MELCOR Pre -Test Calculation of Boil-off test at Quench facility

1. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 MELCOR Pre -Test Calculation of Boil-off test at Quench facility Antoaneta Stefanova & Pavlin Groudev Institute for Nuclear Research and Nuclear Energy Bulgarian Academy of Sciences

2. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 • INTRODUCTION This report presents the MELCOR pre-test calculation, which was performed to investigate behavior of the parameters during the Boil-off test at QUENCH facility. MELCOR 1.8.5 computer code has been used to simulate the investigated transient. • OBJECTIVES OF THE CALCULATION One of the main objective of this calculation is to demonstrate that this test can be conducted successfully at LACOMERA Quench facility. Other objective is to investigate the boil off phase up to the time, when the water has dropped to the lower end of the bundle during the Boil-off test with Quench facility and further core reflood as a successful severe accident management guidance.

3. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 • DESCRIPTION OF THE QUENCH FACILITY • In radial direction the QUENCH fuel rod bundle is composed of one unheated rod at center position, an inner ring of 8 heated rods connected to an electric power supply, an outer ring of 12 heated rods connected to another electric power supply system, and a set of 4 corner rods at the vacant rod positions. In tis way the test section is made from 20 heated fuel rod simulators, approximately 2.5 m long, and an unheated rod in the center. They are filled with a mixture of 95 vol% Argon and 5 vol% krypton at a pressure slightly about fluid pressure in the bundle and connected to a compensating volume at room temperature.

4. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 The bundle is enclosed in a shroud, which is composed of Zircaloy liner (2.38 mm thick), ZrO2 fiber insulation (37 mm thick) and the inner cooling jacket, made of stainless steel. The region between the shroud and the inner cooling jacket, i.e. the ZrO2 fiber insulation and the region (space) above this insulation are flooded with argon before the test, the pressure being about 2 bar. The main contribution of the radial heat losses is due to radiation.

5. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 Scheme of Quench test facility

6. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 • MELCOR QUENCH FASILITY MODEL • The Quench test facility is modeled by using CVH, FL, COR, MP, HS, TF, EDF and CF Packages. • The thermal-hydraulic behavior of liquid and gases are modeled by CVH and FL Packages. It have been used 24 control volumes and 19 flow paths presented below. There are five types of control volumes: • 1.Source – Time - dependent control volumes CV001-CV003, which are sources of argon, superheated steam and liquid water. • 2.Sink – Time in - dependent control volume CV250, which collects off-gases and liquids;

7. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 3. Inlet – Control volumes CV020, CV030 and CV119, which represent the volumes initially available to hydrodynamic materials in the inlet pipes, inlet plenum; 4. Bundle - Control volumes CV120 - CV125, CV920 – 925 and CV998 - CV999, which represent the volumes initially available to hydrodynamic materials within the fuel bundle and shroud, limited in the radial direction by the inner cooling jacket. 5. Outlet – Control volumes CV126 and CV800, which represent the volumes initially available to hydrodynamic materials in the outlet plenum and off-gas, pipe.

8. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 The Quench fuel rod bundle and Zircaloy shroud are modeled with the Core (COR) Package. In the modeling of the COR package are used 88 cells, in 4 rings, each with axial 22 levels. The Axial COR Nodalization is divided into 16 axial levels, each axial level having a height of 100 mm. The computational model includes two additional levels below –300 mm and 4 additional levels above 1300 mm, to allow the proper of axial boundary conditions. Another represents the 100 mm section of the fuel rod simulators above the outlet plenum that contain molybdenum electrodes. The uppermost and lowermost levels, with height 50 mm, represent the portion of the fuel rod simulator, which are cooled by water.

9. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 The MELCOR HS Package calculates heat condition within intact, solid structure and energy transfer across its boundary surfaces into control volumes. There are 15 HS in COR Package. Boundary structures above insulation are 5 HS and below the jacket the numbers of HS are 3. If the heat structure is located at the outer radial boundary of the COR Package cells, the left boundary fluid temperature is calculated by the COR Package. Convective boundary conditions and radiation heat transfers are calculated on all surfaces, which are not insulated or cooled by water or argon.

10. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 In COR Package are modeled fuel rods, everything inside the inner cooling jacket and Zircaloy shroud. The HS Package models the fiber insulation and the inner cooling jacket. The heated and unheated fuel rod simulators are modeled by using the Fuel and Cladding components. The CL component represents the Zircaloy tube. The FU component represents the ceramic pellets. The central rod simulators contain tungsten heating elements, which are connected to the power supply by electrodes formed of molybdenum and copper within the cladding tubes. The corner rods are modeled as non-supporting structure component. The bundle shroud is modeled using the canister components.

