Vladimir Stepanov is deputy director, chief designer of FGUP OKB "GIDROPRESS" (Podolsk, Russia), a honorary designer of the Russian Federation.
If possible, tell us a few words about SVBR -75/100 reactor project.
SVBR-75/100 reactor was born as conversion project from submarine reactor technology cooled by lead-bismuth coolant. Alexander Leipunsky initiated the work on development of this reactor in 50-ies of the last century.
When actuality of using this direction in the navy was canceled, we had to find new usages for lead-bismuth. Naturally, we paid attention to civil nuclear power. Together with Boris Gromov, was being the research leader of this direction, we contacted with Rosenergoatom, in particular, with director general Eugene Ignatenko, we first conceived the idea to try to prolong lifetime of the first generation units with VVER-rectors by means of lead-bismuth technology.
This moment is the start of SVBR lead-bismuth fast reactor development for civil nuclear power.
What do the figures 75/100 mean in the name of the new reactor?
We established a module concept for renovation of the units. We planned to install several SVBR-75/100 units into one VVER-reactor in the premises, where they could be placed. The value of 75 MW (el.) power was chosen proceeding from the specific project of VVER-440 units. These reactor installations have six loops, so six modules with 75 MW (el.) power allowed to keep total power at the level of 450 MW (el.).
After the problem of prolonging lifetimes of the first generation units had settled by other methods with keeping VVER reactor, our idea has not been realized. But we fulfilled feasibility studies and saw that module concept of reactor gave economic effect. Atomenergoproject (Moscow) showed in its economic calculations that the realization of this concept at the second, third and forth units of Novovoronezh NPP would be two times cheaper than the construction of the new unit with power of 1 GW (el.) at the site of Novovoronezh NPP-2.
Our proposals have been considered and approved at the Scientific-Technical Council of Rosenergoatom. The necessity to carry out feasibility studies with fulfillment of a detail design of this reactor was adopted. Nevertheless, the work was finished, because, as I have already said, the problem of Novovoronezh units had been settled by another way.
You said that power of 75 MW (el.) was defined due to renovation of VVER-units. How did you define power of 100 MW (el.)?
To improve safety of unit with fast reactor, it was necessary to use all advantages of high-temperature coolant for actual exclusion of beyond design accident. Whatever situation should be happened at NPP up to full de-energization, aircraft fall or earthquake - it shouldn't lead to melting of the core.
Power of 100MW (el.) was defined proceeding from providing afterheat removal through reactor vessel - without any external systems! - to water in reactor pit. Calculations show that reactor can be safe, without melting of the core in the regime of cooling during 5 days, even if the personnel doesn't have any actions.
Basically there are methods allowing to prolong this period for a long time as you need. The Americans suggest air cooling of the same module reactor. In their project the reactor vessel is cooled by air. But we believe that this decision has own problems. For example, what's happened if traction pipes will be destroyed? In this case the cooling will be terminated. It should be noted that the American designers had the same question in NRC.
There are other differences between our and American projects. We have a condition of transportability of reactor vessel on railway imposing a restriction on vessel diameter up to 4,5 m. In USA this restriction is 6 m. The Americans use vessels with larger diameter. For the Americans it is easier to organize the cooling by air. We had the task to keep transportability on railway, as well as maximum manufacture at plant with the aim of decreasing time for assembling at the site and increasing quality, because quality control at engineering enterprises is always higher than during assembling even of large units.
Who will be a customer of SVBR reactors?
These reactors are designed for regional customers. It is primarily the districts of Siberia and the Far East. We are going to build the first module of SVBR in Obninsk at IPPE site and to demonstrate all advantages of this technology. Further, units with various powers from 100 to 400 MW can be assembled on the basis of such technology.
SVBR has one more potential usage. Atomenergoproject, with which we cooperate tightly on development of lead-bismuth unit, considers it as NPP for heat supply. The level of safety of SVBR allows to locate it near the borders of cities. The sanitary-protection zone of NPP for heat supply with SVBR is limited by the perimeter of this NPP. As it is known, Russia is the north country and the problem of heat supply is very actual for us.
