Control Console for 105-D Hanford plutonium production reactor

Description:

Background on Control Console for 105-D Plutonium Production Reactor; object cat. no. 1993.0138.02

The Manhattan Project, the scientific and military undertaking to develop the atomic bomb, was formally launched by the U.S. government in September 1942. For a short history of it, go to

http://www.atomicarchive.com/History/mp/index.shtml

Author Richard Rhodes has written a highly-regarded comprehensive history of the atomic bomb, including the story of the Hanford reactors, rich in human, political and scientific detail: Rhodes, Richard. 1986. The Making of the Atomic Bomb. Simon and Schuster.

As part of the Manhattan Project, plutonium production reactors were constructed at Oak Ridge, Tennessee and then at Hanford, Washington. The first was the experimental X-10 Graphite Reactor built at Oak Ridge; it went online in 1943 and served as the prototype for the series of reactors at Hanford. The 100 Area is the part of the Hanford Site located along the banks of the Columbia River. It is where the nine reactors built from 1943 through 1965 are found. They were constructed next to the river because they needed plenty of hydroelectric power and cooling water during operation. The first three of these, 105-B, 105-D, and 105-F, were built simultaneously about six miles apart, starting in October 1943. The first completed, the 105-B Reactor, started operations in September 1944, and produced the fissile material for the two plutonium bombs used during World War II, the “Trinity” test bomb and the bomb dropped on Nagasaki. This 105-B Reactor, the world’s first full-scale nuclear reactor, has been designated a U.S. National Historic Landmark, and is also part of the new Manhattan Project National Park. For a detailed description of the construction and operation of this reactor, see the following document:

Historic American Engineering Record; Hanford Cultural and Historical Resources Program,

B REACTOR HANFORD SITE, HAER No. WA. 164, DOE/RL-2001-16

(pdf file posted online at http:/www.b-reactor.org/history.htm)

The world’s second full-scale nuclear reactor was the 105-D. It began operating in December of 1944, ran through June of 1967, and was ultimately “cocooned” in 2004. (Cocooning is a process by which the reactor core is encased in a concrete shell for 75 years to allow residual radioactivity to decay away. This cocoon is designed to prevent any radiation or contamination left over from the nuclear operations from escaping to the environment.)

The control room of each of Hanford’s nuclear reactors, such as the 105-D, received the information necessary for monitoring and controlling the plant and contained the facilities for operating it. These first generation control rooms consisted almost entirely of panel instrumentation with fixed, discrete components such as switches, indicator lights, strip chart recorders, analog gauges, and annunciator windows. The early Hanford reactors were equipped with various safety and control instruments that measured temperature, pressure, moisture, neutron flux, and radioactivity levels. For a description of these measurements, see pp. 51-55 in the HAER document referenced above. Two measurement examples follow.

1) Moisture content in the circulating helium atmosphere surrounding the reactor. “Water was chosen as the coolant for the Hanford piles [reactors] . . . because it was available in large quantities, had a high heat-transfer coefficient, and was well understood among engineers. The decision to use water was not an easy one, because although water is an effective coolant, it is also an oxidizer of uranium and, in a graphite-moderated pile, an effective poison for the chain reaction” (ibid, p. 42). The largest component of air, nitrogen, is a relatively good absorber of neutrons. “Any air within the pile, therefore, would serve to poison the chain reaction. Another problem associated with air in the pile is argon gas. Although it makes up only a tiny portion of a given volume of air (about 0.9 percent), argon readily becomes radioactive when exposed to the intense neutron flux (flow rate or density) of a pile (more so than the all the other gases in air combined). It was almost impossible to make the pile absolutely gas-tight, so any air within the pile could leak into the surrounding work areas, where the radioactive argon gas could present a hazard to the workers. To eliminate both these problems, the pile’s atmosphere was replaced with circulating helium gas. Helium absorbs no neutrons within the pile and is the one element in which radioactivity cannot be induced by neutron bombardment. There were still more advantages to a helium atmosphere. Helium has a fairly high thermal conductivity (five or six times that of air), meaning that it would aid in the transfer of heat from the pile’s graphite shields and control-rod passages to the 2,004 cooling tubes. Helium is inert, which made it easier to detect water leaks within the pile by sampling the gas as it circulated out of the pile, at which point the helium gas could then be dried and purified” (ibid p.36). “The circulating helium was tested for moisture content in order to reveal any leaks within the pile. Samples could be drawn from the main gas duct, or from 10 sampling tubes that penetrated the rear shielding into the 4 in. gas plenum” (ibid p. 37).

