Comparison of Alternatives to the 2004 Vacuum Vessel Heat Transfer System

A study comparing different alternatives for the Vacuum Vessel Primary Heat Transfer System has been completed. Three alternatives were proposed in a Project Change Request (PCR-190) by relocating the heat exchangers (HXs) from the roof of the Tokamak building to inside the Vacuum Vessel Pressure Suppression System (VVPSS) tank. The study evaluated the three alternatives and recommended modifications to one of them to arrive at a preferred configuration that included relocating the HXs inside the Tokamak building but outside the VVPSS tank as well as including a small safety-rated pump and HX in parallel to the main circulation pump and HX. The Vacuum Vessel (VV) Primary Heat Transfer System (PHTS) removes heat generated in the VV during normal operation (10 MW, pulsed power) as well as the decay heat from the VV itself and from the structures/components attached to the VV (first wall, blanket, and divertor {approx}0.48 MW peak). Therefore, the VV PHTS has two safety functions: (1) contain contaminated cooling water (similar to the other PHTSs) and (2) provide passive cooling during an accident event. The 2004 design of the VV PHTS consists of two independent loops, each loop cooling half of the 18 VV segments with a nominal flow of 475 kg/s of water at about 1.1 MPa and 100 C. The total flow for both loops is 950 kg/s. Both loops are required to remove the heat load during normal plasma operation. During accident conditions, only one loop is needed to remove by natural convection (no pump needed) the decay heat of the complete VV and attached components. The heat is transferred to heat exchanger (HXs) located on top of the roof, outside the Tokamak building. These HXs are air-to-water (A/W) HXs. Three alternatives have been proposed for this cooling system. For a detailed discussion of these alternatives, please refer to Project Change Request, PCR-190 (Ref. 1). A brief introduction is given here. Alternative 1 includes only one main forced circulation loop with a small safety-rated pump in parallel with the main circulation pump. In addition, this alternative has two natural circulation safety loops. Both the safety and main loops supply water to the bottom of the VV with six branch lines and collect the heated water at the top of the vessel through six branches. The distribution headers are located in the lower pipe chase and the collection headers in the upper pipe chase. Each of these loops (one main and two emergency) has a HX mounted in the Vacuum Vessel Pressure Suppression System (VVPSS) tank. The main HX is cooled using either Component Cooling Water System (CCWS) or Chilled Water System (CHWS) water, and the emergency HXs are cooled by natural circulation of the VVPSS water. See Fig. 1 taken from PCR-190. Alternative 2 is exactly the same as Alternative 1 except that there is only one emergency loop and one emergency HX. See Fig. 2 taken from PCR-190. Alternative 3 also has one main forced circulation loop with a small safety-rated pump in parallel with the main circulation pump and one natural circulation safety loop. In this case, both the safety and main loops supply water to the top of the VV with three branch lines and collect the heated water at the top of the vessel through three branches. Here, the distribution header is located in the upper pipe chase as is the collection header. As before, each of these loops has a HX mounted in the VVPSS tank. The main HX is cooled using either CCWS or CHWS water, and the emergency HXs are cooled by natural circulation of the VVPSS water. See Fig. 3 taken from PCR-190. The preferred configuration is developed by selecting specific attributes of the other configurations analyzed and the logic for selecting this configuration is discussed at the end of the document. It is a modification of Alternative 2 that eliminates the separate safety loop, but incorporates a small safety rated HX and pump in parallel with the main HX and pump. It uses 18 inlet and 18 outlet branches (as did the 2004 design) and locates the HXs outside of the VVPSS tank. Tables 1 and 2 examine alternatives to the 2004 VV heat transfer system design that were proposed in PCR-190, as well as the preferred option

