Dispersed Ash Dropped in to Airstream or Exposed to Forced Draft Air

DOE-HDBK-3010-94

5.0 Surface Contamination; Contaminated, Combustible Solids

The ARFs from the two sets of experimental data ranged from 7E-5 to 1E-2. This

represents a very significant variation by any standard. Only two values of RF are available,

0.5 and 1.0. Given that a lower value of ARF has already been assigned for burning of

packaged or contained waste, which is defined to include significant compact piles of

combustible waste, the value assessed for uncontained waste should be more conservative.

The experimentally measured ARFs during the burning of contaminated cellulosic material

are bounded by a value of 1E-2 with a median value of 5E-4 and an average value of 2E-3.

The measured RFs are for the release from cellulosics contaminated by a fine, nonreactive

powder. Nonetheless, the conservative measured RF value of 1.0 and an ARF of 1E-2 are

assessed to be bounding. However, the potential extent of the conservatism needs to be

appreciated so that the value is not cavalierly applied to the majority of burning waste

circumstances inappropriately.

5.2.1.3

D is persed A sh D rop p ed in to A irstream or E xp osed to F orced D raft

A ir

Air drawn through the burning material or ash falling into a flowing airstream is a more rigorous

stress upon the relatively light powder formed by combustion (i.e., ash). The

situation is akin to that found in a forced draft incinerator or by dropping dispersed ash into

an active chimney. The experimental data shown in Table 5-2 for "air passing through

burning material" show a maximum experimental ARF of 3.8E-1 with no RF measured. The

maximum measured value is for the entrainment of fine, very loose UO2 particles dropped

into an accelerated airflow as fine combusting substrate lofts and disintegrates. This

condition of updraft suspension is not relevant or related to the pyrolysis driven airflow

phenomena of concern in the fire fuel zone examined in the previous data sets. It is also not

considered representative of most expected combustion phenomena of concern. The data set

examined in this subsection was intended to study maximized release phenomena. It is

discrete from the other data sets discussed in subsections 5.2.1.1 and 5.2.1.2 and is treated

as such.

The conditions generated in this experiment are not similar to the stress imposed by turbulent

air on a pile of ash unless the velocity of the air is greater that 10 m/s at the air/ash

interface, not in the general fire convective updraft. This condition is not foreseeable for

even large fuel fires at nonreactor nuclear facilities. Further, the extremely small quantities

of combustible material used in the experiments are atypical of combustible accumulations at

nonreactor nuclear facilities, which would further minimize the chance of such extreme

phenomena.

This data applies to genuinely extreme circumstances where very light combustible materials

(e.g., light, individual pieces of paper) are injected into a large flame updraft where

particles released by the destruction of the substrate can be immediately suspended in

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