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SPECIAL FEATURE
Robotics Enable Corrosion Inspection Inside Nuclear Reactor
program with the Technical Standards and Safety Authority (TSSA) and the +IVL] 1V[XMK\QWV 9]ITQÅKI\QWV *]ZMI] +19* \PM +IVILQIV OW^MZVUMV\
WZOIVQbI\QWV[ \PI\ IXXZW^M QV[XMK\QWV processes and procedures for the Cana- dian nuclear reactor industry; and train and qualify the personnel who would be conducting the inspection. ;QVKM \PM ÅZ[\ QV [MZ^QKM QV[XMK\QWV
-KTQX[M ;KQMV\QÅK PI[ KWVL]K\ML [QVOTM ZMXIQZ [Q\M QV[XMK\QWV[ QV \PM ZMIK\WZ ^M[- [MT L]ZQVO [PWZ\ W]\IOM[ UW[\ ZMKMV\Ta QV December 2011 and January 2012. The VM`\ IVV]IT QV [MZ^QKM QV[XMK\QWV [KPML- uled to occur in April 2012 during an M`\MVLML W]\IOM WN \PM 6:= ZMIK\WZ _QTT assess a n]UJMZ WN ZMXIQZ [Q\M[ BMTTMZ [Ia[
Corrosion Damage in the Vessel )KKWZLQVO \W )-+4 \PM PWTM NW]VL QV
the 6:= ZMIK\WZ ^M[[MT _ITT QV 5Ia was the result of corrosion of the reactor ^M[[MT¼[ W]\MZ _ITT QV \PM IVV]T][ [XIKM (known as the J-rod annulus) between \PM ZMIK\WZ ^M[[MT _ITT IVL \PM TQOP\ _I\MZ ZMÆMK\WZ _ITT )N\MZ \PM LQ[KW^MZa WN \PM TMIS \PM ZMIK\WZ _I[ LMN]MTML IVL \PM PMI^a _I\MZ _I[ LZIQVML ;]KKMMLQVO PQOP ZM[WT]\QWV VWVLM[\Z]K\Q^M M`IUQVI- tion (NDE) inspections found additional areas of corrosion around the base of the ZMIK\WZ ^M[[MT _PQKP _MZM QLMV\QÅML I[ wall thinning and localized pitting corro- sion. The CNSC directed AECL to repair \PM XIZ\[ WN \PM ^M[[MT \PI\ PIL [\Z]K\]ZITTa [QOVQÅKIV\ _ITT \PQVVQVO L]M \W KWZZW[QWV IVL LM^MTWX I [\ZI\MOa \W UQ\QOI\M \PM KWZZW[QWV JMNWZM \PM ZMIK\WZ ^M[[MT KW]TL JM ZM\]ZVML \W [MZ^QKM The dominant cause of corrosion in
the J-rod annulus was the formation of ni- tric acid (HNO3
) due to radiolysis of air in
the presence of water from the light-water ZMÆMK\WZ JW\P WN _PQKP PIL MV\MZML \PM J-rod annulus. The acidic water in the annulus contIK\QVO \PM ^M[[MT ZM[]T\ML QV loss of wall thickness. The formation of HNO3
was also the cause of a NRU reac-
tor shutdown in 1972 that resulted in the ZMXTIKMUMV\ WN \PM WZQOQVIT ZMIK\WZ ^M[[MT AECL notes that the reactor design was [][KMX\QJTM \W TQOP\ _I\MZ TMIS[ LM^MTWXQVO QV \PM ZMÆMK\WZ IVL TMIS[ QV \PM ZMÆMK\WZ
28 MATERIALS PERFORMANCE March 2012
KWV\QV]ML \W IXXMIZ QV \PM [MKWVL ^M[[MT Although a number of actions to mitigate \PM[M TMIS[ _MZM QUXTMUMV\ML W^MZ \PM aMIZ[ \PM TMIS[ PIL VW\ JMMV MTQUQVI\ML
To suppress the formation of HNO3 \PM 2 ZWL IVV]T][ _I[ ÅTTML _Q\P KIZJWV dioxide (CO2
into the annulus to displace air. Through inspections using a remote
^QLMW KIUMZI 6,- QV[XMK\QWV[ IVL M`- IUQVI\QWV[ WN UI\MZQIT [IUXTM[ ZMUW^ML NZWU \PM ^M[[MT _ITT \PZMM ^IZQI\QWV[ WN the HNO3
KWZZW[QWV _MZM QLMV\QÅML WV
\PM ZMXTIKMUMV\ ^M[[MT¸OMVMZITQbML KWZ- ZW[QWV I\ \PM JI[M WN \PM ^M[[MT IVL WV \PM ]XXMZ ZMOQWV[ WN \PM ^M[[MT _ITT TWKITQbML KWZZW[QWV I\ \PM JI[M WN \PM ^M[[MT IVL highly-localized corrosion pockets at a wall height that corresponded with the IVV]T][ ÆWWZ
