atw 2018-04v6

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atw Vol. 63 (2018) | Issue 4 ı April OPERATION AND NEW BUILD 224 Normal operating conditions Steady State LVR-15 Start up LVR-15 Shutdown Loops Start up Loops Shutdown and during Loss of Flow Accident ( LOFA) and Loss of Coolant Accident (LOCA) accident conditions. In particular, the structural integrity analyses required the temperature profile inside the Pressure Envelope (PE) as boundary condition. For this reason the normal operation and abnormal operation conditions were calculated using TRACE and ATHLET codes with very narrow mesh nodal distribution in the PE. For structural integrity following criteria and limitation due to the non-boiling condition in LVR-15 were used: 1. PE maximum temperature during normal/abnormal transients is less than 450 °C. 2. PE maximum temperature during accident conditions is less than 500 °C. 3. Aluminium surface of the Receiver maximum temperature in contact with LVR-15 coolant less than 45 °C during normal/abnormal conditions. 4. Aluminium surface of the Receiver maximum temperature in contact with LVR-15 coolant less than 60 °C during accident conditions. In the case of accident conditions, both active channels of HTHL and SCWL will have to be replaced. The analysed scenarios are described in the Table 1. 4 Illustrative results The results described in the paper refer to the simulations of SCWL and Pressure tests (not simulated) | | Tab. 1. Operational and Accident Scenarios Description. Abnormal conditions Switch off Loops Electrical Heater for 1 min. LVR-15 SCRAM and switch off of Loops Electrical Heater at t = 0 s + pump trip after 1 min. Switch off Loops Electrical Heater at t = 0 s + LVR15 SCRAM and Pump Trip after 3 min. Parameter Value Unit Pressure 25 MPa Inlet Flow Temperature Outlet Flow Temperature Max Flow Temperature Sample Area Mass flow | | Tab. 2. SCWL main parameters calculated during steady state. HTHL during the steady state operation with continuing in LOFA condition. The results represent an extract of the large number of calculations of various combinations of operational transients with the aim to demonstrate the capabilities of the codes to simulate behaviour the loops. 4.1 SCWL steady state and LOFA analyses The main parameters for the steady state are shown in Table 2. The whole steady state calculation was rather long due to some inertia of the system. The computer model simulated behaviour during the transient of all heat structures representing the complete piping system. In the calculation some numerical instability complicated the steady state due to Accident conditions 385 ºC 406 ºC 600 ºC 35 % By pass flow 65 % Mass flow 200 kg/h Loss of Flow Accident (LOFA) Loss of Coolant Accident (LOCA) small dimensions of the component facing the deterioration flow phenomenon during the heating up process. For these reasons, the whole steady state was completed in 25,000 s, where 15,000 to 20,000 s were needed to adjust the steady state and the rest 5,000 s were used to verify the steady behaviour of the main parameters. After this period the model simulated the accident scenario – LOFA without the reactor SCRAM in order to maximize the consequences and to calculate the time to reach temperature of PE (AC) 500 °C. The scenario is described in the following steps: 1. Pump stops in 1 s after the initialization event (25,001 s) 2. Active channel internal electrical heaters shut down to 0 % on the nominal power in 7s (25,007 s) 3. The LVR-15 SCRAM starts at 40 s when the maximum temperature in the PE rises above the 500 °C. (25,040 s) 4. The whole transient is completed in 15,000 s (40,000 s), when the SCWL and LVR-15 are in the controlled cold state. The Figure 6 and Figure 7 represent the SCW maximum temperature calculated in the sample area and the outlet temperature from the active channel, while the Figure 8 shows the maximum temperature of the PE, where there is the neutron flux peak in the Boltzmann distribution. 4.2 HTHL steady state and LOFA analyses The design conditions calculated for the active channel are described in Table 3. And they are mainly summarized as reported: 1. Mass flow rate of 0.0105 kg/s 2. Design pressure of 7 MPa 3. Design electrical heater power of 11.85 kW 4. Cold helium temperature of 210 °C | | Fig. 6. SCWL Coolant Maximum Temperature in LOFA. | | Fig. 7. SCWL Active Channel Outlet Temperature in LOFA. Operation and New Build Experimental and Analytical Tools for Safety Research of GEN IV Reactors ı G. Mazzini, M. Kyncl, Alis Musa and M. Ruscak
atw Vol. 63 (2018) | Issue 4 ı April Location of the Thermocouples Thermocouple | | Fig. 8. SCWL Maximum EP Temperature in LOFA. Parameter Value Unit Pressure 7 MPa Inlet Flow Temperature Max Flow Temperature Maximum AC Pressure Envelop (PE) Temperature 210 ºC 900 ºC 450 ºC Mass flow 40 kg/h Inlet into the interpiping space of the reheater Output from the interpiping space of the reheater Entry into the test chamber Inlet to the reheater piping space Output from the reheater piping space Output from the primary side of the heat exchanger Maximum helium temperature | | Tab. 4. Thermocouples position and description. T1 T2 T3 T4 T5 T6 Tmax OPERATION AND NEW BUILD 225 | | Tab. 3. HTHL main parameters calculated during steady state. The steady state simulation was run in null transient mode for 5,000 s and the stabilized conditions were reached after 3,500 s. The LOFA transients was characterized by an immediate safety shutdown of the reactor due to the loss of power. As a result of the SCRAM, the temperature went immediately down following the heat generated by decay gamma flux. Figure 9 shows the calculated temperature for various thermocouples positions (according to Table 4), while Figure 10 represents the maximum temperatures in the HTHL PE. | | Fig. 9. HTHL Helium temperatures during LOFA. 5 Conclusions The article provides a brief introduction about the SUSEN project and the experimental facilities built in CVŘ in the Czech Republic for research and development in support of the safe, reliable and long‐term sustainable operation of existing energy facilities and in development of GIF IV and fusion technologies. The SUSEN R&D activities include four complementary programmes, mentioned in the introduction, which are focused on material science, thermal hydraulics, neutronics, radiation protection, nuclear chemistry, waste management and environmental studies. A significant part of the research programme is devoted to HTH and SCW experimental loops, which are going to be installed into the active core of the research reactor LVR-15. Both of | | Fig. 10. HTHL PE temperature during LOFA. these unique facilities are challenging to model and the selection of appropriate codes was a demanding process. A special methodology was used for assessing the abilities of the codes to simulate these advanced coolants and to obtain regulatory certificate/ permit for their use in operational and accident conditions and for preparation of the amendment of the LVR-15 FSAR. These presented activities represent only starting steps for the further codes validation which will be based on benchmarking of the codes with experimental data provided by the SCWL and HTHL loops in their experimental campaigns. Aknoledgment The authors would like to thank Mr. Miroslav Hrehor and Dr. Vincenzo Romanello for their kind revisions and suggestions. The presented work was financially supported by the Project CZ.02.1.01/ 0.0/0.0/15_008/0000293: Sustainable energy (SUSEN) – 2 nd phase, realized in the framework of the Operation and New Build Experimental and Analytical Tools for Safety Research of GEN IV Reactors ı G. Mazzini, M. Kyncl, Alis Musa and M. Ruscak
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