Could small modular reactors be used to create nuclear warheads?

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SMRs are near the top of the agenda in the nuclear industry in the UK. At least four companies – GE-Hitachi, Holtec Britain, Rolls-Royce SMR and Westinghouse Electric Co. – are competing to have their designs adopted by Great British Nuclear, and at the same time, the UK’s nuclear weapons stockpile is due to increase.

Nuclear power was originally created in pursuit of the materials needed for the development of nuclear weapons during and after the Second World War.

While there have been major technological advancements, the process behind nuclear power generation remains similar.

There is an in-built assumption, at least in open discussion about the nuclear industry, that civil nuclear is pursued for exclusively peaceful ends, and in particular as part of the race to net zero.

However, the UK does have a nuclear weapon programme with its Trident nuclear submarines, also called the continuous-at-sea-deterrent (CASD).

NCE asked the Department for Energy Security and Net Zero (DESNZ) under the Freedom of Information (FoI) Act if it had made any assessment of the potential for SMRs to produce material for nuclear weapons.

In its response, DESNZ said that the deployment of SMRs in the UK “will comply with UK civil nuclear safety and security regulations and international conventions to ensure that nuclear material intended for use in civil nuclear deployments is used for that purpose only, and cannot be diverted or manipulated for use in nuclear weapons”.

However, this statement does not mean that SMRs cannot be used to create materials for nuclear warheads. The fissile material that could potentially be used in nuclear weapons is what is produced by the reactor, not what is used within it.

DESNZ went on to say that it “neither confirms nor denies that it holds information” on whether assessments have been made on whether material from SMRs could be used in nuclear weapons.

“This is a qualified exemption, and we have considered the public interest arguments in confirming or denying whether we hold the requested information,” it continued.

“We acknowledge that confirming or denying if information is held would provide assurance that the Department takes the safe and secure deployment of nuclear energy seriously.

“However, confirming or denying that the information relevant to your request is held may itself disclose the presence of sensitive nuclear information. Such information could assist in potential criminal activity if the information was used by malicious parties.

“We have determined, that in all the circumstances of the case, the public interest in maintaining the exclusion of the duty to confirm or deny outweighs the public interest in confirming whether the information is held.

“This should not be taken as an indication that the information you requested is or is not held by the Department.”

Outside of the government, there could be malignant non-governmental actors around the world who could take advantage of the widespread deployment of SMRs to develop nuclear weapons.

Demand for weapons-grade nuclear material in the UK has increased

The Integrated Review 2021 published under the Boris Johnson government said: “In 2010 the government stated an intent to reduce our overall nuclear warhead stockpile ceiling from not more than 225 to not more than 180 by the mid-2020s.

“However, in recognition of the evolving security environment, including the developing range of technological and doctrinal threats, this is no longer possible, and the UK will move to an overall nuclear weapon stockpile of no more than 260 warheads.”

This represented a potential uplift of 16% and it is worth remembering that nuclear weapons have a shelf life. AWE (the Atomic Weapons Establishment) is responsible for creating, maintaining and renewing the stockpile of warheads. The missiles in Trident are supplied by the US Government.

The Integrated Review 2021 also said the UK Government would no longer give public figures for its operational stockpile, deployed warhead or deployed missile numbers.

Nuclear power was developed for weapons proliferation

NCE spoke with University of Glasgow senior lecturer in physics and astronomy Bjoern Seitz and University of Surry NPL (National Physical Laboratory) professor of nuclear metrology Patrick Regan to understand the potential links between SMRs and nuclear weapons.

Regan said: “The reason we have nuclear power in the UK was to make plutonium for the nuclear weapons programme.”

Seitz said the UK is “sitting on the largest stockpile of plutonium in Sellafield”, and noted that only “a few kilograms” are needed to create a nuclear weapon, while there is likely to be hundreds of tons available.

Conventional nuclear power plants producing gigawatt-scale electricity generation are the closest cousins today of the reactors originally used to generate power and weapons-grade material.

SMRs, meanwhile, “are trying to use mass production on more or less existing technology; you use the same nuclear technology as you would do in Hinkley Point C”, according to Seitz.

Reactors generally start with uranium as their fuel. Through a process called ‘neutral capture’, the uranium turns into plutonium.

“If you have a conventional reactor, it creates plutonium, and you can chemically separate the plutonium to produce a weapon,” Seitz explained.

