| Popis: |
The New Production-Modular High Temperature Gas Cooled Reactor (NP-MHTGR) development program sponsored by the US Department of Energy (DOE) has as part of its task the irradiation testing of the lithium target material. The lithium target material tritium ({sup 3}H) production is predominantly through the {sup 6}Li (n,{alpha}){sup 3}H reaction which also produces equal amounts of {sup 4}He ({alpha}). The tritium produced decays to {sup 3}He (12.38 year half-life), with some of this {sup 3}He being converted back to tritium during irradiation via the {sup 3}He(n,p){sup 3}H reaction. From these reactions, and the irradiation time-history, the measurement of the {sup 4}He and {sup 3}He content of a lithium monitor or target material sample can be used to determine several important variables associated with the target material performance, as well as to independently determine the neutron fields associated with the test environment. Helium measurements have been used to determine lithium burnup, tritium retention in target pellets, pellet material composition and variation and threshold temperature for helium release from the pellets. The present paper presents selected results obtained form the various helium measurements and discusses their relevance and importance to the MHTGR target development program. |
