1. China’s plutonium production and nuclear arms buildup

Developments concerning China’s fast breeder reactors (FBRs) in Fujian Province are drawing much attention. A satellite image taken in April 2025 (to be discussed later) shows that a massive amount of water is being discharged from Reactor 1 into the sea, indicating that the reactor is in operation. Reactor 2, under construction in an adjacent lot of land, is expected to come into operation within 2026, with its containment building nearly completed. An FBR can produce ultra-high purity plutonium-239, which is best fit for use in nuclear weapons, by reprocessing spent nuclear fuel. The US Department of Defense points to the possibility that China may use these FBRs as a plutonium supply source for nuclear arms buildup with the aim of achieving military capabilities to counterbalance those of the United States.[1]

These two FBRs have not yet come into full operation. However, when they do, it could mean the completion of a system for mass-producing weapon-grade plutonium. With an eye on this possibility, I have been making periodic observations of the state of the FBRs since 2022, sharing findings in this column or as part of the Satellite Image Analysis Project along with the latest data from Japanese and overseas research institutes.

In the course of this endeavor, the latest set of data on national stocks of plutonium released in April 2025 by the International Panel on Fissile Materials (IPFM), a group of experts investigating trends in fissile material stockpiling around the world, has raised one big question.

According to the data, China’s stockpile of plutonium was estimated to be 2.9±0.6 metric tons as of January 2024, unchanged from the level in the past three years. Based on their analyses, both the US Department of Defense and the Stockholm International Peace Research Institute (SIPRI) estimate that China has been increasing its nuclear arsenal at a pace of 60 to 100 warheads per year since 2022. However, China’s military plutonium production reactors are believed to have been shut down, and the new FBRs mentioned above have yet to come into full operation. Why is it that there has been no significant change in the amount of plutonium stockpiled in China, despite the buildup of nuclear warheads, for which plutonium must have been consumed? Dose China have a separate war-grade plutonium production facility to maintain the stockpile level? These are important questions that need to be asked in assessing the pace of nuclear warhead buildup going forward in China.

With the aim of finding answers to these questions, this article first attempts to grasp the current state of China’s plutonium holdings with reference to newly captured satellite images and various data. The last part of the article is devoted to a consideration of future developments based on findings from analysis of these data.

2. Changes in China’s stockpile of plutonium

(1) History of plutonium production

China had for many years produced plutonium in Plant 404, a military facility located in Gansu Province, and Plant 821 in Sichuan Province. However, in 1987, then-Vice Premier Li Peng declared a plan to discontinue reprocessing for military purposes at Plant 404 and to construct a new reprocessing facility for civilian purposes.[2] Meanwhile, it has been confirmed that Plant 821 had stopped plutonium production by 1989.[3] Since then, China has been focusing on the development of civilian use of nuclear energy (i.e., power generation). As of October 2025, a total of 57 nuclear power reactors—mostly pressurized water reactors (PWRs) built with technology transferred from France—are in operation in China, nearly four times the number of reactors in operation or under construction in Japan.[4] In addition, China is seeking to establish nuclear fuel cycle technology to separate plutonium by reprocessing spent fuel from PWRs and mix it with uranium to fabricate mixed oxide (MOX) fuel for use at efficient fast breeder reactors (FBRs), in view of the possibility of running out of uranium in the future.[5] It is for this purpose that China constructed the two FBRs in Fujian Province and proceeded with the construction of the civilian pilot reprocessing facility at Plant 404. The reprocessing facility at Plant 404 is said to have been commissioned in around 2010, but due to a series of defects, full-fledged operation is estimated to have started only in around 2019.[6]

Satellite Image 1: Plant 404

Source: Google Earth

After 2015, construction work began on two reprocessing plants at a desert in Gansu Province, not so far from the pilot reprocessing facility at Plant 404. Although no details are provided by the Chinese government or the China National Nuclear Corporation (CNNC), the operator of the facilities, civil engineering work on the first reprocessing plant (Plant 1) is believed to have been completed by February 2020, having moved to the equipment installation stage. Also, although no official announcement has been made, construction work on the second reprocessing plant (Plant 2) is believed to have started in around 2020.

