Nuclear Effects Testing - Introduction
A nuclear blast differs from a conventional blast in several ways. It is caused by an unrestrained fission reaction (not chemical reactions). It can be millions of times more powerful than the largest conventional explosions. A one-kiloton blast is equivalent to the explosive energy of 1,000 tons of TNT. It creates much higher temperatures and much brighter light flashes, causing skin burns and fires at considerable distances. It produces highly penetrating and harmful radiation. It spreads radioactive debris, so that lethal exposures can be received long after the explosion.
Energy yield is the total energy released in a nuclear explosion. The energy yield of a nuclear explosion takes three forms: Thermal radiation is the light and heat of a nuclear detonation that travel ahead of the winds and overpressure and are so intense that they can cause "flashblindness" and skin burns. There is evidence that temperatures may exceed 3,000F as far as 3,200 feet away. Blast or shock effect result from the rapid release of energy within a small enclosed space causes a great increase in temperature and pressure, creating huge destructive action. A nuclear explosion releases both initial nuclear radiation and residual nuclear radiation (radioactive fallout).
The first above-ground nuclear weapon test was conducted by the US in southeastern New Mexico on July 16, 1945. Between 1945 and 1963, hundreds of above-ground blasts took place around the world. The number and size (yield) of blasts increased, particularly in the late 1950's and early 1960's. Following the signing of the Limited Test Ban Treaty of 1963 by the US, USSR, and Great Britain, most above-ground blasts ceased. Some above-ground weapons testing by other countries continued until 1980.
In 1992, President George H.W. Bush announced a second unilateral moratorium on testing, which Presidents Bill Clinton and George W. Bush subsequently extended. Despite tests conducted by France, Pakistan, and India in the late 1990s, the United States continued the 1992 moratorium to this day.
The Defense Threat Reduction Agency (DTRA) and its legacy organizations [DASA & DNA] have been involved in test activities at White Sands Missile Range (WSMR) since the 1940s. Today DTRA conducts tests to evaluate the lethality of conventional and advanced weapons against various targets. These tests assist in the development and implementation of new weapon technologies to reduce the threat of weapons of mass destruction (WMD). Mock enemy targets, including deeply buried and concrete-reinforced structures are used to test weapon systems.
On 25 October 1957, the President of the United States and the Prime Minister of Great Britain made a Declaration of Common Purpose containing the following: "The arrangements which the nations of the free world have made for collective defense and mutual help are based on the recognition that the concept of national self-sufficiency is now out of date. The countries of the free world are inter-dependent and only in genuine partnership, by combining their resources and sharing tasks in many fields, can progress and safety be found. For our part we have agreed that our two countries will henceforth act in accordance with this principle."
Immediately afterward, the Canadian Government subscribed to this principle of interdependence and joined in the common effort. The resulting organization was called the Tripartite Technical Cooperation Program. As a result, an exchange of notes was made which reconstituted the Combined Policy Committee (CPC) which comprised the Foreign and Defense Ministers of the United States, the UK and Canada and also the heads of the atomic energy agencies of the three nations. The signatory parties to the TTCP MOU are the Department of Defence of Australia, the Department of National Defence of Canada, the New Zealand Defence Force, the Secretary of State for Defence of the United Kingdom of Great Britain and North Ireland, and the Secretary of Defense of the United States of America.
Two Subcommittees of the Combined Policy Committee were established, one to deal with matters in the atomic field and the other to facilitate cooperation in non-atomic research and development. The latter body, eventually named the Subcommittee on Non-Atomic Military Research and Development (NAMRAD), comprised the heads of defense research and development organizations in the United States, the UK and Canada. Australia joined the NAMRAD Subcommittee in 1965, and New Zealand joined in 1969. These five nations form the current membership, and the organization governed by the Subcommittee is now called The Technical Cooperation Program (TTCP).
When the LTBT prohibited nuclear detonations in the atmosphere, DASA developed large-scale (kiloton-class) HE test beds to generate airblast and ground shock. In 1964, Operation SNOWBALL, a 500-ton HE event, was conducted in Alberta, Canada. The SAILOR HAT test was conducted the following year. These tests simulated nuclear airblast loading of structures and underwater shock on ships. Subsequent DASA tests included PRAIRIE FLAT and DIAL PACK, both of which helped the Air Force assess and improve the survivability of Minutemen II silos.
As HE testing evolved, distributed HE arrays, such as the High Explosive Simulation Technique (HEST) and the Direct-Induced HEST (DIHEST), were developed by the Agency to test reverseengineered Soviet silos and to evaluate candidate silo basing modes for Peacekeeper and the Small ICBM. DASA also employed HE testing for evaluating the dynamics of crater formation.
