Gas generation from water adsorbed onto pure plutonium dioxide powder
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0893-JJ07-03.1
Gas generation from water adsorbed onto pure plutonium dioxide powder D. Kirk Veirs, Nuclear Materials Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. ABSTRACT The production of H2 from α-particle radiolysis of water adsorbed onto plutonium dioxide powders has been studied. Plutonium dioxide powders with specific surface areas of 1.0 and 21 m2/g were used. The specific surface area strongly affects the amount of water adsorbed. At water coverage between 1 and 2 monolayers the H2 yield per unit of energy deposited into the water is found to be between 0.05 and 0.13 molecules of H2 per 100 eV adsorbed dose (5 to 12 nmols/s W). The H2 yield increases to between 0.29 and 0.58 molecules per 100 eV adsorbed dose (28 to 56 nmol/s W) when the number of adsorbed monolayers of water is between 10 and 20. The latter H2 yield is similar to that of liquid water of 0.45 molecules per 100 eV adsorbed dose.
INTRODUCTION Storage and transportation of plutonium dioxide powder is becoming more common due to the disassembly of weapons, reprocessing of nuclear fuel (not in US), and studies to support disposition of plutonium in MOX fuel. Plutonium dioxide powder is a thermodynamically stable ceramic at normal storage and transportation temperatures, and, as such, is an ideal storage form. However, plutonium dioxide powder adsorbs water from the atmosphere with the amount of water depending upon the specific surface area of the powder and the relative humidity.1 DOE’s 3013 Standard for fifty-year storage of plutonium materials requires a sealed container.2 The results of a recent study suggest the possibility of producing flammable or detonable gas mixtures from the radiolysis of sorbed water when plutonium dioxide is stored in a sealed container.3 Gamma and He ion radiolysis studies of water on surrogate oxides show a dramatic increase in the hydrogen G-value to between 5 and 150 molecules of H2 per 100 eV adsorbed dose as the water content decreases and the water coverage approaches a few monolayers.4 At a H2 G-value of 150, a 3013 container with 0.5wt% water would pressurize to the 699 psi maximum working pressure in less than two months. Such rapid pressurization due to H2 gas generation is not seen in practice. In this work, the formation of H2 under conditions that might reasonably be expected to exist within 3013 storage containers is examined. Well characterized pure plutonium dioxide powders were exposed to H2O(g) and sealed into instrumented containers scaled 1:1 and 1:500 to the 3013 storage containers. Gases in the headspace were monitored and the results are discussed below. EXPERIMENTAL DETAILS
Two plutonium dioxide powders were used, labeled PEOF1 and MISSTD-1. Both were prepared by nitric acid anion exchange followed by oxalate precipitation. The oxalate precipitate was dried and calcined to 600 °C to produce PuO2. PEOF1 was further calcined to 975 °C for four hours, allowed to cool overnight, then placed in an airtight container sealed with a Conflat™ flange until use t
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