phase ii: detailed mock up test to confirm design · 2009. 7. 3. · the mock up test helped to...

3 July 2009 1RCM Malaysia

Design of an ice-based cold neutron source for Dhruva

Phase II: Detailed Mock up Test to Confirm Design

Saibal BasuSolid State Physics Division

Bhabha Atomic Research CentreMumbai 400085

India

3 July 2009 RCM Malaysia 2

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


• 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 reactorpowers

• To establish a control logic for safe operation of the source

• To validate the design of the moderator pot so that no stressdevelops 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


LNWater

Water

LN

2

2

Vacuum Jacket

Ø19

4

Ø16

4

48

1.5

2 KW Heater

Design of the prototype moderator pot


Vacuum PumpWatt meter

Temp

eratur

e

Dewar

N2 gas cylinderRotam

eter

Power Supply

Dewar

N2 gas cylinder

Riser

Temperature

Heater

Moderator Pot LN2 LN2

LN2 LN2

Water

Water

LN2

Water

ModeratorPot

Dewar NitrogenGas

Heater Temp

Water

RiserRotameter

HeaterWater T_out

Water T_inMod TempSurf Cen TSurf Per T

LN2

LN2

DewarLN2

N2

LN2

Schematic ofMock Up Test

Various measurementparameters

3 July 2009 RCM Malaysia

Chartless recorderDewars

Vacuum jacket

Transfer linesVacuum pump

Heater power


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 331600 31.8 29.1 2.7 2 375 63 383800 37.3 30.2 7.0 1 492 62 4301000 38.9 30.4 8.5 1 596 60 4721200 40.5 30.4 10.1 1 710 59 5201400 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 heatload on moderator

7


A typical cooling cycle in chartless recorder

Heater Power(W)

EstimatedLoad to

Moderator(W)

Temp.Mod. Centre T1 (°C)

OutsideSurfaceCenterT2 (°C)

OutsideSurface

PeripheryT3 (°C)

Heater Temp(°C)

EstimatedCool down

time(minutes)

LN2Flow (Kg/min)

LN2Loss(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 consumption0.5 Kg/min.

Latent heat

Almost entirelylost


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 indown condition

•Once ice reaches equilibrium, heater power and LN2 flow was increasedHeater Power(W)

EstimatedLoad to

Moderator(W)

Mod Centre TempT1 (°C)

SurfaceCenterT2 (°C)

Surface PeripheryT3 (°C)

LN2 Flow (Kg/min)

LN2 Loss(Kg/min)

Heater Temp(°C)

500 313 -166 -141 -184 0.51 0.14 354600 375 -172 -150 -184 0.38 0.23 354800 492 -168 -136 -183 0.24 0.24 4601000 596 -162 -134 -183 0.34 0.26 4911200 710 -158 -132 -182 0.37 0.31 522


Cooling with heater on

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

Heater

Power

(W)

Estimated

Load toModerat

or(W)

Temp.Mod. Centre T1 (°C)

OutsideSurfaceCenterT2 (°C)

OutsideSurfacePeriphe

ryT3 (°C)

Heater Temp(°C)

Estimated

Cool downtime

(minutes)

LN2Flow (Kg/min)

LN2Loss(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 startedwith the reactor at high power

The cold source and reactor operations are independent** 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 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 fromoperation of the reactor

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


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 on 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.


LNWater

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 duringice formation, then stress will develop. This can’t be allowed

We have undertaken detailed simulation to validate the moderator pot and its cooling arrangement


We tried several cooling coil configurations for temp. profile


135 K82 K

X-axis Bottom Top

Simulated Temperature profile forvarious fins

82 K 135 K

Water pocketsremain duringfreezing


We are trying a new design with inlet and outlets are such that there willbe no enclosed water pockets

Detailed simulations are being carried out before fabrication


Optimization of the moderator thickness by Monte Carlo

Apart from the geometry of the pot a specific thickness of the moderatorwill provide best thermalized neutron beam at the beam hole mouthIn 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 beenobtained. Before fabrication of moderator pot the simulation will be completed

Conclusions

Results of the Mock Up test helped to demonstrate thatFail-safe operation of the ice source will be possibleTo 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 operationDesign of the moderator pot is critical and is being carried out now

Thank You

phase ii: detailed mock up test to confirm design · 2009. 7. 3. · the mock up test helped to...

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