LOS ALAMOS ^^^mof the ^^^m NEW MEXICO University of California UNITED STATES ATOMIC ENERGY COMMISSION CONTRACT W-7405-ENG. 36 AEC RESEARCH AMD DEVELOPMENT REPORT RESTRIi This document contains restricted data as defineg^lR^^tomic Energy Act of 1954. Its transmittal or the disclosure of its contenia.jii^«!^nanne^lkan unauthorized person is prohibited.Group 1, 1-2 CWI^ID^iifT^ OiSlRiSUTION Of THIS DOCUMENT »S UNLIMJTI CTTwnimniHr ABSTRACTThe current series of nuclear-powered rocket reactors are small, graphite-moderated, beryllium-reflected cylinders loaded with U^55 in such a way that the power distribution is roughly flat at high temperatures. Niobium protects the graphite during high-temperature operation. Boron is the shim and control material. Inasmuch as the temperature varies from very low in the reflector (200 R) to very high in the core (5000 R), the reactor assembly has relatively neutronically complex energy and space functions. The median energy for neutron absorption is 100 evj thus, fast neutron transport, resonance absorption, eind -because of the beryllium reflector -thermal neutron transport problems are all important.The data needed for high-temperature reactor design are critical U^55 fuel distribution and kinetic constants. Room-temperature experiments resulted in detailed structural data for experiments having several degrees of geometrical complexity. In turn, these data yielded criticality and structural material value coefficients that were compared with calculated values. These values included U^-', graphite, niobium, and hydrogen as functions of position and fission density distribution.The variety of multigroup reactor physics techniques used to calculate static physics of the critical assemblies included numerical neutron transport, resonauice integral, and thermalization codes for group-averaged cross sections and fast transport cross sections. The Rover reactor studies followed extensive analyses of critical assemblies to establish the overall effects of moderators and absorbers; and, thus, the integral results are expected to be relatively accurate.The results of Kiwi-B studies were partially repeated to compare the computed and experimental fission density distributions. The description of the Phoebus reactor and the results of reactivity distribution studies show that kgff is approximately equal to 1.00 ± 0,005; that the computed fission density distribution is within the experimental uncertainty; and that some errors still remain in resonance integrals, as is shown by the comparison of computed and experimental material reactivity values.TtWFTITETItHH.
This report was prepared as an account of Government sponsored work. Neither the United States. nor the Commieeion. nor any pereon acting on behalf of the Cornmierrion: A. Makes any warranty or repreeentation, expreeeed or implied, with respect to the accuracy, completeneee, or ueefulneee of the information contained in W e report, or that the use of any information, apparatus, method, or proceee disclosed in W e report may not infringe privately owned rights; or B. Assumes any liabilities with reapect to the uea of, or for damagee resulting from the uee of any information, apparatue, method, or procee. d i s c l o d in this report. As u d In the above. "pereon acting on behalf df the Commissionm includes any employee or contractor of the Commiesion, or employee of euch contractor, to the extent that such employee or contractor of the Commiesion. or employee of much contractor prepares, dieseminates, or provides access to. any information pursuant to hie employment or contract with the Comaaieeion, or hin employment with swh contractor. This report expresses the opiniona of the author or authors and doe8 not necessarily reflect the opinions or views of the Los Alamoa hientific Laboratory.
Contract W-7405-ENG. 36 with the U. S. Atomic Energy Commission All LAMS reports are Informal documents, usually prepared for a special purpose and primarily prepared for use within the Laboratory rather than for general distribution. This report has not been edited, reviewed, or verified for accuracy. All LAMS reports express the vlewp^ the authors as of the time they were written and do not necessarl^^^wffibf opinions of the Los Alamos Scientific Laboratory or the flna^<^5*SgC>^thors on the subject.
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