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«ON CONVERSION OF RESEARCH REACTORS IN RUSSIA Anatoli S. Diakov1 The nuclear research facilities (NRF) – research reactor (RR), critical (CA) and ...»

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ON CONVERSION OF RESEARCH REACTORS IN RUSSIA

Anatoli S. Diakov1

The nuclear research facilities (NRF) – research reactor (RR), critical (CA) and sub-

critical assemblies (SCA) – played a crucial role in obtaining basic and applied

knowledge in the field of nuclear physics. As a source of neutrons, the NRF represent

a unique tool for experimental research in various fields of science and technology.

Creation of nuclear weapons and nuclear energy development would be impossible without them. The number of the NRF in the world increased rapidly especially in 50-70s of the last century and by the mid '70s has reached the maximum of 390 NRF.2 Over time, NRF began to be used not only to solve the problems of defense, basic research and nuclear energy, but also in other sectors, including medicine and biology. Dozens of NRF were delivered by the Soviet Union and the United States to other countries. According to IAEA, 692 NRF of different types and different capaci- ties were built in the world over whole period of the development of nuclear physics.3 But by the early 80's the growth of number of nuclear research facilities in the world has stopped. By this time, the powerful RRs have achieved significant neutron flux density (0.5 × 1015 n/cm2 × sec), and attempts to further increase this parameter faced the problem of insufficient stability of RR construction materials. The solution of material science problems required significant research and funding efforts. On the other hand, by this time a significant base of experimental data have been accu- mulated, the use of which allowed to develop and verify computer programs to solve many practical problems in various fields without the use of NRF. For these reasons, since the mid-80s, the construction of new NRF has virtually stopped, and the proc- ess of their decommissioning became predominant. At present, there are 232 active NRFs in the world, and only 7 under construction or planned for construction.4 The principal characteristic of RR is the ratio of the neutron flux density to the reac- tor power. From the very beginning of the NRF development the top priority for re- searchers and designers was obtaining a greatest magnitude of neutron flux density into experimental channels while minimizing power reactor. Achieving the maxi- mum value of this parameter requires minimization of the RR core and the use of uranium fuel with the highest possible enrichment. For this reason, the majority of the RRs in Russia and in the United States were constructed with the use of HEU fuel, the enrichment of which reached 90% of U235.

In the late 70's, both the U.S. and the Soviet Union recognized the importance of the research reactors conversion from HEU to LEU fuel, because these reactors were the main consumers of HEU for civilian purposes, and supply of HEU fuel for the RRs in Chief Research Scientist, Center for Arms Control, Energy & Environment Studies.

1 Aksenov V.L., Archangel’sky N.V., Lopatkin A.V., Tret’yakov I.T. “Research reactors: crisis or milestones’ change?”, report at the International Scientific and Technical Conference “Research Reactors in XXI Century”, June 20-23, 2006, Moscow.

3 IAEA Research Reactors Database, http://nucleus.iaea.org/RRDB/RR/ReactorSearch.aspx?filter=0 4 “Research Reactors: Purpose and Future”, IAEA Report, http://www.iaea.org/OurWork/ST/NE/NEFW/Technical_Areas/RRS/documents/RR_Purpose_and _Future_BODY.pdf http://www.armscontrol.ru/ other countries creates a definite risk to non-proliferation regime.5 For this reason, the two countries initiated programs to develop and produce fuel for the RRs supplied to other countries, in which the enrichment of uranium was decreased from 80to 20-36%. The Soviet program on reducing enrichment of fuel for research reactors was adopted in the early '80s.6 The program included two stages of implementation: the first stage to reduce the enrichment down to 36%, and the second – below 20%.

In 1993, Russia and the United States began collaboration on the development of low-enriched fuel for RRs supplied by Russia (USSR) to other countries. This cooperation, carried out under the program Reduced Enrichment in Research and Test Reactors (RERTR) is currently ongoing. In 1994, the Ministry of Atomic Energy of the Russian Federation initiated the program "Creation of fuel rods and fuel assemblies with 20% uranium-235 enrichment fuel for the cores of research reactors."7 The main goal of the program is the development and organization of the production of fuel assemblies for Soviet design reactors in third countries. The program consists of

three main stages:

