JPS58147680A - Nuclear fuel element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel element, and more particularly, to a nuclear fuel element having a configuration suitable for preventing stress corrosion cracking from occurring in a cladding tube when used in the core of a nuclear fission reactor. It is.

In currently operating nuclear reactors, nuclear fuel elements are placed within a corrosion-resistant, non-reactive, thermally conductive container within a cladding tube, and within a coolant flow channel or region. They are assembled in a lattice shape at regular intervals and assembled to form a fuel system combination (fuel assembly), and an appropriate number of these fuel system combinations are combined to form a nuclear fission chain reaction type assembly or reactor core that can perform a sustained nuclear fission reaction. However, this core is placed inside a reactor vessel through which coolant flows.

OI (cludding) of nuclear fuel material is carried out for several purposes, and one of the main purposes is to separate the nuclear fuel material and the coolant or moderator (if both coolant and moderator coexist). ) and to prevent chemical reactions. The other is to prevent radioactive fission products, some of which are gases, from escaping from the nuclear fuel into the cooling moderator, or into both the coolant and moderator if they coexist. It is in. Common coating materials include stainless steel, aluminum and its alloys, zirconium or its alloys, niobium (coronibium), and some maple! gnesium alloys, etc., but if damage to the coating occurs, i.e., loss of leakage resistance, the coolant Mamarusha reduction materials and their
! Since there is a risk that the compliant system may be contaminated with radioactive long-lived products to the extent that it may interfere with plant operation, great care must be taken in selecting the appropriate option.

When certain metals and alloys are conveniently used as cladding materials to construct nuclear fuel elements and operate nuclear reactors, various mechanical problems can occur with the cladding materials under certain conditions. Otherwise, various problems may occur due to chemical reactions occurring.

Zirconium and its alloys are excellent nuclear fuel cladding materials under normal conditions. The reason is that zirconium and its alloys have a small neutron absorption cross section, and at temperatures below 750'F, demineralized water or This is because it is strong and has treatment properties even in the presence of water vapor, is extremely stable, and is non-reactive.

However, it is clear that during operation of nuclear fuel urea, there is a problem of cracking of the cladding (stress corrosion cracking) due to complex interactions between the nuclear fuel, the cladding material, and the fission products produced during the fission reaction. Song. It has also been confirmed that this undesirable phenomenon is promoted by the localization of mechanical stress due to the expansion difference between the nuclear fuel and the cladding (the stress generated in the cladding is localized at the cracks in the nuclear fuel). Ta. Nine, corrosive fission products are released from the nuclear fuel and are concentrated at the intersection of the nuclear fuel's cracks and the cladding surface. Fission products are generated by the nuclear fuel during the nuclear fission chain reaction during operation of the nuclear reactor, and the above localized stress is magnified by the high friction between the nuclear fuel, the cladding, and the O-ring.

Due to the situation described above, current efforts are being made to restrict rounding and reactor operating methods to prevent the release of fission products and the concentration of stress due to mechanical interactions. However, this is not desirable.

The present invention has been made in view of the above, and an object thereof is to provide a nuclear fuel element that can prevent λ force corrosion cracking from occurring in the cladding tube.

This @01111 mold does not react with zirconium or zirconium alloy in the metal clad tube made of zirconium or zirconium alloy in which nuclear fuel material is loaded, and its iodide is thermodynamically stable at the operating temperature. Loaded with metals that do not react with alloys, it has nine configurations and is at dead center.

It has already been proposed to provide a metal protective film on the inner surface of the metal cladding tube of a nuclear fuel element, but these have been proposed to use a niobium layer as the protective film, or a chromium layer with stainless steel, copper,
Provided with a nickel liner, or with an aluminum liner,
A molybdenum layer is provided. The metal layer described above temporarily captures iodine released as a fission product and becomes an iodide, but zirconium iodide is thermodynamically more stable than this iodide. When metal iodide comes into contact with zirconium or zirconium alloys, it forms zirconium iodide p1
It causes stress corrosion cracking in zirconium or zirconium alloys.

