance has suffered in favor of training and modernization of equipment. The nuclear enterprise has not been unique in that regard.

Talking to reporters in New Mexico on Sept. 27,  Secretary of Defense Ash Carter, warned that infrastructure needs investment, much the same way that the big nuclear delivery systems need investments.

"I think infrastructure is in the same category, therefore it has to be a part of our investment plan moving forward," Carter said. "That includes the scientific facilities, it includes all of the support facilities."

The National Nuclear Security Administration (NNSA), a semi-autonomous office of the Department of Energy that has oversight for the US nuclear warhead stockpile, is particularly concerned about spending on infrastructure.

Speaking at September event in DC, NNSA head Frank Klotz estimated that there is roughly $3.7 billion in deferred maintenance to NNSA buildings, and spoke of a situation where part of a ceiling at a facility crumbled while workers were present.

"Shortly after I came on board into this position we had a portion of a roof at a building, [where] we conduct most of our highly enriched uranium in the enterprise, collapse," he said. "Big chunks of concrete fell onto the work floor. Fortunately, nobody was underneath. Fortunately, no expensive equipment was underneath. But it could have been very different."

"It’s the case with electrical systems at Lawrence Livermore, it’s the case with ventilation systems through our complex. So we have to go do something about this," Klotz added.

As a point of comparison, the fiscal year 2017 budget request for NNSA included $9.2 billion for the upgrade and maintenance of nuclear warheads, and $2.7 billion to infrastructure and operations.

Brad Boswell, senior manager for the Sandia national laboratory’s Weapon Systems Engineering group, told reporters Sept. 27 that "we absolutely have challenges" with the infrastructure, even if the current set up is "adequate" to fulfill the mission.

"I think NNSA works very effectively to identify where those most pressing concerns are. They have to balance those risks across the complex," Boswell said. But, "Am I concerned? Absolutely. As a program manager you see the risks as they bubble up."

It’s not the first time Klotz has begged for funding specific to infrastructure, but the issue has gotten a mixed reception on the Hill. At a February budget hearing, for example, Sen. Jeff Sessions, R-Ala., the chair of the Senate Armed Services Committee Subcommittee on Strategic Forces, pushed back at Klotz’s concerns.

Asked a skeptical Sessions, "We’re in tight budget times — are you sure we need $3.7 billion just to refurbish buildings?"

A former Pentagon official familiar with the nuclear enterprise believes that NNSA’s concerns are valid and should be given proper consideration. Not only do the infrastructure issues mean a drop in productivity, they can lead to major morale issues with a staff that is already stretched thin.

"At the end of the day, you’re sending a message to your people that they aren’t important, if we don’t really care if water is leaking in here and we don’t have the money to fix the door," the former official said.  "That would be bad enough if you were making Ford trucks up in Michigan, but you’re thinking ‘hey this is supposed to be the nation’s number one priority and this is the facility that we give the people in the department of energy?’ So you can see where it can come across as not following through on the things that we’re talking about."