Nuclear Experts Warn Iran Deal Must Address Plutonium Pathway to Bomb, Not Just Uranium

The on-again, off-again nuclear negotiations between Washington and Tehran have fixated on a single element: uranium. Enrichment caps, centrifuge counts, stockpile limits — these have dominated every round of talks since April 2025. But a growing chorus of arms control specialists is raising an alarm about what the negotiations are not discussing: the plutonium sitting in plain sight at Iran's Bushehr nuclear power plant.

Henry Sokolski, a former Deputy for Nonproliferation Policy at the Department of Defense and executive director of the Nonproliferation Policy Education Center, put the stakes bluntly in an April 2026 analysis for the Bulletin of the Atomic Scientists: the 210 tons of spent fuel stored at Bushehr contain more than 2,000 kilograms of plutonium — enough, in theory, for more than 200 nuclear weapons [1]. By comparison, the roughly 440 kilograms of 60%-enriched uranium Iran had stockpiled as of late 2025 could yield material for five to six bombs [2].

The arithmetic alone explains why some analysts believe the current negotiating framework has a structural gap.

The Two Roads to a Bomb

Nuclear weapons can be built from two fissile materials: highly enriched uranium (HEU) or plutonium-239. Iran has pursued both pathways at various points over the past two decades, but diplomatic attention has overwhelmingly centered on uranium enrichment — the route where Iran made the most visible progress before the June 2025 Israeli strikes destroyed much of its declared centrifuge infrastructure [3].

The plutonium route works differently. A heavy-water reactor like the one Iran built at Arak (designated IR-40) irradiates natural uranium fuel; the spent fuel then contains plutonium-239, which must be chemically separated through a process called reprocessing. In its original configuration, the Arak reactor could have produced 8 to 10 kilograms of weapons-grade plutonium per year — enough for one to two nuclear weapons annually, given that roughly 8 kilograms is the threshold for a single device [4].

The Bushehr reactor, a Russian-built 1,000-megawatt light-water power plant, produces far larger quantities of plutonium in its spent fuel, though of a lower "reactor-grade" isotopic quality. The distinction matters — reactor-grade plutonium can be used in a weapon, but doing so is technically more difficult than using weapons-grade material [5].

Source: Arms Control Association / IAEA Reports

Data as of May 1, 2026CSV

What the JCPOA Did — and What Remains

The 2015 Joint Comprehensive Plan of Action addressed the Arak reactor head-on. Iran agreed to remove the reactor's original core, and in January 2016 the calandria — the vessel housing the fuel channels — was extracted and filled with concrete [6]. The reactor was to be redesigned with international assistance into a smaller unit producing far less plutonium, with all spent fuel shipped out of the country [7].

These modifications were verified by the IAEA, which maintained continuous monitoring at Arak. The concrete pour was a physical act that rendered the original core unusable — though it fell short of full dismantlement. The redesigned reactor was never completed; construction proceeded slowly, and by mid-2025 the IAEA had observed only "minor" construction activity at the site [4].

Then Israel struck. The Arak facility was hit during the Twelve-Day War in June 2025, and again in March 2026 [4][8]. The attacks inflicted significant damage to the containment building, and analysts at the Alma Research Center assessed that the strikes aimed to ensure the reactor could not be rebuilt for nuclear purposes [8]. Iran has refused to grant the IAEA access to the damaged sites, making independent verification of the facility's current status impossible [9].

The Bushehr reactor, meanwhile, was never subject to the same restrictions. Under the JCPOA, Iran committed not to reprocess spent fuel — a pledge, not a physical constraint. Russia supplies the enriched uranium fuel for Bushehr and is contractually obligated to take back the spent fuel, but accumulated spent fuel has been piling up in on-site storage pools for years [1].

Breakout Timelines: Uranium vs. Plutonium

The concept of "breakout time" — how long a country would need to produce enough fissile material for a single weapon — has become the central metric in Iran diplomacy. Before the JCPOA, Iran's uranium-enrichment breakout time was estimated at two to three months. The deal extended it to at least 12 months. After the U.S. withdrawal in 2018 and Iran's subsequent breaches, that window shrank dramatically — to less than one week by late 2024, according to IAEA assessments [2][10].

