United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 83-03: Check Valve Failures in Raw Water Cooling Systems of Diesel Generators

                                                  SSINS    6835 
                                                  OMB No.: 3150-0097  
                                                  Expiration Date:  11/85 
                                                  IEB 83-03 

                               UNITED STATES 
                          WASHINGTON, D. C. 20555 

                               March 10, 1983 

                         OF DIESEL GENERATORS 


All nuclear power reactor facilities holding an operating license (OL) for 
action and all those holding construction permits for information. 


The purpose of this bulletin is to (1) notify licensees and construction 
permit holders about numerous incidents of failed check valves in systems 
important to safety; (2) inform licensees of a significant generic matter 
for which additional NRC action is anticipated; (3) to require appropriate 
surveillance and testing of check valves in raw water cooling systems for 
diesel generators. A response to this bulletin is required from all nuclear 
power reactors holding an OL as discussed below. 

Description of Circumstances 

A review of available operating experience, data and licensee event reports 
(LERs) shows that numerous check valve failures have occurred in systems 
important to safety in nuclear power plants. A series of IE generic 
communications (listed in Table 1) has been issued which describes a broad 
range of check valve failures involving various designs, causes, and 
applications. The NRC has evaluated check valve failures in consideration of
the need to request generic action by licensees. The focus of this bulletin 
is directed primarily at the failure mode of disassembly or partial 
disassembly of check valve internals. For example, the check valve disc 
becomes separated from the hinge. 

Title 10 of the Code of Federal Regulation, Section 50.55a(g) requires 
testing of valves whose function is required for safety. This is implemented
by application of Section XI of the ASME Boiler and Pressure Vessel Code and
Addenda. However, our analysis of operating experience with check valves has
shown that disassembly and partial disassembly of check valve internals is 
not effectively found by Section XI testing as it is implemented at this 
time. Tests performed for Section XI or Technical Specifications usually 
require only forward flow through check valves. These tests may not detect 
internal check valve failures unless the disassembled parts move to block 
flow during the test. 

This bulletin is expected to be part of a generic response to check valve 
failures which will result in improved testing to ensure operability and to 
improve reliability of check valves. In addition to the generic 

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                                                            March 10, 1983 
                                                            Page 2 of 5 

communications issued by IE, the NRC Office of Nuclear Reactor Regulation 
requires that licensees consider all check valves in systems important to 
safety for inclusion in the ASME Section XI Pump and Valve Inservice Testing
Programs. Although most check valves in systems important to safety are 
included in current IST program reviews, most are not required to be reverse
flow tested or disassembled to detect gross internal failure because 
licensees have identified each of these valves as having a single safety 
function: the open position. However, forward flow tests to verify the open 
position are inadequate for detecting internal disassembly. Effective check 
valve testing techniques are necessary to the development of a more 
meaningful and productive IST program. Operating experience provides a basis
for determination of what areas of IST check valve surveillance need to be 

The specific requirements of this bulletin stem from analysis of check valve
failures in the raw cooling water supply to the diesel generators at the 
Dresden and Quad-Cities nuclear power stations and other events which are 
described in Table 1. At Dresden and Quad-Cities, it was found that six of 
six check valves in the raw, cooling water systems for the diesel generators
had failed with the disc becoming detached from the pivot arm. Many of the 
failures described in t,he generic communications listed in Table 1 also 
involved detached discs. The Dresden event is described in detail in IE 
Information Notice No. 82-08. Ih summary, the event involved failure of the 
check valves in the raw water cooling systems for the diesel generators 
which resulted in interruption of cooling water flow to the diesel generator 
heat exchangers and subsequent inoperability of the diesel generators. The 
Dresden check valve failures rendered two diesels inoperable at the same 
time when the valve discs moved to the valve outlets and blocked flow. 
However, the true cause of flow blockage was not determined until almost one 
month later. All three Diesel Generator Cooling Water Pump (DGCWP) systems 
at Dresden Units 2 and 3 involved check valve failures which were discovered 
during a short period of time. These failures were not identified by 
operator observations and instrument readings during diesel generator 
surveillance tests, but were discovered by direct inspection of the 
internals of the valves. It is not known how long these check valves were 
broken before their condition was detected. The broken valve discs were 
found to be free to move within the valve bodies and may have been that way 
for some time before coming to rest in a position which restricted flow 
enough to cause the diesels to trip on high engine temperature. The subject 
check valves are horizontally mounted Crane 8-inch, cast iron swing check 
valves, Type 373, and have a pressure rating of 125 psi. 

