Method and apparatus for decontaminating structures

A method and apparatus for decontaminating structures which utilizes abrasive blasting in conjunction with a reverse air flow to remove contaminants from a structure. The apparatus comprises an abrasive blasting device for projecting abrasive material through a nozzle onto a structure at a high velocity. An enclosure is connected to the blasting device which surrounds the nozzle and forms a vacuum envelope around the nozzle and a portion of the structure being decontaminated. A vacuum apparatus is connected to the enclosure for providing a reverse air flow from the enclosure to a collection chamber in the vacuum. A high pressure pump/motor assembly delivers abrasion material at high pressure from a hopper to the blasting device. As contaminants are abraded from the structure, the reverse air flow provided to the enclosure causes the abrasive material and the material abraded from the structure to be collected in the collection chamber. A radiation detecting device which measures neutron activity is located in the collection chamber. The radiation detection device is electrically coupled to a decade meter which measures the rate of increase of neutron activity in the collection chamber. When the rate of increase of neutron activity exceeds a preselected threshold level, a poison injection device injects a poison into the chamber which decreases neutron activity and a warning signal is provided to the operator.

BACKGROUND OF THE INVENTION 
The present invention relates to a method and apparatus for decontaminating 
structures and, more particularly, to an apparatus which projects a 
non-hazardous abrasive onto the surface of a contaminated structure at a 
velocity sufficient to remove a layer of the base material from the 
structure and which immediately reclaims the abrasive material projected 
onto the structure and the base material removed from the structure. 
A major problem now exists in this country with respect to the reuse of 
sites which were once used to store hazardous materials. The costs 
associated with remediating these sites can be astronomical. Moreover, 
once such sites have been remediated, they still may not be suitable for 
other uses. The Comprehensive Environmental Response, Compensation and 
Liability Act (CERCLA) generally governs the cleanup of hazardous sites 
which have been ranked among the most dangerous sites in the country by 
the Environmental Protection Agency (EPA). These sites are placed on the 
national priorities list to ensure that they are among the first to be 
remediated. After a particular site has been listed, the EPA (usually in 
conjunction with the state where the site is located) determines the type 
of remediation to be used. In determining what type of remediation is to 
be used, the EPA looks at several different alternatives and selects the 
best one based on the consideration of nine criteria: (1) overall 
protection of human health and the environment; (2) compliance with or 
waiver of applicable or relevant and appropriate other environmental laws; 
(3) long-term permanence and effectiveness; (4) reduction of toxicity, 
mobility, or volume through treatment; (5) short-term effectiveness; (6) 
implementability; (7) cost; (8) acceptance of the proposed plan by the 
state; and (9) acceptance of the proposed plan by the affected community. 
Although cost is one of the nine criteria considered in selecting a 
remedial plan, cost usually does not play a major role in the selection 
and the importance of the other criteria is emphasized. Therefore, it is 
important to provide a means by which a site, or a particular aspect 
thereof, can be remediated which meets these criteria and which is cost 
effective. 
Until the present invention, there has been no suitable means for 
decontaminating structures, such as buildings, which were once used to 
store or treat hazardous materials. The present invention provides an 
apparatus which utilizes abrasive blasting effectuated by a nozzle 
encompassed in a vacuum envelope which allows a layer of the base material 
of a structure (e.g., a wall, ceiling or floor) to be removed and 
immediately reclaimed in the vacuum envelope. The abrasive material to be 
used is preferably non-hazardous and is reclaimed with the removed base 
material in the vacuum envelope. By immediately reclaiming the abrasive 
and the removed base material, the need for a secondary cleanup is 
eliminated or minimized. 
In accordance with the present invention, the abrasive material to be used 
is preferable dry ice. Dry ice is a non-hazardous substance, which results 
in reduction of the volume of the end product needed to be treated. Also, 
dry ice has the abrasive characteristics necessary to effectuate removal 
of a layer of the base material. Although dry ice has been used in other 
industries as an abrasive, its particular suitability for remediation, in 
conjunction with the concepts of the present invention, has not until now 
been proposed. 
It has been known in the industry to use devices which decontaminate 
structures (e.g., removal of lead-based paint) by utilizing pneumatically 
operated cutting needles encompassed within a stainless steel enclosure. 
