Development of a new district heating reactor&nbsp;concept&nbsp;was recently started at VTT Technical Research Centre of Finland. The concept&nbsp;features a&nbsp;50&nbsp;MW reactor&nbsp;with modular integrated design&nbsp;that is&nbsp;operated&nbsp;at low temperature and pressure.&nbsp;The design combines traditional PWR technology with&nbsp;innovative passive safety features capable of decay heat removal without any mechanical moving&nbsp;parts.&nbsp;This paper presents the&nbsp;preliminary&nbsp;thermal-hydraulic design&nbsp;of the reactor&nbsp;along with transient analysis results.&nbsp;A general overview of the technology and core physics simulations&nbsp;are addressed in separate papers&nbsp;submitted&nbsp;to the ICONE 28 conference.The reactor module consists of two nested pressure vessels, submerged in a pool of water.&nbsp;The reactor core and primary circuit are&nbsp;enclosed&nbsp;inside a primary vessel, which itself is&nbsp;located&nbsp;inside a containment vessel. The containment space between the two vessels is partially filled with water.&nbsp;Primary circulation is&nbsp;maintained&nbsp;by natural convection, and heat is transferred to the district heating network via heat exchangers and an intermediate circuit.&nbsp;In normal operation,&nbsp;water&nbsp;temperature&nbsp;inside the containment&nbsp;remains&nbsp;below boiling point, and heat losses&nbsp;are small. When the primary cooling path&nbsp;through&nbsp;the&nbsp;heat exchanger&nbsp;is lost,&nbsp;temperature inside the containment reaches&nbsp;boiling point,&nbsp;opening&nbsp;an efficient&nbsp;heat transfer path to the pool.The&nbsp;thermal-hydraulic analyses were carried out&nbsp;using the&nbsp;Apros&nbsp;system code.&nbsp;The computational model comprised&nbsp;the primary&nbsp;and&nbsp;intermediate&nbsp;circuits,&nbsp;the containment, and the pool. A&nbsp;point-kinetics model&nbsp;was used&nbsp;for the core&nbsp;neutronics. The&nbsp;transient cases&nbsp;presented in this&nbsp;paper include&nbsp;station blackout&nbsp;(SBO)&nbsp;as&nbsp;an&nbsp;ATWS scenario&nbsp;and&nbsp;a&nbsp;leak from primary&nbsp;vessel&nbsp;to containment.&nbsp;The SBO&nbsp;was simulated for a&nbsp;period of one&nbsp;week to study the long-term decay heat removal capability.&nbsp;The containment functioned as planned,&nbsp;cooling&nbsp;the primary circuit effectively. The temperature&nbsp;and pressure&nbsp;inside the primary vessel&nbsp;stabilized&nbsp;at a safe level, and the&nbsp;pool temperature&nbsp;did not reach&nbsp;boiling point.&nbsp;In the&nbsp;leak scenario,&nbsp;the primary water level dropped below the&nbsp;riser tube&nbsp;stopping the natural circulation and causing boiling in the core.&nbsp;However, the&nbsp;maximum&nbsp;cladding&nbsp;temperature remained low&nbsp;and&nbsp;the water level in the&nbsp;primary&nbsp;vessel was still well above the core&nbsp;after the&nbsp;flow conditions&nbsp;had&nbsp;reached a new equilibrium.&nbsp;&nbsp;The results&nbsp;from the&nbsp;normal&nbsp;operation as well as transient scenarios are promising.&nbsp;The reactor&nbsp;is capable of producing&nbsp;low temperature heat to the&nbsp;district heating network. The containment design works as planned and removes decay heat effectively&nbsp;into the pool in transient scenarios.&nbsp;&nbsp;

A Finnish District Heating Reactor: Thermal-Hydraulic Design and Transient Analyses

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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A Finnish District Heating Reactor: Thermal-Hydraulic Design and Transient Analyses

A Finnish District Heating Reactor: Thermal-Hydraulic Design and Transient Analyses