Lead-bismuth eutectic

Lead-bismuth eutectic, or LBE, is a eutectic alloy of lead (44.5%) and bismuth (55.5%), is used as a coolant in some nuclear reactors and is a possible coolant for the lead-cooled rapid reactor , a generation 5 nuclear reactor . LBE has a melting point of 123.5 ° C (pure lead melts at 327 ° C, pure bismuth at 271 ° C) and has a boiling point of 1670 ° C.

Lead-bismuth alloys with 30% to 75% bismuth all have melting points below 200 ° C. Alloys with between 48% and 63% bismuth have melting points below 150 ° C.

While lead expands slightly when melted and bismuth contracts slightly, LBE has a negligible change in volume when melted.

history

The Soviet Alfa-class submarines used LBE as a coolant for their nuclear reactors.

In Russia it has because of the previous use in VVER light water reactors , as well as the SVBR-75/100 via experience with this alloy.

Gen4 Energy (formerly Hyperion Power Generation ), a US company that worked with the Los Alamos National Laboratory , announced plans in 2008 to design and deploy a uranium nitride- powered Small Modular Reactor , cooled with lead-bismuth for commercial use Generation of electricity and district heating , as well as for seawater desalination . The reactor, called Gen4 modules, is planned to have a capacity of 70 MW and is of the sealed modular type, which is assembled in the factory and installed on the construction site, it is brought back to the factory for refilling.

properties

Compared to sodium-based liquid metal coolants such as sodium or NaK , lead-based coolants have significantly higher boiling points. This means that a reactor can be operated at much higher temperatures without the risk of the coolant boiling. This improves the Carnot efficiency and can enable hydrogen production through thermochemical processes.

In contrast to sodium and NaK , lead and LBE also do not react easily with water or air, which spontaneously ignite in air and react explosively with water. This means that, in contrast to sodium-cooled reactors, lead-cooled or LBE-cooled reactors do not require an intermediate coolant circuit, which impairs the performance and is higher costs for a power plant.

Both lead and bismuth are also excellent radiation shields and block gamma radiation while being practically transparent to neutrons . In contrast, after intense neutron radiation , sodium forms a potent beta emitter with the isotope ²⁴ Na with a half-life of 15 hours. This requires increased radiation protection for the primary cooling circuit.

As heavy nuclei, lead and bismuth can be used as spallation targets for the production of non-fission neutrons, as in the transmutation of waste (see Accelerator Driven System as an amplifier).

Both lead-based and sodium-based coolants have the advantage of relatively high boiling points compared to water, so there is no need to pressurize the reactor even at high temperatures. This increases safety, as it reduces the likelihood of a coolant loss and is considered in the planning as passive safety.

restrictions

Lead and LBE coolants are more corrosive to steel . For safety reasons, this requires an upper limit for the speed of the coolant flow through the reactor. Additionally, the higher melting points of lead and LBE (327 ° C and 123.5 ° C) can freeze the coolant and are more of a problem when the reactor is operated at lower temperatures.

Under neutron radiation , the isotope ²⁰⁹ bismuth present in the LBE coolant tends to capture neutrons and forms the strong alpha emitter ²¹⁰ polonium through beta decay . The presence of radioactive polonium in the coolant would require special precautions with the alpha contamination , both when filling the reactor and when handling components that have come into contact with LBE.

Areas of application

Accelerator Driven System

Individual evidence

↑ MI Bugreev: Assessment of Spent Fuel of Nuclear Submarines Alfa class . In: MRS Proceedings . 713, 2002. doi : 10.1557 / PROC-713-JJ11.61 .
↑ AV Zrodnikov, OG Grigoriev, VI Chitaykin, AV Dedoul, BF Gromov, GI Toshinsky, Yu. G. Dragunov: Multipurposed small fast reactor SVBR-75/100 cooled by plumbum-bismuth . In: International Atomic Energy Agency (Ed.): Proceedings, International Working Group on Fast Reactors . 2001 Working Material, Vienna, Austria, October 23, 2000, pp. 322–335. Retrieved December 4, 2009.
↑ The Gen4 modules, Safety & Security . Retrieved June 25, 2012.

[1] MI Bugreev: Assessment of Spent Fuel of Nuclear Submarines Alfa class . In: MRS Proceedings . 713, 2002. doi : 10.1557 / PROC-713-JJ11.61 .

[SVBR75100-2] AV Zrodnikov, OG Grigoriev, VI Chitaykin, AV Dedoul, BF Gromov, GI Toshinsky, Yu. G. Dragunov: Multipurposed small fast reactor SVBR-75/100 cooled by plumbum-bismuth . In: International Atomic Energy Agency (Ed.): Proceedings, International Working Group on Fast Reactors . 2001 Working Material, Vienna, Austria, October 23, 2000, pp. 322–335. Retrieved December 4, 2009.

[3] The Gen4 modules, Safety & Security . Retrieved June 25, 2012.