The device is used in combination with a vacuum. The stainless steel 
enclosure is designed to prevent the release of dust, debris and airborne 
contamination into the environment. A shroud which is provided on the end 
of the device helps to direct the reverse airflow created by the vacuum so 
that debris removed from the structure is immediately collected. However, 
such a device is generally not suitable for the removal of particular 
types radioactive material, such as those characterized by neutron 
activity which may result in the collected material approaching critical 
mass. One of the primary objects of the present invention is to provide 
detection means in the vacuum which will warn of neutron activity 
indicating that the possibility of critical mass is approaching. 
Abrasive blasting has also been used in the industry for decontaminating 
structures. However, open abrasive blasting operations generate 
dispersions which may be harmful to the operator and others in the 
surrounding area. Containment structures have been used in conjunction 
with abrasive blasting. However, such structures require the operator to 
be located within the containment area while blasting the surface, which 
may produce adverse health consequences to the operator such a device is 
generally not suitable for decontaminating structures contaminated with 
high levels of particular types of radioactive material. 
It is also known in the industry to use super-heated water in combination 
with a spray vacuum to decontaminate surfaces. The super-heated water is 
in liquid state as it strikes the surface. The impact and temperature of 
the water cleans the surface and the vacuum collects the water and the 
material removed from the surface. The present invention proposes the 
removal of not only the contaminated material from a structure but also 
the removal of a layer of the base material of the structure itself. A 
layer of base material should be removed as well as the contaminant due to 
migration of the contaminant into the base material. The use of 
super-heated water does not result in removal of a layer of the base 
material and therefore, will not be suitable for removal of particular 
types of contaminants. 
Therefore, a need exists in the industry for a decontamination device which 
utilizes abrasive blasting and which is capable of removing hazardous 
contaminants, such as radioactive contaminants, from structures and 
immediately reclaiming the contaminants as well as the abrasive. 
SUMMARY OF THE INVENTION 
The present invention is particularly well suited for the removal of 
tightly adherent radioactive contamination, although it is not limited to 
the removal of radioactive contamination. In accordance with the present 
invention, a layer of the base material of a structure is removed by 
abrasive blasting and the abrasive material and the removed base material 
are immediately reclaimed by utilizing a vacuum envelope technique. The 
vacuum apparatus preferably contains a radiation detector for detecting 
when radiation levels have exceeded a certain level, at which time the 
operator ceases operation of the device. Certain types of radioactive 
isotopes, such as plutonium, are neutron emitters. Other types of 
radioactive materials emit alpha, beta and gamma particles. There has been 
a major problem in the industry with respect to the decontamination of 
structures which are contaminated with materials which emit neutrons. This 
is because removal of such materials may result in approaching a mass 
great enough to cause criticality. 
The present invention utilizes a radiation detector, such as a neutron 
detector, located in the vacuum chamber for measuring neutron activity. 
The neutron detector is connected to a decade meter which measures the 
rate of increase of radiation. The decade meter is connected to an alarm 
which notifies the operator that the material contained in the vacuum 
apparatus is approaching a mass great enough to cause criticality. The 
vacuum apparatus may also be equipped with a poison addition device which 
is automatically engaged if the decade meter threshold level is exceeded. 
Once the level is exceeded, the poison addition device automatically 
injects poison, such as a boron compound, into the collected end product, 
thereby reducing neutron activity. 
Accordingly, it is an object of the present invention to provide a method 
and apparatus for decontaminating structures which utilize abrasive 
blasting in combination with a vacuum apparatus. 
It is also an object of the present invention to provide a method and 
apparatus for removing radioactive material from structures where such 
radioactive material is a neutron emitter. 
It is yet another object of the present invention to provide a method and 
apparatus for decontaminating structures wherein the apparatus is equipped 
with a radiation detection apparatus and a means for warning an operator 
that the end product collected is approaching a mass great enough to cause 
criticality. 
It is yet another object of the present invention to provide a method and 
apparatus for decontaminating structures by removing a layer of the base 
material of the structure. 
It is yet another object of the present invention to provide a 
cost-effective method and apparatus for remediating hazardous sites. 
These and other objects of the present invention will become apparent from 
the specification, drawings and claims.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 illustrates a preferred embodiment of the blasting device of the 
present invention. A high pressure abrasion gun 1 is used to remove 
contaminated material from a structure. The abrasion gun 1 receives the 
abrasive, preferably dry ice, which is pumped into the gun at high 
pressure. The high pressure abrasion gun 1 is coupled to a transparent 
Plexiglas or plastic enclosure 2 which functions as the vacuum envelope. 
