VT-1 Atomic Reactor, Submarine
Both the USA and the USSR at an early stage considered two versions of reactors for nuclear submarines: water-water and liquid-metal coolant. In the version with liquid metal coolant in both countries, experimental stands were built and one submarine each. Only in the USSR, despite the problems that arose, such nuclear submarines gained the right to life, and in the USA this project in 1957 was closed completely and irrevocably.
In the USA sodium was chosen as liquid metal coolant (LMC) as it possessed the better thermo-hydraulic characteristics. The ground-based test facility-prototype of the NPI and the experimental nuclear submarine "Sea Wolf were constructed. Yet the operation experience has pointed that the choice of coolant which was chemically active with respect to oxygen and water has not justified itself. After several sodium\water interaction, the reactor was decommissioned together with the compartment and replaced by the pressurized water reactor.
In the USA the scientific and research development works were conducted on using lead-bismuth coolant (LBC), but the alternative to solving the problem of corrosion resistance of structure materials and maintenance of coolant quality (the coolant technology) did not give any positive results and those works were stopped.
The idea of using a liquid metal coolant reactor in a nuclear submarine arose in September 1952, when, by decision of the USSR government, the design of the first domestic nuclear submarine began. A proposal for the use of a reactor with an LMW was put forward by A.I. Leipunsky in his letter to the First Main Directorate, sent that same September. The feasibility of developing this direction, in his opinion, was the possibility of obtaining steam at a higher temperature.
Work began with the release on October 22, 1955 of the Decree “On the Beginning of Work on the Creation of Project 645 Submarines”. The lead ship of the project, which will eventually become the only representative of the class, was intended to deal with surface ships and transport ships of the enemy during operations at ocean and remote maritime theaters.
The design of the first nuclear submarine K-3 was taken as the basis for the nuclear submarine project, which was entrusted to SKB-143, so no pre-draft and outline designs were developed. In the fall of 1956, the technical design of the nuclear submarine was ready. Despite the fact that the initial task was to create an analogue of the K-3 nuclear submarine with a water-water reactor, cardinal differences appeared between the two boats. Heavy nuclear reactors were shifted closer to the bow of the ship, which improved its trim. This decision was largely due to an erroneous opinion about the safety of this type of reactor and entailed a deterioration in the conditions for ensuring the radiation safety of the central compartment.
The hydroelectric design bureau became the developers of the power plant under the scientific supervision of Laboratory “B” (IPPE, A.I. Leipunsky), in 1959 the OKBM joined the project. The terms of reference for the design of a reactor for a steam generating unit (PPU) with a liquid metal coolant developed by Laboratory "B" were issued to the OKBM on February 20, 1959. The terms of reference provided for several reactor options: with a lead-bismuth eutectic alloy, with liquid lithium, for a one- or two-reactor steam generating unit (PPU). Subsequently, taking into account that lithium, as a coolant, was less studied, it was decided to carry out design studies of PPU only with lead-bismuth alloy and in a two-reactor version (OK-250 index). In favor of the lead-bismuth alloy, there was also a low melting point (123 degrees).
The implementation of the installation with a lead-bismuth iron and steel matrix for a number of its features turned out to be much more difficult to develop and required the solution of such problems as:
- ensuring reliable operation of the active zones at significantly higher temperatures (up to 500-600 ° C);
- ensuring the proper quality of the alloy, referred to in the documentation as “heavy heat transfer technology”;
- ensuring the maintenance of the alloy in a hot state by both ship and basic means, which required the creation of special infrastructure in the bases.
The problem of ensuring reliable operation of steam generators with multiple forced circulation, which were adopted in this installation, was also difficult, although, according to the hydrodynamics conditions, in connection with the presence of separators in the secondary circuit, the reliability problem of pipe systems should seemingly be solved more easily than in direct-flow generators.
It was very difficult to solve the problems of sealing the primary circuit pumps. The branching of the primary circuit also gave rise to the problem of “freezing” the alloy in individual sections, which required the adoption of special measures of a constructive plan, and also led to a significant complication of the operation of the installation.
