Nuclear weapons programmes

Defence-related wastes tend to be simpler than those from commercial nuclear applications. Wastes derived from Pu production contain high levels of sodium, due, for example, to the need to neutralise the acidic liquor before it could be stored in the carbon steel tanks built in the early days of the US defence programme at Hanford and Savannah River. Generally, defence wastes do not contain the high concentrations of fission products found in commercial wastes, the exception being the calcined naval reactor wastes currently stored at the Idaho National Laboratory (INL) but des­tined for the Waste Isolation Pilot Plant (WIPP) in New Mexico, USA. Donald (2007) gave generic compositions for both commercial and defence wastes (Table 1.5), and although there are very large compositional ranges for the constituents, it does highlight the lower proportion of fission products but higher proportion of actinides present in defence waste.

In addition to the wastes generated from commercial energy supply and during the manufacture of warheads, there is also excess plutonium which has been declared surplus to requirements following the decision by the US and Russia to reduce their warhead stockpiles. Under the 1993 Non­Proliferation and Export Control Policy, the US declared 55 tons of pluto­nium surplus to national security needs. A similar quantity was also declared

Table 1.5 Generic compositions of typical radioactive wastes (mass%)

Constituent

Commercial waste

Defence waste

Na2O

0-39

0-16

Fe2O3

2-38

24-35

Cr2O3

0-2

0-1

NiO

0-4

0-3

Al2O3

0-83

5-9

MgO

0-36

0-1

MoO3

0-35

0-1

ZrO2

0-38

0-13

SO4

0-6

0-1

NO3

5-25

0

Fission product oxides

3-90

2-10

Actinide oxides

<1

2-23

Other constituents

17-27

Source: Donald (2007).

surplus by Russia. These quantities may be further increased following the 2010 US-Russia strategic arms reduction agreement. It is planned to utilise this where possible in MOX fuel.

Finally, weapons testing has left a legacy of contaminated sites worldwide. These include Semipalatinsk and West Kazakhstan (Kazakhstan), Novaya Zemlya (Russia), Lop Nor (China), Maralinga (Australia) and others in the Pacific islands, India, Pakistan and Korea. The first atmospheric tests were conducted at the Nevada test site (USA) in 1951. Following the Limited Test Ban Treaty of 1963, atmospheric testing ceased, and nearly 90 percent of the US underground weapons tests were detonated in Nevada. Congress imposed a moratorium on testing of nuclear weapons, and in 1992, under­ground testing ceased. A total of 907 underground nuclear detonations were conducted above, near and below the groundwater table in alluvial basins, in volcanic highlands, in shafts and tunnels of zeolitised volcanic rocks, and in tunnels mined in granitic rock. Underground testing at Nevada deposited an estimated 132 million curies of radioactivity below ground, decay cor­rected to 1992. These topics are considered in details in the last three chap­ters of this book.

An underground explosion produces a spherical cavity from combined vaporisation, melting and shock compression of the rock. As the detonation pressure subsides, the rocks above the cavity typically collapse (timeframe of seconds to days after the test) and the cavity is filled with rubble consist­ing of collapsed rock, and solidified rock melt (melt glass). The collapse void can propagate upward variable distances forming a chimney that may or may not extend to the surface forming a subsidence crater. The temperature and pressure history of an explosion and response of the surrounding rock control the distribution of radionuclides around the test. Radionuclides produced underground include tritium, fission products, actinides and acti­vation products. Refractory radionuclides are trapped primarily in the melt glass, and in cavity rubble and compressed rock around the cavity; volatile species circulate outward and condense in cracks and void spaces for dis­tances of 1-3 cavity radii from the test point (Pawloski et al., 2008). The extensive contamination of the land at such sites and the potential for spread via local hydrology and hydro-geological has led to extensive studies of such sites (e. g., Busygin et al., 1996; D’Agnese et al., 1997).

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