United States Nuclear Regulatory Commission - Protecting People and the Environment

Staff Recommended Actions Stemming from NRC Integrated Program for the Resolution of Unresolved Safety Issues Regarding Steam Generator Tube Integrity (Generic Letter No. 85-02)



                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                           WASHINGTON, D.C. 20555

                               April 17, 1985

TO ALL PWR LICENSEES OF OPERATING REACTORS, APPLICANTS FOR OPERATING 
LICENSES, AND HOLDERS OF CONSTRUCTION PERMITS, AND FT. ST. VRAIN 

Gentlemen:  

SUBJECT:  STAFF RECOMMENDED ACTIONS STEMMING FROM NRC INTEGRATED PROGRAM FOR
          THE RESOLUTION OF UNRESOLVED SAFETY ISSUES REGARDING STEAM 
          GENERATOR TUBE INTEGRITY (GENERIC LETTER 85-02) 

The Commission has recently approved issuance of this generic letter to all 
nuclear power plants utilizing steam generators, to obtain information on 
their overall program for steam generator tube integrity and steam generator
tube rupture mitigation. This information will allow the staff to assess the
areas of concern addressed by the staff's recommended actions (see Enclosure
1) which were developed as part of the integrated program for the resolution
of Unresolved Safety Issues A-3, A-4 and A-5 regarding steam generator tube 
integrity. The staff's program report, NUREG-0844 (draft report for 
comment), is provided as Enclosure 3. NUREG-0844 will be issued in final 
form following a 90-day period for public comment. 

Steam generator tube integrity was designated an unresolved safety issue 
(USI) in 1978 and Task Action Plans (TAP) A-3, A-4 and A-5 were established 
to evaluate the safety significance of degradation in Westinghouse, 
Combustion Engineering and Babcock & Wilcox steam generators, respectively. 
These studies were later combined into one effort due to the similarity of 
many problems among the PWR vendors. 

Staff concerns relative to steam generator tube degradation stem from the 
fact that the steam generator tubes are a part of the reactor coolant system
(RCS) boundary and that tube ruptures allow primary coolant into the 
secondary system where its isolation from the environment is not fully 
ensured. The leakage of primary coolant into the secondary system has two 
potential safety implications which were considered. The first is the direct
release of radioactive fission products to the environment; and the second 
is the loss of primary coolant water which is needed to prevent core damage.
An extended, uncontrolled loss of coolant outside of containment could 
result in the depletion of the initial RCS water inventory and ECCS water 
without the capability to recirculate the water. 

An integrated program was initiated by the staff in May 1982 to consider 
initial recommendations from the USI effort, and to assess the lessons which
could be learned from the four domestic SGTR events; Point Beach 1 in 1975; 
Surry 2 in 1976; Prairie Island 1 in 1979; and Ginna in 1982. A number of 
potential requirements for industry were identified and subjected to a value
impact evaluation. 



8504120031  
.

                                    - 2 - 

These analyses indicate that: the probability of core melt from events 
involving steam generator tube ruptures is not a major contributor to total 
core melt risk; that steam generator tube ruptures are an important 
contributor to the probability of significant non-core melt releases; and 
that steam generator tube degradation is a major contributor to occupational
radiation exposure at PWR's. 

Based upon the results of the staff's integrated program, the staff has 
developed recommended actions in the following areas: 

1.   Prevention and Detection of Loose Parts and Foreign Objects 

2.   Steam Generator Tube Inservice Inspection 

3.   Secondary Water Chemistry Program 

4.   Condenser Inservice Inspection Program 

5.   Primary to Secondary Leakage Limit 

6.   Coolant Iodine Activity Limit 

7.   Safety Injection Signal Reset 

The staff's recommended actions have been found to be effective measures on 
a plant specific basis for significantly reducing (1) the incidence of tube 
degradation, (2) the frequency of tube ruptures and the corresponding 
potential for significant non-core melt releases, and (3) occupational 
exposures, and are consistent with good operating and engineering practices.

