Institute for Energy and Environmental Research
By: Hisham Zerriffi
and
Arjun Makhijani, PhD
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The Department of Energy (DOE) proposes to spend billions of dollars in constructing and operating new experimental facilities at U.S. nuclear weapons laboratories. The program is called Science Based Stockpile Stewardship (SBSS). According to the DOE, the need for an SBSS program is a direct result of the moratorium on nuclear testing and new warhead development work and the impending agreement on a Comprehensive Test Ban Treaty (CTB). To the DOE the SBSS program is a "basic need" to meet national security policies which mandate a "safe and reliable stockpile without further nuclear testing and aggressive pursuit of enhanced experimental capabilities." (1) Further, the Department of Defense (DoD) also requires the DOE to maintain the capability to design, fabricate, and certify new weapons. The U.S. government proposes to maintain its nuclear arsenal for an indefinite period of time. (2) The DOE proposes to use the SBSS program to accomplish this by:
These goals are linked. The DOE claims to have established the SBSS program in order to retain the weapons design and testing skills it believes are necessary to maintaining both the safety and reliability of the nuclear arsenal. (3) The Science Based Stockpile Stewardship program, according to the DOE, will be used to provide experimental test data on warhead behavior, aging effects and the basic physical process in warhead detonation. (4) Using this information, gained at the various SBSS facilities, the weapons laboratories hope to create more accurate computer models of warheads. In the past computer models have been used to help design new warheads. The DOE states it will use computer models to anticipate future problems and correct problems as they occur. (5) The SBSS program, according to the DOE, will replace the direct knowledge gained from full-scale nuclear tests with laboratory and computer exploration of the fundamental physical processes that occur in a nuclear weapon. (6) There are a host of documents in which the DOE has set forth their rationale for the SBSS program. The most recent is the Draft Programmatic Environmental Impact Statement for Stockpile Stewardship and Management.
The DOE has large numbers of existing facilities in which it conducts experiments and computer simulations of warheads. It proposes to continue using most of these facilities and to build expensive new ones as part the SBSS program. The DOE has rejected alternatives to the SBSS program which would not have extensive new experimental facilities and the cadre of physicists necessarily attached to them. (7)
The Science Based Stockpile Stewardship program encompasses all three weapons laboratories (the three weapons laboratories are Los Alamos National Laboratory (LANL) in New Mexico, Lawrence Livermore National Laboratory (LLNL) in California, and Sandia National Laboratory (SNL) in New Mexico and California) (8) and the Nevada Test Site. There are various experimental and support facilities and programs located at these sites. The facilities can generally be split into four categories:
The construction cost for new experimental facilities has been estimated at approximately $2 billion. This does not include the cost of operating or decommissioning the facilities. The cost of the Accelerated Strategic Computing Initiative (ASCI), the program to provide enhanced computational capabilities, has also been estimated at approximately $2 billion. (10)
The SBSS program is more than just a collection of facilities and programs. The heart of the program lies with the scientists and engineers who will use those facilities. The DOE itself considers retaining weapons designers and attracting new scientists into these programs an integral part of the SBSS program. This is part of "preserving the core intellectual and technical competencies of the weapons laboratories." (11)
In this paper, we examine
Nuclear warheads contain thousands of components that include the nuclear explosives, the triggering mechanisms, and control, safety, security, and guidance systems. Reliable operation of such a complex device when detonation is intended and preventing detonation when it is not form the core of reliability and safety issues related to warheads.
In order to evaluate the need for the SBSS program it is necessary to understand the basics of how a modern nuclear warhead operates and the different types of components and materials used. Modern nuclear warheads typically consist of two main stages: a fission primary and a secondary that has both fusion (thermonuclear) and fission components. Although these two stages form the core of a nuclear warhead, they only account for a small percentage of the components (in one example, the primary and secondary accounted for five percent of the components). (12) There are a larger number of non-nuclear components in a warhead.
Primary: The primary stage of a warhead has a "pit" of nuclear material that explodes, deriving its energy from nuclear fission. In the fission process, the nucleus of a heavy atom is split into two smaller components by a neutron, releasing excess energy and more neutrons. The neutrons from the first fission event can then fission other nuclei of heavy atoms. If there is enough fissile material arranged in the right geometry (a critical mass) a chain reaction will occur, whereby each fission causes at least one more fission. In a nuclear weapon, the chain reaction grows rapidly so as to yield an explosion. That is, each fission produces more than one fission causing the release of a large amount of energy - enough to generate an explosion before the device assembly is blown apart and the chain reaction stops.
Plutonium-239 and/or highly enriched uranium (uranium with a large concentration of uranium-235) are the two materials used to accomplish the nuclear detonation of the pit. These atoms are chosen because they are fissile and hence can sustain a chain reaction. Some isotopes such as uranium-238 are fissionable by higher energy neutrons, but cannot sustain a chain reaction. A "supercritical mass" is required to achieve an explosion; it is created by compressing uranium-235 (in the form of highly enriched uranium) and/or plutonium-239. The whole nuclear explosion happens very quickly (on the order of one microsecond). In a nuclear warhead primary, high explosives implode a spherical "pit" of plutonium or highly enriched uranium into a supercritical mass.
Boosting: In order to make more efficient use of the fissile material in the primary, a technique called boosting was developed. A mixture of tritium and deuterium is injected into the primary before the implosion. The high pressures and temperatures of the implosion induce fusion reactions between the nuclei of tritium and deuterium, releasing a number of excess neutrons which fission more of the original fissile material before the pit is blown apart by the force of the explosion. The fusion energy of the boosting process is small compared to the fission energy of the primary and does not contribute significantly to the yield of the warhead. But by requiring less fissile material for the same yield, boosting has allowed the DOE to develop lighter warheads which gives DoD missiles greater range and allows for more warheads in multiple warhead missiles.
Secondary: The secondary uses a fusion process to release energy, but relies on the energy of the primary explosion to initiate the fusion process. Neutrons from the primary explosion create tritium from the lithium in lithium-deuteride. X-rays from the primary compress the material, causing fusion reactions between the tritium and deuterium nuclei. The process is aided by reflective barriers and compression from the primary explosion. Secondaries can also use U-235 or Pu-239 and U-238 for added energy. The neutrons from the fission reaction are energetic enough to fission the U-238, which adds to the overall yield of the warhead.
Other Components: As noted above, nuclear warheads can be very complex and may contain thousands of components. Only a small number are located in the "nuclear package" (13) (also called the "physics package"). The nuclear package consists of both the primary (including high explosives, detonators, etc.) and the secondary. The rest are non-nuclear components including arming and firing systems, parachutes, radars, batteries, etc.
Institute for Energy and Environmental Research
Comments to Outreach Coordinator: ieer@ieer.org
Takoma Park, Maryland, USA
August, 1996
1 DOE 1995c, p. 3-3
2 DOE 1996, p. 2-7
3 DOE 1995a p. 4
4 DOE 1995c, 2-10 and 2-11
5 DOE 1995c, 2-10
6 DOE 1996, p. 3-15
7 DOE 1996, pp. 3-5 - 3-7
8 We will refer to these as Los Alamos, Livermore and Sandia respectively.
9 "Draft Accelerated Strategic Computing Initiative (ASCI) Program Plan." Downloaded off the Internet homepage of the Department of Energy's Defense Programs Office. The page was last changed on 12 June 1995. The homepage was taken off the Internet in March of 1996.
10 Weida 1996, Collina and Kidder 1994.
11 DOE 1995a, p. 1
12 DOE 1995b, p. 2-12
13 DOE 1995b, p. 2-12