United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 85-37: Chemical Cleaning of Steam Generators at Millstone 2

                                                        SSINS No.: 6835  
                                                          IN 85-37         

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D. C. 120555 

                                May 14, 1985 

Information Notice No. 85-37:   CHEMICAL CLEANING OF STEAM GENERATORS AT 
                                   MILLSTONE 2 

Addressees: 

All pressurized water reactor (PWR) facilities holding an operating license 
(OL) or a construction permit (CP). 

Purpose: 

This information notice is being provided as notification of a potentially 
significant problem pertaining to corrosion product buildup in the secondary
side of steam generators which may mask eddy current signals. It is expected
that recipients will review the information for applicability to their 
facilities and consider actions, if appropriate, to preclude a similar 
problem occurring at their facilities. However, suggestions contained in 
this information notice do not constitute NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

Millstone 2 is a two-loop, 2700 megawatt-thermal PWR that was licensed in 
1975. Secondary water treatment has been all-volatile since startup. 
Northeast Nuclear Energy Company,(NNECo) had plugged 941 tubes in steam 
generator (SG)-1 and 759 in SG-2 and had sleeved 894 tubes in SG-1 and 1128 
in SG-2 prior to the current outage. The deteriorating condition of the 
tubes has been attributed to the buildup of sludge containing, principally, 
copper and iron. Condenser and feedwater heater tubes made of a copper-alloy 
are thought to be the source of the copper. A sludge pile, the source of 
corrodants causing denting and pitting, existed in the secondary side on the
tube sheet and around the tubes to a maximum depth of 13 inches. 

Before cleaning the secondary side of the steam generators in early April 
1985, NNECo conducted eddy current testing of all 8500 tubes in SG-2 and a 
statistical sample of tubes in SG-l and projected the need to sleeve 300 
tubes in each steam generator. Sludge lancing removed about 300 pounds of 
sludge from each steam generator. Chemical cleaning of the secondary side 
removed about 300 pounds more of the sludge. For the basic chemical process,
NNECo selected the Electric Power Research Institute's Steam Generator 
Owners Group Generic Process. The concentration of the various chemicals in 
the solvents was adjusted to yield the most efficient cleaning of the 
site-specific materials and configuration. The procedure was designed to 
remove the sludge pile with few adverse effects on the steam generators or 
internals. 


8505130034 
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                                                             IN 85-37      
                                                             May 14, 1985  
                                                             Page 2 of 2   

The cleaning process involves the use of iron and copper solvents in a 
specified number of applications under controlled conditions. The iron 
solvent uses an inhibitor to protect the base metal, while the copper 
solvent has been virtually noncorrosive to carbon steel and Inconel 600 in 
tests. Corrosion of the Inconel tubes has been less than 0.1 mil in sludge 
cleaning tests.1 NNECo had qualified the specific solvents and processes for 
use at Millstone 2 before their use. 

Following chemical cleaning, eddy current testing of each of the steam 
generators tubes was again performed. NNECo reported that 1077 tubes in the 
cold leg and 552 tubes in the hot leg of SG-1 will be sleeved. In SG-2, 1074
tubes in the cold leg and 145 tubes in the hot leg will be sleeved. This 
represents an increase of nearly a factor of five in the number of tubes to 
be sleeved, compared to the projections made based on eddy current testing 
prior to cleaning. In addition, 19 tubes (12/7) will be plugged in the two 
SGs. 

This is the first use of this cleaning process at any nuclear plant. The 
tube defects found after cleaning are thought to have been present prior to 
the cleaning. The copper and iron constituents of the sludge apparently 
generated a signal which masked the signal of the smaller defects. Pits of 
0.075 inch diameter and larger can be detected in the presence of copper. 
After cleaning, smaller diameter defects were identified. Essentially all of 
these defects were found in the region of the sludge pile; that is, within a 
height of 13 inches above the tube sheet. 

No specific action or written response is required by this information 
notice. If there are any questions regarding this matter, please contact the
Regional Administrator of the appropriate NRC regional office or this 
office. 


                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Mary S. Wegner, IE 
                    (301) 492-4511 

Attachments:   List of Recently Issued IE Information Notices 
Page Last Reviewed/Updated Tuesday, November 12, 2013