To meet the challenge of proposing a new innovative technology to the European nuclear decommissioning market, LD-SAFE demonstrated, over the last three years, numerous outcomes and evidence for the preparation of future implementation of laser for RPV/RVI segmentation (PWR and BWR components).
WP1 - Analysis of the reactor dismantling with laser cutting:
An overview of all the common techniques of cutting the internals of a nuclear reactor has been presented. In addition, a description of the use of the different techniques and a comprehensive comparison has been made. Cutting technologies for nuclear facilities were then divided into three types: thermal, mechanical and hydraulic. In addition, a presentation of the laser technology was done to highlight the performance criteria for cutting the internals of a nuclear reactor, and to compare it to plasma cutting, band saw cutting and waterjet cutting. As input data for WP2, a definition of the most representative material and most restrictive configurations of RVI cutting was performed. Finally, with the support of Advisory Board, the most complex components to dismantle considered are the bottom plate and upper plate/grid assembly.
WP2 - Laboratory tests and calculations:
The impact of laser beam residual power and the risk of damage on background structures in the context of dismantling of nuclear power reactors has been assessed in laboratory conditions. Tests performed underwater showed the absence of residual power risk, due to absorption of water at the laser wavelength and the scattering of light by air bubbles.
Laser cutting trials were performed in air, nitrogen atmosphere and for underwater conditions to characterize aerosols in terms of particle size distribution and morphology, mass and number concentrations, particle mass flow rate generation and agglomerates composition.
A first experimental study to evaluate hydrogen gas generation during laser cutting of 304L stainless steel of various thicknesses was performed in DELIA Facility (Saclay) by CEA. Preliminary measurements performed showed very low values of hydrogen concentration in air, in the range of few hundreds of ppm for the case of DELIA facility.
WP3 - Protection of workers and environment:
An assessment of the laser system maturity has been performed at the start of the project by developing a technology appraisal report (risk matrix that highlights components where uncertainty and/or risk that was at a level that required mitigation). This report was used as a foundation to create a set of activities and actions assigned to each of the partners and their associated Work Packages. The basis of evidence has been assessed and scrutinized in a Technology Qualification (TQ) process.
Towards the end of the project, a set of guidance notes will be issued, incorporating lessons learnt in LD-SAFE. The guidance notes will be designed to aid end users in how to use lasers correctly, safely and efficiently in decommissioning activities of PWR and BWR components.
WP4 - Safety assessment:
A preliminary identification and evaluation of radiological and non-radiological risks was performed, using IAEA checklists, a HAZOP study, and a benchmarking of risks identified for other RPV/RVI dismantling projects. The preliminary risk analysis was performed following the structure and methodology of IAEA SRS 77, Safety Assessment for Decommissioning, and thus, setting the base for the development of the generic safety assessment.
Based on a summary of risks identified during WP2 and WP3 and by updating the information included within the risk analysis, the initial version of the Generic Safety Assessment has been developed.
A review performed by IRSN of the Generic Safety Assessment has been done to ensure the appropriateness of the identified safety measures. The scope and level of detail of the independent review is commensurate with the safety stakes associated with the maturity of the laser technique and challenges of RPV/PPI dismantling tasks.
WP5 - Case studies and demonstrator:
A case study for the demonstrators was developed incorporating all Key Performance Indicators, the project outcomes and inputs / expectations from the members of Advisory Board. It highlights the main challenges to address with the laser cutting technology and the main answers to provide to the future end users, including nuclear safety management. This step allowed ONET to design, procure, install and commission the complete laser system, at first at CEA Marcoule for in-air cutting tests, and then at ONET Technocenter for underwater cutting tests.
Mock-ups are designed in order to challenge the technology by anticipating difficulties expected to arise at the stage of operation. A design file was written and included a representativeness note. Representative, complex parts are expected to be attached and detached from a crudely designed support system; the complex parts and their arrangement will simulate geometric and congestion-related constraints.
One year is remaining to reach the finalization of the Generic Safety Assessment, the achievements of in-air and underwater demonstrators (to highlight the performance, the ease-of-use, the relevancy of the safety systems of laser cutting technology without forgetting the demonstration of its economic advantage), the delivery of the Technology Qualification Certificate (when all remaining qualification actions are achieved) and guidelines for the use of laser cutting technology in reactor environment.
