Risk Analysis for the exchange of the TAN Copper bars
and the Zero Degree Calorimeter in CMS
Michael Murray and Paul Debbins
Introduction:
The Zero Degree Calorimeters, ZDCs, of the CMS experiment sit 140m on either side of
the interaction point https://twiki.cern.ch/twiki/bin/view/CMS/ZDCWikiHome. They sit
within a slit in the TAN neutral energy absorber and periodically need to be removed
and/or exchanged with copper bars. The ZDCs need to be removed when the TAN is
heated to bakeout the beam pipes that run through it. After the first long pp run at the
design luminosity of L=1034cm2/s the ZDCs will only be used for the heavy ion run that
follows each pp run. The ZDCs need to be exchanged with the copper bars after each
proton run. For subsequent runs the copper bars will be in the TAN slot for pp running
and the ZDCs for heavy ion running. Because the ZDCs, the copper bars and the TAN
can all become activated [Activation] a remotely operated crane has been developed to
exchange the copper bars and the ZDCs [ExchangeCrane].
This document discusses the risk associated with using the exchange crane to remove the
copper bars from the TAN. The likelihood of mechanical or electrical failure is
essentially the same weather the crane is moving the copper bars or the ZDCs. (Note the
copper bars are ~28% heavier than the ZDC). However the consequences of such failure
scale with the activation of the ZDC, bars and TAN. Therefore we shall concentrate on
the worst case. That is the removal of the copper bars from the TAN after a long high
luminosity pp run with luminosity and the subsequent insertion of the ZDCs. This
document follows the risk analysis protocol developed by the CERN AB group
[RiskAnal].
Description of the normal mode of exchange
The full procedure for exchanging the copper
bars from the TAN is described in
[ExchangeCrane] and it will simply be sketched
here. The removal process has 4 steps:
1) The a vertical elevator will lift the ZDCs
into a frame;
2) The frame will be rotated outwards until
it is above the sarcophagus;
3) The elevator will lower the ZDC into the
sarcophagus;
4) The sarcophagus will be wheeled to a bunker for storage.
A schematic view of the operation looking towards the interaction point is shown above.
We assume a dose rate of D Si/hr near the TAN, 0.2 DSi/hr walking between the
operator station and the TAN and 0.005 DSi/hr at the operator station, see [Activation].
Here D represents the maximum safe dose rate at which we will be allowed to remove the
copper bars. For normal operation we estimate a total dose of 0.081 * DSv [Procedures].
Step by Step Inventory of Risks
1)
2)
3)
4)
5)
6)
7)
8)
The operators may trip while setting up the crane, cameras and control station.
Electrocution
Fire caused by overheating motors
The crane may get stuck while lifting the payload
The rotation arm may get stuck
The crane may get stuck while lowering the payload
The crane may drop the payload (If not properly attached)
Loss of power in tunnel
Ranking of Risks by Frequency and Consequence
The AB risk template [RiskAnal] considers 4 categories or risks. The frequency should
be scored Very unlikely = 1, unlikely = 2, possible 3, frequent 4. The serverity of risks
is scored negligible 1, marginal 2, servere 3, catastrophic 4. The score = Max(Frequency
* Severity) over all categories of risk.
Frequency
Physics
Social
Financial
Safety
Score
1 Tripping
Possible
negligible negligible negligible
marginal 6
2 Electic
Unlikely
marginal negligible negligible
marginal 4
shock
3 Fire
Very unlikely marginal negligible negligible
marginal 2
4 Stuck 
Very unlikely marginal negligible negligible
negligible 2
5 Stuck 
Very unlikely marginal negligible negligible
negligible 2
6 Stuck
Very unlikely marginal negligible negligible
marginal 2
rotate
7 Drop
Very unlikely marginal marginal marginal
marginal 2
8 Power
Unlikely
negligible negligible negligible
negligible 1
loss
The worst physics risk is that we would delay the start of the heavy ion run by a week or
so if we damaged the TAN. A secondary physics risk, for incidents 4,5,6 and 7 is that
one ZDC would be lost to the experiment. The worst social risk is that an incident would
be reported to CERN management. The worst financial risk is that the copper bars would
be damaged (~50K ChF ) and that several people would have to spend a few days
cleaning up after the accident (~50K ChF). The largest safety risks are the radiation
exposure if the copper bars become stuck during rotation and the effect.
Mitigation
1
2
3
4
5
6
Tripping
Electrical
Fire
Stuck 
Stuck 
Stuck
rotate
Good housekeeping, development and practice of procedures on surface
Regular inspection of electrical components for aging, good procedures
Regular inspection of electrical components for aging, good procedures
Use hand crank to lower copper bars back into TAN.
Use hand crank to lower copper bars back into TAN.
Move empty sarcophagus perpendicular to beam line and 3 meter towards
IP. Capture copper bar with forklift, rotate forklift and then insert the
copper bar into the sarcophagus. Finally remove the sarcophagus back to
the bunker.
7 Drop
Two people should inspect the connections. If neither side of payload the
crane will lift nothing. If only one side is connected then the ZDC will start
to pivot as it is lifted. It will be constrained by the TAN and BRAN and the
extra resistance will alert the operators. If both sides connected well the
actuators cannot drop it since they are self locking. We are well below the
strength limit of all components.
8 Power loss Put electrical system in lockout mode. Leave tunnel, take elevator to
service, report to assembly area at point 5 and inform appropriate personnel
of the status of the procedure.
Conclusion
We have analyzed the risks associated with the removal of the copper bars from the TAN
using the exchange crane. The worst risk scores associated with this task is for tripping
which has a score of 6 and fire which is 4. These can be mitigated by good procedures
and regular inspection of equipment. The risks associated with the crane itself has a risk
score of 2. The best mitigation is practice on the service and development of good
procedures and checklists.
References
[RiskAnal] Memorandum Document 785548 ver.0.1 Draft For Discussion
"Marche à suivre pour la conduite d'analyses de risques"
by Pierre BONNAL https://edms.cern.ch/document/785548/0.1
[ExchangeCrane] “The ZDC Exchange Crane”, Paul Debbins
[Activation] “Activation of the TAN region”, Markus Fustner and Stefan Roesler
[Procedures] “Procedures for the operation of the ZDC Exchange Crane” , Paul Debbins,
Michael Murray