U.S. sneaks in 'Vega,' its 28th subcritical nuclear test

September 18, 2018
Andrew Kishner

The U.S. National Nuclear Security Administration (NNSA), last December, carried out 'Vega,' its second scaled subcritical nuclear experiment and 28th subcritical nuclear test since 1997.

Smiley face

The U.S. National Nuclear Security Administration (NNSA) revealed in a March 2018 newsletter that it carried out the subcritical nuclear experiment named 'Vega' on December 13, 2017. In the 'Vega' experiment, nuclear weapons-grade plutonium fuel was bombarded by a chemical explosion but did not undergo a chain-reaction nuclear explosion. Per design, these nuclear experiments remain 'subcritical' and thus do not qualify as a 'nuclear test' under the CTBT (Comprehensive Test Ban Treaty). Subcritical experiments are conducted underground at the U.S.'s dormant nuclear test site, the Nevada National Security Site. The justification for these physics experiments, in general, is that they help scientists charged with maintaining the U.S.'s nuclear arsenal understand the properties of aging plutonium in older nuclear warheads.

Vega is the U.S.'s second scaled subcritical experiment since 1997. A scaled subcritical experiment more closely follows the fate of plutonium in a nuclear explosion and is so named because the experiment involves a scale model of a warhead primary. A primary is an arrangement of chemical explosives surrounding a manufactured 'pit,' or hollow sphere, of plutonium that when triggered causes an implosion, or inward explosion. This implosion, when conditions are right, achieves a critical mass, allowing a nuclear explosion. By using less plutonium (in reduced-size warhead mockups) than in a typical nuclear weapon, these scaled experiments remain subcritical, meaning no critical mass is achieved. Hans Kristensen of the Federation of Atomic Scientists wrote in his September 2011 article titled Hydrodynamic Tests: Not to Scale that scaled subcritical nuclear tests are 'experiments in an implosion geometry that is essentially identical to an actual warhead design, but reduced in size.'

Though subcritical in name, these experiments, with scales or not, run counter to nonproliferation efforts for some obvious reasons. Twenty-one years ago, while the U.S. Energy Department was preparing for Rebound, its first post-Cold War subcritical nuclear experiment, forty-four 'extremely concerned' members of the U.S. House of Representatives wrote in a letter of protest to the President:

'The fact that these subcritical experiments would be conducted 900 feet underground--a depth sufficient to contain nuclear explosions with large yields--sets a precedent for conducting underground nuclear tests that a test ban treaty violator would find useful. Because the CTBT is not yet ratified, there are no existing verification standards nor methods by which to determine whether a nuclear weapons experiment violates the CTBT or not. The U.S. is unwisely creating a testing norm under which other nations could justify conducting similar underground nuclear weapons experiments at their test sites.'†

IN CONTRAST: NEVADA'S SCALED-DOWN WORLD - In Las Vegas, Nevada, millions of tourists each year are greeted by dazzling sights such as the half-size replicas of the Statue of Liberty and the Parisian Eiffel Tower. Contrasting with these attractive mockups of the world's most iconic and admired structures are the unannounced plutonium blast experiments involving scale models of nuclear warheads sporadically conducted at a restricted government site eighty miles northwest of the Strip. These warhead mockups host subcritical nuclear experiments, whereby plutonium, a nuclear bomb fuel, is subjected to a chemical explosion for scientific study in an underground laboratory of the dormant Nevada (Nuclear) Test Site. The tests are called 'subcritical' because the plutonium used in the experiments fails to go critical and lead to a nuclear explosion. Subcritical nuclear experiments, including these scaled subcritical nuclear tests, are strongly opposed by peace groups, ambassadors of nuclear non-proliferation and the earliest victims of nuclear arms. These critics say the tests violate the spirit of various non-nuclear treaties and impede their hard-fought progress towards a world without nuclear weapons.

Provocative 'subcritical' tests resemble nuclear tests in the eyes of many nations

In April, North Korea admitted for the first time it has been secretly conducting subcritical tests. North Korea joins the list of States--including Russia, China, and France--that have joined or re-joined in the activity of subcritical nuclear testing since the U.S. commenced its subcritical test program in 1997, five years after its last underground nuclear test. The U.K. government, which has a mutual defense agreement with the U.S., sends it scientists occasionally to Nevada to take part in subcritical experiments with the Americans.

