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AEC Research and Development Report K\ restricted data'-fA of 19S4. Its rfansi contents^ \n any monne Brian is prohibited. This document con'toStas ConfideiitiaVRestricted relating to civilian applications of atomic energy.''* GROUP I ExcludjicLlrnoiMulmftattt duuin-ATOMICS INTEI^JiATIONAL A DIVISION OF NORTH AMERICAN AVIATION, INC.

The nuclear reactor operating in space provides a unique environment which imposes one of the most stringent materials problems confronting the aerospace designer today. Environmental temperatures around the reactor control system range from 700 to 1300F, with radiation levels, per year, of 1019 nvt fast neutrons and gamma to 1013 rad. These conditions, combined with outer space vacuum below 10−7 torr, provide opportunity for contacting surfaces to “weld” together.

Several studies have suggested that low-energy neutrons contribute to reactor pressure vessel (PV) embrittlement through interactions with boron impurities in the steel. Until now, the available information on boron contents in pressure vessel steels has been based on nominal concentrations or estimates provided by the materials manufacturers. To help resolve the question of boron contribution to PV steel embrittlement, samples of 38 different PV steels were analyzed by high-sensitivity gas mass spectrometry for their helium and boron contents. The boron contents were determined by measuring the increase in helium content in each material as a result of additional thermal neutron exposure. The results of these analyses showed natural boron contents that ranged from 0.23 to 5.11 wt. ppm in the various alloys.