Implications for Civilian and Military Applications

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In recent days, discussions about the design of the world’s first and largest 24,000 TEU nuclear-powered container ship released by Jiangnan Shipbuilding Group Co., Ltd., a subsidiary of China State Shipbuilding Corporation, during the 2023 China International Maritime Technical Conference and Exhibition, are gaining momentum online.

According to reports from “China Shipbuilding News,” the 24,000 TEU nuclear-powered container ship, designated as KUN-24AP, features a fourth-generation thorium-based molten salt reactor design developed independently by China. The reactor assembly boasts lower circuit pressures and enhanced safety. The propulsion system of the 24,000 TEU nuclear-powered container ship employs an all-electric propulsion scheme with twin motors driving dual shafts and propellers, delivering high power, speed, and maneuverability.

In summary, the KUN-24AP container ship, whether in overall design or performance, has achieved internationally advanced levels.

Why Does This Stir Military Enthusiasts’ Discussion?

The focal point for military enthusiasts is undoubtedly the power system of this 24,000 TEU large container ship:

On one hand, this marks China as the fifth country, following the United States, Germany, Japan, and the Soviet Union/Russia, to propose a technical solution for nuclear-powered cargo ships. Compared to less successful designs from other countries, such as the U.S. “Savannah,” Germany’s “Otto Hahn,” and Japan’s “Mutsu,” the 24,000 TEU nuclear-powered container ship proposed by Jiangnan Shipyard exhibits advanced overall design, especially with high reliability and safety in the crucial reactor section. It can be considered the best-performing nuclear-powered container ship design overall.

On the other hand, the crucial point lies in the fact that if it is a “shipborne nuclear power unit,” it inevitably leads to speculation. Typically, the construction of nuclear-powered military vessels starts with onshore prototypes before transitioning to actual ships. Installing the unit on container ships first, utilizing it extensively, and then applying the military version to large combat ships should be the logical technological progression. Some military enthusiasts even suggest that the 24,000 TEU nuclear-powered container ship, comparable in tonnage to large military combat ships, can be concurrently designed, using civilian container ships as a “shadow design” for military vessels.

Is it a Test Ship for Nuclear Aircraft Carriers?

Is this indeed the case? Initially, there was speculation that the design of the 24,000 TEU nuclear-powered container ship could be a significant milestone in the development of nuclear propulsion for both military and civilian surface vessels. However, it seems the situation is not that straightforward, especially when considering the performance of the KUN-24AP’s nuclear power unit.

According to “China Shipbuilding News,” the ship employs a fourth-generation thorium-based molten salt reactor. The basic principle of this reactor involves the fission reaction of thorium-233, achieved by bombarding thorium-232 with neutrons, leading to its absorption of a neutron and transformation into thorium-233. Due to the easy decay of thorium-233, it transforms into the fission material uranium-233 after beta decay, thus generating reactor energy. The reactor’s primary loop uses fluorinated salt as a medium, which, after cooling through a secondary loop of fluorinated salt, transfers heat to a tertiary loop using pure water or carbon dioxide as a medium. The heat is then directed to a turbine for electricity generation, subsequently driving an electric motor through a transmission shaft to propel the propeller.

In terms of overall design, the advantages of a thorium-based molten salt reactor include lower pressure vessel requirements, absence of core meltdown risk, and relatively safe reactor byproducts. Therefore, compared to traditional pressurized water reactors primarily using enriched uranium, thorium-based molten salt reactors offer advantages such as high safety, adaptability, and the ability to be constructed in areas with limited water resources. Currently, China has already built experimental thorium-based molten salt reactor power plants in inland regions, demonstrating the specific advantages of this technology.

However, the primary drawback of thorium-based molten salt reactors lies in the use of fluorinated salt as the loop medium. This medium is highly corrosive to pressure vessels and loop pipelines, resulting in a relatively short maintenance interval for the reactor. The power of thorium-based molten salt reactors constructed in inland regions of China is currently lower, and the fluorine corrosion issue is relatively easy to address. As a shipborne reactor, the challenges include solving fluorine corrosion issues within the reactor and loop pipelines, as well as addressing salt spray corrosion during maritime operations—a significantly challenging task.

Returning to the official report from China Shipbuilding News, the KUN-24AP 24000 TEU nuclear-powered container ship, equipped with a fourth-generation thorium-based molten salt reactor, requires maintenance and material replacement every 10 to 15 years. While this interval may be acceptable for civilian ships, it poses challenges for military combat ships—equivalent to spending 3 years in dry dock every 15 years. In comparison, the U.S. Navy’s “Nimitz” class aircraft carriers, using the A4W pressurized water reactor, have a refueling complex overhaul (RCOH) cycle lasting 24 years. The process involves a 39-month, 3.26 million workday maintenance period starting in the 23rd year of service, significantly impacting normal carrier training and duty during that time.

How to extend the RCOH cycle of aircraft carriers and ensure their operational and safety rates throughout their service life has been a top priority in U.S. Navy research on military nuclear reactor development. The latest A1B-type shipborne nuclear reactor on the advanced CVN-78 “Ford” class aircraft carrier is reported to have a core lifespan of 50 years, eliminating the need for RCOH maintenance during its entire service life. This achievement highlights a stark contrast with the 10 to 15-year maintenance interval of China’s shipborne thorium-based molten salt nuclear reactor, presenting a challenge in terms of both time and operational costs and significantly impacting the normal readiness duty of military forces.

Additionally, this analysis does not consider whether civilian nuclear reactors meet military specifications. The extreme conditions and damage resistance performance of civilian nuclear reactors are likely entirely different from those of military reactors, necessitating extensive and lengthy testing and certification processes before obtaining approval to convert civilian reactors for military use. Even without considering the thorium-based nuclear reactor’s maintenance time, transitioning from civilian to military use would undoubtedly be a lengthy process. Therefore, the civilian nuclear reactor presented at the International Maritime Technology Exhibition is genuinely intended for use in civilian nuclear-powered container ships, with little relevance to military shipborne reactors.

Conclusion

After clarifying the technical characteristics and performance of the thorium-based molten salt nuclear reactor, it becomes apparent that this type of reactor is a promising solution for civilian use but falls short of military applications, especially for nuclear-powered surface combat vessels. This holds true not only for nuclear-powered surface combat vessels but also for civilian container ships using nuclear power units, which face significant challenges.

Looking at the history of countries that have built nuclear-powered cargo ships, the U.S. “Savannah” nuclear-powered cargo ship, while well-designed, ceased construction and operation due to high manufacturing and operational costs. Germany’s “Otto Hahn” nuclear-powered ore transport ship faced continuous opposition from European environmental organizations and was almost universally rejected in every port, forcing the abandonment of nuclear power in favor of conventional propulsion. Japan’s “Mutsu” faced challenges such as unreliable reactor design and opposition from local fisheries associations, ultimately leading to its discontinuation.

The only relatively successful example is Russia’s nuclear-powered icebreaker, which operates primarily in local Arctic ports. The sparsely populated and vast Arctic region allows for minimizing the potential losses in case of a nuclear incident, presenting an advantage not easily attainable for other countries’ civilian ships.

Therefore, the recently introduced KUN-24AP 24000 TEU nuclear-powered container ship from Jiangnan Shipyard has a long journey ahead, involving various challenges from crew certification for nuclear operations to gaining acceptance of nuclear-powered cargo ships in foreign ports. Moreover, maintaining a green energy advantage against new energy and bioenergy vessels poses additional hurdles. In this regard, there is much work to be done for China’s nuclear-powered container ships.

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