The Gansu Province’s investment plan released in 2021 calls for investing a total of RMB300 billion (approximately JPY6.4 trillion as of October 2025) for the development of reprocessing facilities including Plants 1 and 2 mentioned above.[7] From a comparison of the following two satellite images (captured in 2021 and 2024), we can clearly see progress in construction work and it is believed that Plant 1 will go into operation within this year or in 2026. Plant 2 has some facilities not roofed yet and it will presumably start operation in or after 2030.

Satellite Image 2: Reprocessing plants in Gansu Province (November 8, 2021)

Source: Google Earth

Satellite Image 3: Reprocessing plants in Gansu Province (November 12, 2024)

Source: Google Earth

Plutonium to be fabricated at the reprocessing plants shown above is expected to be used as fuel for the FBRs in Fujian Province, of which Reactor 1 is observed to be discharging a massive amount of water as discussed at the outset of this article, with whitewater swirling at the discharge outlet (see Satellite Image 4). In order to operate safely, an FBR needs to take in approximately 50 metric tons of seawater per second to cool the peripheral equipment, and a massive discharge of water indicates that the reactor is now in test operation. Meanwhile, construction work on Reactor 2 appears to be nearing completion with the containment building roofed. While it has been confirmed that Reactor 1 began to discharge water in the summer of 2023, the discharge has since been stopped from time to time, indicating that the reactor has yet to reach the stage of full-fledged operation.[8] It would not be until 2026 that China starts obtaining plutonium by reprocessing spent fuel taken out of Reactor 1.

Satellite Image 4: FBRs in Fujian Province

Source: Google Earth

(2) Changes in China’s plutonium holdings in recent years

A comparison of China’s plutonium holdings as assessed by the IPFM and the number of nuclear warheads held by China as estimated by the SIPRI raises one question.

According to assessment by the IPFM, China’s plutonium holdings had been unchanged at 2.9 metric tons in the past few years and were estimated to be 2.9±0.6 metric tons as of the beginning of 2024, with the middle value (2.9) unchanged. Meanwhile, according to the SIPRI, the number of nuclear warheads held by China increased year by year from 350 in 2022 to 600 in 2025. In its annual report to the Congress, “Military and Security Developments Involving the People’s Republic of China 2024,” the US Department of Defense (US DoD) estimated that China “has surpassed 600 operational nuclear warheads in its stockpiles” and “will have over 1,000 operational nuclear warheads by 2030.”[9] The New Strategic Arms Reduction Treaty (New START) between the big two nuclear powers, i.e., the United States and Russia, limits the number of deployed strategic nuclear warheads for each country to 1,550. The US DoD’s report points to the possibility that China will approach that limit in the early 2030s.

However, the pace of China’s nuclear warhead buildup does not necessarily correspond well with the changes in its plutonium holdings. Due to the difference in the timing of data release between the IPFM and the SIPRI, there is no comparing data for 2025. However, from the data for the three years from 2022 to 2024, we can see that the number of nuclear warheads increased by 150. Since it takes 3.5±0.5 kilograms of plutonium to build one nuclear warhead, 450 to 600 kilograms of plutonium should have been consumed. However, the IPFM’s assessment estimates that China held 2.9±0.6 metric tons of plutonium as of the beginning of 2024. This means that despite the consumption of plutonium, China’s overall plutonium holdings have remained unchanged or possibly increased slightly.

3. Relationship between changes in plutonium holdings and nuclear warhead buildup

(1) Three scenarios

Determining the reason for this lack of correspondence is important in assessing the pace of China’s nuclear warhead buildup going forward, and I would like to present three possible scenarios to explain this.

First, it may be the case that the figures have yet to reflect the latest developments. In April every year, the IPFM provides its estimates of national stocks of plutonium as of January of the previous year, whereas the SIPRI releases, usually in September, the numbers of nuclear warheads held by each country at the beginning of the year. As we can see from Table 1, the IPFM’s estimates of plutonium holdings at the beginning of 2025 will be released in or after 2026, at which time China’s plutonium holdings may be estimated much lower than the current level.

