ML19309F231
| ML19309F231 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 04/07/1980 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Parris H TENNESSEE VALLEY AUTHORITY |
| References | |
| NUDOCS 8004290028 | |
| Download: ML19309F231 (2) | |
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m Docket Nos. 50-259 50-260 and 50-296 Mr. Hugh G. Parris Manager of Power Tennessee Valley Authority 500A Chestnut Street Tower II Chattanooga, Tennessee 37401
Dear Mr. Parris:
RE: MODIFICATIONS TO B0ILING WATER REACTOR CONTROL R00 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, hcviever, that arior to our request, modifications were performed at your facility under 10 CFR 50.59. NUREG-0619 vill provide requirements for your facility. We anticipate issuing NUREG-0619 in its "For Corm:ent" fora in April 1980.
If we can be of assistance, please contact your Project Manager.
Sincerely, 0A Thi)ma N e.Ippolito, Chief Operating Reactors Branch #3 Division of Operating Reactors
Enclosures:
As stated cc w enclosures:
See next page
Mr. Hugh G. Parris AFRIL 7
560 cc:
H. S. Sanger, Jr., Esquire General Counsel Tennessee Valley Authority 400 Commerce Avenue E 11B 33 C Knoxville, Tennessee 37902 Mr. Ron Rogers Tennessee Valley Authority 400 Chestnut Street Tower II Chattanooga, Tennessee 37401 i
Mr. E. G. Beasley Tennessee Valley Authority 400 Commerce Avenue W 10C 131C 1
Knoxville, Tennessee 37902 Rober: F. Sullivan U. S. Nuclear Regulatory Commission P. O. Box 1863 Decatur, Alabama 35602 Athens Public Library South and Forrest
. Athens, Alabama 35611 I
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January TS, 198D Generic Technical Activity A-10 Mr. Richard Gridley, Manager Fuel and Services Licensing General Electric Corgany 175 Curtner Avenue San Jose, California 95215
Dear Mr. Gridley:
Since the initial ciscovery of cracking in boiling water reactor (B'n'R) c:ntrol rod drive return line (CRDRL) no::les in early 1977, General Electric (GE) has proposed a number of solutions to the problem in the course of =hich several documents were submitted for NRC staff review.
These documents were as follows:
Letter of March ih,1979, G. G. Shemood (GE) to Y. Stello and 1.
R. Mattson (NRC) regarcing calculation of CED system return flow ca:acity; Letter of April 9,1979, G. G. Sherwood (GE) to Y.' Stello and 2.
R. Mattson (WRC) forwarding results of CRD system solenoid valve en::urance testing; Letter of May 1,1979, G. G. Sherwood (GE) to Y. Stello and 2.
R. Mattson (NRC) f onarding results of CRD system solenoid valve perfor=ance testing; and Letter of Novee=er 2,1979, G. G. Sherwood (GE) to R. P. Snaider 4
(NRC) forwarding adcitional information as requested regarcing CRD l
hydraulic system performance, especially with regard to corrosion procucts emanating from carbon steel piping.
All c:ncerned the GE rationale for the latest proposed system modification to prevent no::le cracking; namely, total removal of the CRDRL and cutting anc cip;ing of the CRDRL no::le. Previous submittals had presented the bases for tne otner socification proposals discussed herein.
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Mrs Ri: nard Gricley January 23, 1980 Specifically, your March 14, 1979 letter discussed the EI analysis performed af ter the NRC's selection of a base case for use in cocparing capability to inject high pressure water into the reactor vessel when other water sourtes were isolated. This base case was the 1975 incicent at arewns Ferry Unit
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No.1. during which the CRD system somtimes was one of the only capanie s urces of high pressure water injection to keep the reactere core covered. The staff recogni:es that the pressure of this capatility had not been directly assume in any previous safety analysis. However, the critical need for the syste: was again revealec. curing the early 1979 incident at the Oyster Creek Nuclear Generating Station. During this incident the reactor vessel also was isolated from otner sources of high pressure water and the CRD system r.aieup.capacility helped prevent urcovering of the active fuel.
