CALLISTO: a PWR experimental facility for scientific in-pile studies

CApabiLity for Light water Irradiation in Steady state and Transient Operation

Performance and safe operation of nuclear power reactors are continuously improving. This process calls for predictive model validation and qualification testing under realistic power reactor operating conditions. The high pressure/high temperature experimental water loop CALLISTO in the BR2 reactor is used intensively for irradiation studies to cover these essential requirements.

CALLISTO: a PWR facility with multiple features

CALLISTO consists of three experimental rigs, called In-Pile Sections (IPS), which are installed in three reactor channels to meet various irradiation conditions. They are connected to a common pressurised loop, which can deliver a wide range of pressure and temperature working regimes. We can provide these IPS's with dedicated instrumentation and we can modify them to perform many dedicated irradiation studies to:

• Investigate the behaviour of advanced fuel under representative PWR operating conditions
• Qualify such fuel for safe, reliable and economical use in power reactors
• Assess the Irradiation Assisted Stress Corrosion Cracking (IASCC) phenomena in typical light water reactor materials
• Study the corrosion process on candidate materials for future fusion reactors
• Characterise the performances of high neutron dose irradiated materials for light water and fusion reactors as well as for ADS systems
• Develop and qualify new on-line in-pile detectors (like neutron and gamma flux detectors, dissolved hydrogen sensors, electrochemical potential reference electrodes …) in a high neutron flux and in a relevant thermal-hydraulic environment

The basic layout of the CALLISTO facility permits the irradiation of clusters of nine fuel rods (fresh or pre-irradiated) in each of the three in-pile sections, thus a total of 27 rods. Normally, the rods are about 1 m long, but variations are possible. Each in-pile section could also accommodate three full-length PWR rods, i.e. over 4 m long. Until now, fuel rods have been irradiated inside CALLISTO in nominal steady state regime in order to achieve their target burn-up. However, the loop can also be operated, within certain limits, in off-normal and transient regimes, e.g. power ramping or cycling, cooling mismatch conditions, loss of flow. CALLISTO is also used for the irradiation of structural materials under representative PWR conditions.

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Achievements

From 1989 to mid-1992, the CALLISTO facility was designed, constructed, tested and fully licensed.

In a second stage (mid-1992 to the end of 1994), we irradiated 31 fuel rods (UO² and MOX) at a peak linear power ranging from 225 to 430 W.cm-1 reaching 57 GWd/tM burn-up.

In 1995, we started a scientific programme studying the PWR vessel steels behaviour under irradiation.

After the refurbishment of BR2 (1995 – 1996), one IPS, which receives higher thermal and fast fluxes, became particularly dedicated to corrosion and material studies. From 1996 till now, many new applications for the CALLISTO facility have arisen, among other things: fuel testing, fusion, PWR vessel steel and ADS materials studies, corrosion studies (crack initiation, crack propagation), basic mechanical material science and modelling, detectors testing …

Regarding fuel testing programmes, the CALLISTO loop permitted the successful burn-up accumulation for the BACCHANAL campaign and is currently used for advanced testing of instrumented rods to improve understanding of fuel microstructure and fission gas release phenomena (OMICO campaign).

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Main CALLISTO characteristics

Each IPS is provided with a basket, the capacity of which is 37 x 37 x 1000 mm³, and can contain fuel rods or any other targets (different basket geometries are possible).

Cross section of the CALLISTO fuel basket

Nuclear data (at 100% BR2 reactor power and at mid-reactor plane):

The axial distribution enables a 350 mm long basket section (centred on the mid-plane) to be exposed to at least 80% of the maximum fluxes. Depending on the fuel composition and its enrichment, the maximum linear rod power (at peak pellet) ranges from 200 to 450 W/cm for commercial PWR fuel rods.

