Allegations of a clandestine Iranian nuclear facility have faced skepticism by observers, but nuclear experts are warning of shrinking nuclear breakout times and the Iranian regime’s deceptive tactics.
On May 8, 2025, a Fox News report, citing claims from the National Council of Resistance of Iran (NCRI) opposition coalition group, claimed to show satellite imagery of an alleged previously undisclosed Iranian nuclear weapons-related facility.
The extensive compound, reportedly codenamed the “Rainbow Site” (“Rangin Kaman” in Persian) by Iranian officials and allegedly operational for over a decade, is said to be located in Semnan province, east of Tehran.
According to the NCRI, as reported by Fox News, the nearly 2,500-acre site operated under the guise of a chemical production company. The primary function alleged for the “Rainbow Site” was the extraction of tritium, a key radioactive isotope of hydrogen used to significantly enhance the yield of nuclear weapons and essential for developing thermonuclear devices (hydrogen bombs).
The report suggested that Iran’s Organization of Defensive Innovation and Research (SPND), long associated with Iran’s past nuclear weaponization efforts, was involved and had recruited nuclear fusion experts for this project.
Iranian Foreign Minister Abbas Araghchi dismissed the report on May 9 as an effort to derail upcoming nuclear talks, writing on X, “Like clockwork, more Very Scary Satellite Images are being circulated as Iran-U.S. indirect nuclear talks are set to resume.”
Stricker urges caution
Andrea Stricker, deputy director of the Washington D.C.-based Foundation for Defense of Democracies’ Nonproliferation and Biodefense Program, and an FDD research fellow, urged caution regarding the latest claims.
“Nuclear experts like David Albright are not seeing signatures of a tritium-related facility here. One must use caution regarding NCRI claims,” she told JNS.
Stricker further noted, “In any case, tritium has dual civil uses and is not inherently a red flag.” However, she also assessed, “Iran is likely experimenting with dual-use nuclear weapons activities, but it remains to be seen if they are already seeking the capability to boost nuclear weapons with a material like tritium.”
Meanwhile, Iran is widely believed to be pushing forward with its uranium enrichment activities.
Shrinking timelines
Sima Shine, director of the Iran and the Shi’ite Axis Research Program at the Tel Aviv-based Institute for National Security Studies (INSS) and former head of the Research and Evaluation Division of the Mossad, told JNS she assumes Iran is continuing to enrich 60% enriched uranium, adding that to confirm this, one needs to wait for the next report by the United Nations International Atomic Energy Agency watchdog.
Iran has been enriching uranium to 60% purity—a short technical step from the 90% considered weapons-grade—for a significant period, drastically reducing potential breakout times. The IAEA in its February 2025 reports highlighted that Iran’s stockpile of 60% enriched uranium had “risen significantly” and expressed “serious concern” over this production by the only non-nuclear weapon state to do so.
The Institute for Science and International Security, which is headed by David Albright, in a May 6 report titled “Iranian Breakout Timelines Under JCPOA-Type Limits,” stressed the “shrinking timelines.”
The report stated that reimposing the original 2015 nuclear deal (the JCPOA-Joint Comprehensive Plan Of Action) limits on Iran’s centrifuge program today “could not achieve a 12-month breakout timeline, only about a four-to-five-month timeline.”
More alarmingly, the organization assessed that if Iran were to return to JCPOA-type limits while storing its excess advanced centrifuges, it could achieve breakout to produce enough weapon-grade uranium (WGU) for one nuclear weapon in approximately “4.5 months.”
Against this backdrop of escalating nuclear concerns, a fourth round of US-Iran negotiations took place in Muscat, the capital of Oman, on May 11, 2025. The talks, originally set for May 3 but postponed amid Iranian objections over recent US sanctions on its oil industry, were described by Iranian Foreign Ministry spokesperson Esmaeil Baqaei as “difficult but useful.”
Delegations led by White House envoy Steve Witkoff and Iranian Foreign Minister Abbas Araghchi aimed to “better understand each other’s positions and to find reasonable and realistic ways to address the differences,” Baqaei stated.
Both parties agreed to continue talks focused on technical aspects, with a future meeting to be coordinated by Oman. However, fundamental disagreements persist.
An Iranian source told CNN on May 11 that prohibiting Tehran’s domestic uranium enrichment is a “definite red line.” Araghchi himself stated after the talks, “From our viewpoint, enrichment is a subject that should definitely continue and there is no room for compromise on that,” although he allowed that “it is possible that we consider some limits on its dimensions, amount and level for trust building, similar to the past,” according to a May 11 ABC report.
Conversely, Witkoff emphasized in a May 8 interview with Breitbart that “an enrichment program can never exist in the state of Iran ever again. That’s our red line. No enrichment.”
He specified that this entailed “dismantlement… no weaponization, and it means that Natanz, Fordow and Isfahan—those are their three enrichment facilities—have to be dismantled.”
Israel has not publicly commented on the talks, but has repeatedly reserved its right to use military force to roll back the Iranian nuclear program.
Experts from the FDD expressed skepticism about the negotiations. Andrea Stricker, commenting on the talks, stated, “An important question is whether the two sides are simply talking for the sake of delaying a U.S. decision over military strikes against Iran’s nuclear program.”
She stressed the need for clarity from the US administration: “The administration needs to fully articulate its position on the dismantlement of Iran’s nuclear fuel production capabilities, weaponization program, and missile delivery work—and know when it is time to walk away.”
Behnam Ben Taleblu, the Iran Program senior director and senior fellow at FDD, said, “If Iranian official statements after every round of talks is a guide, differences in the U.S. and Iranian positions appear to be making themselves much more manifest.”
He added, “Despite earlier statements about the ways with which the Trump administration might achieve its goal of a non-nuclear Iran, standing firm on its demand for no enrichment and full dismantlement will be crucial.”