Comparison of assessment of neutron fluence affecting VVER 440 reactor pressure vessel using DORT and TORT codes

Transcription

1 Comparison of assessment of neutron fluence affecting VVER 440 reactor pressure vessel using DORT and TORT codes P. Montero Department of Neutronics, Research Center Rez, Cz International Conference on Topical Issues in Nuclear Installation Safety: Vienna, Austria,

2 Contents I. Fluence measurement techniques 1. Outer wall of the Reactor s Pressure Vessel (RPV) II. Neutron Transport Calculations 1. Calculation model 2. Results 1

3 Nuclear Reactors operating in CZ Dukovany (EDU): 4 VVER 440 Reactors Temelin (ETE): 2 VVER 1000 Reactors 2

4 Measurements on the RPV s outer wall Annual monitoring of predetermined sectors Special carrier monitors (EDU - 30 symetry) 2 Vertical & 2 horizontal crane (new rack, EDU) Spectrometric Samples: Cu, Fe, Mn, Ni, Ti Fe & Cu foils for measuring axial & azimuthal distribution Manual insertion / removing 3

5 Measurements on the RPV s outer wall (EDU) Till 2012 for bloks 1. & 4. and till 2013 for blocks 2.& 3: Old assembly Horizontally: 38 detectors in 19 boxes (2 per box) every 100 mm placed in the center plane Vertically: 56 detectors in 28 boxes (2 per box) every 100 mm In every position, Fe & Cu detectors with a 8 mm diameter One spectrometric sample in the azimuthal & axial approx. maximum Spectrometric Samples: Cu, Fe, Mn, Ni, Ti 4

6 Measurements on the RPV s outer wall (EDU) From 2012 for blocks 1. & 4. and from 2013 for blocks 2. & 3: New assembly Horizontally: 48 detectors in 24 positions every 100 mm in the weld s 5/6 plane (new) Vertically: 58 detectors in 29 positions every 100 mm In every position a Fe & Cu a 8 mm diameter detector with Two spectrometric samples in the estimated fluence s maximum Spectrometric Samples: Cu, Fe, Mn, Ni, Ti 5

7 Measurements on the RPV s outer wall Production, insertion & removal of detectors by Škoda JS, a.s. Removal 1x per year, or in case of emergency shutdown Determination of neutron fluence by CVŘ, s.r.o. Performed using the passive response of integral fluence monitors placed on a special carrier adjacent to the outer wall of the RPV according to the current methodology. 6

8 Measurements on the RPV s outer wall Methodology includes: - Specification of activation detectors, - Determine their response, - Determination of uncertainties, - Establish reference values for calculations, - Determination of the fluence for RPV and computation fluency in critical RPV s areas using the conversion factors. Detector s specifications: Reakce T 1/2 E [kev] E 5% [MeV] E 95% [MeV] 58 Ni(n, p) 58 Co 70,3 d 811 1,4 8,5 54 Fe(n, p) 54 Mn 312,5 d 835 2,0 8,7 46 Ti(n, p) 46 Sc 83,8 d 889, ,0 10,9 63 Cu(n, ) 60 Co 5,27 r 1173, ,0 12, Mn(n,2n) 54 Mn 312,5 d ,4 16,0

9 Measurements on the RPV s outer wall Relative Azimuthal & axial activity s distribution in the considered symmetry (EDU) 8

10 9 Neutron transport calculations

11 Neutron transport calculations General procedure 1. Determination of geometry and material input data for the reactor s model 2. Determination of neutron source in the reactor s active zone 3. Fundamental fluence & detector s activities calculations with the neutron transport codes: DORT & TORT 4. Comparison of the fluence & detector s activities through experimental data for both codes 10

12 Neutron transport calculations: Standards According to NRC s recommendations, standards NTD ASI & ASTM (USA) Neutron fluence s simulation procedure is validated by comparing it with the experimental data Methodology for determining the neutron fluence through RPV is based on a combination of measurements in boxes (inside) SS and outside the RPV calculations After performing direct calculations in 3D geometry, neutron fluence is adjusted using the measured activity monitors (measures on both sides of the RPV) with adjustment program to determine the most probable neutron fluence in the region 11

