Assessment of Gamma Sensitivity of Platinum SPGD using Monte Carlo Method ,,,,,,

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1 2003 Monte Carlo Assessment of Gamma Sensitivity of Platinum SPGD using Monte Carlo Method,,,,,, Monte Carlo MCNP 4 5 H1-type Instrumentation Thimble MCNP Gamma Source Insulator Electron Charge Effect f-factor A( /cm 2 ) 1 MeV (Emitter, Insulator, Collector, Insulator Charge ) Abstract Gamma sensitivities depending on energy groups of Platinum incore detectors are calculated using the Monte Carlo transport calculation H1-type fuel assembly loaded in Yonggwang Unit 4 cycle 5 is modelled by MCNP4B code to get gamma spectrum in instrumentation thimble region and then calculated gamma spectrum is used as a source term for gamma sensitivity of Pt detector In addition, f-factor was defined to consider the effect of electron charge in insulator region Resulting energy dependent gamma sensitivity was about A( /cm 2 ) per unit length Generally, sensitivity is primarily dependent on gamma or neutron spectrum in sensitivity calculation, thus the accurate spectrum around detector assembly and optimizing the variables affected sensitivity like as density and size of emitter, insulator and collector, charge distribution in the insulator, and minimizing the uncertainties of these variables are required for the exact sensitivity calculation

2 1 (n,e), (g,e), (n,g,e) Platinum 1970 Monte Carlo Transport Code (MCNP MONK) Field Dominic G Napolitano Donald R Harris Seabrook Monte Carlo, SCK CEN, Nuclear Research Center Rh, Co, Hf Emitter Emitter ( ), Platinum LANL (Los Alamos National Laboratory) MCNP4B, H1-type Instrumentation Thimble 2 SPND (Self-Powered Neutron Detectors),,,, /,, Emitter, Emitter Background Noise Emitter < 2-1> Integral SPND (Rhodium )

3 < 2-1> Integral SPND Emitter Insulator Collector ( Sheath) Co-axial Cable SPND Emitter (Rh), (V), (Co), (Hf), (Pt) (Ag), < 2-1> Emitter < 2-1> Element Z V 23 Low depletion Co 27 Large prompt response Rh 45 Very large signal (small uncertainty) Signal interpretation easy Large signal Ag 47 Signal interpretation easy Low depletion Large signal Gd 64 Large prompt response Signal interpretation easy Er 68 Large prompt response Yb 70 Large prompt response Low depletion Hf 72 Large prompt response Pt 78 Large prompt response No depletion Very small signal Prompt response has opposite sign Very small signal Average depletion Small prompt response Average depletion Small prompt response Rapid depletion Rapid depletion Small signal Small signal Small signal Average depletion Small signal Emitter Insulator Collector Collector Insulator Emitter Insulator (+) (-) (n,e), (n,g,e), (g,e) (n,e) SPND Emitter (n,g,e), (g,e) SPGD (Self-Powered Gamma

4 Detector) SPGD Signal-to-Noise Ratio (, Background ) Gamma Spectrum Around the Detector Assembly,,,, ( ) ( ) Instrumentation Thimble H1-type 4 5 < 2-2>, < 2-2> < 2-2> Yonggwang Unit 4 Cycle 5 H1-type FA & 2x2 Instrumentation Thimble MCNP (0699g/cc) Flux Tally (F4:n,p) (Reflective Boundary Condition) < 2-3> Energy (En) Cell Instrumentation Thimble

5 Flux < 2-2> H-type Assembly Description of Yonggwang Unit 4 Assembly Type Fuel Enrichment (wt% U 235 ) No of Fuel Rods per Assembly No of Gd Poison Rods Per Assembly Poison Enrichment (wt% Gd 2O 3) H0 H1 H2 450/ / / /52 176/52 172/ < 2-3> Neutron & Gamma Energy Boundary Upper Energy Group Boundary (ev) Neutron Gamma Group Number 25-G 10-G 18-G E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E+4 MCNP (Particle Flux), < 2-3> ~ < 2-5> Instrumentation Thimble

6 < 2-3> Instrumentation Thimble (25-Group) < 2-4> Instrumentation Thimble (18-Group) < 2-5> Instrumentation Thimble (10-Group) Charge Distribution in the Insulator (+) (-) Emitter Collector Insulator (Space Charge Field) Insulator Charge Space Charge Trap Energy Band Structure Space Charge Space Charge