Potential to co-locate SMRs with military sites

In May 2024, the White House revealed plans for a deployment programme for advanced nuclear reactors, including modular- and micro-reactors, to power “multiple” US Army bases.

In a statement, the White House said: “Small modular nuclear reactors and microreactors can provide defense installations resilient energy for several years amid the threat of physical or cyberattacks, extreme weather, pandemic biothreats, and other emerging challenges that can all disrupt commercial energy networks.”

It confirmed that the United States Army would release a Request for Information to inform a deployment program for advanced reactors to power multiple Army sites in the United States.

The Ministry of Defence (MOD) told NCE it has not assessed the potential benefits of having SMRs located near any of its sites in the UK.

NCE asked Seitz if it could be beneficial for the production process of nuclear warheads in the UK for SMRs to be co-located with military installations.

Seitz said SMRs don’t need to be located near sites for the production of nuclear warheads for one to feed the other.

“You still need the whole reprocessing chain, and you still need to need a Sellafield-type chemical factory,” he said. Seitz added that there would need to be access available for workers to bring the material from the reactor to the processing site.

“You don’t need massive nuclear installations if you want to produce weapons-grade material,” he said. “What you need is the chemical chain [after the fuel has been used in a reactor]

“Afterwards you need access to the fuel rods, and this is where these advanced modular reactors become an interesting field.”

Attempts to design in non-proliferation measures

Reflecting on the potential for SMRs to be used as part of the supply chain for state-sanctioned, as well as illicit proliferation, Seitz said: “If we need all this nuclear power to prevent climate change, one should push for technologies where proliferation [of nuclear weapons] is more difficult.”

Seitz said some AMR designers want to “embed their fissile material in molten salt, which potentially makes it much harder to get access” to the fuel.

He said in parts of the nuclear power research community there’s “a general awareness that whatever nuclear you build needs to have high standards of safeguards” and tampering protections.

He said advanced modular reactors “will have a strength […] where they can be designed to prevent illicit access” compared to conventional nuclear reactors.

Additionally AMRs can be built in a manner where “you weld everything shut” so “nobody can access fissile material”, thereby making them tamper-proof, according to Seitz.

Larger number of smaller reactors could create additional challenges

The pursuit of SMRs will see them deployed in “fleets”, with multiple sites around the country playing host to multiple of the modular nuclar stations.

“One of the issues that people are slightly concerned about is if there’s loads of these, you lose track,” Regan said. “It becomes an accounting problem.”

He added there would be a potential for a similar scenario to what he said happened in the Soviet Union where “the whole system breaks down” because the administration becomes so cumbersome.

Seitz echoed Regan’s concerns, saying: “You’re building many more reactors. When you’re thinking about terrorist activity, the more thinly or widely spread they are. It’s easier to defend one big reactor than many small ones.

“I think the other thing to look into is what the industry is doing to prevent illicit access by looking into special designs.”

Seitz said that would involve “welding a reactor chamber shut or using a molten salt core, where it’s difficult to extract plutonium back out”.

Foreign governments’ potential use of SMRs to create weapons

There is lots of international activity in the SMR space, with countries including the UK, US, Russia, China and India and other states actively pursuing the small reactors.

China and Russia claim to have already built operational SMRs. It is difficult to independently verify these claims.

Seitz said: “The people who are successfully marketing small modular reactors are mainly Russia. At the moment, the west is lagging behind.”

Speaking about access to materials in civil nuclear reactors, Regan said: “If something went missing, that inventory of fuel is very well monitored by the International Atomic Energy Agency (IAEA).” He said it would take a “nefarious, nasty government” to circumvent the IAEA’s monitoring programme.

Speaking about governments like those of Iran and North Korea, he said he thought that if they “were going to make nuclear weapons, [they would] use a normal reactor, like we did in the UK”.

Seitz agreed that it is unlikely that major states already with nuclear weapon capabilities like China and Russia would be pursuing SMRs as a way of advancing their arsenal.

However, “there are other states out there”, Seitz warned.

“At a recent COP, there [was an announcement that there] were 30 states which wanted to consider nuclear new build,” he said. “They will probably be looking for small modular reactors.

“I think it’s fair to say there are countries on the list who, in the past, have expressed nuclear weapons ambitions in one way or another. Then it comes to a question of whether they would allow international inspections and safeguard controls.”

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