In a hearing Thursday, no members of the Senate Armed Services Committee said they would oppose Corey Hinderstein’s nomination to the National Nuclear Security Administration’s (NNSA) top nonproliferation job.

Biden on Aug. 9 nominated Hinderstein to be deputy administration for defense nuclear nonproliferation at the Department of Energy’s NNSA. If confirmed, she’d run a portfolio of programs, funded at more than $2 billion annually, to track radioactive materials domestically and internationally, remove gamma-emitting cesium sources from hospitals and deweaponize tons of excess weapon-usable plutonium.

On Thursday, a few senators, including the committee leaders, asked Hinderstein — a long-time think-tanker who spent time detailed to the NNSA from the Department of Defense during then-President Obama’s second term — to explain public remarks she made in 2019 downplaying concerns about Iran’s nuclear program. 

After Hinderstein testified Thursday that she was “extremely concerned” about Tehran’s uranium enrichment, Sen. Jack Reed (D-R.I.), the Armed Services chair, and Sen. James Inhofe (R-Okla.), the ranking member, dropped the issue. 

But Sen. Marsha Blackburn (R-Tenn.) vowed to send Hinderstein a written question for the record after the hearing “to delve further” into the former NNSA nonproliferation hand’s views about Iran’s advances with uranium enrichment.

Since the Trump administration in 2017 left the Joint Comprehensive Plan of Action, or Iran Nuclear Deal, that the Barack Obama administration forged in 2015, the Islamic Republic has pushed closer and closer to producing weapons-grade uranium. The Iran deal traded sanctions relief for limits on the country’s ability to acquire fissile material.

In April, Iran publicly announced its intention to enrich uranium up to a 60% concentration of the weaponizable U-235 isotope. Weapons grade uranium is at least 90% U-235. Anything over 20% is considered highly enriched and could be used in high-energy power or propulsion reactors, or for producing plutonium.

In 2019, Hinderstein told CNBC that she saw “no indication that Iran is rushing toward a nuclear weapon and they are taking steps that can be reversed.”

On Thursday, though, Hinderstein said that while Iran’s enrichment infrastructure could be turned off or even destroyed, diminishing the country’s technical capabilities at least temporarily,  “the knowledge that they’ve gained in the last few years is not reversible.”

If confirmed, Hinderstein said, “I would need to understand how their basic capacity has changed and whether there needs to be any change to our approach to accommodate that.” She also invoked Secretary of State Anthony Blinken’s remarks last weekend that as Tehran gains more and more enrichment experience, the terms of the old Iran deal “will not be sufficient to recapture the benefits of the agreement.”

Also at Thursday’s confirmation hearing, Hinderstein said she supported the Biden administration’s recent move to shore up the Australian navy by helping Canberra acquire nuclear-powered submarines — a move aimed at complicating China’s military strategy in the Pacific.

“I would say that Australia has been a leader on nuclear nonproliferation and while this doesn’t mean that we can transfer any technology or material capriciously, it means that I believe we will have a good partner in addressing any concerns,” Hinderstein said in response to Sen. Jean Shaheen’s (D-N.H.) invitation to talk about the recently announced AUKUS submarine partnership. 

In the 18 months the U.S., U.K. and Australia have given themselves to figure out the next steps on AUKUS, which was unveiled in September, Washington should be able to “make sure that whatever the arrangement is with Australia, it doesn’t set a bad precedent for any other country that may seek naval nuclear capability,” Hinderstein told Shaheen.

Hinderstein is currently vice president of international fuel cycle strategies at the Nuclear Threat Initiative in Washington and last worked in the government at the Pentagon and the National Nuclear Security Administration from 2014 to 2017.

Hinderstein’s last NNSA job was senior coordinator for nuclear security and nonproliferation policy affairs at the silo she would lead, if approved by the Armed Services Committee and confirmed by the Senate. 

The Armed Services Committee had not scheduled a vote on Hinderstein’s nomination. Democrats have a 51-50 majority in the chamber, with Vice President Kamala Harris’ (D) tiebreaker vote. Committees are split evenly among Republicans and Democrats. Even with that margin, a united Democratic party can get any agency nominee confirmed.