▁the ▁others . ▁ ▁The ▁incident ▁was ▁discovered ▁when ▁employees ▁began ▁leaving ▁bio - ass ay ▁ur ine ▁samples ▁with ▁elev ated ▁tr it ium ▁levels , ▁one ▁with ▁particularly ▁unus ually ▁high ▁levels . ▁The ▁quantities ▁involved ▁were ▁well ▁below ▁levels ▁which ▁could ▁indu ce ▁heavy ▁water ▁to x icity , ▁but ▁several ▁employees ▁received ▁elev ated ▁radiation ▁dos es ▁from ▁the ▁tr it ium ▁and ▁activ ated ▁chemical s ▁in ▁the ▁water . ▁ ▁It ▁is ▁believed ▁that ▁M ast on ▁intended ▁the ▁expos ure ▁to ▁be ▁a ▁practical ▁jo ke , ▁where by ▁the ▁affected ▁employees ▁would ▁be ▁required ▁to ▁give ▁ur ine ▁samples ▁daily ▁for ▁an ▁extended ▁length ▁of ▁time . ▁ ▁In ▁ 1 9 9 5 , ▁a ▁p lywood ▁cover ▁was ▁left ▁in ▁the ▁bo iler ▁after ▁completion ▁of ▁a ▁maintenance ▁out age . ▁When ▁the ▁heat ▁transport ▁p umps ▁were ▁restart ed , ▁the ▁cover ▁was ▁su ck ed ▁into ▁the ▁heat ▁transport ▁system ▁where ▁it ▁caused ▁cat ast roph ic ▁damage ▁to ▁one ▁of ▁the ▁p umps . ▁The ▁cause ▁of ▁the ▁incident ▁was ▁lack ▁of ▁control ▁of ▁temporary ▁modifications , ▁poor ▁work ▁management , ▁lack ▁of ▁foreign ▁material ▁ex clusion ▁( F ME ) ▁measures , ▁and ▁human ▁error . ▁There ▁was ▁no ▁public ▁safety ▁significance ▁to ▁the ▁event , ▁since ▁the ▁re actor ▁had ▁been ▁shut ▁down ▁long ▁enough ▁that ▁decay ▁heat ▁power ▁was ▁below ▁the ▁level ▁that ▁required ▁cool ant ▁flow . ▁However , ▁the ▁bre ach ▁of ▁the ▁pressure ▁boundary