JP2015052558A - Method of carrying out and management of melted nuclear fuel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of easily analyzing content rate of uranium 235 contained in the melted nuclear fuel material during a carrying out step of the melted nuclear fuel material to evaluate and manage the recriticality.SOLUTION: In step 1, a melted nuclear fuel material is picked using a pick-up tool attached to the tip of a lifter. In steps 2 and 3, underwater weight W1 and weight in the air W2 of the picked up melted nuclear fuel material are measured. In step 4, the content rate of uranium 235 contained in the picked up melted nuclear fuel material is calculated by using the density D0 and the content rate U0 of uranium 235 of the nuclear fuel material installed in a reactor core and the measured underwater weight W1 and weight in the air W2 of the picked up melted nuclear fuel material. In step 5, the recriticality of the melted nuclear fuel material is evaluated by using the calculated content rate of uranium 235.

Description

  The present invention relates to a method for carrying out nuclear fuel material melted at the time of an accident in a nuclear power plant.

  A nuclear power plant consists of a circulation cycle in which circulating water heated in a nuclear reactor passes through a steam generator, a high-pressure turbine, a low-pressure turbine, a condenser, a feed water pump, and a feed water heater, and then returns to the reactor again. The high-pressure turbine and the low-pressure turbine are driven by the steam generated by the steam generator to operate the generator to generate power. In a nuclear power plant, in a boiling water reactor (BWR), circulating water is boiled in a nuclear reactor, and the nuclear reactor also serves as a steam generator.

  On the other hand, if the power supplied to the nuclear power plant is lost due to a major disaster or the like, the water supply to the nuclear reactor may stop and the nuclear fuel material loaded in the nuclear reactor may melt. When such a severe accident occurs, it is necessary to safely remove the molten nuclear fuel material from the reactor core and containment vessel after the nuclear reactor has been cooled down.

  As a means for carrying out such molten nuclear fuel material, a means has been proposed in which molten nuclear fuel material deposited in the lower part of a nuclear reactor or a containment vessel is cut by a cutting tool and carried out of the furnace by a transfer device (Patent Document 1). .

JP 2013-19875 A

  By the way, since the molten nuclear fuel material contains uranium 235, if it is handled carelessly during the carrying-out operation, there is a possibility that a fission chain reaction occurs rarely and the criticality is reached. For example, when the molten nuclear fuel material transported from the core or the like is stored in a storage container or the like, or when the molten nuclear fuel material containing uranium 235 is accumulated in one place in the process of transporting the molten nuclear fuel material, recriticality occurs. there is a possibility.

  As one means for preventing such recriticality, it is necessary to analyze the content (concentration) of uranium 235 of the molten nuclear fuel material carried out from the core or the like. However, in order to measure the uranium 235 content of high-activity molten nuclear fuel material, the molten nuclear fuel material taken out from the reactor core, etc. is temporarily stored in a transport container and then transported to a radionuclide management facility. It is necessary to analyze the content of uranium 235 by using a large amount of equipment, strict safety management is required for the analysis, and the analysis time is prolonged.

  The present invention has been made in order to solve the above-mentioned problems, and by safely calculating the content of uranium 235 contained in the molten nuclear fuel material in the molten nuclear fuel material unloading step, the molten nuclear fuel material can be safely unloaded. It is an object of the present invention to provide a method for managing the delivery of molten nuclear fuel material.

  In order to solve the above-described problems, the molten nuclear fuel material carry-out management method according to the present invention includes a step of collecting the molten nuclear fuel material by a sampling tool attached to an end of the lifting device, and a weight of the collected molten nuclear fuel material in water. And the step of measuring the weight in the air, and the density and uranium 235 content of the nuclear fuel material loaded in the core and the measured underwater weight and air weight, the uranium 235 content in the sampled molten nuclear fuel material is determined. And a step of calculating a recriticality of the molten nuclear fuel material from the calculated uranium 235 content.

  Further, the method for carrying out the molten nuclear fuel material according to the present invention includes a step of collecting the molten nuclear fuel material by a sampling tool attached to an end of the lifting device, a volume of the collected molten nuclear fuel material, a weight in water or an air Measuring the weight; calculating the uranium 235 content in the molten nuclear fuel material from the uranium 235 content of the nuclear fuel material loaded in the core and the measured volume and weight in water or in air; And a step of evaluating the recriticality of the molten nuclear fuel material from the calculated uranium 235 content.

