criticality safety is complicated, CARTA just made it easier

What is CARTA?

Criticality safety can be complicated; there are many physical factors that determine the ‘k-effective’ of a system (i.e. if it can become ‘critical’). The interplay between these factors can be counterintuitive and the results are often difficult to explain. This can result in ineffective, PowerPoint heavy training sessions.

CARTA is a virtual reality criticality safety simulation tool that has been developed by Cerberus Nuclear to convey the factors that affect neutron multiplication in a readily intelligible and memorable way. CARTA does this by combining first-person computer game graphics and virtual reality to make immediately apparent the link between an operator’s actions and their effect on k-effective. As a result, trainees gain a deeper understanding of how criticality is prevented and why multi-parameter control is important.

How does it work?

Calculation of k-effective, as the measure of a system’s reactivity, is dependent upon many interacting parameters and accurate estimation generally requires the use of Monte Carlo techniques, which despite the advent of faster computers, cannot yet be used to determine k-effective in real-time.

CARTA is a novel approach that solves this problem by combining the results of Monte Carlo calculations of k-effective with a machine learning algorithm, so that k-effective can be determined ‘on-the-fly’ for a given system. CARTA then incorporates a desktop or VR headset-based visualisation of the scenario, so that users are able to see directly the effect of their actions on the system’s reactivity, both graphically and numerically.

How is it used?

CARTA is a tool, which is best used to enhance any criticality training course.

• The desktop version of CARTA can be woven into individual computer-based training to illustrate important concepts, provide practical examples or test the trainee.

• CARTA can be used as a group training activity; the class can work through an exercise together, encouraging lively interaction between trainer and trainees. This can be performed with the desktop environment or with a VR headset ‘casting’ what the user sees onto a screen.

• For more intensive training, CARTA can be used with small groups, with individuals working through scenarios under the supervision of a trainer. This provides more opportunity to relate the simulations to a particular site or facility.

• Outside of training, the CARTA method can be used as an optioneering tool that allows stakeholders to see the effect of design changes on both on criticality safety but also design parameters such as dose rate, weight and/or costs.

• CARTA can also be used as a fantastic stakeholder engagement tool at conferences or exhibitions.

Cerberus Nuclear can tailor CARTA to align with your existing training programmes, or our experienced criticality safety team can design an entire criticality safety course, with CARTA providing a key highlight.

How do I get it?

We offer two ready-made CARTA simulations, which will provide immediate enhancements to existing training courses. Whilst these simulations do not require any bespoke development, ongoing support can be provided upon request. We can also discuss your training objectives and develop training material to integrate with your existing training programmes.

These scenarios are completing development – please let us know if you are interested; they are scheduled for release in November 2022 (

CARTA – The ‘MAGIC MERV’ Simulation

This simulation is conceptual in nature and so can be used to engage with a wide range of stakeholders, from criticality specialist to the general public. Trainers can use the MAGIC MERV Simulation to create training scenarios to demonstrate the factors that affect criticality:



















The simulation involves the handling of two spheres of plutonium and water mixtures. The environment resembles a laboratory.

In addition to demonstrating lots of the factors that affect criticality, which is useful for introductory criticality training, the conceptualised simulation is easy to understand for wider stakeholders. For more advanced trainees, the ‘moderator-poison-moderator’ flux trap provides more challenging demonstrations or experiments, intended to demonstrate how neutron absorbers can be used to control reactivity.

CARTA – Glove Box Process Simulation

The context is a glove box in a production facility, containing an assay chamber, mass balance and an engineered array.  It is imagined that the operations carried out in the glove box are:

  • Receipt of a canister of fissile material.
  • Weighing of the canister on the mass balance.
  • Assay of the canister to determine its plutonium content.
  • Acceptance or rejection of the canister depending on its plutonium content and/ or other criteria.
  • Temporary storage of accepted canisters in the array in order to assemble a batch for a downstream process which is outside the scope of the simulation.

It could be imagined that the canisters hold swarf, casting residues, fragments of product material or rejected components.

Trainers can use the Glove Box Process Simulation to create training scenarios connected with the definition and implementation of criticality controls or rules based on one or several of:

  • Gross mass.
  • Mass of plutonium.
  • Mass of plutonium-239 (Pu239).
  • Plutonium-240 (Pu240) content.
  • Moderation state.

The simulation includes a mass balance and assay chamber so potential complications due to statistical uncertainty in the assay result and/ or bias in the assay result can be included.

