Military science panel urges research on low-yield nuclear weapons

A US Department of Defense scientific advisory board has called on the Trump administration to rebuild the country’s nuclear weapons infrastructure and modernize its nuclear arsenal. The recommendations, detailed in a December report, include the development of new, low-yield warheads to give the military the option of a limited nuclear strike.

The report , written by a 15-member committee of the Defense Science Board (DSB), warns that Russia and China are well ahead of the US in upgrading their nuclear stockpiles. And it urges the new administration to “re-establish the knowledge base in nuclear matters and the art of deterrence” among civilian and military leadership.

“Although the threat of nuclear Armageddon has subsided, the nation must still hedge against such an existential possibility, no matter how slim,” says the report, Seven Defense Priorities for the New Administration. “However, the threats of proliferation, the potential for the U.S. weakening assurance guarantees of its allies, and the emerging scenarios of limited use in regional conflicts or limited strike against the U.S. homeland—with the potential for escalation—introduce complexities not seen since the early days of the Cold War.”

The DSB committee calls the proposed low-yield weapons “a rapid, tailored nuclear option for limited use should existing non-nuclear or nuclear options prove insufficient.” Those weapons consist only of primaries—the fission stage of today’s multistage thermonuclear weapons. Primaries are grapefruit-size plutonium cores, known as pits, surrounded by shaped high explosives. Implosion of the pit creates uncontrolled fission and a nuclear explosion. Primary-only weapons produce inherently smaller yields relative to the two-stage thermonuclear (fission followed by fusion) warheads that make up today’s US strategic arsenal.

The bomb that destroyed Nagasaki, for example, consisted of a primary stage alone. Primary-only designs were used in compact warheads that have since been retired, such as nuclear artillery shells that were deployed in Europe during the Cold War.

The US arsenal already includes one warhead with low-yield capability: the B-61 bomb. Still deployed in Europe, it is a two-stage weapon that can be adjusted to produce different yields; three of them, ranging from 0.3 kt to 10 kt, deploy only the primary stage. (The Nagasaki blast was around 21 kt.) Lisbeth Gronlund , codirector of the global security program at the Union of Concerned Scientists, notes that although land- and sea-based strategic missiles have a single yield, they could easily be modified to disable their secondary stages.

A DSB member who declined to be named says the low-yield warhead recommendation wasn’t meant to address a particular threat, nor was it a call for deploying such weapons. Instead, low-yield capability would be a hedge in a shifting strategic threat environment. “We have a stockpile that was designed to deter a massive exchange of Cold War threats,” he says. “The question now is that as the threat environment has changed, is that still an appropriate set of capabilities?”

Russia, he says, “explicitly talks about using nuclear options” to threaten its neighbors. In that context, “we ought to be thinking how we could do a number of things, like having open architectures, lower-yield primary-only [options], and advanced manufacturing” for timely modifications of existing weapons.

Trump has spoken of his intention to upgrade the nuclear arsenal. “The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes,” he tweeted on 22 December. A week after his inauguration, Trump ordered Defense Secretary James Mattis to report to him within 30 days on the condition of the nuclear stockpile. Trump’s memorandum cited the need “to ensure that the United States nuclear deterrent is modern, robust, flexible, resilient, ready, and appropriately tailored to deter 21st-century threats and reassure our allies.”

The review is part of a broader assessment of military capabilities and readiness that Trump requested from Mattis to help guide the Office of Management and Budget in preparing the administration’s fiscal year 2018 budget request. The last such review was completed in 2009 for President Obama.

Gronlund says the DSB report “had nothing to do with Trump,” since it was initiated by the Obama administration well before the election. She questions what deterrence role the proposed low-yield weapons would play. “This is exactly a call for increasing the role of nuclear weapons—the opposite of the historical trend,” she says. “I don’t think this is useful to the military. They don’t want to have a conflict with nuclear weapons mixed in.”

Last year in the annual DOD authorization act, Congress urged the Department of Energy to develop new nuclear weapons designs, something the agency hasn’t done since the early 1990s. Most DOE national laboratory weapons research has focused on extending the lives of existing warheads. A 2015 National Academies of Sciences, Engineering, and Medicine report also recommended that weapons design efforts be initiated in the labs. It said that the proper training of weapons designers required that they be allowed to build actual prototype weapons , which would not be tested.

Any increases in US warhead production would be limited by the aging weapons complex, the DSB report notes. Production of the plutonium pits is limited to 30 per year at least through 2026. And new facilities are sorely needed at the Y-12 plant at Oak Ridge, Tennessee, which fabricates the secondary stage of warheads.

An “open question” is how long the need for underground testing, banned since 1992, can be put off, the DSB report says. Such doubts contrast with repeated statements by the directors of the weapons labs that today’s computer simulations and experimental facilities provide a better understanding of warheads than was had during the testing regime.

A newly published report by the nonpartisan Congressional Budget Office estimates that maintaining and modernizing the nuclear weapons arsenal would cost $400 billion over 10 years. That’s 15% higher than the 2015 estimate. The Government Accountability Office has the decadal cost at $320 billion. Both estimates are based on President Obama’s policy to extend the lives of thousands of land-, sea-, and air-deployed weapons. Independent estimates, including a 2014 assessment by the James Martin Center for Nonproliferation Studies and a 2015 report by the Center for Strategic and Budgetary Assessments, peg the cost at up to $1 trillion over 30 years.