Source: Arms Control Association

Data as of May 1, 2026CSV

The June 2025 strikes reset the clock. With centrifuge facilities at Natanz and Fordow severely damaged, analysts estimate Iran would need many months — possibly up to two years — to reconstitute its enrichment capacity [3]. But this window is temporary. Carnegie Endowment analysts have warned that Iran retains "an ability and perhaps greater desire to reconstitute these capabilities, including in smaller, clandestine facilities" [3].

The plutonium breakout timeline operates on a different scale entirely. Iran does not currently possess a functioning reprocessing facility — the prerequisite for extracting plutonium from spent fuel. Building one from scratch would take years, though Sokolski argues that Iran "mastered plutonium extraction chemistry 30 years ago" at its Tehran Nuclear Research Center and could scale the process faster than commonly assumed [1]. The more relevant concern, in his view, is not the construction timeline but the surveillance gap: IAEA cameras at Bushehr record on 90-day cycles, and inspectors last visited the site on August 27, 2025 — a gap he calls long enough "to divert the spent fuel and make it into a plutonium bomb" [5].

What the Trump Framework Does — and Doesn't — Cover

The Trump administration's negotiating position, as it has evolved through multiple rounds of talks in Muscat, Islamabad, and Rome, has centered on two demands: zero uranium enrichment by Iran and a permanent ban on plutonium reprocessing [11][12]. U.S. negotiators proposed a 20-year moratorium on enrichment during weekend talks in Islamabad; Iran countered with a five-year freeze, which Washington rejected [12].

The reprocessing ban, while present in the U.S. framework, has received far less public attention and — according to critics — far less specificity. Andrea Stricker of the Foundation for Defense of Democracies has called for "a permanent and verified ban on plutonium reprocessing in Iran under any deal," paired with monthly IAEA inspections at Bushehr and a mechanism for Russia to remove accumulated spent fuel [5].

Arms control veterans see a gap between the administration's stated goals and the verification infrastructure needed to enforce them. Daryl Kimball, executive director of the Arms Control Association, has argued that the Trump team is attempting to address "problems that had been addressed by the nuclear deal that Trump unilaterally abandoned in 2018," while the JCPOA imposed "clear limits, prohibitions and intrusive IAEA inspection requirements" designed to last 10 to 15 years [10]. The current framework, as publicly described, lacks comparable detail on verification protocols, inspector access schedules, and the disposition of spent fuel.

Comparisons to the New START treaty's verification regime — which included on-site inspections, data exchanges, and continuous telemetry monitoring between the U.S. and Russia — highlight how far the reported Iran framework falls from established arms-control standards [10].

The Steelman Case Against Plutonium Alarmism

Not all experts share the alarm. David Albright, a physicist, former weapons inspector, and president of the Institute for Science and International Security, has described himself as "highly skeptical that Iran would use plutonium from Bushehr's spent fuel to make nuclear weapons" [5].

Albright's counterarguments are specific. First, Iran has never demonstrated a plutonium-weapon design. Second, diverting Bushehr spent fuel would trigger an immediate Russian suspension of fuel supply, shutting down the reactor that provides a significant share of Iran's electricity. Third, the plutonium in Bushehr's spent fuel is reactor-grade, not weapons-grade — it can theoretically be used in a weapon, but "it is tricky to do so if a significant explosive yield is wanted" [5].

The broader case for prioritizing uranium is straightforward: Iran's enrichment infrastructure, even damaged, represents a far more developed and faster pathway to a weapon. The 440 kilograms of 60%-enriched uranium Iran had stockpiled before the strikes could be further enriched to weapons-grade (90%+) in a matter of days once centrifuges were operational [2]. The plutonium route would require building reprocessing facilities Iran does not possess, a process measured in years rather than weeks.

From this perspective, the plutonium issue is real but secondary — and injecting it into already-fraught negotiations risks becoming a poison pill that prevents any deal at all.

Stakeholders Drawing Red Lines

Whatever the technical merits of each side, the political reality is that multiple stakeholders have publicly conditioned their support for any deal on plutonium safeguards.

Jason Brodsky, policy director at United Against Nuclear Iran, has stated that "any proposed deal with Iran needs to address the plutonium pathway to nuclear weapons," noting that Israel's repeated strikes on Arak — and intelligence suggesting Iran had attempted to reconstruct the facility between bombings — demonstrate the pathway remains a live concern [5].

Israel's position has been expressed through action as much as rhetoric. The two strikes on Arak, plus broader attacks on enrichment sites, signal that Israeli military planners view both pathways as requiring physical elimination, not just diplomatic constraint [8]. Israeli officials have not publicly articulated specific red lines for a deal's plutonium provisions, but the strikes themselves constitute a de facto position: verification regimes alone are insufficient.

