Design of an ice-based cold neutron source for Dhruva Phase II: - - PowerPoint PPT Presentation

3 July 2009 1 RCM Malaysia

Design of an ice-based cold neutron source for Dhruva

Phase II: Detailed Mock up Test to Confirm Design

Saibal Basu Solid State Physics Division Bhabha Atomic Research Centre Mumbai 400085 India

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Plan of the talk

• 1. Description of the Mock Up test
• 2. Results of the test
• 3. Various system parameters obtained
• 4. Lacuna of the earlier moderator pot design.

Stress in the pot

• 5. Finite element based calculations for proper geometry
• 6. Monte Carlo simulation for moderator thickness
• 7. Conclusion

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• To design a fail-safe flow loop that can be easily implemented in Dhruva
• To estimate the required flow rate and LN2 consumption at various reactor

powers

• To establish a control logic for safe operation of the source
• To validate the design of the moderator pot so that no stress

develops on thermal recycling For the mock up Test, nuclear heating was simulated by electrical heater

• It is local heating
• Entire heater power does not go to moderator

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LN Water Water LN

2 2

Vacuum Jacket

Ø194 Ø164 48 1.5 2 KW Heater

Design of the prototype moderator pot

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Vacuum Pump Watt meter Temperature Dewar N2 gas cylinder Rotameter Power Supply Dewar N2 gas cylinder Riser Temperature Heater Moderator Pot LN2 LN2 LN2 LN2 Water

Water LN2 Water

Moderator Pot Dewar Nitrogen Gas

Heater Temp

Water Riser Rotameter Heater

Water T_out Water T_in Mod Temp Surf Cen T Surf Per T LN2 LN2

Dewar

LN2 N2 LN2

Schematic of Mock Up Test Various measurement parameters

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Chartless recorder

Dewars

Vacuum jacket Transfer lines Vacuum pump Heater power

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Heater Power (Watt) Outlet Temp. (°C) Inlet Temp. (°C) Diff. in Temp. Water flow rate (LPM) Heat Transfer (W) % Heat Transfer Heater Temp (°C) 500 31.4 29.1 2.2 2 313 63 331 600 31.8 29.1 2.7 2 375 63 383 800 37.3 30.2 7.0 1 492 62 430 1000 38.9 30.4 8.5 1 596 60 472 1200 40.5 30.4 10.1 1 710 59 520 1400 42.7 31.3 11.4 1 797 57 561

Estimating Heater Power to Nuclear Power This was a part that needed careful experimentation to estimate heat load on moderator

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A typical cooling cycle in chartless recorder

Heater Power (W) Estimated Load to Moderator (W) Temp.Mo

• d. Centre

T1 (°C) Outside Surface Center T2 (°C) Outside Surface Periphery T3 (°C) Heater Temp (°C) Estimated Cool down time (minutes)

LN2 Flow (Kg/ min) LN2 Loss (Kg/ min)

1200 710

• 23
• 41
• 58

538 105* 0.15* 0.15

• 153
• 129
• 183

80 0.45 0.33 1400 797

• 144
• 127
• 181

561 110 .48 .38

LN2 consumption 0.5 Kg/min. Latent heat Almost entirely lost

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Heating Cycle Data

• During these cycles, we started cooling the moderator water with heater power off
• This is equivalent to starting the cold source with reactor at low power or in

down condition

• Once ice reaches equilibrium, heater power and LN2 flow was increased

Heater Power (W) Estimated Load to Moderator (W) Mod Centre Temp T1 (°C) Surface Center T2 (°C) Surface Periphery T3 (°C) LN2 Flow (Kg/min) LN2 Loss (Kg/min) Heater Temp (°C)

500 313

• 166
• 141
• 184

0.51 0.14 354 600 375

• 172
• 150
• 184

0.38 0.23 354 800 492

• 168
• 136
• 183

0.24 0.24 460 1000 596

• 162
• 134
• 183

0.34 0.26 491

1200 710

• 158
• 132
• 182

0.37 0.31 522

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Cooling with heater on

• This is equivalent to starting the operation of the source with reactor critical

Heate r Powe r (W) Estimat ed Load to Moderat

• r

(W) Temp. Mod. Centre T1 (°C) Outside Surface Center T2 (°C) Outside Surface Periphe ry T3 (°C) Heater Temp (°C) Estimate d Cool down time (minutes) LN2 Flow (Kg/ min) LN2 Loss (Kg/ min) 1200 710

• 23
• 41
• 58

538 105* 0.15* 0.15

• 153
• 129
• 183

80 0.45 0.33 1400 797

• 144
• 127
• 181

561 110 .48 .38

• This test clearly showed that the cold source operation can be started

with the reactor at high power

The cold source and reactor operations are independent**

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The Mock Up test helped to (a)Design a fail-safe working principle for running the ice-based source inside the reactor with nuclear heating AND (b) To arrive at several system parameters e.g. flow rate of LN2 , cooling rate, rate of rise in temperature in absence of cooling, liquid nitrogen consumption etc. (c)We also find that the source operation can be de-linked from

• peration of the reactor

In absence of cooling ice melts. Water flow will keep the moderator pot safe

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Several important conclusions: The temperature distribution in the entire volume of moderator will remain in the range of 90 K to 120 K depending on the reactor power level. Better uniformity of temperature is expected in the case of uniform nuclear heating, compared to local electrical heating The daily consumption of LN2 will lie between 500 Litres to 700 Litres, depending

• n the reactor power level.

It takes nearly 30 minutes for the moderator to cross 00C if cooling is switched off. This is sufficiently long for control system to initiate any action. A nominal water flow rate of 1 is sufficient to keep the moderator pot cool at reactor full power operation. Vacuum need not be disturbed. We will be able to start the Cold Neutron Source operations, with the reactor in full power. The moderator cools down in 2 hrs time.

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LN Water Water LN

2 2

Vacuum Jacket

Ø194 Ø164 48 1.5 2 KW Heater

There was large bulging near the centre of moderator pot. Almost 15 mm!! Was it due to local heating? OR Stress during ice formation. If water does escape through the discharge during ice formation, then stress will develop. This can’t be allowed We have undertaken detailed simulation to validate the moderator pot and its cooling arrangement

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We tried several cooling coil configurations for temp. profile

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135 K 82 K X-axis Bottom Top Simulated Temperature profile for various fins 82 K 135 K Water pockets remain during freezing

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We are trying a new design with inlet and outlets are such that there will be no enclosed water pockets Detailed simulations are being carried out before fabrication

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Optimization of the moderator thickness by Monte Carlo Apart from the geometry of the pot a specific thickness of the moderator will provide best thermalized neutron beam at the beam hole mouth In Dhruva This needs to be done through MC, provided we have the scattering Kernel for ice at the temperature of interest (100 K) The scattering cross-section for ice has been calculated by Dr. Ronaldo- Granada of Argentina using a synthetic model and has been provided to us. This is a collaboration through the present CRP We have not yet finished the simulation. Only some preliminary results have been

• btained. Before fabrication of moderator pot the simulation will be completed

Conclusions

Results of the Mock Up test helped to demonstrate that Fail-safe operation of the ice source will be possible To maintain ~ 100 K ice we need 500 L to 700 L LN2 per day We could obtain various system parameters for operation of the source The operation of the source can be de-linked from reactor operation Design of the moderator pot is critical and is being carried out now

Thank You