Conference Agenda

Effective verification of irreversible nuclear disarmament requires innovative frameworks capable of addressing the inherent complexities and risks of disarmament processes. Verification authorities must strategically allocate their limited annual inspections across various categories, necessitating a careful balance of priorities regarding inspection objectives, timing, and frequency. Given the importance of these decisions, the lack of research adopting a holistic, systems-level perspective that prioritizes long-term verification activities in line with planned steps toward irreversibility is concerning. Moreover, the effectiveness of verification strategies at different stages of disarmament-particularly in the post-disarmament period-has not been adequately examined. The State-Level Concept (SLC), developed by the IAEA to enhance the effectiveness of nuclear safeguards implementation, represents a transformative shift by moving from facility-specific evaluations to comprehensive state-level assessments. At its core is Acquisition Path Analysis (APA), which systematically identifies and evaluates potential pathways a state could exploit to acquire weapons-usable material. Complementing this, the IAEA's physical model provides a tailored framework that maps the technical processes required to transform source material into weapons-usable nuclear material, customized to each state's unique nuclear infrastructure. By integrating a systems-based approach and physical modeling, the SLC could offer a transparent framework to define precise verification objectives, analyze technically plausible pathways, and prioritize measures strategically, enhancing effectiveness of disarmament treaties. Therefore , this study proposes a systems-based approach to disarmament verification, focusing on optimally allocating limited inspection resources across different nuclear disarmament phases. Adapted physical model is used to address state-specific nuclear infrastructures, incorporating elements such as civilian and military facilities. Through directed graph modeling, the research identifies and ranks technically plausible cheating pathways, with particular emphasis on concealed activities during warhead dismantlement and weapon-usable material disposition. It is coupled with strategic assessments using game theory to optimize inspection priorities and resource allocation. To ground the analysis, a comparative case study examines how different irreversibility steps in disarmament — specifically during the drawdown and complete end-state phases — influence the allocation of verification resources. Verification strategies were tailored to each phase, with resources shifting from verifying the dismantlement of weapons to monitoring against potential rearmament. The findings highlight the critical importance of strategic resource allocation; by directing verification efforts toward the highest-risk pathways, inspection effectiveness increased without additional resources. Another key finding is that although increased budgets generally enhance verification effectiveness, without implementation of safeguards, effectiveness plateaus and cannot reach its maximum. This underscores that strategic resource allocation and cost-effective verification technologies are more crucial than simply increasing funding. These findings yield critical insights for policymakers and international bodies in crafting credible and effective verification frameworks. By integrating a physical model with risk-based resource allocation, the approach ensures flexibility and applicability across a range of geopolitical settings.

The Alva Myrdal Centre for Nuclear Disarmament (AMC) at Uppsala University, Sweden, is an interdisciplinary research center focusing on nuclear disarmament. The AMC was established in 2021 and consists of eight working groups with different focuses and from academic different disciplines. One working group is purely technical and directed towards technical verification and monitoring.

In this presentation, we will first give a short overview of the AMC and its main activities. Then, we will present the current research topics pursued by the technical working group. One of these is radionuclide monitoring and the development of sensitive detectors for measuring small quantities of radionuclides from nuclear test explosions. In collaboration with the Swedish Defense Research Agency (FOI), a technique for measuring weak signals with coincident gamma spectrometry is being developed. This work is intended to strengthen the verification regime used by the Comprehensive Test Ban Treaty Organization (CTBTO).

Another topic is disarmament verification with passive and active interrogation to be able to verify presence or absence of nuclear material. The working group is represented in the International Partnership for Nuclear Disarmament Verification (IPNDV) and has taken part in the BeCamp2 measurement campaign organized by SCK-CEN during 2023.

In the area of fuel cycle analyses, the working group has modelled reactor systems in Pakistan and North Korea to quantify their current possible plutonium production. Furthermore, the group has focused on the Swedish now decommissioned Ågesta reactor, a heavy water moderated reactor that was built in the 50s and 60s for possible use as a source of Swedish plutonium. The Ågesta reactor was eventually used as a civil power reactor, but it is a suitable reactor for developing methods of nuclear archaeology, by using the operator’s archive to extract core geometries, fuel characteristics and power history necessary for reactor modelling.

