ML19352A675
| ML19352A675 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/16/1976 |
| From: | Schroeder F Office of Nuclear Reactor Regulation |
| To: | Ross D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML18025B195 | List:
|
| References | |
| FOIA-80-587 ACRS-CT-0656, ACRS-CT-656, NUDOCS 8104170351 | |
| Download: ML19352A675 (32) | |
Text
{{#Wiki_filter:. e s O =,. cy &: ... _.- l /VovsL. 1 i ROUTING AND TRAN5MITTAL SLIP - 'Y i 10cv .u,..,,, ,,,ou D. Ross < = = - " ~ a ...r.. ,.a V. Stello a ' * ~ ~ ' - .......ga_. S. Hanauer
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..s v s.u sas==a mars se s..tv.s t REMARKS For your information, the attached ACRS consultant report (CT-0656) has been placed in the POR by ACRS. 4 1 l l l Do NOT use this form as a RECORD of approv.ls, concurrences, i l disapprovals, clearances, and similar actions
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.o, u v >.*. s~.um ~sc F. Schroeder 4/16/76 9. eC 27303 OPTIONAL. FORM 43 es.-io-etas t ass-nos 3041 108 auoust se s7 esa FPMst t et C FR) 108-il20e e i l l 8104170351
i 53 T"hwnt.s on the ATifS Subcommittec Meeting of January 7.1976 TI"' Pt Wntations at the meeting focused again on the unresolved areas of the Attu nualysis, including the codcrator temperature coefficient and estimat e* On the various failurc rates. I fcc1 that the relative conser-vatiso dunnest ed by the regulatory staff still has some merits, mainly j because, su q. opinion, both the analytical models and the various reactor l-Parameters n,ed in the analysis are still subject to considerabic uncer-taintic:% RV comments on some specific items follow' 1. Sem,l.t t\\,tt y to the Modcrator Temperature Coefficients f Quentlous were raised at the Subcommittee Meeting on December lith f and 12th,194 as to how sensitive the AT11S consequences could be to the modcrator t enperature coefficient of reactivity. Both ifestinghouse and Combustien g ugineering presented sone results of their parametric studies ~ at this meetLug, which indicate a potential increase in the peak system Pressuro by a few hundred psia if the least negative moderator temperature coeffic1""' e\\pected for 99'., of the core life is. used instead of that for D5t. It is, however, rather interesting to note that this sensitivity m derdh'V t emperature coefficient begins to show when the system pressure t reaches " CeYtain " threshold". This " threshold" pressure appears to be approximalvl) 0600 psi in the loss-of-feedwater transient analysis presented by ifestingh,'u'e. Thus, in case of no turbine trip, the peak system pressure begins to theMase exponentially fron 2600 psia when the' moderator temperature c efficient dNreases in cagnitude from -30 pcm/*F, whereas, with turbine j trip, the e\\Nuential increase in pressure does not start until the modcrator temperature Nefficient is -S pcm/*F. Similarly, for the case with turbine trip and 'Al N ntrol, the peak pressure does not reach 2600 psia and hence l the expon,w,t W rise in pressure does not take place even for a very small magnitude of the moderator temperature coefficient. A similar " threshold" effect seem to be noticeable in the peak pressuri:cr pressure data presen:ed by Combug (Wt hgineering. It h Mhaps also interesting to note that this sensitivity in ATl?S l consequenu' ic parametric variation does not seem to be limited to the
a r temperature coefficient alone. Thus the results.of a parametric present :d by Combustion Engineering at the December lith,1975 meeting . sin show a similar sensitivity in the peal, pressuri:cr pressure to the (ariationintheprimarysafetyvalvearca. This suggests that perhaps we should not single out the moderator temperature coefficient as our villain in the ATWS analysis. That is, once the system pressurc reaches a certain " threshold" pressurc, variation of any one of several parametcrs, including the moderator temperature coefficient, could cenceivably have a considerable effect on the outcome of an ATUS event. This phenomenon could perhaps also account for the fact that, although the three PWR vendors use considerably different values of the least negative moderature coefficient expected for 95% of core life (ifestinghouse -8 pcm/*F,- Combustion Engineering -6 pcm/*F and Babcock and Wilcox -13.4 pcm/*F), any further decrease in the magnitude of their respective values appears to have similarly adverse effects on the-ATWS consequences. I venture to suggest that this phenomenon could be related to the equation of state of water and could be rather inherent in the - analytical models used for ATWS analyses. 