Oxides - Continued - std301320000035

DOE-STD-3013-2000

very much lower G values for liquid or adsorbed water radiolysis (the G value is

near one for liquid water radiolysis) [e.g., see Dautzenberg 1989; Dautzenberg

1990; and Kalashnikov, et al. 1988]. The cited publications conclusively show

that multiple mechanisms exist which should ensure that substantial pressures of

hydrogen and oxygen cannot accumulate in plutonium storage environments.

Additional recent data on gas pressurization in plutonium storage environments

comes from the MIS program, where headspace gas pressure and composition

have been measured for containers from the Plutonium Finishing Plant (PFP) at

Hanford [Mason et al. 1999]. These containers, which include impure oxides, had

been stored for up to 18 years. Common observations for those containers that

apparently remained gas-tight are that pressures were found to be near

atmospheric, significant hydrogen gas fractions were observed (up to about 50%

in one can), oxygen pressures were strongly depressed (or undetectable) and

small partial pressures of carbon dioxide and carbon monoxide sometimes were

observed.

Similarly, pressures have been monitored over as-received and calcined

plutonium-bearing oxides in seven surveillance capsules held at room

temperature and monitored for about two years [Mason et al. 1999]. These

capsules have exhibited little pressure change and, in some cases, an overall

pressure drop has been found. As for the PFP samples mentioned above,

elevated hydrogen and depressed oxygen partial pressures typically were found.

Additional information comes from practical experience in the United States and

United Kingdom weapons complexes over the past five decades. A survey of

plutonium storage failures has failed to identify a single instance of gas-induced

failure where plutonium oxide materials have been calcined and packaged in a

manner similar to that described by this Standard [Eller et al. 1999]. It is also

notable that no plutonium storage package failures have resulted to date at the

United Kingdom's Atomic Weapons Establishment since a good quality-control

regime for stabilizing and packaging in food-pack cans was instituted several

years ago for interim (10 year) storage [Freestone et al. 1998]. The AWE

procedure involves calcination at 400 C and an LOI criterion of 2 wt% [Freestone

1998].