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 3 July 2009 RCM Malaysia 1
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 3 July 2009 RCM Malaysia 2
• To design a fail-safe flow loop that can be easily implemented in Dhruva • To estimate the required flow rate and LN 2 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 3 July 2009 RCM Malaysia 3
Vacuum Jacket 2 KW Heater LN 2 Water Ø194 Ø164 Water 1.5 LN 2 48 Design of the prototype moderator pot 3 July 2009 RCM Malaysia 4
LN 2 LN 2 Riser Temperature Heater Schematic of Moderator Pot LN 2 LN 2 Mock Up Test Water Water Dewar Dewar LN 2 Water Rotameter Temperature Vacuum Pump N2 gas cylinder N2 gas cylinder Power Supply Watt meter Moderator Pot LN 2 Heater Riser Dewar LN 2 Water T_out Rotameter Water T_in Water Mod Temp Surf Cen T LN 2 Surf Per T N 2 Heater Temp Various measurement Dewar Nitrogen LN 2 Gas parameters 3 July 2009 RCM Malaysia 5
Dewars Chartless recorder Vacuum pump Transfer lines Heater power Vacuum jacket 3 July 2009 RCM Malaysia
Estimating Heater Power to Nuclear Power Heater Outlet Inlet Diff. Water Heat % Heat Heater Power Temp. Temp. in flow rate Transfer Transfer Temp (Watt) Temp. (LPM) (W) ( ° C) ( ° C) ( ° C) 500 31.4 29.1 2.2 2 313 63 331 600 31.8 29.1 2.7 2 375 63 383 37.3 30.2 7.0 1 492 62 430 800 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 This was a part that needed careful experimentation to estimate heat load on moderator 3 July 2009 RCM Malaysia 7
A typical cooling cycle in chartless recorder LN 2 LN 2 Estimated Temp.Mo Outside Outside Estimated Flow Loss Heater Load to d. Centre Surface Surface Heater Temp Cool down LN 2 consumption (Kg/ (Kg/ Power Moderator Center Periphery time T 1 ( ° C) ( ° C) min) min) 0.5 Kg/min. (W) (W) T 2 ( ° C) T 3 ( ° C) (minutes) Latent heat 105 * 0.15 * 1200 710 -23 -41 -58 538 0.15 Almost entirely -153 -129 -183 80 0.45 0.33 lost 1400 797 -144 -127 -181 561 110 .48 .38 3 July 2009 RCM Malaysia 8
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 LN 2 flow was increased Heater Estimated Mod Surface Surface LN 2 Flow LN 2 Loss Heater Power Load to Centre Center Periphery (Kg/min) (Kg/min) Temp (W) Moderator Temp T 2 ( ° C) T 3 ( ° C) ( ° C) (W) T 1 ( ° 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 RCM Malaysia 9 3 July 2009
Cooling with heater on • This is equivalent to starting the operation of the source with reactor critical Estimat Temp. Outside Outside Estimate LN 2 LN 2 Heate ed Mod. Surface Surface Heater d Flow Loss r Load to Centre Center Periphe Temp Cool (Kg/ (Kg/ Powe Moderat T 1 ( ° C) T 2 ( ° C) ry ( ° C) down min) min) r or T 3 ( ° C) time (W) (W) (minutes) 105 * 0.15 * 1200 710 -23 -41 -58 538 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** 3 July 2009 RCM Malaysia 10
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 LN 2 , 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 operation of the reactor In absence of cooling ice melts. Water flow will keep the moderator pot safe 3 July 2009 RCM Malaysia 11
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 LN 2 will lie between 500 Litres to 700 Litres, depending on the reactor power level. It takes nearly 30 minutes for the moderator to cross 0 0 C 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. 3 July 2009 RCM Malaysia 12
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 Vacuum Jacket 2 KW Heater LN 2 Water Ø194 Ø164 Water 1.5 LN 2 48 We have undertaken detailed simulation to validate the moderator pot and its cooling arrangement 3 July 2009 RCM Malaysia 13
We tried several cooling coil configurations for temp. profile 3 July 2009 RCM Malaysia 14
Simulated Temperature profile for various fins X-axis Bottom Top Water pockets remain during freezing 82 K 135 K 82 K 135 K 3 July 2009 RCM Malaysia 15
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 3 July 2009 RCM Malaysia 16
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 obtained. Before fabrication of moderator pot the simulation will be completed 3 July 2009 RCM Malaysia 17
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 LN 2 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
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