Modular Optimization Code Package:MOZAIK

Open Access
Author:
Bekar, Kursat Burak
Graduate Program:
Nuclear Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 03, 2008
Committee Members:
  • Prof Yousry Y Azmy, Committee Chair
  • Kenan Unlu, Committee Chair
  • Jack Brenizer Jr., Committee Member
  • Vijaykrishnan Narayanan, Committee Member
Keywords:
  • shape optimization
  • modularity
  • TORT
  • beam port design
  • parallel computation
  • streaming operator
Abstract:
This dissertation addresses the development of a modular optimization code package, MOZAIK, for geometric shape optimization problems in nuclear engineering applications. MOZAIK’s first mission, determining the optimal shape of the D2O moderator tank for the current and new beam tube configurations for the Penn State Breazeale Reactor’s (PSBR) beam port facility, is used to demonstrate its capabilities and test its performance. MOZAIK was designed as a modular optimization sequence including three primary independent modules: the initializer, the physics and the optimizer, each having a specific task. By using fixed interface blocks among the modules, the code attains its two most important characteristics: generic form and modularity. The benefit of this modular structure is that the contents of the modules can be switched depending on the requirements of accuracy, computational efficiency, or compatibility with the other modules. Oak Ridge National Laboratory’s discrete ordinates transport code TORT was selected as the transport solver in the physics module of MOZAIK, and two different optimizers, Min-max and Genetic Algorithms(GA), were implemented in the optimizer module of the code package. A distributed memory parallelism was also applied to MOZAIK via MPI (Message Passing Interface) to execute the physics module concurrently on a number of processors for various states in the same search. Moreover, dynamic scheduling was enabled to enhance load balance among the processors while running MOZAIK’s physics module thus improving the parallel speedup and efficiency. In this way, the total computation time consumed by the physics module is reduced by a factor close to M, where M is the number of processors. This capability also encourages the use of MOZAIK for shape optimization problems in nuclear applications because many traditional codes related to radiation transport do not have parallel execution capability. A set of computational models based on the existing beam port configuration of the Penn State Breazeale Reactor(PSBR) was designed to test and validate the code package in its entirety, as well as its modules separately. The selected physics code, TORT, and the requisite data such as source distribution, cross-sections, and angular quadratures were comprehensively tested with these computational models. The modular feature and the parallel performance of the code package were also examined using these computational models. Another outcome of these computational models is to provide the necessary background information for determining the optimal shape of the D2O moderator tank for the new beam tube configurations for the PSBR’s beam port facility. The first mission of the code package was completed successfully by determining the optimal tank shape which was sought for the current beam tube configuration and two new beam tube configurations for the PSBR’s beam port facility. The performance of the new beam tube configurations and the current beam tube configuration were evaluated with the new optimal tank shapes determined by MOZAIK. Furthermore, the performance of the code package with the two different optimization strategies were analyzed showing that while GA is capable of achieving higher thermal beam intensity for a given beam tube setup, Min-max produces an optimal shape that is more amenable to machining and manufacturing. The optimal D2O moderator tank shape determined by MOZAIK with the current beam port configuration improves the thermal neutron beam intensity at the beam port exit end by 9.5%. Similarly, the new tangential beam port configuration (beam port near the core interface) with the optimal moderator tank shape determined by MOZAIK improves the thermal neutron beam intensity by a factor of 1.4 compared to the existing beam port configuration (with the existing D2O moderator tank). Another new beam port configuration, radial beam tube configuration, with the optimal moderator tank shape increases the thermal neutron beam intensity at the beam tube exit by a factor of 1.8. All these results indicate that MOZAIK is viable and effective and is ready for deployment to address shape optimization problems involving radiation transport in nuclear engineering applications.