Thursday, January 27

Nuclear fission reactors have an ally that will help them continue to evolve: alloy 617

The thermal stress to which the components of the nuclear power plant reactors are subjected by fission that we currently use is extremely high. Light-water reactors operate in the 290-325 ° C range, but the fourth-generation designs engineers are working on pose new challenges. And one of them is the temperature.

Some of the most promising designs are very high temperature reactors (VHTRs) cooled by helium. Gas-cooled fast reactors (GFR), sodium-cooled fast reactors (SFR), supercritical water-cooled reactors (SCWR), lead alloy-cooled fast reactors (LFR) and salt reactors are also very interesting. fused (MSR). All of these designs have one important thing in common: their operating temperature. can easily exceed 600 ºC.

The operating temperature of high-temperature nuclear reactors can easily exceed 600 ° C.

Handling such a high temperature with absolute safety is not easy because it requires the use in the manufacture of the critical elements of the reactor, such as the vessel or the heat exchanger, chemical elements and alloys that are capable of withstand very high thermal stress without its structure being degraded and its volume being altered. This is the reason why currently the BPVC (Boiler and Pressure Vessel Code) standard, which is the one that sets out the requirements that the materials used in the manufacture of high-temperature nuclear reactors must meet, is extremely rigorous.

Until very recently only five materials had managed to exceed the requirements imposed by the BPVC standard for high-temperature nuclear reactors, while in the manufacture of a light water reactor it is possible to use up to 100 different materials. The shortage of elements available for the manufacture of the former seemed to condemn fourth-generation nuclear power plants to an uncertain future, but recently a new alloy has been included on the select list of the BPVC standard, and allows us to view the future of these nuclear fission reactors with optimism.

The fuel rods and the water that must remain in contact with them to absorb their thermal energy are housed inside a tank known as a vessel.

Alloy 617 has the answer

In order for a new material to be used in the manufacture of the critical elements of a high-temperature nuclear reactor, it is essential that it previously pass some very rigorous stress and temperature tests. In fact, for the past 30 years no new material has been added to the BPVC standard list. But the 617 alloy has done it.

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Recently and after 12 years of testing in the American INL (Idaho National Laboratory), this material has passed the validation imposed by ASME (American Association of Mechanical Engineers) and has become part of the select list of the BPVC standard. Alloy 617 is made up of chromium, cobalt, nickel and molybdenum, so that each of these chemical elements is present in a carefully defined proportion.

Alloy 617 can work at temperatures up to 950 ºC

What makes it so attractive is that its unique structural and physicochemical properties, and its resistance to oxidation, will allow it to withstand the thermal stress of high-temperature nuclear reactors with the solvency they require. In fact, according to the INL, the five materials that until recently could be used in the manufacture of these reactors could not be used at temperatures above 750 ºC, while the 617 alloy can work at temperatures up to 950 ° C.

That such promising material is available to engineers involved in the design of fourth-generation nuclear power plants invites us to view the future of nuclear energy with optimism. It is still necessary to solve two of the great challenges posed by this power generation technology: the high cost involved in starting up the power plants and Waste management. But this is another debate, and precisely some of the fourth generation nuclear power plant designs that engineers are working on propose solutions to these challenges.

Cover image | Nuclear Forum
More information | Nuclear Forum | United States Department of Energy