  According to the present invention, the occurrence of recriticality can be prevented by calculating the content of uranium 235 contained in the molten nuclear fuel material in the process of carrying out the molten nuclear fuel material.

The figure which shows the example of carrying out the molten nuclear fuel material which concerns on 1st Embodiment. The flowchart which shows the carrying-out management process of the molten nuclear fuel material which concerns on 1st Embodiment. (A), (b), (c) is a figure which shows the extraction | collection of the molten nuclear fuel material which concerns on 1st Embodiment, and a carrying-out work. The flowchart which shows the carrying-out management process of the molten nuclear fuel material which concerns on 2nd Embodiment. (A), (b) is a figure which shows the extraction | collection and carrying-out operation | work of the molten nuclear fuel material which concern on 2nd Embodiment.

Hereinafter, an embodiment of a method for managing the delivery of molten nuclear fuel material according to the present invention will be described with reference to the drawings.
[First Embodiment]
A method for managing the delivery of molten nuclear fuel material according to the first embodiment will be described with reference to FIGS.

(Constitution)
In a boiling water reactor (BWR), a pressure vessel 4 is accommodated in a containment vessel 3, and a core 1 loaded with a plurality of fuel assemblies is provided on a core support plate 2 in the pressure vessel 4. . When the nuclear fuel material of the fuel assembly is melted in a severe accident, the molten nuclear fuel material 5 may be deposited on the core support plate 2, the lower portion of the pressure vessel 4, or the lower portion of the containment vessel 3, as shown in FIG.

  When carrying out the molten nuclear fuel material 5 from the nuclear reactor, the nuclear nuclear fuel solidified by a crushing tool attached to the tip of the elevating device 7 in a state in which the reactor 3 is cooled down and then submerged in the containment vessel 3. The material 5 is crushed and subdivided (not shown), and then a predetermined amount of the crushed molten nuclear fuel material 5 is collected by a collection tool 8 comprising a bucket or the like attached to the tip of the lifting device 7. Next, the lifting / lowering device 7 is lifted and accommodated in a storage container disposed outside the storage container 3 by the transport device 6 (not shown).

(Calculation method of uranium 235 content)
In the present embodiment, when the crushed molten nuclear fuel material 5 is collected and lifted and carried out by the lifting device 7, the content of uranium 235 in the collected molten nuclear fuel material 5 is calculated and recriticality management is performed. The calculation method and calculation process will be described below. The amount of uranium 235 in the uranium nuclear fuel loaded in the core is expressed as “enrichment” (about 3 to 5%). Here, for convenience of explanation, the amount of uranium 235 contained in the molten nuclear fuel material 5 It explains using the term "content rate".

  A predetermined amount of the molten nuclear fuel material 5 collected by the collection tool 8 such as a bucket passes through the water and the air in the process of being lifted and carried out inside the containment vessel 3 by the lifting device 7. At this time, the underwater weight W1 and the in-air weight W2 of the molten nuclear fuel material 5 are measured by a weighing scale 10 attached to the upper end portion of the sampling tool 8 (see FIGS. 3A to 3C).

From the measured underwater weight W1 and air weight W2, the density D of the molten nuclear fuel material 5 is obtained by the equation (1).
Density of molten nuclear fuel material 5 D = W2 / (W2-W1) (1)

On the other hand, when the density of nuclear fuel material loaded in the core 1 is D0 and the content (concentration) of uranium 235 in the nuclear fuel material is U0, the content of uranium 235 in the collected molten nuclear fuel material 5 is expressed by the formula ( 2).
Uranium 235 content in molten nuclear fuel material 5 = U0 × (D0 / D) (2)

  The content of uranium 235 in the molten nuclear fuel material 5 obtained by the equation (2) is only an approximate value. However, the molten nuclear fuel material 5 contains not only a small amount of low-weight melt such as in-furnace structures (stainless steel, low alloy steel, nickel base alloy, etc.) and cladding tubes (Zircaloy), and nuclear fuel before melting. Uranium dioxide, which is a substance, is a substance that is densely solidified by sintering, and considering that the porosity increases and the density decreases when the substance is melted and solidified, Equation (2) shows that the content of uranium 235 is safe. It is evaluated on the side, and recriticality accidents can be reliably prevented by performing recriticality management using this equation.