Second, the mismatch between the two sets of data may be within the margin of error. Since China does not release data on its military plutonium holdings and the number of nuclear warheads, it is not easy to determine precise estimates. Based on the size and number of years in operation of the two military plutonium production facilities, i.e., graphite-moderate reactors at Plants 404 and 821, the IPFM estimates that China has produced a total of approximately 3.2 metric tons of plutonium for nuclear weapons and consumed some 360 kilograms for nuclear warhead production and nuclear explosion tests, leaving 2.9 metric tons in holdings.[10] However, while it has been confirmed that these two plants stopped plutonium production by 1989, it remains unknown exactly when they ceased operations and the IPFM allows for a margin of errors of ±0.6 kilograms.[11] Therefore, China might have produced a total of nearly 4 metric tons of plutonium at a maximum, and if so, it would be reasonable that China’s plutonium holdings at the beginning of 2024 were within the range of 2.9±0.6 metric tons even with the plutonium consumption associated with the increase in the number of nuclear warheads.

Third, China might have diverted civilian plutonium for military use to maintain or increase its plutonium holdings. China is partly responsible for causing the international community to hold such a suspicion. In September 2017, China, in conformity with the International Atomic Energy Agency (IAEA) Guidelines for the Management of Plutonium (INFCIRC-549), declared to the IAEA that it had 40.9 kilograms of civilian plutonium as of the end of 2016. [12] After that, however, China ceased to submit an annual INFCIRC-549 declaration without giving any specific reasons. Among the five nuclear-weapon states—i.e., the United States, Russian, China, the United Kingdom, and France—authorized under the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), China is the only one to have done so.

Table 2: Composition of derived plutonium by type of reactors

As shown in Table 2, among civilian nuclear reactors, plutonium from light water reactors (LWRs), which are used in many countries including Japan, contains a relatively low portion of plutonium-239 and thus not necessarily suitable for military use. FBRs are suitable for producing weapon grade plutonium but it is technically difficult to ensure their stable operation. Meanwhile, heavy water reactors (HWRs), another type of reactors suitable for weapon grade plutonium, have a track record of operation in various countries. HWRs use heavy water (i.e., water with a higher density than ordinary water, which is referred to as “light water” for distinction) as the coolant and the moderator to control the emission speed of neutrons, a particle that accelerates fission reactions. HWRs are advantageous in that natural uranium can be used as fuel. In addition, a higher proportion of plutonium-239 can be achieved as heavy water has lower neutron absorption in fission reactions than light water. China’s Qinshan Nuclear Power Plant, located in Zhejiang Province, has been operating two HWRs since 2002, each with an output of 728 megawatts. An HWR is capable of producing 0.8 grams of weapon grade plutonium per day per megawatt. If it operates 300 days per year, it can produce 0.8 grams x 728 megawatts x 300 days = 174,720 grams (174.72 kilograms) of weapon grade plutonium. This means that China can obtain approximately 350 kilograms of weapon grade plutonium per year by reprocessing spent nuclear fuel from the two HWRs. Mathematically, this is enough to increase the number of nuclear warheads by 100 per year.

Photo: Qinshan Nuclear Power Plant

Source: IAEA

(2) Relationship between plutonium production and nuclear warhead buildup

In any case, the quantity of plutonium believed to be currently possessed by China (around 2.9 metric tons) is much smaller compared to plutonium stockpiles in other major nuclear states, and it would not be easy to catch up with the United States and Russia in the number of nuclear warheads (see Table 3).

