RCC-MRx Methodology for Design by Analysis of Nuclear Safety Important Components of the LORELEI Device

The LORELEI test device [1] is designed to be placed in the reflector of the Jules Horowitz Reactor, Cadarache, France (JHR), adjacent to the reactor core. This device is basically a double-walled pressure vessel that contains a single fuel rod as well as numerous instrumentation. It is designed to investigate the effect of a Loss of Coolant Accident (LOCA) on the fuel, and is subjected to neutron and gamma fluxes. Since this device contains radioactive substances, most of its parts are categorized as ESPN (Équipements Sous Pression Nucléaire - nuclear pressure equipment) with a certain safety class. For each component, a list of working situations (WS) has been defined. The design and manufacture of the device is subjected to French nuclear regulations as well as the RCC-MRx code [2].

This work presents the methodology used to fulfill the requirements and restrictions derived from the WS and the RCC-MRx code.

As a preliminary step, each component is classified according to a safety analysis. Then, all working situations are drawn and the design levels (A, C and D) are established:

Level A – for normal and incidental WS
Level C – for accidental WS
Level D – for beyond design-basis WS
Each of these levels has a special set of criteria, where the philosophy of the code is that level A is the most stringent due to the high probability of occurrence. For the less probable situations - Level C and Level D – the safety factors are reduced.

In addition to the design levels, the RCC-MRx code categorizes the damages as follows:

Primary damage, which mainly includes damages due to mechanical loads such as pressure, forces and moments
Secondary damage, which mainly includes cyclic related damages, thermal stresses and stresses due to imposed displacement or deformation.
Damage in the welded zone.
Damages related to bolted assemblies.
Damages related to support members.
According to the code, each type of damage has to be investigated.

The RCC-MRx code provides the means for calculating the stresses resulting from each damage type, as well as the effects of irradiation and creep on the material. Finally, the calculated stresses are compared to the allowable stresses in the code.

The RCC-MRx methodology was implemented on the LORELEI`s components. In this presentation, a numerical analysis of a double wall pressure flask with a complex geometry is presented.

References
[1] L. Ferry, D. Parrat, C. Gonnier, C. Blandin , Y. Weiss and A. Sasson, "The LORELEI Test Device for LOCA Experiments in the Jules Horowitz Reactor," WRFPM, Sendai, Japan, 2014.

[2] Afcen, RCC-MRx, 2012 edition, "Design and Construction Rules for Mechanical Components of Nuclear Installations"