The forty-four Congresspersons further warned in their 1997 letter, 'An even more dangerous consequence is that countries with nuclear capability, but lacking the sophisticated testing technology of the declared nuclear weapons states, could be provoked to resume full-scale underground testing.'

In a protest letter condemning a 2012 U.S. subcritical test named 'Pollux,' the group International Physicians for the Prevention of Nuclear War (IPPNW) wrote to President Obama that U.S. subcritical testing

'[goes] against the intent of the [CTBT], which is to ensure that no new nuclear weapons will be designed and that no new capabilities will be developed for weapons that already exist. The nuclear-weapon states—and the US in particular—have a significant technological edge with regard to computer simulation of nuclear tests, derived from decades of actual test explosions. This advantage is not lost upon the rest of the world, which sees any such tests, with or without a nuclear chain reaction, as a means to extend and perpetuate the role of nuclear weapons in security policy, and not as a step toward disarmament. The message subcritical testing sends to other States is that nuclear weapons are here for the long term and that their designs can be modified and enhanced simply by making use of a loophole in a treaty to which the US says it is otherwise committed... For at least a few who may be questioning the wisdom of remaining non-nuclear in the future, subcritical tests are seen as a hypocritical practice that undermines the arguments for non-proliferation.'

Another issue of concern about U.S. subcritical experiments is that the NNSA has been shifting away from standards of transparency put in place in 1997 regarding notifications and the timing of tests.

In 1997, beginning with 'Rebound,' the Department of Energy began to provide a 48 hour notification prior to each test to various governments, organizations, and the media. For over a decade, the Energy Department, and later the NNSA, consistently adhered to this policy of prior notifications and also issuing a press release within hours or a day of each test. In September 2010, for its 24th subcritical nuclear test, named 'Bacchus,' the NNSA abandoned its voluntary policy of providing a 48-hour notice and, months later, the agency first began to opt out of issuing a press release following a subcritical test. In fact, in late 2010 and early 2011, the NNSA conducted two subcritical tests, 'Barolo A' and 'Barolo B,' that were not followed up by any confirmatory announcements for months. In June 2011, the NNSA proudly announced via a press release posted online that it was introducing a new practice of issuing quarterly summaries of its stockpile stewardship experiments, which included reporting on any recent subcritical tests (example of quarterly experiments report) and other stockpile experiments, many of them occurring at Los Alamos National Laboratory. In the press release, the NNSA remarked that the move was in keeping with its 'commitment to promote transparency.' (The first summary posted online provided the first confirmation of Barolo A & B.) For years, a growing collection of quarterly summaries was hosted on a NNSA web page but then in late 2015 the summaries were discontinued and in 2017 the webpage disappeared altogether without any notification or reason given.

For the Vega test, the first subcritical nuclear test in five years, there was no 48-hour prior notification or press release. Vega was confirmed months after the fact in a quarterly newsletter, the NNSA's publication Stockpile Stewardship Quarterly (SSQ). (Basic programmatic details and timeframes of upcoming subcritical tests are often printed in advance in budget, planning or other government documents, but the timeframes given are usually an upcoming month or fiscal quarter, and subject to delays).

Compared to the NNSA newsletter (Stockpile Stewardship Quarterly), the quarterly experiments reports, before they were discontinued in 2015, had a better track record of disclosures about stockpile stewardship plutonium experiments. For example, the NNSA's conduct of several 'Z-Machine tests' involving plutonium (controversial experiments like subcritical tests conducted at Sandia Labs in New Mexico) in 2012 were described both in quantity and timing in a quarterly summary in late 2012 but not in any of the SSQ journal issues in 2012 or early 2013. It makes little sense to discontinue a data summary that was clear and useful for tracking changes in NNSA activities for a substitute that is less complete and less timely in disclosures.