To solve these and other problems in the industry, a powerful experimental base was created, dozens of large and small stands, reactor loops, and finally, in January 1959, a full-scale prototype 27 / VT reactor stand was put into operation at the IPPE. Its operation revealed two major problems.
So, the first campaign of the operation of the stand was completed quite successfully, however, the dismantling of the active zone after the second campaign showed the presence of a large number of slags. This fact showed an underestimation by the supervisor and designers of the importance of solving the coolant problem, as a result of which systematic scientific research in this area began.
The second problem was the “freezing” of the coolant in certain parts of the lead-bismuth circuit, in particular, the first launch of the stand began with the “freezing” of the core. A number of research projects were also launched to solve it.
Another hazard was highly radioactive polonium, which forms in the core. At stand 27 / VT in the 60s, several accidents occurred with a spill of radioactive coolant, which required the development of measures and means of protecting personnel from polonium, which were later transferred to a submarine.
The development of working drawings of the submarine began in 1956 and was carried out during 1957. According to their readiness, in 1958 all the technical documentation of the project was compiled, which received the index 645 (645 ZhMT). The project provided that the main power plant (GEM) of the Project 645 nuclear submarine with a capacity of 35 thousand hp consists of a two-reactor steam generating unit (PPU) and a two-shaft steam-turbine installation. The power plant includes two VT-1 nuclear reactors with a liquid metal coolant with a total capacity of 146 MW.
The construction of the boat began in September 1957, the ship was laid down at the 402 plant (Severodvinsk) in workshop 42. In developing the new boat, a number of new design solutions were introduced and new materials were used.
The project 645 nuclear boat, which received the K-27 code, was launched on April 1, 1962. Immediately after launching, mooring trials began, which were carried out from May 8, 1962 to June 10, 1963. At the same time, the completion of the submarine was carried out, comprehensive checks of the systems, mechanisms and weapons of the ship were carried out. At the same time, the power plant was not yet fully assembled during 1962.
On August 17, 1962, fuel loading began: withdrawal parts with active zones were placed in nuclear reactors. The first reactor circuits were filled with coolant on December 6–7, the coolant was kept warm, and all systems and mechanisms of the reactor were idling. Until the end of the year, both reactors were started, and on January 8, 1963, the break-in of the mechanisms of the first circuits began. The test batch, composed of SKB-143 employees, worked on the boat, along with the tests, the reactor control systems were commissioned and transferred to the crew of the boat. On June 22, 1963, the USSR Naval flag was hoisted on the K-27 nuclear submarine, after which the boat was at sea on joint factory, sea and state tests, which successfully ended on October 30 with the signing of the acceptance certificate. It also proposed to organize a long autonomous trip of the K-27 boat for "a deeper study of the performance of the boat and its nuclear power plant." During the delivery tests, the boat passed 5760 miles in 528 running hours, which is 1.5 times more than the first-born of the Soviet nuclear submarine fleet K-3, with 3370 miles the boat was underwater.
The operation of the K-27 boat has become a series of records in the range of trips, as well as the duration and length of scuba diving. The equipment possessed unique at that time properties and characteristics, which made it possible to show the potential enemy the superiority of Soviet weapons. Moreover, all ship systems, including the power plant, worked to the limit of their capabilities, and underestimating the dangers of such operation may have led, ultimately, to the accident.
The first K-27 campaign began on April 21, 1964 and lasted 51 days. The goal of the trip was to test the boat at extreme conditions to identify the capabilities of the boat and test the systems and mechanisms of the ship in autonomous navigation. During the campaign, an emergency situation occurred with the reactor of the port side of the submarine: molten metal fell into the gas system of the primary circuit and froze there. As a result, a vacuum drop occurred in the system, and the only way to eliminate the malfunction was to work directly at the accident site, near the reactor core. The work was performed by the division commander, Captain 3rd rank A.V. Shpakov, who cut the defective tube and manually cleaned it, while receiving a significant dose of radiation. Then, the welding specialists welded the tube, restoring the reactor.
