Design Criteria for the Hydrogen Supply System of the NPDGamma Liquid Hydrogen Target at ER2
Location: TA-53, east side of bldg MPF-30/ER2, next to FP13 concrete shielding
Organization: P-23
Date: Latest update on November 5, 2005
System Description
The NPDGamma experiment which will run in FP12, requires a 16-liter liquid hydrogen (LH2) target. To have 16 liquid hydrogen liters we need at STP about 14400 liters of hydrogen gas. The gas will be supplied by three pressurized gas cylinders (6230 liters per cylinder at STP) through regulators and gas handling panel. Our goal is to have a condensation rate of about 20 slpm. The condensation of 16 liters would thus take less than one day. A proposal is to locate the covered hydrogen supply station shown in figure 1, to the East side of ER2 building next to the flight path 13 concrete shielding, see FP13 footprint shown in Attachment A. The hydrogen supply station includes three hydrogen cylinders connected to gas panel, three stored hydrogen gas cylinders, one helium cylinder, and gas handling panel. From the proposed FP13 location, it is the shortest distance to the NPDGamma target gas handling system located on the top of the FP12, compared to the other possible locations. When the supply station is properly located and the hydrogen piping from the gas panel to the FP12 is properly attached to FP13 concrete shielding, the piping will be well protected. A plan is to have a welded ¼” hydrogen piping inside a 1” diameter conduit which is strongly anchored to the FP13 concrete shielding blocks.
The LH2 target system, its design, operation, and safety are described in the NPDGamma Liquid Hydrogen Target Engineering Document which is available in
The diagram of the the LH2 target gas handling system is shown in Attachment B and in Fig. 8 of the Engineering Document.
The hydrogen gas supply station should meet the following requirements given by
- NFPA-50, Standard for Gaseous Hydrogen Systems at Consumer Sites
- NFPA-70, The National Electrical Code
- NFPA-497 Classification of Flammable Liquids, Gases or Vapors and Hazardous Locations
- DOE 420.1A, Facility Safety, Section 4.2 "Fire Protection"
- LIR 402-910-01, LANL Fire Protection Program, Section 6.1
Evidently it is not possible to meet all the requirements given by these and other documents, therefore, we have done our best to mitigate hazards and consequences.
1) The proposed locations have the required 15 feet setback from conventional electrical equipment - ignition hazards associated with electrical equipment.
2) This also addresses the requirements of NFPA-50A, Standard for Gaseous Hydrogen Systems at Consumer Sites although again strict compliance is not achieved due to operational requirements and space constraints. Our system falls within the category of 400 to 3500~SCF of hydrogen within the code.
Since it is clear that we cannot be in compliance with all the code requirements, we have instituted a number of administrative and engineering controls that should bring us to achieve equivalent compliance;
1. H2 cylinders can only be changed and gas panel operated by trained and authorized personnel.
2. Formal training and qualification of operations staff are defined and authorized by the line management.
3. We will have approved operating procedures for bottle change, operation of the gas panel, and leak checking of the panel including leak testing of the regulators after a cylinder exchange.
4. Operations of the supply system will be written down to the target logbook.
5. We will have an automatic shut down of the hydrogen flow from the supply panel by valve PV100 in the event of detection of hydrogen in the target vacuum, in gas handling system enclosure, in experimental cave, or pressure in the target vessel passes the set point.
6. We will have an automatic shut down of the hydrogen flow from the supply system in the event of any hydrogen warning or alarm, such as loss of electrical power, loss of main vacuum, or loss of hydrogen flow.
7. Gas cylinder regulators are equipped with fixed 20 SLPM flow restrictors to mitigate consequences of regulator failure.
8. We are using welded joints in the hydrogen piping as many places as possible but if other type of joints iare needed, we will use VCR joints.
7. All the components will be thoroughly pressure tested to 1.2 times to the MAWP of the hydrogen supply system.
8. The supply system and its piping are protected for over pressures by four pressure relief valves, RV101, RV102, RV103, and RV106.