Because of the similarity between the Dresden Units and Quad-Cities Units, 
NRC Region III requested that Commonwealth Edison inspect the DGCWP 
discharge check valves on the Quad-Cities Units on a schedule consistent 
with the availability of valve parts and the availability of the DG units. 
The DGCWP systems at Quad-Cities were inspected and all three DGCWP 
discharge check valves were found with the discs separated from the pivot 

At Quad-Cities, the failures remained latent; although the discs were lying 
free in the valve body, they did not move to the outlet and block flow. The 
DGCWP discharge check valves at Quad-Cities were also Crane, 8-inch, swing 
check valves, Type 373. However, the Quad-Cities valves and the Dresden 
valves were not identical. The Quad-Cities valves had larger, more bulbous 
valve bodies and slightly different internals. 

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                                                            March 10, 1983 
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For all valves, the most dominant failure mode was due to a combination of 
abrasive and corrosive wear of valve internals. In particular, the valve 
disc was held to the pivot arm by a stud with washer and nut. Apparently, 
flow conditions at the valves were such that the discs vibrated (fluttered) 
causing local abrasive wear at the arm bore of the hinge where it joins the 
disc. This same action also resulted in severe degradation of the washer 
used to retain the disc on the hinge, and once the degree of degradation at 
the hinge bore and washer was sufficient, the two components separated. The 
stud and nut wore such that the stud and nut assembly pulled through the 
enlarged hole in the pivot arm and became detached. 

In the case of the Dresden Unit 2 valve, the valve disc remained barely 
attached to the pivot arm and the arm had broken at its hinge to the valve 
hinge pin. In this case, abrasive/corrosive wear was found to have occurred 
at the hinge pin bore. All of the failed valves showed wear at this 
location. The degree of degradation varied from very slight in the 
Quad-Cities 1/2 hinge to extreme in the Dresden Unit 2 hinge which had 
fractured at this location. As plants age, failure modes of these types may 
be expected to become more prevalent. 

The bulletin focuses on check valve failures in the raw water cooling system
of diesel generators for the following reasons: 

     (1)  Six of six check valves in these systems at Dresden and 
          Quad-Cities failed with the potential for interrupting flow of 
          cooling water to the diesel generators. 

     (2)  Both diesels on Dresden Unit 3 tripped on overtemperature due to 
          lack of cooling water flow and the unit was without emergency 

     (3)  The cause of the lack of raw cooling water flow to the Dresden 
          Unit 3 dedicated diesel (failed check valves) was not discovered 
          for almost one month following the event despite numerous test and 
          surveillance procedures and was attributed to other causes. The 
          condition of the swing diesel and the unit 2 dedicated diesel 
          check valves at Dresden was not discovered until more than one 
          month after the initial event. 

     (4)  None of these check valves was included in the plant IST program 
          at the time of the event. Since the event, the NRC Office of 
          Nuclear Reactor Regulation has added these valves to IST 
          requirements for plants currently being reviewed. 

     (5)  Even if the valves had been in the IST program, it is doubtful if 
          the normal forward flow test would have discovered these latent 
          failures except by chance, as occurred at Dresden. The failures 
          were finally discovered by direct inspection of valve internals. 