Does SVBR have prospects of export? Are there any restrictions in the project not allowing to sell it abroad?
In order to make the technology exportable, enrichment of fuel in the core was chosen less 20% in accordance with IAEA standards. The idea of this project is that these reactors will be property of Russia. Our country will construct, operate such reactors and take them back for preparing to a new period of operation, selling to customer the final product - electricity, heat or fresh water.
Now we are ready to provide continuous operation of reactor (core lifetime without fuel reloading) with oxide fuel during 8 years. Technology of this reactor is developed very well. I remind that the lifetime of SVBR reactor is suggested to 60 years.
Lead-bismuth coolant has one very important merit - its melting temperature is about 125°C. After cooling at site the coolant transfers to solid aggregation state, with all rods-absorber being at the bottom of the core and are "frozen" in the coolant. In this kind the reactor can transport to Russia for reloading of the core.
May I ask you a question about coolant? I heard the opinion that bismuth reserves in Russia are not large. Is it dangerous for us to use technology, which will require import of raw?
Actually, this question is often asked when analyzing SVBR-project. I would like to say that mining of bismuth both in Russia and in the world is defined firstly by a demand for this material. Within development of SVBR-project in accordance with our assignment an analysis has been carried out and the corresponding report has been issued, which showed that bismuth reserves at Chita deposits allowed to put into operation plants with total capacity of 70 GW. Certainly, it will require some investments.
The critics often mention about danger of polonium-210 - notorious isotope, which is formed during irradiation of bismuth.
Yes, it is also question, requiring discussion. Really, as a result of neutron irradiation of bismuth, 210Po isotope with half-life time of 138.4 day is formed. This isotope will always present in coolant after the beginning of SVBR operation.
But a part of polonium will be fixed with coolant in the kind of chemical compounds: lead polonide and bismuth polonide that was detected by experiment. Actually it creates additional barrier for 210Po proliferation and the content of volatile polonium in protective gas is decreased by several orders.
The experience of work on submarine and land reactor installations in combination with developed complexes of prohibition measures for handling with lead-bismuth provided the absence of irradiation of operational staff by polonium.
Some specialists believe that during accident with melting of the core the floating up of fuel may take place.
We couldn't find the situation yet, when SVBR core would be melted down. According too existing standards, similar beyond design accident should be analyzed. So this situation is considered in the project. We intend to introduce boron carbide rows-absorbers into that places where accumulation of fission products is possible. Thus, the problem of appearance of the secondary critical masses and spontaneous uncontrolled reaction will be excluded.
What do you say concerning the use of fuel in SVBR? How effective will be use of uranium in lead-bismuth reactor?
Our reactor is preparing to use in closed fuel cycle that corresponds to new technological platform being developed in Rosatom. SVBR is fast reactor, which can transfer to self-provision of fuel, when closed nuclear fuel cycle will be ready.In my opinion, mixed uranium-plutonium nitride fuel should be optimal for SVBR. In this case we can achieve expanded breeding of fuel inside the core without blanket with breeding gain higher than 1 that will provide fuel self-provision of reactor after the first fuel loading.
Thank you very much for interview for AtomInfo.Ru.
Note from OKB GIDROPRESS
SVBR-75/100 - reactor installation was designed within the program for prolongation of lifetime of the first generation NPP with VVER-reactors. The choice of nominal power of 75 MW (el) was due to a necessity of keeping technological scheme, possibility of full manufacture at the plant and transportation on railway. The choice of power of 100 MW (el.) was due to the requirement of safe afterheat removal through reactor vessel.
Parameters of steam generator are unified applied to the schemes of the secondary circuit for all restored units. The project was designed as base with a possibility of multipurpose modernization.
SVBR reactor installation has integral layout of the primary circuit including reactor, twelve steam generator modules and two circulation pumps.
SVBR is two-circuit reactor installation with fast reactor with liquid metal lead bismuth coolant.
SOURCE: AtomInfo.Ru
DATE: August 23, 2007
Topics: NPP, Russia, Fast breeders
