Metal Targets

DOE-HDBK-3010-94

4.0

Solids; Nonmetallic or Composite Solids

at 400 oC. Under these conditions, it is assumed that all the noble gases and volatile

materials (if any) are released and the fraction of non-volatile materials suspended as

particulate materials due to thermal stress is as assessed in section 4.4.1. This results in an

ARF and RF of 6E-3 and 0.01.

4.3.1.3.2 M etal T argets. Production targets are normally clad in aluminum metal.

The cladding material is relatively soft and breaches do occur. For small breaches under

water storage conditions, the base metal near the breach is converted to oxide and hydride.

Eventually, substantial losses may occur.

If the cladding integrity is intact at elevated temperatures in air, the metal is not exposed to

the air and oxidation does not proceed until cladding failure. Uranium metal does undergo

phase changes at elevated temperatures with the attendant volume expansion but the cladding

is ductile. If the uranium metal oxidizes, the noble gases and volatile radionuclides in the

fraction oxidized are released as well as a fraction of the base material containing the non-

volatile radionuclides as defined in subsection 4.2.1.2.1.

4.3.1.3.3 M etal A lloy an d C erm et T argets. The experimental effort to define the

release of radionuclides during the heating of irradiated uranium-aluminum alloys and U3O8

particulate dispersed in aluminum are discussed in Woodley (June 1986, March 1987),

Taleyarkhan (January-March 1992) and Ellison et al. (1994).

The metal alloys used for targets melts at a relatively low temperature (~ 650 oC) and is

molten at cladding failure a few tens of degrees C higher (Ellison et al. 1994). At high heat

input rates, material changes proceed in three phases:

100 oC below the melting temperature of cladding - blistering of the target due

to the gases incorporated during manufacturing and volume expansion during

at slightly higher temperature - cladding cracking and molten fuel flows

through gaps in the cladding; and

for high-burnup metal - molten foam is extruded.

Taleyarkhan (January-March 1992) tabulated experimental release results from various

sources as a function of time and temperature. The lesser temperatures in this tabulation

(800 oC and 900 oC) are more in line with the maximum temperatures anticipated under

industrial fire conditions and the data for the higher temperatures (1000 oC and 1100 oC) are

not included. Under the worst response, close to 100% of the noble gases are released

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