Relief when river is kept outside shelter (7)
I believe the answer is:
detente
'relief' is the definition.
(detente is a kind of relief)
'river is kept outside shelter' is the wordplay.
'river' becomes 'dee' (River Dee).
'is kept' is an insertion indicator.
'outside shelter' becomes 'tent' (tent is a kind of shelter. I am not sure about the 'outside' bit.**).
'dee' placed around 'tent' is 'DETENTE'.
'when' acts as a link.
(Other definitions for detente that I've seen before include "Easing of strained relationships between countries" , "Easing of international tension" , "Easing of hostility between countries" , "Slackening of tension" , "Easing of hostility between nations" .)