ML19209B835
| ML19209B835 | |
| Person / Time | |
|---|---|
| Issue date: | 07/31/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19209B831 | List: |
| References | |
| NUDOCS 7910110019 | |
| Download: ML19209B835 (7) | |
Text
..__
Evaluation of Babcock and Wilcox Licensing Topical Report BAW-10122, "Nonnal Operating Controls" Report No.: BAW-10122 Report
Title:
Nonaal Operating Controls Report Dat=: July 1978 Oi Jnating Organization: Babcock & Wilcox Re iered By: Core Performance Branch /W. Brooks The Power Generatien Group of Babccck and Wildox has submitted licensing topical report BAW-10122 entitled, "Nonnal Operating Centrols" for our review. This report describes the techniques and procedures used to establish core related limiting conditions of operation (LCOs).
It is one of a series of topical reports which have been submitted by Babccck and Wilccx in order to provide the staff with generic information en the nuclear design of B&W reactors and to facilitate the review of such designs.
1.
Sumary of Report Topical Report BAW-10122 describes the criteria and methods used by Babcock and Wilcox to establish the limits for nornal reactor core operation - the limiting conditions for operaticn (LCOs). Core operating limits are established which assure that transients or accidents which are initiated from the limiting conditions do not violate apprcpriate acceptable limits. As a practical matter, the most restrictive cce-ating limits on pcwer distributions are f.urreiltly imposed by the requirements of the loss of coolant accident as expressed in A:pendix K of 10 CR 50.
Limits on control red positions are imcosed by the necessity of having an adequate shutdcwn margin and of limiting the reactivity worth of a potential ejected rod in additien to the power distribution restriction.
1 0 00 791o,1oolg
The calculational methods employed in the analysis are briefly described.
They have been fully described in other topical reports in the series.
Most of the calcolations are three-dimensional and are performed with the P0007 and/or FLAME 3 codes. Total rod worths and detailed radial power distributions are performed with the PDG07 ccde in two dimensiens.
The centrol philosophy of the bleed-and-feed reactor system is described and differences between bleed-and-feed and rodded plants pointed out.
The core parameters which are investigated in the analysis of operating limits are listed and the analyses performed are described.
In general, the parameter is varied over a range larger than is expected and the effect on the core operating condition determined.
For the LOCA limited heat generation rates the effects of five operating parameters are considered - axial offset, quadrant pcwer tilt, control rod position, transient xenen, and fuel depletien. The manner in which each of these parameters affects the core peaking is described. The un-certainties applied to the calculated results are listed and typical values given. The manner in which the varicus limits are combined to obtain final operating limits is also described.
The procedures folicwed in determining the rod insertien limits relative to the shutdown margin requirements are described. Sciefly, the reactivity increase in going frem the operating pcwer to zero power is calculated and one percent reactivity change is added to achieve the required shutdcwn margin. This is the amcunt of reactivity which must be held in control rods at the operating pcwer. The fraction of rods which must be withdrawn to obtain this amcunt of reactivity then determines the insertion limi t.
11'C 064
_3-Another restraint on the amount of reactivity that may be held in control rods is the worth of a rod that could possibly be ejected from the core.
In general this worth is larger for more insertec rod worth. Acceptable ejected rod worths are determined from the analysis of the ejected rod event and are currently one percent reactivity change at zero power and 0.65 percent reactivity change at full power, rarying linearly at inter-mediate powers.
In summary there are three restraints on the amount of inserted rod worth; LOCA-limited power peaking, shutdown margin requirements, and ejected rod worths. The final insertion limits are obtained by combining the most limiting portions of the three insertion limit curves.
In general at low power ejected rod worth considerations will be limiting and at high power the limit will be established by the LOCA.
The uncertainties to be applied to the operating limits are described -
both calculational and measurement uncertainties are considered. Mea-surements of quadrant tilt and axial offset are performed with the incere monitoring system. The measurement uncertainties are described and typical values are presented.
The final step in the process of establishing operating limits is the con-version of the ccmcuted limits to alarm settings. The power decendence of the limits is represented by a series of straight lin'e segments and entered into the alarm unit of the plant cceputer system. Audible and visual alarms are provided as well as an alarm message at the ccccuter censole. The i1'0 065
algorithms used to calculate the various limited parameters are given.
