Subcritical nuclear tests by U.S. since 1997 

1st--------------  2 July 1997, Rebound
2nd --------------18 Sept 1997, Holog
3rd --------------25 March 1998, Stagecoach
4th --------------26 September 1998, Bagpipe
5th --------------11 October 1998, Cimarron
6th --------------9 February 1999, Clarinet
7th --------------27 September 1999, Oboe
8th --------------10 October 1999, Oboe 2
9th --------------6 February 2000, Oboe 3
10th --------------22 March 2000, Thoroughbred
11th --------------9 April 2000, Oboe 4
12th --------------18 August 2000, Oboe 5
13th --------------14 December 2000, Oboe 6  
14th --------------26 September 2001, Oboe 8 
15th --------------13 December 2001, Oboe 7 
16th --------------14 February 2002, Vito 
17th --------------7 June 2002, Oboe 9 
18th --------------29 August 2002, Mario 
19th --------------26 September 2002, Rocco 
20th --------------19 September 2003, Piano 
21st --------------25 May 2004, Armando 
22nd --------------23 February 2006, Krakatau
23rd --------------30 August 2006, Unicorn 
24th --------------15 September 2010, Bacchus 
25th --------------1 December, 2010, Barolo A
26th --------------2 February, 2011, Barolo B
27th (Scaled)------5 December, 2012, Pollux
28th (Scaled)------13 December, 2017, Vega
29th (Scaled)------13 February, 2019, Ediza
30th (Scaled)------3 November, 2020, Nightshade A
31st (Scaled)------? ? 2021, Nightshade B
 

Andrew Kishner

The sky reportedly lit up over Nevada and neighboring states for a few seconds on Tuesday night at about 11:10 P.M. local time and for a brief moment I'm sure that a handful of downwinders and one or two sleepy officials at the NNSA (which oversees the Nevada Test Site [now the 'Nevada National Security Site']) panicked. A momentary rush of fear that a nuclear or chemical explosion had occurred inside one of the myriad of military installations across the Intermountain West quickly deflated when local television networks announced that what was streaking across the night skies had actually left a trail and was embued with colors of the rainbow. It was a fireball.

Is it possible that the Nevada Test Site, which isn't being used currently for full-scale nuclear testing (but it is being kept around for that purpose) and doesn't store trigger-ready nuclear weapons, could generate a bright flash big enough to be seen from surrounding states? Possibly.

In 1998, an anonymous letter was mailed to the State of Nevada Agency for Nuclear Projects (which was formed primarily as a state initiative to oppose Yucca Mountain) that stated 'Hundreds of nuclear weapons have been detonated both above and below ground at NTS; Some of these devices have failed to detonate partially or completely." This letter—which was signed as 'Retired scientists, monitors, and individuals from DOE and EPA who too [sic] great pride in their honest efforts to protect all living things around the NTS'—although it was a critical assault on the DOE's plan to gut radiation and environmental monitoring around the test site in 1998 is the only confession in existence to my knowledge that unexploded nuclear bombs still linger at the Nevada Test Site. (Further reading: Excluding EPA from nuclear checks worries residents near testing site.) Anyone well versed in all things nuclear weapons knows there are unexploded nuclear bombs across the world from U.S. nuclear accidents, dubbed 'Broken Arrows.' There's one off the coast of Georgia and another suspected to be off the seabed of Thule, Greenland. There is even a reference on the internet to a paper titled 'Unexploded Nuclear Device Left Under Semipalatinsk Site,' which is a former nuclear testing ground in present day Kazakhstan.

So, what's the big deal? What is so special about this news - however unsubstantiated - about unexploded bombs under the Nevada nuclear test site? Well, apparently, the DOE said it had already dealt with the problem.

On September 6, 1979, the Department of Energy carried out project 'Hearts,' an unusual underground nuclear blast intended to create a shock environment that would destroy two unexploded nuclear devices 'buried [elsewhere] deep beneath the Nevada Desert.' (If the phrase 'shock environment' sounds familiar, it's because that was the intent of Divine Strake: to shock limestone rock enough with a 0.7 kiloton blast to crush deeply buried, hardened bunkers, supposedly one of the greater national security 'threats' from the 'axis of evil'.)

