Modifications to Boiling Water Reactor Control Rod Drive Systems (Generic Letter 80-29)


                              UNITED STATES 
                          WASHINGTON, D.C. 20555 

                               APRIL 7, 1980 

Docket Nos.   50-277 
          and 50-278 

     Mr. Edward G. Bauer, Jr. 
     Vice President and General Counsel 
     Philadelphia Electric Company 
     2301 Market Street 
     Philadelphia, Pennsylvania 19101 

     Dear Mr. Bauer: 


     Enclosed you will find a copy of our January 28, 1980 letter to General
     Electric which discusses the NRC staff's conclusions regarding proposed
     control rod drive (CRD) system modifications related to the elimination
     of cracking in the CRD return line nozzle. You will also find a copy of
     our February 11, 1980 letter to GE regarding additional analyses of 
     boil-off rates and CRD system makeup capability. This letter also 
     responds to a GE-proposed draft procedure for optimizing CRD pump flow 
     to the reactor vessel. 

     We have requested that no modifications be performed on operating 
     reactors until complete guidance has been issued in NUREG-0619. We 
     understand, however, that prior to our request, modifications were 
     performed at your facility under 10 CFR 50.59. NUREG-0619 will provide 
     requirements for your facility. We anticipate issuing NUREG-0619 in its
     "For Comment" form in April 1980. If we can be of assistance, please 
     contact your Project Manager. 


                                   Thomas A. Ippolito, Chief 
                                   Operating Reactors Branch #3 
                                   Division of Operating Reactors 

     As stated 

     cc w enclosures: 
     See next page 


Mr. Edward G. Bauer, Jr. 
Philadelphia Electric Company     - 2 - 


Eugene J. Bradley 
Philadelphia Electric Company
Assistant General Counsel 
2301 Market Street 
Philadelphia, Pennsylvania 19101 

Troy B. Conner, Jr.
1747 Pennsylvania Avenue, N. W. 
Washington, D. C. 20006 

Raymond L. Hovis, Esquire 
35 South Duke Street 
York, Pennsylvania 17401 

Warren K. Rich, Esquire 
Assistant Attorney General 
Department of Natural Resources 
Annapolis, Maryland 21401 

Government Publications Section 
State Library of Pennsylvania 
Education Building 
Commonwealth and Walnut Streets 
Harrisburg, Pennsylvania 17126 

M. J. Cooney, Superintendent 
Generation Division - Nuclear 
Philadelphia Electric Company 
2301 Market Street 
Philadelphia, Pennsylvania 19101 

Edward Greenman 
U. S. Nuclear Regulatory Commission 
Office of Inspection and Enforcement 
Peach Bottom Atomic Power Station 
P. O. Box 399 
Delta, Pennsylvania 17314 

Philadelphia Electric Company 
ATTN:     Mr. W. T. Ullrich 
          Peach Bottom Atomic 
               Power Station 
Delta, Pennsylvania 17314 

                             UNITED STATES 
                          WASHINGTON, D.C. 20555 

                             January 28, 1980 

Generic Technical Activity A-10 

     Mr. Richard Gridley, Manager 
     Fuel and Services Licensing 
     General Electric Company 
     175 Curtner Avenue 
     San Jose, California 96215 

     Dear Mr. Gridley: 
     Since the initial discovery of cracking in boiling water reactor (BWR) 
     control rod drive return line (CRDRL) nozzles in early 1977, General 
     Electric (GE) has proposed a number of solutions to the problem in the 
     course of which several documents wert submitted for NRC staff review. 
     These documents were as follows: 

     1.   Letter of March 14, 1979, G. G. Sherwood (GE) to V. Stello and R. 
          Mattson (NRC) regarding calculation of CRD system return flow 

     2.   Letter of April 9, 1979, G. G. Sherwood (GE) to V. Stello and R. 
          Mattson (NRC) forwarding results of CRD system solenoid valve 
          endurance testing; 

     3.   Letter of May 1, 1979, G. G. Sherwood (GE) to V. Stello and R. 
          Mattson (NRC) forwarding results of CRD system solenoid valve 
          performance testing; and 

     4.   Letter of November 2, 1979, G. G. Sherwood (GE) to R. P. Snaider 
          (NRC) forwarding additional information as requested regarding CRD
          hydraulic system performance, especially with regard to corrosion 
          products emanating from carbon steel piping. 

