A neutron source shielding barrel

Abstract

This invention belongs to the field of radiation shielding technology, specifically a neutron source shielding barrel. The barrel comprises a barrel body and a shielding cover. A recess for accommodating the neutron source is centrally located within the barrel body, and the shielding cover is detachably attached to the barrel body. Both the barrel body and the shielding cover are made of polyethylene with a 5% boron carbide concentration. This barrel is lightweight while maintaining a high shielding rate against neutron sources. The barrel also requires minimal transport time, effectively reducing radiation dose to personnel.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation shielding, and in particular relates to a neutron source shielding barrel. Background Art

[0002] During the initial construction of the Tianwan Nuclear Power Plant, Russian-supplied stainless steel neutron source casks were used. These casks could simultaneously store five neutron sources and weighed 120 kg. The neutron sources had to be transported approximately 300 meters, resulting in a surface dose rate of 61 uSv / h when transporting a single neutron source. The heavy weight and long transport distances of these casks made transport extremely difficult. While the surface dose rate with the source inside was low, the labor and time required for each transport resulted in high per capita and total dose rates, and vertical lifting was difficult. Shanghai Fulan Trading Co., Ltd. later designed and manufactured a 316 stainless steel cask. This cask weighed 73 kg and had a surface dose rate of 167 uSv / h with the neutron source inside. While this reduced the cask's mass, the surface dose rate increased significantly when the source was inside. However, the cask still presented disadvantages such as heavy weight, long transport times, and significant lifting risks.

[0003] In recent years, with the increase in the operating years of the units, the inspection, pre-overhaul and overhaul of the pipelines and valves of the safety spray system and volumetric boron control system have increased year by year, making the dismantling and transportation of neutron sources more frequent. The number of neutron source transportation times for Units 1 and 2 has increased from less than 10 times per year to more than 20 times per year.

[0004] In order to shorten the transportation time of neutron sources, reduce the neutron radiation dose to personnel, and reduce the risk of neutron source lifting, we urgently need to design a neutron source shielding barrel with small volume and mass, good shielding effect, safety, reliability and strong practicality. Summary of the Invention

[0005] The object of the present invention is to provide a neutron source shielding barrel, which is light in weight and can ensure the shielding rate of the neutron source. The shielding barrel has a short transportation time and effectively reduces the radiation dose of personnel.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] A neutron source shielding barrel comprises a barrel body and a shielding cover. A groove for placing the neutron source is provided at the center of the barrel body. The shielding cover is detachably connected to the barrel body. Both the barrel body and the shielding cover are made of polyethylene material with a 5% concentration of boron carbide.

[0008] The shielding barrel further comprises an outer jacket which is sleeved on the barrel body and the shielding cover and is filled with 5% concentration boron carbide polyethylene particles.

[0009] The barrel body is cylindrical.

[0010] The barrel wall thickness of the barrel body is 12 cm, and the total thickness of the 5% concentration boron carbide polyethylene particles filled in the outer jacket is 4 cm.

[0011] The shielding barrel further comprises a neutron source storage cup, which matches the groove of the barrel body and is detachably installed in the groove of the barrel body.

[0012] The shielding cover is a grinding disc type, and the center position of the shielding cover is a convex block that bulges up and down, and the convex block matches the groove of the barrel body.

[0013] The protrusion of the shielding cover is cylindrical.

[0014] The shielding barrel further comprises a locking hole device, which is fixedly connected to the top of the barrel body. A locking opening is provided on the shielding cover, which matches the locking hole device and is used to lock the shielding cover and the barrel body.

[0015] The outer sleeve is connected with a handle, which is in an arc-cone shape.

[0016] The beneficial technical effects of the present invention are:

[0017] (1) The present invention uses a new shielding material, a shielding barrel (mass 25 kg) made of 5% boron carbide polyethylene material. Compared with the Russian stainless steel neutron source shielding barrel and the Shanghai Fulan stainless steel neutron source shielding barrel, the present invention has the advantages of light weight, short transportation time, low personnel dose rate, and easy vertical lifting, which specifically supplements the shortcomings of the known neutron source shielding barrels at home and abroad;