It should be noted that the popular use of swing check valves in safety 
related plant fluid systems considerably expands the scope of concern for 
check valve maintenance and testing beyond diesel cooling systems. Licensee 
event reports indicate that other systems important to safety have 
experienced failures of check valves which are not included in the IST 
program and have not been 

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                                                            March 10, 1983 
                                                            Page 4 of 5 

discovered during testing. Other licensee event reports indicate that for 
those valves which are not leak tested, both the type and frequency of 
testing may not be adequate to detect valve failure. Maintenance and IST 
programs should be reconsidered in light of detecting and preventing gross 
and multiple check valve failures that can defeat functions of systems 
important to safety. This includes concerns both for check valve opening and

Required Actions For Holders Of Operating Licenses: 

1.   Licensees are requested to review the plant Pump and Valve In-Service 
     Test (IST) program required by Section XI of the ASME Boiler and 
     Pressure Vessel Code and modify it if necessary to include check valves
     in the flow path of cooling water for the diesel generators from the 
     intake to the discharge. Those portions of the cooling water system 
     which do not directly supply the diesel may be excluded from this 
     review. For example, if the cooling water to the diesel is supplied by 
     the normally operating service water system, the loop of piping to the 
     diesel from the service water piping and back must be considered, but 
     not the complete service water system. For those cooling water systems 
     which come into operation only upon demand for diesel cooling, all 
     portions of the system which are required to change state must be 

2.   For the valves described in (1) above, licensees are requested to 
     examine the IST program and modify it if necessary to include 
     verification procedures that confirm the integrity of the valve 
     internals. This may be accomplished by using both a forward flow and a 
     back flow test or by valve disassembly and inspection. Other equally 
     effective means of assuring integrity of the valves may be used. A 
     reasonable schedule for the test of these valves shall also be included
     in the IST program. 

3.   Licensees are requested to perform initial valve integrity verification
     procedures for the valves identified in (1) above using the methods 
     described in (2) above, to be completed by the end of the next 
     refueling outage commencing after April 1, 1983. 

4.   Licensees are requested to submit a report to the NRC within 90 days of
     the date of this bulletin, which lists the valves identified in (1) 
     above and describes the valve integrity verification procedure methods 
     and schedule identified in (2) above. This report should include the 
     history of any known previous failures of these valves at your plant. 

5.   Licensees are requested to submit a report to the NRC within 90 days of
     completion of the results of the initial valve integrity, verification 
     procedure performed in accordance with (3) above. For those valves 
     which are found to have undergone either partial or complete 
     disassembly of valve internals, a description of the failure mode 
     should be included. 

6.   The written reports required shall be submitted to the appropriate 
     Regional Administrator under oath or affirmation under provisions of 
     Section 182a, Atomic Energy Act of 1954, as amended. The original copy 
     of the cover  

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                                                            March 10, 1983 
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     letters and a copy of the reports shall be transmitted to the U. S. 
     Nuclear Regulatory Commission, Document Control Desk, Washington, D. C.
     20555 for reproduction and distribution. 

Required Actions for Holders of Construction Permits: 

None. This information is provided to holders of Construction Permits to 
provide guidance in preparing their proposed IST programs. These programs 
will be reviewed during the licensing process. 

Although no specific request or requirement is intended, the following 
information would help the NRC evaluate the cost of implementing this 

     o    Staff time to perform requested valve integrity verification 

     o    Staff time to prepare written responses 

This request for information was approved by the Office of Management and 
Budget under clearance number 3150-0097 which expires on November 1985. 
Comments on burden and duplication should be directed to the Office of 
Management and Budget, Reports Management, Room 3208, New Executive Office 
Building, Washington, D.C. 20503. 

If you have any questions regarding this matter, please contact the Regional
Administrator of the NRC Regional Office or the technical contact listed 

                         Richard C. DeYoung, Director 
                         Office of Inspection and Enforcement 

Technical Contact:  George F. Lanik, IE 
                    (301) 492-9636 

1. Table 1 - IE Generic Communications 
2. List of Recently Issued IE Bulletins  
Page Last Reviewed/Updated Friday, May 22, 2015