JP2005009982A - Control rod drive mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control rod drive mechanism in which a material having characteristics suitable for use in a shock absorber of a control rod drive mechanism and hardly deteriorating against thermal aging is used. <P>SOLUTION: The control rod drive mechanism for a boiling water reactor drives a control rod and comprises: a shock absorber which has a cylindrical index tube 6, a stop piston 7 provided inside of the index tube; a buffer shaft 8 inserted into the stop piston; and a cylindrical buffer piston 9 inserted between the stop piston and the buffer shaft and moving upward inside the stop piston. As a material for the shock absorber, a material in which Cr of not less than 2 % by weight, Ni of not less than 4 % by weight, C of not more than 0.10 % by weight, and S of not more than 0.01 % by weight are included, Mo of 0.1 to 4 % by weight is added, and indispensable impurities and Fe are included as remaining components, is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control rod drive mechanism for a boiling water reactor, and more particularly to a control rod drive mechanism having a shock absorber.
[0002]
[Prior art]
A schematic configuration of a boiling water reactor (BWR) as a light water reactor will be described with reference to FIG. A large number of fuel assemblies (not shown) and control rods 3 are loaded in the reactor pressure vessel 1 to form a core portion 2. A large number of fuel assemblies constitute a set of four cells, and a cruciform control rod 3 is inserted into a cruciform space in the cell.
[0003]
The control rod 3 is inserted into or pulled out from the core 2 by a control rod drive mechanism (CRD) 4 and the output of the nuclear reactor is controlled by appropriately adjusting the operation setting position. The CRD 4 is inserted and fixed from below into a plurality of control rod drive mechanism housings (CRD housings) 5 disposed on the lower end plate of the reactor pressure vessel 1.
[0004]
The configuration of the CRD 4 and the outline of its operation will be described with reference to FIG. That is, the CRD 4 has the index tube 6 accommodated in the CRD housing 5 so as to be movable up and down, and is connected integrally to the control rod 3 and the index tube 6 by a connecting member provided on the top of the index tube 6.
[0005]
The CRD 4 includes a relatively slow insertion / extraction operation (shim operation) of the control rod 3 that is performed in order to adjust and maintain the reactor power in a predetermined state in normal times, and a control rod that is performed in order to stop the reactor in an emergency. There are three rapid insertions (scrum operation). Both the shim operation and the scrum operation are performed by hydraulic drive.
[0006]
During this scram, the control rod is rapidly inserted into the reactor core by hydraulic operation, but when it reaches the final insertion position, it is necessary to stop rapidly without impacting the entire device as much as possible. It has been.
[0007]
FIG. 3 shows a shock absorber of the CRD 4, which will be described below. In FIG. 3, reference numeral 6 denotes an index tube. A stop piston 7, a buffer shaft 8 and a buffer piston 9 are concentrically inserted into the index tube 6, and the buffer piston 9 is fixed to the buffer shaft 8. The buffer spring 10 is biased toward the concave portion of the index tube 6.
[0008]
The buffer shaft 8 has a plurality of small holes 20 in the radial direction and small holes 22 in the axial direction. The small holes 20 in the radial direction communicate with the small holes 22 in the axial direction. The lower end portion of the small hole 22 in the axial direction is sealed by the plug 11. In the above configuration, the concave portion of the index tube 6 pushes up the buffer piston 9 during scram. Thereby, the pressure of the water of the part surrounded by the buffer piston 9, the stop piston 7, and the buffer shaft 8 rises, and this water passes through the small holes 20 and 22 of the buffer shaft 8 as shown by the arrows in FIG. Then, it flows down from the gap between the buffer shaft 8 and the buffer piston 9.
Note that Patent Document 1 describes a reuse heat treatment method for stainless steel equipment for nuclear reactors.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-273733
[Problems to be solved by the invention]
The shock absorber of the control rod drive mechanism having the above configuration uses a SUS630 material, which is a high-strength material, because a high stress is generated during scram. Recent findings reveal that this material has toughness that decreases over time in the CRD environment, as well as increased hardness and stress corrosion cracking (SCC) sensitivity. When SCC occurs, the shock absorber may be damaged by an impact force generated during scram in combination with a decrease in toughness.
