Working group meeting 07/05/15

Agenda Overview of review and current action list Relief system – Summary of problem – Details of analysis, testing and proposed solution – Discussion on suitability and wider implications of solution HAZOP – Summary of previous HAZOP study – System and contextual changes – Discussion on whether further HAZOP activity is necessary AOB

Review To review the installation and operational methodology of the MICE liquid hydrogen system for its compliance with all relevant safety frameworks Comments: – Recognition that the system is substantially similar to the R&D with the exception of the hydride bed and the beam windows – Removal of the hydride bed is seen as a positive move – Uncertain which previous review actions are still outstanding and relevant – The safety approval method followed before still stands Recommendations – Review relief system by revisiting calculations and carrying out testing where necessary – Consider need for a third HAZOP exercise – Develop a maintenance plan – Revisit emergency procedures – Define competency of ‘expert staff’ – System to be considered in a pre-operations review of the entire integrated MICE system

Relief system LH2 Vacuum Gas panel Two failure scenarios – Heat load into absorber, causing rapid boiling of LH2 through absorber relief line – Absorber window rupture, causing rapid boiling of LH2 predominantly through vacuum relief line AbsorberVacuum Both PRV Δ0.5 bar

Relief system Heat load scenario – Significant heat can only feasibly come from a vacuum failure but… A safety window rupture would not cause a vacuum failure The surrounding vacuum vessels are substantial and unlikely to fail in a catastrophic way Small leaks, such as from seal degradation, would not result in rapid boil-off – Nevertheless, if such a vacuum failure were to occur, two estimates of the heat load into the LH2 were made: Film boiling i.e. maximum possible rate of heat transfer, regardless of ΔT ~ 19kW CERN paper with experimental data suggesting actual max heat transfer would be ~5kW – The latter figure was taken, doubled, and used to calculate a boil-off rate of kg/s – This was used to calculate a total pipe pressure drop from absorber to flame arrestor of 1.92 bar – The assembled absorber was successfully proof tested to 2.2 bar (report pending)

Relief system Window failure scenario - review suggested revisiting both pipe loss calculations and FEA – Calculations by S. Harrison show as installed system would result in a bar pressure rise – Window FEA suggests bar burst pressure with ~20% error – Burst test on thinnest window validates error margin, with FEA saying 9.66 bar and window bursting at 7.66 bar Proposal is to use the existing vacuum line instead of a dedicated relief line – Will completely bypass the gas panel – Line is (almost) exclusively = or > 100mm dia – Turbo pump will be circumvented using a welded burst disc – Two low pressure relief valves will be used to assist backing pump in admitting flow into the enclosure

Relief system Safety windows 009 and 014 are fitted – 009 is 20% thicker than specification, so FEA burst pressure is > 11 bar – 014 is 10% thinner than specification, so FEA burst pressure is bar Taking 20% error margin into account, the burst pressure of the system is 8.5 bar This means relief system must limit pressure rise to 4.25 bar to achieve FoS of 2 Latest calculation shows pressure rise of 4.4 bar (pending update) – Noted that this is “probably an overestimate because there are a few conservative assumptions” No obvious way to reduce line impedance further Is this acceptable based on current evidence?

HAZOP The internal review committee gave a ‘green light’ for the liquid hydrogen R&D work in October 2011 but asked for a second HAZOP exercise to look at the operation of the system in the full experimental context. The purpose of this Procedural HAZOP was to provide a review of the procedures detailed in the Operating Instructions to identify hazards and causes for operational problems, quality problems, and delays, with due consideration for the operation of the hydrogen delivery system within the context of the other surrounding operating facilities.

HAZOP System changes that will impact on operating procedures – Hydrogen from bottle pack Fill procedure now similar to hydride bed charging No hydrogen bottle manoeuvres inside the Hall Bottle regulator outside the Hall No issues associated with heater-chiller unit – Absorber with windows Absorber windows cannot tolerate back pressure – Relief route uses vacuum line Overpressure in vacuum space results in high concentration of hydrogen inside pump enclosure Are these changes sufficient to justify another HAZOP exercise?

AOB