[0018] (2) The present invention optimizes the shielding structure design. A shielding bag filled with boron carbide polyethylene particles is designed on the periphery of the shielding barrel. The shielding bag is detachable. The barrel body and barrel cover are both wearable. The shielding bag has a certain degree of looseness and can be detached at any time. It not only prevents the shielding barrel from being contaminated by external radioactive substances, but also plays a buffering role when the shielding barrel collides. At the same time, the overall mass of the shielding barrel is reduced while ensuring the shielding rate. The actual shielding rate reaches 95%;

[0019] (3) The present invention uses a boron carbide polyethylene shielding cover in the form of a grinding disc, which can quickly open and close the shielding barrel cover. At the same time, the cylindrical protrusion in the middle improves the neutron shielding effect;

[0020] (4) The present invention adds a hole lock device to the barrel body of the neutron source shielding barrel. When the neutron source is stored in the shielding barrel, the shielding barrel cover is locked to prevent any accidental loss of the neutron source;

[0021] (5) The present invention is designed with a detachable neutron source storage cup, which can be detached and assembled at any time according to the size of the neutron source, playing the role of fixing the neutron source and ensuring that the neutron source does not fall over or collide in the shielding barrel during transportation;

[0022] (6) The present invention redesigns the original horizontal handle of the shielding barrel into an arc cone shape, which solves the problem of sliding during the original shielding barrel lifting and improves the safety of neutron source lifting. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the relationship between boride content and thermal neutron shielding efficiency;

[0024] Figure 2 Schematic diagram of the geometric conditions for measuring the neutron shielding performance of polyethylene containing boron carbide;

[0025] Figure 3 For polyethylene containing boron carbide 241 Shielding performance diagram of Am-Be radioisotope neutron source;

[0026] Figure 4 A schematic structural diagram of a neutron source shielding barrel shielding cover provided by the present invention;

[0027] Figure 5 A schematic diagram of the structure of a neutron source shielding barrel provided by the present invention;

[0028] Figure 6 This is a schematic structural diagram of a neutron source shielding barrel jacket provided by the present invention.

[0029] In the figure: 1. Neutron source storage cup; 2. Locking device; 3. Barrel; 4. Shielding cover; 5. Handle; 6. Jacket. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] like Figure 4-5 As shown, the present invention provides a neutron source shielding barrel, comprising a barrel body 3 and a shielding cover 4. The barrel body 3 is cylindrical, with a cylindrical recess in the center thereof for accommodating the neutron source. The shielding cover 4 is a grinding disc-shaped barrel body, with a cylindrical protrusion in the center thereof, which mates with the recess in the barrel body 3. The shielding cover 4 is detachably connected to the barrel body 3. Both the barrel body 3 and the shielding cover 4 are made of polyethylene material containing 5% boron carbide. This material provides excellent radiation shielding and weight performance.

[0032] The shielding cover 4 is of a grinding disc type, which can quickly realize the opening and closing of the shielding barrel cover. At the same time, the cylindrical protrusion improves the neutron source shielding effect.

[0033] like Figure 6As shown, the shield barrel also includes an outer jacket 6, which is fitted over the barrel body 3 and shielding cover 4. The outer jacket 6 is filled with 5% boron carbide polyethylene granules to further enhance shielding effectiveness. The barrel body 3 has a wall thickness of 12 cm, and the total thickness of the 5% boron carbide polyethylene granules filled in the outer jacket 6 is 4 cm.

[0034] The shielding barrel also includes a neutron source storage cup 1, which matches the groove of the barrel body 3. The neutron source storage cup 1 can be detachably installed in the groove of the barrel body 3 to fix the neutron source and ensure that the neutron source does not tip over or collide in the shielding barrel during transportation.

[0035] The shield barrel also includes a locking device 2, which is fixedly connected to the top of the barrel body 3. The shield cover 4 is provided with a locking opening that matches the locking device 2 and is used to lock the shield cover 4 to the barrel body 3. When the neutron source is stored in the shield barrel, the shield cover 4 can be locked to prevent the neutron source from being lost.

[0036] The outer cover 6 is connected with a handle 5, which is in an arc-cone shape, so as to be convenient for single-person operation and lifting and transportation.

