Titanium - hdbk11290024

DOE-HDBK-1129-99

2.5.2.b(3) Titanium

Titanium is a metallic element in group 4 of the Periodic Table. The symbol is Ti, the atomic

number is 22, the atomic weight is 47.90, and the melting point is 1660oC. It is a low-cost metal,

and can absorb and store tritium in a compact solid form at a tritium pressure of approximately 1E-

7 torr.

Titanium hydride, TiH2, in powder form, is a black metallic dust that is less prone to spontaneous

ignition in air than the parent metal. Finely divided titanium hydride is reported to ignite at 440oC

and its dust is an explosion hazard, which dissociates above 288oC. Titanium hydride is used in

powder metallurgy, hydrogen production, foamed metals, glass solder, and refractories, and as a

gas getter in the electronics industry. Titanium tritide in solid or massive form is stable in air for

extended periods of time. Titanium retains the decay helium up to a concentration of 0.3 He atom

per Ti atom. Both SRS [6] and Ontario Hydro [7-11] have selected titanium as their long-term

storage medium. The SRS titanium beds have an expected useful life of less than 10 years, while

the Ontario Hydro beds are expected to be in operation for well over 20 years. The Canadians are

not space-restricted, and therefore do not load their beds to the degree that SRS does.

Additionally, longer times to maximum helium retention ratio (0.3 He/Ti) can be achieved by

diluting the tritium concentration with deuterium or protium.

2.5.2.b(4) Zirconium

Zirconium is a metallic element of group 4 in the Periodic Table. The symbol for zirconium is Zr,

the atomic number is 40, and the atomic weight is 91.22. Zirconium is flammable as a powder and

melts at 1850oC. Zirconium is a hard, lustrous, grayish metal that is strong and ductile, and is used

Zirconium hydride ZrH2 is a flammable gray-black powder and is used in powder metallurgy,

nuclear moderators, and as a reducing agent. Finely divided zirconium hydride suspended in air

will ignite at 430oC. Zirconium hydride contains about twice as many hydrogen atoms per unit of

volume as liquid hydrogen. Massive zirconium hydride is stable in air for extended periods of time

at temperatures below 600oC.

Certain DOE radioactive zirconium fines (which are destined for disposal) are managed as D001

mixed ignitable wastes. These radioactive zirconium fines are pyrophoric under 40 CFR

261.21(a)(2) i.e., they are capable of causing fire through friction. If zirconium used for tritium

storage beds is destined for disposal (i.e., constitutes a waste), the RCRA hazardous waste

characteristic of ignitability must be analyzed. A broader discussion of RCRA hazardous waste is

contained in Section 3.1.3.

2.5.2.b(5) Societ Apparecchi Elettrici e Scientifici (SAES) Getters

During the past several years, investigations have been conducted concerning the use of SAES

Getters to remove tritium from tritium-contaminated gaseous waste streams. These investigations

have concentrated on getters that cracked the gases containing tritium and removed the resulting

free tritium from the gas stream. The primary advantage of these getter systems is that tritium is

not converted by the tritium removal system to the more radiotoxic tritiated water. Additionally, the

tritium can be recovered in gaseous form from the getter, purified, and reused.

The materials being tested include those manufactured in the form of pressed pellets that can be

used in low pressure drop packed bed reactors designed for the size required by the application