[0011]
The present invention addresses the above-described problems, and uses a material having sufficient material characteristics as a material for a shock absorber of a control rod drive mechanism and having little deterioration over time due to thermal aging. An object is to provide a control rod drive mechanism.
[0012]
[Means for Solving the Problems]
The present invention is in accordance with the above object, and the invention according to claim 1 is a cylindrical index tube, a stop piston arranged in the index tube, and inserted into the stop piston. A shock absorber comprising a buffer shaft and a cylindrical buffer piston interposed between the stop piston and the stop piston and the buffer shaft and rising in the stop piston when scramming, and drives the control rod In the control rod drive mechanism for boiling water reactors, the material of the buffer is, by weight, Cr: 12% or more, Ni: 4% or more, C: 0.10% or less, and S: 0.01% or less In which Mo is added in an amount of 0.1 to 4% and the balance is Fe and inevitable impurities.
[0013]
According to a second aspect of the present invention, there is provided a cylindrical index tube, a stop piston disposed in the index tube, a buffer shaft inserted in the stop piston, the stop piston and the stop piston, In a control rod drive mechanism for a boiling water reactor having a shock absorber provided between the buffer shaft and a cylindrical buffer piston that rises in the stop piston during scram, and drives the control rod The material of the shock absorber is, by weight%, Cr 12% or more, Ni 4% or more, C 0.10% or less, S 0.01% or less, Mo 0.1-4%, Cu 2 to 5%, and the balance is Fe and inevitable impurities, and Cu is precipitated by heat treatment at 450 to 650 ° C to improve the strength. , Characterized by.
[0014]
According to a third aspect of the present invention, there is provided a cylindrical index tube, a stop piston disposed in the index tube, a buffer shaft inserted in the stop piston, the stop piston and the stop piston, In a control rod drive mechanism for a boiling water reactor having a shock absorber provided between the buffer shaft and a cylindrical buffer piston that rises in the stop piston during scram, and drives the control rod The material of the shock absorber is, by weight%, Cr 12% or more, Ni 4% or more, C 0.10% or less, S 0.01% or less, Mo 0.1-4%, Al hints 0.5% to 1.5%, the balance being Fe and unavoidable impurities, the intensity precipitating intermetallic compound _Ni 3 Al by heat treatment of 600 to 900 ° C. That was used above is not material, and wherein.
[0015]
According to a fourth aspect of the present invention, there is provided a cylindrical index tube, a stop piston disposed in the index tube, a buffer shaft inserted in the stop piston, the stop piston and the stop piston, In a control rod drive mechanism for a boiling water reactor having a shock absorber provided between the buffer shaft and a cylindrical buffer piston that rises in the stop piston during scram, and drives the control rod The material of the shock absorber includes, by weight%, Cr 12% or more, Ni 4% or more, C 0.10% or less, S 0.01% or less, Mo 0.1-4% was added, further comprising 0.5% to 1.5% of Nb, to characterized in that to improve the strength by precipitating an intermetallic compound _Ni 3 Nb by heat treatment of 600 to 900 ° C. The balance has a material consisting of Fe and unavoidable impurities, characterized.
[0016]
According to a fifth aspect of the present invention, there is provided a cylindrical index tube, a stop piston disposed in the index tube, a buffer shaft inserted in the stop piston, the stop piston and the stop piston, In a control rod drive mechanism for a boiling water reactor having a shock absorber provided between the buffer shaft and a cylindrical buffer piston that rises in the stop piston during scram, and drives the control rod The material of the shock absorber is 12% or more of Cr, 4% or more of Ni, C of 0.10% or less, S of 0.01% or less, Mo of 0.1 to 4%, Ti by weight%. hints 0.5% to 1.5%, the balance being Fe and unavoidable impurities, the intensity precipitate an intermetallic compound _Ni 3 Ti by heat treatment of 600 to 900 ° C. That was used above is not material, and wherein.
