University of Utah Undergraduate Research Abstracts, Volume 12, Spring 2012

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161 THE UNIVERSITY OF UTAH RESEARCH POSTERS ON THE HILL 2012 MCNPX CALCULATION OF FUEL BURNUP FOR UNIVERSITY OF UTAH TRIGA REACTOR Chris Dances (Tatjana Jevremovic) Utah Nuclear Engineering Program (UNEP) University of Utah MCNPX Calculation of Nuclear Fuel Burnup for University of Utah TRIGA Research Reactor Chris Dances: Undergraduate Student in Mechanical Engineering Dr. Tatjana Jevremovic, Chair Professor and Director of UNEP Utah Nuclear Engineering Program Changes in Mass due to Fuel Burnup Predicting Reactor Performance Conclusion Introduction and Background The Effect of Time and Power on Fuel Burnup Preliminary evaluation: This is the first ever MCNPX fuel burnup model developed for the UUTR. With this MCNPX UUTR model we are now able to understand time dependent details about the UUTR nuclear fuel burnup. This research: Based on the MCNP5 model of the UUTR, significant modifications were introduced to incorporate the BURN card and all of its options to successfully model the UUTR fuel burnup in time using MCNPX. To best represent the behavior of the UUTR, each step allowed short lived isotopes to decay out. Future work: The current MCNPX UUTR model represents the reactor historical runs of 1998. The next effort is focused at developing the first ever numerical simulation model of the reactor historical runs spanning from 1975 (first criticality) to date, 2012! This model will then be used to predict future use of the UUTR. Chris Dances Dr. Jevremovic During the lifetime of a nuclear reactor, the isotopic composition of the fuel steadily changes due to nuclear reactions taking place. This is known as burnup that represents the degree at which nuclear fuel is "burned" (used); it is expressed as the amount of energy released from the reactor fuel in units of Mega-Watt-days. The level of burnup that has occurred is dependent on the amount of time that the fuel has been used for generating fission, therefore producing energy and thus power. The fuel burnup for the University of Utah TRIGA Reactor, the UUTR, was evaluated using the MCNPX code, a nuclear engineering simulation tool. The MCNPX code is an extended version of the Monte-Carlo computer code MCNP5 developed at Los Alamos National Lab, with a link to a deterministic code that can calculate the effects of the burnup called CINDER90. Our existing MCNP5 model of the UUTR has been modified to evaluate the fuel burnup with MCNPX, i.e. to determine fuel material compositions, and changes in the UUTR criticality constant, i.e. k-effective, over the time of using the reactor. The goal of this project is to evaluate the UUTR fuel burnup history, by modeling exactly the fuel burnup rates of the UUTR core based on the MCNPX detailed UUTR model. 0 0.2 0.4 0.6 0.8 1 1.2 0 1 2 3 4 5 6 7 8 Power Level (MW) Time (days) UUTR Power Level linear_burn variable burn -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0 1 2 3 4 5 6 7 8 Burnup (MWD/kg) TIime (days) UUTR Fuel Burnup burnup burnup2 MCNP5 burnup3 KCODE: Criticality • CINDER90: • Burnup MCNP5 KCODE: Criticality • CINDER90: • Burnup MCNP5 KCODE: Criticality • CINDER90: • Burnup Step 1 Step 2 Step 3 y = 1.0057e-4E-04x 0.992 0.994 0.996 0.998 1 1.002 1.004 1.006 1.008 0.00 5.00 10.00 15.00 20.00 25.00 Criticality Constant keff Burnup MW-days keff vs. Burnup 250d_10M Fitted Data keff 1 +/- 0.00074 Criticality Constant Burnup 16.01201308 +/- 1.034874877 MW-days FITTED DATA**= B*EXP^(A*burnup) B = 1.005715726 A = -0.000355949 R2 = 0.981673448 * * ** FITTED DATA only applies to the "decayed": data points on top. y = 260.45e-0.002x y = 2.1948x R² = 0.9991 0 50 100 150 200 250 0 500 1000 1500 2000 2500 3000 3500 4000 4500 Mass (Micrograms) Time (Minutes) Xe-135 and I-135 Mass vs. Time Xe-135 Power Off I-135 Power Off Xe-135 Power On I-135 Power On Expon. (I-135 Power Off) Poly. (Xe-135 Power On) Linear (I-135 Power On) MCNPX: Burnup Model of UUTR During the lifetime of a nuclear reactor, the isotopic composition of the fuel steadily changes due to nuclear reactions taking place. This is known as burnup that represents the degree at which nuclear fuel is "burned" (used); it is expressed as the amount of energy released from the reactor fuel in unties of Mega-Watt-days. The level of burnup that has occur-red is dependent on the amount of time that the fuel has been used for generating ssion, therefore producing energy and thus power. The goal of this project is to evaluate the burnup for the University of Utah TRIGA Reactor, the UUTR, by modeling the burnup rates using a full UUTR core model in MCNPX. The MCNPX code is an extended version of the Monte-Carlo computer code MCNP5 developed at Los Alamos National Lab, with a link to CINDER90. Our MCNP5 input le of the UUTR has been modi ed to evaluate the burnup now using the MCNPX version. This input le has been run to evaluate the burnup of the UUTR to determine material compositions, as well as changes in the criticality constant, i.e. k-e ective. This has just been the preliminary evaluation of the MCNPX burn feature, and for these simulations the three di erent materials to be burned have been assumed to be spatially independent. The nuclear fuel experiences depletion of U-235, resulting in generation of ssion products, and the conversion of U-238 to Pu-239. Future work will be focused at evaluating burnup with respect to radial coordinates within the core. An input le for the UUTR has been modi ed to evaluate burnup using MCNPX and the operational history of the UUTR. Preliminary results demonstrate expected changes in both fuel composition and reactor criti-cality. Future work will involve further re nement of the simulation model, and a comparison to another burnup code.