Abstract
This thesis is devoted to the investigation of passive safety and inherent features of subcritical nuclear transmutation systems - accelerator-driven systems. The general objective of this research has been to improve the safety performance and avoid elevated coolant temperatures in worst-case scenarios like unprotected loss-of-flow accidents, loss-of-heat-sink accidents, and a combination of both these accident initiators. The specific topics covered are emergency decay heat removal by reactor vessel auxiliary cooling systems, beam shut-off by a melt-rupture disc, safety aspects from locating heat-exchangers in the riser of a pool-type reactor system, and reduction of pressure resistance in the primary circuit by employing bypass routes. The initial part of the research was focused on reactor vessel auxiliary cooling systems. It was shown that an 80 MW{sub th} Pb/Bi-cooled accelerator-driven system of 8 m height and 6 m diameter vessel can be well cooled in the case of loss-of-flow accidents in which the accelerator proton beam is not switched off. After a loss-of-heat-sink accident the proton beam has to be interrupted within 40 minutes in order to avoid fast creep of the vessel. If a melt-rupture disc is included in the wall of the beam pipe, which breaks at 150 K above the
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Citation Formats
Carlsson, Johan.
Inherent Safety Features and Passive Prevention Approaches for Pb/Bi-cooled Accelerator-Driven Systems.
Sweden: N. p.,
2003.
Web.
Carlsson, Johan.
Inherent Safety Features and Passive Prevention Approaches for Pb/Bi-cooled Accelerator-Driven Systems.
Sweden.
Carlsson, Johan.
2003.
"Inherent Safety Features and Passive Prevention Approaches for Pb/Bi-cooled Accelerator-Driven Systems."
Sweden.
@misc{etde_20358055,
title = {Inherent Safety Features and Passive Prevention Approaches for Pb/Bi-cooled Accelerator-Driven Systems}
author = {Carlsson, Johan}
abstractNote = {This thesis is devoted to the investigation of passive safety and inherent features of subcritical nuclear transmutation systems - accelerator-driven systems. The general objective of this research has been to improve the safety performance and avoid elevated coolant temperatures in worst-case scenarios like unprotected loss-of-flow accidents, loss-of-heat-sink accidents, and a combination of both these accident initiators. The specific topics covered are emergency decay heat removal by reactor vessel auxiliary cooling systems, beam shut-off by a melt-rupture disc, safety aspects from locating heat-exchangers in the riser of a pool-type reactor system, and reduction of pressure resistance in the primary circuit by employing bypass routes. The initial part of the research was focused on reactor vessel auxiliary cooling systems. It was shown that an 80 MW{sub th} Pb/Bi-cooled accelerator-driven system of 8 m height and 6 m diameter vessel can be well cooled in the case of loss-of-flow accidents in which the accelerator proton beam is not switched off. After a loss-of-heat-sink accident the proton beam has to be interrupted within 40 minutes in order to avoid fast creep of the vessel. If a melt-rupture disc is included in the wall of the beam pipe, which breaks at 150 K above the normal core outlet temperature, the grace period until the beam has to be shut off is increased to 6 hours. For the same vessel geometry, but an operating power of 250 MW{sub th} the structural materials can still avoid fast creep in case the proton beam is shut off immediately. If beam shut-off is delayed, additional cooling methods are needed to increase the heat removal. Investigations were made on the filling of the gap between the guard and the reactor vessel with liquid metal coolant and using water spray cooling on the guard vessel surface. The second part of the thesis presents examinations regarding an accelerator-driven system also cooled with Pb/Bi but with heat-exchangers located in the risers of the reactor vessel. For a pool type design, this approach has advantages in the case of heat-exchanger tube failures, particularly if water is used as the secondary fluid. This is because a leakage of water from the secondary circuit into the Pb/Bi-cooled primary circuit leads to upward sweeping of steam bubbles, which would collect in the gas plenum. In the case of heat exchangers in the downcomer steam bubbles may be dragged into the ADS core and add reactivity. Bypass routes are employed to increase the flow speed in loss-of-flow events for this design. It is shown that the 200 MW{sub th} accelerator-driven system with heat-exchangers in the riser copes reasonably well with both a loss-of-flow accident with the beam on and an unprotected loss-of-heat-sink accident. For a total-loss-of-power (station blackout) and an immediate beam-stop the core outlet temperature peaks at 680 K. After a combined loss-of-flow and loss-of-heat-sink accident the beam should be shut off within 4 minutes to avoid exceeding the ASME level D of 977 K, and within 8 minutes to avoid fast creep. Assuming the same core inlet temperature, both the reactor design with heat-exchanger in the risers and the downcomers