Uranium-graphite reactions

In 1942, Enrico Fermi demonstrated the first controlled chain reaction in the Fermi reactor, and that was shortly followed in 1945 by the start-up of the Soviet uranium-graphite reactor in Moscow. The enthusiasm for nuclear energy in 1950s was so great that scientists would say that nuclear is too cheap to meter . 

The uranium-graphite nuclear reactor (or nuclear pile ) was important not merely because it proved the feasibility of a self-sustaining fission chain. It could be used, with minor modification, for neutron irradiation of a sample by placing the sample in the interior of the reactor. Also, the system could be used as a source for the easily fissionable Pu239. This isotope (half-life 24,100 years) is a product in the decay chain from U239, which in turn results from the (n,y) reaction on U238 ... 

Compacted UO2 was used in the assembly of the first nuclear exponential lattice in July 1941. The first self-sustaining controlled nuclear chain reaction was achieved in the CP-1 uranium-graphite reactor on December 2, 1942, using 32,652 kg (36 tons) of uranium oxide (both UO2 and UsOs), as well as uranium metal. 

A small portion of the 94 39 produced may also be changed to 94 4o by absorption of neutrons. The neutronic reactors referred to above may be called isotope converters in that one thermally fissionable isotope is formed (94 ) as another thermally fissionable isotope (U33B) is used up. However, this conversion is not c6m-plete, and the natural uranium, which acts to supply both the reaction isotope (U s) the absorption isotope (U ), will contain two different thermally fissionable isotopes after the reactor has been started. Certain presently known uranium-graphite reactors have been found to have a conversion factor of. 78, U to 94 3 . However, it may be desirable to form other fissionable isotopes in quantity such, as for example, U . Isotopes such as U 3 and Th , which arc not thermally fissionable isotopes, but which, upon absorption of a neutron, produce a thermally fissionable istotope, are called fertile isotopes. ... 

The uranium reactor was built on a squash court of the university (and it was here that the guards donned discarded raccoon coats to protect themselves from the cold). Dubbed CP-1 (Chicago pile number 1), it was called an atomic pile because it was just that The reactor consisted of a pile of containers of uranium oxide interspersed with graphite bricks. There was a neutron source at the bottom to initiate the reaction, and neutron-absorbing cadmium rods could be inserted for control. Fermi s group demonstrated the feasibility of a uranium chain reaction by the end of 1942. 

Fission product-graphite reactions. The products of uranium fission may also react chemically with graphite to form carbides. A. series of experiments have shown that materials such as cerium will definitely react with graphite. When 25 ppm Ce in bismuth was placed in contact with graphite at 700°C for 110 hr, CeC2 was identified as a film on the graphite. Graphite contacted with 140 ppm Sm in bismuth at 800°C for 140 hr, on... 

Uranium-235 is of even greater importance because it is the key to utilizing uranium. 23su while occuring in natural uranium to the extent of only 0.71%, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone. 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

CP-1 was assembled in an approximately spherical shape with the purest graphite in the center. About 6 tons of luanium metal fuel was used, in addition to approximately 40.5 tons of uranium oxide fuel. The lowest point of the reactor rested on the floor and the periphery was supported on a wooden structure. The whole pile was surrounded by a tent of mbberized balloon fabric so that neutron absorbing air could be evacuated. About 75 layers of 10.48-cm (4.125-in.) graphite bricks would have been required to complete the 790-cm diameter sphere. However, criticality was achieved at layer 56 without the need to evacuate the air, and assembly was discontinued at layer 57. The core then had an ellipsoidal cross section, with a polar radius of 209 cm and an equatorial radius of309 cm [20]. CP-1 was operated at low power (0.5 W) for several days. Fortuitously, it was found that the nuclear chain reaction could be controlled with cadmium strips which were inserted into the reactor to absorb neutrons and hence reduce the value of k to considerably less than 1. The pile was then disassembled and rebuilt at what is now the site of Argonne National Laboratory, U.S.A, with a concrete biological shield. Designated CP-2, the pile eventually reached a power level of 100 kW [22]. 

A drum of graphite with magnesium and uranium, stored underwater with a 6mm diameter relief hole, burst and scattered its contents. This was attrributed to insufficient venting of hydrogen evolved by reaction of magnesium and water [1], If the uranium was present as metal, it seems likely to have been an even more potent source of hydrogen [2],... 

Shortly after Japan s December 7,1941 attack on Pearl Harbor, the U.S. became more driven to expedite its timetable for developing the first fission weapon because of fear that the U.S. lagged behind Nazi Germany in efforts to create the first atomic bomb. On December 2, 1942 at 3 49 p.m., Enrico Fermi and Samuel K. Allison achieved the world s first controlled, self-sustained nuclear chain reaction in an experimental reactor using natural uranium and graphite. 

Nuclear power plants use fissionable materials such as uranium-235 as sources of energy. In the core of a nuclear power plant, rods of uranium dioxide (U02) are placed in a matrix containing moderators such as heavy water or graphite that slow neutrons so they can be captured. The neutrons impact uranium nuclei, splitting them to release lighter nuclei and converting a small amount of mass to energy. In order for a chain reaction to occur, a critical mass of fissionable material must be present. 

The only system which seems to be promising for industrial application is ruthenium promoted with rubidium on graphite as carrier (see Section 3.6.2.3). Further information on structure, activity and reaction mechanism of non-iron catalysts is given in [102], [172]-[175], Specific references vanadium [176], uranium [177], molybdenum [178]-[180], tungsten [181]. 

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