Core loss during a severe accident (COLOSS)

FISA-2003, 10-13 novembre 03, Luxembourg
B. Adroguer, J.P. Van Dorsselaere, P. Chatelard, N. Cocuaud, F. Bertrand (1), L. Bellenfant (2), D. Bottomley, D. Knoche (3), V. Vrtilkova (4), K. Müller (5), G. Schanz, A. Miassoedov, M. Steinbrück, J. Stuckert, W. Krauss, W. Hering, C. Homann (6), Z. Hózer (7), G. Bandini (8), J. Birchley (9), I. Kleinhietpass (10), M. Buck (11), F. Benitez (12), E. Virtanen (13), S. Marguet (14), G. Azarian (15), H. Plank (16), A. Berdyshev, M. Veshchunov (17), V. Kobzar, Y. Zvonarev (18), A. Goryachev (19).

The COLOSS project was a 3-year shared-cost action which started in February 2000. The workprogramme performed by 19 partners was shaped around complementary activities aimed at improving severe accident (SA) codes. Unresolved risk-relevant issues regarding H₂ production, melt generation and the source term were studied, through a large number of experiments such as
a) dissolution of fresh and high burn-up UO₂ and MOX by Zircaloy,
b) simultaneous dissolution of UO₂ and ZrO₂,
c) oxidation of U-O-Zr mixtures,
d) degradation-oxidation of B₄C control rods.

Corresponding models were developed in SA computer codes which were then used to apply results in plant calculations and evaluate their consequences on key SA sequences in different plants involving B₄C control rods and on the TMI-2 accident. Significant results have been produced from separate-effects, semi-global and large-scale tests on COLOSS topics. Related models were successfully implemented in some SA codes. Break-throughs were achieved on some issues for which more data are needed for consolidation of the modelling in particular on burn-up effects on UO2 and MOX dissolution and oxidation of U-O-Zr and B₄C-metal mixtures. The plant calculation activity enabled an overall assessment of codes focusing on topics studied in the project. Main results and recommendations for future R&D activities are summarized in this paper.

(1) IRSN, Cadarache (Fr)
(2) IRSN, Fontenay-aux-Roses (Fr)
(3) JRC/ITU, Karlsruhe (Ge)
(4) UJP Praha, Zbraslav (Cz)
(5) JRC/IE, Petten (Nl)
(6) FZK, Karlsruhe (Ge)
(7) AEKI, Budapest (Hu)
(8) ENEA, Bologna (It)
(9) PSI, Villigen (CH)
(10) RUB, Univ. Bochum (Ge)
(11) IKE, Univ. Stuttgart (Ge)
(12) UPM, Univ. Madrid (Sp)
(13) LTKK, Univ. Lappeenrenta (Fi)
(14) EDF, Clamart (Fr)
(15) Framatome-ANP SAS, Paris (Fr)
(16) Framatome-ANP GmbH, Erlangen (Ge)
(17) NSI-IBRAE, Moscow (Ru)
(18) NSI-KI, Moscow (Ru)
(19) RIAR, Dimitrovgrad (Ru)