FERNALD K-65 SILOS - BACKGROUND
Fernald's silos 1 and 2 contain approximately 6,100 cubic
meters of high activity K-65 residues which contain approximately 4,700 Ci of
Ra-226 (about 2.5 times the radium present at the NFSS). This huge activity of
Ra-226 is decaying to radon gas which is present in the airspace below the
roofs of the silos at concentrations of 10 to 20 million pCi/L. (Note: the EPA
indoor air action level is 4 pCi/L.) The current inventory of radon in the
headspace is ~10 Ci in Silo 1 and ~13 Ci in Silo 2. Currently the radon release
from Silo 1 is ~38 Ci/yr and from Silo 2 is 50 Ci/yr. Due to the high energy
gamma emissions from the radon progeny, up to 1.7 MeV, the dose rate on the
surface of the silo domes is very high, in the 50 to 100 millirems per hour
range (i.e. ~10,000 times normal background radiation exposure, or a lifetime's
normal background in 100 hours).
In the 1950s an earthen berm was placed against the silos to
reduce the dose rate out of the sides of the silos, and to reduce the stress on
the concrete sides of the silos. Currently only the tops of the silos are
exposed.
During the early 1990s, bentonite clay was pumped into the
silos on top of the K-65 material in an attempt to reduce radon emanation out
of the waste into the headspace and ultimately out of the silos. The bentonite,
which soon dried out and cracked restoring a high radon emanation rate, now
presents additional difficulties to the efficient removal and stabilization of
the residues.
The initial Record of Decision at Fernald properly called for
maximizing the long-term stability of the waste by vitrifying the residues
prior to their disposal at the Nevada Test Site (NTS). However, the design
chosen for the pilot vitrification facility was an unproven, inexpensive pipe
dream rather than the proven method employed at West Valley, NY and Savannah
River, GA. The pilot plant was destroyed during early testing operations. The
vit project was quickly canceled. (See
IEER article
for details.)
Before publicly calling for the cementation fix, DOE floated a
Health Physics Society-backed "medical uses" proposal involving radium
extraction. This move added to skeptics doubts that DOE was committed from the
outset to providing the best available long-term environmental isolation of the
most dangerous of Fernald's waste materials. Given their large thorium
activity, the K-65 materials will remain extremely hazardous for 100s of
thousands of years.