1. Design and creation of fuel rods and fuel assemblies with fuel based on UO2Al.

2. Design and creation of fuel rods and fuel assemblies with high-density fuel based on uranium-molybdenum alloys.

3. The development of fuel rods and fuel assemblies for the new generation of research reactors.

This program involves JSC TVEL, NIKIET, VNIINM, JSC NCCP, NIIAR, IPPE, IRM, RRC KI, and St. Petersburg Institute of Nuclear Physics of the Russian Academy of Sciences. As a result of the laboratory, design and technological development, and post-irradiation examination the work on the first phase is completed. The production of fuel assemblies (FA) VVR-M2 and FA of IRT-4M with enrichment below 20% is organized at the Novosibirsk Chemical Concentrate Plant for the RRs of Hungary, Ukraine, Vietnam, the Czech Republic, Uzbekistan, Libya, Bulgaria, North Korea.





Implementation of the first stage laid the foundation for the successful implementation of the intergovernmental U.S.-Russian agreement on "Cooperation for import to Russia of nuclear fuel from research reactors, produced in the Russian Federation" (RRRFR program). With the conclusion of this agreement in May 2004, the program of the research reactors conversion and removing Russian-made fresh and spent HEU fuel from third countries to Russia received an additional boost. The program involves 14 countries: Belarus, Bulgaria, Hungary, Vietnam, Kazakhstan, Latvia, Libya, Poland, Romania, Serbia, Ukraine, Uzbekistan, Czech Republic. As the result of RRRFR program implementation some 1930 kg of fresh and spent HEU fuel was returned to Russian Federation by the end of 2012.8 The entire stockpiles of HEU fuel Highly enriched uranium is the uranium with U235 isotope concentration higher than 20%.

5 N.V. Arhangelskiy, “Problems of Research Reactors Conversion from HEU to LEU. History and Perspective”, Russian-American Symposium on the Conversion of Research Reactors to LEU Moscow, 8 June, 2011.

7 Aden V.G., Kartashev E.F., Lukichev V.A., Lavrenyuk P.I., Troyanov V.M., Enin A.A., Tkachev A.A.,Vatulin A.V., Dobrikova I.V., Suprun V.B. “Russian Program of the Decreasing of Fuel Enrichment in Research Reactors: Status and Perspectives”, International Scientific and Technical Conference “Research Reactors in XXI century”, June 20-23, 2006, Moscow.

8 A. Smirnov, and at all, “Ten Years of RRRFR Program”, Safety of Nuclear Technologies and Envi

<

ronment”, №1, 2013

2 were removed from Latvia, Bulgaria, Romania, Libya, Serbia, Ukraine and Vietnam.9 It is important to note that the U.S.-Russian cooperation on the RR conversion and return of fresh and spent HEU fuel was supported by the joint statement of the Russian and U.S. presidents Vladimir Putin and George W. Bush in 2005, and Dmitry Medvedev and Barack Obama in 2009.

In Russia, despite the fact that the country has the largest number of HEU fueled RRs, the task of converting its own reactors to minimize the use of HEU was not considered until recently. Discussion of this topic among Russian experts has started only in connection with the Agreement between Rosatom and the U.S. Department of Energy, concluded in December 2010, to conduct a preliminary study on the possibility of converting six Russian RRs.10 Based on available information about the current status of the RR and plans for their use in Russia, this paper is devoted to the assessment of the prospects for their conversion.

HEU Flies Back to Russia, World Nuclear News, 04 July 2013 9 “Six Russian reactors will be converted to low enrichment fuel”, Nuclear.Ru, 07.12.2010, 10 http://www.nuclear.ru/rus/press/other_news/2118672/

–  –  –

* – reactors for which the preliminary study of the possibility of conversion is carried out according to the agreement between Rosatom and U.S. Department of Energy.

According to the Federal Service for Ecological, Technological and Nuclear Supervision data for 2011, only 22 RRs out of 33 have license to operate. Three RRs (IBR-30, VVRL-02, VVRL-03) are completely stopped and considered as excluded from the list, and eight RRs have a license for decommission or work in the final shutdown mode (MR, Gamma, RBT-10-1, Arbus, BR-10, AM-1, BARS-6 TVR). Only eighteen RRs out of 22 that have a license for operation are of interest for this paper because they use HEU fuel. Brief information on these reactors is presented below.

