ML19312D347
| ML19312D347 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 01/23/1980 |
| From: | Denise R Office of Nuclear Reactor Regulation |
| To: | Sherwood G GENERAL ELECTRIC CO. |
| Shared Package | |
| ML19312D341 | List: |
| References | |
| NUDOCS 8003240248 | |
| Download: ML19312D347 (6) | |
Text
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NUCLEAR REGULATORY COMMISslON
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%d..v JAN 2 31980 General Electric Company Attn: Mr. Glen G. Sherwood Manager, Safety and Licensing
-175 Curtnur Avenue San Jose, California 95114 Gentiemen:
References:
1 NE00-24154 Volumes 1, 2, and 3. "One Dimensional Core Transient Model," October, 1978.
2.
Letter from R. J. Mattson to G. G. Sherwood, dated March 20, 1979.
3.
Letter from G. G. Sherwood to R. J. Mattson, dated April 4, 1979,
Subject:
Implementation of Transient Model (ODYN).
4.
Transcript of ACRS hearings held on March 19-20, 1979, Los Angeles, California.
5.
Letter from T. Ippolito (NRC) to D. Arnold (Iowa Electric Light & Power Co.) dated September 4, 1979.
The staff has completed review of all available information on the ODYN code (Reference 1) and, as stated in our letter'(Reference 2),found that ODYN
.provides acceptable best estimate calculation predictions of the core response i
to pressurization transients.
In your letter (Reference 1), you indicated that ODYN licensing basis calculations will be implemented upon receipt of a staff Safety Evaluation Report (SER) providing approval of all aspects of your ODYN submittal. Based on the available information, we cannot approve all aspects of the ODYN licensing basis as described in-Reference 1.
However, we
.l have come to a position on the ODYN licensing basis (including the interim l
required margin) and are proceeding to prepare an SER based on that position.
The purpose of this letter is to summarize our ODYN licensing position so that General Electric can proceed with ODYN analyses of the transients described in
'Chapter.15 of_ licensing application Safety Analysis Reports. This position is applicable to'all license applications including core reloads. The complete.
SER to be issued at a later date will provide detailed technical justificaticn for our position. The analyses for 4CPR must be performed in accordance with either approach.A or approach B which follow:
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a Mr. Glen.G. She od' JAN 2 3 b80 A.
ACPR' Calculations with Interim Penalty
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This approach is comprised of the three step calculation which follows:
1.
Perform ACPR calculations using the 00YN and SCAT codes for the transients (to be analyzed using the ODYN code) listed in Tables 2-1 and 2-2 of
' Reference 1, Volume 3, and using the input parameters in the manner pro-posed in pages 3-1 through 3-4 of the same reference. Use the scram speed as per technical specifications, use the Haling power shape, and use the power level corresponding to maximum plant capability (approximately 105%
of rated steam flow in most cases).
2.
Determine ICPR (operating initial critical power ratio) by adding ACPR calculated in step 1 above to the GETAB safety limit. Calculate JCPR/ICPR.
- 3. ' Determine the new value of ICPR by adding 0.044 to the value of ACPR/ICPR calculated in step 2 above.- Apply this margin in Chapter 15 analyses of the FSARs submitted for OLs, cps and reloads. The margin of 0.044 is obtained from consideration of uncertainties in components-listed in Table 3-3 of volume 3 of Reference 2. Enclosure 1 presents a sample calculation, B.
Statistical Aoproach for Reduction of Marcin Penalty General Electric (Reference 1) assessed the frabWlity of the ACPR during a limiting transient' exceeding.the 4CPR calcul".ed for i'? proposed licensing basis transient (NEDE-25154-P response to at.estion 4). Their study demonstrated that this probability, based on operating data over several fuel cycles from a group of plants, is very low. The key parameters in their study are scram speed, power level, pour distribution, and an estimate of ODYN uncertainties.
The proposed aoproach utilizes the conservatism inherent in the statistical deviation of the actual operating conditiors from the limiting conditions assumed for the first three parameters in. licensing basis calculations.to ecmpensate for pote.e:ial non-conservatisms from the ODYN uncertainties.
The staff has concluded that the use'of en1-of-cycle power distributions from multi-cycles for several reactors to obtaii credit for margin conservatisms relative to Haling power distribution is nat approprittc. There is no 2ss.irance that the end-of-cycle power distribution conservatisms obtained from operating reactor history are representative of the end-of-cycle conditions which will exist for a specific core. We have also concluded that scram speed data used in the GE statistical assessment must be proved applicaole to specific license and-reload applications. In order to taka credit for conservatism in the scram speed performance for reloads, the plant specific scram speed must be shown to be faster than the Technical-Specificitions speeds used in the safety
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'l Mr. Glen G. Sherwood JAN 2 31980 analysis with 955 reliability at 951 confidence level (Reference 5). Alternately, the scram speed. performance at the plant must be shown to be from the same or more tonservative population than that used in the GE probability study. For CP and OL, the scram speed distribution for the specific plant must be demonstrated consistent with those used in the statistical approach described below. Similar design and prototypic performance characteristics coupled with appropriate technical specifications on scram speed perfomance could provide acceptable evidence of the applicability of the Reference 1 data base.