RELAP5 MODEL OF THE DIVERTOR PRIMARY HEAT TRANSFER SYSTEM

This report describes the RELAP5 model that has been developed for the divertor primary heat transfer system (PHTS). The model is intended to be used to examine the transient performance of the divertor PHTS and evaluate control schemes necessary to maintain parameters within acceptable limits during transients. Some preliminary results are presented to show the maturity of the model and examine general divertor PHTS transient behavior. The model can be used as a starting point for developing transient modeling capability, including control system modeling, safety evaluations, etc., and is not intended to represent the final divertor PHTS design. Preliminary calculations using the models indicate that during normal pulsed operation, present pressurizer controls may not be sufficient to keep system pressures within their desired range. Additional divertor PHTS and control system design efforts may be required to ensure system pressure fluctuation during normal operation remains within specified limits

Comparison of Alternatives to the 2004 Vacuum Vessel Heat Transfer System

A study comparing different alternatives for the Vacuum Vessel Primary Heat Transfer System has been completed. Three alternatives were proposed in a Project Change Request (PCR-190) by relocating the heat exchangers (HXs) from the roof of the Tokamak building to inside the Vacuum Vessel Pressure Suppression System (VVPSS) tank. The study evaluated the three alternatives and recommended modifications to one of them to arrive at a preferred configuration that included relocating the HXs inside the Tokamak building but outside the VVPSS tank as well as including a small safety-rated pump and HX in parallel to the main circulation pump and HX. The Vacuum Vessel (VV) Primary Heat Transfer System (PHTS) removes heat generated in the VV during normal operation (10 MW, pulsed power) as well as the decay heat from the VV itself and from the structures/components attached to the VV (first wall, blanket, and divertor {approx}0.48 MW peak). Therefore, the VV PHTS has two safety functions: (1) contain contaminated cooling water (similar to the other PHTSs) and (2) provide passive cooling during an accident event. The 2004 design of the VV PHTS consists of two independent loops, each loop cooling half of the 18 VV segments with a nominal flow of 475 kg/s of water at about 1.1 MPa and 100 C. The total flow for both loops is 950 kg/s. Both loops are required to remove the heat load during normal plasma operation. During accident conditions, only one loop is needed to remove by natural convection (no pump needed) the decay heat of the complete VV and attached components. The heat is transferred to heat exchanger (HXs) located on top of the roof, outside the Tokamak building. These HXs are air-to-water (A/W) HXs. Three alternatives have been proposed for this cooling system. For a detailed discussion of these alternatives, please refer to Project Change Request, PCR-190 (Ref. 1). A brief introduction is given here. Alternative 1 includes only one main forced circulation loop with a small safety-rated pump in parallel with the main circulation pump. In addition, this alternative has two natural circulation safety loops. Both the safety and main loops supply water to the bottom of the VV with six branch lines and collect the heated water at the top of the vessel through six branches. The distribution headers are located in the lower pipe chase and the collection headers in the upper pipe chase. Each of these loops (one main and two emergency) has a HX mounted in the Vacuum Vessel Pressure Suppression System (VVPSS) tank. The main HX is cooled using either Component Cooling Water System (CCWS) or Chilled Water System (CHWS) water, and the emergency HXs are cooled by natural circulation of the VVPSS water. See Fig. 1 taken from PCR-190. Alternative 2 is exactly the same as Alternative 1 except that there is only one emergency loop and one emergency HX. See Fig. 2 taken from PCR-190. Alternative 3 also has one main forced circulation loop with a small safety-rated pump in parallel with the main circulation pump and one natural circulation safety loop. In this case, both the safety and main loops supply water to the top of the VV with three branch lines and collect the heated water at the top of the vessel through three branches. Here, the distribution header is located in the upper pipe chase as is the collection header. As before, each of these loops has a HX mounted in the VVPSS tank. The main HX is cooled using either CCWS or CHWS water, and the emergency HXs are cooled by natural circulation of the VVPSS water. See Fig. 3 taken from PCR-190. The preferred configuration is developed by selecting specific attributes of the other configurations analyzed and the logic for selecting this configuration is discussed at the end of the document. It is a modification of Alternative 2 that eliminates the separate safety loop, but incorporates a small safety rated HX and pump in parallel with the main HX and pump. It uses 18 inlet and 18 outlet branches (as did the 2004 design) and locates the HXs outside of the VVPSS tank. Tables 1 and 2 examine alternatives to the 2004 VV heat transfer system design that were proposed in PCR-190, as well as the preferred option