[0017]
According to a sixth aspect of the present invention, there is provided a cylindrical index tube, a stop piston disposed in the index tube, a buffer shaft inserted in the stop piston, the stop piston and the stop piston, In a control rod drive mechanism for a boiling water reactor having a shock absorber provided between the buffer shaft and a cylindrical buffer piston that rises in the stop piston during scram, and drives the control rod The material of the shock absorber includes 12 to 14% by weight, 6 to 10% of Ni, 6 to 10% of C, 0.10% or less of S and 0.01% or less of S, with the balance being Fe and inevitable. It is characterized by using a material that has a martensite structure composed of impurities and suppresses the formation of a Cr-rich phase by not including a ferrite phase.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a control rod drive mechanism according to the present invention will be described below. Here, the structure of each part of the control rod drive mechanism is the same as that of the prior art except for the characteristics related to the material of the shock absorber, and therefore, a duplicate description is omitted. In the present specification, all percentages indicating the content of component elements are percentages (wt%) based on weight. Aging degradation studies of precipitation hardening stainless steels revealed that aging degradation occurs in a shorter time as the Cr content increases. Therefore, as a countermeasure against aging deterioration, it is desirable to have material properties equivalent to conventionally used SUS630 steel and to have low Cr.
[0019]
[First Embodiment]
The material of the shock absorber of the control rod drive mechanism according to the first embodiment of the present invention is basically stainless steel containing 12% or more of Cr.
In order to suppress a decrease in toughness and ductility when used in a reactor water environment for a long period of time, 0.1 to 4% of Mo is added. Mo is an element that contributes to the improvement of pitting corrosion resistance in conductive water by coexisting with Cr. In order to exert the effect, addition of 0.1% or more is necessary. However, if the amount added exceeds 4%, the problem of material embrittlement occurs, so the upper limit of the amount added was set to 4%.
[0020]
C is an element that improves strength, but is also an element that adversely affects corrosion resistance. C forms Cr carbide at the grain boundary due to the effect of heat treatment or welding heat, and accordingly, forms a Cr-depleted layer near the grain boundary to lower the corrosion resistance. Therefore, C is desirably 0.10% or less.
[0021]
S is an element that forms non-metallic inclusions MnS together with Mn which is inevitably mixed as a deoxidizing agent at the time of dissolution, and adversely affects corrosion resistance as the content increases. Therefore, the S content is 0.01% or less.
[0022]
When a large amount of C or S is contained, nonmetallic inclusions such as MnS or segregated portions of C are generated. Thereby, when the alloy is exposed to high-temperature water, a potential difference is generated between these sites and the surrounding structure, and the sites where non-metallic inclusions and C segregation portions exist are selectively corroded. In the alloy of the present invention, the C and S contents are controlled in order to prevent such a phenomenon.
It is preferable to contain 4% or more of Ni. Addition of Ni improves toughness and corrosion resistance.
[0023]
Component elements (impurity elements) other than the elements described above, such as Si, Mn, P, etc., can be set to the levels defined in the normal JIS standard (JIS G3214) without any problem.
[0024]
A first embodiment will be described. FIG. 4 shows the chemical composition of the present invention material A having components corresponding to the first embodiment and the conventional material SUS630 steel (conventional material D), and the impact value associated with aging of these materials at 400 ° C. The rate of change is shown in FIG. The material A of the present invention was subjected to a heat treatment of 1020 ° C. × 1 hour + 640 ° C. × 1 hour, and the conventional material D was subjected to a heat treatment of 1050 ° C. × 1 hour + 580 ° C. × 4 hours and then subjected to aging at 400 ° C. This is the result of the implementation. In the present invention material A, the decrease in impact value change rate is longer than that of the conventional material D, and deterioration over time is suppressed.
[0025]
[Second Embodiment]
The material of the shock absorber of the control rod drive mechanism according to the second embodiment of the present invention is wt%, Cr is 12% or more, Ni is 4% or more, C is 0.10% or less, and S is 0.01%. In order to suppress the Cr-rich phase formation accompanying thermal aging, 0.1 to 4% of Mo is added, and the balance consists of Fe and inevitable impurities. In order to further improve the strength, 2-5% Cu is added, 0.5-1.5% Al is added, 0.5-1.5% Nb is added, or Ti is 0%. Add 5-1.5%. The reason for limiting the content of elements to be added for improving the strength will be described below.
