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TW3

Side view (without irradiation sheath) of mock-ups in the TW3 probe

The TW3-TVB-INPILE project, awarded to the EUROATOM –IPP.CR Association under the European Fusion Development Agreement (EFDA), focuses on the development and operation of an active device which would apply, under the conditions of radiation exposure (combined field of neutrons and gamma radiation), a cyclic load on irradiated mock-ups with an approximate heat flow 50 W/cm2. Within the EUROATOM – IPP.CR Association, the project was awarded to ÚJV Řež a.s. for solution because this Institute was the only one within the Association to possess an appropriate neutron source, research reactor LVR-15. Under the reorganization and redeployment of the entire research team for the TW3-TVB-INPILE project and the operation of the reactor LVR-15 from ÚJV Řež a.s. to the Centrum výzkumu Řež, the project has been passed to the Centrum výzkumu Řež as of January 2011.

TW3 probe loading into the reactor LVR-15

The research team for the TW3-TVB-INPILE project has long-term experience in the field of cyclic testing of primary wall mock-ups of the ITER Tokamak fusion reactor: under the TW4-TVB-TFTEST2 and TW6-TVM-TFTEST projects, the team designed, constructed and put into operation an inactive facility BESTH, which tested, on a long-term basis, the primary wall mock-ups of the ITER Tokamak fusion reactor by applying a cyclic heat flow outside the neutron field. Six mock-ups from suppliers from USA, EU, Russian Federation, South Korea and China were tested under the operation of the BESTH facility. The BESTH facility, as well as the TW3 probe, is based on the principle of non-contact heating of mock-ups by applying ohmic heating which is generated by a graphite-heating panel. The principle of both facilities can be compared to an alternately switch on/off “old” bulb containing a tungsten wire: when connected, the heater heats and generates thermal power. This is transmitted through a narrow helium gap to the sample; the heat passes through the sample to the cooling water and is removed out of the sample.

The TW3 probe is ready for insertion into the LVR-15 reactor pool

Since the voltage is applied to a heating panel at cycles of approximate length 6-7 minutes and the generated power is sufficient, the fusion power pulses are simulated in this way and the sample or the bond between beryllium and CuCrZr alloy is tested for withstanding this cyclic load. Beryllium, which is used as “plasma-facing material” (material closest to plasma in the Tokamak reactor), is bound with a CuCrZr alloy by means of a HIP bond (HIP = hot isostatic pressing), which is actually a diffusion bonding of two different elements. This bond is the critical point at which a beryllium plate can release, so testing its ability to withstand the load is therefore required, both in inactive (no radiation) and in active operation.

TW3 Start-Up Schedule

TW3 probe after insertion into the LVR-15 reactor core (connected using blue and red cables)

The TW3 probe has been developed in Rez in the past years and has been subjected to a series of inactive tests before inserting into the reactor LVR-15. On the basis of these tests, an application for a permit to install the TW3 probe into the reactor LVR-15 was submitted to the State Office for Nuclear Safety on 19 April 2011. The State Office for Nuclear Safety issued this permit under identification number SUJB/OAP/18713/2011 on 9 September 2011.

A series of tests followed the insertion of the TW3 probe into the LVR-15 reactor core that occurred on 16 January. The calibration of probe radiation heating was the last step before starting up at full power of 9.2 kW: the reactor LVR-15 increased its power in steps.
The critical state of reactor at zero power was achieved on 19 January at 9:00 a.m.

  • 2 MW of thermal power (20% of nominal capacity) was achieved at 9:20 a.m.
  • 4.5 MW of thermal power (45% of nominal capacity) was achieved at 9:33 a.m.
  • 7 MW of thermal power (70% of nominal capacity) was achieved at 9:47 a.m.
  • 8.5 MW of thermal power (85% of nominal capacity) was achieved at 10:03 a.m.
  • 10 MW of thermal power (100% of nominal capacity) was achieved at 10:14 a.m.

All these steps were carried out without electric heating of the probe – this started at 11:35 a.m. and like the reactor power, was increased gradually:

  • The power of 1 kW was set at 11:35 a.m.;
  • The power of 2 kW was set at 11:50 a.m.;
  • The power of 4 kW was set at 12:10 p.m.;
  • The power of 6 kW was set at 12:30 p.m.;
  • The power of 8 kW was set at 12:51 p.m.;
  • The full power of 9.2 kW was set at 1:10 p.m. and has maintained this power level since then.

TW3 Objectives

The objective of the TW3-TVB-INPILE project is to reach 20,000 cycles (of length 7 minutes) while achieving a heat flow of 50 W/cm2 for 3 minutes at each cycle. Another criterion is to achieve a dose of 0.6 dpa. In order for the probe to achieve these parameters, its operation in the reactor LVR-15 is planned until at least May 2012.

The probe will be then removed from the reactor core and cut in hot cells in order to be able to send the irradiated samples for further testing in the JUDITH I facility to Forschungszentrum Jülich GmbH (FZJ).

Cartogram of K136 zone where the TW3 probe was inserted into for the first time

Thermal neutron flux density at half height of reactor core with TW3 probe

Fast neutron flux density at half height of reactor core with TW3 probe