Redox Reactions - doe-std-1128-98

DOE-STD-1128-98

0.001M (0.24 g/L) of plutonium solution is on the order of 2 x 1014

eV per minute. Thus, the hydrogen evolution would be

approximately 3.8 x 1015 molecules per liter per day for a 1M

solution, or about 73 cm3 of hydrogen per year.

The G-values for H2 in solids irradiated by gamma rays are lower:

0.1 for ice (Johnson, 1970) and 0.01 for the hydrates of a large

number of sulfates (Huang 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

2-23