JPS5826012A - Manufacture of plutonium mononitride - Google Patents

Abstract

PURPOSE:To obtain high-purity PuN by a simple manufacturing method by mixing PuO2 with a chemical equiv. or more of C, reacting the mixture at a prescribed temp. in a mixed gaseous flow consisting of H2 and N2, and cooling the reaction product. CONSTITUTION:PuO2 is mixed with a chemical equiv. or more of C to increase the reaction rate and to reduce the amount of residual O2. The mixture is reacted in a mixed gaseous flow consisting of H2 and N2 to allow the reduction and nitriding of the PuO2 and a reaction for removing excess C to proceed simultaneously. After finishing the reactions, the reaction product is cooled to obtain PuN. Said PuO2 is mixed with C in 2.1-3.0mol ratio of C/PuO2. The mixture is reacted at 1,450-1,700 deg.C in a mixed gaseous flow consisting of 8-75% H2 and 92-25% N2. After finishing the reactions, that is, after finishing the discharge of CO and hydrocarbon, the reaction product is cooled to obtain PuN.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing stabilized plutonium (PuN). More specifically, the present invention provides plutonium dioxide (P
This invention relates to a method for producing stabilized plutonium by reacting a mixture of carbon (C) and a gas mixture of hydrogen and nitrogen.

For the production method of plutonium, which is a constant nuclear fuel material.

There are various methods using metals, halides and oxides as raw materials. Among these methods, development of methods using oxides as raw materials is desired because the oxides as raw materials are inexpensive and chemically stable. Among plutonium oxides, plutonium dioxide (PuO2), which is a stable phase in the atmosphere at room temperature, is a desirable raw material. Carbon is the reducing agent in the production process using plutonium dioxide as the raw material. Therefore, the main impurities are oxygen and carbon.

A conventional method for producing stabilized plutonium from plutonium dioxide will be described below.

The first method is to produce constant plutonium by reacting a mixture of plutonium dioxide and a chemical equivalent of carbon at 1.100 to 1.700° C. in a nitrogen stream. Here, chemical equivalent means that 2 moles of carbon are required for 1 mole of plutonium dioxide (PuOz) (1 mole of PuOz)
O2==271. Q y, 1 mo, 11/carbon 1
2.02). The advantage of this method is that the production reaction can be completed in one heating step. However, the disadvantage is that there is a tendency to have too much or too little carbon in the reducing agent (and as a result, the purity of the nitride tends to decrease).For this reason, there are almost no reports on plutonium-9ide produced by this method.Other nitrides From the example of product manufacturing, the amount of impurities can be expected to be 0.6% by weight or more of oxygen and 0.15% by weight of carbon.

A second method is to reduce the amount of impurity oxygen by mixing carbon in a chemical equivalent or more in advance. In this method, a mixture of plutonium dioxide and more than the chemical equivalent of carbon is reacted in a nitrogen stream at 1.600 to 1.700°C, and then
Excess carbon is removed with a hydrogen stream (afterwards, a nitriding reaction is performed to produce soltonium mononitride.

In this method: 1. Mixing of plutonium dioxide and carbon is easy. (2) Impurity oxygen in nitride can be reduced to 0.11%. It has many advantages such as), but on the other hand, the reaction process is complicated. ■Therefore, the reaction time becomes longer. There are disadvantages such as

An object of the present invention is to provide a method for producing plutonium -9ide that eliminates the disadvantages of conventional production methods. That is, it is possible to synthesize high-purity plutonium -9ide using plutonium dioxide as a raw material and provide a simple manufacturing method.

According to the present invention, in order to improve the reaction rate and reduce the amount of residual oxygen, plutonium dioxide is mixed with more than a chemical equivalent of carbon, and this mixture is reacted in a hydrogen-nitrogen mixture to reduce plutonium dimide. The reaction, nitriding reaction, and excess carbon removal reaction are allowed to proceed simultaneously, and after the reaction is completed, it is cooled to produce plutonium -9ide. To explain in more detail, the molar ratio of plutonium dioxide and carbon (C/Pu
O2) Mix at 2.1-60. This is 8-75% hydrogen
and 1.450 to 1 in a mixed stream of 92 to 25% nitrogen.
．． React at 700°C. After the reaction is completed, that is, the carbon oxide and hydrocarbons have been discharged, the reaction mixture is cooled.

Obtain plutonium mononitride using the above steps. In the method of the present invention, the reduction reaction of plutonium dioxide with carbon and the decarburization reaction of carbon with hydrogen proceed simultaneously. Therefore, it was confirmed that a minimum mixing ratio of 2.1 exists in order to prevent unreduced plutonium dioxide from remaining. Note that in the present invention, the specified temperature range (j , 450 to 1,700°C) is practically disadvantageous. Furthermore, if the hydrogen concentration in the hydrogen-nitrogen mixture gas is less than 8%, the removal of carbon by the decarburization reaction is extremely slow, which is disadvantageous in practice.

Further, at a ratio of 75 or higher, no particular increase in the carbon removal reaction rate is observed.

The structure and effects of the present invention will be specifically explained below with reference to Examples.

Example Mixing ratio of plutonium dioxide and carbon (graphite) powder (C
/PuO2: molar ratio)2. 2.6 and 6.0. Each mixture is about 0.5'? was molded into a throwlet with a diameter of 6 mm. Each R-let was reacted for a predetermined period of time in a hydrogen/nitrogen mixture of 1410 °C in a high-frequency heating furnace, and then the atmosphere in the reactor was replaced with helium and cooled.

In the example, the powder sample was molded into a pellet to prevent it from scattering, but it is clear that other shapes would have the same effect. Further, although the gas was replaced with helium during cooling, it is clear that other inert gases, nitrogen, or vacuuming would have the same effect. Furthermore, it will be obvious to those skilled in the art that cooling in a hydrogen/nitrogen gas mixture will have a similar effect.

In the method of the present invention, (1) mixing of plutonium dioxide and carbon is easy; The mixing ratio may be any value from 2.1 to 6.0. ■
The reduction of plutonium dioxide proceeds rapidly due to the addition of more carbon than is chemically acceptable. ■Since a mixed gas flow of hydrogen and nitrogen is used, the nitriding reaction and the reaction for removing excess carbon proceed simultaneously, reducing the time required for production. ■The manufacturing process is simplified and only requires one heating process. ■The purity of the plutonium mononitride produced is comparable to that produced from high-purity metals.

It has such characteristics.

Claims (1)

[Claims] 1. A mixture of plutonium dioxide and more than a chemical equivalent of carbon in a hydrogen-nitrogen mixed gas stream consisting of hydrogen and nitrogen.
A method for producing stabilized plutonium comprising reacting at a temperature of 450 to 1.700°C followed by cooling. 2. The method according to claim 1, wherein the molar ratio of carbon having a chemical equivalent or more is 2.1 to 5.0 per 1 plutonium dioxide. 3. The method according to claim 1, wherein the mixed gas of hydrogen and nitrogen comprises 8 to 75 parts of hydrogen and 92 to 25 parts of nitrogen.