On the questions of AtomInfo.Ru web-edition answers the Designing manager of reactor facility energy channels of the Federal State Unitary Enterprise NIKIET Anatoly Petrov.
Anatoly Aleksandrovich, first of all we would like to ask you to remind our readers of how was the channel reactor direction in domestic reactor building industry arising.
Main stages of the development of domestic channel researches are the following.
The first domestic industrial uranium-graphite reactor (UGR) "A" was built at the Enterprise "Mayak" in Chelyabinsk according to the design, elaborated by the hydraulic department of NIIHIMMASH (later NIKIET) under the direction of I.V.Kurchatov (research manager). Reactor was launched on the 19th of June 1948, and now it is the sixties anniversary from the date of its launch. Materials for our first nuclear devices were recovered at this reactor.
The reactor differs constructively from the industrial US reactors built earlier that had horizontal disposition of fuel channels. All domestic channel reactors have vertical channel disposition.On the base of the reactor "A" project, taking into account experience of its exploitation, the whole series of UGR was elaborated and created. Part of these reactors was designed in NIKIET, and another part in KB (designing bureau) - today OKBM named after I.I.Africantov.
At the early fifties N.A.Dollegal and I.V.Kurchatov paid attention to the ineffective use of heat by the weapon materials producing. At their suggestion a project of the first double-purpose reactor in the world "EI-2" was elaborated and realized that used technological heat for electricity producing. All UGRs, built after "EI-2" (launched in 1958) were dual-purposed. Simultaneously the task of using nuclear energy for generating electricity had been solved. Project of the first NPP in the world in Obninsk was elaborated. In summer 1954 launch of this small (5 Mwe) nuclear facility with uranium-graphite reactor took place. We have left Englishmen over for two weeks then.
N.A. Dollegal's passion was increasing the effectiveness of the nuclear energy, and he came out with the idea of nuclear steam overheating that allowed increasing of NPP efficiency. So in 1964 and in 1967 at Beloyarskaya NPP power units with AMB-1 and AMB-2 reactors with the capacity of 100 and 200 Mwe were born. In sixties the stable development of national economy demanded a rapid growth of electricity generating, and a plan of an intensive development of nuclear energy with the launch of 3-4 power units with 1000 Mwe capacity annually to the end of seventies was adopted.
At that time own possibilities were estimated rather precisely. Analysis of our energy machine building industry showed, that it was impossible to achieve the desired results using only one type of reactors (VVER). Equipment for NPPs should be produced parallel at different plants. At that time a task to design and organize producing of main equipment for low-capacity channel reactor power units (RBMK), at large defense and common machine building enterprises was put forward. The task was successfully fulfilled and in December 1973 at Leningradskaya NPP main unit with RBMK-1000 reactor was launched. The first unit with VVER-1000 reactor was launched some years later. Replicating of nuclear power units with RBMK reactor has begun (6 units of the first generation) at Leningradskaya, Kurskaya and Chernobilskaya NPPs.
Restless N.A.Dollegal demanded increasing of a unit capacity in 1.5 times at the expense of heat exchange intensification. And in December 1983 at Ignalinskaya NPP reactor RBMK-1500 with the highest at that time capacity in the world was launched. Later in 1986 happened a Chernobyl tragedy, assertion of channel reactors right for the existence before foreign and domestic experts, a chain of continuous reconstructions and modernizations, safety increasing procedures followed.
Nowadays channel reactors have already worked more than 500 reactor-years, their contribution to the energy producing at Russian NPPs is something about 50%.
Lifetime of power units of the first generation with RMBK reactors comes to the end. Are there any plans of prolongation their lifetime? How do you estimate the results of the lifetime prolongation of the first unit at Leningradskaya NPP?
A designed lifetime of power units with RBMK reactors as of all the other reactors operating in the country is 30 years. All over the world work on specification of a real resource of the main unchangeable NPP equipment is carried out in order to define for how long it is really possible to operate a NPP safely.
We are also carrying out such a type of work. We have specified that so-called "critical" elements are the graphite laying and metal constructions of the reactor. Examination of a real state of this junctions and estimation of their residual life showed that by a proper exploitation it is possible to prolong the lifetime of power units with RBMK reactors for 15 years above the 30 designed. Nowadays unit #1 at Leningradskaya NPP has worked completely 5 years after its first designed lifetime period. Today there are no any reasons to doubt the correctness of our estimations. Today another 3 units of the first generation - the 2nd of Leningradskaya NPP, the 1st and the 2nd of Kurskaya NPP have passed the procedure of their lifetime prolongation.
Works on modernization before the lifetime prolongation are close to the end at the 3rd power unit of Leningradskaya NPP. This way lifetime of other 6 power units will be prolonged.
At least one more unit with RBMK reactor - the 5th unit of Kurskaya NPP may appear in Russia. What are the main changes made in the design of this reactor comparing with the old one?