The most extreme operating conditions during the campaign were in equatorial waters, when the temperature of sea water exceeded 25 degrees. The reactor cooling systems worked to the limit of their capabilities, while the temperature in the reactor and turbogenerator compartments was about 60 0C, and the remaining compartments of the boat were heated to a temperature of 45 0C at a humidity of up to 100%. In the campaign, the boat went 12,425 miles, and almost all of them were passed under water - at that time it was a world record.
The second trip of the boat began on July 15, 1965 and lasted 60 days. The purpose of the campaign was to indicate the presence of the Soviet submarine fleet in the Mediterranean Sea, where the 6th US fleet was located. Several abnormal situations occurred during the campaign, including one “nuclear” - on August 25, the reactor power decreased as a result of its “poisoning” with xenon, which caused the ship’s power plants to operate at 35-80% of capacity.
During the trip, 15,000 miles were covered, and the boat returned to the base in Severodvinsk for repair, during which a large number of cracks were found on the light hull of the boat.
In preparation for the new campaign in January-February 1967, active zones with doubled company duration were installed on the boat. The reloading operation took place with certain difficulties, since the nuclear ship was contaminated with radioactive elements from the first to the ninth compartment. October 13, 1967 the submarine went to sea to check the systems and mechanisms of the boat. An emergency was created in the sea, the result of which was the casting of a liquid metal alloy into the gas system 1 of the starboard reactor loop. The cause of the incident was the oxidation of the lead-bismuth alloy, which resulted in the formation of slags that clogged the passage for the coolant. As a result, two pumps were flooded with a solidified radioactive alloy. For the operation of the reactor it was urgently necessary to eliminate the consequences, The cleaning of the radioactive alloy from the compartment was carried out upon returning to the base by the personnel of other combat units and divisions, as well as by the second crew of the boat. For cleaning, it was necessary to use a sledgehammer and chisels to remove radioactive metal frozen among the pipelines of the reactor. Due to the high radioactivity, the working hours were limited to ten minutes, the sailors made two to three five-minute calls, but still received high doses of radiation.
After finishing work, preparations for the campaign began. As part of the preparation, high-temperature regeneration of the alloy was carried out to eliminate oxides, but under the pressure of the Northern Fleet management the terms of work were reduced from the requested three weeks to one.
On May 24, 1968, the K-27 nuclear submarine left for the Barents Sea to test the power plant and practice combat training tasks. At 11:30, when the units were set to full speed (80% of power), the power of the port side reactor began to decrease spontaneously. The personnel, not understanding the situation, tried to increase the capacity of the nuclear reactor, but to no avail. At 12:00, the radiation level in the reactor compartment rose to 150 R / h, there was a release of radioactive gases into the premises of the reactor compartment, which was a sign of damage to nuclear fuel, and the operator reset the emergency protection of the left reactor.
As a result of low understanding of physical and chemical coolant operation processes, the substantiated specifications on impurity compositions in coolant, instrumentation for coolant quality control and equipment to provide the maintenance of required coolant qualities in the course of operation have been lacked. This level of LBC knowledge can be compared with that of water coolant when it was allowed to convey water from the water pipeline into the steam boiler.
As a result of that operation, uncontrollable accumulation of significant masses of lead oxides in the primary circuit happened, they could have formed when the pipelines of the primary circuit gas system, which were necessary for its repair, were depressurized, and thus the air penetrated into the primary circuit. Besides that, the primary circuit was contaminated by products of oil pyrolysis, which was the working medium for seals of rotational shafts of pumps that provided the gas leak proofhess of the primary circuit. Masses of oil were spilled into the primary circuit because the oil seals had not been reliable enough.
When the rate of leakage increased suddenly (it had started some time before the accident), the oxides accumulated and other impurities filled the core, that was the cause of the violent decline of heat removal. Negative temperature reactivity effect was the cause of transfer the automatic power control rod up to the upper switch terminal and spontaneous power reducing to 7% of nominal one. This was the first symptom of the accident.