7 Quasi-Static Charge Zero Point de dr Concentric Ring Emitter Insulator + E r = ρ (r) ε E (Electric Field) Insulator Potential Difference (zero), = 1 r 1 ro 1 r E ( r) r ρ( r ) dr dr r ρ( r ) dr rε ri ln( r ri ri o / ri ) r Poisson r i, r o Insulator r i~~r o (Critical Radius) Emitter Charge Emitter, f-fraction f ln( ro ) 1 = 1 = n ln( ro / ri ) ln( ro / ri ) n r ln( r ) ρ r = 1 r ρ r f-fraction Insulator 20 (typically n=20 or 30) r (Concentric Ring) Charge ( ) MCNP (,, ) f-fraction < 2-4> Platinum Emitter Insulator Collector Material Platinum Al 2O 3 Inconel Density(g/cc) Length(cm) 40 < 2-6> < 2-4> MCNP Platinum Emitter Platinum 2145g/cc Insulator Al 2O 3 19g/cc Collector Inconel 842g/cc Concentric Ring

8 0025cm-0056cm-0079cm SPND < 2-7> MCNP Insulator Charge Density, ( 3) f-fraction 047 < 2-5> < 2-6>, < 2-4> f=047 Rc : 0079 cm Re : 0025 cm Ri : cm L: 40 cm < 2-6> Platinum < 2-7> Insulator Charge Density Profile Emitter-Insulator Net Current J ei, Insulator-Collector Net Current J ic Emitter Collector Net Current, J ec J ei, J ic MCNP Current Tally MCNP Electron Current J ei, J ic Incoming (cos( )<0) outgoing (cos( )>0) Net Current Upper Limit Energy PHYS:E J ec = J f ( J J ) = (1 f ) J ei ei ic ei Current ( ) + f J ic (n,e) Rhodium Platinum Energy Dependent Gamma Sensitivities of Pt Detector Instrumentation Thimble MCNP SDEF Gamma Source Collector cos( ) Net Current Fn:e, Cn, Ftn elc, ( ) Current ( )

9 ( ) MCNP Gamma Source Collector cos( ) φ = 4/( π d h) d, h 0158cm, 1cm ( 3) f-fraction ( 4) Net Current ( 5) < 2-8 > A( /cm 2 ) 1 MeV (n,e) SPND (10-21 ~ A( /cm 2 )) Photoelectric, Compton Scattering, Pair Production (g,e) High-Z Emitter Low-Z (Surrounding Materials) < 2-8> Energy Dependent Gamma Sensitivities of Pt SPGD 3 Monte Carlo Transport Platinum MCNP4B 4 5 H1-type Instrumentation Thimble Platinum MCNP Insulator Charge f-factor

10 10-23 A( /cm 2 ) SPND (g,e) Emitter-Insulator-Collector Current f-fraction Insulator (Unperturbed Condition) ( ) (Perturbed Condition) 4 1 H D Warren "Calculational Model for Self-Powered Neutron Detector," Nuclear Science and Engineering, 48, p , H D Warren and N H Shah, "Neutron and Gamma-Ray Effects on Self-Powered In-Core Radiation Detectors," Nuclear Science and Engineering, 54, pp , H D Warren and M F Sulcoski, "Performance of Prompt- and Delayed-Responding Self-Powered In-Core Neutron Detectors in a Pressurized Water Reactor," Nuclear Science and Engineering, 86, pp 1-9, D G Napolitano and D R Harris, " Sensitivity of Seabrook Station's Incore Platinum Detectors," Advances in Mathematics, Computations, and Reactor Physics, Topical Meeting, Pittsburgh, PA April 25-May 2, J P Gorski and a G Merrill, "Incore Power Monitoring Using Platinum Incore Detectors at Seabrook Station," Advances in Mathematics, Computations, and Reactor Physics, Topical Meeting, Pittsburgh, PA, April 28-May 2, J P Gorski and R J Cacciapouti, "Experience with Fixed Incore Detectors at Seabrook Station," International Conference on the Physics of Nuclear Science and Technology, Long Island, NY, October 5-8, R J Cacciapouti and J P Gorski, "Experience with Fixed Platinum Incore Detectors," Core Monitoring for Commercial Reactors: Improvements in Systems and Methods, Stockholm, Sweden, October 4-5, S Levy et al, "Integral Transport Computation of Gamma Detector Response With the CPM2 Code," EPRI NP-6527, Proect , Final Report, December J F Briesmeister, "MCNP - A General Monte Carlo N-Particle Transport Code, version 4B", LA-1265-M,