The dispersion nozzle of the gun 13 is contained within the vacuum 
envelope. The front 4 of enclosure 2 is equipped with a flexible rubber 
edge. The side edge of the front 4 of the enclosure 2 has air holes formed 
therein for facilitating the reverse air flow generated by the vacuum 
(item 8 in FIG. 2). The rubber edge of front 4 of the enclosure 2 provides 
a loose suction fit between the abrasion apparatus and the structure being 
decontaminated (not shown). A skirt 9 located around enclosure 2 prevents 
the end material (i.e., abrasive+layer of base material+contaminant) from 
exiting through the air holes. A vacuum hose 5 connected to enclosure 2 
pulls the end product (not shown) into the vacuum apparatus 8. 
As shown in FIG. 1b, a set of micro switches 3 are engaged when the 
abrasion device is placed flush against the structure. The decontamination 
apparatus will not operate unless all of the micro switches are engaged 
and trigger 15 is depressed. Although the micro switches 3 are not 
necessary, they comprise a fail-safe mechanism which prevents operation of 
the decontamination apparatus unless the front 4 of the enclosure 2 is 
flush against the structure being decontaminated. The balls of the micro 
switches allow smooth, rolling movement along the structure being 
decontaminated. FIG. 1c illustrates one embodiment of the dispersion 
nozzle 13 located within enclosure 4, as shown in FIG. 1b. Many different 
designs can be selected for the dispersion nozzle 13 to provide the 
desired projection and velocity of the abrasive onto the structure being 
decontaminated. 
FIG. 2 illustrates a schematic diagram of the hopper and vacuum device of 
the decontamination apparatus of the present invention. As the abrasive 
(not shown) is added to the hopper 7, a high-pressure pump/motor assembly 
6 causes the abrasive to be pumped to the blasting device. As material is 
removed from the structure being decontaminated, vacuum apparatus 8 
collects the abrasive and the material removed from the structure. 
Preferably, the hopper is automatically fed, but it may be manually fed as 
well. The pump/motor assembly 6 only operates when the micro switches 3 
are engaged and the trigger 15 is depressed. A radiation detector 16 
located within vacuum 8 measures radioactivity and the aggregate level of 
radiation within vacuum 8. The radiation detector 16 may be connected to a 
decade meter 18 which measures the rate of change neutron activity within 
the vacuum 8. The decade meter may be connected to a warning device 20 
which warns the operator that the end product in the vacuum may be 
approaching a mass great enough to cause criticality. Such a detection and 
warning system is extremely important when decontaminating a structure 
contaminated with neutron-emitting radioactive isotopes, such as 
plutonium. However, certain radioactive materials, such as gamma or beta 
emitters, do not emit neutrons and therefore, there is no danger of the 
collected end material approaching critical mass. The warning and 
detection system is only needed where the contaminant is a 
neutron-emitting radioactive isotope. 
Preferably, a poison addition device 22 is also provided in the vacuum 
chamber. The poison addition device 22 automatically injects a 
neutron-absorbing compound into the vacuum 8 to reduce neutron activity. 
The poison addition device is activated when neutron activity exceeds a 
preselected threshold level. A suitable boron compound may be used as the 
poison due to its relatively high neutron absorbing cross section. In 
accordance with a preferred embodiment, the detection device 16, the 
poison addition device 22, the decade meter 18, the warning device 20, the 
pump/motor assembly 6 and the micro switches 3 are all electrically 
coupled to a central control unit 25 which controls all of the automatic 
operations of the decontamination apparatus. FIG. 3 illustrates a 
schematic diagram of an alternative embodiment of the abrasive blasting 
device of the present invention. The enclosure 2 and the nozzle 13 can be 
of the type discussed above with respect to FIGS. 1a-1c. The blasting 
device of FIG. 3 is comprised of a support structure 12, motion control 
motors 10 and tracks 11 for the motion control motors. Once the blasting 
apparatus is placed against the structure to be decontaminated, the motion 
control motors 10, which can be electrically controlled by an operator or 
central control unit 25, move the enclosure 2 in the x and y directions 
along tracks 11. The abrasive blasting and end product collection are 
essentially the same as that provided by the abrasive blasting apparatus 
of FIGS. 1a-1c. 
Although the present invention has been described with respect to 
particular embodiments, the present invention is not intended to be 
limited to these embodiments. It will be apparent to those skilled in the 
art that the concepts of the present invention can be embodied in a 
variety of different forms which accomplish the goals of the present 
invention and which are consistent with the spirit and scope of the 
present invention.