BORAL CONTROL BLADE THERMAL-MECHANICAL ANALYSIS

Transcription

1 BORAL CONTROL BLADE THERMAL-MECHANICAL ANALYSIS Srisharan G.Govindarajan, J.Alex Moreland and Dr. Gary L.Solbrekken Department of Mechanical and Aerospace Engineering University of Missouri, Columbia, Missouri, USA And Charlie McKibben and Nickie Peters University of Missouri Research Reactor 1513 Research Park Drive Columbia, Missouri USA October 24 th

2 Introduction and Purpose Control Blades : Control blades are an important technology for maintaining the desired state of neutrons and help with real time control of the fission process. This is crucial to keep the fission chain reaction active and prevent it from accelerating beyond control. Purpose : The composite structured control blades used by University of Missouri Research Reactor (MURR ) experience a thermally induced deflection during reactor operation. Due to thermal expansion mismatch and temperature changes, the blade may have a tendency to deform. Of interest to this study is to establish the magnitude of the deflection and compare it with the channel gap to determine if there is a significant risk of the control blade binding during reactor operation. The results from this analysis will help MURR with their re-licensing efforts. 2

3 MURR Control Blade BORAL [1] = Boron Carbide + Aluminum mixture Neutron absorber is Boron Figure 1. The MURR control blade dimensions BORAL meat and the aluminum cladding are bonded together through powder metallurgy to establish an adherent bonded plate as illustrated in Fig 1. The control blade travels within a narrow annular water channel between the outer surface of the outer reactor pressure vessel and the inner wall of the beryllium reflector. [1] BORAL Composite Standard Specifications, SP-BORA-001en, Rev , Ceradyne Canada, ULC. 3

4 Monte Carlo N- Particle(MCNP) Simulations A B Control Blade Use of MCNP [2] to study the energy deposition in the control blade. For the MCNP [2] the control blade was divided into 154 independent zones (cells). D C Water Channel 10 B(n, α) 6 Li reaction, the major component of the energy deposited in the blade. Figure 2. A cross-sectional view of the MCNP MURR core model showing the four positions of the control blades in a narrow water channel between the outer surface of the outer reactor pressure vessel and the inner wall of the beryllium reflector. The F6 neutron tally in MCNP [2] was used to recover the energy-release from the 10 B fission within the blade. Gamma rays (2 nd most significant source of energy deposition) originate from uranium fission in the fuel and (n,γ) interactions. F6 photon tally in MCNP [2] in addition to the method described in [3] was used to predict the contribution from gamma rays. The bottom of the blade is found to be the region of highest energy deposition. [2] X-5 Monte Carlo Team, MCNP-A General Monte Carlo N-Particle Transport Code, Version 5 Volume I, II and III, LA-UR /LA-CP /LA-CP , Los Alamos National Laboratory (2003). [3] N. J. Peters, J.C. McKibben, K. Kutikkad, W.H. Miller, Refining the Accuracy of Predicting Physics Parameters at Research Reactors due to the Limitations in Energy Balance Method using MCNP and the ENDF Evaluations, Nuclear Science and Engineering, ANS Nucl. Sci and Eng. 171, (2012). 4

5 Finite Element Model of the Control Blade A fully coupled thermal mechanical model was built in Abaqus FEA [4] to assess the thermally induced deflection of the control blade. The material properties used for the cladding and the BORAL are as illustrated in Table 1. Table 1. Material properties of the BORAL and cladding used in the analysis Material Property Aluminum 1100 BORAL Thermal Conductivity (W/mK) , 98, 132 Density (Kg/m 3 ) Elastic Modulus (GPa) Poisson s Ratio Thermal Expansion Coeff (K -1 ) 2.36E E-05 Specific Heat (J/KgK) Perfect interfacial contact between the BORAL and aluminum cladding. [4] Abaqus FEA, Version 6.10, D S Simulia. Dassault Systemes