Apart from these research topics, the working group is involved in teaching activities on topics of nuclear disarmament. We teach basic physics of nuclear weapons as well as advanced topics like verification of nuclear test explosions. Members of the technical research group have also contributed to a learning module on nuclear weapons hosted by the EU Non-Proliferation and Disarmament Consortium. This module will be launched shortly.

The Democratic People’s Republic of Korea’s (DPRK) nuclear programme continues to expand without limits from a nonproliferation or arms control agreement. Since the departure of the IAEA in 2009, beyond what the DPRK chooses to reveal itself, much of the information we have gained about the trajectory of the programme has come from satellite imagery.

Large electro-optical satellite constellations have enabled day-to-day monitoring of key DPRK facilities, particularly at Yongbyon. After the destruction of the cooling towers in 2008, the 5MWe reactor’s operational status was determined by observation of water outflow that was primarily visible in tasked sub-1m resolution imagery. In contrast, operations of the Experimental Light Water Reactor have been linked to a larger water outflow that is visible in daily 3m resolution imagery.

In addition, satellite imagery beyond the visible spectrum has provided new insights into the DPRK programme. Notable applications of synthetic aperture radar (SAR), high resolution thermal imagery and night imagery from the Visible Infrared Imaging Radiometer Suite (VIIRS) have provided new insights into the programme.

This presentation will demonstrate, with new observations from 2025, how emerging satellite capabilities can be used to monitor a complex and evolving nuclear programme, such as the DPRK’s.

In the case of new disarmament treaties aimed at reducing the number of nuclear warheads, reliable mechanisms for warhead dismantlement must be established. Warhead confirmation systems can assist in these processes, as they are capable of verifying whether nuclear warheads, warhead components, or fissile material are either present or absent. Several systems based on gamma spectroscopy have already been proposed, including the Trusted Radiation Identification System (TRIS) by the Sandia National Laboratories, as well as the Information Barrier eXperimental II (IBX II) developed at Princeton University.

These systems measure the energy distribution of emitted photons using sodium iodide scintillators. In the context of nuclear warhead confirmation, the measured emissions are referred to as a signature. If two objects exhibit the same signature, they are assumed to be identical. During a disarmament process, for instance, the signature of a confirmed nuclear weapon can be compared to that of an object the dismantling state claims to be a nuclear weapon.

However, such signatures are not guaranteed to be unique – meaning that alternative configurations could potentially replicate the signature of a genuine weapon. This issue was already identified in 1997 by the US Office of Arms Control and Nonproliferation as a key unresolved challenge in gamma spectroscopy.

It has since been confirmed that existing systems could, in fact, be deceived by cleverly constructed hoax objects. These could consist, for example, of an optimized combination of radioactive isotopes that would produce the same signature as a nuclear warhead. Additionally, the question arises, of whether shielding effects from other materials could also contribute to a hoax, introducing additional possibilities for constructing more sophisticated hoaxes. A malicious actor could, for instance, suppress secondary emission lines through selective shielding or generate additional spectral lines via characteristic X-ray emission from the shielding material.

To investigate this matter is the focus of our work. We examined whether combinations of shielded radioactive isotopes can produce gamma emission signatures that are indistinguishable from those of actual nuclear warheads. For this, we performed extensive OpenMC simulations of photon transport through different materials. In a subsequent analysis, the simulated transmission rates for different photon energies were used to calculate shielded emission spectra of radioactive isotopes. A minimization algorithm was applied to identify configurations of shielded isotope whose signatures most closely resemble those of actual nuclear warheads.

Our results demonstrate that shielding effects can give rise to new types of hoax objects capable of deceiving gamma spectroscopy based warhead confirmation systems. Consequently, ensuring signature uniqueness in these systems remains a challenge that needs to be addressed on an even broader scale.