Advanced Heavy Water Reactor. Amit Thakur Reactor Physics Design Division Bhabha Atomic Research Centre, INDIA

Transcription

1 Advanced Heavy Water Reactor Amit Thakur Reactor Physics Design Division Bhabha Atomic Research Centre, INDIA

2 Design objectives of AHWR The Advanced Heavy Water Reactor (AHWR) is a unique reactor designed in India for the large scale commercial utilisation of thorium and integrated technological demonstration of the thorium cycle Design objectives / Challenges Maximise the power from thorium Maximise the in-situ burning of 233 Negative power coefficient Heat removal through Natural Circulation niform coolant flow ; flat radial power distribution, short active core height Low power density Bottom peaked axial power/flux distribution Fuel cycle aspects Self-sustainance in 233 Plutonium as make-up fuel ; minimise the Pu inventory and consumption Maximise the burnup

3 Physics design criteria Maximize power from thorium Core averaged negative void coefficient of reactivity at operating conditions. The discharge burnup of the fuel should be greater than 30 GWd/Te. Minimize consumption of plutonium. Initial plutonium inventory should be as low as possible. The system should be self-sustaining in 233. The total thermal power to the coolant should be 920 MW.

4 Thermal hydraulic considerations of uniform coolant flow Local peaking factor has to kept within the TH margins Suitable enrichments Better TH margins - Higher MCHFR Relatively bottom peaked power distribution Axially graded fuel pins (Outer pins)

5 Properties of thorium Major Advantages Availability Improved nuclear characteristics Improved technological performance compared to O 2 Stable crystal structure Higher thermal conductivity High melting point lower thermal expansion coeff. Improved fuel behaviour Dimensional stability at high burn-up Reduced generation of actinides in Th--233 cycle Major disadvantages Reactor safety Low delayed neutron fraction β eff Reactor operation Photoneutron production ( start-up) Radiation problem --Association of 232 with 233 Reactor control problem due to Pa 233 Reprocessing issues Dissolution of thorium fuel is more difficult than uranium fuel, due to its high material stability

6 Thorium decay chain α β Th-232 Ra-228 Ac e+10 y 6.7 y β 6 hrs -232 α 69 y α α α Th-228 Ra-224 Rn-220 Po y 3.64 d 56 s α 0.15 s β 3.1 m Pb-208 α 0.3μs Tl MeV γ Po-212 α 33.7 % β 66.3% Bi m Pb-212 β 10.6 hrs MeV γ

7 230 Th 7.54x10 4 y 230 Pa 17 d 23b 231 Th h β - n,2n 231 Pa 3.27x10 4 y n,2n E>6.34Mev 200b 232 Th 1.41x10 10 y 232 Pa 1.31 d β y 7.4b 460 b 74 b n,2n 233 Th 22.3 m β Pa β d x10 5 y 1500 b 20 b 19 b 46b 234 Th 24.10d β - 234m Pa 1.175m 234 Pa 6.75 h β x10 5 y 1.8 b 100 b m β Pa 24.2m β x10 8 y 98b Thorium burnup chain x10 7 y d β Np 2.14x10 6 y

8 Comparison of fertile species 238 and 232 Th n, γ β β 232 Th 233 Th 233 Pa x y 7.37 barns Fertile 22.3 min 1500 barns 27 days 20 barns 1.59 x 10 5 y σ c 47 b ; σ f 530 b Fissile n, γ β Np 239 Pu β 4.5 x 10 9 y 2.7 barns Fertile 23.5 min 22 barns 2.36 days 32 barns 2.4 x 10 4 y σ c 270 b ; σ f 752 b Fissile

9 Neutronic properties of some fissile and fertile isotopes 233 Pa Np 239 Pu 240 Pu 241 Pu 242 Pu Thermal Data σa b (0.025 ev) 7 σ σf b (0.025 ev) α ν η Resonance Integral (0.625 ev 10 MeV) Absorption (barns) Capture (barns) Fission (barns) α

10 Comparison of eta for different fissile isotopes 233, 235 and 239 Pu Pu η Energy ev

11 AHWR D5 lattice D5 lattice consisting of 54 fuel pins placed in three arrays of 12, 18 and 24 pins in each array and a central displacer region Fuel composition : Ring 1 (Th,)MOX % 233 (12 pins) Ring 2 (Th,)MOX % 233 (18 pins) Ring 3 (Th,Pu)MOX 4.0% Pu (24 pins) (Lower) 2.5% Pu (24 pins) (pper) 3.25 % Pu (average) Displacer rod Cross section of AHWR D5 cluster Displacer region (Zircalloy-2 rod) Pu composition : Discharge composition of Pu from PHWR at 6700 MWd/T Core average discharge burnup : MWd/T

12 Placing the Pu pins in the outer ring where it sees a significant thermal flux is responsible of Pu burning Initially the plutonium isotopes contribute about 46 % of the total absorptions and this reduces to 15 % at the end of the cycle. Plutonium burning in AHWR Isotopic concentration % H.M Pu-239 Pu-240 Pu-241 Pu Pu absorptions reduces by about 90 % at discharge due to its depletion. In the initial core cluster, the burnups achievable are relatively low and hence lower burning Burnup MWd/T Plutonium burning in the composite cluster Discharge composition of the Pu fuel 238 Pu 239 Pu 240 Pu 241 Pu 242 Pu Initial (PHWR) Composite cluster

13 ranium : In-situ generation and burning (Th,Pu) MOX pins placed in well thermalised spectrum to maximise 233 production Thorium utilisaiton in AHWR D5 cluster Self-sustenance in 233 can be achieved by proper neutron spectrum Fuel utilisation has to be traded off with TH parameters and safety parameters like negative void reactivity At core average burnup, the power from Th- 233 is about % Weight of ranium kg Total Inner (Th,)MOX pins Total Outer (Th,Pu)MOX pins Total in cluster Burnup MWd/T Cluster averaged compositions Composite cluster

14 Salient features of the core design Boiling light water cooled Heavy water moderated Fuel cycle based on (Th,) and (Th,Pu) Axially graded fuel for bottom peaked flux distribution for better TH characteristics on power fuelling Two independent fast acting S/D systems Total No. of channels No. of fuel channels Fuelling rate (annual) - 82 (ch) Average dis. burnup MWd/t Core layout of AHWR equilibrium core

15 Optimised core power distribution A B SOR C SOR D AR SOR E RR F SOR SOR G SR SOR H AR I RR J SOR SR SOR K SOR L M SOR SOR SR AR 1.88 SOR 1.84 Zone Exit burnup MWd/ T

16 SAFETY FEATRES OF AHWR The main aim of AHWR design is to make the void reactivity ve (in order to gain extra degree of safety) To achieve this it is a nightmare for the designer but a delight for the operator. Different approaches for making the void reactivity negative. 1) Addition of some slowly burnable absorber in the displacer region of the fuel cluster. 2) Decrease the lattice pitch.

17 THANK YO