Thermal-hydraulic data:

• Temperature: 80 ºC ≤ T ≤ 300 ºC (inlet of the in-pile section)
• Pressure: 1.0 MPa ≤ P ≤ 15.7 MPa
• Flow rate in the IPS: 1.8 kg/s ≤ G ≤ 2.5 kg/s

Chemical data:

• The cooling water in CALLISTO is representative of that of a PWR primary circuit
• Boron (boric acid): ± 400 ppm - 600 ppm
• Lithium (lithium hydroxide): 1.8 ppm ≤ [Li] ≤ 3.5 ppm
• pH: 7.00 ≤ pH(25 ºC) ≤ 7.08 or 7.26 ≤ pH(300 ºC) ≤ 7.34
• Dissolved hydrogen: 25 ccSTP/kg ≤ [H2] ≤ 35 ccSTP/kg

Some outstanding features

250 analogue and 350 digital signals are scanned and stored to generate diagnostics, to initiate corrective actions, to set alarms off and to collect measurements from the dedicated experimental devices loaded in the IPS. Integrated within the BR2 data acquisition system, CALLISTO data is remotely accessible from each user's office.

In the context of the non-stationary operation regarding chemical conditions, the chemistry of the primary loop of CALLISTO is monitored both continuously by on-line measurements and by regular analyses of water samples.

In conclusion, the CALLISTO experimental facility is a powerful tool for many scientific programmes in which irradiation studies and testing are involved!

References

• Philippe Gouat, "SCK•CEN: Your partner in fuel research", SCK•CEN – ER-15 (2006) ER-15 (91 MB)

• Ludo Vermeeren, Jean Dekeyser, Philippe gouat, Silva Kalcheva, Edgar Koonen,Vadim Kuzminov, Alfons Verwimp, Marcel Wéber, "Qualification of the on-line power determination of fuel elements in irradiation devices in the BR2 reactor", SCK•CEN – BLG-1006 (January 2005) BLG Report 1006 (663 kB)

• Charles De Raedt, Edouard Malambu, Serge Bodard, Marcel Wéber, Marcel Willekens, "Assessment of the fission power level in fuel rods irradiated in the high flux material testing reactor BR2 with the aid of fluence dosimetry - Comparison with other methods" 10th International Symposium on Reactor Dosimetry (ISRD), Osaka (Japan), Sept. 12-17, 1999
• Edouard Malambu, Charles De Raedt, Marcel Wéber, "Assessment of the linear power level in fuel rods irradiated in the CALLISTO loop in the high flux materials testing reactor BR2", 3rd Int. Topical Meeting on Research Reactor Fuel Management (RRFM), March 28-30, 1999, Bruges (Belgium)
• Klaas van der Meer, Marcel wéber, Peter De Regge, Charles De Raedt, Danièle Boulanger, Thierry Maldague, Pierre D'hondt, "A comparison of in-pile and out-of-pile methods for the determination of burn-up and linear power of an irradiated fuel rod", Int. Conf. on the Physics of Reactors (Physor-96), Mito (Japan), Sept. 16-20, 1996
• Charles De Raedt, Serge Bodard, Bernard Ponsard, Marcel Wéber, Thierry Maldague, "Two-dimensional neutron and gamma calculations for devices irradiated in BR2 reflector positions" 8th ASTM-EURATOM Reactor Dosimetry Symposium, Vail, Colorado (USA), Aug. 29 – Sept. 3, 1993
• Marcel Wéber, Philippe Benoit, Jean Dekeyser, Alfons Verwimp, "Chemical behaviour of the CALLISTO experimental PWR rig during start-up, irradiation and shutdown periods of the BR2 reactor" Proceedings RC-1334, Int. Symposium on activity transport in water cooled nuclear power reactor", Ottawa (Canada), Oct. 24-25 1994
• Marcel Wéber, Philippe Benoit, Jean Dekeyser, Alfons Verwimp, "Results of water chemistry control in the in-pile "CALLISTO" loop – (An experimental PWR rig installed in the BR2 reactor" Int. Conf. on Chemistry in water reactors – Operating experience & new developments", Société Française d'Energie Nucléaire. Nice (France), 24-27 Avril 1994
• Philippe Benoit, Camiel Decloedt, Jean Dekeyser, Charles De Raedt, Frank Joppen, Alfons Verwimp, Marcel Wéber, "CALLISTO: a PWR in BR2 – Design, construction and licensing", Int. Conf. on Irradiation Technology, Saclay (France), May 20-22, 1992

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For further information please contact:

Dekeyser Jean