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Conference Article: Fuel irradiation experiments on HFR-K6 and HFR-B1 with intermittent water vapour injections

Nabielek, H. (Forschungszentrum Juelich GmbH (Germany)); Conrad, R. (Joint Research Centre, Petten (Netherlands)); Roellig, K. (ABB Kraftwerke AG, Mannheim (Germany)); Meyers, B.F. (Oak Ridge National Lab., TN (United States))

Abstract

Accident sequence are considered for the gas-cooled High-Temperature Reactor (HTR), in which as a consequence of pipe rupture in the steam generator water may enter into the primary circuit and thus the reactor core. In two recent irradiation experiments in the High Flux Reactor Petten, the effect of water vapour injections on the release of fission gases has been investigated. In the test HFR-K6, data on the release from UO2 are presented for burnups up to 9% FIMA. These results from water vapour injections yield information, heretofore lacking, on the influence under oxidation conditions on fission gas release in pebble bed reactors. In test HFR-B1, water vapour has been injected into fuel elements containing a definite number of UCO particles with exposed kernels dispersed in a fuel compact held in a graphite body. Intermittent water vapour injections were varied between 3 and 1050 Pa. The time profile of fission gas release consists of (i) an initial rapid release. (ii) a subsequent steady release. And (iii) a decline in release following termination of the water vapour injection. These three features correspond to the release of stored fission gas plus diffusional release, to diffusional release only and to the sintering and densification of the fuel in the absence of water vapour. The experiments indicate that the water vapour induced release may contribute significantly to the radiological impact. As a major task for the future evaluation, the relation between the release fraction and the water vapour partial pressure has to be established.

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key words: Gas Cooled Reactor, Nuclear Technology
Reference:
Technical committee meeting on response of fuel, fuel elements and gas cooled reactor cores under accidental air or water ingress conditions. Beijing (China). 25-27 Oct 1993
International Atomic Energy Agency, Vienna (Austria)
IAEA-TECDOC--784, pp:17-24