Rad resistant E-Stop push button

[RWJ]

This may sound silly, but I need to find an E-Stop push button switch that can handle very high radiation doses. Doses of 40 Mrad can be expected.

Does anyone know of anything that can withstand this? Any information (no matter how insignificant you think it may be) is greatly appreciated.

Thanks,
Rob

 

[Perrins]

This sounds like an industrial gamma sterilisation application. This is a common challenge with production irradiators. There isn't very much that will survive in that environment, given that most switches have some plastic in them. Look for switches with Bakelite parts. It will hold up longer, but will still break down. You can also try some lead shielding to at least reduce the field (use a hinged flap to activate the switch). 1/8" to 1/4" thick will greatly increase component life. The best solution is to get the switch out of the field, e.g. use and emergency stop pull cable where the pull switch can be remotely located.

 

[Perrins]

One other point to be aware of is that switch failure can also be caused by oxidisation of the switch contacts. This is caused by the high ozone (O-3) content in the air. The ozone is of course a by-product of irradiating the air.

 

[MiltonS]

RWJ, try contacting some of the nuclear test labs or third party qualifiers out there. Most have probably already qualified a push button switch for harsh environment and they can verify that the switches they have qualified earlier envelopes your requirements and could provide you with one via commercial item dedication along with a test report documenting the actual testing that was done to qualify the switch originally.

If not they can perform new testing for you though it will be costly.

Good luck!!!

 

[HamishMcTavish]

RWJ

Never mind if the E-Stop Button can stand the dose, what about the person who will have to press it!

If the dose is 40 Mrad, ie 40 x 10^6 rads, then that is WAY past the lethal dose.

(in UK speak 1 rad = 0.01 Gray, LD50 = 3-5 Grays)

 

[Perrins]

I'm not sure what RWJ's application is, but for an industrial steriliser, the cobalt source is typically contained in a large shielded room (6’ thick concrete walls). The source is stored in a 25' deep pool. The emergency stop is for when the source is in the storage position and personnel are in the cell. Given that there is a lot of conveyor type equipment in there, an E-stop is required. The challenge has always been to find ingenious ways to get anything to survive in the cell. As for the radiation approved components for power reactors, they don’t hold up either. A power reactor, in general, only has a fraction of the gamma field that exists in a steriliser and neutron particles are not very penetrating compared to gamma energy. Typically if a switch can withstand about 4 GRad then it might last 2 or 3 years (depending on the magnitude of the source in the cell) if it doesn’t fail from oxidisation from the high ozone content in the air.

 

[RWJ]

Thanks for your input everyone! I submitted this question a while back, and have since solved my problem. I'm using a standard Allen Bradley safety E-Stop. Turns out the materials in the switch can withstand fairly significant doses, and we will replace the switch periodically.

In terms of the application, it is really quite silly. The switch will be located on a power reactor fuelling machine. The radiation doses are very high (I forget the numbers, but they were very lethal) and no operator would be in the reactor vault when the machine was running. However, the customer wanted it for when the machine was out for servicing and testing. Why the supplied detachable "dead man" switch was not sufficient is beyond me...

 

[Wirenut]

Contact these people

http://www.spectrumtechnologies.net/

They will know.... Wirenut