United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 83-55: Misapplication of Valves by Throttling Beyond Design Range

                                                            SSINS No.: 6835 
                                                            IN 83-55       

                                UNITED STATES
                           WASHINGTON, D.C. 20555
                               August 22, 1983

                                   BEYOND DESIGN RANGE 


All nuclear power facilities holding an operating license (OL) or a 
construction permit (CP). 


This information notice is provided to alert licensees to a potentially 
generic problem regarding the throttling of valves outside the design limits
of these valves. No new requirements are imposed in this notice but 
licensees should review this notice for applicability to their facilities. 


Pressurized Water Reactors 

Based on analysis of the Crystal River Unit 3 (CR-3) plant by Babcock and 
Wilcox (B&W), Florida Power Corporation reported by letter addressed to NRC 
Region II dated July 27, 1983, that throttling of the high pressure 
injection (HPI) valves as described in the emergency operating procedure 
guidelines for small-break LOCA could result in unacceptable valve damage. 
The emergency operating procedures require the throttling of coolant flow 
through the HPI valve in order to prevent overcooling and pressurized 
thermal shock. The HPI valves at CR-3, manufactured by the Walworth Company, 
are not designed for throttling and such activity could result in damage to 
the valve from cavitation, high velocity erosion of seat, and/or excessive 
vibration of valve stem and plug. Degradation of the integrity of these 
valves would impose a significant safety hazard. B&W believes that CR-3 is 
the only B&W plant that uses the Walworth valve as an HPI valve. 

It is our understanding that Westinghouse plants do not throttle the safety 
injection valves but rather vary the flow with the safety injection pumps. 
However, some Combustion Engineering (CE) plants do throttle and could be 
susceptible to the same problems encountered in the B&W plant. 

The requirement for restricting safety injection flow was not imposed until 
after most operating plants were designed and constructed. Thus, it is 
possible that plants constructed before the requirements for throttling 
contain valves 


                                                            IN 83-65       
                                                            August 22, 1983 
                                                            Page 2 of 3    

that are not specifically designed for these purposes. Throttling of valves 
not designed for throttling could also be a problem in other systems in 
addition to the high pressure safety injection systems. 

Boiling Water Reactors 

On February 18, 1983, while in the shutdown mode of operation at Susquehanna
Station, a local operator discovered a low pressure coolant injection (LPCI)
valve in the "B" loop of the RHR system severely vibrating. Upon further 
inspection the valve was found to have lost its packing, the valve position 
indicator had vibrated off, and the adjacent saddle-type pipe hanger had 
broken welds. At the time of the discovery, the valve was being used to 
control the shutdown cooling flow to the vessel. This loop of the LPCI was 
immediately declared inoperable and the "A" loop was put into service for 
shutdown cooling. 

On June 9, 1983, at Susquehanna Station, shift personnel noticed that the 
keep fill system pressure in the RHR system was less than normal on the 
upsteam side of the LPCI throttle valve. The loss of pressure indicated 
possible blockage at this normally open valve. Further investigation showed 
that the throttle valve disc to skirt nut tack welds were broken and the 
skirt nut had separated from the valve disc. This allowed the disc to 
separate from the stem block the keep fill system flow, and render the "B" 
loop of LPCI inoperable. It is suspected that the skirt nut tack welds broke
as a result of high vibrational loadings during testing and normal operation
early in 1983. 

Following the February 18 event it was concluded that the shutdown cooling 
flow rates were outside the optimum throttling range of the LPCI throttle 
valve causing severe valve vibration. The system was being operated in this 
manner to afford finer control of reactor coolant temperatures. The 
operating procedures were subsequently changed to operate the system 
intermittently at higher flow rates. The separation of the throttle valve 
disc and stem by June 9 was also attributed to severe valve vibration 
experienced before the February 18 event, but it was not until June 9 that 
the skirt nut had finally worked itself free. 

Similar problems occurred during startup and the early operational phase at 
Browns Ferry 1 (circa 1975). In order to adjust cooldown rates, the residual
heat removal (RHR) service water valves were throttled. Severe vibration 
occurred which caused extensive damage to valve internals. When the RHR 
24-inch angle valves were used to throttle RHR flow, these valves also 
vibrated excessively and similar damage occurred. TVA consulted with the 
valve manufacturer, the Walworth Company, and was advised that the disc 
characteristics were improper for the throttling that was necessary for 
controlling the cooldown rate. A "fluted flow-disc" was installed in each of
the angle valves and the system has provided satisfactory service since 

Operating personnel should be made aware of the operating characteristics of
throttle valves, and procedures should be provided to limit valve operation 
outside the optimum throttling range. 

                                                            IN 83-55       
                                                            August 22, 1983 
                                                            Page 3 of 3    

If you have 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:  P. R. Farron, IE

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