Prompt neutron decay for very loosely coupled delayed critical 38.1-cm-diam uranium (93.2) metal cylinders

Journal Article · Tue Dec 31 04:00:00 EST 1996 · Transactions of the American Nuclear Society

OSTI ID:426526

Mihalczo, J T ^[1]

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1. Oak Ridge National Laboratory, TN (United States)

A delayed critical very loosely coupled configuration of coaxial right circular 38.1-cm-diam, {approximately}7.62-cm-thick uranium (93.15 wt% {sup 235}U) metal cylinders was assembled in 1965 at the Oak Ridge Critical Experiments Facility to study interaction effects for unmoderated and unreflected uranium metal and described in 1996. Each of the two interacting cylinders was carefully adjusted by inverse kinetics rod drop (IKRD) measurements to have the same subcritical reactivity ({approximately} 85{cents}). For these reactivity determinations, each cylinder was alternately and separately assembled to delayed criticality with a small piece of polyethylene reflector present on the top surface. The system was raised to the appropriate power level by the use of a small additional reflector worth {approximately}10{cents} until delayed neutron precursors reached equilibrium. All reflectors were rapidly removed, and the subcriticality was obtained by IKRD interpretational algorithms. Several adjustments of the mass and configuration of each cylinder were required until the configuration of each cylinder had a subcritical reactivity of 85 {cents}. These adjustments were made by small variations in the mass of each of the cylinders so that the mass of the upper cylinder was 163.1 kg and that of the lower cylinder was 162.8 kg. Once each individual cylinder reactivity was adjusted to 85 {cents} subcritical, the distance between the flat surfaces of each of the two cylinders was adjusted to achieve delayed criticality. The delayed critical spacing between cylinders was 1.3 m. At this spacing for delayed criticality, the coupling reactivity exactly compensates for the subcriticality of the individual cylinders. Thus, the coupling reactivity is 85 {cents}, and using a delayed neutron fraction of 0.0066, the coupling reactivity in k units is 0.0056. This paper describes the prompt neutron decay constant measurements for this assembly.

• OSTI ID: 426526
• Report Number(s): CONF-961103--
• Journal Information: Transactions of the American Nuclear Society, Journal Name: Transactions of the American Nuclear Society Vol. 75; ISSN TANSAO; ISSN 0003-018X
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
CYLINDERS
DECAY AMPLITUDES
PROMPT NEUTRONS
ROD DROP METHOD
SUBCRITICAL ASSEMBLIES
URANIUM