silo 3 - U.S. Department of Energy

, "I
4 ; .
c: ," ir f 5069
Description of Calculation:
E N 0 I N E E R I N GQ
Calculation Number: 40430-CA-0003
Page Nod of _18
This calculation determines the location and magnitude of dose consequences to a maximally exposed public
receptor from Silo 3 Exhaust Stack emissions, which consist of radioactive particulates and radon associated
with the Silo 3 remedial action operations. Dose rate data are also determined at specific air monitoring
locations. Silo 3, the process equipment, and the process building associated with the remedial action project
will be ventilated and the radon and uncaptured particulates will be discharged to the atmosphere through an
elevated stack system.
The Silo 3 material is retrieved by using two systems: pneumatic (Phase 1) and mechanical (Phase 2). The
Process Vent System (PVS) collects and treats the air streams from both retrieval systems. The pneumatic
retrieval system is operated first and continues to operate until it is no longer effective and until the silo wall
can be safely breached to enable mechanical retrieval. During the first phase, the Silo 3 waste is
pneumatically retrieved-by vacuuming the powdered .material and removing the air-entrained. waste .in a
collector, feed conveyor, and bags. The air discharged from the pneumatic retrieval collector is filtered and
discharged to the elevated stack. This post process filtration removes most of the particulate activity prior to
venting the process air through the Exhaust Stack. The concentrations of the residual radioactive particulates
and radon released to the environment are reduced by atmospheric dispersion occurring between the stack
release location and the exposure location.
After Phase 1 is complete, Phase 2 commences by cutling an access hole in the silo wall and the remaining
material is removed by a mechanical excavator. The material is transferred to a retrieval bin, conveyors, and
packaging system. In this phase, the suspended solids are filtered by the PVS and discharged to the Silo 3
Exhaust Stack.
In addition to the PVS air streams, the building Exhaust Air System draws from building "clean" rooms and
areas with a potential for contamination. The exhaust air is also directed to HEPA filters and discharged to
the Exhaust Stack.
The computer calculation of the dose rate (mrembear) from particulates and radon Is based on the activity
emitted by the pneumatic retrieval system, mechanical excavator area, and building ventilation. The
radioactive material released from the stack and the dose to potential human receptors depends on:
0
The radioactive particulate and radon-219/220/222 concentrations in the stack discharge,
The stack height and diameter,
0 The rate of exhaust air discharge (momentum release model) and its temperature (buoyant release
model),
0 Meteorological parameters, and
0 Potential receptor locations and exposure scenarios.
An EPA atmospheric dispersion code, CAP88-PC, was used to estlmate atmospheric dispersion of
radioactive particulates and to determine the dose at the location of maximum exposure. This computer code
is based on Gaussian dispersion of gases and airborne particulates from area or stack sources, and uses
site-specific meteorological data and source design considerations.
. .
000212