---
title: "Plutonium-239: Fissile Isotope Explained | Model Diplomat"
description: "Plutonium-239 is a fissile isotope crucial for nuclear weapons and breeder-reactor fuel, impacting global nonproliferation policies."
url: "https://modeldiplomat.com/learn/glossary/plutonium-239"
---

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Model Diplomat Research Team · Last reviewed June 22, 2026

TL;DR

- Plutonium-239 is a fissile isotope of plutonium, produced by neutron capture in uranium-238, used as the primary material for nuclear weapons and breeder-reactor fuel.
- What is the difference between weapons-grade and reactor-grade plutonium-239?
- Why is plutonium-239 central to India's nuclear programme?
- How does plutonium-239 differ from uranium-235?
- What is a significant quantity of plutonium under IAEA safeguards?

[Civil Service & Diplomatic Exams](https://modeldiplomat.com/learn/civil-services/glossary)Updated June 22, 2026

Plutonium-239 is a fissile isotope of plutonium, produced by neutron capture in uranium-238, used as the primary material for nuclear weapons and breeder-reactor fuel.

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## Timeline

1. 16 July 1945

   Its discovery underpinned the Manhattan Project's plutonium implosion route, culminating in the Trinity test on and the device detonated over Nagasaki on 9…

2. 9 August 1945

   Its discovery underpinned the Manhattan Project's plutonium implosion route, culminating in the Trinity test on 16 July 1945 and the device detonated over Na…

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Example

In 2008 the Nuclear Suppliers Group granted India a waiver allowing civil nuclear trade, separating its plutonium-239 breeder programme from military reactors under an India-specific IAEA safeguards agreement.

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