[0026]
When Cu is heat-treated at 450 to 650 ° C., it is precipitated in the base material, and the strength is increased by so-called precipitation hardening. If it is 2% or less, the contribution of precipitation hardening is small, and if it is 5% or more, embrittlement is promoted, so addition of 2 to 5% is desirable.
[0027]
When Al is heat-treated at 600 to 900 ° C., it precipitates as an intermetallic compound Ni ₃ Al in the base material, and the strength increases by so-called precipitation hardening. If it is 0.5% or less, the contribution of precipitation hardening is small, and if it is 1.5% or more, embrittlement is promoted, so addition of 0.5 to 1.5% is desirable.
[0028]
When heat treatment is performed at 600 to 900 ° C., Nb precipitates as an intermetallic compound Ni ₃ Nb in the base material, and the strength increases by so-called precipitation hardening. If it is 0.5% or less, the contribution of precipitation hardening is small, and if it is 1.5% or more, embrittlement is promoted, so addition of 0.5 to 1.5% is desirable.
[0029]
When Ti is heat-treated at 600 to 900 ° C., it precipitates as an intermetallic compound Ni ₃ Ti in the base material, and the strength increases by so-called precipitation hardening. If it is 0.5% or less, the contribution of precipitation hardening is small, and if it is 1.5% or more, embrittlement is promoted, so addition of 0.5 to 1.5% is desirable.
[0030]
A second embodiment will be described. FIG. 4 also shows chemical components of the present invention materials B and C having components corresponding to the second embodiment, and changes in impact value with aging at 400 ° C. with conventional SUS630 steel (conventional material D). The rate is shown in FIG. Inventive material B is heat treated at 1038 ° C. × 1 hour + 593 ° C. × 4 hours, Invented material B is heat treated at 1038 ° C. × 1 hour + 593 ° C. × 4 hours, and Invented material C is 927 ° C. × 1 hour + 593 ° C. It is the result of performing aging at 400 ° C. after heat treatment for 4 hours and conducting a Charpy impact test. Inventive materials B and C have a lower rate of change in impact value than that of conventional material D for a longer time, and the deterioration over time is suppressed.
[0031]
[Third Embodiment]
The material of the shock absorber of the control rod drive mechanism according to the third embodiment of the present invention is 12-14% for Cr, 6-10% for Ni, 0.10% or less for C, and 0.01% or less for S. And the balance consists of Fe and inevitable impurities. Hereinafter, the reason for limiting the content of each component element will be described.
[0032]
In this embodiment, the reason why Cr is set to 12 to 14% and Ni is set to 6 to 10% is determined in order to make the metal structure a single martensite structure having no ferrite phase. This is because the ferrite phase has a higher Cr content than the martensite phase and is likely to cause spinodal decomposition, and easily forms a Cr-rich phase that promotes deterioration over time.
[0033]
[Fourth Embodiment]
In the fourth embodiment of the present invention, the material described in the first to third embodiments from SUS630 steel is used as the material of the buffer shaft 8 among the shock absorber parts of the control rod drive mechanism. The buffer shaft 8 is one of the shock absorber parts of the control rod drive mechanism, but receives an impact force at the end of the scrum operation. When the buffer shaft is damaged, the shock absorber does not work at the end of the scrum operation and an impact force is applied to the CRD. In the worst case, there is a possibility that the CRD and the control rod are separated and the pulling operation is impossible.
[0034]
[Fifth Embodiment]
In the fifth embodiment of the present invention, the material described in the first to third embodiments from SUS630 steel is used as the material of the stop piston 7 in the shock absorber parts of the control rod drive mechanism. The stop piston 7 is one of the shock absorber parts of the control rod drive mechanism, but receives an impact force at the end of the scrum operation. When the stop piston 7 is damaged, the shock absorber does not work at the end of the scrum operation and an impact force is applied to the CRD.
