US 3432666 A
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March 11, 1969 c, NASH ETAL 3,432,666
CONTAINERS FOR TRANSPORTING RADIOACTIVE AND/OR FISSILE MATERIALS Filed March 12, 1965 United States Patent 10,719/ 64 US. Cl. 250-108 Int. Cl. G21f /00 7 Claims ABSTRACT OF THE DISCLOSURE A transport container for radioactive material comprising a casing which includes a radiation attenuating substance dispersed in a matrix including a moderator material, the substance also affording fire protection for the container. Fire protection is achieved by employing a hydrated salt of boron which absorbs heat as its water of crystallization is driven off through vent holes in a layer surrounding the casing.
This invention relates to containers for use in transporting radioactive and/ or fissile materials.
It has been suggested that an efficient container for transportaation of radioactive materials should withstand a drop test from thirty feet without damage sufficiently severe to cause a release of the contents and a fire test at 800 C. for thirty minutes without appreciable reduction of radiation shielding effect.
Containers so far designed have incorporated steel or lead for gamma attenuation, wood for neutron moderation and cadmium to absorb neutrons.
However, the known arrangement of wood and cadmium is no barrier to fast neutrons originating inside the container.
Additionally, wood gives rise to certain drawbacks in use. Thus, it is of variable density and water content, requires to be fabricated to fit into an outer canister and to receive the isotope vessel. Furthermore, wood is liable to split as it dries out and may give rise to wood acids which could corrode adjacent metals.
It is one object of the present invention to avoid these drawbacks.
According to the present invention a container for use in transporting a radioactive material comprising an inner vessel to receive the radioactive material and a casing surrounding the vessel comprising a neutron moderating substance and a neutron capturing substance uniformly distributed in a matrix of cast plastic material, said casing also affording fire protection to the vessel.
In this arrangement neutrons emitted from fissile material inside or outside the container will be sufliciently moderated by the matrix material for the probability of their capture to be very high.
An embodiment of the invention will now be described, by way only of example, with reference to the accompanying drawing which is a sectional elevation.
In the drawing is shown a transport container having an aluminium vessel 1 for carrying non-irradiated fissile material, with a screw cap or lid 2. The vessel 1 is enclosed in a casing 3 of a mixture of borax and epoxy resin in the weight ratio 1:1. The casing has a lid 4 of the same mixture. The casing is surrounded by a metal layer including a steel canister 5 having a lid 6 with suitably placed vent holes V, the lid 6 being retained in place on the canister 5 by a retaining band 7. The shuttering 8 is 3,432,666 Patented Mar. 11, 1969 provided to define the space in the matrix material for receiving the vessel 1 and the lid 4.
In using the container, the fissile material to be transported is deposited Within the vessel 1 and cap 2, lid 4 and lid 6 are placed in position and secured.
In this arrangement neutrons emitted from fissile material inside or outside the container will be sufiiciently moderated by the hydrogen contained in the borax and resin matrix for the probability of their capture by the boron in the borax present, to be very high.
Borax is used in the above example as a typical hydrated salt. Such salts act to introduce extra hydrogen into the casing as well as absorber atoms. They also serve as heat insulators insofar as they absorb heat in having their water of crystalisation driven off through ventholes V in the casing. Gamma shielding can also be added in the form of a heavy metal or such of its compounds, for example lead chromate, as may conveniently be added to the plastic. The final choice of loading material will depend, for a fissile material container, on the optimum combination of hydrogen and neutron absorber to give a minim-um casing thickness and hence minimum overall size. It is an advantage in utilising a plastic as casing as opposed to wood, in that it can be pumped, whilst liquid, into the canister to fill any cavity so as to surround the vessel and provide a casing of uniform hydrogen and radiation attenuating distribution.
The plastic afiords adequate fire resistance for the contents whilst the steel canister serves mainly as shuttering during the casing and is retained to provide additional impact and abrasion protection to the casing.
1. A container for use in transporting radioactive material comprising an inner vessel to receive radioactive material, a means for attenuating radiation and a casing around the vessel comprising a neutron moderating substance and a neutron capturing substance uniformly distributed in a matrix of cast plastic material, and a means, including vents, for venting from said casing water of crystallization derived from said neutron capturing substance of said matrix.
2. A container according to claim 1 wherein said means for attenuating radiation includes a radiation attenuating substance uniformly distributed in said matrix.
3. A container according to claim 2 wherein said radiation attenuating substance is a heavy metal.
4. A container for use in transporting a radioactive material according to claim 1 in which the neutron capturing substance comprises a hydrated salt.
5. A container for use in transporting a radioactive material according to claim 4 in which the hydrated salt is borax.
6. A container according to claim 3 in which the radiation attenuating substance is lead chromate.
7. A container for use in transporting a radioactive material according to claim 4 wherein the casing is mounted in a metal canister which affords impact and abrasion protection to the casing.
References Cited UNITED STATES PATENTS 3,106,535 10/1963 Blanco 250-108 3,114,838 12/1963 Pontet 250-108 X 3,114,839 12/1963 Peters 250-108 3,133,887 5/1964 Alliegro et al. 250-108 3,126,351 3/1964 Blair et al. 250-108 X 3,229,096 1/1966 Bonilla et al. 250-108 ARCHIE R. BORCHELT, Primary Examiner.
US. Cl. X.R. 250-106