DASA conducted additional experiments on forest blowdown in Australia and Canada. British and Canadian scientists played key roles in the development and refinement of HE simulation of nuclear effects. The results achieved by those two countries and the U.S. were coordinated and exchanged through The Technical Coordinating Panel (TTCP). The TTCP played a major role in establishing a series of multinational shock physics conferences on the military applications of airblast.
The Defense Nuclear Agency sponsored these large explosive tests as part of their program to study airblast effects. A wide variety of experiments are fielded near the explosive by numerous Department of Defense (DOD) services and agencies. Measurement programs are independent of this work. Researchers use these tests as energetic known sources, which can be measured at large distances. Ammonium nitrate and fuel oil (ANFO) is the specific explosive used by DNA in these tests.
The history of the development and use of ANFO as a nuclear weapons blast, cratering, and ground shock simulation source, traces from 1966. The concept for using ANFO for nuclear weapon effects simulation was first conceived in August 1966, when two NSWC (Naval Surface Weapons Center, formerly Naval Ordnance Laboratory) scientists were discussing the general subject of nuclear weapon blast simulation, and in particular, the forthcoming large scale field tests (to which they had been invited as official observers), of a new simulation technique. This new method used detonable gases as the explosion source. One of the men, L. D. Sadwin, had some experience with ANFO and knowledge of its uses by the mining industry; the other, J. Petes, was familiar with the Navy's and DNA's (Defense Nuclear .Agency, formerly Defense Atomic Support Agency) requirements and endeavors to find an adequate replacement for TNT, the then current explosive used for large scale nuclear weapon blast simulation tests. They knew of the problems associated with the use of TNT, and they were aware of the July 1966 attempt to detonate 20 tons of an oxygen propane mixture in a hemispherical balloon which test was aborted when the balloon suffered structural failure. In 1976 the first full scale target testing operation was conducted on DICE THROW with a 600-ton ANFO charge. In October 1976, the DICE THROW tests exposed a number of expedient shelters to the blast from a 600-ton ammonium nitrate-fuel oil explosion. One of the findings from this test program was that unshored covered trenches collapsed from ground motion at relatively low overpressures. The results of the development tests, of DICE THROW, and of subsequent tests with ANFO through PRE-DIRECT COURSE in 1982, indicate that ANFO is a safe, economical and reliable explosive source for effects simulation purposes.
By 1983 several large blast tests had been conducted, including Pre DICE THROW, DICE THROW, MISERS BLUFF, MILL RACE, and DISTANT RUNNER. As a result of these tests, an extensive array of pressure-distance and impulse-distance data was accumulated. There were sufficient data now available to ask and answer the question, How reproducible are ANFO detonations? Composite pressure-distance and impulse-distance curves have been generated along with their associated error bands. In addition, the absolute yield of each event has been determined. Similar computations are made for several test series utilizing TNT in a target sphere configuration. Comparisons are made between the reproducibility of the ANFO and TNT sources. ANFO appeared to be slightly more reproducible than TNT. Moreover the equivalent weight of ANFO relative to TNT (over the pressure range of 1 to 1000 psi) was determined to be 0.71, as opposed to the standard value of 0.83.
At the White Sands Missile Range in New Mexico, and the Nevada Test Site, DTRA and its predecessors have conducted a series of large scale Ammonium Nitrate and Fuel Oil detonations. ANFO had been used by the mining and excavating industries since about 1956, ten years before the concept of using ANFO for nuclear weapons effects simulation purposes and twenty years before it was accepted for large scale test operations. ANFO properties relevant to uses by these industries were adequately documented. However, the properties and characteristics of ANFO in unconfined multi ton charges as used on DNA test operations had not been studied in any great depth. With more thaq two dozen variables of ANFO physical and chemical properties to consider, the task was complex and formidable. Such things as shock front and fireball anomalies, jets, spikes, protuberances are observed but no conclusive reasons were initially available to explain their occurrence. Detonation pressures and, velocities as computed using equation of state data and as measured in field tests showed wide variations, again with no certain reason for the variations. Even equation of state formulations showed significant differences.
In simulating nuclear blasts though tests such as MINOR SCALE, MISTY PICTURE, MISERS GOLD, DIRECT COURSE and others, the designers use many primary charges spread through the mix to assure that the ANFO goes efficiently.
The Comprehensive Nuclear Test Ban Treaty (CTBT), signed but not ratified by the US bans nuclear explosions from weapons testing or peaceful purposes. A provision of the CTBT also calls for the establishment of an International Monitoring System (IMS) to detect nuclear explosions. Large-scale chemical explosions, such DTRA static HE tests, are allowed for certain purposes including calibration of detection equipment. Chemical explosions greater than 300 tons TNT equivalent must be reported with information on the blast (for example, location, time, and type of explosive).
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