Summary of the second

Hydrogen CEDAR Safety Meeting

24 November 2008

Present: J.Gulley/ SC-GS, A.Sharma/PH-FGSO,

Augusto, Cristina, Lau, Niels

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Reminder:

A first discussion with safety took place on 5 January 2005

See summary on web page of Beam WG

Since then studies concentrated on light detection

The agreed next step is to install a “standard” CEDAR on

the new K12 beam and operate it with Hydrogen at 3.6 bar

absolute pressure

The meeting concentrated on this option only.

Note that the volume of the counter is ~1.1 m3

This corresponds to ~4 m3 of gas at atmospheric pressure

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Entrance and exit windows The material and thickness of the entrance and exit windows (0.4

mm of Al, AFNOR=AZ5GU in the standard CEDAR, for Helium

pressures up to 15 bars) must be discussed with Benoit Delille in

SC/GS. It may well be that the safety factor is gas dependent.

B.Delille explained that the safety factors for a group 1 gas (H2)

are the same as for group 2 gases (e.g. He), but there is a more

stringent quality control on the fabrication, e.g. radiography of

welds.

A risk analysis is needed and EN13445 resp CODAP norms must

be respected. Note that the required thickness goes with Ø2 !

Preliminary ANSYS calculations have been made by

Ans Pardons to compare the windows of a standard CEDAR

counter (for 15 bars of He of N2) with windows for 4 bars of

Hydrogen.

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ANSYS calculations (non-linear) with elastic Aluminium for several cases. A thickness of 0.2mm seems ok. Stress plots are attached.

Not taking into account: Stress from clampingStress from heating

Stress in centre:(stress plots shown from center to 0.9* radius, to not show the stress

concentration due to the clamping)Thickness=0.4mm & pressure= 15 bar: 520MPa

(above plasticity limit of some aluminium grades) 0.2mm & pressure= 3bar: 275 MPa

(heat-treated aluminium grades have yield limits around this value 0.1mm & pressure= 3bar: 430 MPa

(above plasticity limit of some aluminium grades)

Deflection in centre: Thickness= 0.4mm & pressure= 15 bar: 5.4mm

0.2mm & pressure = 3bar: 4mm0.1mm & pressure = 3bar: 5mm

CEDAR WINDOW THICKNESS CALCULATIONS BY A.PARDONS

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Insulating material Polyurethane is admitted in small quantities, whereas polystyrene

is strictly forbidden. The material used in the CEDAR is

polyurethane.

As it is very unlikely that the material specification can be found

back 30 years later, and as the polyurethane has degraded over

the last 30 years anyway, it is strongly suggested to replace the

thermal insulation.

Check with J.Gulley before purchase, supply data sheet.

If this is not done, a sample must be provided to S.Sgobba and

S.Clement in TS/MME for analysis and a fire test.

Check with J.Gulley which fire test is suitable.

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Protection of motors and HV The diaphragm motors, the PMTs and the control unit

below the nose must be enclosed in a Nitrogen

enclosure at slight overpressure.

Inside this enclosure a Hydrogen detector must be

placed (by David Hay in TS/ASE).

No special precaution is needed for the X/Y motors for

the CEDAR alignment with the beam.

The small gap between the exit window and the beam

vacuum will be put under Nitrogen.

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Hydrogen bottles and transport

The Hydrogen bottle will be stored in a gas building outside the cavern.

Gas will be brought to the counter via a stainless tube of minimum diameter 6 mm (André Castel in TS/LEA). The gas pressure will be limited by a safety valve to a maximum of about 4 bars. This valve will be inspected regularly like all pressure valves.

The return tube must be stainless steel as well and of at least 8 mm diameter, to avoid the build up of local gas concentrations. It should be equipped with no-return valves. It should release the gas outside at a sufficient height (about 3 metres above ground level).

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Pressure control

The CEDAR pressure pumps must be Hydrogen rated

(“EX” norm).

Similarly the nearby pumps in the beam vacuum sections

just upstream and downstream. Note that the vacuum

window may be damaged by the Cedar entrance or exit

windows in case they rupture.

Ferdi Hahn in PH/DT can be consulted concerning EX

rated pressure gauges. The Hamilton gauges heat the gas

to 40oC and are not obviously EX-rated.

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Dear Lau,

I send you two links to Vega (our standard) and to Endress and

Hauser (high pression).

You have to choose the ATEX versions for a zone 2 application.

Endress and Hauser can probably do the accuracy you need,

Vega might  not be as good (on paper)...

As an alternative you could also consider to build a small reference

pressure volume and measure relative pressure to increase the accuracy.

….

Ferdi

Vega: http://www.vegacontrols.co.uk/products.asp?fixedRangeID=10

Endress Hauser: http://www.uk.endress.com/

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e.g. Endress and Hauser:

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or:

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Leak detection and alarms Two domes shall be installed, one above the nose and control unit

and one above the exit window.

In case all purged Nitrogen enclosures are equipped with H2 detectors,

the domes are probably not necessary.

Both shall be equipped with Hydrogen detectors.

In case of rupture of one of the windows or Hydrogen detection by

one of the detectors, a Level-3 alarm will be sent automatically to

the Fire Brigade.

And the Cedar pumps, motors and PMTs, as well as nearby beam

vacuum pumps will be stopped.

Sector valves will be closed in the nearby beam line vacuum

sectors.

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N2 enclosure

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N2 enclosure (but not R.Malleyran, please…)

H2 detector

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Procedures

Procedures will be made available that describe all

steps in the normal operation of the CEDAR (empty

before filling with Hydrogen, how to vent), as well in

case of e.g. leak detection or window rupture.

This includes the technical intervention, but also whom

to inform and what alarms to send where.

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Final remark

The safety experts reacted very positively to the fact

that we involved them from the start.

They came to our meeting, as well as to TCC8 and to a

CEDAR in the COMPASS beam line to understand

better.

Many thanks to them!