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IVMR · Project

Proven Safety Strategy to Keep Molten Fuel Inside Nuclear Reactor Vessels

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Imagine a nuclear reactor overheats so badly that the fuel literally melts. The big question is: can you keep that molten mass trapped safely inside the steel reactor vessel instead of letting it burn through the floor? This project brought together 23 organizations from 14 countries to figure out whether that containment strategy — already used in smaller reactors — can work for larger power plants around 1000 MWe. They built better computer models, ran experiments, and created a shared European methodology for proving this safety approach works.

By the numbers
EUR 4,831,454
EU research funding
23
consortium partners
14
countries represented
1000 MWe
target reactor power class
35
project deliverables
7
industry partners in consortium
The business problem

What needed solving

Nuclear power plant operators running higher-power reactors (around 1000 MWe) lack proven, best-estimate methods to demonstrate that molten fuel can be safely retained inside the reactor vessel during a severe accident. Current conservative calculation approaches — adequate for smaller reactors like VVER 440 — do not provide sufficient confidence for larger designs, creating regulatory uncertainty and potentially costly over-engineering of safety systems.

The solution

What was built

The project delivered 35 outputs including improved numerical simulation tools for analyzing maximum heat loads on reactor vessel walls during melt scenarios, validated experimental data on external vessel cooling and direct water injection, and a harmonized European methodology for assessing IVMR feasibility across different reactor types (VVER, PWR, BWR).

Audience

Who needs this

Nuclear utilities operating VVER 1000 or large PWR/BWR reactorsNuclear safety consultancies preparing severe accident analyses for licensingReactor vendors designing Gen.III plants (AP-1000, APR 1400 class)National nuclear regulators updating severe accident management guidelinesNuclear engineering firms specializing in reactor vessel and cooling system design
Business applications

Who can put this to work

Nuclear power plant operations
enterprise
Target: Nuclear power plant operators running VVER or PWR reactors

If you are a nuclear utility operating reactors in the 1000 MWe class and need to demonstrate severe accident management to regulators — this project developed best-estimate evaluation methods and a harmonized methodology for In-Vessel Melt Retention that can replace overly conservative assumptions. The work covers VVER 1000 type 320 units specifically, plus PWR and BWR designs, backed by a consortium of 23 partners across 14 countries.

Nuclear engineering and safety consulting
mid-size
Target: Engineering firms providing nuclear safety analysis and licensing support

If you are a nuclear safety consultancy helping clients with severe accident analysis — this project produced improved numerical simulation tools for evaluating heat loads on reactor vessel walls during melt scenarios. These tools enable best-estimate analysis rather than conservative bounding calculations, which matters when regulators demand proof of adequate safety margins for higher-power reactors.

Nuclear reactor design and manufacturing
enterprise
Target: Reactor vendors developing Gen.III or Gen.III+ designs

If you are a reactor vendor designing new builds like AP-1000, APR 1400, or similar Gen.III plants — this project analyzed the technical feasibility of external vessel cooling and direct water injection into degraded cores. The results from 35 deliverables provide validated data and methods you can reference in your safety case documentation for licensing new reactor designs.

Frequently asked

Quick answers

What would it cost to implement these findings at our plant?

The project itself received EUR 4,831,454 in EU funding for research and methodology development. Implementation costs at a specific plant would depend on your reactor type and existing safety systems. The project focused on analysis methods and feasibility studies rather than turnkey installation packages.

Can this scale to large reactors beyond VVER 440?

That was the core purpose of the project. While IVMR is already proven for smaller reactors like VVER 440 (around 440 MWe), this project specifically tackled the challenge of scaling to 1000 MWe class reactors including VVER 1000 type 320, plus future PWR and BWR designs. The results include best-estimate methods that replace conservative assumptions needed at higher power levels.

Who owns the IP and how can we access the tools?

The project was coordinated by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) in France, a public research institution. As a publicly funded RIA project with 23 partners, access to results and numerical tools would typically be negotiated through the coordinator or relevant consortium members. Licensing terms would depend on each partner's contribution.

Does this meet current nuclear regulatory requirements?

The project aimed to produce a harmonized European methodology for IVMR assessment, which directly supports regulatory compliance. With 12 research organizations and 7 industry partners from 14 countries involved, the methodology reflects broad European regulatory perspectives. However, specific licensing applications would still require plant-specific analysis.

What concrete tools came out of this project?

The project delivered 35 deliverables including improved numerical simulation tools for analyzing heat loads on vessel walls during melt retention scenarios, validated experimental data, and a harmonized methodology for IVMR feasibility assessment. These cover both existing reactors and future Gen.III designs.

How long before these methods can be used in practice?

The project ran from 2015 to 2019 and is now closed. The simulation tools and methodology are developed and available. However, applying them to a specific reactor requires plant-level analysis and regulatory review, which varies by country and reactor type.

Consortium

Who built it

The IVMR consortium is notably broad for nuclear safety research: 23 partners spanning 14 countries with strong representation from both Eastern and Western European nuclear nations (France, Finland, Hungary, Czech Republic, Slovakia, Bulgaria, and others). The 30% industry ratio (7 out of 23 partners) signals real commercial interest, while 12 research organizations provide deep scientific backing. Coordinated by IRSN — France's national nuclear safety institute — the project carries significant regulatory credibility. The 3 SMEs in the consortium suggest niche engineering firms with specialized capabilities. For a business looking to adopt these methods, the wide geographic spread means you likely have a consortium partner in or near your country who understands your local regulatory environment.

How to reach the team

Coordinated by IRSN (Institut de Radioprotection et de Sûreté Nucléaire) in France — SciTransfer can facilitate an introduction to the project team.

Order a report on this consortiumSee INSTITUT DE RADIOPROTECTION ET DE SURETE NUCLEAIRE profile →
Next steps

Talk to the team behind this work.

Want to access IVMR's simulation tools or methodology for your reactor safety case? SciTransfer connects you directly with the right consortium partner for your reactor type and regulatory jurisdiction.

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