EP1460641B1 - Radiation shielding device - Google Patents

Abstract

At least one screening component comprises a material containing bound water.

Description

The invention relates generally to a radiation shielding arrangement and to a radiation shielding arrangement for shielding neutron radiation and gamma radiation from particle accelerators or storage rings, in particular for synchrotron radiation sources in particular.

When particles are accelerated, biologically harmful radiation, in particular gamma radiation, is produced. high-energy photon radiation or electromagnetic radiation. To shield gamma radiation, concrete has typically been used.

However, in recent decades, the maximum possible energy and intensity of the particles has increased in particle accelerators, particularly those that are near-surface. These include synchrotron systems for generating synchrotron radiation, the new Free Electron Laser (FEL) TESLA at DESY in Hamburg and new accelerator systems at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. For future accelerators, especially synchrotrons, particle energies in the range of several hundred GeV or even more than 1 TeV are to be expected.

In such high-energy accelerators, however, not only high-energy photon radiation is produced, but also it In particular, fast neutrons are also produced. The latter can even occur at particle energies in the MeV range and are biologically particularly effective, ie harmful. For example, in the above-described synchrotrons with particle energies of several 100 MeV or greater than 1 TeV, a significant number of fast neutrons with energies in the range of 100 MeV are generated. On the other hand, concrete is not suitable for shielding fast neutrons.

Therefore, especially for such accelerators and storage rings, but also for target devices and experimental and analytical devices, there is a need for effective radiation shields, which also effectively shield fast neutrons, especially in the MeV or even GeV range, which compared to electromagnetic radiation and thermalized or at least relatively slow neutrons in the range of a few electron volts (eV) represents a completely new requirement. Especially the combination of an effective shielding against electromagnetic radiation and at the same time against fast neutrons proves to be difficult in practice.

Another problem results from the activation, in particular by the fast neutrons, which leads in part to long-lived radionuclides. This makes the degradation and disposal of the shielding material highly problematic. Also in this regard, there is a need for an advantageous alternative to concrete.

Furthermore, the above development towards higher energies is naturally associated with a substantial increase in equipment. For example, HERA has a scope of 6.3 km, so that cost savings are of particular interest.

The EP 0 585 184 A1 relates to a building material for shielding electromagnetic radiation containing, for example Portland cement or gypsum. However, the gypsum only serves as a building material and has no radiation-shielding function. Furthermore, the manufactured plate is provided as a shield against electrosmog and not suitable for high-energy gamma radiation and / or fast neutrons.

The JP 11202090 describes a neutron shielding body with combustion ash. The gypsum is only used as a binder and not as a shielding material.

The U.S. Patent 3,705,101 describes a neutron absorber with gypsum as a hydrogen source for moderating neutrons. The material is intended for a container for transporting nuclear fuel and does not seem to be suitable for shielding particle accelerators.

The RU 19950119981 describes a radiation shield in which gypsum wastes are used. A plate only 150 mm thick is described for the shielding of beta and gamma radiation. This does not appear to be suitable for shielding neutrons from accelerator systems.

The DE 36 07 190 A1 relates to a gypsum radiation protection plate. However, this is based on a conventional drywall of only 12.5 mm thickness, wherein the gypsum barium is added as an absorber for X-rays.

Therefore, the plate is neither suitable for shielding gamma radiation nor neutrons, in particular not for particle accelerators and the energies occurring. Furthermore, the plate is also not suitable for the absorption or moderation of high-energy neutrons.

The GB 1 200 926 relates to radiation shielding for gamma rays and neutrons for which dysprosium and carbon are used as moderators and gadolinium as absorber after the thermalization of the neutrons. This material is only designed to shield spacecraft and rockets. Gypsum is not mentioned as a hydrogen supplier for moderating fast neutrons nor is it suitable for shielding high-energy accelerators.

The WO 96/36972 relates to a method for producing shielding elements. The shielding elements are apparently intended for immersion in a sinking basin. For this purpose, an electrolytic coating with cadmium of a thickness of only up to 300 μ is proposed. Thus, these shielding elements are neither intended nor suitable for shielding particle accelerators.

