“Alternative Requirements ”
PART 2: MATERIAL AND PACKAGE TEST PROCEDURES 8.13. Introduction to test procedures
8.15. Material tests
8.15.1. Test for LSA-III material
This test is designed to provide assurance of the low solubility of the LSA-III material.
The test involves immersing a representative sample of the material for 7 days in water at ambient temperature, with a specified initial pH and conductivity (paragraph 703 of TS-R-1).
The free volume of the water remaining must be at least 10% of the volume of the solid test sample and the activity in the water must not exceed 0.1 A2 (paragraph 601 of TS-R-1).
8.15.2. Tests for special form radioactive material
There are four tests for special form radioactive material, each of which has to be followed by a leaching assessment or volumetric leakage test. The four tests comprise the impact test, the percussion test, the bending test and the thermal test. A separate specimen may be used for each test. The purpose of the tests is to provide assurance that the radioactive material will not be released under any but the most severe circumstances.
It should be noted that certain sealed capsules may be excepted from the impact, percussion and thermal tests provided they are subjected to similar tests from ISO 2919 [7]
(paragraph 709 of TS-R-1).
8.15.3. Impact test
8.15.3.1. Percussion test
The specimen must first be placed on a supported sheet of lead, which has an area larger than the specimen, and which has a specified hardness and maximum thickness. It is then struck by the flat face of a mild steel bar to cause an impact equivalent to that of a free drop of 1.4 kg through 1 m. The lower part of the bar must be 25 mm diameter and have 3 mm rounded edges. It must strike the specimen to cause maximum damage (paragraph 706 of TS-R-1).
8.15.3.2. Bending test
As might be expected this test is only applicable to long, slender sources (paragraph 707 of TS-R-1). The specimen is clamped horizontally so that half of its length protrudes from the clamp, in an orientation that will cause the maximum damage. The free end of the specimen is then subjected to the same impact as that specified in the percussion test.
8.15.3.3. Thermal test
The specimen is heated to 800oC for 10 minutes and then allowed to cool (paragraph 708 of TS-R-1).
8.15.3.4. Acceptance criteria, leaching and volumetric leakage methods
In addition to not breaking, shattering, or melting when subject to the above tests, a special form design must also meet certain leaching or leakage requirements following each of the tests. Generally, this means that the activity in the water after the leaching or leakage test must not exceed 2 kBq, although other criteria can apply to sealed sources (paragraph 603 of TS-R-1).
For indispersible solid material, the leaching assessment method must be used. For sealed capsules, either this or the volumetric leakage assessment may be performed.
The leaching assessment is made by immersing the specimen under conditions similar to that for LSA-III, then heating it to 50oC for 4 hours and determining the water activity. The specimen is kept for at least another 7 days in warm, humid air and the previous process repeated (paragraph 710 of TS-R-1).
The volumetric leakage test is similar, except that it does not require the initial 7-day soaking period (paragraph 711 of TS-R-1). Alternatively, ISO 9978 [8] may be used with leakage rates acceptable to the Competent Authority.
8.15.4. Leaching tests for LSA-III material and low dispersible radioactive material The tests to assure the low probability of dispersal in the event of an aircraft accident involve subjecting the LDM specimen to the enhanced thermal test (800oC for 1 hour) discussed later in 8.7.2., and the high speed (90 m/s) impact test discussed in 8.7.3.
(paragraph 712 of TS-R-1). A different specimen may be used in each test. The airborne release in gaseous and particulate forms must not exceed 100 A2 (paragraph 605 of TS-R-1).
After each test the specimen is subjected to the leaching test and the activity in the water must not exceed 100 A2.
8.16. Tests for normal conditions of transport 8.16.1. Acceptance criteria
There are certain acceptance criteria associated with satisfactorily meeting the test requirements.
8.16.1.1. Industrial Type 2, Industrial Type 3, and Type A packages
The criteria that must be met for the subject package designs following exposure to the applicable normal conditions of transport tests, are that the package design will prevent:
- Loss or dispersal of the radioactive contents; and
- Loss of shielding integrity that would result in more than a 20% increase in the radiation levels at any external surface of the package.
8.16.1.2. Type B and Type C packages
The criteria for a Type B and a Type C package design are similar to those above, but in this case, a small rate of release is allowed. Following exposure to the normal conditions of transport tests, the package design must:
- Restrict the loss of its radioactive contents to not more that 10-6 A2 per hour (paragraph 656(a) of TS-R-1); and
- Prevent loss of shielding integrity that would result in more than a 20% increase in the radiation level at any external surface of the package (paragraph 656(b) of TS-R-1).
