silo 3 - U.S. Department of Energy

2. Radon Release Rate
35H19605
The radon release rate (pCi/min) is determined for the pneumatic retrieval system, and the mechanical
retrieval system. It is assumed that the building ventilation system discharges 7,200 cfm of air to the stack
with negligible radon concentration. The pneumatic retrieval system discharges 1,200 cfm to the stack
during Phase 1 only.
The mechanical retrieval system exhaust path discharges 5,500 cfm to the stack during both project
phases. This stream is made up of the silo vent exhaust (1,000 cfm), the retrieval bin hood (2,900 cfm),
the conveyor bottom (300 cfm), the conveyor top (300 cfm), and the packaging system (1000 cfm).
A. Silo Ventina Prior to Phase 1
The silo vent removes radon from the silo headspace at the initiation of the Silo 3 Project prior to
initiating the pneumatic retrieval of waste in Phase 1. The half-life of the radon isotopes *{'Rn and
"'Rn generated by %a and in the waste are short lived (4s and 55s, respectively) relative to
the diffusion rate through the waste to the headspace volume. Therefore, the concentrations of *"Rn
and ='Rn in the headspace are negligible. The measured headspace =Rn concentration is 300,000
pCi/L and the headspace volume is 5,600 ft3, yielding a headspace activity of 0.0475 Ci =Rn. If the
entire headspace were vented in one day, the release would be 48 mCi =Rn.
Assuming an equilibrium headspace activity (emanation from solids equals radon decay with no
leakage), the emanation rate equals activity times the decay constant. It is also assumed the vent
removes radon at the same rate it emanates from the stored solids.
Emanation rate = release rate = 0.0475 Ci =Rn x 0.693/5500 min
B. Pneumatic Retrieval - Phase 1
= 6.0 x lo6 DCi/min =Rn
1. The pneumatic retrieval system removes 8,100 Ibhr of silo material, which is based on 6 cyhr at
50 Ib/cf. It is assumed that approximately 35 percent of the radon generated in the solid matrix
material is free to diffuse from the solid into the waste pore space. Therefore, during retrieval
operations, it is assumed that 35 percent of the radon in equilibrium with its radlum parent is residing
in the solid matrix and is potentially released to the exhaust stream. Radon isotopic release rates for
algRn, ='Rn, and =Fin, respectively, are:
R (2'gRn) = 8,100 lbihr x 925 pCi/g x 454 gAb x hr/60 min x 0.35,
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R= 1;
R (220Rn) = 8,100 Ibhr x 367 pCVg x 454 ghb x hr/60 min x 0.35,
R = 7.87 x 10' DCilmin pORn = 4.1 CiEvr =Rq;
R (=Rn) = 8,100 Ibhr x 3870 pCVg x 454 gAb x hr/60 min x 0.35,
222
R = 8.30 x lo' pCimin =Pn = 43.5 CW Rn
The annual release assumes continuous operation for one year.
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