Current Status of Research and Development on System Integration Technology for Connection between HTGR and Hydrogen Production System at JAEA Hirofumi Ohashi, Yoshitomo Inaba, Tetsuo Nishihara, Tetsuaki Takeda, Koji Hayashi and Yoshiyuki Inagaki Japan Atomic Energy Agency, Japan 1
Contents Concept of the HTGR hydrogen production system R&D items on the system integration technology Control technology to keep reactor operation against thermal disturbance caused by the hydrogen production system Estimation of tritium permeation from reactor to hydrogen Countermeasure against explosion of combustible gas Development of a high-temperature isolation valve to separate reactor and the hydrogen production system in accidents Conclusion 2
Concept of the HTGR Hydrogen Production System HTGR Hydrogen Production System Secondary helium hot gas duct Chemical reactor Reactor Isolation valve Intermediate heat exchanger (IHX) 3
R&D Items on System Integration Technology Reactor scram Blast Isolation valve Explosion Reactor IHX Chemical reactor Raw material Tritium Tritium Hydrogen Hydrogen Primary He gas Secondary He gas Process gas Control technology to keep reactor operation against thermal disturbance caused by the hydrogen production system Estimation of tritium permeation from reactor to hydrogen Countermeasure against explosion of combustible gas Development of a high-temperature isolation valve to separate reactor and the hydrogen production system in accidents 4
Control Technology (1/3) Objective Development of the control technology to keep reactor operation against thermal disturbance caused by the hydrogen production system. Approach JAEA proposed to use a steam generator (SG) as the thermal absorber which is installed downstream the chemical reactor in the secondary helium gas loop. In the HTTR hydrogen production system, target value of the mitigation for the helium gas temperature fluctuation is within 10 o C at SG outlet. Simulation test on the loss of chemical reaction was carried out using a mock-up test facility Reactor IHX SG Chemical reactor Raw material Hydrogen Primary He gas Secondary He gas Process gas 5
Control Technology (2/3) Simulation test on loss of chemical reaction Mock-up test facility LN 2 tank Nitrogen feed line LNG tank Natural gas feed line 600 o C Flare stack Steam feed line Radiator 450 o C Chemical Reactor Water tank (Steam reformer) 650 o C CH 4 +H 2 O Steam generator 880 o C 3H 2 +CO Helium gas circulation loop 4MPa Hot gas duct Circulator Electric heater With electrical heater instead of IHX of HTTR Helium gas temperature and pressure at the chemical reactor inlet (880 o C, 4MPa) are same as those of the HTTR hydrogen production system. Steam reforming of methane is used instead of the IS process. Chemical reactor Steam generator Steam generator (SG) Flare stack Helium gas circulator Electric heater 6
Control Technology (3/3) Simulation test on loss of chemical reaction Procedure The supply of the raw gas for the hydrogen production, methane, was suspended during the normal operation. Experimental result Helium gas temperature [ o C] 1000 800 600 400 Chemical reactor inlet Chemical reactor outlet SG inlet SG outlet 200-1 0 1 2 3 4 5 6 Elapsed time [h] The fluctuation of the helium gas temperature could be mitigated at SG outlet within the target range of 10 o C. Radiator Feed water Natural Circulation Raw gas SG Loss of chemical reaction Radiator Nitrogen SG Hydrogen Chemical reactor Helium gas (840 o C, 4MPa) Chemical reactor Helium 7gas (840 o C, 4MPa)
Estimation of Tritium Permeation (1/2) Objective To investigate the permeability on the material of the IHX tubes, Hastelloy XR. Apparatus Hydrogen and deuterium are used instead of tritium Hastelloy XR (Test Pipe) Pre-Heater (1kW) Measurment System -Temperature -Pressure -Flow Rate Automatic Control System Measurement Pipe (Hastelloy X) Heating System Main Heater (6kW) Exhaust System Measurment System -Hydrogen Flow Control Molecular Sieve Gas Supply System H2/He,D2/Ar,etc. Cooling System Vacuum System Flow Control Molecular Sieve Gas Purge System Ar, He,etc. 8
Estimation of Tritium Permeation (2/2) Experimental result Permeability : K p = F 0 exp(-e 0 / RT) Hydrogen Temperature [ o C] 570 820 Partial pressure of H2 [Pa] E 0 [kj/mol] F 0 [cm 3 (NTP)/(cm s Pa 0.5 )] 1.06 10 2 3.95 10 3 67.2 ± 1.2 (1.0 ± 0.2) 10-4 deuterium 670 820 9.89 10 2 4.04 10 3 76.6 ± 0.5 (2.5 ± 0.3) 10-4 The basic data on the permeability of hydrogen and deuterium has been obtained for the Hastelloy XR tube. Next research items To investigate the permeability on the heat transfer tube material of the chemical reactor in IS process, SiC. To estimate the tritium concentration in the IS process and the produced hydrogen. 9
Countermeasure against Explosion (1/2) Principal countermeasures against explosion of combustible gas Take a distance between the reactor and the hydrogen production system enough to mitigate the overpressure within an allowable range. Protect blast with barriers such as wall, bank and so on. Limit the leak amount of combustible gas. 10
