In-Service Inspection & Repair strategy for newcleo Lead-cooled Fast Reactor

newcleo is designing and building the next generation of nuclear lead-cooled fast reactors (LFRs) fueled with MOX. A fast-spectrum Small Modular Reactor of 30 MWe will be commissioned in 2030 (the Demonstrator) and a First-Of-Kind 200 MWe a few years later. To this end, newcleo develops an incremental strategy, starting first with the consolidation of mature and promising technologies with its own R&D laboratories and collaborations with major institutes and companies. This step aims to demonstrate the applicability of chosen technologies to a full mock-up of the reactor (the Precursor) available in 2026 for experiments. Inclusion of ISI&R (In Service Inspection and Repair) at the earliest stages of designs is a necessity to achieve a sufficient level of maturity and confidence in the technologies, and to increase safety, availability, and preservation of investments of experimental devices and reactors during their whole life.


Introduction
This article reviews the methodology, technologies, and main experimental setups which newcleo will use in the coming years to build the In-Service Inspection and Repair program for its LFR reactors, considering an ambitious timeframe.
Emphasis is put on inspections made on site, corresponding to inline monitoring or regular maintenance, as opposed to expertise and repair that will be essentially applied when needed to removable components (Steam Generators, Pump, DHR), with specific handling tools and processes, but using similar ISI&R techniques, or only available in laboratories (microscopy…) such as the one newcleo is building for its own purposes.
construction at the Brasimone site in Italy in collaboration with ENEA with an online date of 2026.
The LFR Demonstrator is a fully operational 30MWe reactor (LFR-AS-30) for demonstrating LFR technology and integrated power plant operations and ISI&R, as well as testing and validating novel materials, and components; it is expected that the initial power output will be limited to 20 MWe until high temperature (530 °C) nuclear material qualification test programs are completed. The Demonstrator will be constructed in France, with support of the French Government "France 2030" grant.
The FCU Prototype (LFR-AS-200) will be built in the UK. It will be the first commercial unit by 2032, fueled by MOX.

ISI&R Methodology
During the past 10 years, there has been many publications on ISI&R for the development of high temperature reactors, in particular for the French SFR PHENIX and SUPERPHENIX [4] [5] including decommissioning [13] , for the ASTRID project [12] , and for the Belgian LBE project MYRRHA with an emphasis on US examinations and robotics [7] [8] [9] .
Literature on pure Lead reactors is not as common. However, if Lead shares some properties with Sodium or LBE (opacity), it presents specificities that will drive the motivation for new approaches regarding inspection, and in particular (Table III).
• The need to monitor corrosion and erosion to get a return on experience (for phases 1 and 2). • The need to protect the surfaces with new materials, potentially changing sensor sensitivities, and even the way inspections were done till now. • The need to protect sensors from temperature, which remains high in outages and fuel handling phases (> 350°C). This temperature is considered a technological limit for many systems. • The need to adapt the inspection methodology to the buoyancy effect that is counterintuitive for specialists of Sodium or PWR fields. As a consequence, the inclusion of ISI&R at the earliest stages of designs is a necessity to achieve a sufficient level of maturity and confidence in the technologies, and to increase safety, availability, and preservation of investments of experimental devices and reactors during their whole life.
As a future operator of nuclear plant, newcleo is also legally bound to observe the strictest rules set by the French Safety Authority (ASN) on this matter. Chapter 4.2.5.2 of [3] says that the Equipments that are Important for the Protection (of the environment) must be designed in such a way as to allow their maintenance and monitoring in operation (in-service inspection, periodic tests) to ensure: • Integrity of their components and their tightness, in particular when they are designed to confine a radioactive fluid. • The availability and performance of system components, including if necessary when the reactor is working. • And maintaining the required performance of the systems for all the events of the reference design domain and extended design domain.
Another motivation to start ISI&R studies very early comes from the fact it is linked to many interfaces, with which it will act either as an input, or an output. These interfaces are: • Operations and maintenance phases, Safety, ESPN.
Finally, ISI&R is also traversing the whole life cycle of the plant and its components.
• Manufacturing requirements sets the reference of quality (welds, homogeneity…). These requirements are checked and reported for further comparisons. • Commissioning will set a reference state and start the "lifecycle" of the plant.
• Once the reactor is started, 4 levels of inspections are generally distinguished: N1 for monitoring, N2 for maintenance, N3 for expertise (when maintenance is not sufficient), N4 for repair.
This global approach is shown on Fig. 2.
The time taken to set this methodology in place must not be underestimated, whether it be during the development, erection, commissioning, operations, and decommissioning phases, as experienced by PWRs or SFRs in France.