The DOE hoped that the shock wave resulting from Hearts' 20 to 150 kiloton blast would travel through the geology to nearby underground test shafts holding unexploded remains of nuclear devices and cause the unfissioned nuclear masses to break apart, but not blow up. That last part was made especially clear from a DOE statement at the time: that the unexploded would not explode, but by smashing the device with surrounding rock, and throwing it about, the critical mass of plutonium or uranium cores would disperse. The theory is that with enough rocking of the earth, critical masses of fissionable materials would lose density and become non-critical masses.. This is not just a problem relating to unexploded nuclear devices. Quantities of plutonium waste lying around Rocky Flats (1) and Hanford Nuclear Reservation might be - or accumulate - in masses that can go critical. That has prompted environmental managers at the DOE's Hanford Nuclear Reservation to 'move around' plutonium in waste storage so it won't go critical.

Back to the DOE's experiment, two unexploded nuclear devices that Hearts was supposed to 'terminate' included that of 'Transom,' a test on May 10, 1978 that failed and resulted in zero-yield, and that of 'Peninsula,' from a test attempt of October 23, 1975. 'Peninsula,' it turns out, was never carried out because the device was damaged during emplacement.

According to DOE/NV-209-REV 15, project 'Hearts,' which came in at 140 kilotons, was successful at destroying just 'Transom,' so it took another nuclear blast shock experiment dubbed 'Azul' on December 14, 1979 to destroy the Peninsula device. (Azul's yield was 'less than 20 kt'.)

So, when in 1998 the anonymous group of scientists claimed there are partially or wholly unexploded nuclear bombs lying underneath the Nevada desert, did they mean that the Hearts and Azul tests weren't successful, or that they were successful but there are more Transoms and Peninsulas out there? Although unexploded weapons devices, if any are left, probably wouldn't go off by themselves, environmental conditions could cause critical masses of fissionable materials to reach a state of supercriticality, which is the physical state needed to sustain a fission chain reaction, aka nuclear explosion. (I'm not a nuclear physicist, so I'm just taking a shot at explaining this.) According to Wikipedia, criticality depends on a number of factors including 'fuel, shape, temperature, density...,' so an increase in temperature near unexploded devices or increased density or compression from rock movement or earthquakes or other geological causes might cause critical or sub-critical masses within unexploded nuclear devices to reach supercriticality, and explode (2).

The DOE, at least in 1978, didn't share that view. An agency spokesperson told the Las Vegas Associated Press after the failed test 'Transom' that there was 'no possibility of any additional explosion.' No danger. No hazard. (Heard that before).

So, then, why did the DOE in 1979 twice blow up nuclear bombs under the desert to shock other unexploded nuclear bombs? Common sense would tell us that the DOE wouldn't have conducted the Azul and Hearts tests for no reason. The devices must have posed a danger.

So, if there still are unexploded devices that could go supercritical under the Nevada Test Site (NTS), it's unlikely that residents of the Southwest would see the sky light up. But you could have a Baneberry. Baneberry was one of the worst underground nuclear test leaks at the NTS that precipitated radioactive snow on northern Utah and sent radioactive fallout all the way to Canada. More likely, we'd have a 'pop,' a really small nuclear yield that would easily be detected seismically across the globe and end up really pissing off other nuclear nations who would naturally think 'Hey. I thought you guys stopped testing.'

Perhaps this is all wasted energy and I've been victim to a prank of a disgruntled employee who added a comment about unexploded ordnances to an otherwise appropriate critique of the DOE's failed monitoring practices hoping that DOE critics will use the unreliable information to undermine their former employer's credibility. Perhaps there is no Baneberry surprise in store for us and the only light show over Nevada will be another fireball in 200 years. Or not? Who knows?

(1) http://web.mit.edu/newsoffice/1995/nuclear-kendall-0315.html
(2) Every ground-zero of past nuclear tests contains remains of unfissioned plutonium or uranium. That residue is the result of the imperfect 'efficiency' of nuclear bombs. That is why the vast majority (91.65% of the plutonium for Fat Man) of the bomb materials from the attacks on Hiroshima and Nagasaki were dispersed across the globe and to such an extent that plutonium from the Nagasaki attack was later detected in ice cores near the North Pole.
Anonymous letter: http://www.state.nv.us/nucwaste/nts/anon/loux03.htm
Title: 'Unexploded nuclear bombs at the Nevada Test Site: Fact or Fiction,' Nov.18, 2009, by Andrew Kishner