The basis for the release rates, which were re-established during the Q-system deliberations for TS-R-1 are summarized below.
In the determination of the maximum allowable release rate for Type B packages under the conditions of normal transport in the 1973 Edition of the Regulations, the most adverse expected condition was judged to be represented by a worker spending 20% of his or her working time in an enclosed space in the conveyance of 50 m3 volume, with ten air changes per hour. The space in the vehicle was considered to contain a Type B package leaking at a rate of r (Bq/h), and it was conservatively assumed that the resulting airborne activity concentration was in equilibrium at all times.
On this basis, the annual intake of activity via inhalation Ia for a person working 2000 hours per year with an average breathing rate of 1.25 m3/h was evaluated. This intake was then equated with the historic maximum permissible quarterly dose for occupational exposure (30 mSv to whole body, gonads, and red bone marrow; 150 mSv to skin, thyroid, and bone; 80 mSV to other single organs). From the determination of A2 values, this corresponded to an intake of A2 × 10-6. This quantitatively established a value for r (i.e. the release rate limit) as:
r ≤ A2 × 10-6 per hour.
This assumes that all of the released material becomes airborne and can be inhaled.
This may be a gross overestimate for many materials. There is additional conservatism in the
radiation workers [9]. In addition, this level of conservatism was considered adequate to cover the unlikely situation of several leaking packages contained in the same vehicle.
In the 1985 Edition of the Regulations, the maximum allowable release rates for Type B packages under normal transport conditions were unchanged, although some of the parameters used in the above derivation were updated.
The dose criterion of 50 mSv used in the Q-system is such that, under the BSS, the system lies within the domain of potential exposures. In determining the allowed routine release limits for Type B packages it was necessary to consider the most recent dose limits for workers of 20 mSv per year, averaged over 5 years [9]. The earlier models assumed an extremely pessimistic exposure model of 2000 hours per year. Retaining this value, together with exposure within a room of 30 × 10 × 10 m3, with 4 air changes per hour, and an adult breathing rate of 1.25 m3/h, the permitted release rate, r, for an effective dose of 20 mSv was calculated. The assumed room size is larger than that assumed for an acute release under the Q-system. However, the assumed exposure time is very pessimistic. Exposure for 200 hours in a much more confined space of 300 m3 would lead to exactly the same predicted effective dose. For incidental exposure out of doors for persons near a leaking Type B package the maximum inhalation dose would be significantly lower.
The limit of 10–6 A2 per hour from a Type B package under normal conditions of transport (see paragraph 656(a) of TS-R-1) is thus justified, and was retained at the value used in early Editions of the Regulations. This value, as summarized above, was shown to be conservative. Experience has shown that it is rare for packages in routine transport to leak at rates anywhere near the permitted limit. Indeed, such leakage for packages carrying liquids would lead to very severe surface contamination in the vicinity of the seals and would be readily obvious from any radiological surveys during transit or on receipt by the consignee.
8.16.2. Water spray test
This test (paragraph 721 of TS-R-1) is intended for packages in which internal package space to reduce dose rates is provided by fibreboard components. It must be conducted using the same sample before each of other normal conditions of transport tests (paragraph 719 of TS-R-1): the free drop test, the stacking test, and the penetration test.
The water spray test (Figure 8.14.) simulates rainfall at a rate of approximately 50-mm per hour and is applied for at least one hour. The specimen is left to allow water to soak in to the maximum extent before the next test is carried out. This is normally two hours when all faces of the packages are soaked simultaneously. No soak time is required when all faces are soaked sequentially (paragraph 720 of TS-R-1).
If it is clear from the nature of the construction materials that the package is not vulnerable to this test, then the test may be omitted.
FIG. 8.14. Water spray test.
8.16.3. Free drop tests
These tests (paragraph 722 of TS-R-1) are designed to produce the kind of damage that is likely to be sustained by some packages during normal handling from minor drops and shocks.
In this test the specimen has to be dropped onto a flat, unyielding target. The height of the drop is graded according to the package mass as follows:
package mass < 5000 kg = 1.2 m 5000 kg ≤ package mass < 10000 kg = 0.9 m 10000 kg ≤ package mass < 15000 kg = 0.6 m
15000 kg ≤ package mass = 0.3 m
The package must be dropped in such a way that it will suffer the maximum damage. If there is any doubt, then the package will need to be dropped on all suspect features, including lids, closures and corners.