2) Neutron flux levels. “The primary measure of the pile’s chain reaction was the neutron density, or flux, within the pile. One problem with the design of the instrumentation that measured this reactivity was the incredible range of neutron density involved. . . . When it was running at full power, the neutron flux was 100 billion times greater than when it was shut down or running at very low power. To handle this range, two different sets of neutron monitors were needed. The high-level flux was measured by four ionization chambers installed in different tunnels under the pile. . . . The very small current developed by these chambers was measured by picoammeters located in the control room. At the time, these Beckman meters (named after the company that made them) were called micro-microammeters, and were state of the art” (ibid p.53). “When the pile was shut down or running at very low power levels, the low-level neutron fluxmonitor system, or subcritical monitor, would measure its reactivity. Its primary use was to determine when the pile achieved criticality and the rate of rise of power level. The galvanometer system consisted of one ionization chamber under the pile connected to two galvanometers in series. One galvanometer provided a signal (deflection) proportional to the neutron flux, while the other registered the deviation from a preset level. In this way, the system could show small changes in the neutron flux. This system also included shunts and potentiometers at the control room console to compensate for range changes” (ibid, p. 54).

The control console, the separate water temperature control panel, and some related artifacts from the 105-D Reactor are in the Smithsonian’s Modern Physics Collection (accession no. 1993.0138). The control console closely resembles the console at Oak Ridge for the X-10 Reactor. It consists of a wooden cabinet with black metal instrument panels occupying the upper part and the right side of the front (see accompanying media images). A console projecting below the center and left portion contains three small inclined control panels designed for a seated operator. Indicators include two chart recorders (one is "Differential Pwr. Recorder"), two translucent glass galvanometer scales (presumably for the neutron flux monitoring function quoted above), and gauges for fuel rods. There are also numerous switches and knobs for equipment such as control rods, pumps, and bypasses. [See curator's file for details on location, dimensions, markings and condition of each section (including details on gauges, recorders, switches, lights, buttons, etc.)].

Brief description of nuclear fission using slow neutrons

Several heavy elements, such as uranium, thorium, and plutonium, undergo both spontaneous fission, a form of radioactive decay, and induced fission, a form of nuclear reaction. Neutrons, because they have no electrical charge, are not repelled by the positively charged atomic nucleus of an atom. Slow neutrons have a greater probability than fast neutrons of being absorbed in the nucleus of certain isotopes. Elemental isotopes that undergo induced fission when struck by a free neutron of any energy are called fissionable; isotopes that undergo fission when struck by a “thermal,” slow moving, neutron are also called fissile. A few particularly fissile isotopes, notably U-233, U-235 and Pu-239, can be used as nuclear fuels because under certain conditions assemblies of these isotopes can sustain a chain reaction through the release of additional neutrons among their fission products. This makes possible a self-sustaining nuclear chain reaction that releases energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in a nuclear weapon. Although Pu-239 is exceedingly rare in nature, it was discovered that U-238 atoms could be transmuted to Pu-239 (capture of extra neutrons by U-238 to form U-239, which then undergoes a series of decays to form Pu-239). The required quantities of Pu-239 were produced in the nuclear reactors at Hanford, in which U-238 atoms absorbed neutrons that had been emitted from U-235 atoms undergoing fission. The plutonium so produced was then chemically separated from the uranium in dedicated separation facilities.

For the basic concepts of nuclear fission, chain reactions, critical mass, fission of uranium and plutonium isotopes, and the basic principles used for atomic bombs developed in the Manhattan Project, go to: http://www.atomicarchive.com/Fission/Fission1.shtml