WASHINGTON — Top National Nuclear Security Administration (NNSA) officials went in front of skeptical Ssenators Tuesday to warn of an upcoming bow wave of costs that will likely require an infusion of cash above what Congress authorized last year.

Frank Klotz, the retired Air Force Lt. Gen. lieutenant general who now heads the NNSA, told the Senate Armed Services Committee Subcommittee on Strategic Forces that while he was "very satisfied" with the fiscal year 2017 budget request, more funding will be needed shortly to  make sure the department can keep up with future costs.

An August report by the Government Accountability Office (GAO) found that NNSA needs "more than $290 billion" over the next 25 years to support its modernization plan, an annual average bill of $11.6 billion. NNSA's annual budget request for fiscal 2017 was $12.9 billion; of that funding, $9.2 billion is slated for upgrade and maintenance of nuclear warheads themselves, with $2.7 billion going to infrastructure and operations.

"Our emphasis has been on what we see as a coming bow wave of expenses to make sure the nuclear security enterprise is able to be responsive for the long term," Klotz said. "DoD has talked a lot about the bow wave it faces; we have a similar bow wave; although in absolute terms it's much smaller, relative to our overall budget, it's fairly significant."

While largely a friendly hearing, Klotz received skepticism from Ssubcommittee chairman Sen. Jeff Sessions, R-Ala., over a letter — first revealed in an editorial published by the Wall Street Journal — written by Secretary of Energy Ernest Moniz to White House budget director Shaun Donovan warning that without an extra $5.2 billion over the FYDP, the agency would "lack credibility" with Congress.

Driving the need for a funding bump, Klotz said, is the need for serious upkeep on nuclear facilities.

"We have a very old structures, many building go back to the early days of the Cold War, go back to the Manhattan pProject and need to be either replaced or significant work done to reduce the deferred maintenance," Klotz said. "Right now deferred maintenance for NNSA alone is $3.7 billion just in the buildings we have now."

However, Sessions questioned whether those are serious concerns, or simply the result of bad management, adding "We're in tight budget times — are you sure we need $3.7 billion just to refurbish buildings?"

Klotz countered by pointing that when the budget gets tight, the first thing to get cut is money in infrastructure, but that the buildings are now becoming a safety issue for workers.

"At some point you just have to stop accepting risk and get onto the business of rearing the facilities you have, because they do create the kind of safety and security concerns" that can impact a workforce and product, Klotz said.

The NNSA is a semi-autonomous department within the Department of Energy. While the Defense Department manages the delivery systems of the nuclear force — ships, planes and missiles — NNSA has oversight over the development, maintenance and disposal of nuclear warheads.

The agency is perusing a modernization plan known as the "3+2 Strategy," under which the agency is consolidating the American arsenal of warheads into five variants. Five bomb and cruise missile warhead types are being consolidated into two replacement warhead designs, the W80-4 and the B61-12. Meanwhile, the five ballistic missile warheads now in service are being consolidated into three new interoperable warheads known as the IW-1, IW-2, and IW-3.

Email: amehta@defensenews.com

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Aaron Mehta was deputy editor and senior Pentagon correspondent for Defense News, covering policy, strategy and acquisition at the highest levels of the Defense Department and its international partners.