     All concerned the GE rationale for the latest proposed system 
     modification to prevent nozzle cracking; namely, total removal of the 
     CRDRL and cutting and capping of the CRDRL nozzle. Previous submittals 
     had presented the bases for the other modification proposals discussed 


Entire document previously entered into system under: 

     ANO 8002250136 
     No. of pages:  5 


Specifically, your March 14, 1979 letter discussed the GE analysis performed
after the NRC's selection of a base case for use in comparing capability to 
inject high pressure water into the reactor vessel when other water sources 
were isolated. This base case was the 1975 incident at Browns Ferry Unit No.
1, during which the CRD system sometimes was one of the only capable sources
of high pressure water injection to keep the reactor core covered. The staff
recognizes that the pressure of this capability had not been directly 
assumed in any previous safety analysis. However, the critical need for the 
system was again revealed during the early 1979 incident at the Oyster Creek 
Nuclear Generating Station. During this incident the reactor vessel also was 
isolated from other sources of high pressure water and the CRD system makeup
capability helped prevent uncovering of the active fuel. 

Your analysis of March 14, 1979, included several assumptions which the NRC 
staff has found acceptable. Principal among these was that concurrent 
operation of the two CRD pumps was possible at any plant. This of course 
implies that there will be no electrical supply limitations and no pump net 
positive suction head (NPSH) limits that will be reached. Licensees and 
applicants will be required to demonstrate this to be valid, by testing, 
prior to our approving CRD return line removal. 

The letters of April 9, and May 1, 1979, discussed the solenoid valve 
testing program initiated in response to earlier NRC concerns. The original 
analysis of CRDRL removal without rerouting determined that return flow to 
the reactor vessel from drive operation would enter CRD cooling water lines 
and return to the vessel through the CRD mechanisms themselves. During 
testing, however, you discovered that the actual path would be a reverse 
flow path through the insert exhaust directional control valves of the 
non-actuated Hydraulic Control Units. The long-term cycling of the control 
valves in the reverse direction was a cause of NRC concern with regard to 
possible deleterious effects upon the operation of the CRD hydraulic system.

In response to this concern, GE tested ten valves which had been removed 
from an operating reactor on which the return line had been isolated for six
months. These valves were then compared against tests performed on five new 
valves. The results showed that the reverse flow characteristics of all 
valves were similar and that degradation of the valves to the point of 
causing system malfunction would not be expected during long-term normal 
operation of the system. The NRC staff is satisfied with these results. 

Simulated life cycle testing also was performed on five valves, resulting in
the determination that no adverse effects were caused by the backflow. The 
NRC staff has found this acceptable. 

                                 - 3 - 

Your final letter of November 2, 1979, discussed in detail your response to 
staff concerns regarding possible degradation of the CRD system ana 
individual CRD mechanisms because of corrosion problems from carbon steel 
piping. Certain modifications were suggested to solve these problems . You 
also discussed your recommendations regarding the installation of pressure 
equalizing valves in the CRD system to prevent, under a hypothetical 
transient, a large pressure differential across the CRD system which could 
result in excessively fast movement of a selected control rod. The valves 
also prevent flow from the carbon steel piping of the normal exhaust water 
header to the drive cooling water header. 

We have reviewed your submittals and have concluded the following: 

1.   Only licensees of the following classes of plants will be allowed at 
     this time to implement the recommendation to cut and cap with no 
     rerouting of the CRDRL and without further analysis. Each applicable 
     plant must demonstrate, by testing, concurrent two CRD pump operation 
     (with one exception), satisfactory CRD system operation, required, flow
     capability, and each will be required to install the system 
     modifications listed in 4. below. 

     a.   218" BWR/6 

     b.   251" BWR/6 

     c.   183" BWR/4 (only one pump needed to satisfy base case requirement)

     d.   251" BWR/4 

     No modifications should be performed on operating reactors prior to 
     issuance of the "For Comment" issue of NUREG-0619, scheduled for 
     release in January 1980. 

2.   We do not accept the hypothesis that the calculations for the above 
     plants were bounding. Therefore, prior to our approval of modification 
     of other plant classes, we shall require analysis similar to that 
     performed on the plant classes of 1. above. The same testing and system
     modifications will also be required. 

3.   We found the 251" BWR/S (the fifth class analyzed in the March 14, 1979
     letter) presently to be unacceptable for modification in that its 
     calculated flow fell below the acceptable base case value. Further 
     analysis or plant-specific testing could prove flow capacity to be 

                                  - 4 - 

4.   We will require that the following modifications be implemented on all 
     plants requesting the removal of the CRDRL without rerouting and those 
     which reroute but choose to operate with CRD return line flow valved 

     a.   Installation of equalizing valves between the cooling water header
          and the exhaust water header.  

     b.   Flush ports installed at high and low points of exhaust water 
          header piping run if carbon steel piping is retained; and 

     c.   Replacement of carbon steel pipe in the flow stabilizer loop with 
          stainless steel and rerouting directly to the cooling water 

5.   Each licensee mst establish readily-available operating procedures for 
     achieving maximum CRD flow to an otherwise isolated reactor vessel. 