The free drop test, in the case of small packages where a 1.2 m drop height applies, is intended to simulate the kind of impact that would be suffered by a package falling from a vehicle tailgate or from a stacker truck. In many cases, packages would be expected to continue their journey after such minor mishaps.
Since heavier packages are less likely to be subjected to such large drops, (at least without undergoing close examination afterward), the drop height is scaled down with increased package weight.
free drop onto each corner from a height of 0.3 m. In the same manner, cylindrical fibreboard packages not exceeding a mass of 100 kg must be subjected to a free drop onto each of the quarters of each rim from the same height of 0.3 m. These tests are intended to demonstrate the capability of such packages to resist the general rough handling to which they are particularly vulnerable.
8.16.4. Stacking test
In the stacking test (paragraph 723 of TS-R-1), the specimen is required to withstand for a period of 24 hours whichever is the greater of:
- The equivalent of 5 times the mass of the actual package; or
- The equivalent of thirteen kPa multiplied by the vertically projected area of the package.
This test (Figure 8.15) is intended to ensure that the effectiveness of containment and shielding is maintained when the package is submitted to the kind of damage that is likely to be sustained by having other packages stacked on top. The test is not required for packages whose shape effectively precludes stacking.
FIG. 8.15. Package stacking test.
8.16.5. Penetration test
A 6 kg metal bar with a 32 mm diameter having a hemispherical end is required to be dropped onto the package from a height of 1 m (paragraph 724 of TS-R-1). The direction and point of impact must be chosen to produce maximum potential damage to the containment system, and the test item must be placed on a rigid, flat horizontal surface.
This test (Figure 8.16) is intended to demonstrate the capability of the package to withstand the kind of puncture damage, which may arise in normal transport, from such causes as sharp objects falling on the package as well as from loading hooks.
FIG. 8.16. Penetration test for normal conditions of transport.
8.16.6. Additional tests for Type A packages containing liquids or gases
The tests described so far are relevant to packages with solid contents (including solid in powder form). They were based originally on the hypothesis that only a small fraction of the contents is likely to be released during a typical accident. Appendix I of TS-G-1.1 quotes the likely range of the release fraction over a range of severe accidents (but short of a major accident) to be 0.1% of the contents.
In the case of liquids and gases, the possible release fraction is clearly higher for a given accident severity level. Since it is inconvenient to have A1 and A2 values dependent on the physical form of the material, the approach adopted has been to require additional tests for packages designed for liquid or gaseous contents. Packages designed for such contents are thus required to undergo additional testing (using separate specimens from those of the earlier tests). These involve a free drop test from a height of 9 m and a penetration test from a height of 1.7 m. Type A packages designed for tritium or noble gases are excepted from these more stringent tests.
8.17. Tests for accident conditions of transport 8.17.1. Overview and basis
unambiguous, quantifiable input to these calculations. Recognition of the statistical nature of accidents is now implicit in the requirements. A major aim of the package tests is international acceptability, uniformity, and repeatability. The tests are designed so that the conditions can be readily reproduced in any country.
The accident conditions of transport tests consist of sequences of mechanical tests, a thermal test, and a submersion test.
The purpose of the mechanical tests and the subsequent thermal test is to impose on the package damage equivalent to that which would be observed if the package were involved in a severe accident. The order and type of tests are considered to correspond to the sequence of damage to the packaging in a real transport accident, i.e. mechanical impacts followed by thermal exposure. The test sequences also ensure mechanical damage to the package prior to the imposition of the thermal test. In this manner, the package is most liable to sustain maximum thermal damage.
The mechanical effects of an accident can be grouped into three categories: impact, puncture, and crush loads. Although the original figures for the test requirements were not derived directly from accident analyses at that time, subsequent risk and accident analyses have demonstrated that they represent a very severe transport accident.
The combination of a 9 m drop height, an unyielding target and the most damaging attitude (paragraph 727(a) of TS-R-1) produce a condition in which most of the drop energy is absorbed in the structure of the packaging. In real transport accidents, targets such as soil or vehicles yield, absorbing part of the impact energy and only high velocity impacts may create damage which approaches that equivalent to the test.