Accordingly, operating reactor licensees and applicants for an operating 
license (this letter is for information only for those utilities that have 
not applied for an operating license) are requested to furnish to the 
Director, Division of Licensing, Office of Nuclear Reactor Regulation, no 
later than 60 days from the date of this letter, a description of their 
overall programs for assuring steam generator tube integrity and for steam 
generator tube rupture mitigation. The description of the plant specific 
programs should be sufficiently detailed to allow the staff to compare these
actions with the staff recommended actions as presented in Enclosure 1. 

The staff recommended actions above do not address supplemental tube sample 
inspections for the case where Category C-2 results are obtained during 
initial sample inspections. The staff initially considered a proposed 
upgrading of existing Technical Specification requirements in this area (see
Section 2.2.1. of the enclosed draft NUREG-0844), and this proposal was 
commented upon extensively by industry. The staff has concluded that the 
particular proposal considered was not warranted as a generic staff position
or recommendation. However, as part of the information requested by this 
letter, licensees and applicants are requested to describe practices they 
employ to ensure adequate inspection samples are taken in the event that 
Category C-2 results are obtained during initial sampling. The information 
requested is described in additional detail in Enclosure 2. 
.

                                    - 3 - 

The staff will review each response from licensees and applicants, and 
evaluate the overall effectiveness of plant-specific programs to prevent and
mitigate the occurrence of steam generator tube ruptures. The staff 
recognizes, however, that plants specific programs may differ from the staff
recommended actions, and still be adequately effective. The results of the 
staff review will be reported directly to the Commission. The Commission has
specifically requested that the staff include in its report the number and 
quality of the responses, noting in particular any utilities delinquent in 
providing the requested information and any recommended corrective actions. 

The staff will continue to monitor licensees' commitments and programs 
relative to steam generator integrity and SGTR mitigation to determine if 
they are being effectively implemented. As has been true in the past, 
additional actions may become necessary in plant specific instances of 
extensive or severe degradation. 

This request for information was approved by the Office of Management and 
Budget under clearance number 3150-0011 which expires April 30, 1985. 
Comments on burden and duplication may be directed to the Office of 
Management and Budget, Report Management Room 3208, New Executive Office 
Building, Washington, D. C. 20503. 

Mr. Emmett Murphy, Operating Reactors Assessment Branch, will be the point 
of contact. If you have questions or desire additional information, he can 
be reached on (301) 492-7457. 

                              Sincerely, 


                              Hugh Thompson, Jr., Director  
                              Division of Licensing  
                              Office of Nuclear Reactor Regulation 

Enclosures: 
1.   Staff Recommended Actions 
      Stemming from NRC Integrated 
      Program for the Resolution 
      of Unresolved Safety Issues 
      Regarding Steam Generator 
      Tube Integrity 
2.   Request for Information 
      Concerning Category C-2 
      Steam Generator Tube 
      Inspections 
3.   NUREG-0844 (Draft Report For 
      Comment), NRC Integrated
      Program for the Resolution 
      of Unresolved Safety 
      Issues 
4.   List of Generic Letters 
.
                                 ENCLOSURE 1
               STAFF RECOMMENDED ACTIONS AND REVIEW GUIDELINES
                    STEMMING FROM NRC INTEGRATED PROGRAM
               FOR THE RESOLUTION OF UNRESOLVED SAFETY ISSUES
                  REGARDING STEAM GENERATOR TUBE INTEGRITY

1.a  PREVENTION AND  DETECTION OF LOOSE PARTS (INSPECTIONS)  

     Staff Recommended Action 

     Visual inspections should be performed on the steam generator secondary
     side in the vicinity of the tube sheet, both along the entire periphery
     of the tube bundle and along the tube lane, for purposes of identify 
     loose parts or foreign objects on the tubesheet, and external damage to
     peripheral tubes just above the tubesheet. An appropriate optical 
     device should be used (e.g., mini-TV camera, fiber optics). Loose parts 
     or foreign objects which are found should be removed from the steam 
     generators. Tubes observed to have visual damage should be eddy current
     inspected and plugged if found to be defective. 

     These visual inspections should be performed: (1) for all steam gener-
     ators at each plant at the next planned outage for eddy current 
     testing, (2) after any secondary side modifications, or repairs, to 
     steam generator internals, and (3) when eddy current indications are 
     found in the free span portion of peripheral tubes, unless it has been 
     established that the indication did not result from damage by a loose 
     part or foreign object. 