13 1) Geometry Model s Configuration geometry Arrangement of individual layers/ Reactor s layers components / components surrounding the core, till biological shielding (concrete) in (r; ϑ; z) direction including the geometry, dimensions and material s composition 60 R: 0 to 260 cm ϑ: 0 to 60 Deg Z: 0 to cm, origin 50 cm bellow active zone 12

14 Calculation model: materials 1: fuel f = h= j = m= o: Stainless steel g = i: water k: RPV u: Aluminum l = n: Air p: concrete R- ϑ view Envelope Basket Shaft Surveilance Samples Overlay RPV 13

15 2) Source preparation Input files: thermal powers distribution provided by ČEZ prepared by online diffusion code MOBY DICK, developed by ŠKODA company Neutron s distribution in terms of space and energy throughout reactor s active zone Spatial Discretization: Described by R -> 43 meshes, ϑ -> 118 meshes, Z -> 44 meshes Geometry: Consider of sextant s 59 FA, containing 126 FR Energy distribution: Consider the fission spectrum and change the neutron fission s yield. Reactor s thermal power: 1444 MW 14

16 Source preparation: Discretization R: 42 meshes describing fuel, 126 for the whole model Theta: 118 meshes describing the sextant Z: 91 meshes, 42 for AZ E: 56 Intervals 15

17 Source preparation: Thermal power distribution Fuel rods: 127 ( central tube) Fuel assemblies: 59 Regulators: 7 Assemblies description

18 3) Neutron transport calculations Comparison between: TORT (3D code) & DORT (2D code) Deterministic codes developed by Oak Ridge Laboratory, U.S.A Same Reactor model considered for both codes Method of Resolution of the Boltzmann equation: discrete ordinates Calculations: on (R; θ; Z) geometry S 8 P 3 Approximation Cross section s library type collapsed : ELXSIR, 56 Energy groups <0.1; 17.33> MeV 2D synthesis method: Φ(r, ϑ, z, e) = Φ(r, ϑ, e). Φ(r, z, e) Φ(r, e) 17

19 Relative Fluence Relative Azimuthal fluence distribution TORT / DORT Relative Azimuthal Distribution 1,00E+00 8,00E-01 6,00E-01 TORT 1MeV TORT 0.5MeV DORT 1 MeV 4,00E-01 DORT 0.5 MeV 2,00E-01 0,00E Angle (in ) 18

20 Relative Fluence Relative Axial fluence distribution TORT / DORT Relative Axial Distribution 1,00E+00 8,00E-01 TORT 1MeV TORT 0.5MeV DORT 1 MeV 6,00E-01 DORT 0.5 MeV 4,00E-01 2,00E-01 0,00E Z (in cm) 19

21 Relative Fluence Radial fluence distribution in axial & azimuthal maximum TORT / DORT Relative Radial Distribution 1,0 0,8 Dort > 1 MeV Norml Dort > 0.5 MeV norml 0,6 Tort > 1 MeV Norml Tort > 0.5 MeV norml 0,4 0,2 0, R (in cm) 20

22 4) Fluences & Activities After Irradiation (AAI) Experimental AAI & fluence for E > 0.5 & 1 MeV provided yearly for detectors behind RPV. Relative error Fluence behind RPV DORT TORT Rel. Error C/E % 17.7% More accurate results delivered by the TORT code systematically Relative error AAI behind RPV 54 Fe 58 Ni 46 Ti 63 Cu Rel. Err C/E-1 (DORT) 33.2% 27.7% 26.2% 27.6% Rel. Err C/E-1 (TORT) 29.1% 21.7% 22.0% 25.3% 21

23 Conclusion & Further steeps Comparison of AAI & fluence behind RPV with DORT & TORT Goal: Unify both Czech NPP s assessment to a unique procedure using the same neutron transport code When compared to experimental data, TORT gives a closer value to exp. Uncertainty exceeds 20% rel.error for both codes Perspectives: Extend comparison to Surveillance samples Reactor s inner parts Different libraries: Bugle 96 & Bugle B7 22

24 2 3 Thank you for your attention