HOW THE DUMP RESISTOR’S TANKLOOKS LIKE

COOLING OF THE LHC ENERGY EXTRACTION RESISTORSG. Peón (ST/CV), K. Dahlerup-Petersen, G. Coelingh (AT/MEL)

Air closed circuit

3D MODEL OF A PROTOTYPE COOLING STATION

Radiation constraints⇒ Bellow the beam, the expected dose is 20 Gray/year. For a 20 years 400 Gray. ⇒ According to literature, EPDM, Nitrile rubber (NBR), PVDF, Viton, PEEK, PUR, PP, PE and Nylon can withstand it.

Position in the main LHC tunnel below the beams Position in the UA galleries

CONCLUSIONS ST/CV participates in the design and construction of dedicated cooling stations for the dump resistors of the LHC dipoles The dump resistors have very particular features that imply constraints for the different components in the cooling stations. The delivery to CERN of the first of the 16 cooling station is foreseen for January 2004.

INTRODUCTION

In the LHC, there are:

8 dipole magnet chains,

154 dipoles each

each chain stores 1353 MJ at 13 kA

2 energy extraction systems for each chain.

The energy extraction system is mainly composed of:

eight 4 kA d.c. breakers a current-equalising busway, a powering and control system

and a dump resistor assembly.

The heat dissipation to the air in the LHC underground has to be minimized,

Each dipole dump-resistor assembly has a dedicated water-cooling station.

In total, there are:

8 water cooling stations in the LHC tunnel and dipole magnet chains,

8 in the UAs

DESCRIPTION OF A COOLING STATION

Inside the dump resistor’s tank, the air cools the resistor body by flowing through its plates and it is cooled down by the water when passing through the air pipes

Water tank (secondary circuit of the cooling station)

Resistor body

Maximum relative pressure in the resistor’s tanks 1 bar

The expansion vessel must be at 0.25 bar for the dump resistor vertical configuration

This implies that the nominal pressure in the pump must be lower than 0.65 bar (a pressure relief valve will avoid a higher pressure if the pump works at zero flow).

The pressure loss in the tank 0.15 bar, 0.5 bar for the rest of the circuit.

(This requirement is demanding for the filter, the heat exchanger and the flow switch).

2 dump resistors’ configurations, 2 particularities⇒ The position in the tunnel limits the height of the equipment. ⇒ The position in the UA gallery reduces the available pressure drop in 0.2 bar.

REQUIREMENTS AND DESIGN CONSTRAINTS

Able to work with no cooling in the primary sideAssuming all the energy going to the secondary water circuit: 5 m3 water volume -> the increase in temperature is 33.5 K and the volume change is about 70 liters. Main input for the expansion vessel.

Temperature recovery time in the resistor less than 2 hoursA simulation shows that for inlet water temperature in the secondary always equal to 25oC:

⇒ The hottest part in the resistor’s body gets below 50oC after 1.6 hours. ⇒ After 2 hours is 38oC. ⇒ The maximum outlet temperature is 41oC -> The maximum power needed in the heat exchanger is 100 kW.

In the real case the maximum inlet water temperature will be about 30oC.

Dimensioning of the heat exchanger and the water flow in the primary circuit.

Both circuits use demineralised water for cooling.

In the primary circuit (cold circuit), the quality of the demineralised water is generally kept to values of 0.1S/cm In the secondary circuit (hot circuit) the electrical conductivity of the water is not an important issue as it can rise to 300 S/cm without any risk for the equipment.

The main components of the cooling station are:

The heat exchanger, the expansion vessel and the pump There are two flow switches, one to indicate the availability of enough water flow in the secondary circuit and a second one to indicate a major water leak.

A pressure switch avoids the circuit to reach a gauge pressure higher than 1 bar.