United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-01: RHR Valve Misalignment Causes Degradation of ECCS in PWRS

                                                     SSINS No.: 6835 
                                                        IN 87-01       


                               UNITED STATES 
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555 

                               January 6, 1987


Information Notice No. 87-01:   RHR VALVE MISALIGNMENT CAUSES 
                                   DEGRADATION OF ECCS IN PWRS 

Addressees: 

All pressurized-water reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This information notice is provided as notification of a potentially 
significant problem pertaining to residual heat removal (RHR) valve 
alignment in the low-pressure emergency core cooling system (ECCS). It is 
expected that recipients will review the information for applicability to 
their facilities and consider actions, if appropriate, to preclude a similar 
problem from 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: 

In late May 1985, plant operators at Callaway isolated the RHR crossover 
line (by closing the normally open valves X1 or X2 in Figure 1 on the next 
page) to perform an operability test of train A of the low-pressure ECCS. 
This action would allow the B train to feed only two reactor coolant system 
(RCS) loops. When an NRC inspector questioned the advisability of this 
configuration, the licensee requested technical assistance from 
Westinghouse. Westinghouse indicated that the licensing bases for the ECCS 
analysis assume that all four RCS cold legs are being supplied water from at 
least one RHR pump. Isolation of the crossover line to place the A train in 
the test condition violated this analysis assumption. At this facility, 
however, the degraded configuration was never in existence for longer than 1 
hour. 

Subsequently, Byron Unit 1 identified numerous occasions in 1985 when the 
RHR system would have been capable of injection to only two RCS loops. 





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                                                            IN 87-01 
                                                            January 6, 1987 
                                                            Page 2 of 3 

On March 31, 1986, Trojan issued licensee event report (LER) 50/344-86/03 
informing the NRC that their technical specification (TS) requirements for 
injection by RHR to all four RCS cold legs was violated when the A pump 
discharge valve was closed for maintenance while the plant was at 100% 
power. Closing of the A pump discharge valve (A2) prevented flow to two RCS 
cold legs. Escalated enforcement action was taken against the licensee for 
this violation. 

Discussion: 

The ECCS analyses for the plants mentioned assumes RHR injection into all 
four RCS cold legs. The isolation of RHR flow to any of the RCS cold legs 
including surveillance while the reactor is in modes 1, 2, or 3 will place 
these facilities outside their design bases. In some instances, confusion 
has existed with regard to the appropriate lineup to test a "train" of RHR. 
The diagram below (Figure 1) depicts a typical RHR schematic. Neither the A 
pump nor the B pump delivers flow to all four RCS loops, so that no 
independent set of pumps, pipes, and valves that would constitute a "train" 
exists. In this design configuration, the crossover valves (X1 and X2) must 
be open when one pump is inoperable. Further, to account for a potential 
failure of one of the RHR pumps during a loss-of-coolant accident, these 
valves may be required to be open at all times. The decision to isolate 
components of this system therefore, has to consider the operability 
requirements and design basis analysis for ECCS. 

Figure 1 is a simplified diagram of RHR flow. Valves A1 and B1 can isolate a 
pump with valves A2, B2, X1, and X2 open and provide flow to all four RCS 
loops, but the closure of A2 or B2 or the closure of X1 or X2 with one pump 
inoperable would render the system capable of providing flow to only two RCS 
loops. 


Trojan opened their crossover valves and revised their procedures to ensure 
that they were operating within licensing bases during surveillance. 
Callaway also revised their procedures. Byron not only revised procedures 
but also submitted a revised ECCS analysis based on the 
one-pump-to-two-cold-legs configuration and requested a TS change to allow 
one-pump-to-two-cold-legs operation for a short time in mode 3 to allow for 
maintenance.
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                                                            IN 87-01 
                                                            January 6, 1987 
                                                            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 
Regional Administrator of the appropriate 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 

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