United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-60: Unanalyzed Post-LOCA Release Paths

                                                            SSINS No.: 6835 
                                                            IN 86-60       

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

                                July 28, 1986

Information Notice No. 86-60:   UNANALYZED POST-LOCA RELEASE PATHS 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This information notice is being provided to alert recipients to a 
potentially significant problem pertaining to substantial possible leakage 
of radioactive water flowing in pipes outside containment after a 
loss-of-coolant accident (LOCA). The NRC expects that recipients will review
this notice for applicability to their facilities. Suggestions contained in 
this notice do not constitute NRC requirements; therefore, no specific 
action or written response is required. 

Reference: 

     NUREG-0737: "Clarification of TMI Action Plan Requirements," November 
     1980. Item III.D.1.1: Integrity of Systems Outside Containment Likely 
     to Contain Radioactive Material for Pressurized Water Reactors and 
     Boiling-Water Reactors. 

Description of Circumstances: 

On August 2, 1985, the licensee at Haddam Neck Nuclear Power Plant reported 
to the NRC that two potential post-LOCA release paths from containment had 
been identified: 

1.   The following potential post-accident release path resulted from TMI 
     Action Plan modifications completed in 1981. The release path can come 
     about in two ways (Figure 1): 

     a.   When the charging system is running and normally aligned, borated 
          water is injected from the volume control tank (VCT) to the 
          reactor coolant pump (RCP) seals past the thermal barrier and into 
          the reactor cooling system (RCS). Some of the seal injection water 
          flows through the Number 1 seal and returns through a filter and 
          the seal water heat exchanger to the charging pump suction.  
          Because a charging pump is operating, the seal water return header 
          does not pressurize. In the post-LOCA situation, the system 
          operates essentially the 


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                                                              IN 86-60 
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                                                              Page 2 of 3  

          same except the injection water is drawn from the refueling water 
          storage tank (RWST) rather than the VCT and the charging pumps 
          will automatically start only if normal power is available. To 
          preserve for the operator the option of running the RCPs after an 
          accident, the licensee removed automatic safety injection and 
          containment isolation signals to the isolation valves for the RCP 
          auxiliaries [i.e., seal water (valve A in Figure 1), thermal 
          barrier, and oil cooler returns]. These isolation valves remain 
          remotely operable from the control room. 

          Under post-accident conditions, if offsite power is lost, the 
          charging pumps stop and are not automatically restarted. With no 
          operator action, the unisolated RCP seal water return line will 
          pressurize from the seal leakage that is normally routed to the 
          charging pump suction. This line relieves to the VCT at 140 psig; 
          eventually the VCT will overflow to the waste treatment system. If
          no action is taken to stop the seal water leakage, a flow path for
          highly radioactive fission products to the plant stack would 
          eventually exist through the waste treatment system. Manual 
          isolation of the seal water return header (closure of valve A in 
          Figure 1) to the VCT or manual start of a charging pump would 
          terminate the scenario. 

     b.   At some time after a LOCA when 100,000 gallons have been pumped 
          from the RWST, the ECCS will take suction from the containment 
          sump (recirculation mode). If the RCS pressure exceeds the shutoff 
          head of the residual heat removal (RHR) pumps, the charging system 
          will be manually aligned to take a suction on the RHR system and 
          discharge to the RCS at a higher pressure. In this mode of 
          operation, if the seal return header isolation valve (valve B in 
          Figure 1) downstream of the relief valve to the VCT were to be 
          manually closed or to fail closed (for example, on loss of control 
          air), the seal water return header would again pressurize to the 
          point of safety relief at 140 psig. 

The licensee informed plant operators of these potential post-accident 
release pathways, of expected indications, and appropriate actions to stop 
the leakage (either start a charging pump or isolate the return line, based 
on operator judgment). 

2.   The second release path is related to the post-LOCA recirculation mode.
     The licensee had considered only RHR system leakage outside containment
     as a source of radioactive release during sump recirculation. Because 
     the charging system may also be used in this recirculation, it could be
     moving highly radioactive water outside containment. Previously, the 
     licensee was monitoring RHR system leakage to assure that it was below 
     the Technical Specification, but not the charging system leakage. The 
     licensee has now expanded its surveillance to include both systems. 
.

                                                              IN 86-60 
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                                                              Page 3 of 3  

Discussion: 

These release paths are associated with low frequency events, but because 
the associated offsite doses may be significant, licensees may want to 
consider these release paths and other release paths that may be unique to 
their plants in post-LOCA analyses. Such release paths are related to the 
referenced TMI Action Plan item for a program to reduce to 
as-low-as-reasonably-achievable (ALARA) levels the leakage from systems 
outside containment that would or could contain highly radioactive fluids 
during a serious transient or accident. 

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:  Vern Hodge, IE
                    (301) 492-7275

Attachments:
1.   Figure 1
2.   List of Recently Issued IE Information Notices 
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