Phoenix (reactor)

In 1945, Enrico Fermi said: "The first country to develop a fast neutron reactor will gain a competitive advantage in the use of atomic energy."

The first fast neutron atomic reactor was the American EBR I , launched on December 20, 1951, while it was the first nuclear reactor of any type to produce some amount of electricity; it was not connected to the electric networks; the energy was used mainly to illuminate the building where the reactor was located.

Work on fast neutron reactors was carried out in different countries. January 8, 1956 in Michigan (USA) began construction of the first power unit of the nuclear power plant to them. Enrico Fermi ( English Enrico Fermi Nuclear Generating Station ), which supplied electricity to the network on May 8, 1966. In the USSR, the experimental reactors BR-2 (1956), BR-5 (1959), BR-10 (1973), and BOR-60 (1968) were built; industrial BN-350 (1973). In the UK, DFR (1962) and PFR (1975) were built.

In France, such work began in the 1960s. Although the main emphasis was placed on pressurized water reactors , fast neutron reactors were also considered an important area - the task was to create a class of commercially efficient fast neutron reactors that would allow the efficient use of nuclear material reserves for hundreds of years ^[12] .

Fast neutron reactors are characterized by the fact that they are able to produce more fissile material than to spend it. Thus, the energy resources contained in uranium ore can be used approximately 70 times more efficiently ^[13] .

By the end of 1958, a draft version of the Rhapsody experimental fast reactor was developed ( fr. Rapsodie ). Its characteristics corresponded to energy reactors (fuel from a mixture of uranium and plutonium dioxide , sodium coolant , energy intensity , materials, temperatures), except for the possibility of electricity production. On January 28, 1967, it was transferred to a critical state, and two months later it was brought to its design capacity of 20 MW ^[14] .

Considering the American and British achievements, it was decided to build a prototype of the energy reactor, without waiting for the results from the Rhapsody. Pre-design studies for the plant with a capacity of 1000 MW were carried out in 1964. The name “Phoenix” was proposed and unanimously approved for the station. In 1965, the main characteristics were determined. The fuel was chosen similar to that used at Rhapsody - plutonium reserves in France were insufficient, and along with plutonium dioxide it was decided to use enriched uranium dioxide. Electric power was selected at 250 MW ^[15] . As in Rhapsody, it was decided to use a sodium coolant. An integrated circuit was chosen when all the elements of the primary cooling system are mounted in the same volume as the reactor. In 1967, a detailed pre-project was developed. It had three pumps and six intermediate heat exchangers. Operating temperatures were taken at 400-600 ° C. ^[sixteen]

In 1969, the Commissariat of Atomic Energy of France and Electricity de France signed a protocol on the joint construction and operation of the station (80% of the expenses were borne by the Commissariat, 20% by Electricity de France) ^[17] .

It was decided to place the reactor north of the center of Markul . The options Kadarash (lack of water resources) and La Hag (located too far from Kadarash, where the production capacities related to sodium technology were concentrated) were also considered. Work on the construction site began in October 1968. The foundation pit had dimensions of 180 by 50 m and a depth of 11.5 m. Excavation was carried out for 18 months ^[18] .

A feature of the construction was the use of a continuous metal lining of the underground part of the reactor compartment. The cladding was mounted from prefabricated blocks - metal sheets with an area of ​​14 m², equipped with stiffness angles and fixtures, the thickness of the sheets for the horizontal part (base) was 10 mm, for the vertical (wall) 5 mm. The design was fixed by a system of special supports. The metal sheets were fastened together by welding , the welded joints underwent radiographic inspection and capillary inspection. After the construction of the structure, the concrete foundation of the building was built in the resulting metal cladding. The cavities between the outside of the cladding and the ground were flooded with concrete and rubber.

The aboveground part of the reactor building was composed of approximately 270 prefabricated concrete blocks 25 cm thick, which were subjected to horizontal prestressing after the construction of the walls ^[18] .

Timeline of construction ^[19] :

• 1968 year
  • October - the beginning of construction (pit).
• 1969 year
  • May 5 - the first concrete.
• 1970 year
  • January - the construction of the main volume has begun.
  • May - the construction of the containment began .
  • November 2 - the primary volume is built.
  • November 25th - The amount of security built.
• 1971
  • July 28 - the first batch of sodium.
  • August 2 - the dome was built.
  • October 18 - the first circuit is filled with sodium.
• 1972
  • February 21 - the generator stator is installed.
  • March 24 - generator rotor installed.
  • December 15 - the second (intermediate) circuit is filled with sodium.
• 1973
  • January 10 - the reactor is filled with sodium and the loading of nuclear fuel has begun.
  • February 1 - steam turbine launched.
  • August 31 - the first exit into critical condition.
  • December 13 - connection to the mains.

Over the entire period of operation, a reactor generated 24440,402 GWh of electricity ^[20] .

• energy readiness coefficient - 45.81%
• installed capacity utilization factor - 39.91%
• coefficient of technical use - 41%.

During the operation of the reactor, a number of problems were observed. Most of them were associated with leaks in the intermediate heat exchangers. The duration of downtime after any problems was associated with the fact that each reactivation of the reactor required a political decision ^[11] .

Most of these problems were observed on other reactors of this type. However, in 1989-1990, four cases of the same type of emergency situations that were not encountered in other fast neutron reactors were recorded at the reactor. On August 6, August 24 and September 14, 1989 and September 9, 1990 ^[8] , the reactor emergency protection was triggered due to sharp reactivity fluctuations recorded by the neutron flux monitoring equipment ^[11] .

The incidents were called AURN ( fr. Arrêt d'urgence par réactivité négative - automatic emergency stop by negative reactivity). They were observed when the reactor was operating at full power or close to it (the first three cases were at a power of 580 MW, the fourth at 500 MW). At the time of the incident, the reactor was continuously operating for 4-15 days. The stop occurred as a result of the value of negative reactivity of the emergency protection threshold ^[11] .

The script was the same every time:

1. An almost linear sharp increase in negative reactivity and, accordingly, a decrease in power. In just 50 m s, the power dropped to 28-45% of the initial one (at that moment emergency protection was triggered).
2. Symmetrical sharp rise in power almost to the initial value.
3. Again, a drop, albeit less sharp and deep, 200 ms after the start of the event.
4. Again, raising the power to values ​​slightly above the initial one.
5. Power loss as a result of the introduction of absorbing rods into the active zone by automation.

The problem has not received a final explanation, despite years of research initiated by CEA. The most plausible explanation is the explanation using a phenomenon called “core-flowering” or “outward movement phenomenon”, a situation where deformation in the form of an increase in the size of one heat-generating assembly causes mechanical stress in the assemblies surrounding it, which leads to the expansion of the entire core in radial direction. A slight increase in the distance between the assemblies leads to a sharp decrease in k _eff and, accordingly, an increase in negative reactivity and a decrease in power ^{[21] [11]} .

• BN-600
• BN-800
• BN-1200

• Jean-François Sauvage. Phènix - 30 years of history: the heart of a reactor . - 2004.