Absorbed Water

DOE-HDBK-1129-99

flow rate and lifetime requirements. The basic strategy currently being implemented in prototype

systems is to crack the molecules on a hot getter and remove the non-tritiated reactive impurities

that interfere with the performance of the hydrogen gettering alloys. Following purification, the gas

is passed through a hydrogen gettering bed to remove the hydrogen isotopes from the gas stream.

2.5.2.b(6) LaNi5 Based Alloys

The use of lanthanum-nickel hydrides has been a continuing topic of interest, and as recently as

1997, promising results for hydrogen storage have been reported ("LaNi5 Intermetallic Hydride,"

extracted from State-of-the-Art Review of Hydrogen Storage in Reversible Metal Hydrides for

Military Fuel Cell Applications, Gary Sandrock, Ph.D., for the Department of the Navy, Office of

Naval Research, N00014-97-M-0001, July 24, 1997). Promising research results were also

reported in the literature in 1988 ("Hydrogen Isotope Sorption Properties of LaNi3Mn2 Alloy as a

Candidate for the Tritium Storage Material," T. Ide et al., Sumitomo Heavy Industries, Ltd. and H.

Yoshida et al., Japan Atomic Research Institute, published in Fusion Technology, September

1988). Earlier research at Mound, however, in the 1970s and early 1980s indicated that

lanthanum-nickel-based alloys were not appropriate for tritium service due, in part, to

disproportionation. When cycled, the LaNi5 had a tendency to separate to form the parent metals

(La or Ni) or different alloys. The disproportionation tended to change the pressure, concentration,

and temperature properties of the metal/alloy mix and increase the quantity of tritium bound in the

heel that was not easily recoverable.

Further investigations will be needed to better ascertain the capabilities of LaNi alloys for tritium

service.

2.5.2.c Absorbed Water

Molecular sieve material is used in tritium removal systems for removal of water contaminated with

tritium. Systems such as tritium removal systems, effluent recovery systems, and cleanup systems

remove tritium from a gas by cracking the tritium-containing components on a heated precious

metal catalyst. The free tritium then combines with oxygen in the gas stream to form tritiated

water. The gas stream is then cooled to room temperature, and the water contained in the gas

stream, including the tritiated water, is removed by a molecular sieve trap.

A molecular sieve will hold about 18 percent water by weight, and the sieve may be regenerated to

remove the water so it can be reused. The issue of flammability limits of these containers is

discussed in Section 3.1.2. Tritiated water absorbed on molecular sieve is not corrosive and may

be stored in this way for long periods without damage to the container wall.

Water contaminated with HTO is also stored on clay. The common method of solidification of

tritium-contaminated wastewater for disposal is to solidify the water on clay so that it can be

classified as solid waste. Clay will hold approximately 60 percent water by volume. Waste

disposal sites generally require the use of 100 percent more clay than required to solidify the

water, and, as a result, the water is generally limited to 30 percent of the volume of the clay for

waste solidification purposes. Water absorbed on clay is not corrosive and may be stored for long

periods without damage to the container wall.