ML20212A425
| ML20212A425 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 02/23/1987 |
| From: | Whittier G Maine Yankee |
| To: | Thadani A Office of Nuclear Reactor Regulation |
| References | |
| 8449L-GDW, GDW-87-31, MN-87-15, NUDOCS 8703030350 | |
| Download: ML20212A425 (11) | |
Text
4 MAIRE HARHEE MGMICPOWERCOMPARUe
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(207) 623-3521 e
February 23, 1987 HN-87-15 GDH-87-31 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Hashington, D.C.
20555 Attention: Mr. Ashok C. Thadani, Director PHR Project Directorate #8 Division of Licensing
Reference:
(a) License No. DPR-36 (Docket No. 50-309)
(b) HYAPCo Letter to USNRC dated November 10, 1986 (HN-86-141)
(c) USNRC Letter to HYAPCo dated January 6, 1987-ECCS Evaluation Model Hodifications Related to Axial Power Shape Issue, Phase I (d) HYAPCo Letter to USNRC dated January 12, 1987 (HN-87-04)
Proposed Change #128 - Cycle 10 Technical Specifications
Subject:
Maine Yankee LOCA Analysis Gentlemen:
Maine Yankee submitted justification for a revised delta P injection penalty for the reflood phase for LOCA analysis in Reference (b).
The method which would be used to determine the limiting axial power shapes for the analysis was also described in Reference (b). Your staff reviewed the proposed revisions and found them " acceptable and in compliance with Appendix K to 10 CFR Part 50", Reference (c).
The approach and results of the break spectrum analysis for the revised LOCA analysis method described above are provided in the enclosure.
Included is the identification and justification for the limiting spectrum chosen for analyses for future reloads as required by Reference (c). The approach and results are consistent with those described to Mr. N. Lauben and Mr. R. Jones of your staff during a conference call with members of Yankee Nuclear Services Division's staff on January 9, 1987.
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M AINE YANKEE ATOMIC POW ER COMPANV United. States Nuclear Regulatory Commission Page Two MN-87-15 The results of the analysis demonstrate that the limiting break size for axial power shapes with peaks at 52% and 65% elevations is 0.8G (a guillotine break with flow area 80% of twice the cold leg flow area). The limiting break size shifts for peaks at 731 and 85% elevations to 1.0S (a pipe crack with flow area of twice the cold leg flow area).
He are currently applying the revised method 31ogy to Cycle 10 using the limiting break sizes identified above. This analysis will result in revised LOCA limits similar to that conceptualized in Figure 1 of the enclosure. He plan to submit a proposed Technical Specification change for these limits in late February in accordance with Reference (d) and subsequent discussions with your staff.
If you have any questions, please do not hesitate to call.
Very truly yours, MAINE YANKEE ATOMIC P0HER COMPANY kbW G. D. Whittier, Manager Nuclear Engineering and Licensing GDH/hbg Enclosure cc: Mr. Richard H. Vallmer Mr. Pat Sears Mr. Cornelius F. Holden 8449L-GDH
MAINE YANKEE ATOMIC POWER COMPANY Enclosure MN-87-15 Page 1 of_9 BREAK SPECTRUM ANALYSIS FOR REVISED MAINE YANKEE LOCA METHODOLOGY 1.
BACKGROUND Large break LOCA calculations for Maine Yankee were performed for Cycle 5 through Cycle 9 using YAEC's.NREM based generic PHR ECCS Evaluation Model (Reference 1). The basis for selecting the most limiting break was-the complete break spectrum analysis done for Cycle 5.
For Cycle 10 and subsequent analyses, this model has been modified to include (1) an improved ECCS-steam interaction model and (2) a more complete spectrum of possible axial power shapes than that previously analyzed. These model improvements require a detailed examination of the Cycle 5 break spectrum analysis in order to determine if the limiting break remains the same.
This document summarizes the calculations approach followed in performing the break spectrum examination and presents a summary of the results.
First, a brief description of the two model modifications is presented.
2.
MODEL MODIFICATIONS The following revisions to the NY LOCA methodology were submitted to the NRC in References 2 and 3.
The NRC staff has issued a Safety Evaluation Report (Reference 4) in which these modifications were judged as acceptable and in compliance with Appendix K of 10CFR50.
ECCS Water - Steam Interaction Model In the YAEC reflood model, the interaction of ECCS water with steam is evaluated by means of a frictional pressure loss penalty (delta P penalty).
As discussed in Reference 2, the magnitude of this parameter in Cycle 5 through Cycle 9 analyses was overly conservative. A more realistic value of this parameter was developed from the EPRI data base for the Cycle 10 and
. subsequent analyses.
Axial Power Shanes To determine the LOCA limit at an axial location in the core, a limiting axial power shape with its peak at the specified location is used in the LOCA i
analysis.
If the results of the analysis meet the LOCA design criteria, the l
peak linear heat generation rate (PLHGR) is the derived limit at the specified location.
The process is repeated for several axial locations so that a curve through the established PLHGR's forms the axially dependent LOCA limit curve.
I In the analyses for Cycle 5 through Cycle 9, two axial power shapes were i
considered:
a top skew design shape with its peak at 68 percent of the core height (68% shape) and a chopped cosine shape (50% shape).
These analyses t
derived the LOCA limit curve shown in Figure 1.
In a recent review of the l
YAEC LOCA methodology this curve was found to be non-conservative at higher elevations (greater than approximately 75%). A new LOCA limit curve also shown in Figure I was conceptualized.
