Nuclear - Energy Policy Analysis: A Conceptual Framework - page 44

Immediately after a retention system is put to use, there will be small losses of radioactive mill
waste liquids through and around the dam (USNRC 1976; Humble Oil and Refining Co. 1971).
This will be seen as surface water seeping from the foot of the dam. The radiological significance
of this seepage will depend on the location of the pond. In arid regions, the seepage may evaporate
before leaving the site, leaving the radioactivity entrained and absorbed on soil. Should the tailings
pond be located next to a river, leakage might be discharged to the river. Discharge of pond seepage
into streams providing insufficient dilution and not under the control of the licensee would not be
acceptable. In such cases, a secondary dam may be built below the primary dam to catch seepage,
which may then be pumped back into the tailings ponds. It is sometimes stated that this seepage
will diminish over a period of about two years because of the sealing effect from accumulation of
finer particles between the sandstone grains (Humble Oil and Refining Co. 1971).
Radium-226 is a radionuclide of great concern because levels as high as thirty-two picocuries
per liter (pCi/1) have been found in seepage from current operating mills (USEPA 1975a). As-
suming a seepage rate of 300 liters per minute, the concentration of radium-226 seeping into a
streamflow of 140 liters per second (five cubic feet per second) is approximately one pCi/1. In the
applicant's environmental report for the Highland Uranium Mill, a seepage concentration of 350
pCi/1 of radium-226 was assumed (Humble Oil and Refining Co. 1971). There is no safe level of
radioactivity exposure for human beings (Gofman 1981).
Unless prevented by an impermeable layer of clay or a plastic liner, considerable quantities of
mill waste solution may seep downward into the soil beneath an impoundment area. Ordinarily
this is not expected to result in off-site releases of radioactive materials because the radionuclides
are strongly absorbed onto clay soil particles. They are removed from solution and considered
to be permanently retained on the mill site. However, this is a continuing problem requiring
monitoring programs to ensure there is no significant movement of contaminated liquids off-site
(USEPA 1975b). There are now some 140 million tons of uranium mill tailings scattered around
the western United States. Former Commissioner of the U.S. Nuclear Regulatory Commission
Victor Gilinsky considered them “the dominant contribution to radiation exposure” of the entire
nuclear fuel cycle (Wasserman and Solomon 1982).
For example, in July 1979, at Church Rock, New Mexico, about twenty miles from Gallup, a
temporary dam holding an evaporation pond of several hundred million gallons of liquid mill tail-
ings burst, sending 1,100 tons of radioactive mill wastes and 90 million gallons of contaminated
liquid pouring into a gulley that ran into the Rio Puerco, and carrying toxic tailings seventy miles
downstream into Arizona. It left residues of radioactive uranium, thorium, radium, and polonium,
as well as traces of metals such as cadmium, aluminum, magnesium, manganese, molybdenum,
nickel, selenium, sodium, vanadium, zinc, iron, and lead and high concentrations of sulfates along
its path. The spill degraded the western Rio Puerco as a water source and contaminated livestock in
the region (Wasserman and Solomon 1982). The dam had been built by United Nuclear Corporation
on unstable ground, its temporary permit had expired, and the U.S. Congress heard testimony to
the effect that the entire incident could have been avoided (U.S. Congress 1979).
Conversion
Conversion chemically purifies and converts U 3 O 8 to UF 6 , a volatile chemical form that is fed into
enrichment plants. Gaseous, solid, and liquid wastes are produced by these processes (USEPA
1973a, 77). Gaseous effluents in conversion areas are controlled using a wet scrubber system
combined with hydrogen fluoride recovery and a hydrogen burner. Dry bag filter systems are
used to control uranium dust in both processes. Dust is deposited in the porous fabric of woven