The third edition of our Quarterly Nuclear Memo tracks the nuclear developments shaping the Asia-Pacific between July and September 2026. It was a quarter of mounting strain: the US-Iran ceasefire collapsed and the IAEA Board referred Iran to the UN Security Council, US-ROK messaging on denuclearisation was ambiguous, the US-Saudi nuclear cooperation agreement hinted at enrichment, and concerns over AI-related risks grew. Yet the region also offered some encouraging developments. Tonga ratified the CTBT and acceded to the TPNW, Japan reaffirmed its Three Non-Nuclear Principles, and Pacific leaders welcomed an independent review on nuclear contamination. The Memo also flags key events to watch next quarter, including the first TPNW Review Conference and the 40th anniversary of the Rarotonga Treaty.

This Memo was prepared by APLN’s Senior Research Adviser Manpreet Sethi, Senior Policy Fellow Tanvi Kulkarni and Strategic Risk Reduction Fellow Hree P. Samudra.

Ariel (Phantitra) Phuphaphantakarn examines how quantum technologies and perceptions of their potential capabilities could reshape undersea nuclear deterrence in the Asia-Pacific. While quantum sensing could eventually challenge the stealth and survivability of nuclear-powered ballistic missile submarines (SSBNs), Ariel argues that “quantum anxiety” could fuel arms racing and heighten escalation risks well before these capabilities become operational. To address these challenges, she proposes the SIREN framework (Strategy, Investigation, Reassurance, Evaluation and Navigation) to strengthen international cooperation, transparency and nuclear risk reduction.

Julius Cesar Trajano assesses the environmental and socioeconomic risks of accidents involving nuclear-powered submarines in Southeast Asian waters and the region’s preparedness to respond. He warns that a radiological release could affect marine ecosystems, fisheries, food security and coastal livelihoods across national borders. While ASEAN already has regional nuclear emergency mechanisms in place, these are not adequately tailored to maritime incidents involving mobile, nuclear-powered vessels. Rather than establishing an entirely new system, the paper calls for ASEAN to strengthen existing arrangements by incorporating submarine accident scenarios into regional exercises, expanding marine radiation monitoring and improving coordination among relevant regulators.

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