¹1V \PM V]KTMIZ QVL][\Za IVa inspection is potentially a
LQNÅK]T\ IVL KWUXTM` WVM 1N aW]¼ZM _WZSQVO WV [WUM\PQVO \PI\ Q[ XIZ\ WN \PM ZMIK\WZ Q\[MTN
Q\
is rather a unique situation that QV^WT^M[ I TW\ WN LM^MTWXUMV\ and planning." —Brent Zeller
Although corrosion from HNO3 had
been occurring at the bottom of the annu- T][ W^MZ \PM TQNM WN \PM ZMXTIKMUMV\ ^M[[MT it was not detected in a 2004-2005 assess- UMV\ [\]La WN \PM 6:= ^M[[MT JMKI][M the focus had been on the upper parts of \PM ^M[[MT _PMZM \PM WZQOQVIT ^M[[MT PIL failed. The localized corrosion at the base WN \PM ^M[[MT IT[W _MV\ ]VLM\MK\ML QV prior to the license renewal for Chalk :Q^MZ 4IJWZI\WZQM[ 7VKM \PM KWZZW[QWV _I[ NW]VL ILLQ\QWVIT QV[XMK\QWV[ _MZM LWVM \W KWVÅZU \PI\ ILLQ\QWVIT IZMI[ WN \PM ^M[[MT PIL VW\ LMOZILML 6WUQVIT corrosion was identified elsewhere in \PM ^M[[MT# PW_M^MZ \PM ZMXIQZ [\ZI\MOa focused on rehabilitating areas of the re- IK\WZ ^M[[MT \PI\ PIL IV M`Q[\QVO TMIS IVL or did not meet structural requirements. )KKWZLQVO \W )-+4 IZMI[ _Q\P KWZZW[QWV
) gas that was injected low
damage that still met structural require- ments and had an adequate corrosion allowance were not repaired. )N\MZ UWV\P[ WN LM^MTWXUMV\ _MTLQVO
wall build-up was chosen as the primary ZMXIQZ UWLM \W IKPQM^M I XMZUIVMV\ ZM- pair with a corrosion allowance and meet all applicable codes and standards. The repairs are expected to extend the life of \PM ZMIK\WZ ^M[[MT \W During the public hearing in July 2010
to determine whether or not the NRU ZMIK\WZ _W]TL JM IXXZW^ML NWZ ZM\]ZV \W [MZ^QKM +6;+ [\INN KWUUMV\ML \PI\ WZOIVQbI\QWVIT NIK\WZ[ _MZM QLMV\QÅML I[ major contributors responsible for the TMIS M^MV\ QV \PM 6:= ZMIK\WZ ^M[[MT 7VM problem pointed out by AECL during the discussion was that staff who were _WZSQVO _Q\P \PM ^M[[MT LQLV¼\ ZMKWOVQbM \PM KWZZW[QWV ZQ[S IVL \PM WZOIVQbI\QWV¼[ KWZZW[QWV M`XMZ\[ _MZM VW\ QV^WT^ML QV OMVMZIT WVOWQVO KWZZW[QWV UWVQ\WZQVO AECL noted that organizational changes PI^M JMMV QUXTMUMV\ML \W UISM KMZ\IQV this does not reoccur.
KWV[Q[\MV\ IVV]IT KIXIKQ\a WN Biblography
"Application to Refuel the NRU Reactor Past the Guaranteed Subcritical Condi- \QWV º )-+4 2]Ta
VZ]KIVILI KI [Q\M UMLQI +PITS:Q^MZ CNSC_NRU_Restart_July5_Eng.pdf. .MJZ]IZa
+W` , ; ¹:MXIQZ WN \PM 6:= :MIK- \WZ >M[[MT"
]XTWIL[ 6:=G:MXIQZG G+6; +6;+G ,MKG
G G.QVIT XLN .MJZ]IZa
¹:MY]M[\ NWZ \PM )XXZW^IT WN \PM :M\]ZV \W ;MZ^QKM WN \PM 6I\QWVIT :M[MIZKP =VQ^MZ[IT 6:= :MIK\WZ º +IVILQIV 6]KTMIZ ;INM\a +WUUQ[[QWV :MKWZL WN 8ZWKMMLQVO[ 1VKT]LQVO :MI[WV[ NWZ ,MKQ[QWV QV \PM 5I\\MZ WN )\WUQK -VMZOa WN +IVILI 4\L 2]Ta
NACE International, Vol. 51, No. 3 P\\X" ___
5? \PMZUIT I\ I 5WZM
information on the NRU reactor can be found at www.nrucanada.ca.