Underground nuclear weapons testing
When the device being tested is buried at sufficient depth, the nuclear explosion may be contained, with no release of radioactive materials to the atmosphere.
[2] The fallout from the March 1954 Bravo test in the Pacific Ocean had "scientific, political and social implications that have continued for more than 40 years".
[3] The multi-megaton test caused fallout to occur on the islands of the Rongerik and Rongelap atolls, and a Japanese fishing boat known as the Daigo Fukuryū Maru (Lucky Dragon).
In a Public Broadcasting Service (PBS) interview, the historian Martha Smith argued: "In Japan, it becomes a huge issue in terms of not just the government and its protest against the United States, but all different groups and all different peoples in Japan start to protest.
"[4] The Prime Minister of India "voiced the heightened international concern" when he called for the elimination of all nuclear testing worldwide.[who?
[6] Agreement was facilitated by the decision to allow underground testing, eliminating the need for on-site inspections that concerned the Soviets.
[6] Underground testing was allowed, provided that it does not cause "radioactive debris to be present outside the territorial limits of the State under whose jurisdiction or control such explosion is conducted".
[5] Following analysis of underwater detonations that were part of Operation Crossroads in 1946, inquiries were made regarding the possible military value of an underground explosion.
[7] The US Joint Chiefs of Staff thus obtained the agreement of the United States Atomic Energy Commission (AEC) to perform experiments on both surface and sub-surface detonations.
[16] The resulting mushroom cloud rose to a height of 12,000 ft (3,700 m) and subsequent radioactive fallout drifted in an easterly direction, travelling as far as 140 mi (225 km) from ground zero.
"[19] As compared with an above-ground test, the radioactive debris released to the atmosphere was reduced by a factor of ten.
[23] Analysis of samples collected after the test enabled scientists to develop an understanding of underground explosions that "persists essentially unaltered today".
[23] The information would later provide a basis for subsequent decisions to agree to the Limited Test Ban Treaty.
[24] The effects of an underground nuclear test may vary according to factors including the depth and yield of the explosion, as well as the nature of the surrounding rock.
[25] In contrast, if the device is buried at insufficient depth ("underburied"), then rock may be expelled by the explosion, forming a subsidence crater surrounded by ejecta, and releasing high-pressure gases to the atmosphere (the resulting crater is usually conical in profile, circular, and may range between tens to hundreds of yards in diameter and depth[26]).
The rebound after the shock wave causes compressive forces to build up around the cavity, called a stress containment cage, sealing the cracks.
Hard basement rock may reflect shock waves of the explosion, also possibly causing structural weakening and venting.
Massive, prompt, uncontrolled releases of fission products, driven by the pressure of steam or gas, are known as venting; an example of such failure is the Baneberry test.
[25] However, fault movements and ground fractures have been reported, and explosions often precede a series of aftershocks, thought to be a result of cavity collapse and chimney formation.
[6] Due to the Soviet government's concern about the need for on-site inspections, underground tests were excluded from the ban.
[30] Over the next decade, this system was improved, and a network of seismic monitoring stations was established to detect underground tests.
The resulting data is used to locate the epicentre, and distinguish between the seismic signatures of an underground nuclear explosion and an earthquake.
[30][32] Additionally, eighty radionuclide stations detect radioactive particles vented by underground explosions.
Certain radionuclides constitute clear evidence of nuclear tests; the presence of noble gases can indicate whether an underground explosion has taken place.
