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Description
The European Spallation Source ERIC (ESS) will provide long-pulsed cold and thermal neutron fluxes at very high brightness to the research community. Spallation neutrons are produced by a linear proton accelerator with an average beam power of ultimately 5 MW. These neutrons are moderated to cold and thermal energies by the moderators. Initially, the ESS will install two hydrogen moderators above the target wheel. The nuclear heating is estimated to be 6.7 kW. The ESS cryogenic moderator system (CMS) plays a role in circulating subcooled liquid hydrogen at a temperature of 17 K and a pressure of 1 MPa with a flow rate of 0.5 kg/s to remove the nuclear heating at the moderators. The heat load will be efficiently removed through a plate-fine type He-H2 heat exchanger (HX11) located in the CMS cold box by a large-scale 20 K helium refrigeration system, which is called the Target Moderator Cryoplant (TMCP), with the cooling capacity of 30.3 kW at 15 K. High-pressure helium streams, operating at a temperature of 16 K, are transported from the TMCP cold box to a valve box called the Jumper spool box (JSB) through a 300 m-vacuum insulated cryogenic helium transfer line (CTL). The return temperature is maintained at 21.2 K by warm helium streams via a mixing valve in the JSB in order to apply no thermal disturbance to the TMCP cold box.
When the proton beams are injected, an immerse heat load is suddenly applied to the CMS. The feed helium flow rate to the heat exchanger is adjusted by the feed control valve in the JSB to compensate for the heat load, while the JSB bypass valve is automatically adjusted to maintain a pressure drop through the bypass line. This allows the available cooling capacity to be regulated without applying any thermal disturbance to the TMCP cold box. The hydrogen temperature supplied to the moderators remains consistently at 17.5 K.
In this study, a one-dimensional simulation model of the heat exchanger was developed to comprehend the propagation of the thermal fluctuations when the return hydrogen temperature was rapidly changed due to proton beam injection or trip event. The thermal propagations through the heat exchanger were analyzed by varying the speed of ramping up the feed helium flow rate and the timing to initiate the ramp-up mode. The operational parameters can be optimized to mitigate the fluctuation of the hydrogen supply temperature within ±0.1 K.
| Submitters Country | Sweden |
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