Accessible Unlicensed Requires Authentication Published by De Gruyter April 5, 2013

Assessment of different mechanisms of C-14 production in irradiated graphite of RBMK-1500 reactors

Einschätzung verschiedener Mechanismen der C-14-Produktion im bestrahlten Graphit von RBMK-1500-Reaktoren
E. Narkunas, A. Smaizys, P. Poskas and R. Kilda
From the journal Kerntechnik

Abstract

Two RBMK-1500 water-cooled graphite-moderated channel-type power reactors at the Ignalina Nuclear Power Plant (INPP) are under decommissioning now. The total mass of irradiated graphite in the cores of both units is more than 3600 tons. The main source of uncertainty in the numerical assessment of graphite activity is the uncertainty of the initial impurities content in graphite. Nitrogen is one of the most important impurities, having a large neutron capture cross-section. This impurity may become the dominant source of C-14 production. RBMK reactors graphite stacks operate in the cooling mixture of helium-nitrogen gases and this may additionally increase the quantity of the nitrogen impurity. In this paper the results of the numerical modelling of graphite activation for the INPP Unit 1 reactor are presented. In order to evaluate the C-14 activity dependence on the nitrogen impurity content, several cases with different nitrogen content were modelled taking into account initial nitrogen impurity quantities in the graphite matrix and possible nitrogen quantities entrapped in the graphite pores from cooling gases.

Kurzfassung

Zwei wassergekühlte, graphitmoderierte RBMK-1500-Leistungsreaktoren des KKW Ignalina (INPP) befinden sich zur Zeit im Rückbau. Die gesamte Masse des bestrahlten Graphits in den Kernen beider Blöcke beträgt mehr als 3600 Tonnen. Die Hauptunsicherheitsquelle bei der numerischen Bestimmung der Graphitaktivität ist die Unsicherheit über die anfänglichen Verunreinigungen des Graphits. Stickstoff ist eine der wesentlichen Verunreinigungen mit einem großen Wirkungsquerschnitt für Neutronenabsorption. Diese Verunreinigung kann zur dominierenden Quelle für die C-14-Produktion werden. Die Graphitblöcke der RBMK-Reaktoren werden durch ein Helium-Stickstoff-Gemisch gekühlt und dies kann zusätzlich die Menge an Stickstoffverunreinigung erhöhen. In diesem Beitrag werden die Ergebnisse der numerischen Modellierung der Graphitaktivierung für den Reaktor des Blockes 1 im KKW Ignalina vorgestellt. Um die Abhängigkeit der C-14-Aktivität von der Menge der Stickstoffverunreinigung zu bewerten, wurden verschiedene Fälle mit unterschiedlichem Stickstoffgehalt unter Berücksichtigung der Menge an anfänglicher Stickstoffverunreinigung in der Garphitmatrix und möglichen in den Graphitporen des Kühlgases eingeschlossenen Stickstoffmengen modelliert.


* E-mail:

References

1 Almenas, K.; Kaliatka, A.; Uspuras, E.: Ignalina RBMK-1500: A source book. 2nd Ed. Kaunas: Lithuanian Energy Institute, 1998 Search in Google Scholar

2 Characterization, Treatment and Conditioning of Radioactive Graphite from Decommissioning of Nuclear Reactors: IAEA TECDOC No. 1521. Vienna: International Atomic Energy Agency, 2006 Search in Google Scholar

3 Graphite Decommissioning: Options for Graphite Treatment, Recycling, or Disposal, Including a Discussion of Safety-Related Issues. EPRI, Palo Alto, CA: 2006. 1013091 Search in Google Scholar

4 Bylkin, B. K.; Davydova, G. B.; Krayushkin, A. V.; Shaposhnikov, V. A.: Computational Estimates of the Radiation Characteristics of Irradiated Graphite after Final Shutdown of a Nuclear Power Plant with an RBMK Reactors. Atomic Energy96 (2004) 411416 Search in Google Scholar

5 Bylkin, B. K.et al.: Induced Radioactivity and Waste Classification of Reactor Zone Components of the Chernobyl Nuclear Power Plant Unit 1 after Final Shutdown. Nuclear Technology 136 (2001) 7688 Search in Google Scholar

6 Virgilev, Y. S.: Impurities in and Serviceability of Reactor Graphite. Atomic Energy84 (1998) 61310.1007/BF02430647 Search in Google Scholar

7 Bushuev, A. V.; Zubarev, V. N.; Proshin, I. M.: Impurity Composition and Content in Graphite from Commercial Reactors. Atomic Energy, 2002, vol. 92, no. 4, p. 33133510.1023/A:1016506110872 Search in Google Scholar

8 Ancius, D.et al.: Evaluation of the Activity of Irradiated Graphite in the Ignalina Nuclear Power Plant RBMK-1500 Reactor. Nukleonika 50 (2005) 113120 Search in Google Scholar

9 Ignalina NPP Safety analysis Report. Ignalina, 1996 Search in Google Scholar

10 Safety Analysis Report for INPP Unit 2. Ignalina, 2003 Search in Google Scholar

11 Narkunas, E.; Smaizys, A.; Poskas, P.: Numerical modelling of neutron activation processes in reactor RBMK-1500 structural elements. 3. Modelling of neutron activation processes in fuel channels employing modelled neutron fluxes. Power Engineering55 (2009) 200–208. (in Lithuanian) Search in Google Scholar

12 Smaizys, A.; Narkunas, E.; Poskas, P.: Modelling of activation processes for GR-280 graphite at Ignalina NPP. Radiation protection dosimetry116 (2005) 270275 Search in Google Scholar

13 Davis, W.: Carbon-14 Production in Nuclear Reactors, NRC Report, ORNL/NUREG/TM-12, Oak Ridge National Laboratory, NTIS, February 1977 Search in Google Scholar

14 Khripunov, V. I.; Kurbatov, D. K.; Subbotin, M. L.: C-14 Production in CTR Materials and Blankets. Proceedings of 21st Fusion Energy Conference (FEC 2006), 16–21 October 2006. Chengdu, China. SE/P2-3 Search in Google Scholar

15 Hacker, P. J.; Neighbour, G. B.; Levinskas, R.; Milcius, D.: Characterization of Ignalina NPP RBMK Reactors Graphite. Materials Science20 (2001) 6266 Search in Google Scholar

16 Bondarkov, M. D.et al.: Activity Study of Graphite from the Chernobyl NPP Reactor. Bulletin of the Russian Academy of Science. Physics, 2009, no. 2, p. 261265 Search in Google Scholar

17 Poncet, B. R.: Characterization of Graphite Sleeves from BUGEY 1 EDF Plant for Permanent Disposal – Measurement and Calculation of Scaling Factors for Difficult-to-Measure Nuclides. WM'03 Conference, February 2003, Tucson, Arizona, USA Search in Google Scholar

18 Fachinger, J.; von Lensa, W.; Podruhzina, T.: Decontamination of Nuclear Graphite. Nuclear Engineering and Design238 (2008) 3086309110.1016/j.nucengdes.2008.02.010 Search in Google Scholar

19 Final Decommissioning Plan for Ignalina NPP Units 1 & 2. A1.1/ED/B4/0004 Search in Google Scholar

20 IAEA Power Reactor Information System, http://www.iaea.org/programmes/a2/ Search in Google Scholar

Received: 2010-2-8
Published Online: 2013-04-05
Published in Print: 2010-08-01

© 2010, Carl Hanser Verlag, München