     For PWR OL applicants, such inspections should be part of the 
     preservice inspection. 

     For steam generator models where certain segments of the peripheral 
     region can be shown not to be accessible to an appropriate optical 
     device, licensees and applicants should implement alternative actions 
     to address these inaccessible areas, as appropriate. 

     Licensees should take appropriate precautions to minimize the potential
     for corrosion while the tube bundle is exposed to air. The presence of 
     chemical species such as sulfur may aggravate this potential, and may 
     make exposure to the atmosphere inadvisable until appropriate remedial 
     measures are taken. 

     Reference 

     Section 2.1 of NUREG-0844. 
.

                                    - 2 - 

1.b  PREVENTION AND DETECTION OF LOOSE PARTS (QUALITY ASSURANCE) 

     Staff Recommended Action Quality assurance/quality control procedures 
     for steam generators should be reviewed and revised as necessary to 
     ensure that an effective system exists to preclude introduction of 
     foreign objects into either the primary or secondary side of the steam 
     generator whenever it is opened (e.g., for maintenance, sludge lancing,
     repairs, inspection operations, modifications). As a minimum, such 
     procedures should include: (1) detailed accountability procedures for 
     all tools and equipment used during an operation, (2 appropriate 
     controls on foreign objects such as eye glasses and film badges, (3) 
     cleanliness requirements, and (4) accountability procedures for 
     components and parts removed from the internals of major components 
     (e.g., reassembly of cut and removed components). 

     Reference 

     Section 2.1 of NUREG-0844. 
.

                                    - 3 - 

2.a  INSERVICE INSPECTION PROGRAM (FULL LENGTH TUBE INSPECTION) 

     Staff Recommended Action 

     The Standard Technical Specifications (STS) and Regulator Guide 1.83, 
     Part C.2.f, currently define a U-tube inspection as meaning an 
     inspection of the steam generator tube from the point of entry on the 
     hot-leg side completely around the U-bend to the top support of the 
     cold-leg side. The staff recommends that tube inspections should 
     include an inspection of the entire length of the tube (tube end to 
     tube end) including the hot leg side, U-bend, and cold leg side. 

     This recommended action does not mean that the hot leg inspection 
     sample and the cold leg inspection sample should necessarily involve 
     the same tubes. That is, it does not preclude making separate entries 
     from the hot and cold leg sides and selecting different tubes on the 
     hot and cold leg sides to meet the minimum sampling requirements for 
     inspection. 

     Consistent with the current STS requirement, supplemental sample 
     inspections (after the initial 3% sample) under this staff recommended 
     action may be limited to a partial length inspection provided the 
     inspection includes those portions of the tube length where degradation
     was found during initial sampling. 

     Reference 

     Section 2.2.2 of NUREG-0844. 
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                                    - 4 -

2.b  INSERVICE INSPECTION PROGRAM (INSPECTION INTERVAL) 

     Staff Recommended Action 

     The maximum allowable time between eddy current inspections of an 
     individual steam generator should be limited in a manner consistent 
     with Section 4.4.5.3 of the Standard Technical Specifications, and in 
     addition should not extend beyond 72 months. 

     Reference 

     Section 2.2.4 of NUREG-0844. 
.

                                    - 5 -

3.a  SECONDARY WATER CHEMISTRY PROGRAM 

     Staff Recommended Action 

     Licensees and applicants should have a secondary water chemistry 
     program (SWCP) to minimize steam generator tube degradation. 

     The specific plant program should incorporate the secondary water 
     chemistry guidelines in SGOG Special Report EPRI-NP-2704, "PWR 
     Secondary Water Chemistry Guidelines," October 1982, and should address 
     measures taken to minimize steam generator corrosion, including 
     materials selection, chemistry limits, and control methods. In 
     addition, the specific plant procedures should include progressively 
     more stringent corrective actions for out-of-specification water 
     chemistry conditions. These corrective actions should include power 
     reductions and shutdowns, as appropriate, when excessively corrosive 
     conditions exist. Specific functional individuals should be identified 
     as having the responsibility/authority to interpret plant water 
     chemistry information and initiate appropriate plant actions to adjust 
     chemistry as necessary. 

