ML19312E444
| ML19312E444 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 04/03/1980 |
| From: | Varga S Office of Nuclear Reactor Regulation |
| To: | Atomic Safety and Licensing Board Panel |
| Shared Package | |
| ML19312E413 | List: |
| References | |
| TASK-AS, TASK-BN-79-18 BN--79-18, BN-79-18, NUDOCS 8006040410 | |
| Download: ML19312E444 (1) | |
Text
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E WASHINGTON D. C. 20555 k..v APR 0 31980 MEMORANDUM FOR: All Boards Listed Below FROM:
Steven A. Varga, Acting Assistant Director for Light Water Reactors, Division of Project Management
SUBJECT:
ADDITIONAL INFORMATION - ANALYSIS OF SINGLE ROD DROP EVENT -
WESTINGHOUSE PLANTS (BN-79-18)
On May 18, 1979, the Atomic Safety and Licensing Appeal Board for North ' Anna was provided information concerning an analysis of the single rod drop event relative to Westinghouse three-loop plants.
Enclosed is a memorandum from Roger Mattson, dated February 20, 1980, which provides additional information on this subject.
It should be noted that the staff has accepted a new interim Westinghouse position for plants which have the negative flux-rate trip circuit.
In accordance with the recomendation contained in the enclosed memorandum, this follow-up information is being provided to Boards that have cognizance over all. LWR-assigned Westinghouse plants (i.e., two-loop, three-loop, and four-loop plants).
stev a
. Jarga, ti g Assistant Director for Light Water (y actors Division of Project anagement
Enclosure:
As Stated Plants For BN-79-18 Braidwood 1 & 2 Marble Hill 1 & 2 Byion 1 & 2 McGuire 1 & 2 Comanche Peak 1 & 2 Midland 1 & 2 Diablo Canyon 1 & 2 North Anna 2 FW3 2-Seabrook 1 & 2 FNP l-8 South Texas 1 & 2 Ft. Calhoun 2 Sterling 1 Harris 1-4 Summer 1 Haven 1 & 2 Sundesert 1 & 2 Jamesport 1 & 2 Wolf Creek 800 esse.d/O
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!e*ntr R4111iams ELicitra JLee BNFile MEMORANDUM FOR: Steve scott, Assistant to the Director, Division of Technical Information and Document Control FROM:
Steven A. Varga, Acting Assistant Director for Light Water Reactors Division of Project Management
SUBJECT:
BOARD NOTIFICATION - ANALYSIS OF SINGLE ROD DROP EVENT -
WESTINGHOUSEPLANTS(BN-79-18)
Please provide the enclosed documents to the Board Notification Service Lists for the following plants:
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Braidwood 1 & 2 Marble Hill 1 & 2 Byron 1 & 2 McGuire 1 & 2 Comanche Peak 1 & 2 Midland 1 & 2 Diablo Canyon 1 & 2 North Anna 2 Farley 2 Seabrook 1 & 2 FNP l-8 South Texan 1 & 2 Ft. Calhoun 2 Sterling 1 Harris 1-4 Summer 1
. Haven 1 & 2 Sundesert 1 & 2 Jamesport 1 & 2 Wolf Creek Steven A. Yarga, Acting Assistant Director' for Light Water Reactors l
Division of Project Management
Enclosures:
As Stated
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H. Denton W. Gamill E. Case B. Grimes D. Eisenhut J. Stoiz i
D. Ross R. Baer D. Vassallo
- 0. Parr
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R. DeYoung
.L. Rubenstein V. Moore E. Christenbury IE (7)
D. Fieno L. Nichols g
R. Mattson 3
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,i APR 0 31980 MEMDRANDUM FOR: All Boards Listed Below FROM:
Steven A. Varga Acting Assistant Director for Light Water Reactors, Division of Pmject Management
SUBJECT:
ADDITIONAL INFORMATION - ANALYSIS OF SINGLE ROD DROP EVENT -
WESTINGHOUSEPLANTS(BN-79-18)
On May 18, 1979, the Atomic Safety and Licensing Appeal Board for North Anna j
was provided information concerning an analysts of the single rod drop event relative to Westinghouse three-loop plants.
Enclosed is a memorandum from Roger Mattson, dated February 20, 1980, which pmvides additional information i
on this subject.
It should La noted that the staff has accepted a new interim Westinghouse position for plants which have the negative flux-rate trip circuit.
In accordance with the recomendation contained in the enclosed memorandum, this follow-up information is being provided to Boards that have cognizance over all LWR-assigned Westinghouse plants (i.e., two-loop, three-loop, and four-loop plants).
