United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-81, Supplement 1: Broken External Closure Springs on Atwood & Morrill Main Steam Isolation Valves

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              January 11, 1988

Information Notice No. 86-81, SUPPLEMENT 1:  BROKEN EXTERNAL CLOSURE 
                                                 SPRINGS ON ATWOOD & MORRILL
                                                 MAIN STEAM ISOLATION VALVES

Addresses: 

All holders of operating licenses of construction permits for nuclear power 
reactors. 

Purpose: 

This notice is provided as a supplement to Information Notice No. 86-81 to 
alert recipients of information about additional closure spring failures on 
main steam isolation valves (MSIVs) that have been reported at Fermi Unit 2. 
The MSIVs were manufactured by Atwood & Morrill and the springs that failed 
were manufactured by Duer Spring and Manufacturing.  It is expected that 
recipients will review the information for applicability to their facilities
and consider actions, as appropriate, to avoid similar problems.  However, 
suggestions contained in this information notice do not constitute NRC 
requirements; therefore, no specific action or written response is required.

Background: 

At Fermi 2, in May 1986, the licensee observed that four external closure 
springs (the inner members of the affected pairs of external springs) were 
broken into several pieces.  The licensee analyzed two of the broken springs
and determined the failure to be quench cracking caused by the heat 
treatment process during manufacturing.  The spring manufacturer, Duer 
Spring and Manufacturing, also performed laboratory metallographic 
examination of the failed springs and verified that the failure was the 
result of quench cracking.  Both Atwood & Morrill and Duer recommended that 
all the external closing springs on all MSIVs be cleaned and subjected to 
magnetic particle testing at the earliest opportunity.  Duer provided an 
inspection procedure. In addition, General Electric (GE) issued Service 
Information Letter No. 422, dated July 18, 1986, recommending a visual 
inspection and in some cases load tests.  It also stated that springs 
passing the 105 percent load compression test would be expected to provide 
satisfactory service at normal loads.  The broken springs at Fermi were 
replaced with springs that had been compressed to 105 percent normal load.  
No magnetic particle inspection was conducted at that time. 



8801050394 
.

                                                    IN 86-81, Supplement 1 
                                                    January 11, 1988 
                                                    Page 2 of 3 

Description of Circumstances: 

At Fermi 2, on March 21, 1987, the licensee found two additional broken 
springs of the same type and location.  These springs had been inspected 
according to the GE recommendations.  The licensee attributed the failures 
to pre-existing seams and quench cracks (induced during heat treatment) that 
had propagated as brittle fracture failures.  The spring material, which is 
the same as that of the springs that had previously failed, had undergone 
temper embrittlement.  The licensee plans to replace all currently installed 
valve springs in early 1988.  After heat treatment, but before they are 
painted, the replacement springs will be subjected to the following tests:  
magnetic particle, full compression (108 percent of the maximum operating 
stress), and spring constant. 

Discussion: 

The licensee performed a fracture mechanics analysis of the data, taking 
into account temper embrittlement.  Their calculated value for critical 
crack size in temper embrittled material under 100 percent maximum operating 
stress is 0.03 inch.  Their estimate for critical crack size in temper 
embrittled material under 105 percent maximum operating stress is 0.027 
inch.  These results are essentially equal.  Measurements of critical crack 
size on 7 actual fractures varied from 0.044 inch to 0.077 inch.  These 
crack sizes are smaller than those visually detectable, particularly when 
the surface is coated.  Consequently, the licensee concluded that the 105 
percent load test followed by a visual examination would not suffice for 
separating defective springs.  It should be noted that a previous analysis 
contracted for by the licensee did not take into account temper 
embrittlement effects and did lead to an earlier conclusion that the 105 
percent load test would suffice. 

The failures of springs which had been subjected to 105 percent load tests 
and visual inspection appear to confirm the licensee's conclusion that the 
root cause is temper embrittlement, quench cracking, and surface 
imperfections. The licensee's corrective action of conducting full 
compression testing followed by magnetic particle testing thus appears to be 
appropriate. 

Springs from Duer Spring and Manufacturing have been supplied to both 
pressurized-water reactor and boiling-water reactor nuclear power plants on 
MSIVs manufactured by Atwood & Morrill.  Atwood & Morrill has identified 
those plants that would be affected by the problem.  This list is attached. 

.

                                                    IN 86-81, Supplement 1 
                                                    January 11, 1988 
                                                    Page 3 of 3 


No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
technical contact listed below or the Regional Administrator of the 
appropriate regional office.  

                               Charles E. Rossi, Director 
                               Division of Operational Events Assessment 
                               Office of Nuclear Reactor Regulation 

Technical Contacts:  R. L. Cilimberg, NRR
                     (301) 492-9656

                     Vern Hodge, NRR
                     (301) 492-8196

Attachments:
1.  List of Affected Plants as Identified
      by Atwood & Morrill
2.  List of Recently Issued NRC Information Notices 
Page Last Reviewed/Updated Tuesday, November 12, 2013