The U.S. Patent 3,995,163 describes a device for neutron therapy in which neutrons with the characteristic energy up to 14 MeV are generated during tritium decay. Thus, the neutron energies are orders of magnitude lower than at High-energy accelerators. Further, no gypsum is used, but metals such as iron, nickel or copper are used to decelerate the neutrons. Again, this does not seem to be suitable for high energy particle accelerators or storage rings.

Therefore, it is an object of the present invention to provide a radiation shielding arrangement for shielding neutron radiation and gamma radiation from particle accelerators or storage rings which effectively shields both gamma radiation and fast neutrons and is cost-effective to produce on a large scale.

Yet another object of the invention is to provide a radiation shielding arrangement for shielding neutron radiation and gamma radiation from particle accelerators or storage rings which has low activation even at high gamma and neutron energies.

Another object is to provide a radiation shielding arrangement for shielding neutron radiation and gamma radiation from particle accelerators or storage rings which avoids or at least mitigates the disadvantages of the prior art.

The object of the invention is achieved in a surprisingly simple way already by the subject matter of the independent claims. Advantageous developments are the subject of the dependent claims.

Advantageously, the radiation shielding arrangement according to the invention comprises a shielding element of hydrous material, e.g. with chemically bound water, especially water of crystallization. Preferably, the water content of the material is at least 5, 10 or 20 percent by weight. The hydrogen nuclei contained therein, or protons, almost perfectly neutralize neutrons due to the almost identical mass and the associated maximum momentum transfer.

Preferably, the shielding element is at least 75 weight percent, at least 90 weight percent or im essentially entirely of plaster. The use of gypsum, in particular a gypsum wall consisting essentially of set or hardened gypsum, chemically CaSO ₄ .2H ₂ O, has proven to be particularly suitable since the calcium absorbs gamma radiation relatively effectively due to its nuclear charge of 20. The bound water of crystallization, about 20% by weight relative to the total weight of the gypsum, in turn provides the protons.

In contrast to normal concrete, which in addition to smaller amounts of calcium, aluminum, iron or considerably more expensive barium in heavy concrete, contains as the main constituent of silicon with the atomic number 14, calcium shields even better with the atomic number 20 gamma radiation. This at least compensates for the density difference between gypsum (2.1 g / cm ³ ) and normal concrete (2 to 2.8 g / cm ³ ). This gypsum is advantageously lighter than concrete with the same screening effect for gamma radiation.

The thickness of the shielding element is particularly related to the radiation spectra of a high energy particle accelerator and / or high energy particle storage ring for electrons, positrons or ions, e.g. a synchrotron, especially adapted for particle energies of greater than 10 GeV or greater than 30 GeV.

With respect to the shielding of neutrons, it is further advantageous to provide a neutron absorber layer of a material which absorbs the moderated neutrons. Boron, boron-paraffin, cadmium and / or gadolinium have proved particularly suitable for this purpose.

A multilayer arrangement, in particular the attachment of a separate neutron absorber layer on the plaster wall is particularly advantageous in this regard, since the stability of the gypsum is maintained. Preferably, therefore, in this embodiment no boron or other neutron absorbing material has to be mixed into the gypsum.

Alternatively or additionally, the assembly may be modular, e.g. block formed.

Nevertheless, it may be further advantageous to have one-sided or two-sided support layers or cladding, e.g. to provide concrete, which cause a double benefit, namely a stabilization and an additional shield against gamma radiation. Depending on the desired height, the concrete formwork can provide the necessary stability, so that radiation shielding arrangements can be used whose gypsum wall alone would not be self-supporting, but then self-supporting in connection with the shuttering, i. the radiation shielding arrangement has self-supporting stability properties due to the base layer or base layers. The thickness of the base layer will be especially dimensioned accordingly.

