Potential Hazards Relating to Pyrolysis of c-C{sub 4}F{sub 8} in Selected Gaseous Diffusion Plant Operations

Abstract

Boolean logic expressions are ollen derived in safety and reliability analysis. Since the values of the operands are rarely exact, accounting for uncertainty with the tightest justifiable bounds is important. Accurate determination of result bounds is difficult when the inputs have "constraints." One example of a constraint is that an uncertain variable that appears multiple times in a Boolean expression must always have the same value, although the value cannot be exactly specified. A solution for this "repeated variable" problem is demonstrated for two Boolean classes. The classes, termed iimctions with "unate" variables (including, but not limited to unate fictions), and "exclusive-or" finctions, frequently appear in Boolean equations for uncertain outcomes portrayed by logic trees (event trees and fault trees). * Sandia is a multiprograrn laboratory operated by Sandia Corporation a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000 ThE report has been reproduced from the best available copy. Reports are available to the publicfrom the followingsource.

Potential Hazards Relating to Pyrolysis of c-C{sub 4}F{sub 8}O, n-C{sub 4}F{sub 10}, and c-C{sub 4}F{sub 8} in Selected Gaseous Diffusion Plant Operations

“…Under conditions at which fluorocarbons can thermally degrade (above a few hundred degrees Celsius), potentially hazardous unsaturated fluorocarbon compounds may form, most notably perfluoroisobutylene (PFIB; also known as perfluoroisobutene, octafluoroisobutene, and octafluoroisobutylene, or by its chemical formula, i-C 4 F 8 or iso-C 4 F 8 ). This degradation has been experimentally observed for c-C 4 F 8 , but chemical kinetics studies described by Trowbridge (1999a) suggest that the actual operations examined are unlikely to produce serious concentrations of PFIB. Rather, the main toxic decomposition products are likely to be HF or COF 2 .…”

“…Three candidates are presently being considered: cycloperfluorobutane (also known as FC-c318 or by its chemical formula, c-C 4 F 8 ), normal perfluorobutane (also known as FC-3110, n-C 4 F 10 , or simply as C 4 F 10 ), and perfluorotetrahydrofuran (also known as f-THF or c-C 4 F 8 O). Two earlier reports documented investigations into the thermal and chemical stability of c-C 4 F 8 at conditions expected to apply during the most severe high-temperature operations at the Portsmouth and Paducah Gaseous Diffusion Plants (Trowbridge 1999a) and in cascade operations (Trowbridge 1999b). This report documents a similar examination of the two additional coolant candidates.…”

An Equilibrium-Based Model of Gas Reaction and Detonation

“…Pure c-C 4 F 8 , for example, is predicted to generate a constant-volume adiabatic equilibrium temperature of 1977 K simply by decomposition to C(s) and CF 4 . but, in fact, does not form these products at any significant rate even when heated to elevated temperatures (Trowbridge 1999b and references therein). At flame temperatures, however, formation of C(s) is sometimes observed.…”

Chemical Characterization and Thermal Stressing Studies of Perfluorohexane Fluids for Space-Based Applications

“…Trowbridge 18 conducted a literature survey of the decomposition of perfluorocyclobutane, perfluoroethylene and other polymeric perfluorocarbons such as PTFE. The presence of oxygen suppressed the formation of PFiB, but also led to the formation of other toxic compounds such as HF (hydrogen fluoride), CO (carbon monoxide), COF 2 (carbonyl fluoride), CF 4 (methane) and CO 2 (carbon dioxide).…”

“…Trowbridge 19 later conducted an analysis of the reaction kinetics for additional 4-carbon compounds, namely c- With regards to the residence time, there have been several studies also on this topic. Hauptschein, et al, in their study found that for short duration, "flow-like" exposure conditions, perfluoropropene exposure to high temperature resulted in no decomposition, but batch reactions did.…”