ML19122A302

ANS 2019 Effect of Fouling on Quenching of Simulated Fuel Rods

ML19122A302
Person / Time
Issue date:	02/18/2019
From:	Stephen Bajorek, Beck F, Cheung F, Garrett G, Hoxie C, Jin Y, Kirk Tien NRC/RES/DSA/CDB, Pennsylvania State Univ, University Park, PA
To:
Tien K
References
Download: ML19122A302 (3)

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Effect of Fouling on Quenching of Simulated Fuel Rods Faith R. Beck*, Yue Jin, Grant Garrett, Fan-Bill Cheung*, Stephen M. Bajorek, Kirk Tien, Chris L. Hoxie

• Mechanical Engineering Department, 127 Reber Building, University Park, PA 16803, frb115@psu.edu; fxc4@psu.edu Nuclear Engineering Department, 127 Reber Building, University Park, PA 16803, yuj118@psu.edu; grg5094@psu.edu Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Washington, DC 20555, stephen.bajorek@nrc.gov, chris.hoxie@nrc.gov, kirk.tien@nrc.gov EXPERIMENTAL SETUP INTRODUCTION The NRC/PSU RBHT test facility has a full-length 7x7 Mineral deposits on fuel rods in subcooled flow boiling electrically heated rod bundle that simulates a portion of a are a common occurrence and can significantly impact the 17x17 PWR reactor fuel assembly. The test section consists power distribution in the bundle as well as the anticipated of a full-length rod bundle arranged in a rectangular array neutron flux [1-3]. These corrosion deposits typically have housing structure in a square channel of 90.2 mm (3.55 in) a nickel iron-ferrite composition and can have a profound [4, 6]. The flow housing is connected to the lower and upper effect on the heat transfer mechanisms. Oxide growth on plenums, see Fig.1. The flow housing is made of Inconel steel and zircaloy clad rods is a porous, non-uniform layer 600, which has a wall thickness of 6.4 mm so that it can on an otherwise smooth, flat surface. In nuclear plants, safe withstand higher temperature and pressures. The flow operations require oxide layers not exceed a certain housing has 23 pressure taps at different elevations through thickness in relation to the base fuel rod material, which which DP (differential pressure) cells are connected to houses the uranium pellets. There are limitations on oxide measure pressure drop. There are 45 full-length heater rods growth because it compromises the structural integrity of and four unheated corner rods in the bundle. The diameter the rod, which may lead to failure of the material. of the heater rods is 9.5 mm, the heated length is 3.657 m In 2010, oscillatory reflood experiments were and the pitch is 12.6 mm. Four corner rods provide performed at the NRC/PSU RBHT facility that varied the structural support to the bundle and accommodate the magnitude and frequency of flow rate oscillations [4]. After wiring for the grid thermocouples.

processing the data, noticeable corrosion and silicon dioxide deposits were observed on the heater rods. Once recognized, the rods with fouling and corrosion were replaced and stationary components were power-washed. The bundle was rebuilt and ready for testing again in 2013. Since then, oscillatory reflood experiments have been repeated in the clean bundle to identify the effect of fouling on rod bundle thermal-hydraulics.

Multiple characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) associated with Energy-dispersive X-ray spectroscopy (EDS), and field emission scanning electron microcopy (FESEM) were used to identify the phases, chemical composition, and surface microstructure of the Iconel600 rods before and after use in the NRC/PSU RBHT facility

[5]. Micro- and nanoparticles composed of NiO, Cr2O3, and Fe2O3 were observed on the surface of the fouled heater rods. The oxide layer has been characterized as porous with Fig. 1. NRC/PSU RBHT Facility.

a maximum thickness of 2µm. The water contact angle is found to decrease overtime for the fouled surfaces, RESULTS AND DISCUSSION indicating an increase in the surface wettability and liquid spreading. Owing to the thin oxide layer, the variation in the Oxidation can be likened to a surface roughness, and analyzed surface roughness of the clean and fouled surfaces the added porosity is known to enhance heat transfer due to is negligible. The porous microstructure coupled with the capillary forces, which disperse, and breakup liquid films increase in surface wettability play a significant role in the faster than a clean, bare surface [7]. For these reasons, it is enhancement of film boiling heat transfer. expected that the fouled bundle would quench faster than the clean bundle, as seen in Fig. 2. When comparing the minimum film boiling temperature, or Tmin, from the

fouled bundle, the effect of oxidation is apparent. Test TABLE I. EXPERIMENTAL CONDITIONS conditions for clean and fouled bundle experiments are shown in Table I. For the clean bundle (Exp. 7184), it was Set Exp. Flow velocity Oscillation found that Tmin 895 K and for the fouled bundle (Exp. No. (m/s) period 5231), Tmin 940 K. Oxidation acts to break up the vapor (s) film in film boiling faster and by so-doing, the minimum A 8069 0.0254+/-0 film boiling temperature increases with oxidation and 7184 0.0254+/-1 4 decreases the quench time.The experimental uncertainty B 5238 0.0254+/-0 associated with the thermocouple is +/- 1.11 K [8]. In terms 5231 0.0254+/-1 4 of experimental repeatability, the largest variation in a temperature and time measurement is 13 K and 16 s, respectively [9].