Preferably, a neutron absorber layer containing a neutron absorbing material is provided. This is mounted on the side facing away from the accelerator, in particular directly on the shielding element. The neutron absorber layer contains e.g. Boron, boron-containing glass or boron paraffin.

Furthermore, the neutron absorber layer is preferably arranged within the casing and / or between the casing and the wall made of gypsum.

According to a particularly preferred development of the invention, the casing, in particular the concrete casing, itself contains a neutron-absorbing material, e.g. a boron-containing material. It can e.g. Boric acid or boron carbide the casing material, e.g. be mixed with the concrete. However, it has proved to be even more advantageous if the casing has boron-containing glass. This is significantly less expensive than boron carbide and, even when blended, preserves the stability of the concrete better than boric acid. Boron-containing glass may in particular be used instead of or in addition to commonly used additives such as e.g. Gravel are added. Alternatively or additionally, the material of the shielding element, in particular the gypsum, may also contain boron-containing glass.

Particularly preferred is the use of gypsum from flue gas desulphurisation plants (so-called REA gypsum). This is deposited at millions of tons expensive dumps. Every year more than 3 million tonnes of REA gypsum are produced in Germany. Therefore, the electricity providers may even be grateful if they can deliver the material.

The advantage of using REA gypsum is amazingly even complex.

First, a material is used whose physical shielding effect is better than that of concrete.

Second, the REA gypsum is chemically very pure, thereby diminishing long-lived radiant activity from high atomic number elements. Therefore, REA gypsum is also more suitable as concrete from the point of view of activation.

Third, power generators no longer have to dump the gypsum, which is generated as waste from flue gas desulphurisation. Even the transport is currently subsidized, as well as the German railway disposed gypsum.

The inventors have further found that to shield upcoming generations of high energy particle accelerators and / or high energy particle storage rings which can have particle energies of the order of 100 GeV to 1 TeV or greater, shielding or gypsum walls of about 1 m to 10 m, preferably 2 m to 8 m, more preferably 4 m to 7 m thickness will be required. Depending on the accelerator, the quantity of gypsum should therefore be at least 100,000 tonnes or even a multiple thereof.

The radiation shielding arrangement according to the invention is thus prepared, in particular with regard to the shielding effect or the thickness of the shielding element, to shield neutron radiation and gamma radiation from high energy particle accelerators, storage rings, target, experimental and / or analytical devices, in particular at particle energies greater than 1 GeV or even greater than 10 GeV.

In the following the invention will be explained in more detail by means of embodiments and with reference to the drawings.

Brief description of the figures

Figur 1:

Ergebnisse einer Monte-Carlo-Simulationsrechnung und

Figur 2:

einen schematischen Querschnitt durch eine beispielhafte Ausführungsform einer erfindungsgemäßen Strahlungsabschirmungsanordnung.

Show it

FIG. 1:

Results of a Monte Carlo simulation calculation and

FIG. 2:

a schematic cross section through an exemplary embodiment of a radiation shielding arrangement according to the invention.

Detailed description of the invention

A simulation calculation was performed on the radiation that results when 30 GeV protons are shot at a 10 cm thick iron target. This corresponds approximately to the conditions prevailing in the high-energy accelerators for which the invention is to be used. This results in a significant proportion of fast neutrons with energies in the range up to a few GeV.

FIG. 1 Figure 4 shows the simulation results of penetrating dose or residual radiation dose through a shielding element or screen in Pico-Sievert (pSv) per proton as a function of shielding or wall thickness in centimeters (cm).

The results are broken down by neutron dose and dose of electromagnetic radiation (gamma dose) as well as the total dose each for gypsum and concrete.

• Die Kurve 1 die Gesamtdosis für Beton,
• die Kurve 2 die Gesamtdosis für Gips,
• die Kurve 3 die Gammadosis für Beton,
• die Kurve 4 die Gammadosis für Gips,
• die Kurve 5 die Neutronendosis für Beton und
• die Kurve 6 die Neutronendosis für Gips.

