Épure / Teutates

Épure (also referred to as Teutates, after the Celtic deity) is a joint French-UK nuclear weapons simulation program that represents one of the most significant areas of nuclear cooperation between the two European nuclear powers. The program provides both nations with access to advanced high-performance computing (HPC) resources for nuclear weapons stockpile stewardship—the science of maintaining and certifying nuclear weapons without underground nuclear testing.

The program was established under the 2010 Franco-British Defence Cooperation Treaty signed by President Nicolas Sarkozy and Prime Minister David Cameron. The treaty established a framework for unprecedented nuclear cooperation between France and the UK, including:

1. Shared computing facilities: The Épure/Teutates program involves shared access to high-performance computing resources for nuclear weapons simulation. The French Alternative Energies and Atomic Energy Commission (CEA) and the UK's Atomic Weapons Establishment (AWE) collaborate on computational physics problems relevant to nuclear weapons stewardship.

2. Joint technology development: The two nations collaborate on the development of simulation codes, numerical methods, and verification and validation techniques for nuclear weapons physics.

3. Data sharing: Limited sharing of nuclear weapons physics data to validate simulation codes and improve the accuracy of computational predictions.

4. Personnel exchange: Scientists from CEA/DAM (France) and AWE (UK) participate in exchange programs to share expertise and build collaborative relationships.

The Épure/Teutates program is distinct from the US-UK nuclear cooperation (under the Mutual Defense Agreement) and the US-French nuclear cooperation. France and the UK maintain independent nuclear deterrents and do not share warhead designs or nuclear weapons components. The cooperation is limited to computational science and simulation methodology, not weapons design or production.

The program reflects the common interest of both nations in maintaining nuclear weapons stockpile stewardship without nuclear testing. Both France and the UK have signed and ratified the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and rely on science-based stockpile stewardship to maintain the safety, security, and reliability of their nuclear arsenals.

The high-performance computing resources involved in Épure/Teutates are among the most powerful in Europe. Nuclear weapons simulation requires exascale-class computing to model the complex physics of nuclear explosions, including radiation transport, hydrodynamics, and materials science at extreme conditions.

The program connects to the broader nuclear weapons modernization efforts of both nations. France is modernizing its nuclear arsenal with the M51.3/M51.4 SLBMs, the ASN4G air-launched missile, and the SNLE 3G submarines. The UK is modernizing with the Dreadnought-class SSBNs, the Trident D5LE2 missile, and a new nuclear warhead (the Astraea warhead replacement). Both nations need advanced simulation capabilities to certify these new and modified warheads without nuclear testing.

The Épure/Teutates program represents a unique model of nuclear cooperation between two independent nuclear powers. While not as deep as the US-UK cooperation (which includes warhead design sharing under the Mutual Defense Agreement), the French-UK cooperation provides both nations with valuable scientific collaboration and cost-sharing for expensive computing infrastructure.