TVEL outlines innovation in nuclear fuel

Tuesday, 30 April 2019

In an exclusive interview with World Nuclear News, Konstantin Vergazov, TVEL's senior vice-president for Science, Technology and Quality, explained progress in these areas. Vergazov spoke to WNN on 16 April, during the XI International Forum Atomexpo 2019 held in Sochi, Russia.

MOX and REMIX

Last year Rosatom adopted a strategy with a 100-year outlook based on fast neutron reactors and thermal neutron reactors. For this, TVEL is developing mixed-oxide (MOX) fuel and REMIX fuel, with both using recycled uranium together with plutonium. This is the dual-component approach.

"We're very actively engaged in this and right now it is cost-intensive," Vergazov said. "That's just the first stage, but in the future, once we've involved plutonium and regenerated uranium into the fuel cycle, then the fuel cost of electric power production will decrease."

Rosatom plans to launch commercial fast neutron reactors first. "No other country currently has such technology in operation," Vergazov said. "At the Siberian Chemical Combine [SCC] site, in Seversk, we’re building a demonstration centre, a reactor installation, a facility for recycling used nuclear fuel and a shop floor for fabrication of nuclear fuel for the fast reactor. This is an R&D investment project and once we obtain the results we’ll apply them all over the world in the nuclear market, but we’ll start in Russia first."

The site is "at a high stage of readiness", he said. "All the necessary equipment for that fuel fabrication facility has been purchased and delivered to the site. The next stage will be to build the fast neutron reactor BREST-OD-300."

The BREST-OD-300 lead-cooled fast-neutron reactor is part of Rosatom's Proryv, or Breakthrough, project to enable a closed nuclear fuel cycle. The ultimate aim is to eliminate production of radioactive waste from nuclear power generation. The Breakthrough project comprises a fuel production/refabrication module for production of dense uranium plutonium (nitride) fuel for fast reactors; a nuclear power plant with a BREST reactor; and a used fuel retreatment module.

In December last year, TVEL launched batch production of MOX fuel assemblies for the BN-800 fast neutron reactor - constructed as unit 4 of the Beloyarsk nuclear power plant in the Sverdlovsk district - which entered commercial operation in October 2016. The 789 MWe unit's capacity exceeds that of the world's second most powerful fast reactor - the 560 MWe BN-600 Beloyarsk 3.

"But these are the first steps in a long journey," Vergazov said. "To build a commercial fast reactor is unique in the global nuclear industry and to build a new shop floor for batch production of MOX fuel means a certain amount of investment. But as our strategy is looking 50 to 100 years ahead we are ready to invest today in order to pick the fruits in the future. The strategy is based on saving costs for nuclear fuel because by incorporating plutonium and recycled uranium in the nuclear fuel cycle we save raw materials and gain economic efficiency. And we will also reprocess the nuclear waste from thermal neutron reactors - from VVER units - to obtain fuel for fast neutron reactors."

Asked whether vibropacked MOX is still seen as the way forward, or whether future production is likely to be conventional sintered MOX, Vergazov said: "We’re taking both approaches and are not limiting ourselves to just one." He added: "Although there are certain difficulties with vibropacked fuel, during fabrication, we still think this direction is a prominent one. This type of fabrication is technologically more complex than classical ceramic fuel pellets made from uranium dioxide. If we’re talking about the so called MNUP fuel - mixed nitride uranium-plutonium fuel - then this involves nitrate technology. We’ve fabricated a number of such fuel samples that are currently loaded in the BN-600 fast reactor, and we’ve also completed a feasibility study into the safety and reliability of the reactor core exploitation."

TVEL's site in Seversk is working on MNUP fuel, but it might one day also produce MOX fuel, he said.
Rosatom loaded three experimental REMIX fuel assemblies into VVER-1000 powered unit 3 of the Balakovo nuclear power plant in the Saratov region in June 2016, following issuance of a licence by regulator Rostechnadzor.

"Everything is going well with this," Vergazov said, "and we decided this year we will extend to the third cycle, each cycle being 18 months."

TVEL is still prolonging the irradiation of REMIX (from regenerated mixture) fuel in the MIR research reactor at the State Research Institute of Atomic Reactors in Dimitrovgrad, he added. "We're making very detailed studies on this and the project is not over yet, but as soon as it is we’ll provide official information on the results. It's a new experience for us and we are currently looking at the preliminary results."

On plans for a BN-1200 reactor, for which a target date of 2027 has been reported, Vergazov said: "In the near term we will be studying the idea at the site in Seversk where we are building the demonstration centre and energy complex, but there hasn't yet been any official decision about building that reactor installation, nor on making an investment into it. Within our strategy with a 100-year outlook, there are still two options of how we should develop the fast neutron reactor technology, whether we will have sodium or lead coolant."