(Calculation process)
The process of calculating the uranium 235 content in the molten nuclear fuel material 5 using the above calculation method will be described with reference to FIGS. 2 and 3A to 3C.

Step 1: The crushed molten nuclear fuel material 5 is sampled by the sampling tool 8 attached to the end of the lifting device 7 (FIG. 3A).
Step 2: The crushing tool 8 is lifted by the elevating device 7, and the underwater weight W1 of the collected molten nuclear fuel material 5 is measured by the weigh scale 10 attached to the upper end of the crushing tool 8 (FIG. 3 (b)).

  Step 3: The crushing tool 8 is further lifted by the lifting device 7, and when the crushing tool 8 is exposed to the air, the air weight W2 of the molten nuclear fuel material 5 is measured by the weigh scale 10 (FIG. 3 (c)).

Step 4: Calculate the uranium 235 content in the molten nuclear fuel material 5 from the equations (1) and (2).
Step 5: Based on the uranium 235 content, the criticality evaluation of the molten nuclear fuel material 5 is performed.

Step 6: Based on the recriticality evaluation, the molten nuclear fuel material 5 is transported to and stored in a storage container as long as the recriticality is not reached.
In step 6 described above, the molten nuclear fuel material 5 collected a plurality of times can be accommodated in one storage container as long as the molten nuclear fuel material 5 does not reach recriticality.

  Moreover, in the said embodiment, what is called a grab bucket which can be divided into 2 is used as the extraction tool 8 of molten nuclear fuel material, However, It is not limited to this, You may use extraction tools, such as a shovel.

(effect)
According to the present embodiment, since the recriticality evaluation can be easily performed by measuring the weight in water and the weight in the air of the molten nuclear fuel material in the process of unloading the molten nuclear fuel material, the unloading operation of the molten nuclear fuel material is performed. It can be done safely and efficiently.

[Second Embodiment]
A method for managing the delivery of molten nuclear fuel material according to the second embodiment will be described with reference to FIGS.
In the first embodiment, the content of uranium 235 is calculated by measuring the weight in water and the weight in the air of the molten nuclear fuel material. In this embodiment, the volume V of the molten nuclear fuel material and the weight in water W1 are calculated. Alternatively, the content of uranium 235 is calculated based on the air weight W2.

  Specifically, as shown in FIG. 5A, a weight meter 10 is installed at the upper end of the sampling tool 8 and a distance meter for measuring the surface height of the molten nuclear fuel material 5 sampled by the sampling tool 8. 11 is installed. In the case of a grab bucket, the internal shape of the sampling tool 8 is, for example, an inverted pyramid shape that is divided into two parts, and since the internal shape is known, the distance from the surface of the molten nuclear fuel material 5 in the sampling tool 8 by the distance meter 11 If the surface height from the bottom of the sampling tool 8 for the molten nuclear fuel material 5 is determined from the distance, the volume V of the molten nuclear fuel material 5 can be determined by simple calculation.

  For example, when the volume is V and the weight of water corresponding to the volume V is W3, the density of the molten nuclear fuel material 5 is expressed by the equation (3) or (4) using the air weight W1 or the underwater weight W2. Can be obtained.

Density of molten nuclear fuel material D = W2 / V (3)
Density of molten nuclear fuel material 5 D = (W1 + W3) / V (4)
The calculation process based on the second embodiment is as follows (FIG. 4).

Step 1: The crushed molten nuclear fuel material 5 is sampled by a sampling tool 8 attached to the end of the lifting device 7 (FIG. 5A).
Step 2a; The sampling tool 8 is lifted by the lifting device 7, and the volume V of the molten nuclear fuel material 5 is measured by the distance meter 11 attached to the upper end of the bucket 4 (FIG. 5B).

