The 2nd NPDGamma Experiment Safety Review- Liquid Hydrogen Target

Seppo PenttilaNPDGamma project manager

June 09, 2008 SNS

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We try to cover

• Findings from the 1st LH2 Target Review

• Introduction to the LH2 target systems - technical introduction

• LH2 target interface with Target Building

• NPDGamma Experiment; hazards identification

• Impact of H2 Target on SNS Safety basis; - USID, hazard and accident analysis

• H2 target fire safety aspects: protection of workers and mission

• Discussion:

– the target system details; OPCs, flow restrictions, …

– interlock system, H2 monitors, ODH,…

– operation, training, procedures, controlled documents,…

Report of the 1st conceptual design review

A Committee composed of

Robert Dean, Ian Evans, Phil Ferguson, Max Gildner, Ken Herwig, Hal Lee,

George Rennich, Patrick Thorton, Steve Withrow, and Allen Crabtree.

It met in Room C-156 of the CLO on September 25, 2007 at your request to

review the Preliminary Design of the NPDGamma Hydrogen Target.

The Committee heard presentations from you and Seppo Penttila on the

overall design of this instrument and in particular details regarding the liquid

hydrogen target.

On the basis of this limited review, we hereby make the following findings:

• The overall design is quite mature due to the fact that this instrument was actually

previously operated at LANL.

• The test enclosure that houses the hydrogen target has not yet been classified.

• The decision to fabricate an ASME code-stamped cryostat ensures a robust design.

• Some mechanical fittings and couplings could be eliminated or located in ventilated

areas.

• Hydrogen cylinder storage cabinet location has not been finalized.

• Hydrogen vent lines are currently routed through normally occupied areas between the

sample cave and the roof (in particular, next to the mezzanine walkway).

• Currently the projected dose rate at the sample cave roof exceeds the 0.25 mrem/h

limit.

• In some areas, Beamline 13B relies on beamline 14 shielding in order to meet design

objectives for radiation exposure during operations.

• The 13A beamline pipe stub extends into the 13B sample cave.

• ODH issues have not been adequately addressed.

Based on these findings, we recommend:• The test enclosure be classified according to its appropriate hazard category. The

Committee will provide whatever assistance may be needed in this effort, as this important step will very likely impact others in the Target Building. Once the area has been classified, one should identify any exemptions or equivalencies that will need to be submitted to DOE for approval.

• Hydrogen cylinder storage cabinets be located external to the Target Building so as to minimize any impact to the building’s combustible loading.

• Hydrogen vent lines be armored where necessary to protect against potential damage.

• Roof shielding be reworked to meet the dose rate goal of 0.25 mrem/h or roof access be restricted during operation.

• Beamline shielding (temporary or otherwise) be coordinated with Beamline 14 to ensure that the design objective of 0.25 mrem/h or less in occupied areas is met during operations.

• Neutronics be consulted regarding the 13A beamline pipe stub that extends into the 13B sample cave.

• Discussions be initiated with Paul Wright regarding your various PPS needs (will ODH monitors be required, etc; if so, will it be considered an credited system).

NPDGamma Experiment Requires 16 liter Liquid Hydrogen Target

• To measure -ray asymmetry in the capture reaction of

a 16 liter liquid hydrogen target is required.• The size of the target is determined by

– The goal error of the experiment - -asymmetry is very small. The experiment has to run for several months with the full SNS power for reaching the statistical error goal.

– The n-p capture cross section is small. • Target has to be more than 99% in the para-hydrogen

molecular state.• Target has to be safe, reliable and not labor intensive.

€

rn + p → d +γ (2.2 MeV)

Today’s LH2 Target design is based on the target operated at LANSCE

Most of proposed technical and safety concepts were tested at LANSCE. Improvements and modifications are proposed to the LANSCE baseline target. These are changes required by physics performance, facility, or mandated by Code.

The LH2 Target - Main Design Documents

Design Documents:

Draft of the NPDGamma SNS Liquid Hydrogen Target Engineering Document V2.00, June 5, 2008.