4 Steven A. Varga, Acting Assistant Director for Light Water Reactors Division of Project Management
Enclosure:
As Stated Plants For BN-79-18' Braidwood 1 & 2' Marble Hilf 1 & 2 Byron 1 & 2 McGuire 1 & 2 Comanche Peak 1 & 2 Midland 1 & 2 Diablo Canyon 1 & 2 North Anna 2 Farley 2 Seabrook 1 & 2 FNP l-8 South Texas 1 & 2 Ft. Calhoun 2 Sterling 1 Harris 1-4 Summer 1 Haven 1 & 2 Sundesert 1 & 2 Jamesport 1 & 2 Wolf Creek emca )...
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FEB 2 01980 MEMORANDU!i FOR:
Steven A. Varga, Acting Assistant Director for Light Water Reactors, DPM FROM:
Roger J. Mattson, Director Division of Systems Safety
SUBJECT:
WESTINGHOUSE R00 DROP ANALYSIS You requested (Ref.1) that we provide you with an assessment of the information provided in the November 15, 1979 Nestinghouse letter (Ref.
- 2) to determine whether Boards should be notified. He would first like to briefly review this matter. Westinghouse (Ref. 3) alerted us in March of 1979 of a Part 21 notification concerning the analysis of the single rod drop event. Fe subsequently met with Westinghouse on April 12, 1979 to discuss this matter..(Ref. 4). He then issued a Board notifi-cation request (Ref. 5).
This Board notification request was applicable to Westinghouse 3-loop plants which have the negative flux-rate trip circuit.
Nestinghouse proposed, and we found acceptable, an interim position wherein the affected plants would change the setpoint and time constant in the negative flux-rate trip circuit to ensure a reactor trip when a rod drops. Westinghouse recommended that 2-loop and 4-loop plants which have this negative flux-rate trip circuit also makes these changes. Me also found this recommendation to be acceptable.
In addition, Westinghouse cave us a commitment for a topical report to be provided in about six months (October 1979).
Westinghouse later reported to us by telephone and letter (Ref. 2) that analyses being performed by them for submittal in the topical report indicated that 2-loop and 4-loop plants that have the negative flux-rate trip circuit have non-conservatisms in the analysis, and single failures in the rod controller circuit, that may result in a response similar to that previously identified for 3-loop plants. This response is a potentially larger power overshoot (and possibly DNB) than previously analyzed in the SARs for rod drops. We met with Westinchouse to discuss this new information on November 19,1979 (Ref. 6).
At the meeting Hestinghouse reviewed the work they had done and recom-mended an interim procedural position for 2-loop, 3-loop, and 4-loop plants which have the negative flux-rate trip circuit as follows:
Contact:
Daniel Fieno, x29445
Steven A. Varga FE3 2 01330 (a) The plant may operate in manual control from 0 to 100 power with no changes in the current rod insertion limits.
(b) The plant may operate in automatic control from 0 to 90% power with no changes in the current rod insertion limits; above 90",
power the D control rod bank would have to be withdrav;n to 215 steps or greater (220 steps is full-out; one step is 5/8 inches) when in automatic rod control, or the plant placed in manual control.
The analyses leading to this interim procedure assumed no plant trip when single or multiple rods drop, and that the automatic rod controller functioned to return the plant to power.
Based on current plant experience, however, the plant should trip under these rod drop conditions.
Some benefit still accrues to the plant when it is above 90% power and in the automatic rod control mode in that rods can be inserted for xenon or to ainimize the effects of load rejection transients. Westinghouse also stated that these interim procedures would apply both to plants that have a negative flux rate trip setpoint of 5% and a time constant of 2 seconds and to those plants that have changed the setpoint to 35 and the time constant to 1 second. Thus, Westinghouse did not recommend any further changes to these quantities.
We found that this interim Westinghouse position is acceptable on the basis that the larger than previously analyzed power overshoots would be eliminated. We will review this matter further for the Westinghouse,
topical report, now scheduled to be submitted in June 1980.
Our recommendation is that you should proceed with Board notification for affected Hestinghouse 2-loop, 3-loop, and 4-loop plants which have the negative flux-rate trip circuit.
The 2-loop and 4-loop plants were not included in the previous Board notification request (Ref. 5). Appli-cable Boards should be informed of this new information and interim position concerning the 3-loop plants. Boards should also be notified of our acceptance of the new interim Westinghouse position.
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R' er J. Mattson, Director
'/b" Division of Systems Safety Office of Nuclear Reactor Regulation cc:
See next page
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Steven A. Varga :. ;.,,,,,.,
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cc:
H. Denton L. Nichols E. Case W. Gammill D. Eisenhut B. Grimes V. Stello J. Stolz D. Ross
- 0. Parr D. Vassallo R. Baer R. DeYoung L. Rubenstein V. Moore E. Christenbury P. Check K. Kniel D. Fienc
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References 1.
Memorandum for Roger J. Mattson from Steven A. Varga, " Westinghouse Rod Drop Anal 3 is," Feb. 6, 1980.