Countermeasure against Explosion (2/2) Limit the leak amount of combustible gas Design of coaxial pipe of combustible gas Filled with nitrogen gas Manhole Combustible gas Outer pipe Support Inner pipe Next research item A conceptual design using a wall and/or a bank is under way from the viewpoint of mitigation of blast 11
Development of High-Temperature Isolation Valve (1/4) Objective Development of an isolation valve for the high-temperature condition around 900 o C. Technical issues Prevention of the valve seat from thermal deformation An angle valve with an inner thermal insulator was selected. Development a new coating metal for the valve seat surface A new coating metal was developed based on the Stellite alloy that is used for valves at around 500 o C. High-temperature Isolation Valve (HTIV) Selection of a valve seat structure having a high sealing performance A flat type valve seat was selected. Confirmation of the seal performance and structural integrity A component test was carried out using 1/2 scale model of HTIV. 12
Development of High-Temperature Isolation Valve (2/4) 1/2 scale model of HTIV Actuator Rod Body (HastelloyX) Seat (HastelloyX) Coating metal (Stellite No.6 + 30wt%-Cr 3 C 2 ) Electric heater Thermal insulator (Glass wool) Casing (Carbon steel) HTIV 1/2 scale model Nominal Size 22 B 16 B Bore 200 mm 100 mm Design Temp. (Casing) 350 o C Design pressure 5.0 MPa 4.5 MPa 13
Development of High-Temperature Isolation Valve (3/4) Component test Apparatus Actuator Ar gas supply system Electric heater Electric heater Cooling water Thermal insulator To He gas detector Exhaust 1/2 scale model of HTIV He gas supply system Experimental condition and procedure (1) Helium gas was supplied to the 1/2 scale model of HTIV and increased up to 4.0MPa and heated up to 900 o C. (2) Valve seat was closed and helium gas at the upstream of the closed valve seat was exhausted. The pressure difference across the valve seat was set to 4.1MPa. (3) The electric heater was shut off and the helium gas leak rate through the closed valve seat was measured from 900 o C to 200 o C by the helium gas detector. 14
Development of High-Temperature Isolation Valve (4/4) Component test Experimental result Leak rate of helium gas (cm 3 /s) 10 1 10-1 10-2 10-3 10-4 4.4 cm 3 /s : Target value 0 200 400 600 800 1000 Temperature of valve seat ( o C) The current technology can be applied to the HTTR hydrogen production system, however, the lapping of the valve seat is necessary after closing at a high temperature. Next research item The improvement of the durability of the valve seat 15
Conclusion (1/2) The system integration technology has been developed for connection of the hydrogen production system to HTGR. The following conclusions were obtained. The control technology to keep reactor operation against thermal disturbance caused by the hydrogen production system JAEA proposed to use SG as the thermal absorber, which is installed downstream the chemical reactor in the secondary helium gas loop, to mitigate temperature fluctuation of secondary helium gas. By the simulation test with the mock-up test facility, it was confirmed that SG could be used as the thermal absorber. Tritium permeation from reactor to hydrogen The permeability on Hastelloy XR which is the heat transfer tube material of IHX was obtained. Next research item is to investigate the permeability on the heat transfer tube material of the chemical reactor in IS process, SiC, and to estimate the 16 tritium concentration in the IS process and the produced hydrogen.
Conclusion (2/2) Countermeasure against explosion of combustible gas The coaxial pipe of combustible gas was designed from the viewpoint of protection of the leakage aiming at arrangement of the hydrogen production system closed by the reactor. A conceptual design using a wall and/or a bank is under way from the viewpoint of the mitigation of the blast. Development of the high-temperature isolation valve to isolate reactor and hydrogen production systems in accidents The new material for the coating of the valve seat surface was developed and the seal performance of the valve was confirmed to satisfy the design target with the 1/2 scale model of the high-temperature isolation valve. The improvement of the durability of the valve seat is the next target for the development. 17
Acknowledgement The present study is the results of Development of Nuclear Heat Utilization Technology in fiscal year from 1997 to 2001, 2003 and 2004 entrusted by Ministry of Education, Culture, Sports, Science and Technology (MEXT) to Japan Atomic Energy Research Institute (JAERI) succeeded by into Japan Atomic Energy Agency (JAEA). The authors are indebted to Dr. S. Shiozawa and Dr. M. Ogawa for their useful advice and discussion in this research. 18
19
Control Technology Simulation test on loss of chemical reaction Experimental result Flow rate [g/s] Hydrogen production rate [m 3 /h] 80 60 40 20 0 140 120 100 80 60 40 20 Steam Methane Nitrogen 0-1 -0.5 0 0.5 1 Elapsed time [h] He temperature [ o C] Pressure in SG [MPa] 1000 800 600 400 200 Chemical reactor inlet Chemical reactor outlet SG inlet SG outlet 6 5 4 3 2 1 0-1 0 1 2 3 4 5 6 Elapsed time [h] 20