Contaminated, Combustible Solids

DOE-HDBK-3010-94

5.0 Surface Contamination; Contaminated, Combustible Solids

5.2

C O N T A M I NA T E D , C O M B US T I B LE S O L I DS

There are a wide variety of contaminated, solid, combustible materials found in nuclear

facilities. These materials are generally trash, such as paper, rags, cardboard, plastic from

wrapping, sheeting, bags, containers, windows, tools, casings, and ion exchange resins.

There could also be contaminated structural material such as wood and wall board. The

nature of the contaminant also shows great variation, ranging from solid particles adhering to

the surfaces (resulting from wiping smearable contamination) to materials absorbed in the

surface or matrices of the substrate (e.g., dilute aqueous solutions that have evaporated,

solutions that have been absorbed in the material). Trash is generally held in a plastic bag in

a container that is sealed after filling. Other forms of contaminated solid combustibles (e.g.,

windows, gloves) are uncontained until retired from use. Because each combination of

substrate and contaminant may react differently to the various stresses imposed and suspend

materials on their surfaces or absorbed into their matrices by different mechanisms, different

ARFs are defined for different types of materials.

5.2.1

T h erm al S tres s

Contaminants on solid, combustible materials can be suspended by the destruction of the

substrate and vapor flow generated during the formation of pyrolyzates or smoldering

combustion and subsequently entrained in the overall fire convective currents for airborne

transport. Various factors may affect either the burning rate (such as the availability of

oxygen or the surface area of the combustible material exposed) or the entrainment (such as

whether air passes through a burning mass). For example, individual thin layers of cellulose

such as sheets of paper or tissue will burn rapidly and release the mineral content as ash.

Burning of solid materials is a heterogeneous process; volatile vapors are released and mix

with the air to form a flammable mixture. This action forms the commonly observed

diffusion flame. Strands of cellulose also burn by smoldering combustion, which produces

the glow observed in wood fires.

Particles that comprise the contaminant are released by the destruction of the substrate within

the burning mass and are contained within the waste mass, general inorganic remains, and,

for the period of combustion, an increasing depth of mineral ash. The vapors that are

generated below the released particles by pyrolyzation of the cellulose may carry the released

particle but must pass through the waste and ash mass before release into the atmosphere. It

is the total waste matrix form and mass and this flow internal to the waste matrix from

pyrolysis gases that are the controlling features in particulate releases for even large fires on

the industrial scale associated with nonreactor nuclear facilities. The material in the waste

matrix is not subject to the overall fire convective flow external to the waste. If the external

flow intrudes upon the fuel-rich zone of combustion to a significant extent, the flame is

displaced and less heat is radiated to the surface lessening the burning rate. If the intrusion

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