6.   Licensees who choose to reroute the CRDRL, either with or without 
     continuous return line flow to the system being tapped into, must add 
     the GE-recommended pressure control station to the cooling water 
     header. This station acts to buffer hydraulic perturbations from any 
     connected system in order to prevent pressure fluctuations in the CRD 
Modification 4.c is based upon our decision not to accept the "do nothing" 
alternative addressed in your November 2. 1979 letter. We consider the "more
absolute solution" (your characterization) to be the correct one and agree 
with your recommendation, made in accordance with this "more absolute 
solution", that the carbon steel piping should be eliminated. We do not 
accept the option of filter installation as a means of trapping corrosion 
particles that have a deleterious effect on the CRD mechanisms. Our concern 
is that improperly maintained filters on the cooling water header could 
result in heatup of drive mechanisms and the possibility of multiple drive 
failures of a type not previously analyzed. 

Note that we have discussed only the acceptability of the latest GE        
recommendation discussed in the four letters. We continue to accept CRDRL 
re-routing to a line outside containment that in turn provides the return 
flow to the reactor vessel (valving out after re-routing results in other 
requirements - see 4. and 6. above). We also find acceptable, as a strictly 
interim measure, the valving out of the CRDRL. However, this will require 
inspection, during each refueling outage, of that portion of the line 
containing stagnant water. No matter which option is chosen, we will require
complete inspection, by dye penetrant techniques, of the CRDRL nozzle, the 
apron area beneath the nozzle, and the subsequent removal of any cracks 
found during the inspection. 

                                  - 5 -

For the BWRs undergoing licensing review and designed and constructed 
without the CRDRL and its nozzle or modified with the CRDRL cut and capped 
without rerouting, we will require testing (similar to that for operating 
plants) to prove satisfactory system operation, return flow capability equal 
to or in excess of the base case requirement discussed above, and two pump 
operation. Applicable modifications of 4. above also must be implemented. We 
shall require the establishment of operating procedures for achieving 
maximum CRD flaw to an otherwise isolated vessel. Calculations with regard 
to base case return flow requirements should be submitted, but in lieu of 
such calculations, the staff may accept reference to a bounding analysis if 
necessary justification is provided. 

Additional guidance on this subject will be contained in NUREG-0619. This 
document is tentatively scheduled for publication in February 1980. 


                                        Darrell G. Eisenhut, Acting Director
                                        Division of Operating Reactors 
                                        Office of Nuclear Reactor Regulation

                              UNITED STATES 
                          WASHINGTON, D. C. 20555 

                            February 11, 1980 

Generic Task No. A-10 

     Mr. Richard Gridley, Manager 
     Fuel & Services Licensing 
     General Electric Company 
     175 Curtner Avenue 
     San Jose, California 95125 

     Dear Mr. Gridley: 

     By letter dated November 27, 1979, you forwarded results of analyses of
     boil-off rates and Control Rod DRive (CRD) System Pump makeup 
     capability for plants not previously addressed in earlier related 
     submittals. The letter also included a draft procedure for optimizing 
     CRD pump flow to the reactor vessel. 
     The November 27, 1979, letter was not included in the NRC;s Unresolved 
     Safety Issue A-10 review and the analyzed was not included in the 
     NUREG-0619, which resolves A-10 and is tentatively scheduled for 
     issuance in "For Comment" form by February 29, 1980. However, we see no 
     reason why licensees and applicants cannot use the results in the 
     plant-specific analyses (and testing) required by NUREG-0619. 
     Significantly more detail will be required in their submittals, 
     however, particularly with regard to the assumptions utilized in 
     derivation of the various flow rates. 
     We concur that the GE-proposed procedure for optimization of CRD system
     flow to the pressure vessel provides a necessary first step toward 
     reaching the desired goal. However, in our opinion it is too cumbersome
     with regard to measurement of pump discharge flow. When faced with the 
     need to maintain water level upon loss of other capable high pressure 
     water injection systems, the operator simply cannot be burdened with 
     the need to refer to pump curves or the need to consider what, if any, 
     other portions of system flow are not included in a respanned flow 
     We believe that operator should be provided one or two meters capable 
     of reliable direct measurement of one and two pump flow. 


                                   Darrell G. Eisenhut, Acting Director 
                                   Division of Operating Reactors 
                                   Office of Nuclear Reactor Regulation 


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