THE SAFE HANDLING OF ENRICHED URANIUM

1969 film, with transcript

Catalog description: Filmed primarily at the ERDA Y-12 Plant in Oak Ridge, the motion picture introduces new employees in nuclear production plants to the concept of nuclear fission and criticality , and explains the reasons for safety procedures that are observed in the handling of enriched uranium and other fissionable materials. The film will be understood by persons with or without a technical background. Its contents include: an animated sequence which explains the difference between U-238 and U-235, and the concepts of nuclear fission and criticality; a brief summary of the uses of enriched uranium; animated sequences explaining how criticality may be prevented by proper handling procedures; scenes of persons working with U-235 in various forms (gas, powder, metal, liquid) in several work areas; emergency procedures; and a few scenes of U-233 and plutonium work areas

This is film 88303 in our catalog.

Show transcript
00:11 Enriched uranium, one of man's most valuable resources.
00:30 This enriched uranium button weighs 5 kilograms, 11 pounds.
00:47 Its value, $55,000.
00:52 These buttons will be alloyed, cast, rolled, or machined to make the various forms and
00:58 shapes useful to industry, science and defense. Because enriched uranium is
01:05 worth almost ten times its weight in gold, the many forms of salvage and waste
01:11 products will be recycled again and again to recover the last salvageable
01:16 quantity of enriched uranium. Throughout these operations certain basic
01:23 principles of nuclear safety will be followed to prevent accidents caused by
01:28 the phenomenon called criticality.
01:45 Today most people find no strangeness in our concept that all matter is made up
01:51 of atoms. Natural uranium is a mixture of two kinds of metallic atoms, uranium-238
02:00 and uranium-235. Most of these atoms are relatively stable uranium-238 or more
02:08 simply U-238. Only one of every 140 natural uranium atoms is of the more
02:16 excitable U-235. Both metals look the same. In fact, they can't be chemically separated.
02:25 Now, if one of the tiny wandering particles that we call neutrons happens to collide with an atom
02:31 of U-238, it may simply bounce off or it may be captured or absorbed into the atom. If, on the
02:40 other hand the neutron happens to hit a u-235 atom it may split or fission the
02:46 atom into several fragments part of the fissioning atom turns into pure energy
02:52 most of it appearing as heat or in the form of powerful x-rays in this release
02:59 of energy atomic power is born the leftover pieces of the broken atom are
03:06 called fission products. They are intensely radioactive and are now entirely different
03:14 elements of lighter weight, no longer uranium of any kind. A very important part of the fission
03:22 process is that the breaking atom throws out two or three of its own neutrons, each of which may
03:28 in turn hit and fission still another atom of U-235. Thus we may obtain a
03:35 constantly increasing number of fissions, a self-sustaining chain reaction,
03:41 criticality. We can put criticality to work in a nuclear reactor. Excess
03:48 neutrons not required to maintain criticality may be directed at special
03:54 targets and if captured transform them into radioisotopes used in medicine,
04:01 agriculture, industry and many types of research.
04:14 Heat emitted during a chain reaction can be used to generate electricity to power
04:20 large cities, desalt the seas or power submarines.
04:30 There is another side to criticality.
04:41 Nuclear explosives have constructive applications such as digging canals and
04:47 and inland waterways, recovering valuable mineral deposits,
04:52 and creating new exotic elements.
04:55 The ability of the U-235 atom to fission
04:59 has opened a limitless future to mankind.
05:03 Like fire and electricity, this new tool
05:07 must be properly controlled.
05:10 Through the mining and milling stages, uranium can be handled very much like any other valuable metal,
05:16 Although slightly radioactive, it can be touched without the use of gloves.
05:21 Some operations, which involve extensive handling of uranium, however,
05:25 may require the use of gloves or respirators.
05:30 Following the milling operation, uranium is put through a processing step
05:34 which no other metal undergoes.
05:36 This process, known as gaseous diffusion,
05:41 separates the U-238 atoms from the fissionable U-235 atoms.
05:46 The uranium in the form of gaseous uranium hexafluoride is pumped through
05:51 specially constructed porous barriers. The end product is uranium hexafluoride
05:57 highly enriched in U-235. Later this gas will be converted to powder or to metal.