Thin walled package designs or designs with sandwich walls could be sensitive to puncture loads (paragraph 727(b) of TS-R-1) with respect to loss of containment integrity, loss of thermal insulation or damage to the confinement system. Even thick walled designs may have weak points such as closures of drain holes, or valves. Puncture loads could be expected in accidents, as impact surfaces are frequently not flat. In order to provide safety against these loads, the 1 m drop test onto a rigid bar was introduced. Again, the drop height and punch geometry parameters were more the result of engineering judgement than deductions from accident analyses.
The crush test (paragraph 727(c) of TS-R-1) applies specifically to lightweight packages with high potential hazards.
The thermal test (paragraph 728 of TS-R-1) provides an envelope of environments that encompasses most transport-related accidents involving fires. The Regulations specify a test condition based on a liquid hydrocarbon-air fire with a duration of 30 minutes. Other parameters relating to fire geometry and heat transfer characteristics are specified in order to define the heat input to the package.
Because of a transport accident near or on a river, lake, or sea, a package could be subjected to an external pressure from submersion under water. To simulate the equivalent damage from this low probability event, the Regulations require that a package be able to withstand external pressure resulting from submersion at reasonable depths. Engineering estimates indicated that water depth near most bridges, roadways or harbours would be less than 15 m (paragraph 729 of TS-R-1). Consequently, this was selected as the immersion test depth for packages. While immersion at depths greater than 15 m is possible, this value was
selected to envelop the equivalent damage from most transport accidents. In addition, the potential consequences of a significant release would be greatest near a coast or in a shallow body of water. The eight-hour period is sufficiently long to allow the package to come to a steady state from rate dependent effects of immersion, such as flooding of exterior compartments.
It should be noted that an enhanced water immersion test to a depth of 200 m is necessary for packages containing radioactivity in excess of 105 A2 (paragraph 730 of TS-R-1), with separate acceptance criteria as discussed in section 8.18 of this chapter.
8.17.2. Pass criteria
In order for a Type B package to pass the accident conditions of transport test series, it must (paragraph 669(b) of TS-R-1):
- Restrict the accumulated loss of its radioactive contents, in a period of one week following the test procedure, to not more than A2 (or 10 A2 in the case of 85Kr); and - Not allow the radiation level at 1 m from the package surface to exceed 10 mSv/h.
A discussion of the basis for the release criteria follows. Accidents of the severity simulated in the accident conditions of transport tests specified in the Regulations are unlikely to occur in a confined indoor space. Or, if they did occur indoors, the resulting conditions would be such as to necessitate immediate evacuation of all persons in the vicinity [10].
Hence, the exposure scenario of interest in this context is that of an accident occurring out of doors. The maximum allowable release in a period of one week from a Type B package is A2, or 10 A2 for 85Kr, (see paragraph 656(b)(ii)(ii) of TS-R-1). In this situation, the radiological implications may be expressed as an equivalent dose limit by considering the exposure to a person remaining continuously downwind of the damaged package throughout the period of the release [11].
In practice, it is unlikely that any accidental release would persist for the full period of one week. In most situations emergency services personnel would attend the scene of an accident and take effective remedial actions to limit the release of activity within a period of a few hours. On this basis the maximum effective dose via inhalation to persons exposed in the range 50-200 m downwind from a damaged Type B package under average weather conditions is 1-10 mSv. This may increase by a factor of about 5 under generally less probable and persistent stable meteorological conditions [12]. Local containment and atmospheric turbulence effects close to the source of activity, plus possible plume rise effects if a fire were involved, will tend to minimize the spatial variation of doses beyond a few tens of metres from the source towards the lower end of the dose ranges cited above. Disregarding potential doses to persons within a few tens of metres of the source is considered justified by:
In practice, it is unlikely that any accidental release would persist for the full period of one week. In most situations emergency services personnel would attend the scene of an accident and take effective remedial actions to limit the release of activity within a period of a few hours. On this basis the maximum effective dose via inhalation to persons exposed in the range 50-200 m downwind from a damaged Type B package under average weather conditions is 1-10 mSv. This may increase by a factor of about 5 under generally less probable and persistent stable meteorological conditions [12]. Local containment and atmospheric turbulence effects close to the source of activity, plus possible plume rise effects if a fire were involved, will tend to minimize the spatial variation of doses beyond a few tens of metres from the source towards the lower end of the dose ranges cited above. Disregarding potential doses to persons within a few tens of metres of the source is considered justified by: