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Dhaka Saturday,  Jun 3, 2023

Interview with Aleksey Dub

Interview with Aleksey Dub the Head of TsNIITMASH Russian State Scientific Center – Scientific and Production Association the Central Research Institute of Machine Engineering Technology

New steels virtually lift limits for the operational lifetime of reactors:

Being the heart of any nuclear power plant, the reactor vessel is one of its key components. Its primary role is to prevent release of radioactive products outside the core. It is the state of the vessel that preconditions safe and reliable operation of the nuclear reactor and eventually determines the whole operational lifespan of the power system of a NPP.
Aleksey Dub, Head of PJSC RPA “TsNIITMASH”, D.Eng.Sc., Professor and a laureate of the state prize of the Russian Federation in science and technology for the set of works in developing a new class of high-strength radiation-resistant materials for nuclear reactor vessels, has told us about the new-generation materials and reactors.

What does «vessel annealing» stand for?:

During the process of operation of nuclear reactors, including those of the VVER type, weld metal changes its properties as a result of neutron irradiation, which eventually limits the safe operational lifespan of reactor vessels. Properties can be restored by thermal treatment of the reactor vessel carried out under a specific mode. In the course of this process, the vessel is slowly heated to a temperature specified and is left in the heated state for as long as required (for quite a long period of time), after which it is slowly cooled. The whole procedure takes up to 10 days. This measure allows to extend safe operation of the vessel by a minimum of 20 years, after which the procedure may be re-conducted.

What are the key role and primary objective of “CNIITMASH”?:

We have long been engaged in the development of equipment intended for the recovering thermal treatment and have been participating in such works at NPPs.

Does the reactor vessel need to be dismantled before being heated?:

No, all the work is performed without dismantling. The reactor remains in its proper location, e.g. in the reactor hall. This type of technology was used for treating VVER-440 reactors produced in Russia. For VVER-1000 reactors, “CNIITMASH’, in cooperation with “ThermIKS Ltd” and under the Rosenergoatom Concern’s program, has designed annealing equipment. The equipment comprises a heating device inserted inside the reactor vessel and a device for the external thermal insulation of the vessel.

What is the current stage of the equipment’s development and when will it be ready for operation?:

The equipment is due to be assembled this year; however, due to specific reliability requirements, its fitness for operation will only be verified after a full range of integrated tests are conducted.

What are the plants/units where it is going to be used first?:

The equipment is planned to be used at Balakovskaya NPP in 2017 and at Rostovskaya NPP afterwards. Annealing facilitated by the application of this equipment will ensure extension of lifetime for reactor vessels and, as a result, for power units.

What do technologies of forecasting metal behaviour in a reactor vessel mean? Are these technologies represented by computer software?:

At present, the basic acknowledged technique is the assessment of the state by applying the program of surveillance specimens. It is not a probabilistic program, rather it is direct testing. Significant experience has been gained in terms of the effect that various factors have on the degradation rate of metal properties. The behaviour of metal during operation is largely dependent on its initial state. To improve the characteristics that later have a significant impact on the properties, it is essential to predict metal behaviour at the stage of production. This behaviour is largely determined by the presence of impurities and the manufacturing technology used. Currently, it is being effectively studied by applying computer modelling: solidification, deformation and thermal treatment. Such a forecast allows to identify the possibility of changes in the properties of metal at the earliest stages of the technological cycle and, on this basis, to adjust the technological mode in order to obtain the required values of the metal quality characteristics.

The following question is concerned with decreasing the number of welds in the reactor vessel: are 4- and 3-weld technologies already applied?:

The reactor vessel under the AES-2006 project consists of seven parts. For VVER-TOI, “CNIITMASH” has designed a technology and equipment for a 4-weld structure. Most importantly, this structure eliminates the necessity of making a weld in the core of the reactor.
The technology has not been applied yet; it is planned to implement it at the TOI project nuclear plants that are currently under construction. A 3-weld version is also a near-term prospect as we have developed all the modes and all the necessary equipment for it.

Do you have plans for further decreasing of weld number? For example, to 2 welds?:

Further decreasing of weld number would be unreasonable.

How many parts do reactors welded by other manufacturers (the Koreans, the French, the Americans) consist of?:

So far, foreign projects do not imply such a significant reduction in the number of welds on reactor vessels. Moreover, in foreign projects even nozzles are welded to reactors, rather than forged, as in the case of our reactors.

New-class materials allow to weld billets into the vessel which is 4 m in diameter and 10 m in height. Their corrosion resistance allows them to withstand water heated up to 300° С as well as pressure of 16 MPa.

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