Here represent:

• The curve 1 the total dose for concrete,
• the curve 2 the total dose for gypsum,
• the curve 3 the gamma dose for concrete,
• the curve 4 the gamma dose for plaster,
• the curve 5 the neutron dose for concrete and
• the curve 6 the neutron dose for gypsum.

It can be seen that especially the neutron dose at the maximum for gypsum is lower by more than a factor of 2, i. the shielding effect is more than a factor of two higher than for concrete and the total dose shielding is about 20% to 25% better for gypsum than for concrete.

The maximum of the curves represents the secondary radiation equilibrium, from which an attenuation effect occurs. The secondary radiation equilibrium thickness is approximately between 60 cm and 70 cm.

This significantly higher shielding effect of the neutron dose of gypsum compared to concrete in the high neutron energies generated by such high energy particle accelerators was also quite surprising to those skilled in the art of accelerator technology.

The calculations show that with a total number of 10 ¹² protons and already a wall thickness of 4 m, a total dose of only about 25 Micro-Sievert (μSv) penetrates the wall.

In the following the advantages regarding the activation of gypsum against concrete are shown.

Table 1 shows values for the generation of radioactivity during a 30-year blasting operation and a subsequent cooldown of 5 years for concrete and gypsum.

The radionuclides listed in Table 1 are mainly produced, namely H-3, Na-22, Mn-54 and Fe-55.

The values for the activity are normalized to the total activity of gypsum.

C_i:

die spezifische Aktivität in Becquerel pro Gramm [Bq/g] und

C_i/R_i:

das Verhältnis aus der freizugebenden spezifischen Aktivität und dem jeweiligen Freigabewert nach dem zum Anmeldezeitpunkt in Deutschland geltenden Strahlenschutzrecht.

Tabelle 1: C_i C_i/R_i Nuklid Beton Gips Beton Gips H-3 1,01E+00 9,74E-01 6,05E-02 5,86E-02 Na-22 1,20E-01 2,61E-02 4,34E+00 9,41E-01 Mn-54 1,03E-03 0,00E+00 1,24E-02 0,00E+00 Fe-55 7,63E-02 0,00E+00 1,38E-03 0,00E+00 Summe 1,20E+00 1,00E+00 4,41E+00 1,00E+00 Here are:

c_i:

the specific activity in becquerels per gram [Bq / g] and

C_i / R_i:

the ratio of the specific activity to be released and the respective clearance value according to the radiation protection law applicable at the time of filing in Germany.

Table 1: c_i C_i / R_i nuclide concrete plaster concrete plaster H-3 1,01E + 00 9,74E-01 6,05E-02 5,86E-02 Na-22 1,20E-01 2,61E-02 4,34E + 00 9,41E-01 Mn-54 1,03E-03 0,00E + 00 1,24E-02 0,00E + 00 Fe-55 7,63E-02 0,00E + 00 1,38E-03 0,00E + 00 total 1,20E + 00 1.00E + 00 4,41E + 00 1.00E + 00

It can be seen that gypsum produces a radioactivity which is lower by a factor of about 1.2. Furthermore, the type of radioactivity generated, i. the distribution of the radionuclides produced in gypsum more favorably than in concrete, if one takes the release values according to the current radiation protection law as a yardstick (factor 4.41). It follows that the costs for a subsequent disposal after the end of the use of the radiation shielding arrangement according to the invention will be lower than in conventional shields.

FIG. 2 shows a multilayer radiation shielding assembly 10 having one, the radiation source and the particle beam 20 facing first layer or spallation layer 11 consisting of or containing a metal, in particular with a core mass> 50 atomic mass units (amu), eg iron. Immediately following the spallation layer 11, a first shielding element, a wall or a first shielding layer 12 consisting of or containing a material for decelerating neutrons, eg plaster and / or concrete, is arranged. Immediately following the first shielding element 12 is a neutron absorber layer 13 consisting of or containing a material which is suitable for absorbing thermalized neutrons, for example boron, cadmium or gadolinium. Again immediately after the neutron absorber layer 13, a second shielding layer 14, which is of a smaller thickness than the wall 12, consisting of or containing a material for decelerating neutrons, such as plaster and / or concrete arranged.