06:04 Once uranium has been enriched in U-235 it must be handled in a strictly
06:09 prescribed manner to prevent accidental criticality that can cause injury or
06:15 or death personnel must avoid assembling a critical mass that is the amount of you
06:21 to 35 necessary to sustain a chain reaction this amount will differ according to the shape
06:29 or geometry of the u-2 35 in addition to certain other factors when criticality occurs gamma
06:37 radiation and neutrons are emitted which can cause injuries to personnel ranging from flesh
06:44 burns to the damage of internal organs. Although such accidents are extremely
06:50 rare, they can occur if safety rules are not followed. These rules are derived
06:57 from experiments with uranium assemblies conducted in special criticality
07:01 laboratories.
07:14 Data obtained in experiments assist in determining the safety limits for handling or storing
07:21 certain enrichments, quantities or shapes of uranium.
07:44 Such information is used by nuclear safety engineers to make the practical decisions regarding the moving or storing of enriched uranium within a nuclear plant.
07:56 Although rules and procedures may vary slightly at different installations, certain basic principles of nuclear safety are always valid.
08:05 The first principle, awareness of the degree of enrichment, the percentage of U-235 contained
08:14 in any unit of uranium.
08:18 The higher the percentage of U-235 within any batch of uranium, the lower the quantity
08:24 of uranium that may be safely placed within a given space.
08:29 For instance, uranium enriched to only 2% U-235 would not reach the danger stage until it filled a drum.
08:39 On the other hand, uranium with a 50% enrichment of U-235 under optimum conditions could reach the critical stage with only two cups of material.
08:50 At a 90 percent enrichment, under optimum conditions, only one cup of U-235 would be
08:58 required for criticality.
09:02 The second principle for nuclear safety is the control of the quantity or mass of enriched
09:08 uranium within a given space.
09:11 This control is subject to such factors as the volume and shape of containers, the concentration
09:17 of U-235 in mixed materials and interaction. Since handling large quantities of U-235 increases
09:27 the risk of accidental criticality. Quantity can be controlled in some operations by the
09:33 use of small volume containers. But if certain operations require the movement or storage
09:41 of large quantities of U-235, criticality can be avoided by the use of special shapes.
09:50 In the thin container, the uranium is spread out. Neutrons are more likely to escape the
09:56 boundaries of the containers without coming into contact with U-235 atoms.
10:03 In the fat container, the U-235 atoms are massed, thereby increasing the chance that
10:09 neutrons within the mass will be trapped and set off a chain reaction. These unusual looking
10:17 containers are used for storage of various solutions of U-235. Their small diameter makes
10:24 them nuclear safe. These pipes contain many gallons of solutions rich in U-235, but their
10:32 shape prevents the U-235 from assembling a critical mass. When U-235 is mixed with other
10:42 materials, the concentration of U-235 becomes important in maintaining criticality control.
10:49 Very often U-235 in a mixture with other materials is potentially more dangerous than U-235 in pure
10:57 concentration. The reason is that some materials such as water or the various
11:03 forms of carbon tend to slow or moderate the speed of neutrons. When neutrons are
11:11 moving at slower speeds, they are more readily trapped by U-235 atoms, a
11:17 situation which can lead to criticality. If U-235 is mixed with the material
11:25 tends to moderate neutrons, there is usually an optimum concentration point
11:30 at which criticality is most likely to occur. While below or above this point,
11:36 criticality would be less likely to occur. Personnel handling enriched
11:43 uranium must always be aware of the possibility of interaction. Interaction
11:49 can occur when neutrons escaping from one batch of uranium cause fissions in a
11:55 neighboring match this can be avoided by allowing sufficient distance between
12:00 individual containers of uranium to allow neutrons to escape the birdcage
12:08 container is designed and constructed to provide sufficient spacing between
12:13 uranium masses but even the birdcage spacing system has its limitations
12:19 containers should never be stacked above the height limit designated for each
12:23 storage area. Proper distances between authorized storage areas also will
12:30 prevent interaction. Proper spacing on vehicles, elevators, and transport dollies
12:38 must be observed to prevent criticality caused by interaction. Another important
12:45 principle is the control of neutron reflection. When neutrons escape from a
12:51 fission atom. They tend to bounce about until their energy is spent and they are captured
12:58 by other atoms. Certain materials placed near a mass of U-235 tend to act as neutron reflectors
13:06 which bounce the neutrons back into the U-235 mass and cause more fissions. A wall, a ceiling,
13:14 a drum of water, or even persons can reflect neutrons.
13:20 When a reflecting material is present, less U-235 is required to cause criticality.
13:29 A final principle for criticality control is the use of neutron absorbers.