Your ar.alysis of March ic,1979, included several assumptions which the NRC staff nas found acceptable. Principal among these was that concurrent o;eration of the two CRD pumps was possible at sny plant. This of course icolies that there will se no electrical supply limitations and no pump ne: pcsitive suction. head (NPSM) limits that will te reached. Licensees and a::licants will be re:uirec to demonstrate this to be valid, by testing, prior to our approving CRD 'retu n line removal.
The letters of April 9, and May 1,1979, discussed the solenoid valve testing ;rogram initiatec in response to earlier NRC concerns. The original analysis of CRDRL renoval vita:ut rerouting 6eter=ined that return flow to tne reactor vessel from drive operation would enter CRD cooling water ifnes end re arn to the vessel through the CRD nechanis:s themselves. During testing, however,. you disc:vered that the actual path would be a reverse flow path through the inser; exhaust directional cont ol valves of the ncn-ac.uated Hydraulic Con: ci Units. The long-ter : cycling of the control valves in the reverse direction was a cause of WRC concern with regard to possi:le celeterious effects upon the operation of the CED hydraulic system.
In response to this concern, EE tested ten valves which had been removed free in ocerating reactor on which the re*arn line had been isolated for six m:ntns. These valves were then cccparec against tests perfor. sed on five new valves. The results shewed tnat the reverse flow characteristics of all valves were sir.ilar anc that degradation of the valves to the point of causing system r.alfuncti:n would not be expected during long-term nc:--i o;eration of the sys en.
The NRC staff is satisfied with these resul s.
Sirulated life cycle testing also was perforaed on five valves, resulting in tne cete-cination tna no acverse effects were caused by the bactflow.
Tne WR staff has founc :nis acceptable.
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Kr. Richarc Gricley January 28, 1980 Your final letter of Novemoer 2,1979, discussed in detail your response to staff concerns regarding possible degradation of the CR0 system anc incivioual CRD mechanis=s because of corrosion proble:s f rom caroon steel piping. Certain modifications were suggested to solve these probless.
You also ciscussed your recommendations regarding the installation of p res su rt equalizing valves in the CR0 sy, tem to prevent, under a hypo-thetical transient, a larpe pressure differential across tne 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 heacer to the drive cooling water header.
We have reviewec your submittals and have concluced the follewing:
1.
Only licensees of the following classes of plants will be allowed at this time to implement the recommendatier to cut and cap with no re-routing of tne CRDRL anc w tnout further analysis. Each tpplicable i
plant must demonstrate, by testing, concurrent two CRD pump operation
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(with one exception), sa;isfactory CRD system operation, required flow capability, and each will be requirec to install the system mocifications listed in 4. below, a.
218' BWR/6 b.
251' BWR/6 183* BWR/4 (only one pumo needed to satisfy base case requirement) c.
d.
251 ' S WE/4 No occifications should be performed on operating reactors prior to issuance of ne "For Comment" issue of NUREG-0419, scheocled for release in January 1980.
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We do not accept the hypothesis that the calculations for the above plants were bouncing. Therefore, prior to our approval of modification l
of other plant classes, we shall require analysis similar to that per-formed on :ne plant classes of 1. above. The same testing and system socifications will also be requirec.
3.
We found tne 251' BWR/S (the fif tn class analy:ed in the March 14, 1979 letter) presently to be unacceptacle for mocification in that its calcu-latec flow fell below ne acceptacle base case value. Further analysis or plant-specific testing coule prove flow capacity to de acceptable.
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Mr. Richard Gridley January 28, 1980 l
4.
We will require that the following modifications be implemented on all plants requesting the removal of the CRDRL without rerouting and those l
which reroute but choose to operate with CRD return line flow valved j
out; Installation of equali:ing valves between the cooling water header a.
and the exhaust water header.
i Flush ports installed at hign.and low points of exhaust water b.
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header piping run if carbon steel piping is retained; and l
Replacement of carden steel pipe in the flow stabili:er loop with c.
stainless steel and rerouting directly to the cooling water header.