Choise of Technologies
During the development phases, the maturity level of the technologies is regularly assessed using the TRL (Technology Readiness Level) scale given by Table II.   TABLE II -TRL SCALE The methodology is applied as follows: for each of the 4 levels depicted above, appropriate structures are selected for control and regular inspection/maintenance (frequency to be defined).
For each structure, appropriate technologies are identified, developed, manufactured, and tested in representative environments using the common V-Cycle approach.
The timeframe of the project being a constraint, it is recommended to choose technologies with sufficient robustness and readiness levels or showing the lowest risk (defined as a matrix of Probability of Failure versus Risk of not doing it). This is why: • Priority is given to TRL above 8, with a potential application in a few years on the precursor. • For existing technologies on PWR or Sodium RNR never applied in LFR but used in a similar environment (in terms of temperature in particular), a TRL of minimum 5 is required. Application target is 3 years (qualification on the precursor). • For emerging technologies, a readiness level of 3 is required. Application target is 4 to 6 years. • For mid-term or long-term R&D a readiness level of 2 is required. Application target is 8 to 10 years.  [14] [15] ): Thermocouples and RTD, Pressure gauges, level meters, strain gauges, accelerometer, flowmeters. These sensors are either set in place or moved on a carrier: the development of the carrier itself is treated afterwards. Table IV lists the sensors that will need developments, mainly US and EC sensors, and high temperature fission chambers.
In particular, inspection of welds and cracks of the reactor vessel in gas will be made at 360°C, and potential excursions to 400°C are possible. The developments will address: • High temperature coupling fluids (for US).
• High temperature US sensors.
• Optimized use of US and advanced simulations.
Inspections of welds under Lead will be made with US sensors sustaining more than 400°C.
Fission chambers are developed with a partner having an important return on experience of existing reactors, including advanced reactors. Calculations and core are made by ENEA, design integration and overall project management by newcleo.    A dedicated line of study also concerns the carriers that are needed to access the measurement locations, in particular between the reactor vessel and the safety vessel, to insert or retrieve probes (Steam Generators), and also make various automated tasks on the roof. See Fig. 3.
The main criteria for the carriers of devices used to access the zones of inspection are: • Compactness.
• Robustness to shock and ageing.

Experimental Means
In spite of the fact that Lead technology is under development in Europe since two decades, newcleo needs its own experimental means to develop, test and qualify the instrumentation for operation. In particular the need to increase the TRL of proposed instrumentation is mandatory, based on the experience acquired so far on LBE and partially on Lead.
The experimental strategy in support of instrumentation is based on a strong collaboration with ENEA to use and update existing non-nuclear facilities, as well as building new ones, with a total of 50 million euros of investments and more than 30 people involved on site, as listed on Fig. 4. NACIE-UP is a rectangular loop which allows to perform experimental campaigns in the field of the thermal-hydraulics, fluid-dynamics, chemistry control, corrosion protection and heat transfer and to obtain correlations essential for the design of nuclear plant cooled by heavy liquid metals. See Fig. 5. Instrumentations that could be tested on this loop are related to chemical balance (O2, H2…), corrosion/erosion detection by US… The HELENA loop has been designed as a multipurpose facility to support the technological development of the LFR. The first relevant feature of the facility is that it is operated in pure lead. See Fig. 7. Instrumentations that could be tested on this loop are the pump instruments, flowmeters, thermocouples… The CIRCE facility basically consists of a reduced diameter, full-height, cylindrical vessel filled with about 90 tons of molten Lead with an argon cover gas and a recirculation system. The testing approach gives CIRCE the flexibility not only to accommodate several test sections but also to carry out experiments that may be conceived later by ENEA. It is used for natural circulation investigation, fluid structure interactions, thermal-hydraulic studies, performance of the secondary loop, material corrosion and instrumentation immersed in flowing Lead (pressure gauges, TC, flow meters, US) … The COR-E and OTHELLO loops are under conceptual design, with COR-E ready to be operated on begin of 2024. Additional facilities like SOLIDX at ENEA will also be refurbished for smaller tests of US or acoustic sensors, see Fig. 10. The precursor is a scale-1 mockup of the reactor. It will be scaled in power (10 MWth versus 90 MWth of the Demo LFR) and will be equipped with a turbogenerator to confirm the startup procedures. It will represent in scale 1:1 the control rods and shutdown rods and the tubes of the STSG (tubes scaled in number). The precursor is a perfect loop for tests and qualification of instrumentation, inspection, and potential repair procedures.
Finally, for applications where robustness to irradiation must be proven and qualified, the TAPIRO reactor will be used. It is located at the ENEA Casaccia Research Centre near Rome. It is a fast neutrons source, and its design is based on the Argonne Fast Source Reactor -Idaho Falls. TAPIRO is able to provide a family of neutron spectra of extremely variable hardness (about pure fission spectrum near the core center). This remarkable feature makes the TAPIRO most suitable to many metrology applications. The TAPIRO reactor can operate at the maximum power of 5 kW, and the neutron flux at the center of the core at full power is about 4.10E12 n.cm-2.s-1. The fission chambers could be tested on this equipment.

Conclusion
This document provides the general methodology formulated for the ISI&R (In Service Inspection and Repair) for the LFR-AS-30 FR project. The ISI&R approach is based on: • The definition of the methodology.
• The identification of main needs in terms of importance for safety, ISI&R levels, and TRL • The development of related sensors, processes, technologies and methodologies in the short term, or mid-term for promising technologies that have no sufficient TRL.
The timeframe constraints are pushing to formulate the main following recommendations for the successful deployment of the methodology: • Write detailed specifications for each component. In general, this complementary work shows new and unforeseen constraints on sensors and carriers. • Define the critical locations that must be inspected.
• Schedule necessary calculations to define the defect sizes vs. proper instrumentation.
The choice of defect sizes with regards to the detection means is very important (and consistency between manufacturing and inspection must also be checked carefully). • During the design phase, always focus on sufficient accesses (for instrumentation, for robots…), especially for structural and critical welds. • Limit the number of welds and place them where dynamical temperature gradients are less. • Identify technologies that must be checked on the precursor as fast as possible.
• For others, propose longer term R&D programs, with key milestones to be sure it is possible to stop de development in due time. • In any case, always propose a backup solution (technology or design).