Draft of the Modifications and Improvements to the NPDGama Liquid Hydrogen Target System and Safety, June 5, 2008.

Draft of the NPDGamma External Ortho-para Converter (OPC) Document, June 5, 2008.

Target system diagrams

Drawings

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LH2 Target at BL13

LH2 Target - H2 Supply

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LH2 Target - H2 Supply

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• Supply H2 during filling of target.• For 2 days 13.6x103liters/2.88x103 min=4.7 slm.• We can have up to 15 slm condensing rate limited by cooling power of the cryo refrigerator.

sieve

Controlled byinterlock system

FR (NEW)

Pressure in H2 cylinder up to 1800 psi

• Particle sieves and flow restrictors (FR) are before H2 regulators. • Throughput of FR=P x C, P_int=1800 psi.• 100 psid relief valve RV101 protects against over pressures• PV100 is source shutoff valve connected to interlock system • Operations like change of cylinders, are administratively controlled• When manifold not in use, lines filled with He.

LH2 Target - Gas Handling System

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• GHS is needed for: H2 flow control - metering valve pressure monitoring pump for cleaning the lines to clean the H2 by LN2 cold trap o-p conversion by external OPC

• Flow control; metering valve and flow gauge. • Most joints are welded, except…

• Cabinet ventilated by chimney-effect + H2 buoyancy.• 100 psid relief valves.• In GHS H2 only during target fillings otherwise He .• 2x H2 monitors of the cabinet connected to interlock system.• Operations administratively controlled.

• H2 proof mech. pump• LN2 trap to clean H2• External OPC (NEW)

30 cm

30 c

m

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The LH2 Target - Cryostat and LH2 Vessel

LH2 Target- physics requirements:- Size 16 liters; about 27 cm in diameter and 30 cm long Al vessel.- Thin 0.063” vessel Al entry window for background reduction (NEW).- Thin 0.08” cryostat Al entry window for background reduction (NEW).. - LH2 has to be over 99.9% in para-hydrogen state.- No boiling in liquid - steady-state operation at 17-18 K.

The LH2 Target - Cryostat and LH2 Vessel

• Plan is to have the H2 vessel an ASME code (NEW) stamped pressure vessel.•In H2 boundary in cave has three demountable CF joints. • H2 boundary surrounded by vacuum in cave.• Vacuum has six demountable joints surrounded by He channels in cave.• Also welded Al joints have He channels.

Operation:• filling of target• steady-state run• emptying the target

InternalOPC

Cryo-refrigerator

Cryo-refrigerator

LH2 Target - LH2 Vessel a stamped pressure vessel

The most probable event scenario is a loss of the

isolation vacuum: In Interlock System: isolation vacuum pressure gauge and RGA would close H2 source, isolation vacuum valves, and local (at LANL) H2 Alarm buzzer+red flashing light will turn on.

t=40 min

LH2 Target - Cryostat

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LH2 Target - Vent isolation box and vent stack

• Function is to isolate air and H2 and perform a safety release of the H2.• Relief system designed to handle normal or any abnormal situations.

Lines have many of CF and VCR joints inside enclosure.Enclosure ventilated by chimney-effect and H2 buoyancy.No ignition sources in enclosure. Vent stack filled with Ar (NEW)

LH2 Target - Vent isolation box and vent stack

The relief system; piping, relief valves, check valves, and rupture disks form the H2 boundary and thus isolate the H2 from air and allow safe relief of hydrogen gas outside the Target Building during normal and emergency venting.

LH2 Target - sizing of relief and vent stack components

Sizing of the relief and vent stack components is based on event and

consequent heat transfer rate to the LH2 target.This is considered in the draft document:

“Hydrogen release rate from the NPDGamma liquid hydrogen target into the BL-13 shielding structure in a failure of target vacuum and hydrogen boundaries”

• Heat flow to the liquid hydrogen -> boil off rate = mass flow rate.

• The flow friction of the components have to be selected so that MAWP of the vessel is not exceeded.

• There is additional safety added to the calculations.• Results in some level verified by LANSCE runs.