The DTT secondary cooling water systems

https://doi.org/10.1016/j.fusengdes.2020.111712Get rights and content

Highlights

  • Thermal Power Load, cooling water system, energy saving, water saving, heat exchanger, water storage.

Abstract

The new Tokamak machine DTT (Divertor Tokamak Test), planned under construction by Enea Frascati Research Center, is a machine actively cooled by water. Although DTT is an intermittently operating machine, the thermal power that must be cooled is more or less 127 MW emitted within 100 seconds. Geographically the DTT site, at the Enea Frascati center, doesn’t allow the construction of water basins and the cooling wet towers. Furthermore, it doesn’t have enough water supply coming from the municipal aqueduct. Therefore, the best solution is to project a close loop cooling water system, divided into 2 circuits: primary circuits (Divertor, First Wall, ECRH, ICRH, NBI, Electrical Power Supply and Cryoplant) filled with demineralized water and a secondary circuit filled with cooling water designed for working with pressure under 16 Bars. The thermal Power transferred by the primary circuits using dedicated heat exchangers (plates or shell-and-tube) is delivered to a centralized “warm tank” developed in order to store all the energy emitted during the plasma discharge and to prevent the total water temperature in the tank from reaching boiling point. Afterwards, the warm fluid is transferred to another “cold tank” where the chillers are continuously working between two successive machine pulses every 3600 seconds. The two tanks are designed to optimize the minimum power required by the chillers. Moreover, a recovery energy system will be incorporated in order to heat all components (First Wall, Divert or, Vacuum Vessel) which should be maintained warm between the two pulses. The same logic of centralization is applied to the demineralization with reverse osmosis.

Introduction

The DTT (Divertor Tokamak Test) Machine will be build replacing the FTU (Frascati Tokamak Upgrade) in ENEA research Center in Frascati, Rome, Italy. This new machine is born to test the different types of divertors of ITER or ITER\DEMO relevant. The plasma parameters, the heatings (NBI, ICRH, ECRH) are foreseen in order to be more flexibles following different plasma scenarios and to reach several megaWatt per square meter as thermal load on the Divertor tiles. Although the DTT is a pulsed machine with a dwell time of one hour, in order to recharge all systems, the high specific power require an active cooled system in most of components (First Wall, Divertor, Vacuum Vessel, ICRH, ECRH NBI, Cryoplant and Power Supplies) The first target was to collect from different components the thermal loads with their operation conditions (Power Duration, Inlet and Outlet Temperature, Drop Pressure and Dwell time). In Table 1 is summarized the inventory of all thermal load for each component.

The total thermal Power emitted during the plasma operation is more or less 127 MW, most of it emitted in less than 150 seconds, divided mainly by Divertor, First Wall, ECRH, ICRH,NBI and Electrical Power Supply. Otherwise the Cryoplant and the Toroidal Field Systems they need to be cooled continuously.

Section snippets

Cooling Water System close loop

In order to find the best water cooling system for 127 MW of DTT, we should consider the boundary conditions related to the site of Enea Research Center of Frascati: it is located on the slopes of the hill, where there is not place for a warm and a cold basin as in ITER [1] and MITICA too, the ITER HNB Test Facility in Padua [1,2]. There are not rivers or lakes in the proximity where take water; even if there had been the inhabitation next to the research center prevent to utilize any cooling

Secondary circuit

In order to minimize the chilling power, electricity consumption and space, all cooling circuits lead to the top of “Warm Tank” as shown in the Fig. 1, where all flows-rate with different temperatures mix up. The heat stored in the warm tank has been calculated in such a way that the temperature does not exceed the boiling point, as shown in Table 2. In order to optimize the heat stratification, the warm tank is divided in 2 insulated tanks, more than 60 m3 each with a the height of 7 m. From

Chillers selection

All the calculation procedure carried out so far (shown in Table 2) to accumulate the thermal energy during plasma operation, in two tanks, was made to reduce the power and therefore the dimensions and electrical consumption of the chillers. The chillers during the dwell time must restore the initial thermal conditions of the Tokamak machine, rebalancing the temperatures inside the cold tank. From the manufacturer's technical manual, the inlet maximum allowable temperature for the chillers is

Conclusions

In order to optimize spaces, existing buildings, energy and water resources in Enea Frascati Research Center the DTT secondary cooling water systems, arriving from different facilities located in different places, is concentrated and mixed in two (pairs) types of vertical and pressurized tanks. The chillers are dimensioned not only to adapt to different thermal loads running in cascade but also to reduce the noise impacting to neighborhood (see Fig. 4 – other Owners) and on the other hand avoid

credit author statement

Alexander Rydzy: Nuclear & Energy Engineer expert and responsible in DTT Cooling Water Systems

Gianluca Barone: Nuclear Engineer expert in thermofluidinamics simulations (RELAP)

Andrea Marini: mechanical technical expert by Daikin Air Conditioning Italy spa contributed with technical requirement provided by chillers

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This paper was prepared as an account of work by Enea’s colleague who made simulations of the temperature arised in the tank using RELAP tool. At the same time the chillers technical feature provided by Daikin Air Conditioning Italy spa was useful for understanding the chillers best operation range mode applied to this project.

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