Preparations for the construction of the MARIA reactor - 1964

In 1964, a programme was developed for the use of the second Polish research reactor, according to which the reactor was to be used for:

  • conducting physical research on neutron beams; conducting radiochemical research;
  • conducting materials research in probes and loops;
  • irradiation of target materials for isotope production;
  • use of gamma radiation from spent fuel elements for radiochemical research;
  • conducting exposures for short-lived isotope spectrometry;
  • research in reactor engineering and nuclear energy.


Start of construction of the MARIA reactor - 1970

Construction of the MARIA reactor began in 1970 and the reactor reached criticality for the first time on 18 December 1974. This reactor, designed and built by Polish specialists and technicians, was constructed as a multipurpose reactor with a high neutron flux - with the task of complementing the research capabilities of the EWA reactor. The reactor was also built to carry out materials research, necessary for nuclear power plant construction and operation programmes.

From the first start-up (1974) to the present day

A major overhaul of the MARIA reactor began in mid-1985. The subjects of the overhaul activities were:

  • replacement of the control system with the SAKOR-B reactor apparatus block system, inspection and condition diagnostics of the graphite blocks constituting the reactor reflector, completion of the core configuration with additional beryllium blocks,
  • construction of a biological shield for the pressure stabiliser, modernisation of the reactor cooling system equipment,
  • modernisation of the reactor air-conditioning and ventilation systems,
  • installation of a circulating temperature and flow control system in the reactor fuel cooling channels (OKCR system).

After the Chernobyl power reactor accident, there was a change in the approach to nuclear reactor safety analyses. As a result of these analyses, the MARIA reactor was equipped with a number of state-of-the-art systems to eliminate the occurrence of certain events or minimise their consequences. A passive system for flooding the fuel channels with pool water in the event of a pressure drop in the fuel element cooling circuit was implemented, and new structures for the horizontal channels leading the neutron beams out of the reactor were installed.

The reactor was restarted in December 1992 and from 1993, after going through the power start-up procedure, the MARIA reactor undertook normal operation, which continues to this day.


Since the shutdown of the EWA reactor in 1995, MARIA has been the only nuclear reactor in Poland. It is worth noting that the current utilisation programme of the reactor corresponds almost exactly to the utilisation programme proposed before its construction.

The reactor is undergoing continuous modifications to improve its safety and functionality related to its utilisation programme. The most significant modifications concern the nuclear fuel. Originally, the MARIA reactor operated on fuel with isotope 235U of an enrichment of 80%. In 2000, fuel with 36% enrichment began to be introduced, and in September 2012, testing of fuel below 20% enrichment began. Also in 2012, the fan cooler was upgraded.

In 2014, the conversion of the reactor to low-enriched fuel was completed, this change was combined with an upgrade of the fuel channel cooling circuit - the main circulating pumps were replaced and new post shutdown pumps were installed. In the same year, the export of spent fuel elements to the Russian Federation was completed as part of the international Global Threat Reduction Initiative (GTRI) under the auspices of the US Department of Energy and the International Atomic Energy Agency.

A further upgrade was initiated in 2023.

Currently, the MARIA reactor is licensed to operate until 2025 and, with continuous upgrades, will be able to operate until 2053.

The history of the MARIA reactor is an important part of the history of the Institute as a whole, and you can read that history here >