Therefore, in the present invention, zirconium is made from a zirconium alloy so that the metal iodide produced by capturing iodine released as a fission product is thermodynamically more stable than zirconium iodide. One of thulium, cerium, lanthanum, yttrium, neodymium, praseodymium, and strontium was selected and loaded into the cladding tube. There are also cesium and rubidium as such metals, each of which has a melting point of 28
5Ci385C, which is not suitable due to its low melting point, is sufficiently high to maintain a rigid state at the operating temperature. FIG. 1 shows the free energy of formation when the metal oxide described above reacts with zirconium. A to g in the figure are each L”Is *
”Is * S'Im @ Cel5 +P'I 婁e
In the case of YIs * Ndl5, τ, the free energy of formation is positive i[t-, and these metals OW
This shows that chlorides do not react with zirconium.

The present invention will be described below with reference to FIGS. 2 and 3.
This will be explained in detail using figures.

JII8IlI is a section 11Fr side view showing one embodiment of the nuclear fuel element according to the present invention. In Figure 42, 1 is plutonium dioxide or plutonium dioxide or their O
A nuclear fuel pellet (nuclear fuel quality) made of a hot compound, 2 is a metal sheathed tube made of zirconium or zirconium alloy (zircaloy) loaded with a nuclear fuel pellet 1, and a metal insulation film 3 made of lanthanum is provided on the entire inside of the temporary volume t2. are loaded in close contact.

According to the embodiment described above, the fission products released from the nuclear fuel pellet 1 during use, the fission products, first react with lanthanum to form a lanthanum iodide (LaIs) shadow. Once lanthanum iodide is formed, this iodide is thermodynamically stable.For example, as shown in FIG. Even if it comes into contact with the cladding tube 2 made of Zircaloy, it does not react, and the occurrence of stress corrosion cracking in the cladding tube 2 can be prevented.

FIG. 3 corresponds to FIG. 2 showing another embodiment of the present invention.
In FIG. 3, which is a side view of #r, a metal retainer 111Jig3 made of lanthanum is loaded at a distance from the inner surface of the 41 tube 2. With this configuration, the S effect is the same.

In Figs. 2 and 3, lanthanum was used as the metal barrier film 3, but as can be seen from Fig. 1, barium, cerium, yttrium, neodymium, praseodymium, strontium, or their alloys were used. may also be used to achieve the same effect.

Furthermore, the metal retaining film 3 may be provided on a part of the inner surface of the cladding tube 2, and a similar effect can be obtained.

As explained above, according to the present invention, it is possible to prevent stress corrosion cracking from occurring in the cladding tube.

[Brief explanation of drawings]

Figure M1 is a diagram IIi showing the relationship between the free energy of 110 formation and iii* and - when each metal sulfide suddenly reacts with zircoela, and Figure 2 is a partial wR view showing an embodiment of the nuclear fuel element of the present invention. , Figure 1 is a partial cross-sectional view showing an example of the present invention O and others;
A theory showing the state in which the llW compound is in contact with the tube sheath fIAw
It is J. 1.-Nuclear fuel pellet, 2-.Claying tube, 3...Huntan 1st item 500 JOOO';A
Skin (Vera 2nd Calculation 3 Figure l! 4 Figure

Claims (1)

[Scope of Claims] 1. A nuclear fuel element in which a nuclear fuel material is loaded into a metal cladding tube made of zirconium or a zirconium alloy, in which the iodine in the cladding tube does not react with the zirconium or the zirconium alloy, and the iocide is present at the operating temperature. The nuclear fuel element is loaded with a metal that is thermodynamically stable and does not react with the zirconium alloy. 2. The metal charged in the tube is cerium, cericum alloy, lanthanum, lanthanum alloy, yttrium, yttrium alloy, neodymium, neodymium alloy, and praseodymium, praseodymium alloy, strontium or strontium alloy. Nuclear fuel element according to item 1. 3. The nuclear fuel element according to claim 1 or 2, wherein the metal loaded into the cladding tube is partially or entirely loaded inside the cladding tube. 4. The nuclear fuel element according to claim 1, 2, or 3, wherein the nuclear fuel element is uranium dioxide, plutonium dioxide, or a mixture thereof.