IMPROVED CRUD HEAT TRANSFER MODEL FOR DRYOUT ON FUEL PIN SURFACES AT PWR OPERATING CONDITIONS

Open Access
Author:
Wang, Guoqiang
Graduate Program:
Nuclear Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 03, 2009
Committee Members:
  • Seungjin Kim, Dissertation Advisor
  • Seungjin Kim, Committee Chair
  • Fan Bill B Cheung, Committee Chair
  • Arthur Thompson Motta, Committee Member
  • Kostadin Nikolov Ivanov, Committee Member
  • Digby D Macdonald, Committee Member
  • William A Byers, Committee Member
  • Mr Michael Y Young (Special Member), Committee Member
  • Mr Zeses Karoutas (Special Member), Committee Member
  • Mr Robert L Oelrich, Jr (Special Member), Committee Member
  • Dr Lawrence E Hochreiter (Deceased), Committee Member
Keywords:
  • VIPRE/BOA
  • PWR Conditions
  • Thermal Conductivity
  • Crud Dryout
Abstract:
ABSTRACT Researchers have performed many studies to understand crud formation on fuel rod cladding surfaces, which have been observed in Pressurized Water Reactors (PWRs) as a result of sub-cooled nucleate boiling and oxidation/reduction reactions. Crud deposits with high concentration of boron species will result in an axial offset anomaly (AOA), usually named Crud Induced Power Shift (CIPS) due to the effect of the boron on the power shape distribution. If the crud deposit is thick enough at high heat flux level, it may cause fuel rod surface dryout and accelerate cladding corrosion. This study examines and measures the crud thermal conductivity at PWR operating conditions, which is one of the most important parameters for simulating CIPS and thick crud dryout phenomena. To better understand crud formation and measure crud thermal conductivity on the fuel rod cladding surfaces at pressurized water reactor operating conditions, a single rod crud Thermal-Hydraulic test facility was built at the Westinghouse Science and Technology Center (STC) in October 2005. Since then, a number of updates have been made to the test facility, which was named the Westinghouse Advanced Loop Tester (WALT). Recently, a four regime theory and methodology has been proposed for crud thermal conductivity study and measurement. Meanwhile, a number of preliminary tests have been performed in the WALT loop, which was utilized to successfully generate crud and measure its thermal parameters as a function of crud thickness and fluid conditions. In the WALT test loop, crud is deposited on the heater rod surface, then the crud characteristics are confirmed to be similar to these observed in the PWRs and the crud from the WALT loop has been determined to be representative of crud observed in PWRs. After the WALT loop crud thermal conductivity is calculated based on other direct measurements, it can be used to evaluate cladding surface temperatures at various crud thicknesses and thermal-hydraulic conditions. In this dissertation, the method for crud thermal conductivity measurement and some preliminary test results from the WALT loop is presented and discussed. Furthermore, since the WALT system is also being utilized by Westinghouse to perform crud dry-out testing, these test results are also used to validate models used in the thermal-hydraulic codes and to support the industry goal of zero fuel failures by 2010 and beyond, established by commercial nuclear industry executives at an Institute of Nuclear Power Operations (INPO) meeting.