We all hope that this long-suffering unit will be launched soon. But it is not wisely to launch a unit, that is completed only on 70%. Remaining equipment, devices, control systems are still being produced for the modernization of operating power units. Safety level of this power unit corresponds with the safety of NPPs that are built today in Russia and abroad.
During the years of the forced conservation design of the unit was improved many times. Perfect neutron-physic characteristics achieved at the expense of 20% graphite layer volume reducing differs this unit from the operating ones. Reactor is equipped with system of localization of radioactive wastes from the upper rooms of the reactor. Modern deep redundant inspection, control and safety systems are installed their. Dehydration effect of the safety control system cooling circuit is 4 times reduced at the expense of using cluster rods in the composite inspection and control system. Power unit is equipped with the modern monitoring systems of main technological processes and has an optimal set of safety systems.
Please, tell us some words about the experience of exploitation and perspectives of fuel elements and RBMK fuel assemblies modernization.
RBMK has gone through many changes during its 35 years history. Fuel enrichment was increased from 1.8% to 2% (235U) to increase the burnup. Then, after Chernobyl incident, uranium enrichment was increased to 2.4% in order to reduce the steam radioactivity effect. This way within the active zone was remaining a big amount of so-called supplementary absorbers (SA) that reducing αφ worsened economic characteristics of power units because of the supplementary neutron capture.
Fuel with the addition of burning out erbium absorber was worked out some years ago for RBMK. In 1996 loading of this fuel of 2.6% enrichment started and from 2001 enrichment was increased to 2.8%. As the old fuel was replaced by uranium-erbium one, systematic SA unloading and αφ reducing began, and a burnup fraction of the unloaded fuel increased. At the expense of uranium-erbium fuel this characteristics increased today from 20.9 to 25.8 Mwe×day/kgU. Burnup will be increasing further as the reactors will be loaded with uranium-erbium fuel.
Next step in the improvement of fuel using efficiency at RBMK will be the introduction of a so-called profiled uranium-erbium fuel. Central part of fuel elements in such fuel assemblies is filled with the fuel of 3.2% enrichment, and a profiled zone has a 2.5% enrichment with the corresponding erbium content.
Nowadays the factory is going to produce the pilot batch of such fuel assemblies. Designed burnup depth by the transition to this fuel will be 33-35 Mwe×day/kgU.
Fuel elements and assemblies construction has been changing. Mainstreams of fuel elements modernization was a transition to the fuel pellets with the central aperture and corresponding faces and a modernization of end plugs welding junctions. Spacer grids made from stainless steel were replaced by zirconium ones in fuel assemblies, fuel element clusters were made with central fastening, besides fuel assemblies with antidebrise filters were designed.
MKERs (small channel power reactor) are often called "concentration of experience of domestic channel reactors building". What is the state of this project nowadays?
Unfortunately there is nothing to boast here.
In 2001 Minatom administration took a decision to develop in Russia only one direction of reactor building - vessel one.
With the support of Leningradkaya NPP, Russian scientific research center of designing managers we have made engineering, designing and calculating elaborations of power characteristics of some reactor facilities of the third generation: MKER-860, MKER-1000, MKER-1500 in 1989-2002. First two reactor facilities - with the natural coolant circulation, intensified by ejectors, the third reactor facility - with the forced coolant circulation.
In these elaborations we tried to realize the most useful characteristics and advantages of the channel reactor conception. But it didn't come further than to designing, moreover channel direction was not included in the plans of innovative technologies development. Principally, if it is necessary to have an implementable second reactor technology for the rapid development of domestic nuclear sector as it was in early seventies, we are ready to help. Still we have factories, ready to produce main equipment for channel reactor facilities, there is experience and specialists to cope with this task operatively.
What new concepts of channel reactors may appear in Russia in the future?
All civilized world is choosing new innovative energy producing technologies. Developed countries have already decided a lot.
Among six reactor technologies, that are recognized as worthy of rapid development (Program G-IV), there are reactors with supercritical coolant parameters (SKD). Over this direction are actively working Canada, France, Japan, South Korea and so on. In Russia we have a unique experience of designing and exploiting reactors with steam overheating. At that time technological unavailability of the industry and a lack of materials made us a bad turn. Situation is better now, but problems of elaborating and choosing necessary materials are also playing a paramount role.
In order not to drop behind from the leading mainstreams in reactorbuilding we have conceptually elaborated channel SKD reactors with heavy-water and graphite moderator, estimated their safety and technological performability. It became clear, that the channel design is much better for the reactor with SKD then the vessel one. This way efficiency of this reactor will be 43-45%, it will be much simpler, especially using direct-flow scheme of steam branching to the turbine. Capital spending on building of such reactors will be significantly lower.
Everything goes well, but a lot of spending should be made on necessary materials elaborating and testing. It is impossible without serious financial support either from the federal budget or from Rosatom. There is no such a direction in the list of the innovative technologies.
Thank you for the interview for the AtomInfo.Ru web-edition.
SOURCE: AtomInfo.Ru
DATE: May 10, 2008