11. CV150 CV130 Water cooling jacket FL201 CV250 CV800 1500 mm CV998 CV126 Upper Plenum Ar source 1300 mm FL004 FL126 CV004 Mo CV925 CV125 1024 mm FL925 FL25 W CV924 CV124 800 mm FL924 CV999 FL124 CV923 CV123 600 mm FL923 FL123 Ar cooling jacket CV922 CV122 300 mm FL922 FL122 CV921 CV121 FL921 FL121 0 mm CV920 CV120 Ar Source FL001 CV001 -300 mm FL120 Steam Source to LP FL021 CV119 CV020 FL002 CV002 Lower Plenum -475 mm Quench Water to LP CV050 CV030 FL031 FL003 CV003

12. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 • RESULTS and DISCUTION of Boil-off Test • Boil-off conditions can be observed in the NPP calculations in the late phase of SBO or SBLOCA. Due to additional available coolant at that time in the downcomer and lower plenum in RPV after starting boil-off phase saturated water enters into the core region from these volumes. Based on this phenomena dry-out velocity is reduced up to approximately 0.1 cm/s. So, to reduce the effective dry-out velocity in the QUENCH facility there was need of additional steam supplying in the fuel bundle. Based on plant analyses the initial heat-up rate was derived to be approximately 0.5 K/s.

13. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 It have been used for calculation presented below input data based on draft test protocol of Quench L-Q2. Some insignificant deviation have been done based on discussions from previous slide. Water injection (g/s) Heaters power (W) Auxiliary heaters power (W) 0.0 0.100 0.0 100.0 0.0 0.0 90.0 0.100 8.0 100.0 49.0 0.0 91.0 0.0 10.0 2500.0 50.0 1000.0 3299.0 0.0 1999.0 2500.0 3000.0 1000.0 3500.0 0.001 2000.0 5500.0 3300.0 3000.0 8300.0 0.001 3599.0 5500 5400.0 3000.0 8301.0 0.020 3600.0 6200.0 5499.0 3000.0 8569.0 0.020 4809.0 6200.0 5500.0 2200.0 8570.0 0.003 4810.0 6000.0 6600.0 2200.0 8700.0 0.003 4890.0 6500.0 8299.0 2200.0 8850.1 0.001 5000.0 7500.0 8300.0 2300.0 9000.0 0.0 8299.0 7500.0 8301.0 0.0 8300.0 7000.0 9000.0 0.0 8301.0 4000.0 8700.0 4000.0 8710.0 100.0 9000.0 100.0

14. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 Some of important parameters during the Boil-off test are shown in next three figures. The calculation was performed up to 9000.0 sec into the transient time. Coolant temperature in the Bundle Fuel Cladding Temperature

15. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 The test section is filled up from 0 s to 90 s at approximately 1.1 m water level with flow rate of 100 g/s cold water (initial temperature is 363 K) and heat up with initial bundle power 2.5 kW to the saturated temperature, which is approximately 393 K. The pressure in the bundle is 0.2 MPa. There is injection of 3g hot Ar at the top from 0 s during the whole transient, and injection from the bottom with approximately of 2-3 g/s hot Ar to 8300 s. The test starts with initial boil-off phase, which is controlled with the bundle heating system. To avoid increasing of cladding temperature in the upper part of bundle, start injection of additional water 1.0 g/s (the temperature of injected water is 363 K) at 3500 s and heated up injected water with 3 kW auxiliary heaters power.

16. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 The auxiliary heaters are located at the lower plenum of the test facility. In this phase a Boil-off velocity is approximately 0.1 cm/s until reaching water level of 0.25 m at the lower end of the bundle. The heated rate is 0.45 K/s. The reflood phase is initiated with injections of 20 g/s reflood water from quenching pump (See Table 1) at 8300 s, when peak bundle temperature reached value > 1837 K. The temperature in bundle didn’t reach the desired value > 1900 K. Reflood water temperature at lower end of the bundle is approximately 363 K. Cold water from the quench pump is heated up in the quench pipe and enters the lower plenum volumes.

17. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 During reflood phase, the auxiliary heaters were terminated and the bundle heaters power was reduced to the decay heat level of 4 kW. Injection of reflood water is terminated when water level in the bundle reached 1.1 m. Water Level in the Bundle

18. 11th International QUENCH Workshop Forschungszentrum Karlsruhe (FZK), October 25-27, 2005 • CONCLUSIONS • This pre-test calculation shows that this test can be conducted successfully and observe the degraded core reflood and includes the preceding of boil-off phase up to the time, when the water has dropped to the lower end of the bundle during the Boil-off test with Quench facility.