Engineering topics

Koo, Y. H.

Publications and source records attributed to Koo, Y. H..

3 records

DOE OSTI2016

A study on the assessment criteria of DHC in PWR spent fuel

One of the major degradation mechanisms of PWR spent fuel cladding is delayed hydride cracking (DHC), which can activate within a relatively low temperature range. Its maximum crack growth rate is estimated to be within the range of 10{sup -7} m/s, at which the cladding can rupture in 1 to 2 years during dry storage. For this reason, it is essential to prevent DHC crack growth itself, but most of the existing DHC studies have been focused on the crack growth rate. In this regard, the values and characteristics of the threshold stress intensity factor (K{sub IH}) for PWR Zircaloy-4 cladding were described. Based on the limited existing test results and analysis, the experimentally measured K{sub IH} were compared with the predicted K{sub IH}. The comparison shows that the predicted values are much lower than the measured ones and both theoretical estimation and measured values of K{sub IH} increase as the temperature increases. The possibilities of degradation by DHC were also discussed during long-term dry storage. For a more reliable analysis, additional information on a pre-existing crack of spent fuel is needed.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2016

Development of surface modified Zr cladding by coating technology for ATF

It is expected that the accident tolerance fuels (ATF) will provide an enhanced fuel performance of active cooling in the reactor core for a longer time period during design-basis events as well as maintain or improve the fuel performance during normal operations and operational transients. Thus, various ATF cladding concepts have being suggested and developed in many countries. Among them, the coated cladding concept is studied in this work after the considerations of various performances in both the accidents and normal operation of LWRs. In the surface coated cladding concepts, the combination of coating material and coating method is a very important factor to determine the ATF cladding performance. As a new coating material, Cr-based alloy was developed to increase the corrosion resistance under normal operation as well as the oxidation resistance during an accident. From the high temperature oxidation test at 1200 Celsius degrees, the Cr-based alloy showed a superior oxidation resistance to Zircaloy-4 cladding, and showed more improved corrosion resistance than Zircaloy-4 cladding under 360 Celsius degrees PWR simulated loop conditions. The 3D laser coating and a combination of arc ion plating and laser beam scanning were developed to obtain a good adhesion property of corrosion resistance alloy coated on a Zr substrate. The corrosion resistance alloy (Cr-based alloy and FeCrAl alloy) coated layer used by two types of coating methods was maintained without peeling off during the ring compression test at room temperature, although some cracks were formed on the coated layer. After a high-temperature oxidation test at 1200 Celsius degrees for 2000 s, a very thin oxide layer, which was a few microns, was formed on the corrosion resistance alloy layer. However, the ZrO{sub 2} phase, which was thicker than 100 μm was formed on the Zr alloy cladding surface. Thus, it is known that the high-temperature oxidation resistance of commercial Zr alloy cladding can be considerably improved by the coating of corrosion resistant alloys. In addition, the partial oxide dispersion strengthened (ODS) treatment using a laser beam scanning (LBS) method was applied to decrease the ballooning and rupture opening during accident conditions. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2013

Evaluation of effective-stress-function algorithm for nuclear fuel simulation

In a pressurized water reactor (PWR), the mechanical integrity of nuclear fuel is the most critical issue as it is an important barrier for fission products released into the environment. The integrity of zirconium cladding that surrounds uranium oxide can be threatened during off-normal operation owing to a pellet-cladding mechanical interaction (PCMI). To analyze the fuel and cladding behavior during off-operation, the fuel performance code should calculate an inelastic analysis in two - or three-dimensional calculations. In this paper, the effective stress function (ESF) algorithm based on a two-dimensional FE module has been implemented to simulate the inelastic behavior of the cladding with stability and accuracy. The ESF algorithm solves the governing equations of the inelastic constitutive behavior by calculating the zero of the appropriate effective-stress-function. To verify the accuracy of the ESF algorithm for an inelastic analysis, a code-to-code benchmark was performed using the commercial FE code, ANSYS 13.0. To demonstrate the stability and convergence of the implemented algorithm, the number of iterations in the ESF algorithm was compared with that in a sequential algorithm in the case of an inelastic problem. Consequently, the evaluation results demonstrate that the implemented ESF algorithm improves the efficiency of the computation without a loss of accuracy for an inelastic analysis. (authors)

22 GENERAL STUDIES OF NUCLEAR REACTORS↗