Synopsis and outcome of the QUENCH experimental program

Transport and deposition in the Phébus FP circuit

https://www.irsn.fr/EN/Research/publications-documentation/Publications/DSR/Documents/Coloss_pub_NED_2003.pdf

Core Loss during a Severe Accident (COLOSS).

Study of boron behaviour in the primary circuit of water reactors under severe accident conditions: A comparison of Phebus FPT3 results with other recent integral and separate-effects data

Investigation on boron carbide oxidation for nuclear reactor safety: Experiments in highly oxidising conditions

Boron carbide is widely used as neutron absorbing control rod material in Western Boiling Water Reactors (BWR) and Russian RBMKs and WERs and some Pressurised Water Reactors (PWR). During a hypothetical severe accident the B 4 C reacts with the surrounding stainless steel cladding forming eutectic melts at temperatures above 1200 °C which is far below the melting temperatures of all components. The remaining uncovered absorber material as well as the B 4 C/metal mixtures may be exposed to the steam in the reactor core. The oxidation of boron carbide is highly exothermic and produces various gaseous reaction products like H 2 , CO, CO 2 and CH 4 which may affect the fission product chemistry. Extensive test series were performed to study the oxidation behaviour of boron carbide at high temperatures. Four types of B 4 C specimens with quite different properties were investigated under various atmospheres in the temperature range between 800 and 1600 °C. In contrast to most of the data published so far mainly at lower temperatures which are based on the evaluation of mass changes, gas production data were used to determine the oxidation kinetics of B 4 C in steam. The oxidation kinetics of boron carbide are determined by the formation of a liquid boron oxide barrier diffusion layer and its loss due to the reaction with surplus steam to form volatile boric acids andlor direct evaporation at temperatures above 1500 °C. The overall reaction kinetics are paralinear. Under the conditions typical for severe accidents (high temperatures and steam flow rates) linear oxidation kinetics establishes soon after initiation of the oxidation. The oxidation kinetics are strongly influenced by the surrounding conditions, in particular by the steam flow rate and the steam partial pressure. On the other hand, the properties of the B 4 C sample itself have only a limited effect on the oxidation. Only very low amounts of methane - which is of interest for the fission gas chemistry due to the formation of organic iodine - were produced in these tests. The highest methane release was measured at the lowest test temperatures in agreement with thermo-chemical pre-test calculations. This report updates and replaces the internal report SAM-COLOSS-P026 published as one deliverable of the EC COLOSS program (5 t h Framework Program 2000-2003).

/pdf/experiments-on-the-oxidation-of-boron-carbide-at-high-4lnqimi27u.pdf

Experiments on the oxidation of boron carbide at high temperatures

Boron carbide is widely used as neutron absorbing control rod material in Western Boiling Water Reactors (BWR) and Russian RBMKs and WERs and some Pressurised Water Reactors (PWR). During a hypothetical severe accident the B4C reacts with the surrounding stainless steel cladding forming eutectic melts at temperatures above 1200 °C which is far below the melting temperatures of all components. The remaining uncovered absorber material as well as the B 4 C/metal mixtures may be exposed to the steam in the reactor core. The oxidation of boron carbide is highly exothermic and produces various gaseous reaction products like H 2 , CO, CO 2 and CH 4 which may affect the fission product chemistry. Extensive test series on the degradation of boron carbide absorber rods and the oxidation of the resulting absorber melts were performed. Two types of 1-pellet-size as well as 10-cm long control rod segments manufactured from commercial materials used in French 1300 MW PWRs were investigated in the temperature range between 800 and 1700 °C in steam atmosphere. The gaseous reaction products were quantitatively analysed by mass spectroscopy allowing the evaluation of oxidation rates. Extensive post-test examinations by light microscopy, scanning electron microscopy as well as EDX and Auger spectroscopy were performed. Rapid melt formation due to eutectic interactions between stainless steel (cladding tube) and B 4 C on the one hand and between the steel and Zircaloy-4 (guide tube) on the other hand was observed at temperatures above 1250 °C. Complex multi-component and multi-phase melts were formed. An outer ZrO 2 oxide scale kept the melt inside the guide tube and prevented early relocation and oxidation of the melt. Rapid oxidation of the absorber melts and the remaining boron carbide pellets took place after failure of the protecting oxide shell above 1450 °C. Local oxidation of the B 4 C pellets and internal melt relocation was seen at the longer CR specimens. Separate-effects tests on the oxidation of SS/B 4 C/Zry-4 absorber melts of various compositions confirmed the fast oxidation seen in the tests with control rod segments. The oxidation rates of such mixtures increased by a factor of up to 30 after reaching their melting points at temperatures of about 1200°C. Furthermore, it was shown that B 4 C can liquefy huge amounts of stainless steel 200 K below its melting temperature. Only very low amounts of methane - which is of interest for the fission gas chemistry due to the formation of organic iodine - were produced in these tests. This report updates and replaces the internal report SAM-COLOSS-P028 published as one deliverable of the EC COLOSS program (5 t h Framework Program 2000-2003).

A. Meier

Papers

Experiments on the oxidation of boron carbide at high temperatures

Degradation and oxidation of B4C control rod segments at high temperatures