JPS5823337B2 - conversion device - Google Patents

Description

Detailed Description of the Invention The present invention is a conversion method for removing nitric acid from a mixed solution of plutonium nitrate and uranyl nitrate (hereinafter referred to as nitric acid solution) produced after reprocessing spent nuclear fuel to produce a cake of plutonium dioxide and uranium dioxide. Regarding equipment.

Generally, in order to denitrify a nitric acid solution containing nuclear material to produce only nuclear material, as shown in FIG. When the nitric acid solution is heated by irradiating microwaves from part 4, the water evaporates first.

Next, a denitration reaction begins due to an azeotropic phenomenon between water and nitric acid.

If the steam or nitrogen oxides produced by heating are evacuated, for example through the microwave inlet 4, a cake converted from the nitric acid solution is obtained.

However, with a conversion device that only irradiates microwaves, the cake does not have uniform properties and exhibits the appearance shown in FIG. 2.

That is, the cake converted in the container 2 consists of yellow-green uranium nitrate crystals 5, and yellow uranium nitrate semi-solids that remain without decomposition of nitrogen oxides 6. A reddish-brown target nuclear substance 7 and a black dried substance 8 in a peroxidized state are separated and precipitated.

The reason why the desired nuclear material is not produced uniformly is that firstly, most of the microwave energy irradiated toward the liquid surface is absorbed at the surface layer of the liquid, so it does not reach the inside of the nitric acid solution. One example is that the heating is not uniform.

Naturally, if only the upper layer of the liquid is heated locally, the solution will not undergo convection, so as a countermeasure to this, a shallow container with a flat bottom is used, but even this still does not eliminate uneven heating.

The second reason why nuclear materials are not uniformly generated is that the timing of stopping microwave oscillation is not appropriate, and if microwaves are irradiated unnecessarily, some of the dry matter may become the target UO.
U3O8 does not exist as U3O8 in the overoxidized state.

The present invention has been made to eliminate the above-mentioned drawbacks.
The purpose of the present invention is to provide a conversion device that uniformly heats a nitric acid solution and efficiently produces a cake.

Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 3 is a sectional view showing the configuration of the conversion device according to the present invention.
In the figure, 11 is a microwave oscillator, 12 is a waveguide, 13 is an enclosure surrounding the microwave and nitrogen oxides to prevent them from leaking to the outside, 14 is a wind barrel for discharging generated gas, and 15 is a nitric acid solution injected. 16 is a heater, 17 is a heat insulating material, 18 is a turntable on which the container is placed and rotates the liquid to be irradiated with microwaves for each container, 20 is a rotating container. A motor that rotates the turntable 18 via a shaft 19, 21 a light intensity detector that detects the light generated during the reaction of the nitric acid solution, 22 a liquid supply pipe that supplies the nitric acid solution, 23 an exhaust fan, and 24 a reaction gas. Scrubbers 25 each represent a baffle having a ventilation hole on the side not facing the nitric acid solution in order to prevent nitric acid droplets generated when the nitric acid solution boils from traveling inside the wind barrel 14.

The operation of the converting device of the present invention constructed as described above will be explained below.

First, the nitric acid solution 1 injected through the liquid supply pipe 22 is heated by the heater provided at the bottom of the container 15, causing convection, and the temperature difference between the upper and lower parts becomes extremely small.

This promotes liquid exchange and convection between the upper layer of the microwave, which absorbs the energy of the microwave irradiated from above and partially heats the liquid, and the lower layer of the liquid, which is heated by the heater. , the temperature difference between the upper and lower parts can be kept small.

In this case, it is clear that the addition of a heater in addition to microwave heating significantly increases the conversion efficiency.
To make it difficult for the heat from the heater to dissipate to the outside, the container is double-layered and heat insulating material is packed inside.

Next, the turntable 18 is rotated to eliminate uneven heating due to microwaves or the directionality of the enclosure 13 in the direction along the liquid surface, and uniform heating conditions are applied to the liquid surface. , measures are taken to maintain a uniform temperature throughout the nitric acid solution.

In addition, when the nitric acid solution heated as described above reaches a predetermined temperature, the denitrification reaction starts, and this reaction gas is transferred to the cavity 1.
4 and is about to be discharged to the outside by the exhaust fan 23.

However, since the nitrogen oxides in the reaction gas are absorbed by the scrubber 24, no toxic gases are released outside the enclosure.

On the other hand, near the end of the denitrification reaction, a portion of the dry matter converts from UO3 to U3O8, and light is emitted during this reaction, making it possible to perceive the end of the denitrification reaction, but this conversion time is relatively short. Thus, the oscillation of the microwave and the energization of the heater must be stopped at an appropriate time.

Therefore, if heating operation is continued even after this period, most of the dry matter will be U3O8.
Therefore, the desired UO3 cannot be obtained.

For this purpose, a light amount detector 21 is provided in a part of the enclosure 13 so that the microwave oscillation and the power supply to the heater are automatically cut off at the same time as a part of the dry matter emits light. be.

FIG. 4 is a diagram showing another shape of the container constituting the conversion device according to the present invention. A drain pipe 26 is provided to maintain a constant injection level of the nitric acid solution, and the solution overflowing the drain pipe is directed to a place where it is not heated by microwaves or a heater.

In b, the solution overflowing from the drain pipe is kept warm in the same container by doubling the container and guiding it to the bottom.The heat insulating material is also thick so that the microwave and heater do not act directly on it. By adopting this container, it is possible to homogenize the produced substances and also to easily manage the nitric acid solution overflowing from the drain pipe.

As is clear from the above explanation, according to the conversion device of the present invention, the nitric acid solution containing nuclear material is heated not only by microwaves but also by the heater provided at the bottom of the container. Convection was generated, and since the container was rotated by the driving device, the temperature of the entire nitric acid solution could be maintained uniformly while being heated, making it possible to generate a homogeneous nuclear material.

In addition, the end point of the denitrification reaction can be accurately detected by the light detector, and as a result, microwave oscillation and heater energization can be stopped instantaneously, so that the progress of the nuclear material to the appropriate oxidation state can be monitored. can be prevented.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a conventional conversion device, FIG. 2 is a diagram showing the properties of a cake produced using the same device, and FIG. 3 is a diagram showing the configuration of an embodiment of the conversion device according to the present invention. The sectional views and FIGS. 4a and 4b are views showing other shapes of the container constituting the same embodiment. 1... Nitric acid solution, 2,15... Container,
3, 13...Envelope, 11...Microwave oscillator, 14...Wind barrel, 16...
Heater, 18... Turntable, 20...
...Motor, 21...Light level detector, 23...
...Exhaust fan, 24...Scrubber.

Claims (1)

[Claims] 1. A container capable of injecting a nitric acid solution containing nuclear material and irradiating this solution with a microfluid; 5. A heater attached to the bottom of the container, a drive device for rotating the container, and a container for the reaction of the nitric acid solution. The nitric acid solution is irradiated with a microfluidic solution to heat it, and the nitric acid solution is heated by a heater to cause convection in the nitric acid solution, and the container is rotated to irradiate the nitric acid solution with microwaves. A conversion device configured to denitrify the nitric acid solution while uniformly heating the nitric acid solution with less unevenness, detect the end point of the denitrification reaction with the light amount detector, and generate a homogeneous nuclear material.