Preparation of the programme for the use of the 2nd research reactor

Approval of reactor design (construction decision)

Official start of construction - laying of foundation act (16 June)

Technological start-up with the participation of E. Gierek and P. Jaroszewicz (12 July)

Critical experience - criticality achieved on 18 December at 0:17

Fuel element instrumentation failure - escape of gaseous fission products into the primary circuit and further into the process rooms. Cause: coolant flow too low during an experiment to determine the allowable power generated in the fuel element (16 May)

First period of reactor operation:

thermal power 20-30 MW,

operating time 700-3500 h/year,

installation of probes for material tests,

Unplanned shutdowns of the reactor (malfunction of the main fuel channel cooling pumps, the so-called Guinard pumps),

difficulties with fuel changeover,

lack of required ventilation system parameters

Reactor modernisation:

- installation of a passive system for flooding the fuel channels with water from the reactor pool

- improving the containment of the pressure stabiliser

- modernisation of the ventilation system

- removal of deformed graphite blocks

- purchase of beryllium with technical assistance from the International Atomic Energy Agency

- upgrade of the beryllium matrix from 20 to 48 units

- replacement of cooling water flow in heat exchangers of the primary cooling circuit

- modernisation of the fan coolers in the 2nd circuit

The second critical experience (30 December)

A turning point in the operation of the MARIA reactor - shutdown of the EWA reactor (20 February) and takeover of radioactive isotope production and transfer of equipment from the horizontal channels of the EWA reactor

Control rod failures involving detachment of the lower neutron absorbing section. Cause: significant reduction in the flow rate of water cooling the rods due to insufficient sealing of the core matrix after the upgrade, overheating of the lower absorber section of the rod (5, 11, 25 and 27 July)

Removal of SBM-EJ core section due to abandonment of nuclear power plant safety testing programme

First conversion step of fuel enrichment from 80% to 36% U-235 content

Completion of core conversion to fuel with 36% enrichment

Further improvements to the reactor:

- replacement of control and safety system apparatus

- upgrade of the fuel element leak detection system (WNEP)

- improvement of the secondary circuit pumps (removal of flywheels and shortening of the drive shaft)

- removal of spent fuel from the MARIA reactor to the spent fuel storage facility

Reactor shutdown due to lack of fuel, supply of new fuel with 36% enrichment

Upgrading of the dosimetry system

Upgrading the SAREMA system for collecting process measurement data

Testing of French fuel with 19.7% enrichment

Installation of three new fans in the cooling tower

Export of spent fuel elements to the Russian Federation - Polish-American-Russian cooperation under the Global Threat Reduction Arrangement (GTRI) for highly enriched fuel in research reactors

Irradiation of uranium targets for molybdenum production

Core conversion to French fuel with 19.7% enrichment

Testing of Russian fuel with 19% enrichment

Replacement of the main pumps of the cooling circuit of the fuel ducts and installation of new after pumps

Conversion of irradiated uranium targets for molybdenum production to low-enriched targets 19.7%

Upgrading the system for measuring cooling temperatures from fuel elements

First Periodic Safety Assessment (PSR)

Start of holmium-166 irradiation in microspheres for liver cancer therapy

Replacement of some of the depleted beryllium blocks of the core matrix

Construction and use of new high-temperature (1000 °C) materials testing probes

Modernisation of the reactor control room, main switchgear and several upgrades to smaller systems as part of Phase I of the MARIA reactor upgrade included in the ‘Programme for the modernisation of the MARIA research nuclear reactor to enable its operation beyond 2027’.

Second Periodic Safety Assessment (PSR)