ML19312D461
| ML19312D461 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 02/28/1980 |
| From: | Ziemann D Office of Nuclear Reactor Regulation |
| To: | Linder F DAIRYLAND POWER COOPERATIVE |
| References | |
| TASK-15-13, TASK-RR NUDOCS 8003240441 | |
| Download: ML19312D461 (5) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION o.k g-WASHINGTON, D. C. 20555
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-t February 28, 1980 Docket No. 50-409-
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'Mr. Frank Linder General Manager b;.
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-Dairyland Power Cooperative 2f15 East Avenue South La Crosse, Wisconsin 54601 f'
Oear Mr. Linder:
SUBJECT:
LACBWRR00DROPPROBABILITYSTUDY(NES-81A0033)
We are continuing our review of the document titled "LACBWR Rod Drop Probability Study," (NES-81A003), transmitted by your letter of March 29, 1979, and have detemined that additional infomation described in the enclosure to this' letter is needed. We request your response within 60 days of-your receipt of this letter.
- incerely,
.Y 3.i i,
Li w Dennis L. Zieman Chief Operating Reactors Branch #2 Division of Operating Reactors
Enclosure:
Request for Additional Infomation
.a cc w/ enclosure:
See next page n
u;- a
.'Mr2 Frank Linder-
' -2 February 28, 1980 Jcc 'w/ enclosure:.
Fritz Schubert, Esquire Director, Technical Assessment Staff Attorney-Division
. Dairyland Power Cooperative.
-Office of Radiation Programs 12615 East Avenue South (AW-459)
- La Crosse,-Wisconsin 54601 U. S. Environmental Protection Agency Crystal Hall #2 O. S. Heistand, J r., Esquire Morgan, Lewis & Bockius Arlington, Virginia 20460 1800 M Street,-N. W.
- Washington, D. C.
20036 U. S. Environmental Protection Agency Mr. R. E. Shimshak Federal Activities Branch La Crosse Boiling Water Reactor Region V Office Dairyland Power Cooperative ATTN: EIS COORDINATOR P. O. Box 135 230 South Dearborn Street Genoa, Wisconsin 54632 Chicago, Illinois 60604 Coulee Region Energy Coalition Charles Bechhoefer, Esq., Chairman ATTN: George R. Nygaard Atomic Safety and Licensing Board P. O. Box 1583 U. S. Nuclear Regulatory Comission La Crosse, Wisconsin 54601 Washington, D. C.
20555 La Crosse Public Library Dr. George C. Anderson 800 Main Street Department of Oceanography -
La Crosse, Wisconsin 54601 University of Washington Seattle, Washington 98195 Mrs. Ellen Sabelko Society Against Nuclear Energy Mr. Ralph S. Decker 949 Cameron Trail Route 4, dox 193D Eau Claire, Wisconsin 54701 Cambridge, Maryland 21613 Town Chairman Dr. Lawrence R. Quarles
- Town of Genoa Kendal at Lonpood, Apt. 51 Route 1 Kenneth Square, Pennsylvania 19348
. Genoa, Wisconsin 54632 Chairman, Public Service Comission Thomas S. Moore, Esq.
of Wisconsin Atomic Safety and Licensing Appeal Board Hill Farms State Office Building U. S. Nuclear Regulatory Comission Madison, Wisconsin 53702 Washington, D. C.
20555
' Alan S. Rosenthal,Esq., Chairman Atomic Safety and Licensing Appeal Board
.U. S. Nuclear Regulatory Comission Kashington, D. C.
20555 I
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I
e 1sj REQUEST FOR ADDITIONAL INFORMATION NES-81A003 (LACBWR)-
Our< understand 1ng of the context in which this report is written follows:
A calculation using a' three-dimensional kinetics code is used'to determine a value for dropped rod worth which will produce peak enthalpy of 280 cal /gm in. the LACBWR reactor fuel. _Once this value has been detemined the nomal rod withdrawal sequence-is followed and potential dropped rod worths are calculated. These calculations show that it is not possible to achieve the critical rod worth until the core is at essentially full power.