2. Uncertainties in the Moderator Coefficient Determination I would like to, discuss two different types of uncertainties associated eith the determination of moderator temperature coefficient of reactivity applicable for 95'. of core life. The first uncertainty appears in the deter-nination of the moderator coefficient itscif at a given time in a core life. It can be perhaps accepted that the nedcrator temperature coefficients ocasured at hot :cro power conditions are subject to little errors. However, similar measurements of moderator temperature coefficients at hot full power ~ (HFP). conditions could involva, in my opinion, greater uncertaintics or crrers. This is because of the inherent difficultics and coepicxitic; in reactivity leterminations under the presence of distributed thermal-hydraulic feedbacks. Thus, in my opinion, determinarica of control rod worth itself at liFP condi-
- icns could normally be subject to considerabic uncertaintics. And, of
- ourse, the control rod worth is the very basis fer all other reactivity 1cterminations, including that of the moderator temperature coefficient of cactivity.
1
the other uncertainty is related to the determination of the 95'. of ,/* /11(c. Let us assume now that one has determined the modcrator ten-r'ature coefficient corresponding to IIFP, equilibrium xenon conditions as a function of fuel burnup, llowever, it would be an entirely different matter to determine the Icast negative moderator temperature coefficient applicable for 95t of the clapsed time during which the core is critical. In order to do this, one may have,to account for, c.g., frequent shutdowns and start::ps during the initial startup physics tests, which take place over a fairly long period of. time and often without the full equilibrium xenon cor.-:entrations. Thus the least negative codcrator temperature coeffi-cients applicable for 95% of the elapsed time at criticality may be con ' siderably s.siler in cagnitude than those presently used by reactor venders,' which are strictly applicable for 95% of core burnup with equilibrium xenon 6, concentrations. By the same token, if one were to calculate the fraction { of the elapsed ti e at criticality, for which the moderator coefficients presently used would be valid, the fraction would be considerably 1,arger than O.05. a 3. Thermal '4arrins and Fuel Failures It appears to be a prudent practice, in my opinion, to apply, as a thernal design criterion, a minimum DNB ratio of 1.30 for PhR cercs and a ninimum critical pcwer ratio of 1.04 or 1.05 for Bh2 cores even for the [ ATWS analysis. Although it may be true that fuel cladding will not necessarily fail at or above the ')NB heat flux, it.is my opinion that we do not have enough 'xperimental data on fuel-clad behavior in this heat flux regime. Thus a l
- onscrtive criterien seems to be recommendabic.
.7 l Credits fer Svster I=provecents j ..f One of the co:non cocplaints by the vendors seems to be that credits j re seldom given for improvements in the various hardwares in the plants. t here may be soce merits in their complaints. Efforts should be made by he regulatery staffs to study the effects of any system icprovements, and f possibic, credits should be given for them promptly. One important system improvement wou'ld be a'diverr.e means of inserting
- me control rods, no.catter how few, since this will considerably reduce l
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r r. s 4 ,,. consequences of any ATWS cvent. This has been, of course, emphasi:cd I in NASil-1270. S. Common Mode Failures and Failure Probabilitics l As was amply emphasized by I'. ?!. Jacobs in his presentation, perhaps there is no way of really proving that the probability of a given ATIVS cvent is less than 10/ reactor / year. The Icast we could do is to study the potential common mode failurcs thoroughly and try to eliminate any such identifiable failures rather than merely trying to calculate the probabilities of such occurrences. 9 O 9 0 e 8 9 4 6 4 9 E e 9 4 e ? S /
f
- o 578. May 17,1974 ANS-51 Selection of Initial Plant Conditions for Analyzing ATWS Draft (3 pages) 579.