5 BOR-60 (NIIAR) Large experimental fast reactor with sodium coolant and 60 MW thermal power BOR-60 is designed to test fuel elements based on different fuel compositions containing plutonium. It is also used for engineering and technological studies to substantiate projects on the development of fast neutron reactors with sodium coolant, including safety studies. In addition this reactor is used for irradiation of structural materials for nuclear and thermonuclear reactors by neutrons with hard spectrum in temperature range from 300 to 1000 C.

Reactor core may consist of 85 to 124 fuel assemblies. Either uranium dioxide enriched to 90% or a mixture of uranium and plutonium dioxide is used as the fuel composition. Enrichment of uranium is within 45-90%, and the concentration of plutonium reaches 30%. In recent years, the reactor is operating at a power of 53 MW about 220-230 days per year. The time factor of utilization (the ratio of the number of full days of full power operation to the number of days in calendar year) in recent years remained at the level of 0.60-0.65. These data allow to estimate annual U235 consumption. On condition that the discharged fuel burn-up is 30%, annual consumption is up to 39 kg.

The reactor’s 20 year design lifetime was already exceeded twofold. The reactor was supposed to be renovated in 2009 with life extension until 2030. However, assessment of the performance of various reactor systems showed that the reconstruction is inappropriate. Therefore it was decided to extend the life of the BOR-60 only for the period from 2010 to 2015. However, the decision was taken recently to extend the operation of the BOR-60 up to 2020, because its use is very important for implementation of the Federal Targeted Program “The new generation for nuclear power technologies for the period 2010-2015 and further to 2020”. The operation of BOR-60 will continue until the completion of the construction of a multipurpose fast neutron research reactor (MBIR) which is to be commissioned in 2019 -2020.11 Unique characteristics of BOR-60, its use for solving scientific and practical problems, as well as approaching its decommissioning time, exclude the possibility of its conversion.

SM-3 (NIIAR) A high-flux water-cooled water-moderated tank-type SM-3 reactor with a thermal power of 100 MW is designed primarily for production of trans-uranium elements and radioactive isotopes of light elements, as well as for irradiation of reactor materials samples and for studying their properties in the process of irradiation.12 The reactor has an extremely compact core consisting of 28 fuel assemblies and with a metal beryllium reflector placed in steel vessel. FA consists of fuel rods having cruciform cross-section. Fuel meat is a composition of 90% uranium dioxide dispersed 11 “The operation term of BOR-60 will be extended after 2015”, Nuclear.Ru, 01.11.2010.

http://www.nuclear.ru/rus/press/other_news/2118217/ 12 Golovanov V.N., Yefimov V.N., Klinov A.V., Makhin V.M.

“Research Reactors of GNTs RF NIIAR:

Main Results of Operation and Use. Proposals on Using for the Development of Nuclear Technologies of XXI Century”, International Scientific and Technical Conference “Research Reactors in XXI Century”, June 20-23, 2006, Moscow.

6 in a copper matrix with addition of beryllium bronze. Mass of U235 in FA is 1,128 kg.

Average annual fuel consumption is 70 fuel assemblies or 79 kg of U235.13 The utilization factor of the reactor is sufficiently high (0.7). The design service life of the reactor is 25 years, until 2017. However, accomplished technological improvements of various reactor systems, as well as the results of calculations and experimental studies allow to talk about the possibility of its further operation beyond design service life.

Currently, work is underway to expand the experimental capabilities of the reactor in order to ensure the possibility of long-term irradiation of large-size samples of materials for NPPs. For this purpose, the amount of fuel in the core has been reduced by increasing of uranium-235 content in the existing fuel rods to 20%. Works to replace the central reactor core were planned for 2012-2014.

According to experts the conversion of reactor to LEU fuel with protection of its characteristics is not possible because of its design features.14 RBT-6 and RBT-10/2 (NIIAR) RBT-6 and RBT RBT-10/2 are the pool type research reactors designed as neutron sources for irradiating materials in order to investigate changes in their properties as well as for production of sources of radionuclides with the required properties. The reactors are used for research that does not require high rate of neutron fluence, but require the possibility of long-term experiments with high stability of parameters.

The core of RBT-6 consists of 56 spent FAs of SM-3 reactor. Average burnup of fuel assemblies loaded no less than 35%, and the burnup of discharged FAs no less than 50%. The total mass of U235 in the reactor core at the beginning of the campaign is 32-34 kg. The average duration of the campaign is about 40 days.



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