ZA200509729B

ZA200509729B - Zirconium alloy and components for the core of light water cooled nuclear reactors

Info

Publication number: ZA200509729B
Application number: ZA200509729A
Authority: ZA
Inventors: Garzarolli Friedrich; Seibold Angelika; Ruhmann Heinrich
Original assignee: Framatome Anp Gmbh
Priority date: 2003-07-16
Filing date: 2005-12-01
Publication date: 2006-10-25
Also published as: KR100766202B1; WO2005007908A2; US20060225815A1; JP4417378B2; TW200510550A; DE502004001861D1; TWI315343B; WO2005007908A3; DE10332239B3; ATE343655T1; EP1627090B1; KR20060027865A; JP2009513821A; ES2274482T3; EP1627090A2; CN1833038A; CN100372954C

Description

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Description

Zirconium alloy and components for the core of light-water-cooled nuclear reactors

The invention relates to a zirconium alloy and to structural parts made from an alloy of this type for the core of light-water-cooled nuclear reactors, in particular of pressurized-water reactors. Structural parts of this type are in particular fuel cladding tubes, spacers and control rod guide tubes.

For physical reasons, zirconium, which has a low . neutron absorption, is used as base metal for structural parts used in reactor cores. On account of . the separation of the neutron absorber hafnium, it is customary to use reactor-pure zirconium sponge, the composition of which is governed by standards.

Zircaloy-2 (for boiling-water reactors) and Zircaloy-4 (for pressurized-water reactors) or other zirconium- ‘based alloys, for example those known from

DE 38 05 124 Al, DE 690 10 115 T2 and WO 01/24193 Al, are nowadays generally used for the abovementioned

BE 25 purpose. Binary Zr-Nb alloys are also used to a lesser extent.

The table which follows gives the compositions of zirconium sponge and the standardized alloys which have hitherto been customary in Western engineering. In this context, it should be mentioned that nowadays some of the permitted impurities can be set in a ‘particularly controlled way or even, by using suitable additions, set to specific values. By way of example, on account of its hardening action on zirconium, oxygen was originally controlled only to levels corresponding to manufacturing requirements, but nowadays it is actually used deliberately as a hardening addition.

Table

Reactor-pure zirconium (maximum contents in ppm):

Al B Cd C Cl H HE Fe 0 Si - 75 0.5 0.5 250 1300 25 100 1500 1600 20

Composition of Zircaloy and ZrNb alloys (in % by mass):

Sn Fe Cr Ni Other stipulations

Zircaloy-2: 1.2 - 1.7 0.07 - 0.20 0.05 - 0.15 0.03 - 0.08 0.18 - 0.36

FeCrNi _. Zircaloy-4: 1.2 - 1.7 0.18 - 0.24 0.07 - 0.13 <0.007 0.28 .- 0.37 : FeCr

Zr-2, 5%Nb: <0.05 <0.150 £0.02 <0.007 2.40 - 2.80%

Nb

It is an object of the invention to propose a further zirconium alloy and structural parts produced therefrom for the core of light water reactors.

This object is achieved as described in claims 1 and 5.

The alloy proposed according to claim 1 is composed of a matrix of reactor-pure zirconium together with 0.2 to 0.5% of Sn, 0.2 to 0.5% of Nb, 0.05 to 0.40% of Fe and 0.02 to 0.20% of V, with the carbon content being } restricted to at most 120 ppm, and a range of from 80 to 120 ppm for Si and from 0.12 to 0.20 ppm for O being maintained. It has been found that alloys of this type can be used to produce components, e.g. cladding tubes, spacers, guide tubes and further structural elements of a fuel element, for the core of light water reactors, in particular of pressurized-water reactors, which have an improved resistance to corrosion compared to components made from Zircaloy-4, while maintaining substantially the same production and comparable heat treatment. This property is particularly pronounced if the sum of the alloying constituents Sn, Nb, Fe and V does not exceed a value of approximately 1.3%. This means that the Sn and Nb contents cannot be selected completely freely. Rather, to achieve optimum results with regard to the corrosion properties, the level of the transition metal Fe or the transition metals Fe and

V must drop if the total amount of Sn and Nb increases.

Values higher than 0.5% of Sn, for example up to 0.75%, have an adverse effect on the corrosion resistance, increase the radiation~induced growth, while the mechanical properties are significantly improved, which means that the proposed value of at most 0.5% represents a good compromise. The minimum Sn content at ; which components with good mechanical properties can still be produced is 0.2%.

Vanadium is an addition which is not absolutely . imperative with a view to improving the corrosion properties. For example, it is possible to increase the corrosion resistance with a high burn-up using Sn contents of 0.4% to 0.5%. However, if some of the iron is replaced by V or if V is added to the alloy in small ) quantities (0.02 to 0.20%), the hydrogen pickup factor (HPUF) and therefore the formation of hydrides, which in addition to embrittling the material also cause . material growth, is reduced.