[0037] (1) Material selection involved in the technical solution of the present invention:

[0038] The shielding effect of materials on neutrons is divided into two processes: fast neutron moderation and thermal neutron absorption. Fast neutrons undergo inelastic scattering with heavy nuclear elements such as iron and tungsten, or elastic scattering with light nuclear elements such as hydrogen. Among all elements, H has the largest scattering cross section, and each time a neutron collides with an H atom, it loses the most energy, thus having the best moderation effect on neutrons. Polymer materials such as natural latex, polyethylene, paraffin, polyurethane, and some hydrogen-based polymers with a large H content are all good neutron moderation materials. Considering that other properties are difficult to take into account, such as the poor structural properties of paraffin and the high price of polymer materials, we finally chose polyethylene as the moderator material for the following reasons: ① The molecular formula of polyethylene is (C2H4)n, and the hydrogen element has a high specific gravity, so its moderation effect is better than that of natural latex, polyurethane and other materials; ② The density of polyethylene is low, at 0.962g / cm3, which is lower than the density of water, and can effectively reduce the mass of the shielding barrel; ③ Polyethylene has good impact resistance, is not easily damaged, and is odorless and non-toxic; ④ It has good chemical Stablize ⑤It is resistant to corrosion by acid, alkali and salt aqueous solutions at room temperature; ⑤It is cheap and widely used.

[0039] Boron has a strong ability to capture and absorb thermal neutrons, and its neutron absorption effect is significant. Borides used at home and abroad include boron carbide (B4C), magnesium borate (Mg2B2O5), aluminum borate (Al4B2O5) and pure boron. The neutron shielding effect of materials is: pure boron > boron carbide > magnesium borate > aluminum borate. Since pure boron is expensive and the shielding rate is not much different from that of borides, it is not considered.

[0040] Effect of boride content on thermal neutron shielding efficiency of composite materials Figure 1 As shown. With the increase of boride content, the thermal neutron shielding rate of the composite material increases rapidly. After that, as the boride content increases, the thermal neutron shielding rate increases slowly. The thermal neutron shielding performance enhancement effect of magnesium borate composite material is better than that of aluminum borate, but there is still a certain gap with boron carbide. In natural boron element, 10 The abundance of B is 19.8%, 10 The capture cross section of B for thermal neutrons with an energy of about 0.025 eV is 3.838×10 -21 cm 2 Therefore, the capture and absorption reaction of thermal neutrons by boron in borides is the main reason for the rapid increase in neutron shielding of composite materials.

[0041] The thermal neutron source used in this experiment is 252 The Cf (californium) neutron source is obtained by passing through a polyethylene moderator of a specific thickness. In fact, it is a mixed radiation field of thermal neutrons and some high-energy neutrons. The ability of boron to capture neutrons will decrease with the increase of neutron energy. Therefore, when the neutron energy is large, after the boride content reaches a certain level, the reduction in the proportion of moderator material makes the neutrons still in the fast neutron range, and it is difficult for boride to capture neutrons in this range, causing the growth rate of neutron shielding rate to slow down or even regress.

[0042] like Figure 1 As shown in Figure 2, when the boron carbide content of the polyethylene moderator is around 5%, the shielding efficiency against thermal neutrons is basically saturated. Meanwhile, boride compounds that absorb thermal neutrons are mostly used in powder form; adding too much can reduce the overall performance of the shielding material.

[0043] In summary, we finally used polyethylene material containing 5% boron carbide to make the neutron source shielding barrel.

[0044] (2) Structural design involved in the technical solution of the present invention

[0045] The thickness of the shielding material is also an important factor affecting the neutron shielding performance of the material. In order to understand the protective effect of polyethylene materials with different thicknesses containing 5% boron carbide on fast neutrons, the National Defense Science and Technology Industry Ionizing Radiation Level 1 Measurement Station used 241 The fast neutron transmittance of polyethylene sheets containing boron carbide of different thicknesses was experimentally studied using Am-Be standard neutron source irradiation.

[0046] A 3.2 cm thick polyethylene plate containing boron carbide was cut into 7 circular test samples with a diameter of 5.5 cm and a thickness of 3.2 cm, and then stacked into samples of 6.4 cm, 9.6 cm, 12.8 cm, 16 cm, 19.2 cm and 22.4 cm, for a total of 7 test samples.

[0047] The measurement method is to place the sample to be tested on 241 Irradiation is performed under an Am-Be standard neutron source, and the neutron shielding performance of materials of different thicknesses is measured by the change in the net count rate of the counter (the effect count rate minus the room scattered neutron background count rate) when the sample is present or not. The measurement geometric conditions are as follows: Figure 2 shown.

