Author(s) Jin-Soo Choi, Seung-Chul Park, Kyoung-Rok Park, Ho-Yeon Yang, O-Bong Yang

Affiliation(s)
KHNP-Central Research Institute, Korea Hydro & Nuclear Power Corporation, Daejeon, South Korea;.
School of Chemical Engineering, Chonbuk National University, Jeonju, South Korea.

ABSTRACT

The accumulation of corrosive and radioactive wastes in the primary system, including nuclear fuel assembly, significantly increases workers’ exposure to radiation. Zinc injection from 5 to 40 ppb into the Reactor Coolant System (RCS) of Pressurized Water Reactors (PWRs) has been known as an effective method to decrease the radiation fields and Primary Water Stress Corrosion Cracking (PWSCC). Zinc injection affects both corrosion product concentrations and characteristics of the deposited crud on oxide layers, because zinc is incorporated into the oxide films by displacing nickel, cobalt, and iron in primary systems. Radiation fields and corrosion might be mitigated as radioactive products, such as Co, which are removed by zinc injection. However, the zinc injection effects on fuel assembly in Nuclear Power Plants (NPPs) have not been much reported yet, even though some lab tests were carried out in USA and France. In this paper, we studied effects of zinc injection on the fuel assemblies in the Ulchin 1 NPP. The chemical and radiation analysis of radioactive corrosion products was performed to evaluate zinc injection effects on the fuel assembly in the Ulchin 1 NPP. Gamma spectroscopy was used to analyze crud samples for radioisotope contents. The Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) was used to analyze crud samples for elemental contents. The concentration of radioisotope Co-58 was decreased after zinc injection to 1/22 times that before the zinc injection. 1% - 2% wt% of zinc was incorporated through the substitution of Ni in the crud oxide layer. The Ni/Fe ratio was decreased to 0.69 from 1.12 after the injection, due to the Ni substitution by zinc. It was found that NiO and NiFe₂O₄ were converted to ZnO and ZnFe₂O₄, respectively. In conclusion, zinc injecttion was found to be an essential method to reduce the amount of radioactive Co-58 in the fuel assemblies of primary systems in NPPs.

KEYWORDS
Zinc Injection; Dose Rates; PWSCC; RCS; Oxide Layers

Cite this paper
Choi, J. , Park, S. , Park, K. , Yang, H. and Yang, O. (2013) Effect of zinc injection on the corrosion products in nuclear fuel assembly. Natural Science, 5, 173-181. doi: 10.4236/ns.2013.52027.

References
[1]   Maeng, W.Y., et al. (2009) Nuclear chemistry guidance, KAERI, Taejon.

[2]   EPRI (2011) PWR dose reduction efforts at Exelon. Pro- ceedings of the August 2011 EPRI PWR Primary Zinc Ad- dition Workshop, Palo Alto, August 2011, 2-9.

[3]   EPRI (2011) EPRI chemistry update. Palo Alto, August 2011, 1022547.

[4]   EPRI (2005) Mechanisms of zinc interaction with oxide films in high-temperature water. Proceedings of the Au- gust 2004 EPRI PWR Primary Zinc Addition Workshop, Toronto, 19-20 August, 2004, 2-5.

[5]   Byers, A. (2005) Zinc and CRUD, how they interact. EPRI Fuel Reliability Program WG1 Meeting, Las Vegas, 1 September 2005, 2-6.

[6]   EPRI (2002) Effects of zinc addition on mitigation of PWSCC of alloy 600. Palo Alto, 1003522.

[7]   EPRI (1995) PWR primary water chemistry guidelines. Revision 3, Appendix A, Palo Alto, TR-105714.

[8]   Beverskog, B. (2004) The role of Zinc in LWRs. Interna- tional Conference: Water Chemistry of Nuclear Reactor Systems, San Francisco, 11-14 October 2004, 2-12.

[9]   Choi, I.-K., et al. (2006) Development of analytical tech- niques for characteristics of CRUD, KAERI, Taejon, CR-270.

[10]   Yeon, J.-W., Choi, I.-K., Park, K.-K., Kwon, H.-M. and Song, K. (2010) Chemical analysis of fuel crud obtained from Korean nuclear power plants. Journal of Nuclear Material, 404, 160-164. doi:10.1016/j.jnucmat.2010.07.024

[11]   McClure, D.S. (1957) The distribution of transition metal cations in spinels. Journal of the Physical Chemistry of Solids, 3, 311. doi:10.1016/0022-3697(57)90034-3

[12]   EPRI (1986) The solubility of simulated PWR primary circuit corrosion products. Palo Alto, NP-4248.

[13]   EPRI (2006) Pressurized water reactor primary water zinc application guidelines. Palo Alto, 1013420.

[14]   Tigeras, A., Debec, G., Jeannin, B. and Rocher, A. (2006) EDF zinc injection: Analysis of power reduction impact on the chemistry and radiochemistry parameters. Proce- edings of International Conference on Water Chemistry in Nuclear Reactor Systems, Jeju, 23-26 October 2006, 1-2.

[15]   Lister, D. (1993) Activity transport and corrosion proc- esses in PWRs. Nuclear Energy, 32, 103-114.

[16]   (2006) Zinc acetate dihydrate, depleted in isotope Zn-64. Material Safety Data Sheet of DZA, ISOFLEX, San Fran- cisco.

[17]   EPRI (2000) Evaluation of zinc addition in cycle 13 at Farley Unit 2. Palo Alto, TR-1000251.

[18]   EPRI (1996) Evaluation of zinc addition to the primary coolant of PWRs. Palo Alto, TR-106358-V1.

[19]   Ultrasonic Fuel Cleaning Efficacy Campaign Results at Callaway. CA:2002, TR-1003229.

[20]   Moon, J.H., Chung, H.H., Sung, K.W. and Kim, U.C. (2005) Nuclear engineering and technology. 37, 375-384.

[21]   (1977) Chart of nuclides. 12th Edition, General Electric Company, Schenectady.

[22]   EPRI (2003) PWR operating experience with zinc addi- tion and the impact on plant radiation fields. Palo Alto, 1003389.

[23]   EPRI (1989) Corrosion product release in light water reactors. Palo Alto, EPRI NP-6512.

[24]   KAERI (2005) The evaluation for zinc injection into primary water in Korea. Taejon