The Glove Box Process Simulation is aimed at plant operators, with the training scenarios aimed at reinforcing the need to comply with and understand criticality controls. The simulation is equally effective for criticality assessors who must understand the impact of their designated criticality controls on the operators who will need to comply with them.

CARTA – Bespoke Development

One of the strengths of CARTA is that bespoke scenarios can be developed to simulate your fissile processes and systems. It is possible to recreate facilities down to minute details in the VR environment or use the CARTA method to quickly model a range of design options to assist optioneering. These bespoke training scenarios can be integrated with the existing ‘off the shelf’ MAGRIC MERV Simulation and Glove Box Process Simulation to give your trainees a wider, more effective training experience.

Our process for developing a bespoke CARTA simulation is outlined below:

  • Enquiry
    Get in touch by emailing
  • Initial discussions
    We’ll hold an initial consultation via videoconference to discuss your requirements and possible solutions using CARTA. Alternatively, we can visit your site to gain a deeper understanding of the process and/ or existing training programme.
  • Deliverable – Proposal
    We will produce a written proposal, which broadly sets out the deliverables, timescales and costs.
  • Design meetings
    We’ll work with you to design a simulation that makes best use of the capabilities of CARTA [or within the capabilities and constraints of the CARTA method?], with a focus on your training objectives and desired user experience.
  • Deliverable – Storyboarding
    We’ll develop storyboards to show how the user will experience the simulation to ensure that you’re happy with the approach.
  • Scoping calculations
    We will run Monte Carlo scoping calculations to determine an appropriate ‘parameter space’ to model. This ensures that the proposed simulations align with the training objectives.
  • Deliverable – Agreement of specification
    We’ll produce a detailed written specification, accounting for the findings of the previous stages. There will be an opportunity to consider options for additional or simplified functionality to control costs.
  • Monte Carlo production runs
    Tens of thousands of Monte Carlo calculations are run to determine k-effective values. The exact number depends on the complexity of the simulation and number of parameters considered. A typical CARTA simulation may consider five to ten parameters or ‘variables’.
  • Develop a Machine Learning algorithm
    Machine Learning techniques are used to produce a program that is able to interpolate, effectively in real-time, between the Monte Carlo results.
  • VR and/or desktop environment development
    The environments are developed along with the interface to the Machine Learning algorithm. Attention is paid to user controls and visuals so that the simulation is completely immersive for the user.
  • Deliverable – Production of associated documentation
    If required, we can produce various types of user documentation and training material, including user guides, lesson plans, mock-up Safety Case documentation, etc.

We will deliver the software making sure you are comfortable setting up and using any associated hardware. Our criticality assessors can support any training or integration activities, as required.

How much does it cost?

The MAGIC MERV simulation, in desktop format, is available to use for free in the browser. Follow the link and sign up for a free account here [coming soon!].

These scenarios are completing development – please let us know you are interested; they are scheduled for release November 2022. (

Alternatively, if you would like some more information, please use the form below.

    We recognise that procurement and integration of software on to company infrastructure can be difficult in the nuclear industry, hence, we also offer the software pre-installed on standalone hardware. This hardware is sold with standard manufacturer’s warranty.

      Software (lifetime licence, per organisation) Standalone Laptop Pico Neo 3 Pro Additional Training Material and Integration
    MAGIC MERV £4000 Sold at cost + £200 handling and admin fee for installation. ‘Cost’ is approximately £1000. Sold at cost + £200 handling and admin fee for installation. ‘Cost’ is approximately £800. Contact us
    Glove Box Process £6500
    MAGIC MERV and Glove Box Process bundle £7000
    Bespoke Scenarios Contact us

    Prices excluding VAT
    For countries outside the UK, there may be additional tax and administrative fees.

    Contact Us


    Criticality Safety

    We are the largest independent criticality safety team in the UK. We provide support across the full nuclear fuel cycle and offer a complete range of criticality safety services.


    Criticality Training

    CARTA™ is an immersive training environment for criticality safety. It allows real-time system reactivity feedback for effective operator training.


    Nuclear Characterisation

    We are at the forefront for the development of non-destructive techniques for characterisation of highly challenging environments where personnel access is limited.


    Code Development

    Our team has extensive experience in development of software projects. We use the Agile methodology for rapid release and short development cycles.

    Machine Learning

    We are experts in data science specifically for nuclear engineering applications and the analysis very large data sets.



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