In addition to quenching behavior, thermal-hydraulic parameters are shown in Fig. 3. of the inner 3x3 with bundle fouling. Hollow and filled shapes represent oscillatory and constant reflood experiments, respectfully. Experiments No.s in the 5000s are fouled and those in the 7000/8000s are clean. A decrease in the bundle quench time occurs, regardless of oscillatory reflood, when there is bundle fouling. This is expected due to enhanced entrainment which occurs when there is oscillatory reflood in the bundle.

In addition, steam temperatures are shown for the two experimental sets in Fig.s 4 and 5. For the clean bundle experiments in Set A (Fig. 4), the steam temperature for the oscillatory reflood experiment is approximately 200 K lower than for the constant reflood experiment, confirming Fig. 2. Quench front profiles with and without fouling for enhanced entrainment. However, for the fouled bundle oscillatory reflood experiments.

experiment, the trend in the steam temperatures is not as clear. Both temperatures in Fig. 5 are the same at the start of the experiment, however, the constant reflood experiment appears to wet sooner than the oscillatory reflood test. The peak temperatures for the fouled bundle experiments were approximately 200 K lower than the clean bundle tests, see Fig. 5. This significant difference in surface conditions may have contributed to the observed steam temperatures for these tests. Additionally, it can be concluded from Fig.s 4 and 5 that the effect of fouling dominates the effect of oscillatory reflood when comparing the steam temperatures.

CONCLUSIONS In conclusion, the effect of fouling decreases bundle quench time, and decreases the steam temperatures when compared to clean bundle experiments. The effect of oscillation period serves to increase the required bundle quench time and decreases the steam temperatures for the clean bundle tests. Fig. 3. Quench time of clean and fouled bundle experiments.

The effect of fouling dominates the effect of oscillatory Hollow and filled shapes represent oscillatory and constant reflood when comparing the steam temperatures. reflood experiments, respectively. Experiments No.s in the 5000s are fouled and those in the 7000/8000s are clean.

5. S.A. Ebrahim, V. Fudurich, F.R. Beck, F.B. Cheung, S.M.

Bajorek, K. Tien, and C. L. Hoxie, Effects of liquid subcooling and initial rod temperature on the minimum film boiling temperature, in 3rd International Topical Meeting on Advances in Thermal Hydraulics 2016, ATH 2016.

American Nuclear Society, 2016.

6. L. Hochreiter, F. Cheung, T. Lin, S. Ergun, A. Sridharan, A. Ireland, and E. Rosal, RBHT reflood heat transfer experiments data and analysis, tech. rep., NUREG/CR-6980, US Nuclear Regulatory Commission, Washington, DC, 2012.

7. F. A. Sohag, F. R. Beck, L. Mohanta, F.-B. Cheung, A. E.

Segall, T. J. Eden, and J. K. Potter, Enhancement of downward-facing saturated boiling heat transfer by the cold spray technique, Nuclear Engineering and Technology, 2016.

Fig. 4. Steam temperatures for clean bundle tests. 8. Mohanta, Lokanath. "Theoretical and experimental study of inverted annular film boiling and regime transition during reflood transients." (2015).

9. Beck, Faith R. "Experimental and theoretical study of oscillatory two-phase flows with heat and mass transfer."

(2019).

Fig. 5. Steam temperatures for fouled bundle tests.

REFERENCES

1. J. Sawicki, Analyses of crud deposits on fuel rods in PWRs using Mossbauer spectroscopy, Journal of Nuclear Materials, vol. 402, no. 2, pp. 124-129, (2010).

2. M. Jin and M. Short, Multiphysics modeling of two-phase film boiling within porous corrosion deposits, Journal of Computational Physics, vol. 316, pp. 504-518, 2016.

3. H. Seo, J. H. Chu, S.-Y. Kwon, and I. C. Bang, Pool boiling CHF of reduced graphene oxide, graphene, and sic-coated surfaces under highly wettable fc72, International Journal of Heat and Mass Transfer, vol. 82, pp. 490-502, 2015

4. Beck FR, Jin Y, Mohanta L, Qiao S, Rau A, Miller DJ et al. Effects of period and flow rate on liquid entrainment and the droplet field under forced oscillatory reflood conditions.

Paper presented at 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017, Xi'an, Shaanxi, China., 2016