Conceptual Design Review of the NPDGamma Experiment in Beam Line 13 Seppo Penttila NPDGamma project manager September 25, 2007 at SNS

Conceptual Design Review of the NPDGamma Experiment in Beam Line 13

Seppo PenttilaNPDGamma project manager

September 25, 2007 at SNS

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NPDGamma Experiment Requires 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 state.• Target has to be reliable and not labor

intensive.• Target has to be absolutely safe. It needs to

meet a number of codes, rules and regulations but it still needs to meet the physics goals.

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rn + p → d +γ (2.2 MeV)

NPDGamma Experiment was Successfully Operated at LANSCE

• The NPDGamma Experiment with the LH2 target was operated successfully at LANSCE during the 2006 run cycle.

• LANSCE’s neutron beam intensity is not enough for achieving the

physics goal. The experiment requires SNS beam intensity.

Proposed technical and safety concepts are based on the results

of the LANSCE run, necessary improvements and modifications, and requirements of the facility.

Proposed technical and safety concepts are based on the results of the LANSCE run, or they are necessary improvements and modifications, or they are requirements from SNS facility.

The NPDGamma Liquid Hydrogen Target System in Beam Line 13

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20slpm

3x

cold trapopc

The NPDGamma Liquid Hydrogen Target System - Main Design Documents

A general description of the design, operation, and safety criteria can be found in:

The NPDGamma Liquid Hydrogen Target Engineering Document

Some of design criteria are presented in:Design Criteria for the NPDGamma Liquid Hydrogen Target Vent Stack on Target BLDG 2086 in Beam Line 13. Design Criteria for the Hydrogen Supply System of the NPDGamma Liquid Hydrogen Target in Beam Line 13. Design Criteria for the Gas Handling System and its Ventilation of the NPDGamma Liquid Hydrogen Target in Beam Line 13 at SNS.

The NPDGamma Liquid Hydrogen Target - H2 Supply



• Enclosure for 3xH2+He cylinders• Ventilated with chimney-effect

enclosure• In H2 regulators 20 slpm flow

restrictors• 100 psi relief valve RV106, see

Diagram of Target Gas Handling System• Source shutoff valve PV100 • Target filling takes about 2-3 days• H2 monitors in enclosure

The NPDGamma Liquid Hydrogen Target - Gas Handling System



• Ventilated - chimney-effect - enclosure that includes:

valves pressure gauges metering valve cold trap 2 pcs 100 psi relief valves RV 102 and RV103 hydrogen proof mechanical vacuum pump H2 monitors

• Most joints welded • Needed only during target fillings - 2-3 days

The NPDGamma Liquid Hydrogen Target - Cryostat and LH2 Vessel


are needed to see this picture. 30 cm

30 c

m

Target volume is 16 liters and it is operated at 17-18 K by two mechanical cryo-coolers

Target in para-state

The NPDGamma Liquid Hydrogen Target - Cryostat and LH2 Vessel

Modifications to LH2 vessel effecting on safety:• We need a thin - 0.063” - beam entry window but design pressure has to be larger than MAWP to allow safe operating range.• LH2 vessel has to be a pressure vessel • FAE buy C. Luttrell shows that internal pressure up to 130 psi is possible.• MAWP is set by the relief valve RV104 to 20 psid

The worst possible accident scenario is the loss of the

isolation vacuum:

t=40 min

The NPDGamma Liquid Hydrogen Target - Cryostat

Isolation vacuum chamber of the cryostat is not a pressure vessel; MAWP has to be kept below 15 psi. Modifications to cryostat effecting on safety:• Beam windows are double windows He between; we need 0.063” thick each window.• Preliminary analysis indicates that the internal design pressure of the single window is 18 psi. • MAWP is set by rupture disks RD201 and RD202.

A safety feature of the cryostat isolation vacuum chamber:

Helium channels around weldings and demountable joints form a buffer between air and the hydrogen. RGA (residual gas analyzer) monitors helium level in the isolation vacuum chamber.

In general, if possible, He gas volumes are used between air and the H2.

The NPDGamma Liquid Hydrogen Target - Relief Chamber and Vent Stack







The relief system - piping, relief valves, check valves, and rupture disks - allows safe relief of hydrogen gas outside the Target building in emergencies and during normal venting.

Sizing of the vent stack for event where the isolation vacuum is ruptured:

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

2. Define MAWP = source pressure of the venting hydrogen gas.

3. Select the flow friction of the components of the vent stack so that MAWP of the vessel is not exceeded.

Table 1: Calculation of the total resistance coefficient K for the relief line from the target vessel to the vent isolation box; reference diameter 1.5 inch.

Component Res. Coeff. K Res. Coeff. Kref.

5 feet pipe 1.89

1 - 90° elbow 0.63

2 - 45° elbows 0.68

3 - 90° elbows 1.89

8 feet pipe 1.34

2 - 90° elbows (2.5” ID) 1.08 0.14

25 feet pipe (2.5” ID) 2.16 0.30

1 – standard tee (flow through branch)

1.26

Enlargement 1.5″ → 2.5″ 0.41

Contraction 2.5″ → 1.5″ 0.32

1 – relie f valve* 0.82

1 – pipe entrance 0.50

1 – pipe exit 1.00

TOTAL 11.18

* according to manufacturer (Anderson Greenwoo )d f or type 83 safety valve with J orifice at 90%

flow capacity

Diagram of the Safety Interlock System

Other Target Safety Related Issues

1. Target operators -Senior and Junior Operators - are OJTed. At LANSCE we had an approved training program.

2. Target User’s Guide includes a number of step-by-step operating procedures for different target operations.