The IAEA's posture is constrained by Iran's refusal to grant access. The Agency's Board of Governors, at the urging of Germany, the United Kingdom, and France, adopted a resolution calling on Tehran to grant inspectors "immediate and full access to all nuclear facilities" [9]. Iran has not complied. IAEA Director General Rafael Grossi has repeatedly called for the restoration of monitoring capabilities, but the Agency lacks enforcement power beyond referral to the UN Security Council — where Russia and China have historically blocked punitive action [9].

Gulf states have expressed growing anxiety but have largely operated through diplomatic channels rather than public ultimatums. The broader regional concern is that a deal perceived as leaving open a plutonium pathway would accelerate interest in nuclear hedging among Saudi Arabia, the UAE, and Turkey [3].

The North Korea Precedent

Non-proliferation scholars consistently point to North Korea as the cautionary tale for reactor-based commitments. Under the 1994 Agreed Framework, Pyongyang froze its plutonium-producing reactor at Yongbyon in exchange for heavy fuel oil shipments and the construction of two light-water reactors. IAEA inspectors monitored the freeze, and 8,000 spent fuel rods were placed under seal [13].

The arrangement collapsed in 2002 when the U.S. accused North Korea of running a covert uranium enrichment program. Pyongyang expelled IAEA inspectors, removed the seals on the spent fuel, restarted the Yongbyon reactor, and reprocessed the fuel rods to extract weapons-grade plutonium [13]. In January 2003, North Korea announced its withdrawal from the NPT — the first and only country to do so — and went on to conduct its first nuclear test in 2006 [13][14].

The lessons are specific. First, reactor freezes without physical dismantlement are inherently reversible. The Yongbyon reactor was "frozen," not destroyed; the fuel rods were sealed, not removed from the country. When the political framework collapsed, the technical constraints evaporated overnight [14]. Second, the UN Security Council's response was hampered by veto dynamics, with China blocking the most stringent proposed sanctions [14]. Third, verification access that depends on the host country's consent is only as durable as that country's political will.

Applied to Iran, these lessons cut in competing directions. On one hand, the JCPOA's treatment of Arak — pouring concrete into the core — represented a more physically irreversible step than the Yongbyon freeze. On the other, the Bushehr spent fuel sits in storage pools under an inspection regime that experts describe as inadequate, creating a parallel to the sealed-but-accessible Yongbyon fuel rods [1][13].

The Cost Question

Physical dismantlement of a reactor core is expensive, and no arms-control agreement has imposed that financial burden unilaterally on a signatory without some form of compensation or buy-out arrangement. The JCPOA addressed this through a cooperative model: the P5+1 agreed to assist Iran in redesigning the Arak reactor, with China taking a lead role in the conversion project [6].

The closest historical precedent for externally funded dismantlement is the Nunn-Lugar Cooperative Threat Reduction Program, through which the United States spent over $10 billion helping former Soviet states secure and dismantle nuclear weapons, delivery systems, and related infrastructure after the Cold War [15]. Libya's 2003 denuclearization involved a different model: the U.S. and UK physically removed nuclear-related equipment and materials in a process completed within months, though Libya's program was far less advanced than Iran's [16].

For Bushehr, the most discussed option involves Russia fulfilling its contractual obligation to repatriate spent fuel — a step that would remove the plutonium from Iranian territory entirely. Whether Russia would cooperate with this arrangement under current geopolitical conditions is an open question. The alternative — building a domestic dry-cask storage or vitrification facility — would cost hundreds of millions of dollars, and no framework for financing it has been publicly proposed [1][5].

What Happens Next

The negotiations remain in flux. Iran insists on its right to enrich uranium. The Trump administration insists on zero enrichment. The plutonium question sits in the background, acknowledged in broad U.S. demands for a reprocessing ban but lacking the specific verification architecture that arms-control experts say would make such a ban enforceable.

The technical reality is that Iran's uranium pathway, though temporarily degraded by military strikes, remains the faster route to a weapon. The plutonium pathway is slower but potentially larger in scale — and, critically, subject to weaker international monitoring. Whether negotiators treat plutonium as a core agenda item or a secondary concern will shape not only the durability of any agreement but also the calculations of regional states weighing their own nuclear options.