Redox Reactions - STD-1128-98master0049

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

and Johnson, 1964). Because the stability of PuSO4 . 4H20 was found to be

remarkably high (Cleveland, 1970), one of the sulfates may well serve as an

alternate interim waste form. Dole (1974) summarized the radiation chemistry of

polyethylene, quoting G-values for hydrogen as 5 molecules per 100 eV.

Destruction of plutonium hexafluoride as the solid phase amounts to about 1.5%

of the material per day (Weinstock and Malm, 1956). Cleveland (1970)

calculated the mean change in average oxidation number in 0.52M of perchloric

acid to be 0.018 moles per day, corresponding to a G-value of 3.2 equivalents per

100 eV. The formation of hydrogen peroxide from the radiolysis of water is

believed to be the mechanism for the reduction of plutonium (VI) ions. Lower

oxidation states are formed by the disproportionation of the plutonium (V)

species.

Pressurization of storage containers holding TRU wastes is a potential hazard for

both long and interim storage periods (Kazanjian et al., 1985). Sampling of TRU

waste drums shows that hydrogen is usually created (Roggenthem et al., 1989).

Waste drums with pinholes can "breathe" when the atmospheric pressure

changes, thereby introducing water vapor. Water vapor adsorbed on plutonium

compounds is radiolytically decomposed, thereby producing hydrogen. It may

be possible to add pressure relief valves and appropriate in-line filters to waste

drums. (See Section 2.7 for more information on storage and containment.)

2.5.2.2 Redox Reactions

In most chemical processes for purifying plutonium, it is essential to maintain its

valence state. The formation of hydrogen peroxide from the radiolysis of water

is believed to be the mechanism for the reduction of plutonium (VI) ions. Lower

oxidation states are formed by the disproportionation of the plutonium (V)

species. Cleveland (1970) calculated the mean change in average oxidation

number in 0.5-2M of perchloric acid to be 0.018 moles per day, corresponding to

a G-value of 3.2 equivalents per 100 eV.

In the radiolysis of solutions, the presence of other ionic species can accelerate or

inhibit the disproportionation of plutonium valence states. For example, the

presence of the chloride ion in plutonium (VI) solutions prevents reduction to

plutonium (IV). Reactions may reverse after long irradiation periods, in which

case a steady-state condition should ultimately be reached, resulting in a net

decomposition rate of zero. An excellent review of the radiation chemistry of

plutonium nitrate solutions may be found in Miner and Seed (1966). In dilute

solution (0.1M), GH2 is about 0.5 and GO2 increases to 1.45. Self-reduction of

plutonium hexafluoride as the solid phase amounts to about 1.5% of the material

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