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Conference Article: Chemical reactions during nuclear drying of the AVR primary circuit following a water ingress

Nieder, R.; Vey, K. (Arbeitsgemeinschaft Versuchs-Reaktor G.m.b.H., Juelich (Germany, F.R.))

Abstract

In May 1978, after the AVR had been operating for more than 10 years, a small leak was discovered in the superheater of the steam generator, the cause of which has still not been identified. When the reactor was shut down a volume of some 30 tons of water entered the primary circuit through this tiny leak over a period of four days. Figure 1 shows a cross-section of the AVR reactor. The broken line indicates the maximum water level. The course of the interruption, the repair and maintenance work carried out and the technical details of restarting the reactor after a period of 15 months for repairs have been reported on in detail (Ref. 1, 2, 3). Ref. 4 contains a list of the activity measurements of the water. The greater part of the water, approximately 25 tons, was drained through a valve in the fuel element handling system and pumped into a vessel. During the repair phase the primary circuit was repeatedly evacuated, thus allowing another 2 tons of water to be disposed of. In the evacuation process the inner reactor vessel was heated up externally. Pressure was reduced to 1 mbar in the primary circuit by the vacuum pump. This paper will describe how the remaining moisture and other impurities were removed during the start-up phase, dealing also with the chemical reactions in the primary circuit during this period.

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key words: avr reactor; chemical reactions; drying; feedwater; impurities; leaks; outages; primary coolant circuits; radiation monitoring; reactor accidents; accidents; cooling systems; enriched uranium reactors; gas cooled reactors; graphite moderated reactors; helium cooled reactors; homogeneous reactors; htgr type reactors; hydrogen compounds; monitoring; pebble bed reactors; power reactors; reactor components; reactor cooling systems; reactors; solid homogeneous reactors; thermal reactors; thorium reactors; water
Reference:
Specialists meeting on coolant chemistry, plate-out and decontamination in gas-cooled reactors Juelich, Federal Republic of Germany 2-4 December 1980
International Atomic Energy Agency, Vienna (Austria)
IWGGCR--2, pp:137-144