5.
Each licensee mast establish reactly-available operating procedures for achieving maxim;m CRD flew 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 taoped into, must I
acc the GE-recommended pressure control station to the cooling water hea de r.
This station acts to buffer hydraulic perturbations from any connected systec in orcer 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 Novemoer 2,1979 letter. We consider the
" sore assolute solution" (your characterization) to be the correct one and agree with your reconnendation, sade in accordance with this "more absolute We ce not solution", tnat the caroon steel piping should be eliminated.
accept the option of filter installation as a means of trapping corrosion Our con-particles that have a deleterious effect on the CRD mechanis=s.
cern is that improperly maintained filters on the cooling water header could result in heatup of drive mechanisms and the possibility of cultiple i
drive f ailures of a type not previously analyzed.
l Note that we have discussed only the acceptability of the latest GE recom-mencation discussed in the four letters. We continue to accept CRDRL re-routing to a line outside containment that in turn provides the retum flow to the reactor vessel (valving out af ter re-routing results in other requirements - see 4. and 6. above). We also find acceptaole, as a strictly interim neasure, tne 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 unich option is chosen, we will requirt complete inspection, by dye penetrant techniques, of.the CRDRL no::le, the acron area beneath the no::le, and the subsequent removal of any cracks found during the inspection.
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Mr. Ricnard Gridley January 28, 1980 For the Ms uncergoing licensing review and designed and constracted without the CRDEL and its nc::le or edified with the CRDRL cut and capped without rerouting, we will require testing (similar to that for operating plants) to prove satisf actory systee operation, return flow capability equal to or in excess of the base case require::ent discussed above, and two pu:np operation.
Applicaole codifications of 4. above also sust be i::ple:nented.
We shall re uire the establish.ent of operating procecures for achieving maxisum CRD flow to an otherwise ~isciated vessel. Calculations with regarc to base case re*.u rn fi cw requirements should be submitted, but in lieu of such calculations, the staff say accept refe tnce to a bounding analysis if necessary justification i s p rovi ce d.
Adcitional raidance on this subject will be contained in NUREG-0619. This c o c=e r.: is tenatively scheculec f or publication in February 1980.
Yincerely, fv p
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5 W ASHINGTON, D. C. 20555 February 11, 1950 Generic Task N. A-10
?>r. Richard Gridley, Manager Fuel & Services Licensing General Electric Company 175 Curtner Avenue San J se, California 95125
Dear !'.r. Gridley:
3y le::er dated f:vember 27, 1979, you forwarded results of analyses of bcil-off rates and. Control Rod Drive (CRD) System Pump makeup capability fcr plants not previously addressed in earlier related submittals. The le:ter also included a draft procedure for optimizing CRD pump flow to the reactor vessel.
The h:vember 27, 1979 letter was not included in the NRC's Unresolved Safety Issue A-1: review and the analyzed classes of plants will not be included in N.RE: ^519, which resolves A-10 and is tentatively scheduled for issuance ir "F:r C: rent" form by February 29, 1950. However, we ses r.o reason why licenstes and ap;licants cannot use the results in the plant-specific analyses (and testing) required by NUREG-0619. Significantly more detail will be re:uired in their submittals, however, particularly with regard to the assump-tiens utilized in derivation of the various flow rates.
We c:n:ur that the GE-proposed procedure for eptimization of CRD system flow to the pressure vessel provides a necessary first step toward reaching the desire: goal.
However, in our opinion it is too cumbersome with regard to citsersment of pu p discharge flow. When faced with the need to maintain water level upon loss of other capable high pressure water injection systems, the c:erator sim:ly cannot be burdened with the need to refer to pump curves cr the need to consider what, if any, other portions of system flow are not included in a respanned flow meter.
We believe that operators should be provided one or two meters capable of reliable direct msasurement of one and two pump flow.
Sincerely,
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D rrell G. cisenhut, Acting Director Division of Operating Reactors Office of Nuclear Reactor Regulation Y
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