Modifications to Boiling Water Reactor Control Rod Drive Systems (Generic Letter 80-29)
GL80029
UNITED STATES
NUCLEAR REGULATORY COMMISSION
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:
RE: MODIFICATIONS TO BOILING WATER REACTOR CONTROL ROD DRIVE SYSTEMS
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.
Sincerely,
Thomas A. Ippolito, Chief
Operating Reactors Branch #3
Division of Operating Reactors
Enclosures:
As stated
cc w enclosures:
See next page
.
Mr. Edward G. Bauer, Jr.
Philadelphia Electric Company - 2 -
cc:
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
NUCLEAR REGULATORY COMMISSION
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
capacity;
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
herein.
DUPLICATE DOCUMENT
Entire document previously entered into system under:
ANO 8002250136
No. of pages: 5
.
-2-
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
acceptable.
.
- 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
out;
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
header.
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
system.
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.
Sincerely,
Darrell G. Eisenhut, Acting Director
Division of Operating Reactors
Office of Nuclear Reactor Regulation
.
UNITED STATES
NUCLEAR REGULATORY COMMISSION
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
meter.
We believe that operator should be provided one or two meters capable
of reliable direct measurement of one and two pump flow.
Sincerely,
Darrell G. Eisenhut, Acting Director
Division of Operating Reactors
Office of Nuclear Reactor Regulation
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