Among other things, the iron, induced by the high-energy neutrons 21, causes spallation reactions, which in turn release neutrons 22 with lower energy. This achieves an indirect first moderation.

Thereafter, the spallation neutrons 22 are further decelerated in the wall 12, to be finally captured and absorbed by the atomic nuclei of the neutron absorbing layer 13.

The material for the spallation layer 11 can also come from the disposal of materials from nuclear facilities, where weakly activated metals are produced in larger quantities.

It will be apparent to those skilled in the art that the invention is not limited to the embodiments described above and that the invention can be varied in many ways.

Claims (17)

1. Radiation shielding arrangement for shielding neutron radiation and/or gamma radiation from particle accelerators, storage rings, target, experimental or analytical devices, comprising a spallation layer (11), in which neutrons (22) are released in spallation reactions and at least one shielding element made of a first material which contains gypsum, in order to slow the spallation neutrons (22) down.
2. Radiation shielding arrangement according to Claim 1, characterized in that the first material contains gypsum in the hydrated state in the chemical composition CaSO₄*2H₂O.
3. Radiation shielding arrangement according to one of the preceding claims, characterized in that the shielding element comprises a wall made of gypsum.
4. Radiation shielding arrangement according to one of the preceding claims, characterized in that the wall made of gypsum has a thickness which is adapted to the radiation spectra of a high-energy particle accelerator and/or high-energy particle storage ring for electrons, positrons or ions.
5. Radiation shielding arrangement according to one of the preceding claims, characterized in that the wall has a thickness which is greater than or equal to the secondary radiation equilibrium thickness, in particular a thickness of at least 2 m, at least 5 m, or at least 7 m.
6. Radiation shielding arrangement, according to one of the preceding claims, characterized by a multilayer construction.
7. Radiation shielding arrangement according to one of the preceding claims, characterized by a modular construction.
8. Radiation shielding arrangement according to one of the preceding claims, characterized by a loadbearing layer which is arranged on a first side of the shielding element and has at least a minimum thickness which is dimensioned such that the radiation shielding arrangement, in particular the arrangement. of shielding element and loadbearing layer, is self-supporting.
9. Radiation shielding arrangement, according to Claim 8, characterized in that the loadbearing layer comprises concrete formwork.
10. Radiation shielding arrangement according to one of the preceding claims, characterized in that the shielding element is provided with formwork on both sides, in particular of concrete.
11. Radiation shielding arrangement according to one of the preceding claims, characterized by a neutron absorber layer which contains a neutron-absorbing material.
12. Radiation shielding arrangement according to one of the preceding claims, characterized by a neutron absorber layer which contains boron, cadmium and/or gadolinium.
13. Radiation shielding arrangement according to one of the preceding claims, characterized by a neutron absorber layer which contains boron-paraffin.
14. Radiation shielding arrangement according to one of the preceding claims, characterized in that, the neutron absorber layer is arranged within the formwork and/or between the formwork and the gypsum wall made of gypsum.
15. Radiation shielding arrangement according to Claim 8, characterized in that the loadbearing layer comprises a neutron-absorbing material.
16. Radiation shielding arrangement according to one of the preceding claims, wherein the spallation layer contains a metal.
17. Use of REA gypsum from flue gas desulphurization plants for producing a radiation shielding arrangement, the REA gypsum being used as a shielding material, for shielding neutron radiation and/or gamma radiation from high-energy particle accelerators, storage rings, target, experimental or analytical devices, wherein the REA gypsum is used in the form of a wall (12) made of hydrated REA gypsum, wherein the water of crystallization bound in the REA gypsum provides the hydrogen nuclei for moderating the neutrons and wherein the REA gypsum wall (12) has a thickness which is greater than or equal to the secondary radiation equilibrium thickness.

Images