Khaski [Husky] - Propulsion
As reported, the new Russian warships can be equipped with nuclear reactors of the RITM-200 type, which are to undergo operational testing on the new icebreaker Arktika, launched in St. Petersburg in the summer of 2016.
However, iT is reported that a reactor with a liquid-metal coolant will be installed on the Husky. Such reactors on a lead-bismuth alloy were installed on the "Lira" [Alfa], and in their time they were examples of advanced developments. Atomic reactors with a liquid-metal coolant are much more efficient and compact than water-water reactors. On the one hand, the installation of such a reactor will make the boat compact: a displacement of only 6,000 tons, but on the other it will require the creation of specialized port service systems. However, all this was worked out even on the "Lira" in the Soviet era. In the early 1950s in the Soviet Union, research and design of the use of lead-bismuth alloy as the coolant for nuclear reactors was initiated by Academician A.I. Leipunsky at the Institute of Physics and Power Engineering (IPPE) in Obninsk. The principal objective of these efforts was the design and construction of nuclearreactors for submarine propulsion.
The first of these systems, a 70 MWth 27/VT land prototype reactor, achieved criticality and started full power operation at IPPE in 1959. In 1963, the first nuclear submarine with a heavy liquid metal cooled reactor was put into operation. It was designated “Project 645, Submarine K-27, NATO designation November class K-27 variant” and utilized two 73 MWth reactors.
Beginning in 1971, two new series of nuclear powered submarines termed “Projects 705 and 705K, NATO designation Alfa class” were put into operation. Both of these series utilized a single 155 MWth reactor. The distinction between the two was based on their steam supply systems, one type of which was designed by the Experimental Design Bureau of Machine Building (OKBM) and the second was designed by the Experimental Design Bureau “Gidropress” (OKB Gidropress).
In total, seven nuclear submarines of the Project 705/705K type were constructed following the original single submarine of the “Project 645” type. In addition, a second land-based prototype designated the KM-1 and mainly supporting Project 705K was put into operation at the A. P. Aleksandrov Scientific Technical Research Institute (NITI) in Sosnovy Bor in 1978. An extensive research and development program focusing on HLM coolant technology and materials, was carried out with emphasis on the chemical control of the liquid metal to avoid the possibility of plugging due to the formation of slag and to enhance corrosion resistance of internal components made from steels specifically developed for such service.
In the 1990s, there was a renewal of interest in Russia concerning lead and LBE ascoolants for civilian fast reactors. The lead-cooled BREST (the Russian acronymfor Pb-cooled fast reactor) concept developed beginning in the early 1990s isthe most widely known; in addition, the Russians placed considerable effort in the development of the LBE-cooled SVBR (the Russian acronym for lead-bismuth fast reactor) concept. The SVBR-75 was designed as a modular compact unit to be installed in the Steam Generator (SG) compartments of shut down VVER-440 type reactors.
Nuclear reactors use a wide variety of coolants, and fast reactors utilize a fission chain reaction that is sustained by fast neutrons. Liquid metal coolants (e.g., lead or sodium) are used in fast reactors, because these types of coolants do not significantly impact or moderate neutrons. However, a sodium coolant, for example, burns when exposed to air, and is corrosive, thereby resulting in safety issues. High boiling temperature (1670°C) and high heat of vaporization of lead-bismuth coolants (versus 883°C for sodium), which eliminates boiling and related loss of cooling as a realistic accident scenario.
A lead-bismuth cooled fast reactor was considered in the United States in the 1950s. However, it was abandoned in favor of sodium cooling for two reasons. Lead-bismuth coolant at the temperatures of interest can be very corrosive to structural materials. The doubling time of sodium cooled fast reactors can be significantly shorter than that of lead-bismuth cooled reactors as a result of the higher power density achievable in sodium cooled cores. There has not been any work done in the US on lead-bismuth since the 1950’s.
A liquid lead-bismuth eutectic is an alloy 44.5% lead and 55.5% bismuth with the melting temperature of 123.5°C and boiling temperature of 1670°C. This liquid’s relatively low melting point and high boiling point in addition to good heat transfer properties make it a very good candidate for a reactor coolant.
The lead-cooled reactor is possible due to the sizeable experience on lead-bismuth alloy coolant in Russian Alpha-class submarine reactors. Neutronically, the lead/bismuth energy loss due to the elastic scattering is significantly smaller than that for sodium. However, due to the presence of several thresholds for inelastic scattering in the energy interval from 0.57 to 2 MeV, the neutron energy loss in inelastic scattering is notably larger than for sodium. Therefore, the neutron spectrum of lead/bismuth cooled reactors will be decreased for energies above 1 MeV.
Liquid-metal cooled fast reactors have the following advantageous characteristics:
- Their heat transfer capability enables compact, high power-density cores. This attribute is essential to developing a relatively small (and economic) core.
- Their excellent capability for natural circulation, especially for lead-alloy cooled fast reactors with an open (loose pitch) core, provides important safety advantages and offers significant potential for heat transport system simplification.
- They have unique passive safety and autonomous operability characteristics attributable to the fast neutron energy spectrum.
Liquid lead-bismuth eutectic (LBE) is an important candidate to become the primary coolant of future, generation IV, nuclear fast reactors and Accelerator Driven System (ADS) concepts. One of the main challenges with the use of LBE as a coolant is to avoid its oxidation which results in solid lead oxide (PbO) precipitation. The chemical equilibria governing PbO formation are well understood. However, insufficient kinetic information is currently available for the development of LBE-based nuclear technology. The metastable region, above which PbO nucleation can occur, has been determined under conditions relevant for the operation of LBE cooled nuclear systems and was found to be independent of setup geometry and thus thought to be widely applicable.
Additionally, the neutron mean free path in sodium is larger than that of lead/bismuth. Therefore, the leakage of neutrons and their contribution to overall neutron balance in the system is more significant for sodium. Further, higher scattering in lead/bismuth without increasing the moderation for neutrons below 0.5 MeV prevents the neutrons from escaping from the internal parts ofthe lead-alloy cooled cores and, at the same time, provide an excellent reflecting capability for the neutrons, which escape the core.
Lead-bismuth eutectic provides a low melting point (398 K) limiting problems with freezing in the system and features a low chemical activity with water and air excluding the possibility for fire or explosions. A drawback connected with lead/bismuth is the accumulated radioactivity in lead/bismuth (mainly due to thea-emitter 210Po, T1/2 = 138 days), which could pose difficulties during fuel reloading or repair work on the primary circuit. However, IPPE Obninsk staff has developed methods to cope with the polonium during refueling and maintenance.
The Russians were able to deploy lead-bismuth cooled reactors for use in their most advanced nuclear submarines, the so-called “Alpha” class submarines, which are the fastest in the world. The Russians have built and operated seven lead-bismuth reactors in submarines and two on-shore prototypes. More recently, they have studied the design of a variety of lead and lead-bismuth reactors for electric power generation, some of which can operate with one core loading for many years and do not require any fuel reprocessing ( much of the Russian heavy metal technology is not available in the West).
Elsewhere, very long-lived core, lead-bismuth cooled, fast reactors have continued to be investigated in Japan, Korea, and in the United States.
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