have similar temperature evolutions after a total-loss-of power accident. A large accelerator-driven system of 800 MW{sub th} with a 17 m tall vessel may eventually become a standard size. For this higher power ADS, the location of the heat-exchangers has greater impact on the natural convection capability. This is due to that larger heat exchangers have more influence on the distance between the thermal centers during a loss of- flow accident. The design with heat-exchangers in the downcomers, the long-term vessel temperature peaks at 996 K during a loss-of-flow accident with the beam on. This does not pose a threat of creep rupture for the vessel. However, the location of the heat-exchangers in the downcomers will probably require secondary coolant other than water, like for example oil (for temperatures not higher than 673 K) or Pb/Bi coolant.}
place = {Sweden}
year = {2003}
month = {Mar}
}
title = {Inherent Safety Features and Passive Prevention Approaches for Pb/Bi-cooled Accelerator-Driven Systems}
author = {Carlsson, Johan}
abstractNote = {This thesis is devoted to the investigation of passive safety and inherent features of subcritical nuclear transmutation systems - accelerator-driven systems. The general objective of this research has been to improve the safety performance and avoid elevated coolant temperatures in worst-case scenarios like unprotected loss-of-flow accidents, loss-of-heat-sink accidents, and a combination of both these accident initiators. The specific topics covered are emergency decay heat removal by reactor vessel auxiliary cooling systems, beam shut-off by a melt-rupture disc, safety aspects from locating heat-exchangers in the riser of a pool-type reactor system, and reduction of pressure resistance in the primary circuit by employing bypass routes. The initial part of the research was focused on reactor vessel auxiliary cooling systems. It was shown that an 80 MW{sub th} Pb/Bi-cooled accelerator-driven system of 8 m height and 6 m diameter vessel can be well cooled in the case of loss-of-flow accidents in which the accelerator proton beam is not switched off. After a loss-of-heat-sink accident the proton beam has to be interrupted within 40 minutes in order to avoid fast creep of the vessel. If a melt-rupture disc is included in the wall of the beam pipe, which breaks at 150 K above the normal core outlet temperature, the grace period until the beam has to be shut off is increased to 6 hours. For the same vessel geometry, but an operating power of 250 MW{sub th} the structural materials can still avoid fast creep in case the proton beam is shut off immediately. If beam shut-off is delayed, additional cooling methods are needed to increase the heat removal. Investigations were made on the filling of the gap between the guard and the reactor vessel with liquid metal coolant and using water spray cooling on the guard vessel surface. The second part of the thesis presents examinations regarding an accelerator-driven system also cooled with Pb/Bi but with heat-exchangers located in the risers of the reactor vessel. For a pool type design, this approach has advantages in the case of heat-exchanger tube failures, particularly if water is used as the secondary fluid. This is because a leakage of water from the secondary circuit into the Pb/Bi-cooled primary circuit leads to upward sweeping of steam bubbles, which would collect in the gas plenum. In the case of heat exchangers in the downcomer steam bubbles may be dragged into the ADS core and add reactivity. Bypass routes are employed to increase the flow speed in loss-of-flow events for this design. It is shown that the 200 MW{sub th} accelerator-driven system with heat-exchangers in the riser copes reasonably well with both a loss-of-flow accident with the beam on and an unprotected loss-of-heat-sink accident. For a total-loss-of-power (station blackout) and an immediate beam-stop the core outlet temperature peaks at 680 K. After a combined loss-of-flow and loss-of-heat-sink accident the beam should be shut off within 4 minutes to avoid exceeding the ASME level D of 977 K, and within 8 minutes to avoid fast creep. Assuming the same core inlet temperature, both the reactor design with heat-exchanger in the risers and the downcomers have similar temperature evolutions after a total-loss-of power accident. A large accelerator-driven system of 800 MW{sub th} with a 17 m tall vessel may eventually become a standard size. For this higher power ADS, the location of the heat-exchangers has greater impact on the natural convection capability. This is due to that larger heat exchangers have more influence on the distance between the thermal centers during a loss of- flow accident. The design with heat-exchangers in the downcomers, the long-term vessel temperature peaks at 996 K during a loss-of-flow accident with the beam on. This does not pose a threat of creep rupture for the vessel. However, the location of the heat-exchangers in the downcomers will probably require secondary coolant other than water, like for example oil (for temperatures not higher than 673 K) or Pb/Bi coolant.}
place = {Sweden}
year = {2003}
month = {Mar}
}