The implication here is that a control rad drop accident, RDA, exceeding 280 cal /gm is possible without any errors in the rod withdrawal sequence having been made during operation. Please provide responses to the
.following:
1.
Comment on our understanding of the situation.
Provide corrections or. explanations where appropriate.
- 2.. A.
What conditions were assumed for the calculation of the rod worth required for 280 cals/gm?
B.
Was the initial power assumed to be in the 80-100 percent full power range?
C.
Was moderator feedback included in the calculation?
D.
Was the dropped rod the central rod or was an off center one assumed?
E.
If both were calculated does-it make any difference?
3.-
If the acceptance criterion was reduced from 280 cal /gm to 200 cal /gm
.would this make any significant difference in the conclusions of this study?
.4.
A.
If rod withdrawal errors (f.e., withdrawal of an out-of-sequence rod) were not considered in the startup and power escalation phases of operation, what would be the effect of including such errors?
' B.
Could an RDS c.. ang 280 cal /gm result?
C.
If so,.are the probabilities, e.g., the nondetection probability, quoted in this study still applicable?
,-e
'C,
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- 5. ' A. ~ : Has Lthe effect 'of normal power level changes been included?
B.' During such changes, rods-might be moved in larget increments
-than were considered.. Discuss such changes with respect to their effect 'on-the statistics.
6."
Provide' a brief description of the methods used to obtain rod L
- worths and parameters for input to the BWKIN code.
- 7. Coninent' on' the following probability an'alysis bf the staff, The LACBWR rod drop probabilities in Table 1 appear to have been
~7 incorrectly calculated and'may be greater than the criterion.of 10 per reactor year.
From the event definitions in Section 4.2 and the multiplication of the probabilities of rod disconnection (RD) and non-detection (ND) in -Table 1, it is evident that " rod disconnection" is the event that
.a. rod disconnnects,' whether or not -it is detected. However, the event whose probability is estimated in Section 5.1 appears to be " rod disconnectio'n with non-detection" (RDND). ~ The report bases its estimate of the'. probability. of RDND on an observed value of zero occurrences of RDND ("no disconnects which have not been detected")
and makes no apparent use of e in GE plants. Based on~ 2.x 10gght disconnects which have been detected withdrawals from Ref. 3, the report calculates an upper 95% confidence limit-(incorrectly beferred to as a probability) on the probability of RDND of 1.5 x 10- per withdrawal.
It is certainly possible to estimate 'the LACBWR rod drop probability based on a direct estimate of the. probability-of RDND rather than by multiplying the probabilities of RD and ND, as was done in Table 1.
~ However, if this approach is taken, then the factor of 10-8 for the probabiitty of ND in Table'1 must be omitted. The resultant estimate of the LACBWR rod drop probability is 5 x 10-7, a factor of 5 larger than the safety criterion.
The' data quoted in Section 5.1 can be.used to estimate the probability
.of RD.'5 From Ref. 3, the GE plants have experienced 8 disconnects in -
- 2 x 10 w thdrawals :This yields a maximum likelihood esgimate of 4.0 x 10- and an upper 95% confidence ~1imit of ~ 7.2 x 10- for the L-l
. probability of;RD.
(Note that these results are consiste
- LACBWR experience.
If the probability of RD is 4.0'x 10 gt with the
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probability of the observed event of no disconnects in 2.5 x 10g the
, the L
_withdrawalsis.37.)-
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Q JIf we use maximum likelihood and the GE data from Ref 3 to estimate the probabilgty of RD..then the estimate of.1.5 x 10-5 must be replaced Furthemore, the estimate 'of 10-8 for the by-4.0 x 10. in Table 1.
probability of ND may be too'small. From Section 5.3, this estimate is calculated by assuming that there are 8 independen
- opportunities, each with a _. failure probability of 10 y detection.
However, if ND is a common cause failure, so that the fajlures are dependent, then the probability ofiND may. be as large as -10. Thu
'the estimated probability gf'LACBWR may be as ~ 1arge as 1.3 x 10 y, somewhat larger than the 10- safety criterion.
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