Recent Zirconium Fire Experience at Hanford and the General Zirconium Fire Problem Page: 9 of 11
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Arg>.;c work(l) has also shown that the propogation of combustion is closely
related to the specific area factor. For a given specimen length and width,
the burning propogation rate has exhibited a nearly linear dependence on the
thickness in a log-log plot, the propogating rate increasing with decreasing
thickness. For a given thickness, zirconium ranks relatively high in propo-
g;ation ability.
Both ignition temperature and burning propogation data have shown that
ignition and fire destruction of massive zirconium components are extremely
improbable events under atmosphere and temperature conditions which could,
conceivably, obtain during reactor accident corAditions.
C. Water and water vapor are known to have a potent influence on the pyrophoric
behavior of zirconium, although the nature of this influence remains obscure.
In virtually every recorded instance of major fire, or explosion, action. in-
volving zirconium, water, in some quantity, is known to have been involved
at some stage of the accident history. Hydrogen evolution accompanies a
Zr-H20 reaction and undoubtedly E--in free or hydride form--participates in
fire or explosion events involving moist zirconium aggregates. There is some
evidence that zirconium powder--H20 mixtures containing roughly 5 to 15 percent
H20, by volume, yield the rrayc um energy release upon suitable activation in
shock sensitivity equipment.\') Small aggregates of zirconium fines covered
with water should be indefinitely stable. A large aggregate, however, altno~uh
completely immersed in water could present a serious fire, or explosion, h<.
Water seeping into such a mass could create a pyrophorically sensitive zon
within the core of the aggragate which, upon suitable activation, could IL;:.
with explosive violence. Piles of uranium machining wastes, immersed un:tr
twelve feet of water, have exhibited such a phenomenon. The properties of
zirconium do not disqualify zirconium for a similar performance.
D. Certain surface films generated by the reaction of zirconium with various
gases, such as: 02, C02, N2, H2 and H20, have exhibited a tendency to
pyrophoric behavior, i.e., sparking when scratched, but no fire prcpogation.(2)
While this phenomenon may be significant to the ignition characterstcs of
aggregates of particles- -possibly providing the trigger action--it would not
be expected to markedly change the fire situation with respect to massive
zirconium components.
E. Zr-2 wires (50 to 100 mil diameter) have demonstrated ignition and propo-
gation ability in steam-oxygen mixtures.(3) These tests were conducted
under high total pressures (900-2000 psi), and high oxygen partial pressures
(60-1000 psi). The Aerojet work suggests that, for Zr-2, an oxygen concen-
tration of the order of three volume percent in steam may be critical with
2. Herickes, J. A., et al, "Zirconium Hazards Research," TID-5749, June 1958.
3. Higgins, H. M., "The Reaction of Zr-2 With Wazcr a.;d Witn U n r r
Fuel Solutions," AGC-AE 0, Ma-r, Ya .I
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Zima, G. E. Recent Zirconium Fire Experience at Hanford and the General Zirconium Fire Problem, report, September 29, 1960; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc1035263/m1/9/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.