JPH04175700A - Boron compound neutron shielding material - Google Patents

Abstract

PURPOSE:To obtain a shielding material excellent in heat resistance and processability by forming a mixed molding of calcium silicate powder and powder of a boron compound, and using boron carbonate (B4C) or europium boride (EuB6) as the boron compound. CONSTITUTION:A structure wherein a boron compound serving as a neutron absorbing material and a heat-resisting binder 2 of calcium silicate are uniformly and finely dispersed at a porosity of preferably within 45% is provided. The neutron absorbing material is a boron compound (B4C, EuB6, etc.) and the heat- resisting binder is dopamolite, zenolite, etc. The boron compound is provided by at least 50 parts by weight for 100 parts by weight of calcium silicate. A reinforcing material such as glass fiber is added when needed. Powder of the boron compound is added and mixed in silica powder and lime powder both of which are the synthetic raw material of the calcium silicate. Further, water is added in the range 0 to 50wt% to the mixture and the mixture is hardened through a reaction in steam at high temperatures and high pressures.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a neutron shielding material that contains a high volume fraction of boron compounds that have excellent neutron shielding (neutron moderation and absorption) ability, and is stable as a structure up to a high temperature of 800°C, and does not require neutron shielding. It can be applied to a wide range of fields. In particular, for nuclear reactors, it is suitable as a neutron shield around the core in the reactor vessel, a control rod in the core, etc. In addition, it can be preferably used as a neutron shielding material in facilities that use nuclear fuel and nuclear raw materials, a shielding material for spent nuclear fuel transportation containers, a shielding material in a hot radio, a shielding material for radiation generating devices (accelerators, etc.), and the like.

[Conventional technology and its issues]

Stainless steel and B4C have traditionally been used as neutron shielding or control materials in fast reactors. Although stainless steel has excellent strength and stability as a structure, it has low neutron shielding ability and requires excessive weight and volume. In addition to being used as a control rod material, 84C is also being considered for use as a neutron shield. 84C has excellent neutron moderating ability, absorption ability, and stability at high temperatures, or has high H
Swelling caused by e-gas has become a problem. Boron compounds are generally hard and brittle, and have poor moldability and processability.
The methods used were to disperse it in an organic material or to form it into pellets and store them in a cladding tube.

[Problem to be solved by invention]

Conventionally, it has been difficult to manufacture structures with sufficient mechanical strength and dimensional stability to withstand the increase in internal pressure due to He gas generated due to absorption of neutrons even under high temperatures exceeding 300°C and neutron irradiation environments. Molded into any shape
It was difficult to process. Therefore, the present invention solves the problems of the prior art described above, and
The present invention provides a boron compound-based neutron shielding material having the following features. ■It can stably hold boron compounds with high volume fraction. ■Has the dimensional stability and mechanical strength necessary for a molded product. ■Can be molded and processed into any shape. ■The above features of ■ to ■ are not lost even under a high temperature of 800℃ and neutron irradiation environment.

[Means to solve the problem]