The fact that China is in possession of a relatively small amount of military plutonium is related to its nuclear strategy. After its successful nuclear test in 1964, China has pursued a minimum deterrence policy, which aims to deter nuclear attacks from adversaries by maintaining minimum retaliatory capabilities. More specifically, this involves building nuclear capabilities that could survive a first strike from the United States or the Soviet Union, so that China would be able to strike urban targets in the attacker country with the remaining warheads. Being inferior in economic power at the time, China sought to achieve an asymmetric equilibrium, which is to deter adversaries from using nuclear weapons by maintaining the ability to strike their urban targets, rather than a symmetric equilibrium, which is to build sufficient nuclear capabilities to destroy the attacker country with a second strike.[13] However, following the end of the Cold War, the United States began to modernize its nuclear arsenal. In 2001, the United States announced its withdrawal from the Anti-Ballistic Missile Treaty (ABMT)[14], which it had concluded with the Soviet Union, to reinforce its missile defense capabilities. These developments have undermined the assumptions upon which China’s minimum deterrence policy is based. This is because it has become difficult for China to secure a second-strike capability against the United States, due to the increased probability of any remaining warheads being nullified by the enhanced US missile defense capabilities.[15] Against this backdrop, China appears to have begun pursuing the ability—comparable to that of the United States—to mutually deliver a decisive blow to the other, by increasing the number of nuclear warheads and diversifying means of transport.[16]

With approximately 2.9 metric tons of plutonium at hand, China is capable of producing 725 to 965 additional nuclear warheads. Assuming that China has a stockpile of 600 warheads, its plutonium holdings would run out when the number of warheads reaches a level nearly equal to the upper limit for deployed nuclear warheads that had been imposed on the United States and Russia under the New START. However, if China is to follow standards for the management nuclear weapons and materials similar to those applied in the United States, it would be impractical to deploy all of the nuclear warheads available. As nuclear warheads require periodic checkups, including the replenishment of tritium every four to five years, to maintain their explosive capability, both the United States and Russia have more than 3,000 non-operational nuclear warheads. If China aims to parallel the United States in the number of warheads deployed, it needs to establish a rotational deployment system by increasing the number of non-operational nuclear warheads. However, this cannot be achieved with the current level of plutonium holdings.

Meanwhile, even though China has stopped reporting its plutonium holdings under INFCIRC-549, it would face a significant hurdle to putting the plutonium produced by reprocessing spent nuclear fuel from the self-proclaimed civilian FBRs and HWRs to military use, because such an act would imperil the national credibility of China. As a nuclear-weapon state under the NPT, China is not subject to IAEA safeguards, but in its agreement with the IAEA in 1988, China declared that “nuclear material and equipment imported to China will only be used for peaceful purposes.”[17] China’s FBRs use fuel imported from Russia, while its HWRs are of Canadian origin. At least, diverting plutonium derived from those currently operational FBRs and HWRs for military purposes would likely amount to a grave violation of an international agreement.

4. Future developments concerning plutonium production and nuclear in China

In light of these circumstances, how China’s stockpile of plutonium will change in the next two years would be an important indicator in assessing the pace of nuclear warhead buildup going forward in China and the upper limit for the number of nuclear warheads. It is thus necessary to continue tracking the stockpile of plutonium and the number of nuclear warheads held by China. I would like to point out a couple of things that need to be done for that purpose.

First, we need to think how to improve the transparency of China’s nuclear strategy. To achieve that end, a nuclear arms control agreement should be entered into between the United States and China, or possibly among the three countries including Russia, to establish a mutual verification system including onsite inspection. However, we cannot expect this to happen under the ongoing difficult international situation. Furthermore, there is unfortunately very little, if any, room for Japan to get involved in arms control negotiations between or among those nuclear-weapon states.

Meanwhile, in preventing the diversion of civilian nuclear technology, which should be pursued as a second option, Japan can play a role and there is room for cooperation with China. Should China divert its civilian technology for military purposes in violation of its agreement with the IAEA, it would lose its face before those countries that joined the NPT as non-nuclear-weapon states and have been subject to stringent IAEA safeguards. The emergence of a country daring to withdraw from the NPT to become a nuclear-armed state could cause a nuclear proliferation domino effect, which would be an unwelcome situation for China. As a country holding fast to its commitment to peaceful use of civilian nuclear technology in cooperation with the IAEA, Japan should strongly urge China to abide by its commitment to peaceful use of civilian nuclear technology. This would contribute to improving the national security environment of Japan, a country that would be directly impacted by China’s nuclear buildup.