13:36 Neutron absorbers are materials which remove neutrons from circulation and prevent them
13:42 from causing further fissions.
13:45 Elements such as boron and cadmium are effective neutron absorbers and may
13:50 be used to prevent or to stop criticality.
13:55 Again, the nuclear safety principles.
13:59 Awareness of degree of enrichment.
14:02 Control of mass or quantity through the control of volume,
14:07 shape, concentration, and interaction.
14:10 control of neutron reflection, and use of neutron absorbers.
14:18 These metal buttons, highly enriched in U-235,
14:22 are about to begin a typical production cycle.
14:26 They are stored in properly spaced trays to prevent the assembly of a critical mass.
14:32 When enriched uranium is being moved within a building, it is transported over an approved route.
14:40 When U-235 is moved by truck, load limits
14:43 are strictly observed to prevent assembly of a critical mass.
14:49 If the U-235 is being transported from one building
14:52 to another within a plant, the driver goes directly to his destination without stopping or parking
14:59 en route.
15:01 The U-235 should never be stored at a dock,
15:04 but should be taken directly to an authorized holding area.
15:09 When enriched uranium metal is machined, special care is taken to prevent the loss of valuable chips
15:16 and shavings, and to prevent the assembly of a critical mass.
15:21 The chips remain in containers on a special rack at the workstation until they are collected
15:29 and emptied into a nuclear safe container half filled with the neutron absorber perchloroethylene.
15:43 Eventually, these chips will be moved to another location for cleaning and return
15:49 to the production cycle.
15:52 During the dimensional inspection of enriched uranium components, only one component at a time
15:58 is permitted on an inspection table.
16:01 The next component to be inspected waits its turn in an authorized holding area.
16:07 In some inspection areas where other types of metals share the inspection equipment with
16:11 enriched uranium, special provisions are required to prevent possible misidentification.
16:19 In the radiography room, safe loading procedure is used to prevent a critical mass from forming.
16:27 The new 235 components are always well separated.
16:57 In a typical packaging operation, U-235 components are wrapped in plastic, placed in a can which
17:11 then is sealed, and loaded into a foam glass shipping container approved for interstate
17:20 transport.
17:36 Throughout a production cycle, many types of U-235 waste products are generated.
17:44 These chips and shavings are cleaned and bracheted for reentry into the production system.
17:54 Mop water, filters, and combustibles all contain tiny, but nonetheless valuable quantities
18:04 of U-235.
18:07 Solutions from this and other liquid salvage operations are stored in nuclear safe containers.
18:15 Eventually these solutions will be fed into a central uranium recovery system consisting
18:21 of extraction columns.
18:24 After passing through the columns, the uranium is evaporated and converted to uranium trioxide,
18:31 to uranium tetrafluoride and reentry into a production cycle.
18:37 In all production and recovery areas, gamma radiation detection systems are installed
18:43 for the protection of personnel.
18:45 If the radiation level should rise because of an accidental criticality,
18:50 an alarm system is activated.
18:53 In an emergency, personnel would evacuate a building by well-marked routes
18:57 and regroup at designated assembly points.
19:03 If radiation contamination is suspected,
19:07 persons are monitored by health physicists.
19:11 Other post-accident aids for determining extent of radiation levels
19:15 include special materials inside the personnel identification badges
19:19 and dosimeters located in work areas.
19:23 In some installations, criticality control is made more complex because of the presence of
19:31 uranium-233, a uranium isotope produced in a nuclear reactor. U-233 requires stricter handling
19:46 procedures than U-235 because less U-233 is required for criticality, and because it is
19:55 often associated with highly radioactive products.
20:00 Some installations handle plutonium, also a nuclear reactor product.
20:07 Plutonium is more highly fissionable than either U-235 or U-233, and has a high alpha
20:14 radiation activity that requires special facilities
20:18 for handling.
20:20 The handling of fissionable materials such as U-235,
20:23 U-233, and the isotopes of plutonium
20:27 requires a constant alertness on the part of personnel
20:31 to prevent criticality accidents.
20:34 Workmen in the enriched uranium processing industry have established an enviable safety record
20:40 by adhering to established rules for nuclear safety.
20:44 As the need for nuclear power continues to grow,
20:48 and as national defense commitments continue,
20:52 more and more enriched uranium will be processed
20:55 in production plants.
20:58 It is the responsibility of every person employed in the processing and fabrication
21:03 of enriched uranium to prevent the waste of this valuable resource and to maintain the excellent nuclear
21:11 safety record.