RELAP5 MODEL OF THE DIVERTOR PRIMARY HEAT TRANSFER SYSTEM

This report describes the RELAP5 model that has been developed for the divertor primary heat transfer system (PHTS). The model is intended to be used to examine the transient performance of the divertor PHTS and evaluate control schemes necessary to maintain parameters within acceptable limits during transients. Some preliminary results are presented to show the maturity of the model and examine general divertor PHTS transient behavior. The model can be used as a starting point for developing transient modeling capability, including control system modeling, safety evaluations, etc., and is not intended to represent the final divertor PHTS design. Preliminary calculations using the models indicate that during normal pulsed operation, present pressurizer controls may not be sufficient to keep system pressures within their desired range. Additional divertor PHTS and control system design efforts may be required to ensure system pressure fluctuation during normal operation remains within specified limits

RELAP5 Model of the First Wall/Blanket Primary Heat Transfer System

ITER inductive power operation is modeled and simulated using a system level computer code to evaluate the behavior of the Primary Heat Transfer System (PHTS) and predict parameter operational ranges. The control algorithm strategy and derivation are summarized in this report as well. A major feature of ITER is pulsed operation. The plasma does not burn continuously, but the power is pulsed with large periods of zero power between pulses. This feature requires active temperature control to maintain a constant blanket inlet temperature and requires accommodation of coolant thermal expansion during the pulse. In view of the transient nature of the power (plasma) operation state a transient system thermal-hydraulics code was selected: RELAP5. The code has a well-documented history for nuclear reactor transient analyses, it has been benchmarked against numerous experiments, and a large user database of commonly accepted modeling practices exists. The process of heat deposition and transfer in the blanket modules is multi-dimensional and cannot be accurately captured by a one-dimensional code such as RELAP5. To resolve this, a separate CFD calculation of blanket thermal power evolution was performed using the 3-D SC/Tetra thermofluid code. A 1D-3D co-simulation more realistically models FW/blanket internal time-dependent thermal inertia while eliminating uncertainties in the time constant assumed in a 1-D system code. Blanket water outlet temperature and heat release histories for any given ITER pulse operation scenario are calculated. These results provide the basis for developing time dependent power forcing functions which are used as input in the RELAP5 calculations

RELAP5 Model of the Vacuum Vessel Primary Heat Transfer System

This report describes the RELAP5 models that have been developed for the Vacuum Vessel (VV) Primary Heat Transfer System (PHTS). The models are intended to be used to examine the transient performance of the VV PHTS, and evaluate control schemes necessary to maintain parameters within acceptable limits during transients. Some preliminary results are presented to show the maturity of the models and to examine general VV PHTS transient behavior. The models can be used as a starting point to develop transient modeling capability in several directions including control system modeling, safety evaluations, etc, and are not intended to represent the final VV PHTS design. Preliminary calculations using the models indicate that during normal pulsed operation, heat exchanger control may not be necessary, and that temperatures within the vacuum vessel during decay heat operation remain low

Turbulent Properties in Star-forming Molecular Clouds Down to the Sonic Scale. II. Investigating the Relation between Turbulence and Star-forming Environments in Molecular Clouds

We investigate the effect of star formation on turbulence in the Orion A and Ophiuchus clouds using principal component analysis (PCA). We measure the properties of turbulence by applying PCA on the spectral maps in (CO)-C-13, (CO)-O-18, HCO+ J = 1-0, and CS J = 2-1. First, the scaling relations derived from PCA of the (CO)-C-13 maps show that the velocity difference (delta v) for a given spatial scale (L) is the highest in the integral-shaped filament (ISF) and L1688, where the most active star formation occurs in the two clouds. The delta v increases with the number density and total bolometric luminosity of the protostars in the subregions. Second, in the ISF and L1688 regions, the delta v of (CO)-O-18, HCO+, and CS are generally higher than that of (CO)-C-13, which implies that the dense gas is more turbulent than the diffuse gas in the star-forming regions; stars form in dense gas, and dynamical activities associated with star formation, such as jets and outflows, can provide energy into the surrounding gas to enhance turbulent motions