That is, the boron compound-based neutron shielding material according to the present invention is
A mixed molded body consisting of calcium silicate powder and boron compound powder, with respect to 100 parts by weight of calcium silicate,
Contains 50 to 500 parts by weight of a boron compound, calcium silicate has a silicate and calcareous CaO/SiO2 molar ratio of 0.5 to 2.0, and contains boron compound, boron carbide (84C) or boron. Europium chloride (Eu B
s). The structure, chemical structure, and molding process of the neutron shielding material of the present invention will be described below. 1) Molded object structure The molded object has a structure as schematically shown in the attached drawings. That is, the boron compound powder 1, which is a neutron absorbing material, and the heat-resistant binder 2 made of silicic acid are uniformly and finely dispersed, and the structure preferably has a porosity of 45% or less. The heat-resistant binder is stable up to a high temperature of about 800°C and has excellent moldability, so it improves the mechanical strength of the molded product.
It not only improves thermal stability such as dimensional stability, but also enables molding and processing into any shape. 2), Chemical composition - Neutron absorbing material: Boron compounds (B4C, EuB6, etc.) - Heat-resistant binder Calcium silicate, such as tobermorite: 5Ca0, 6S10, 5H20 Zonotlite, 6Ca0, 6SiO, H0 Boron compounds contained as neutron absorbing materials include: , boron carbide (B4C), europium boride (E u B
e) etc. The average particle size of the boron compound used is preferably in the range of 5 to 100 microns. Examples of the calcium silicate contained as a heat-resistant binder include tobermorite and xonotlite. These calcium silicates can be synthesized using silicate powder and calcareous powder as raw materials, and in that case, the CaO/S 102 molar ratio of the silicate powder and calcareous powder is 0.6 to 10 in the synthesis of tobermorite, and 0.6 to 10 in the synthesis of xonotlite. 0.8 in the synthesis of
~1.2 is desirable. The average particle diameter of the calcium silicate used is preferably in the range of 1 to 1. The greater the amount of the boron compound added, the better the shielding performance.The suitability as a shielding material is lowered if the amount of the boron compound exceeds 500 parts by weight per 100 parts by weight of calcium silicate. It becomes difficult to create the body. Also, in order to make the shielding effect more effective, at least 50 parts by weight of the boron compound is required. Furthermore, to increase the strength of the shielding material, glass fiber, carbon fiber,
It is possible to add reinforcing materials such as metal whiskers. 3) Molding process The molding process involves adding boron compound powder to silicate powder and calcareous powder, which are raw materials for calcium silicate synthesis.
Mix thoroughly. For this mixed powder, θ ~ 50wL%
After uniformly adding water, the material is press-molded or filled into a mold, and reacted and cured under high-temperature, high-pressure steam to obtain a shielding material. The molded body can be machined as required and used as a shielding material.

【Example】

l), Manufacturing Example In order to obtain sample No. 1.2.3 in the recipe in Table 1, the raw material powders were mixed uniformly in a dry method, and the mixed powder was 100 w.
Add 10 wt % of water to t % and disperse uniformly. Thereafter, it was press-molded at a pressure of 100 Kg/Cl112, and then cured in an autoclave for 15 hours under a pressure of 15 Kg/Cl12 to produce Samples No. 1 and 2.3. Table 2 shows the results of measuring the physical properties of these. Table 1 Combination table (w1%) Table 2 Physical properties Heat treatment conditions 700℃-1 (llr 2) Shielding performance evaluation example The neutron shielding performance against the neutron source of the fission spectrum was evaluated for sample No. 1.2.3.5US316 and BC. The evaluation results are shown in Table 3. Table 3 Example of shielding performance evaluation Comparison of shielding thickness required for attenuation 5US316 1 1 B4CO, 450, 55 Sample spacing, 1 0.57 0.612
0.56 0.603
0.55 0.58 Neutron source, fission spectrum In this shielding performance evaluation example, a neutron source with a fission spectrum is placed in contact with the shielding material, and the dose equivalent rate is 1/1000.
(10=), 1/1 millionth (10-6) As for the thickness of the shielding material required to attenuate, the thickness in the case of 5US316 is shown as 1.

【Effect of the invention】

l) Excellent heat resistance By using a boron compound with excellent heat resistance as a raw material and molding it with a heat-resistant binder, it can be used at high temperatures. 2) Can be molded and processed into any shape. Since the method involves wrapping a boron compound in a heat-resistant binder and molding it, it can be molded into any shape as a mechanically strong structure. 3) Shielding performance can be designed by changing the components and their blending ratios. Shielding performance can be designed by changing the blending ratio of the boron compound and heat-resistant binder. 4) The shield can be made thinner and lighter. Compared to the conventionally used stainless steel such as 5US316, it is possible to manufacture a shield that has much better neutron shielding ability and contains a high volume percentage of low-density boron compounds, making the shield much thinner. and weight reduction can be achieved.

[Brief explanation of drawings]

The accompanying drawings are conceptual diagrams of the structure of the molded body of the shielding material of the present invention. 1...Boron compound powder, 2...Heat-resistant binder (calcium silicate). Patent applicant: Power Reactor and Nuclear Fuel Development Corporation
ASRI Co., Ltd.

Claims (1)

[Claims] 1. A mixed molded body consisting of calcium silicate powder and boron compound powder, which contains 50 to 500 parts by weight of a boron compound per 100 parts by weight of calcium silicate, and the calcium silicate contains silicate and calcareous CaO/ The SiO_2 molar ratio is in the range of 0.5 to 2.0, and the boron compound is boron carbide (B_4C) or europium boride (E
A boron compound-based neutron shielding material characterized by being uB_6).