To achieve an optimum creep rupture strength and at the same time a yield strength with a high value, it is possible to add Nb to the alloy in an amount of up to 0.8%, preferably up to its solubility limit, i.e. up to 0.5%. If this 1limit is not significantly exceeded, there is no risk of uncontrolled phase transitions, which result at relatively high temperatures, e.g. when welding spacers or cladding tubes to their end stoppers, on account of the complicated phase diagrams of ZrNb. Consequently, it should not be necessary for the alloy according to the invention to be subjected to a further heat treatment following welding.

Furthermore, the alloys are relatively insensitive to the effects of high heating surface stresses and local boiling processes at the interface with water. In this context, in particular a low uptake of lithium and a low level of nodular corrosion - as 1s found with cladding tubes made from Zirkaloy-4 under standard pressurized-water conditions - are observed. Moreover, they have a low radiation-induced growth.

Exemplary embodiments: lsn(e) |wo(s) [rey [ vin) [o0s) [sippm | cippm) |] 8 10.30 0.45 [0.15 [0.10 [0.14 [130 [100 c Jo.40 o.45 [0.10 Jo.07 Jo.aa]ai0 [100 p [0.30 0.75 [0.13 [0.07 [ozafaz0 J1o0 remainder: in each reactor-pure unalloyed zirconium with permitted foreign substances or impurities. ’

To produce cladding tubes, ingots of the alloys A to D are melted in vacuo in a number of melting steps and then forged in the p-range of the alloys below the melting point. The forgings are heated again to a g 20 temperature in the B-range and then quenched in a water bath with a cooling rate of at least 30 K/s. The forgings are then forged to form rods.

The forged rods are machined and cut into pieces which are used to extrude tubes. To obtain a fully recrystalized microstructure, an anneal is carried out after the extrusion. The tubes treated in this way are pilgered in a number of steps by cold-forming to form cladding tubes. Prior to each deformation operation, an intermediate anneal is carried out in vacuo at temperatures of approximately 700°C, which brings about recovery and recrystalization. The final deformation, which leads to the definitive cross section of the cladding tube, is followed by a final anneal at approximately 600°C. In this way, a low creep deformation with a high yield strength is set for the intended reactor use. A cumulative annealing parameter in the range A = 10-40 E-18 h is maintained during production. It is in addition optionally possible to carry out an anneal in the alpha range following - production of the forged rods.

The cladding tubes which have been produced in the manner outlined are finally filled with fuel pellets and welded to end stoppers in a gastight manner at both ends. This concludes production of the fuel rods. . Control rod guide tubes are also produced by the same process.

In another exemplary embodiment, following corresponding heating and quenching of an ingot of the same composition, the forging is hot-rolled (once or in a number of steps with anneals between them) to form plates. For the hot-forming and intermediate annealing steps, the temperatures are selected in such a way that they are in the a-range of the alloys. Then, the plate is cold-rolled in a number of steps to form a metal ; 25 sheet of the desired thickness. Between the deformation steps and following the final deformation, a vacuum anneal is carried out, which can also take place as a continuous process and brings about complete recrystalization. These metal sheets are processed further to form spacers.

If spacers, guide tubes and fuel rods produced in this way are used in a pressurized-water reactor, these components have better corrosion properties, in particular after a prolonged operating period, compared to components made from conventional Zircaloy-4 with a low tin content (low tin Zirc-4), as can be established from empirical calculations. The results of these calculations are disclosed in the diagram below.

The burn-up is plotted on the abscissa and the oxide layer thickness on the ordinate.

It can be seen that the alloys according to the invention can remain in the reactor for approximately twice as long (6 cycles) as the conventional alloys (3 cycles) before they have to be replaced for corrosion reasons. (All percentages are in percent by mass). )

Claims

1. A zirconium alloy having the following composition (per cent by mass):

5 . Sn: 0.2 - 0.5% Nb: 0.2 - 0.8% Fe: 0.05 - 0.40% Vv: 0 - 0.20% 0: 0.12 - 0.20% Si: 80 ~ 120 ppm C: < 120 ppm

}

2. The alloy as claimed in claim 1, characterized by an Nb content of at most 0.5%.

3. The alloy as claimed in claim 1 or 2, characterized in that it contains at least 0.07% of V.

4. The alloy as claimed in one of claims 1 to 3, characterized in that the sum of the Sn, Nb, Fe and V contents is at most 1.3%.

5. A component for the core of a light water reactor, J 25 in particular a pressurized-water reactor, characterized in that it is made from the alloy as claimed in one of claims 1 to 4.

6. The component as claimed in claim 5, characterized in that it is produced maintaining a cumulative annealing parameter of (10 - 40)E-18 h.