Safety Overview

1. Safety Overview Work done by RAL Group Contributors Elwyn Baynham Tom Bradshaw Iouri Ivaniouchenkov Elwyn Baynham RAL

2. Safety Overview • Contents • Basic model • Model from Columbia mtg with separated magnet and absorber • Safety Criterion • To prevent the condensation and freezing of O2 on any surface which could come into contact with a hydrogen leak • Analysis without 3rd window or Ar Jacket • Similar to Mike Green assessment – we have now thought through the stages at RAL • What is added by 3rd window / Ar jacket ? Elwyn Baynham RAL

3. MICE Focus Absorber Module Magnet Vacuum He feed/return Absorber vacuum General MICE vacuum Absorber vacuum pipe external Elwyn Baynham RAL

4. Assumptions • Focus Coil / Absorber general vacuum space is common with RF and detector vacuum • Absorber vacuum vessel and secondary windows are at a temperature which is high enough to prevent O2 freezing on windows or vessel • H2 feed pipe to absorber is jacketed with vacuum inside the cryostat • He absorber pipes are not jacketed at present Elwyn Baynham RAL

5. Observations (1) • Magnet Cryostat is independent - leaks into magnet vessel are not a problem • Leaks between the absorber vacuum and the general MICE vacuum will be negligible due to the differential pressures • The only place where O2 can be cryopumped is on the He feed or return pipes – these should/can be jacketed • If the He pipes are jacketed then leaks into the RF or detector vacuum can be detected and an alarm sounded above a certain level – there is no storage method for O2 Elwyn Baynham RAL

6. Observations (2) • The biggest risk comes from a leak into the absorber vacuum space • This will bring O2 directly to freeze on the H2 window • The greatest risk for a leak is on the vacuum pipe to the absorber when it is outside the focus absorber cryostat ; pumping and dump vacuum vessel • These areas should be jacketed by Ar rather than vacuum • The H2 feed to the absorber will be at +ve pressure so there should be no access for O2 into the H2 space • The vacuum screening of the H2 pipe should end as close to the outer vessel as possible – any screening outside the vessel should be Ar jacketed Elwyn Baynham RAL

7. Observations (3) • If all the above criteria are met then it is difficult to see what additional safety features the 3rd window or the Ar jacket will bring - but • We need a good solution for the external part of the absorber vacuum • We need to jacket the He feed/return pipes • We need a robust design for the temperature control of the absorber vacuum vessel – thermal analysis + mechanical design • What are the operating temperature margins • Too low gives O2 freezing • Too high gives too much heat load on the H2 window and vessel • What is the response of this system under other failures – vacuum ;refrigeration etc • Will discuss this with RAL safety in the next week or two Elwyn Baynham RAL

8. Welded vs non welded • The RAL safety preference is for welded • However there is no fixed statement that non welded is not allowed • Both systems must pass through a rigorous qualification process and have well established procedures for production ; installation and commissioning Elwyn Baynham RAL