[0048] The centers of the sample to be tested, the shadow cone and the long counter are on the same central axis, and the front surface of the sample to be tested is 2 cm away from the geometric center of the neutron source. 241 When Am-Be neutron source is used for irradiation, the front surface of the long counter is 146 cm away from the geometric center of the neutron source.

[0049] First, measure the long counter counts caused directly by the source neutrons when there is no sample to be tested, and then put the sample to be tested into Figure 2 Neutrons from the radioisotope neutron source are measured in the long counter after passing through the test object. The background of scattered neutrons in the room is subtracted using the shadow cone method.

[0050] Results and analysis: The boron carbide-containing polyethylene was measured 241 Neutron shielding performance of Am-Be source, normalized to net count rate (counts / s). Figure 3 shown.

[0051] Depend on Figure 3 , and combined with the experimental results, it is proved that the shielding efficiency theoretical curve is basically consistent with the actual one. When the thickness of the boron carbide polyethylene plate reaches 12.8cm, it can shield 91% of the 241 Am-Be source neutrons, and a thickness of 16 cm can shield 94.9% 241 Am-Be source neutrons, the shielding effect does not increase significantly when the thickness is increased. When the thickness is 22.4 cm, 241 The efficiency of Am-Be source neutrons can reach 97.9%. Shielding is optimized for protection, with a 16cm thick polyethylene sheet containing 5% boron carbide. 241 Am-Be source neutrons are sufficiently safe.

[0052] The manufacturer produced the shielding drum according to the design drawings and submitted it to us for on-site acceptance testing. The drum weighs 20 kg and has a diameter of 30 cm. Excluding the 6 cm diameter of the intermediate source chamber, the actual shielding thickness is 12 cm. With the cooperation of radiation protection personnel, a handheld neutron detector was used to measure the surface dose rate of the drum with the neutron source. The result was 163 uSv / h, indicating a shielding efficiency of approximately 90%. If the thickness of the drum were increased by an additional 4 cm, the weight of the drum would increase by 12 kg, which would reduce the transfer efficiency.

[0053] Therefore, the original shield barrel design was improved. A shielding bag filled with 4cm thick boron carbide polyethylene particles was designed on the outer ring of the shield barrel. The shielding bag has a certain looseness and can be removed at any time. Figure 4 、 5 The mass of the device (as shown) is 25kg, the neutron detector measurement value is 98uSv / h, and the shielding effect is about 95%, which is basically consistent with the laboratory measurement results and meets the requirements for on-site use.

[0054] The present invention has been described in detail above with reference to the accompanying drawings and embodiments. However, the present invention is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Any content not described in detail in the present invention may be adapted from existing technologies.

Claims

1. A neutron source shielding barrel, characterized in that: The shielding barrel comprises a barrel body (3) and a shielding cover (4); a groove for placing a neutron source is provided at the center of the barrel body (3); the shielding cover (4) is detachably connected to the barrel body (3); and both the barrel body (3) and the shielding cover (4) are made of polyethylene material with a 5% concentration of boron carbide; The shielding barrel further comprises an outer jacket (6), which is sleeved on the barrel body (3) and the shielding cover (4), and the inner portion of the outer jacket (6) is filled with 5% concentration boron carbide polyethylene particles; The barrel wall thickness of the barrel body (3) is 12 cm, and the total thickness of the 5% concentration boron carbide polyethylene particles filled in the outer jacket (6) is 4 cm; The shielding cover (4) is of a grinding disc type, and the center of the shielding cover (4) is a convex block that protrudes upward and downward, and the convex block matches the groove of the barrel body (3); The shielding barrel further comprises a locking hole device (2), which is fixedly connected to the top of the barrel body (3). A locking opening is provided on the shielding cover (4), which matches the locking hole device (2) and is used to lock the shielding cover (4) and the barrel body (3).

2. A neutron source shielding barrel according to claim 1, characterized in that: The barrel (3) is cylindrical.

3. A neutron source shielding barrel according to claim 1, characterized in that: The shielding barrel further comprises a neutron source storage cup (1), the neutron source storage cup (1) matches the groove of the barrel body (3), and the neutron source storage cup (1) is detachably installed in the groove of the barrel body (3).

4. A neutron source shielding barrel according to claim 1, characterized in that: The protrusion of the shielding cover (4) is cylindrical.

5. The neutron source shielding barrel according to claim 1, characterized in that: The outer sleeve (6) is connected to a handle (5), and the handle (5) is in an arc-conical shape.

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