Hazard Description, Consequences, and their Mitigations
1. Hazard: Hydrogen burning
Consequences: Pressure build-up and rupture of a component of the piping and a possible hydrogen gas leak to ER2.
Mitigation:
The supply system is designed to handle safely any emergency situations. The piping and components of the supply system are built to take high pressures. MAWP of the piping is more than 250 psid. MAWP of the target gas handling system (GHS) is 100 psid and is protected by two relief valves set to 100 psid. We will use welded joints and if required we use VCR joints. Components and piping is thoroughly leak checked and pressure tested. During a condensation process only one cylinder is open to the gas panel. Hydrogen gas flow rate is limited to about 20 SLM by fixed flow restrictors on the regulators. The system can only be operated by trained and authorized personnel. Training and qualifications of operations staff are approved and authorized by the line management. We will have extensive operating procedures for the use of the hydrogen supply system and for leak testing of the system. We will have controls that automatically stops the hydrogen flow from the supply panel to the target GHS in the event of detection of hydrogen in the target GHS enclosure, in the target main vacuum, in experimental cave, or pressure in the target vessel passes the set point, or in the event of any hydrogen warning or alarm, such as loss of electrical power, loss of main vacuum, or loss of hydrogen flow in target GHS.
The fire will stop because of the hydrogen supply will be shut down. The conduit around the hydrogen piping will prevent the fire to spread. The ends of the conduit will be open to the outside of ER2 but and into the GHS ventilated enclosure.
2. Hazard: Hydrogen leaking out from the hydrogen piping into the conduit.
Consequences:Hydrogen fire
Mitigation:
The end of the conduit is open in the supply side but closed in target GHS side. In an event of hydrogen leak in the hydrogen piping, the leaked gas will flow out from the conduit outside the ER2 building.
The piping and components of the supply system can tolerate high pressures. MAWP of the piping is more than 250 psid. We will use only welded joints but if requird VCR joints will be used. Components and piping are thoroughly leak checked and pressure tested. Hydrogen gas flow rate is limited to about 20 SLM by fixed flow restrictors on the regulators. The system can only be operated by trained and authorized personnel. Training and qualifications of operations staff are approved and authorized by the line management. We will have extensive approved operating procedures. We will have extensive approved procedures for leak testing of the system. We will have controls that automatically stops the hydrogen flow from the supply panel to the target GHS in the event of detection of hydrogen in the GHS enclosure, in the target main vacuum, in experimental cave, or pressure in the target vessel passes the set point, or in the event of any hydrogen warning or alarm, such as loss of electrical power, loss of main vacuum, or loss of hydrogen flow in target GHS.
During a condensation process only one cylinder is open to the gas panel. The leak will bleed in the worst possible situation part of one cylinder.
3. Hazard: Air leak into the hydrogen supply system.
Consequences:Possible hydrogen fire inside the piping.
Mitigation:
See hazard above "Hydrogen burning inside pipe." The leaked air is condensed in the cold trap of target GHS. When the target is filled, the hydrogen gas left in the GHS is pumped out and the GHS piping backfilled with helium. The cold trap is isolated with valves V125 and V117. When the cold trap will warm up, the condensed air vaporizes and can cause an overpressure in the trap. The pressure relief valves RV102 and RV103 will protect the system. Before new hydrogen gas is introduced to the GHS, it is always carefully pumped and leak checked. To prevent air leaks into the piping of the hydrogen supply system, welded joints are used and if required VCR joints can be used.
4. Hazard: Physical damage of the hydrogen supply system by car, fork lift, or crane at ER2.
Consequences: Rupture of the piping and hydrogen fire
Mitigation:
Use physical barricades to stop cars and forklifts to reach the supply station. In ER2 the piping has to be located so that it is protected against crane operations. In places at ER2 where a possible interaction with forklifts or crane can be possible, an extra protection will be provided like a steel channel.
Fig. 1. The hydrogen gas supply station with three hydrogen and one helium cylinders connected to the gas panel and three hydrogen cylinders are stored next to MPF-35.
ATTACHMENT A