But the operational documentation did not include any necessary instructions for the operator how to act when that kind of situation arose. Instead of resetting the emergency protection (EP) at the left side reactor, he followed the commander's directions (it occurred in the course of navy training) and tried to maintain the given power level by continuous removal of compensative rods (CR) out of the core. All reactivity reserve for 12 CR was released in about 30 minutes, though it was intended to provide for the power reserve generation about 4000 efficient hours. When CR were removed, the fuel in the local core area, where heat removal was deteriorated, melted and left the core together with the coolant flow. Signals of radiation hazard in the compartment that called for shutting down the RJ and removing the crew into the compartments being distantly removed from the RI were not taken into account.
As it turned out, about 20% of the heat-generating elements collapsed due to a violation of heat removal from the core. The boat surfaced, vented the infected compartments, and on one starboard reactor, which worked for both turbines, reached the base.
On May 25, a headquarters was created to deal with the consequences of the accident on the K-27 boat, which made a decision to strengthen the reactor protection and lay the emergency compartment with bags of lead shot in order to localize the zone of radioactive contamination and the consequences of radioactive contamination of the left side propulsion system.
In early June 1968, the condition of the boat was assessed by a special commission, which decided to dampen the reactors. By June 20, 1968, the submarine’s machinery and mechanisms were stopped and mothballed, the boat was decommissioned and put in Gremikha Bay.
In January-February 1973, an important experiment was conducted on the K-27 nuclear submarine. Serviceable starboard PUFs were successfully thawed and brought to a power of 20% of the nominal with steam supply. The experiment substantiated the ability to restore the operability of a reactor with a liquid metal coolant after a long shutdown.
In April 1980, it was decided to mothball the reactor compartment of the boat in order to flood the K-27 into the sea. Since May 1980, the boat was docked at the Zvyozdochka Central Station, where the reactor units with all the pipelines were filled with a special compound. On top of this compartment, 270 tons of bitumen were poured, which completely closed the reactors to prevent the penetration of sea water to the radioactive parts of the boat, leaching and contamination of the sea.
On September 10, 1981, the K-27 nuclear submarine was sunk at Karskoye at a depth of 75 meters.
The use of a reactor with a liquid-metal coolant gave rise to many problems. So, for example, in order to keep the reactor “hot” in West Face, a boiler house was built on the shore for supplying steam to submarines, and a destroyer and floating base were moored. But due to the low reliability of the coastal complex, submarines “basked” from their nuclear reactor, which was constantly operating at a minimally controlled power level.
Even in the process of designing, the imperfection of the reactor design was revealed, so several scientists opposed its use in real conditions. So, one of the leading specialists in SKB-143 energy RI Simonov at the scientific and technical council for the nomination for the prize for the development of PPU at the Iron and Steel Works asked to withdraw his candidacy because he considered the application of these installations to be erroneous.
Nevertheless, the created VT-1 reactor was a significant step in the development of ship nuclear energy. He showed the fundamental possibility of realizing the benefits of polyurethane foam with iron-ore fouling and determined the range of problems that needed to be addressed in the future when creating installations of this type.
In order to eliminate the accumulation of oxides the maintenance of some excess inert gas pressure in the gas system of the primary circuit has been provided when repair works of equipment and fuel reload are to be performed. In order to eliminate the possibility of air penetration into the primary circuit and the radioactivity yield into the environment the most possible tightness of it has been provided. For this purpose special repairing and refueling equipment have been developed.
The sensors of thermodynamic oxygen activity which enable to control the content of oxygen dissolved in LBC and detect alloy oxidizing at the very early phases have been designed and introduced Rejecting the use of the oil seals of the pumps shafts and adoption of water seals or gas-tight electric drivers of the primary circuit pumps. This eliminates the oil penetration into the primary circuit and contamination of LBC by the products of oil pyrolysis.
Using the ejection system of high-temperature hydrogen regeneration that has been built into the RI and ensures chemical recovery of lead oxides by hydrogen (the explosion proof compound of helium and hydrogen is used) and enables, if necessary, to purify even hard contaminated circuit from lead-oxides.
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