     The referenced SGOG guidelines above were prepared by the Steam 
     Generator Owners Group Water Chemistry Guidelines Committee and 
     represent and consensus opinion of a significant portion of the 
     industry for state-of-the-art secondary water chemistry control. 

     Reference 

     Section 2.5 of NUREG-0844. 
.

                                    - 6 -

3.b  CONDENSER INSERVICE INSPECTION PROGRAM 

     Staff Recommended Action 

     Licensees should implement a condenser inservice inspection program. 
     The program should be defined in plant specific safety-related 
     procedures and include: 

     1.   Procedures to implement a condenser inservice inspection program 
          that will be initiated if condenser leakage is of such a magnitude
          that a power reduction corrective action is required more than 
          once per three month period; and 

     2.   Identification and location of leakage source(s), either water or 
          air; 

     3.   Methods of repair of leakage; 

     4.   Methodology for determining the cause(s) of leakage; 

     5.   A preventive maintenance program. 

     Reference 

     Section 2.6 of NUREG-0844. 
.

                                    - 7 - 

4.   PRIMARY TO SECONDARY LEAKAGE LIMIT 

     Staff Recommended Action 

     All PWRs that have Technical Specifications limits for primary to 
     secondary leakage rates which are less restrictive than the Standard 
     Technical Specifications (STS) limits should implement the STS limits. 

     Reference 

     Section 2.8 of NUREG-0844. 
.

                                    - 8 - 

5.   COOLANT IODINE ACTIVITY LIMIT 

     Staff Recommended Action 

     PWRs that have Technical Specifications limits and surveillance for 
     coolant iodine activity that are less restrictive than the Standard 
     Technical Specification (STS) should implement the STS limits. Those 
     plants identified above that also have low head high pressure safety 
     injection pumps should either: (1) implement iodine limits which are 
     20% of the STS values, or (2) implement reactor coolant pump trip 
     criteria which will ensure that if offsite power is retained, no loss 
     of forced reactor coolant system flow will occur for steam generator 
     tube rupture events up to and including the design basis double-ended 
     break of a single steam generator tube, and implement iodine limits 
     consistent with the STS. 

     Reference 

     Section 2.9 of NUREG-0844. 
.

                                    - 9 - 

6.   SAFETY INJECTION SIGNAL RESET 

     Staff Recommended Action 

     The control logic associated with the safety injection pump suction 
     flow path should be reviewed and modified as necessary, by licensees, 
     to minimize the loss of safety function associated with safety 
     injection reset during an SGTR event. Automatic switchover of safety 
     injection pump suction from the boric acid storage tanks (BAST) to the 
     refueling water storage tanks should be evaluated with respect to 
     whether the switchover should be made on the basis of low BAST level 
     alone without consideration of the condition of the SI signal. 

     Reference 

     Section 2.11 of NUREG-0844. 
.

                                 ENCLOSURE 2
               REQUEST FOR INFORMATION CONCERNING CATEGORY C-2
                      STEAM GENERATOR TUBE INSPECTIONS

Information Requested 

The enclosed draft NUREG-0844 Section 2.2.1.2 describes certain limitations 
which the staff believes to be inherent in the present Technical 
Specification steam generator ISI requirements pertaining to Category C-2 
inspection results.  Licensees and applicants are requested to provide a 
description of their current policy and actions relative to this issue and 
any recommendations they have concerning how existing Technical 
Specification steam generator ISI requirements pertaining to Category C-2 
inspection results could be improved to better ensure that adequate 
inspections will be performed. This description should include a response to 
the following questions: 

     1.   What factors do, or would, the licensee or applicant consider in 
          determining (a) whether additional tubes should be inspected 
          beyond what is required by the Technical Specifications, (b) 
          whether all steam generators should be included in the inspection 
          program, and (c) when the steam generators should be reinspected. 

     2.   To what extent do these factors include consideration of the 
          degradation mechanism itself and its potential for causing a tube 
          to be vulnerable to rupture during severe transients or postulated
          accident before rupture or leakage of that tube occurs during 
          normal operation. 

Reference 

Section 2.2 of NUREG-0844. 
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