Critical mass variation of {sup 239}Pu with water dilution

Journal Article · Mon Jan 01 04:00:00 EST 1996 · Nuclear Technology

OSTI ID:201352

Pearlstein, S ^[1]

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1. Brookhaven National Lab., Upton, NY (United States). Dept. of Applied Technology

The critical mass of an unreflected solid sphere of {sup 239}Pu is {approximately} 10 kg. The increase in critical mass observed for small water dilutions of unreflected {sup 239}Pu spheres is paradoxical. Introducing small amounts of water uniformly throughout the sphere increases the spherical volume containing the same amount of {sup 239}Pu as the critical solid sphere. The increase in radius decreases the surface-to-volume ratio of the sphere, which has the effect to first order of decreasing the neutron leakage, which is proportional to the surface, relative to the fissions, which are proportional to the volume. The reduction in neutron leakage is expected to reduce the critical mass, but instead, the critical mass is observed to increase. It is discussed how changes in the fast neutron spectrum with corresponding changes in the nuclear parameters result in an increase in critical mass for small water dilutions.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 201352
• Journal Information: Nuclear Technology, Journal Name: Nuclear Technology Journal Issue: 1 Vol. 113; ISSN 0029-5450; ISSN NUTYBB
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
CRITICAL MASS
CRITICALITY
FAST NEUTRONS
NEUTRON REFLECTORS
NEUTRON SPECTRA
PLUTONIUM 239
REACTORS