2.
Letter to V. Stello of NRC from T. M. Anderson of Westinghouse, "RoJ
) Analysis," Nov. 15, 1979.
3.
Letter to John G. Davis of NRC from T. M. Anderson of Westinghouse, (untitled letter on the rod drop analysis), March 30, 1979.
4.
Memorandum for K. Kniel from D. Fieno, "Meetina with Westinghouse on the Part 21 Notification Concerning the Single Rod Drop Analysis,"
April 16,1979.
5.
Memorandum for D. B. Vassallo from R. L. Tedesco, " Board Notification -
Analysis of Single Rod Drop Event - Westinghouse Plants," April 23, 1979.
6.
Meeting summary prepared by Leon Engle, " Summary of November 19, 1979 Meeting with Westinghouse and Licensees Regarding Dropped Rod Protection," January 13, 1980 i
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Hovember 15, 1979 hS-TMA-2162
[.. l Ref: NS-TMA-2063, I 3 )*/
March 30,1979 I
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'tr. V. Stello
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Office of Inspection and Enforcement
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Jircctor U. S. Nuclear Regulatory Commission
.,3 1717 H Street Washington, D. C.
20555
Subject:
Rod Drop Analysis
Dear Mr. Stello:
This letter confirms a telephone notification by Westinghouse made onThe n 15, 1979.
November plants and 10CFR50.55e for plants under construction.
On March 28, 1979 a previous notification (reference) under 10CFR50.59 was made by Westinghouse which identified the potential for certain single.
dropped rod events leading to calculated CNS ratios lower than reported to A com:aitment was made the NRC for certain classes of Westinchause olants.
by Westinghouse at that time to review the SAR dropped rod accident analysis A meeting methodology and to revise Technical Specifications as recuired.
was subsequently held with the NRC on April 12 to discuss the status of our evaluations at the time and a further commitment was made to keep the NRCAs a result of t x
informed as to the results of an ongoing investigation.
involve
.. _.--ongoing review, we have determined that this original concern mayIn addition, a concern relative additional classes of Westinghouse plants.
This results from three to multiple dropped rod events has been identified.
newly identified potential problem areas.
- The assumption.of ~a single failure in the rod controller circuits of two and four loop plants may result in a response similar to that previously identi-The error allowances for the Positive and Mega-fied for three loop plants.
tive High Flux Rate Trip protection system as specified in the TechnicalThe pow Specifications may be non-conservative. insertion profiles for dropped rod se The following Negative Rate Trip Setpoints may also be non-conservative.
paragraphs further elaborate on these concerns.
1 I
791 23Q em e
Mr. Y. S,tello November 15, 1979 fS-TMA-2162
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A review'of all rod control systems was made to define failure modes with respect to postulating a single failure in the Rod Control System, t-The review shows that for three loop plants, a single failure in the Pro-tection System is most limiting.
The two and four loop plant review shows that a single failure in the nuclear power auctioneering unit of the rod control system may result in more limiting DNB ratios than previously
?,
reported.
Therefore, the SAR analysis may not represent the most limit-hw ing assumption for credible single failure.
When the assumption of a single failure in the rod control system is made, the two and four loop I
plant responses to dropped rods may be similar to the three loop con-cerns discussed in the referenced March 28 notification.
The second concern involves a potential reduction in conservatism in the error allowances assumed in the analysis for the Power Range Neutron
. Flux High Negative Rate.
The value currently listed in the Technical Specifications is.5% of Rated Thermal Power.
This v;1ue assumed that the differentiation of the NIS power signal by the circuitry would eliminate all steady state errors in the circuit before the differen-tiation; therefore, only precision and accuracy errors after the dif-ferentiation were considered.
This assumption is now believed to be non-conservative since errors associated with precision (hysterisis, repeatability, etc.) may not be entirely eliminated by differentiator circuit. When these potential additional errors are factored into the analysis, a reactor trip may not occur in some cases previously assumed.
The third concern involves a potential reduction in conservatism in the method utilized to generate power distributions and rod worths for dropped rod events.
New analyses have been performed using a more conservative reactivity feedback model and the results indicate that certain multiple rod drops may not trip the reactor as previously assumed.
These concerns are basically a result of application of the single failure criteria in conjunction with conservative methodology.
Past experience shows that dropped rod events have always resulted in a reactor trip for a Westinghouse plant from the present Negative Flux Rate Trip logic and setpoint.
The attachment-identifies the affected Westinghouse plants.
This in-formation has been communicated to the utility owners of these affected plants. Westinghouse recommends a meeting with appropriate NRC Staff
. members (and affected utilities) to review these findings and determine
' an appropriate course of action.
If you require further information, please call D. W. Call of my staff.
I V
truly you,rs, o
T. M. Anderson, Manager
/bek Attachment Nuclear Safety Department I
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