December 17, 1974 to Denwood F. Ross from W. R. Corcoran (7 pages) 580. May 3,1977 Note to Thomas M. Novak from Ashok Thadani
Subject:
GE ATWS (2 pages) 581. January 6,1977 Memorandum for R. E. Heineman from D. F. Ross
Subject:
GE ATWS MEETING (3 pages) 582. February 14, 1978 Note to D. Ross from A. Thadani
Subject:
GE PROPOSED ATWS MITIGATION SYSTEM, attaching June 30, 1977 Note to D. Ross from T. Novak
Subject:
RECIRCULATION PUMP TRIP FOR AWS (BWR OPERATING PLANTS)(3 pages) 583. February 4,1975 to D. F. Ross from Fuat Odar
Subject:
QUESTIONS ON COMBUSTION ENGINEERING ATWS MODEL (12 pages) 584. September 13, 1979 Memorandum for S. H. Hanauer from A. Thadani
Subject:
NRC - CE ATWS MEETING
SUMMARY
(3 pages) 585. March 11,1975 Note to Files from R. F. Audette
Subject:
BNL - ATWS RESULTS FOR B&W - 0TSG PLANT (27 pages) 586. October 2,1975 to V. Stello from R. R. Maccary (2 pages) 587. February 21, 1980 to William Russell from Michael W. Golay, attaching Policy Recommendations for the Treatments of ATWS Events for Standardized Nuclear Power Plants (41 pages) 588. February 14, 1977 Routing and Transmittal Slip to D. F. Ross from Thomas Novak, attaching November 17, 1976 letter to Gerald S. I.ellouche from Ben C. Rusche, November 3,1976 Record Note from Stephen H. Hanauer, October 7, 1976 Letter to 8.C. Rusche from Gerald S. Lellouche (10 pages) 589. January 2,19/9 to R. J. Mattson from R. G. Cockrell
Subject:
ATWS COST WPPSS NUCLEAR PROJECTS NOS. 1/4 (14 pages) 590. January 26, 1979 Note for R. Mattson et al., from A. Thadani
Subject:
ATWS ANALYSES (65 pages) 591. October 22, 1979 Note to R. A. Birkel from A. Thadani
Subject:
DRAFT ATWS PROCEDURES FOR MCGUIRE NUCLEAR STATION, attaching September 25, 1979 Letter to Harold R. Denton from William 0. Parker (8 pages) 592. December 5,1979 Note to C. Stahle from Ashok Thadani (5 pages) 593. May 24,1978 Note to D. Ross from A. Thadani (17 pages) / 594. June 22, 1978 Memorandum for T. G. McCreless from R. J. Mattson
Subject:
ACRS i ATWS WORKING GROUP QUESTIONS, attaching Response No. I to ACRS Questions on i DSS Staff Report NUREG-0460 dtd June 1978, April 27,1978 Memcrandum for E. G. Case from R. J. Mattson
Subject:
ALAB-444 - TAP A-9 (69 pages) l
o, 30 595. June 23,1978 Routing and Transmisttal Slip to S. Hanauer et al., from Ashok C. Thadani, attaching June 20, 1978 Memorandum for A. Thadani from W. Minners
Subject:
RRRC QUESTIONS ON ATWS (12 pages) 596. July 6,1978 Handwritten Note to D. Ross from Ashok (23 pages) 597. July 19,1978 Note to Steve Varga from A. Thadani
Subject:
ATWS (21 pages) 598. July 28, 1978 Memorandum for E. Case from R. Mattson
Subject:
ALMS (20 pages) 599. September 11, 1978 Memorandum for V. Stello et al., from R. J. Mattson
Subject:
REVIEW 0F SUPPLEMENT 10F NUREG-0460, attaching Oraft, Anticipated Transients Without Scram in Light Water Reactors, September 1978 (41 pages) 600. September 26, 1978 Note to D. Ross et al., from A. Thadani (39 pages) 601. December 18, 1978 to R. J. Pattson from R. G. Cockrell (15 pages) 602. February 3,1977 Memorandum for Stephen Hanauer from Ashok Thadani (14 pages) 603. March 14,1977 Note to Distribution from Ashok C. Thadani (23 pages) 604. March 25, 1977 Routing and Transmittal Slip to S. Hanauer from A. Thadani (4 pages) 605. March 28, 1977 Note to S. H. Hanauer from Fuat Odar and Ashok Thadani
Subject:
PWR ATWS EVALUATION MODELS (3 pages) 606. April 14,1977 To ATWS Distribution from Ashok Thadani (25 pages) 607. Pay 23,1977 Memorandum for Thomas M. Novak from Ashok Thadani
Subject:
BNL ATMS MEETING (3 pages) 608. May 24, 1977 Memo to Distribution from Ashok Thadani (9 pages) 609. June 15,1977 Memorandum for T. M. Novak from A. C. Thadani
Subject:
BNL ATWS MEETING - BROOKHAVEN (11 pages) 61 0. June 20,1977 Note to A. Thadant from M. Tokar
Subject:
ATWS FUEL DAMAGE (2 pages) 611. August 11, 1977 Note to D. Ross from A. Thadani
Subject:
GERMAN ATWS REPORT (5 pages) 612. Undated Routing and Transmittal Slip to A. Thadani, attaching November 16, 1977 SECY-77-586 January 14, 1976 letter to William A. Anders from Dade W. Moeller (7 pages) 61 3. January 28, 1976 to Zoltan R. Rosztoczy from Fuat Odar
Subject:
ATWS SAMPLE PROBLEM RESULTS (57 pages) 614. March 3,1976 Routing and Transmittal Slip to D. Ross from Frank Schroeder attaching August 21, 1974 letter to H. O. Monson (11 pages) 61 5. November 5,1976 Note to Thomas M. Novak from Ashok C. Thadani
Subject:
ATWS MANPOWER REQUIREMENTS, attaching May 6,1976 to Denwood F. Ross from Ashok C. Thadani
Subject:
ATVS CATEGORY B LETTERS (5 pages)
l 31 -f i 616. November 29, 1976 Note to T. M. Novak from Ashok Thadani
Subject:
SOME I THOUGHTS ON REACTOR PROTECTION SYSTEM UNRELIABILITY (3 pages) 617. Handwritten Notes, PWR ATWS Analysis (13 pages) 618. Janua ry 23, 1975 to D. F. Ross from F. Odar
Subject:
SUMMARY
OF MEETING HELD TO DISCUSS FUTURE (FY 76) AND PRESENT BNL EFFORTS ON ATWS ANALYSES AND ADVANCE CODE DEVELOPMENT, attaching January 14, 1975 Memorandum to M.M. Levine 1 from V. L. Sailor
Subject:
ESTIMATED COSTS FOR THERMAL REACTOR SAFETY DIVISION, January 15, 1975 Letter to Herbert J. C. Kouts from G. H. Vineyard (13 pages) 619. ATWS Topical Reports Since WASH-1270 (September 1973) (1 page) 620. May 2,1975 to Victor Stello from L. Olshan (8 pages) 621. Working Paper, Discussion of Alternatives to the Previous Staff Position on Anticipated Transients Without Scram for Construction Permit Applications Made After October 1,1976, September 12,1975 (18 pages) 622. November 18,1975 SECY-75-668 (26 pages) 623. November 18, 1975 For the Commissioners from Ben C. Rusche
Subject:
MODIFICATION j OF STAFF POSITION ON ANTICIPATED TRANSIENTS WITHOUT SCRAM (ATWS) (6 pages) t 4 l l i l l
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0 r COMBUSVION DIVislON, C MBUSTION EN GINEEQlNG. IN WIN DSOR. CONN. 0 60 9 203 688 1911 CABLE; COM B EN m "J COMBUSTION DIVISION DRAFI T May 17, 1974 . </ W. C. Copp g] C. L. Klin i ANS-51 Selection of Initial Pla A Conditions for Analyzing (ATW9 v In a letter from Mr. Peter A. Morris, Director of the Division of Reactor Licensing dated December,1970, to all commercial Nuclear Steam Supply System vendors, he enclosed a set of " Guidelines for Investigation of ATWS". In these guidelines, he included the following statement concerning initial conditions: ' Assumed initial conditions and syst'em parameters ~ (e.g., power level, flow, pressure, power distri-bution, feedback coefficients) need be no more stringent than those normally anticipated for the reactor state under consideration. i l This statement shall be the basis for selection of initial conditions for [ the analyses of those ATUS transients listed in Section of this Standard. In demonstrating compliance with the P. A. Morris guidelines, each submittal shall include a section in which definitive statements i are made justifying the choice of initial conditions delineating how each 1 complies with the P. A. Morris guidelines. The following list of parameters shall be addressed in that section: i 1. Moderator Temperature Coefficient of Reactivity; j 2. Core Power Distribution; I 3. Core Power; 4. Core