Statistical convolution of the power measurement uncertrinties to take credit for full power operation at a power level value below that used in licensing calculations is acceptable to the staff. However, plant specific procedures to operate within the licensing limit must be taken into account in these calculations.
The code uncertainty penalty (0.044 in ACPR/ICPR) applied to the licensing calculations described in (A) does not account for unknown contributors.
Past experience has shown that additional margin in safety calculations is often needed to compensate for unknown non-conservatisms in licensing calcu-lations due to code errors or other factors. The ODYN prediction of three Peach Bottom transient tests and one KXM transient test demonstrated a 2 r.
uncertainty of approximately 37% of aCPR/ICPR at a 955 confidence level.
This was detemined' using XZ distribution. No credit was r' ven for measure-ment errors. This results in a 2e ACPR/ICPR uncertainty or 0.068 for a transient which degrades the CPR from an initial value of 1.30 to the limit of 1.06.
Since these tests represent a very limited data base, it is likely that the 2e uncertainty can be reduced significantly by the acquisition of additional test data for comparison to code predictions. Therefore, the magnitude of the code uncertainty used in the statistical convolution may be reduced to a value consistent with the 2c value of ACPR/ICPR uncertainty at a 95% confidence level when such a reduction can be justified by additional trt.nsient test data.
In sumary, the staff has concluded that the Reference 1 statistical approach to compensate for potential non-conservatisms from the ODYN uncertainties is acceptable with the following limitations.
-(1) Power discribution conservatisms should be excluded.
(2) Scram speed conservatisms must be demonstrated to be applicable to plant specific cases.
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Mr. Glen G. Sherwood
-4 JAN 2 31980 (J) Calculations should be performed using a code uncertainty value which is 37% of the ACPR/ICPR for a' limiting transient to account for cod 2 uncertainties, including unknown contributors (e.g.,
code errors), based on the approved. transient test data base in Reference 1.
This results in a value of + 0.068 in ACPR/ICPR uncertainty for a transient extending over a CPR range of 1.30 to 1.06.
(4) The transient test data base must be expanded and submitted for staff review to justify any reduction in the value of ODYN Code uncertainty (2e value of ACPR/ICPR at a 95% confidence level).
(5) A new statistical analysis confo[ ming with these limitations must be provided.
- C.
Pressure Calculations Calculations should be performed for the MSIV Closure event with position switch scram failure using the values listed in Enclosure 2 and conbining statistically the uncertainty (2e) frem each component to arrive at the overall code uncertainty in pressure calculation. Add this oncertainty to the ODYN calculated pressure for this event in OLs,. cps.and reloads.
- If General Electric can-demonstrate that this uncertainty is very small (e.g., by a factor of 10 or more) relative to the uncertainty in detemining ASME Vessel Overpressure limit, no addition of uncertainty to the calcu-lations of pressure is needed.
t D.
Other Limitations 1.
The ODYN,%de is limited to analyses where fuel temperatures are less than 1500'K (approximately 2240*F).
2.
Complete listing of the values of input variables should be included with each submittal.
3.
A minimum of eight nodes should be'used to represent the steam line.
However, the maximum length of any node should not be more than 100 ft.
We trust that the above sunnary of the staff position on ODYN will suffice e
L to-permit you to proceed with ODYN licensing calculations until our SER can be completed.
Sincerely
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Richa-d P. Denise, Acting Assistant Director for Reactor Safety Division of Systems Safety ff0! jp w
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.o Sample ACPR Calculations with Interim Penalty
' Step 1 Assume that ACPR calculations using the ODYN licensing basis have been performed and the result is aCPR =.14 g
where the subscript c refers to calculations.
Steo 2 Calculate ICPR based on the calculations.
ICPR = 1.06 +.14 = 1.20 g
where the GETAB limit is 1.06.
ACPR*
14 77pp = p yg =.117 C
Steo 3 ACPR '"
=.117 +.044 =.lil ICPRnew aCPRnew ICPRnew
.16' acPRnew " acPR aCPR = 733f J4 = A92 g
e ICPRc
.06 +.19 = 1.25 ICPR
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. Enclosure-2 List of Parameters To 8e Used in Code Uncertainty Analysis And Their Values Limiting Values To Be Used in Uncertainty Calculation I.
Reector Core Model (1) Nuclear Model (a) Void Coefficient my i 115 (b) Doppler Coefficient a d 1105 (c) Scram Reactivity r i 10%
a (2) Thermal-Hydraulics Model (a) Drift Flux Parameters Co 1,3%
Vg i 20%
(b) Subcooled Void Model n = 0.5 n = 2.0 II.
Recirculation System Model (1) System Inertia L/A + 200%
- 0%
(2) Jet Pump Losses
'K - 20%
+ 0%
(3) Core Pressure Drop AP + 1.5 psi
- O psi (4) Separator L/A L/A + 0%
- 200%
-III. Steam Line Model (1) Pressure Loss Coefficient g M%
.- 20%
(2). Specific Heat Ratio Y + 0.10
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