Project 705 Lira / Alfa class - Propulsion
Project 705 used a revolutionary liquid-metal-core reactor that allowed the attack submarine to reach the fantastic speed of over 40 knots (over 75 km/h) in just one minute. The reactors required a heater to prevent the liquid metal coolant from solidifying. In 1972 the reactor on K-377 suffered a casualty during sea trials and the metal coolant "froze" destroying the reactor. In 1982 the reactor on K.316 was destroyed when the heating system was accidentally turned off. A special facility was constructed the submarines were moored to supply superheated steam to heat the liquid metal when the reactors were shut down. External heating proved unsatisfactory, and the reactors had to be kept running even while the submarines were in port.
Due to the peculiarities of its energy installations, which did not require a special switch to for higher power settings with increasing speed, as it was on other boats with water reactors, the submarines of Project 705 could develop full speed within one minute. High speed allows quickly going to the "shadow" sector of any surface or underwater craft, even if the boat was discovered by underwater acoustic sensors of the enemy. High speed and maneuverability of the Project 705 allowed working out effective evasive maneuvers of the enemy torpedoes fired followed by a counterattack. In particular, the boat can travel at maximum speed to carry out the circulation at 180° and within 42 seconds to reverse course.
Two different models of liquid metal (probably lead-bismuth) reactors were used. The four boats built at the Admiralty shipyard used the BM-40A reactor with two separate steam loops and circulating pumps. The boats built at Severodvinsk [Project 705K] used the OK-550 with branched first-loop lines and triple circulating loops and pumps.
There were significant drawbacks to both plants because the use of a liquid-metal heat carrier required always keeping the alloy in a liquid (heated) condition of 257°F (125°C) and, in order to avoid it “freezing up,” the plant could not be shut down as was done on submarines with a pressurized-water plant. If the solution hardens, it will be impossible to restart the reactor, for the fuel assemblies will have been frozen in the solidified coolant.
At Zapadnaya Litsa on the Kola Peninsula, the base for these submarines, a special land-based complex was built with a system to provide steam to keep the liquid metal in the submarine reactors from solidifying when the reactors were turned off. Near the piers where the submarines were moored, a special facility was constructed to deliver superheated steam to the vessels' reactors when the reactors were shut down. A smaller ship was also stationed at the pier to deliver steam from its steam plant to the Alfa submarines; however, this method of external heating proved to be unsatisfactory, and the submarine reactors consequently had to be kept running even while they were in harbor.
In addition, a frigate and floating barracks barge supplied supplemental steam to the submarines at the piers. Because of the inherent dangers of using these external sources of heat, the submarine reactors were usually kept running when in port, albeit at low power.
The facilities completely broke down early in the 1980s, and since then, the reactors of all of the operational Alfa submarines were kept constantly running. This led to extra wear on the reactors and required that the vessels be constantly manned. Indeed, the difficulty of trying to externally heat the submarine reactors was one of the reasons that the Alfa class was taken out of service in the late 1980s.
The reactors of the Alfa class submarines were never refuelled as were the pressurised water reactors of other types of submarines, for it was simply not technically possible to remove the fuel assemblies without the metal coolant solidifying in the process. The term "single use reactors" is therefore applied to the Alfa reactors.
|
NEWSLETTER
|
| Join the GlobalSecurity.org mailing list |
|
|
|