[0035]
[Sixth Embodiment]
In the sixth embodiment of the present invention, the material described in the first to third embodiments from SUS630 steel is used as the material of the buffer piston 9 among the shock absorber parts of the control rod drive mechanism. The buffer piston 9 is one of the shock absorber parts of the control rod drive mechanism, but receives an impact force at the end of the scrum operation. When the buffer piston 9 is damaged, the shock absorber does not work at the end of the scrum operation and an impact force is applied to the control rod drive mechanism.
[0036]
[Seventh Embodiment]
In general, because the sliding parts of the shock absorber parts of the control rod drive mechanism slide at high speed, the performance of the shock absorber deteriorates due to wear when used for a long time so that impact force is applied to the control rod drive mechanism. Become. Therefore, as a seventh embodiment of the present invention, the material described as the first to third embodiments from SUS630 steel is used as a countermeasure against aging deterioration, and the sliding portion of the shock absorber component is used to prevent wear. Is subjected to nitriding treatment. Thereby, abrasion resistance can be improved.
[0037]
[Eighth Embodiment]
Since the sliding parts of the shock absorber parts of the control rod drive mechanism slide with each other at high speed, the performance of the shock absorber deteriorates due to wear when used for a long time, and an impact force is applied to the control rod drive mechanism. As an eighth embodiment of the present invention, the material described as the first to third embodiments from SUS630 steel is used as a countermeasure against aging deterioration, and the sliding portion of the shock absorber component is hard to prevent wear. Apply chrome plating. Thereby, abrasion resistance can be improved.
[0038]
[Ninth Embodiment]
Since the sliding parts of the shock absorber parts of the control rod drive mechanism slide at high speed, the performance of the shock absorber is deteriorated due to wear when used for a long time, and an impact force is applied to the control rod drive mechanism. As a ninth embodiment of the present invention, the material described as the first to third embodiments from SUS630 steel is used as a countermeasure against aging deterioration, and the sliding portion of the shock absorber component is used to prevent the wear. 6 (product name of self-fluxing alloy according to the standards of Wallcolmonoy) is applied. Thereby, abrasion resistance can be improved.
[0039]
【The invention's effect】
According to the present invention, by using the material of the present invention that can suppress the aging deterioration associated with thermal aging as the material of the shock absorber of the control rod drive mechanism, there is room for both toughness and SCC sensitivity during the life of the nuclear power plant, The shock absorber is unlikely to be damaged by the impact force generated during scram.
[Brief description of the drawings]
FIG. 1 is a partial vertical sectional view showing a schematic configuration of a boiling water reactor including a control rod drive mechanism according to the present invention.
FIG. 2 is an elevational sectional view showing a schematic configuration of the control rod drive mechanism of FIG. 1;
3 is a partial vertical sectional view showing a schematic configuration of a shock absorber of the control rod drive mechanism of FIG. 2;
FIG. 4 is a table showing chemical components of invention materials and conventional materials.
FIG. 5 is a graph showing an impact value change rate at 400 ° C. of the inventive material and the conventional material.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reactor pressure vessel, 2 ... Core part, 3 ... Control rod, 4 ... Control rod drive mechanism (CRD), 5 ... Control rod drive mechanism housing (CRD housing), 6 ... Index tube, 7 ... Stop piston, 8 ... buffer shaft, 9 ... buffer piston, 10 ... buffer spring, 11 ... plug.