Asked when REMIX will be commercially available, Vergazov said TVEL has completed all the necessary studies into using mixed uranium-plutonium fuel in the reactor cores of thermal units as well and not only fast neutron reactors. "We carried out irradiation tests at Balakovo NPPs to prove the results of those studies, but we ought to understand that including plutonium in the nuclear fuel cycle will have an impact on the whole fuel cycle, including the back-end. It seems very attractive to use both recycled uranium and plutonium, but that will require different approaches to handling the uranium and plutonium nuclear waste and used fuel, both in terms of recycling and storage.

"Therefore we haven't yet made the final decision on production of REMIX fuel. We're in the process of R&D work. We're not in a hurry to plan commercialisation of REMIX. Firstly we want to test our ideas in Russian-designed reactors here in Russia because in order to commercialise any technological innovation you need to be able to demonstrate to the client that it is operational. And the transportation of plutonium cross-border is also an issue which would need to be tackled. It’s not that it can’t be done, but it’s a delicate matter that would require a special approach."

Other countries could one day use the technology with their own plutonium, he said, as long as they are signatories to the Non-Proliferation Treaty.

The technology could possibly be used without modifications in a standard pressurised water reactor, he said, "but first we have to be very accurate and precise in our studies and irradiation and post-irradiation tests here in Russia and testing in our domestic market first. To offer the technology to a foreign customer, we would have to come up with a 100% robust experience of it ourselves first."

China has decided to build a fast neutron reactor - the CFR 600 - and wants the technology to be of Chinese origin, Vergazov said, adding that TVEL will fabricate fuel for it. "This fuel is currently under development and as soon as it's developed TVEL will start its fabrication at Machine Building Plant in Elektrostal," he said. "For our Chinese partners it's a completely new experience and we wish them success with it. It will mean that our strategy for involving fast reactors can be applied not just in Russia but around the world. For the whole global industry the China project will be a good reference point that proves this strategy works."

Accident-tolerant fuel

TVEL is working on four options for ATF simultaneously and all of them are being irradiated at the MIR reactor in Dimitrovgrad. The "most revolutionary" solution is non-zirconium cladding, Vergazov said.

The four are two for the cladding - coating over zirconium cladding; and non-zirconium cladding (chromium-nickel alloy) - and two for the fuel matrix - classical uranium dioxide; and uranium and molybdenum alloy. Another possible option, Vergazov said, is a uranium and silicon matrix.

"In January, we loaded the first experimental fuel cycles into the reactor. One fuel assembly is for a classical VVER reactor, another is for a PWR reactor. Each fuel assembly has fuel rods with four different combinations of the cladding materials and fuel matrix materials and that’s why we say that all four options are being irradiated now. We’re testing them simultaneously using different water loops," he said.

Asked which foreign ATF technology he finds the most interesting, he said: "We know that they are also testing uranium and silicon fuel and they are adding coatings without zirconium. Like other global players, we are trying to manufacture fuel rod cladding of silicon carbon material."

Each fuel assembly contains 24 fuel rods with different combinations of materials which are being tested in the MIR reactor under conditions as close as possible to operational ones, including the parameters of the VVER and PWR coolant. The research reactor design enables parallel studies in separate loops, which is especially important given the simultaneous fuel testing for reactors of Russian and foreign design.

VVER-1000 fuel

TVEL has developed a "fourth-generation" fuel line - TVS-4 - for VVER-1000 reactors. These fuel assemblies, with increased capacity and more advanced design, should significantly improve the economic performance of nuclear power plants while maintaining the same level of safety, the company says. Thus, the fuel component in the cost of electricity of nuclear power plants may be reduced by 2-4%. Fourth generation fuel assemblies are being introduced at European nuclear power plants with VVER reactors - last year, the third batch of TVSA-12 fuel was loaded into the Kozloduy reactors in Bulgaria and the first batch of TVSA-T.mod.2 fuel cassettes was loaded into the Temelín nuclear reactor in the Czech Republic. TVEL has plans to supply fourth-generation fuel assemblies to other countries.

TVEL is also ready to introduce fuel with an enrichment of more than 5% (up from 4.85% currently). It will allow nuclear power units to switch to the 24-month fuel cycle - that is, shutting down operations to load fresh fuel assemblies into the reactor will occur once every two years, instead of every year and a half, as it is now.

Rosenergoatom, the nuclear power plant operator subsidiary of Rosatom, has already transferred its VVER-1000s from the 12-month fuel cycle to the 18-month one. The same is planned for the VVER-1200 reactors.