The calculated values are comoared to the error-corrected limits and appropriate alarms sounded.
Finally, an example of the normal coerating limits for the standard B&W plant, Babcock-205 cycle 1 is oresented. An appendix to the report de-scribes the differences between the current techniques and those used for curre.it generation plants with 177 fuel assemblies. The chief difference is in the use of axial imbalance rather than offset to characterize the axial power distribution where imbalance is the product of offset and the fraction of full power in the core.
2.
Summary of Evaluation We have reviewed the description of methods and techniques used for obtaining normal operating limits gi.en in topical report BAW-10122. The following comr.ents summarize our evaluation.
The calculational methods and procedures employed for obtaining the infor-matien on pcwer distributiens, controi rod worths, and core reactivity balances have been described in other topical report supplied by Sabccck anc Wilcox. These reoorts have been reviewed and approved and their use for establishing limiting ccnditiens of operatien is acceptable.
The choice of parameters to be considered for establishing LOCA pcwer dis-tribution limits is state-of-the-art and is acceptable. The use of axial offset to characterize the axial pcwer distributien s an industry-wide practice 4
11'O 066
. and is acceptable. Allowance is made in the power distribution limits for a quadrant tilt of the order of five percant. This is conservative
~
since normally the core will have negligible tilt. A further conservatism in the analysis is the fact that when the limit for a particular parmeter is derived all other parameters are assumed to be at their respective limits.
The uncertainties applied to the determination of pcwer peaking 3re state-of-the-art and the values for these uncertainties have been shown to be bounding. On the basis of the stated conservati,sms and the use of aporcariate uncertainties we conclude that the procedure and techniques are used to establish LOCA related limiting operating carameters are acceptable.
Calculations of the number of control rods that must be withdrawn in order t) assure that the shutdown margin is adequate have been reviewed. The assilable rod worth is first corrected for the assumed stuck rod and for loss of reactivity due to burnout and the corrected value is reduced by ten percent to account for calculational uncertainty. Com0arisons to measured values have shown that this is a conservative value of the.. certainty. The reactivity defect is calculated and a flux redistribution correction added.
The corrected available rod worth and the corrected react'vity defect are then compared to obtain the rod withdrawal limits. This is an acceptable pro-cedure.
The pcwer dependent values of the ejected rod worth limiting values are reduced by fif teen percent to account for calculational uncertainty in the red worth. Ccmoarisens between calculated and measured ejected red worths have shown that this is a censervative uncertainty value. The li'0 067
,. comparison of calculated ejected rod worth to the error-corrected limit establisher the withdrawal limit. This is an acceptable procedure.
The use of the most limiting of the withdrawal curves at each power level is an acceptahle precedure which is industrywide practice.
Measursment uncertainties are applied in addition to the calculated ones described above. The incare monitoring system and rod position indication system meacurement uncertainties are described in sufficient detail to permit the conclusion that proper techniques and methods are used in their evaluation. Algorithms are presented for certain portions of the errors and typical values given for other portions. We conclude that an acceptab'= discursion of measurement errors has been given.
The calculational and measurement errors are ccmbined and the limiting conditions of operation (Technical Specification limits' are adjusted by the amount of the combined error. It is these error-adjusted limits to which core parameters are compared in orc r to give alarms. This is an acceptable procedure.
3.
Evaluation Procedure The review of topical report 3AW-10122 has been conducted within the guidelines provided by the Standard Review Plan, Section 4.3.
Sufficient information is included to permit a kncwledgeable person to ccnclude 1kf
~
.. that the methods and techniques employed are state-of-the-art and are acceptable. The parameters chosen to characterize the core power dis-tribution are those widely used in the industry and are acceptable.
The calculational and measurement uncertainties have been shown to be conservative and are appropriately applied.
a.
Regulatory Position Based en our review of licensing topical report BAW-10122 we conclude that it is acceptable for referencing in licensing actions by Sabcock ar,d Wilcox with respect to the establishment of limiting conditions of operation for the parameters discussea above.
11'O O69
. - - -