Claims (9)

A cylindrical index tube, a stop piston arranged in the index tube, a buffer shaft inserted in the stop piston, and interposed between the stop piston and the stop piston and the buffer shaft A control rod drive mechanism for a boiling water reactor that has a shock absorber comprising a cylindrical buffer piston that rises in the stop piston, and drives the control rod;
As a material of the shock absorber, Cr contains 12% or more, Ni contains 4% or more, C contains 0.10% or less, S contains 0.01% or less, and Mo is added by 0.1 to 4%. And a control rod drive mechanism characterized in that the balance is made of a material composed of Fe and inevitable impurities. A cylindrical index tube, a stop piston arranged in the index tube, a buffer shaft inserted in the stop piston, and interposed between the stop piston and the stop piston and the buffer shaft A control rod drive mechanism for a boiling water reactor that has a shock absorber comprising a cylindrical buffer piston that rises in the stop piston, and drives the control rod;
As the material of the shock absorber, Cr is 12% or more, Ni is 4% or more, C is 0.10% or less, S is 0.01% or less, Mo is 0.1 to 4%, and Cu is used by weight%. A control rod drive mechanism comprising: a material containing 2 to 5%, the balance being Fe and inevitable impurities, and Cu being deposited by heat treatment at 450 to 650 ° C. to improve the strength. A cylindrical index tube, a stop piston arranged in the index tube, a buffer shaft inserted in the stop piston, and interposed between the stop piston and the stop piston and the buffer shaft A control rod drive mechanism for a boiling water reactor that has a shock absorber comprising a cylindrical buffer piston that rises in the stop piston, and drives the control rod;
As the material of the shock absorber, Cr is 12% or more, Ni is 4% or more, C is 0.10% or less, S is 0.01% or less, Mo is 0.1 to 4%, and Al is used by weight%. It is characterized by using a material containing 0.5 to 1.5%, the balance consisting of Fe and inevitable impurities, and depositing the intermetallic compound Ni ₃ Al by heat treatment at 600 to 900 ° C. to improve the strength. Control rod drive mechanism. A cylindrical index tube, a stop piston arranged in the index tube, a buffer shaft inserted in the stop piston, and interposed between the stop piston and the stop piston and the buffer shaft A control rod drive mechanism for a boiling water reactor that has a shock absorber comprising a cylindrical buffer piston that rises in the stop piston, and drives the control rod;
As a material of the shock absorber, Cr contains 12% or more, Ni contains 4% or more, C contains 0.10% or less, S contains 0.01% or less, and Mo is added by 0.1 to 4%. Furthermore, the balance is characterized by containing 0.5 to 1.5% of Nb and precipitating intermetallic compound Ni ₃ Nb by heat treatment at 600 to 900 ° C. to improve the strength, and the balance consists of Fe and inevitable impurities A control rod drive mechanism characterized by using a material. A cylindrical index tube, a stop piston arranged in the index tube, a buffer shaft inserted in the stop piston, and interposed between the stop piston and the stop piston and the buffer shaft A control rod drive mechanism for a boiling water reactor that has a shock absorber comprising a cylindrical buffer piston that rises in the stop piston, and drives the control rod;
The material of the shock absorber is, by weight%, Cr 12% or more, Ni 4% or more, C 0.10% or less, S 0.01% or less, Mo 0.1-4%, Ti It is characterized by using a material containing 0.5 to 1.5%, the balance being Fe and inevitable impurities, and depositing the intermetallic compound Ni ₃ Ti by heat treatment at 600 to 900 ° C. to improve the strength. Control rod drive mechanism. A cylindrical index tube, a stop piston arranged in the index tube, a buffer shaft inserted in the stop piston, and interposed between the stop piston and the stop piston and the buffer shaft A control rod drive mechanism for a boiling water reactor that has a shock absorber comprising a cylindrical buffer piston that rises in the stop piston, and drives the control rod;
As a material of the buffer device, it contains 12 to 14% Cr, 6 to 10% Ni, 6% to 10% C, 0.10% or less, and 0.01% or less S, with the balance being Fe and inevitable impurities A control rod drive mechanism characterized by using a martensite structure made of a material that does not contain a ferrite phase and suppresses Cr-rich phase formation. 7. The control rod drive mechanism according to claim 1, wherein the material of the shock absorber is used for at least part of the buffer shaft, the stop piston, and the buffer piston. . 8. The control rod drive mechanism according to claim 1, wherein the sliding portion of the shock absorber is subjected to nitriding treatment. 8. The control rod drive mechanism according to claim 1, wherein a hard chromium plating is applied to a sliding portion of the shock absorber.

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