Coolant Flow; 5. Core Inlet Temperature; 6. Control Rod Insertion; 7. Soluble Boron Concentration in the Core; 8. Secondary Side Water Inventories of Steam Generators; 9. Reactor Decay Heat Function; 10. Pressurizer Water Level. l AHs-51,: Initial Cond Draft 5/17/74 The above list defines the minimum number of parameters to be addressed in the compliance section. There is no intent to exclude other parameters from this list. There are various approaches that might be employed in supporting a particular value for an initial condition. For example: 1. If results are not sensitive to a particular parameter, then selection of the initial condition limit for that parameter as that limit defined by the Technical Specifications is sufficient. 2. If results are sensitive to a particular parameter, then reduction of some or part of the measurement or calculational uncertainty on this parameter, relative to the Technical Specification value, - might be sufficient, given adequate justification. 3. There may also be operational limits, including alarm limits, that could form the basis for selecting a particular parameter , value. 4. The " design" value of the parameter plus an allowance for l control deadband (that is, excluding any allowance for calculational or measurement uncertainty) might be used. i 5. If a probability argument can be developed to support a particular parameter value, then the choice might be made on that basis if adequate statistics are presented. l 6. There may also be cases for which the most convenient way to select and justify a particular initial condition value is to modify a Technical Specification. In any event, the method for selection and justification of initial conditions should not be confused with modifying plant operation or design to mitigate effects of ATWS, although it should be recognized that defensible adjustment of certain initial conditions values is a viable method of controlling results of ATWS. ,, i ANS-5'l t- . Initial Conditi Drcft 5/17/74 The following discussion is given as an example of how one might provide justification for selection of an initial condition. This example is for selection of the moderator temperature coefficient of reactivity: Since insertion of control and shutdown reactivity is excluded during an ATWS event, unless a diverse shutdown system is included in the reactor protection system, other reactivity feedback mechanisms are important to the ATUS transient. In terms of immediate shutdown of the reactor the most important feed-back mechanism is the moderator reactivity coefficient. This parameter varies significantly throughout plant lifetime and the most adverse design value generally results in unrealistically adverse ATWS consequences. However, the most adverse design value will exist for only a small fraction of the plant lifetime (i.e., the few hours required to reach equilibrium Xenon). In addition, the moderator reactivity coefficient generally decreases during each fuel cycle and then increases to a value less than the most adverse design value at the start of each subsequent. cycle. A realistic method of developing the most adverse, yet nominally expected, moderator reactivity coefficient would be to provide a table or graph of the expected moderator reactivity coefficient as a function of plant lifetime (including any measured values that might be used to verify the analytical l calculations). The moderator coefficient would be chosen such that a more positive moderator would not exist for more than 5 percent of plant lifetime. t [ \\ ~~.}}