silo 3 - U.S. Department of Energy

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2.0 ACCESS AND RETRIEVAL SEQUENCE
Access and Retrieval Strategy for the Silo 3 Project
Document No. 40430-PL-0002, Rev. 1
September 2003
Radon and radionuclide emissions to the environment, as well as to project work areas, are
monitored during all access and retrieval operations. Operations are planned and
implemented to maintain emissions and work area conditions within defined, acceptable
ranges. The following sections describe the planned Silo 3 access and retrieval sequence.
2.1 INITIAL SILO ACCESS
Before startup of pneumatic retrieval, the radon concentration in the silo headspace is
reduced. An exhaust air hose is connected to one or more existing vent/sounding ports on
the silo dome and conveys silo headspace air to the Process Vent System (PVS) dust
collectors. Makeup air (for air displaced by the PVS) is introduced from a high efficiency
particulate air (HEPA) filter into the silo by another hose, connected to other existing
venthounding ports on the silo dome. This arrangement provides a slightly negative
pressure in the silo and routes the exhaust air through the PVS dust collector and
HEPA/ultra low penetrating air (ULPA) filters. The air is then discharged through the
Exhaust Stack, where radon and particulate emissions are continuously monitored. Air
flow during this initial activity is closely monitored and metered to ensure that stack
emissions, and the resultant fence-line impacts, are acceptable, within established
limitations, and correspond to steady-state emission estimates. These estimates can be
found in the Environmental Control Plan (FEMP 2003~).
Weather conditions will be evaluated before the start of this initial radon release, to 'ensure
that atmospheric stability conditions are consistent with as low as reasonably achievable
(ALARA) principles. The silo dome connections will be designed, and radiological work
permits planned, to protect workers and control radon releases.
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2.2 PNEUMATIC RETRIEVAL
Silo 3 material is initially retrieved pneumatically from six of the existing silo dome man
ways (retrieval from the northernmost man way is not currently planed. The Vacuum
Wand Management System (VWMS) equipment will be placed on'the silo dome during
project construction. Installation of VWMS equipment on the man ways will be performed
after construction, following reduction of radon in the silo headspace, and in accordance
with radiological work permits.
Retrieval operations will be performed from man way to man way, with a limited amount
of material removed for each man way retrieval event, in order to achieve a near uniform
removal of material from top to bottom. A primary objective of the pneumatic retrieval is
the removal of sufficient material from behind the eastern wall of the silo before creating
the wall opening. Pneumatic retrieval will be performed until it is no longer effective in
material removal.
2.3 SILO WALL ACCESS
An opening will be cut in the silo wall'to enable mechanical retrieval. This opening will not
be made until operations determines that the pneumatic retrieval system is no longer
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