Small Modular Reactors

NRGroup is investigating SMR concepts since 1997, when the NILUS project was launched (an idea by prof. Carlo Lombardi).

NILUSNatural circulation Integrated Layout Ultimate Safety

The integration of all the PWR primary system components (steam generators, pressurizer, pumps and control rods) inside a tall Reactor Pressure Vessel was the key idea of NILUS concept.

The limited size of the core (1000 MWth), the adoption of a “full passive safety systems” strategy and a pressure-suppression containment were the other characteristic features of NILUS.

The NILUS experience allowed NRGroup to be involved since the beginning into the IRIS adventure on 2000.

NILUS concept

IRISInternational Reactor Innovative & Secure

The IRIS project was launched on 2000 by Westinghouse, MIT, UC Berkeley and Politecnico di Milano-NRGroup. On 2007, the IRIS Consortium was gathering 20 organisations from 10 countries. At that time, IRIS was considered as the reference SMR project by US-DoE and a pre-licensing process was under way with US NRC.

The IRIS main features are:

  • an integral PWR layout, with all the primary systems integrated into the RPV (Steam Generators, Pressurizer, Pumps and Control Rod Drive Mechanisms),
  • a spherical, steel containment, pression-suppression type,
  • a fully passive Emergency Heat Removal System,
  • a passive long-term cooling strategy (for both core and Containment), including an in-vessel core retention capability by flooding the RPV cavity, in case of severe accident,
  • an Emergency Planning Zone reduction methodology (i.e. EPZ close to the fences of the nuclear power plant),
  • a staggered and self-financing deployment, to reduce the financial,
  • a modular and in-shop manufacturing process, to reduce the deployment delays.
IRIS concept


The french company DCNS (now Naval Group) on 2010 started developing the concept of a fully submerged SMR, based on their historical experience on manufacturing nuclear submarines.

Key features of the concept are:

  • a compact PWR,
  • a steel hull, containing the reactor and all the systems of the nuclear power station,
  • passive safety systems with a practically infinte cooling capability, offered by the sea water,
  • a remote control room on-land, to manage the submerged modules,
  • long-life core, with no need of on-site refuelling.
FlexBlue concept


The NUWARD project has been launched by a french consortium involving EdF, CEA, TechnicAtome and Naval Group (see news here).

That concept is the basis for the LWR-SMR type analysis and investigation, within the ELSMOR project (EURATOM funded project 2019-2022).

The integral PWR type reactor is located inside a steel containment, submerged into a large water pool, hosting several SMR modules.

NUWARD concept