Step 3a; In the process of lifting the sampling tool 8 by the lifting device 7, the underwater weight W1 or the in-air weight W2 of the molten nuclear fuel material 5 is measured by the weigh scale 10 (FIG. 5B).
Step 4a: The content of uranium 235 in the molten nuclear fuel material 5 is calculated from the formula (3) or the formula (4) and the formula (2).

Step 5: Based on the uranium 235 content, the criticality evaluation of the molten nuclear fuel material 5 is performed.
Step 6: Based on the recriticality evaluation, the molten nuclear fuel material 5 is transported to and stored in a storage container as long as the recriticality is not reached.

  According to the present embodiment, the weight of the molten nuclear fuel material 5 may be measured either in water or in air, and the uranium 235 content in the molten nuclear fuel material 5 can be calculated more easily.

[Third Embodiment]
In the above embodiment, the content of uranium 235 is calculated by measuring the underwater weight W1 and / or the air weight W2 of the molten nuclear fuel material. In this embodiment, the uranium of the nuclear fuel material loaded in the core 1 is calculated. The uranium 235 content in the molten nuclear fuel material 5 is calculated from the content (concentration) of 235 and the operating time of the reactor.

  Specifically, the operation time of the reactor at the time of occurrence of a severe accident is obtained, and the content of uranium 235 in the core 1 at the occurrence of the severe accident is obtained by calculation analysis processing using a nuclear fuel burnup analysis code or the like.

This method can more accurately determine the content of uranium 235 in the nuclear fuel material immediately before melting, but on the other hand, it requires a large arithmetic device for nuclear fuel burnup analysis and also requires a long calculation time. .
Therefore, this calculation method is preferably used for verification of the calculation methods described in the first and second embodiments.

  As described above, according to the first to third embodiments, it is possible to evaluate the uranium 235 content in the molten nuclear fuel material deposited in the core, the pressure vessel, or the containment vessel by a simple process. Therefore, criticality management and storage management of the molten nuclear fuel material can be efficiently performed, and unexpected accidents in the transportation and storage processes can be prevented in advance.

  Moreover, the molten nuclear fuel material carry-out management method described in the first to third embodiments can be applied not only to a BWR plant but also to a pressurized water nuclear plant (PWR plant) and a fast breeder reactor.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, combinations, replacements, and changes can be made without departing from the spirit of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Core, 2 ... Core support plate, 3 ... Containment vessel, 4 ... Pressure vessel, 5 ... Molten nuclear fuel material, 6 ... Conveying device, 7 ... Lifting device, 8 ... Sampling tool, 10 ... Weigh scale, 11 ... Distance meter .

Claims (5)

  A step of collecting molten nuclear fuel material with a sampling tool attached to the end of the lifting device, a step of measuring the weight of the collected molten nuclear fuel material in water and air, the density of nuclear fuel material loaded in the core and uranium Calculating the uranium 235 content in the collected molten nuclear fuel material from the measured 235 content and the measured weight in water and air, and recriticality of the molten nuclear fuel material from the calculated uranium 235 content A method for managing the delivery of molten nuclear fuel material, comprising the step of:   A step of collecting the molten nuclear fuel material with a sampling tool attached to the end of the lifting device, a step of measuring the volume of the collected molten nuclear fuel material, the weight in water or in the air, and the nuclear fuel material loaded in the core The step of calculating the uranium 235 content in the molten nuclear fuel material from the uranium 235 content, the measured volume and the weight in water or in the air, and reconstitution of the molten nuclear fuel material from the calculated uranium 235 content. And a step of evaluating the criticality. A method for managing the delivery of molten nuclear fuel material.   3. The method for managing the delivery of molten nuclear fuel material according to claim 1 or 2, wherein a weight meter and / or a distance meter is installed at an upper end portion of the sampling tool.   4. The weight in water and / or the weight in the air is measured in the process in which the molten nuclear fuel material sampled by the sampling tool is lifted and carried out of the containment vessel by the lifting device. The method for managing the delivery of molten nuclear fuel material according to item 1.   5. The uranium 235 content in the molten nuclear fuel material is further calculated from the uranium 235 content in the nuclear fuel material loaded in the core and the operating time of the nuclear reactor. 6. Management method of molten nuclear fuel material.

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