IE Circular 76-06, Stress Corrosion Cracks in Stagnant, Low Pressure Stainless Piping Containing Boric Acid Solution at PWR's

 


CR78006 

                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                         WASHINGTON, D. C.  20555 
                                     
                                NOV 22 1976 

J. P. O'Reilly, Director, Region I 
N. C. Moseley, Director, Region II 
J. G. Keppler, Director, Region III 
E. M. Howard, Director, Region IV 
R. H. Engelken, Director, Region V 

IE CIRCULAR 76-06, STRESS CORROSION CRACKS IN STAGNANT, LOW PRESSURE 
STAINLESS PIPING CONTAINING BORIC ACID SOLUTION AT PWR's 

The subject document is transmitted for issuance by close of business three 
days after date of this letter.  The Circular should be issued to all 
holders of OL's for PWRs for action.  Also enclosed is a draft copy of the 
transmitted letter. 


                                        Dudley Thompson, Acting Director 
                                        Division of Field Operations 
                                        Office of Inspection and Enforcement

Enclosures:
1.   Circular 76-06
2.   Draft transmittal letter
.

Transmittal letter for Circular 76-06 to each holder of a NRC Operating 
License for a PWR. 

Addressee: 

     The enclosed Circular 76-06 is forwarded to you for action. If there 
are any questions related to your understanding of the actions required, 
please contact this office. 


                                        Signature 
                                        (Regional Director) 

Enclosure: 
IE Circular 76-06 
.

IE Circular 76-06                                               Date: 

STRESS CORROSION CRACKS IN STAGNANT, LOW PRESSURE STAINLESS PIPING 
CONTAINING BORIC ACID SOLUTION AT PWR's 

DESCRIPTION OF CIRCUMSTANCES: 

During the period November 7, 1974 to November 1, 1975 several incidents of 
through-wall cracking have occurred in the 10-inch, schedule 10 type 304 
stainless steel piping of the Reactor Building Spray and Borated Water 
Make-up Systems at Arkansas Nuclear Plant No. 1. 

On October 7, 1976 Virginia Electric and Power also reported through-wall 
cracking in the 10-inch schedule 40 type 304 stainless discharge piping of 
the "A" recirculation spray heat exchanger at Surry Unit No. 2. A recent 
inspection of Unit 1 Containment Recirculation Spray Piping revealed 
cracking similar to Unit 2. 

On October 8, 1976 another incident of similar cracking in 8-inch schedule 
10 type 304 stainless piping of the Safety Injection Pump Suction Line at 
the Ginna facility was reported by the licensee. 

Information received on the metallurgical analysis conducted to date 
indicates that the failures were the result of intergranular stress 
corrosion cracking that initiated on the inside of the piping. A commonality 
of factors observed associated with the corrosion mechanism were: 

1.   The cracks were adjacent to and propagated along weld zones of the 
     thin-walled low pressure piping, not part of the reactor coolant 
     system. 

2.   Cracking occurred in piping containing relatively stagnant boric acid 
     solution not required for normal operating conditions. 

3.   Analysis of surface products at this time indicate a chloride ion 
     interaction with oxide formation in the relatively stagnant boric acid 
     solution as the probable corrodant, with the state of stress probably 
     due to welding and/or fabrication. 
.

                                  -2- 

The source of the chloride ion is not definitely known.  However, at ANO-1 
the chlorides and sulfide level observed in the surface tarnish film near 
welds is believed to have been introduced into the piping during testing of 
the sodium thiosulfate discharge valves, or valve leakage. Similarly, at 
Ginna the chlorides and potential oxygen availability were assumed to have 
been present since original construction of the borated water storage tank 
which is vented to atmosphere. Corrosion attack at Surry is attributed to 
in-leakage of chlorides through recirculation spray heat exchange tubing, 
allowing buildup of contaminated water in an otherwise normally dry spray 
piping. 

ACTION TO BE TAKEN BY LICENSEE: 

1.   Provide a description of your program for assuring continued integrity 
     of those safety-related piping systems which are not frequently 
     flushed, or which contain nonflowing liquids. This program should 
     include consideration of hydrostatic testing in accordance with ASME 
     Code Section XI rules (1974 Edition) for all active systems required 
     for safety injection and containment spray, including their 
     recirculation modes, from source of water supply up to the second 
     isolation valve. Similar tests should be considered for other 
     safety-related piping systems. 
     
2.   Your program should also consider volumetric examination of a 
     representative number of circumferential pipe welds by nondestructive 
     examination techniques. Such examinations should be performed generally
     in accordance with Appendix I of Section XI of the ASME Code, except 
     that the examined area should cover a distance of approximately six (6)
     times the pipe wall thickness (but not less than 2 inches and need not 
     exceed 8 inches) on each side of the weld Supplementary examination 
     techniques, such as radiography, should be used where necessary for 
     evaluation or confirmation of ultrasonic indications resulting from 
     such examination. 

3.   A report describing your program and schedule for these inspections 
     should be submitted within 30 days after receipt of this Circular. 
.

                                   -3-

4.   The NRC Regional Office should be informed within 24 hours, of any 
     adverse findings resulting during nondestructive evaluation of the 
     accessible piping welds identified above. 

5.   A summary report of the examinations and evaluation of results should 
     be submitted within 60 days from the date of completion of proposed 
     testing and examinations. 

     This summary report should also include a brief description of plant 
     conditions, operating procedures or other activities which provide 
     assurance that the effluent chemistry will maintain low levels of 
     potential corrodants in such relatively stagnant regions within the 
     piping. 

Your responses should be submitted to the Director of this office, with a 
copy to the NRC Office of Inspection and Enforcement, Division of Reactor 
Inspection Programs, Washington, D.C. 20555. 

Approval of NRC requirements for reports concerning possible generic 
problems has been obtained under 44 U.S.C 3152 from the U.S. General 
Accounting Office. (GAO Approval B-180255 (R0062), expires 7/31/77).