water vapor, followed by a relatively long, much smaller trailing release.
Because several curies of HTO can be released in a few seconds, and several
tens of curies can be released in a few minutes, the speed of the " uff"portion
of the release should not be underestimated. The duration of the trailing
portion of the release should not be underestimated either. Depending on the
concentration gradients involved and/or the time frames involved in the plate-
out portion of the exposure, the trailing portion of the release can easily last
from several days to several months or even years.
As the trailing portion of the release asymptotically approaches zero, the
outgassing part of the release becomes too small to measure on a real-time
basis, and the tritium levels involved in any given release can only be
measured by surface contamination measurement techniques. Under such
circumstances, the situation reverts back to the circumstances described above
under the heading of " late-Out Expectations." With no additional influx of
tritium, tritium incorporated into all of the mono-molecular layers of water vapor
will eventually return to background levels, without human intervention,
regardless of the method or level of contamination.
Bulk Contamination Modeling . When an overpressure of tritium is added to
the system (i.e., the surface of an idealized material), Le Chatelier' Principle
indicates that the tritium levels in the mono-molecular layers of water will be
shifted to the right; that is,
2H2O + 2D2O + 2T2O v H2O + HDO + D2O + HTO + DTO + T2O .
Tritium is incorporated first into the loosely bound, outer layers, then into the
intermediate layers, and finally into the very tightly bound, near-surface layers.
As the tritium loading in the near-surface layers builds, the disassociation
processes that proceed normally as a result of the tritium decay make an
overpressure of tritium available in a mono-molecular form (i.e., as T). Relative
to the normal amounts of elemental hydrogen that can be expected to be
dissolved in the material, the availability of excess tritium in the mono-
molecular form represents a different type of perturbation on a system, and the