6 Boundary Conditions : Thermal : Coolant temperature = 325 Kelvin. Heat transfer coefficient = 1000 W/m 2 K ( Obtained based on a heat transfer coefficient sensitivity study). Mechanical : Applied to the bolt holes to prevent translation of these holes in the radial and longitudinal direction as illustrated in Fig 3. Figure 3. Mechanical boundary condition applied to the bolt holes Figure 4. BORAL meat split into 4 sections Load : Internal heat generation profile can be obtained by curve fitting the MCNP data. Reactors, October Columbia, MO

7 Curve Fitting the MCNP Data to Obtain a Heat Generation Profile for Abaqus FEA Radial direction (t) Even polynomial profile. Longitudinal direction (z) Decaying exponential profile. Figure 5. BORAL partition locations. Figure 6. MCNP data plots. 7

8 Equation (1) is used to relate ln qꞌꞌꞌ to z at each thickness location as shown in Fig 7. qꞌꞌꞌ= f(t, z)= A(t) e B(t)z (1) ln qꞌꞌꞌ = ln A(t) + B(t)z = B(t)z +C(t) (2) Slope - B, Intercept - C Similar results were then obtained for the gamma heating profile. Figure 7. Linearized exponential decay function for a given thickness and azimuthal location for alpha heating. Due to discontinuities at the aluminum cladding- BORAL core interface - overall function for qꞌꞌꞌ was defined in piecewise fashion. A and B coefficients remained constant with thickness through the cladding on the fuel side and beryllium side and vary with the thickness through the BORAL core. 8

9 Figure 8. A and B coefficient variations with thickness in BORAL core for alpha heating at left edge location A coefficient variation 4 th order polynomial for alpha heating. 2 nd order polynomial for gamma heating. B coefficient variation 2 nd order polynomial for alpha and gamma heating. Figure 9. A and B coefficient variations with thickness in BORAL core for gamma heating at left edge location 9

10 Figure. 10 Alpha heat generation data and fit at the fuel-side BORAL face. The data shows that one side of the blade has a higher heat generation than the other. This is illustrated in Fig 10a. In the above plots thickness t was held a constant while the width w and longitudinal position z were varied to generate the surface plots. 10

11 Results Temperature Distribution Figure 11. Temperature distribution contour of the control blade and variation of temperature along the cladding centerline. The temperature distribution drops off in the longitudinal direction in a manner similar to the heat generation rate. The contour also shows that there is some asymmetry in temperature along the curvature. This behavior is consistent with the curve fits based on the data provided by MURR ( Fig 10 ) 11

12 Results Deflection (a) (b) Figure 12. Radial deflection contour and deflection variation on the sides of the control blade. Figure 12a. gives the impression that the deflection is symmetrical when Fig 11 showed that the asymmetry in temperature exists along the curvature of the blade. Figure 12b. illustrates that the right edge of the blade (which is the hotter side) deflects slightly more than the other side and that the difference in deflection is inch. Reactors, October Columbia, MO

13 BORAL Thermal Conductivity Study The BORAL thermal conductivity used until now = 76.8 W/mK. Experiments at MU (MAE) suggested that the value was 115±17 W/mK. Lower Bound = 98 W/mK. Upper Bound = 132 W/mK. Figure 13. Deflection variation along the length of the blade with varying BORAL thermal conductivity. For K BORAL = (76.8, 98, 132) W/mK, the change in maximum radial deflection was 4x10-4 inch ( small). Figure 13 illustrates that the maximum radial deflection < control blade channel gap. 13

14 Conclusions The task was to help MURR with their relicensing efforts by establishing that the deflection of the blade due to heating will be within the control blade channel gap of 0.26ꞌꞌ (6.5 mm). The heating profile showed some asymmetry in temperature and the corresponding asymmetric deflection along the blade curvature has been discussed. Thermal conductivity parametric studies on the BORAL suggested that the maximum radial deflection of the blade is still within the control blade channel gap limit even at a BORAL thermal conductivity of 132 W/mK, which was considered to be the upper bound in the thermal conductivity study. Reactors, October Columbia, MO

15 Questions? 15