Metallurgical interactions - std301320000050

DOE-STD-3013-2000

fatigue loading on the storage containers and showed that the storage

containers meet the requirements of the ASME B&PV Code, Section VIII,

Division 2 [Flanders/ Krishnan 1999]. Confirmatory tests and analyses at the

beta-gamma transition have reinforced the Flanders/Krishnan conclusions

[documentation and peer review are underway].

3) Metallurgical interactions

Maximum plutonium-container interface temperatures up to approximately 189C

(see Table A-1) have been postulated for plutonium metal storage containers

under bounding conditions. The potential for forming low-melting eutectics has

been evaluated recently based on the available phase diagram data, diffusion

data, and effect of surface oxides [Williamson 1999]. This study concluded that

the storage of Pu metal and Pu-Ga alloys in stainless steel containers will not

lead to the formation of liquids, or result in direct release of plutonium by means

of diffusion mechanisms, as a result of storage at temperatures up to 250C. The

lowest melting liquid system identified in this study (about 400C) results from

the addition of small amounts of Ga (~1 wt%) to a two-phase Pu-Pu6Fe mixture.

The margin of about 150C between the melt temperature and the

conservatively assumed metal storage temperature of 250C is judged to be

adequately safe.

However, while directly applicable data are limited, this study could not

categorically exclude the possibility of reduction of inner storage can mechanical

strength due to Fe diffusion into Pu, if a 250C theoretical storage condition

extended for a long time period (10 years or more) and the plutonium metal

intimately contacts the container. However, these analyses were very

conservative in not taking credit for protective oxide films and the small surface

area of metal-metal contact that will occur in practice. In addition, problems of

this type have not been observed in numerous applications involving direct

plutonium-stainless steel interactions, including stainless steel clad nuclear fuels

[Louthan 1998]. Failure of inner welded cans by this mechanism therefore

appears to be highly unlikely.

3. The assurance of safe storage embodied in this Standard rests on the premise that

the outer storage container is capable of withstanding credible pressure,