U.S. subcritical nuclear tests are conducted at the U1a complex at the former Nevada Test Site (the site was renamed to the Nevada National Security Site (NNSS) in 2010). From 1951 through 1992, nearly 1,000 nuclear bombs and devices were detonated at the Rhode Island-sized test site in the open-air or in underground cavities or tunnels. Radiation and fission products generated by the tests, especially atmospheric detonations of the 1950s and early 1960s, resulted in significant biological harm to test site workers, atomic veterans and people living in the path of the fallout clouds (known as 'downwinders'). Since 1992, when the U.S. initiated a unilateral moratorium on nuclear testing, the test site has maintained a 'readiness' program in the event that resumption of testing is deemed necessary by U.S. authorities. In its Fiscal Year 2018 Stockpile Stewardship and Management Plan (SSMP) report, the NNSA, which oversees the NNSS, noted “there is no current requirement to conduct an underground nuclear test to maintain certification of any nuclear warhead.” However, the agency did alter the 'readiness timeline' for resumption of testing at the NNSS from the pre-Trump era waiting period of 24 to 36 months to “6 to 10 months for a simple test, with waivers and simplified processes;...” This means that at the order of the President, nuclear bomb detonations could resume in the U.S. in six months time from any moment. Hans Kristensen noted in an analysis in late 2017, 'This reassessment of the test readiness requirement appears to erode the US commitment to the testing moratorium.'

Thanks to online public documents, we know that U.S. nuclear weapons labs have put together an aggressive schedule for subcritical nuclear experimentation through 2024. The next subcritical test, 'Ediza,' is planned for sometime in December 2018.

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PDF of 2 letters of protest by Greenpeace (with dozens of peace groups) and Congresspersons

1 Moscow radio station Radiovesti interviewed international security expert Vladimir Sotnikov regarding Russian subcritical testing resumption. Sotnikov remarked Russia feels compelled to take care of its own security needs and proceed with these subcritical nuclear tests for its own modernization plans.

2 The Lenta.ru article also noted that the increased pace of subcritical testing is a sign that nuclear powers are in a new phase of the nuclear arms race. Another Lenta.ru article published around the same time, 'Russia resumes subcritical tests at Novaya Zemlya,' mentioned U.S. plans to carry out 'Pollux' in late 2012 (the first time a Russian news source mentioned 'Pollux').

3Blogpost (recommended reading) reads in part: [translated] '...Transparency: It still exists but is becoming increasingly blurred anyway. Before (period 1997-2006), the firing was announced to various international bodies concerned 48 hours before their executions. But the firing was announced in September 2010 with a day late, for the last two shots, their achievements were revealed several months after ...France also conducts subcritical tests at the site of Moronvilliers (near Reims). As it will be closed, there are high chances that future experiments are conducted on the future complex created on the site Valduc.'


For more about subcritical tests (and 'Pollux,' the predecessor to 'Vega'), read 'NNSA Keeps Conducting 'Nuclear Tests' and Mentioning Them Well After the Fact' (skip to 'First U.S. Subcritical Nuclear Test Involving Warhead Mockup To Happen By Year's End').

Here's my 'Slideshare' (powerpoint) from 2011 that outlines the degradation of transparency about subcritical nuclear tests since 1997

The Nobel Laureate group IPPNW (International Physicians for the Prevention of Nuclear War) has taken a stand against subcritical tests - Read their 2012 letter to President Obama urging him to end future subcritical tests

Some good past articles on subcritical nuclear testing:

A Subcritical Fallout - Planned nuclear tests by Washington raise a storm of protest, Outlook India, April 23, 1997, By Ludwina A. Joseph

Take a hard look at subcritical tests - Bulletin of the Atomic Scientists, November 21, 1996, by Frank von Hippel and Suzanne Jones

NUCLEAR SECURITY: Nevada Test Site getting new life - Las Vegas Review Journal, September 14, 2009, By Keith Rogers

How Bush Learned To Love the Bomb - Salon (via Der Spiegel), March 30, 2005, By Leigh Flayton

#6 - U.S. Nuclear Program Subverts U.N.'s Comprehensive Test Ban Treaty, 'CENSORED 1999 - The News That Didn't Make the News - The Year's Top 25 Censored Stories,' (Seven Stories Press) by Peter Phillips and Project Censored

Moratorium stimulates simulating bomb tests - Associated Press, July 8, 1993


'U.S. sneaks in 'Vega,' its 28th subcritical nuclear test' -- Copyright © Andrew Kishner 2018