The magnitude of the LOCA limits will be optimized as permitted by the analyses.
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MAINE YANKEE ATOMIC POWER COMPANY Enclosure MN-87-15 Page 2 of 9 This curve is generated by determining the LOCA limit at four axial locations (52%, 65%, 73%, 85%). The axial power shapes used in these calculations are determined according to the methodology outlined in Reference 3.
The LOCA limit is assumed to be constant between 0 and 52% core height and linear between the analyzed points, and is determined assuming a conservative fall off rate between 85 and 100% core height.
These assumptions are discussed in detail in Reference 3.
To calculate the LOCA limit at the four specified axial locations, the limiting break for each limiting power shape needs to be identified.
The break spectrum analysis workscope for identifying these limiting breaks is discussed in the following section.
BREAK SPECTRUM ANALYSIS CONSIDERATIONS The four axial power shapes identified for the cycle 10 analysis have peaks at 52%, 65%, 73%, and 85% core height.
The purpose of the break spectrum analysis is to identify the limiting break for each axial power shape.
The calculational matrix for the break spectrum analysis is outlined in Table 1.
In these analyses the following judgements were developed and utilized to determine the appropriate workscope.
1.
The break spectrum analysis performed with a 68% axial power shape is applicable to the 65% power shape.
The previous (Cycle 5) break spectrum analysis was performed with the 50%
(chopped cosine) and 68% (top skew, design) axial power shapes. Hence, an updated version of this analysis, with the new injection delta P penalty model in place, was a convenient starting point for this work.
The break spectrum analyses with 68% shape and with 50% shape both identify 0.8G (a guillotine break with flow area 80% of twice the cold leg flow area) as the limiting break.
In light of these results and the small difference in the peak location between the 68% shape and the 651 shape (4 inches), utilizing 0.8G as the limiting break for the 65% power shape is judged to be appropriate.
2.
The break spectrum analysis performed with cosine (50%) shape is applicable to 52% power shape.
This judgement is valid for the reasons provided above.
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MAINE YANMEE ATOMIC POWER COMPANV Enclosure MN-87-15 Page 3 of 9 3.
The limiting break for.the cosine shape (an'd thus the 52% power shape) can be identified by analyzing three of the six break sizes.
The break spectrum analysis for the cosine axial power shape was limited to the 1.0G, 0.8G and 1.0S (a pipe crack with flow area of twice the cold leg flow area) breaks. The other three breaks were eliminated from the analysis by examining the results of the 68% power shape break spectrum analysis. The results of this analysis indicate that 1.0G among the guillotine breaks and 1.0S among the slot breaks experience the most heatup during reflood. Among the six breaks, the three guillotine breaks show a higher PCT at the start of reflood and at the end of transient.
Therefore, the analysis of two guillotine (1.0G and 0.8G) breaks and one slot (1.05) break should be sufficient to identify the limiting break.
4.
The limiting break for 731 axial power shape can be identified by analyzing three (0.8G, 1.0G, 1.05) of the six break sizes.
The limiting break for the 85% axial shape can be identified by analyzing four breaks-(0.8G, 1.0G, 1.0S, 0.8S).
These judgements are valid for the reasons provided above.
5.
The blowdown response of the system is independent of axial power shape.
In the YAEC LOCA methodology, the blowdown system response is calculated to determine the conditions in the upper and lower plenum. These conditions are used in the hot channel analysis to predict the detailed temperature distribution in the core.
In this methodology it is presumed that minor changes in the power distribution do not impact the plenum conditions.
6.
The reflood rates calculated with a 68% axial power shape can be used in the analysis of a 50% (cosine) axial shape.
The sensitivity of the PCT response to reflood rate was examined for the 50% axial shape.
First, the T000EE calculations for 0.8G break and 1.0S l
break were performed with the flooding rates calculated with the 68% power shape.
The same calculations were then performed with the flooding rates d
calculated with the 50% power shape.
The resulting peak cladding temperatures are presented in Table 2.
The difference in the PCTs for the 0.8G break is 5'F and that for the 1.0S break is 8'F.
These minor differences demonstrate that the PCT response is insensitive to reflood i
rate for this power shape.
(
Similar sensitivity studies were performed for the variation between 68%
l and 85% power shapes and the 68% and 73% power shapes.
These comparisons showed differences in PCTs of more than 20*F.
Therefore, revised reflood j
rates were calculated for the analysis of 73% and 85% power shapes.
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MAINE YANKEE ATOMIC POWER COMPANY Enclosure MN-87-15 Page 4 of 9 BREAK SPECTRUM ANALYSIS RESULTS The summary results of the break spectrum analysis are shown in Table 3.
The limiting break size for elevations 65% and 52% is 0.8G.
Between the 68% peak and 73% peak elevation, there is a shift in the limiting break to 1.0S.
The 1.0S break will be used in the analysis of 73% and 85% peak power shapes.
In addition to the large break spectrum analysis, the results of the small break licensing basis analysis for MY were also examined.
In the analysis a 68% peak top skew design shape and a PLHGR of 16 KW/ft were used.
The results of this analysis indicate a short period of core uncovery and cladding heatup leading to a PCT of 1230*F for the limiting (0.5 ftZ) break. Given the large differences in predicted PCTs for the large and small breaks (600-700*F), the large break results should be limiting over the full range of axial power shapes considered.
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. MAINE YANKEE ATOMIC POWER COMPAN'1 Enclosure NN-87-15 Page 5 of 9 REFERENCES 1.
YAEC-Il60, " Application of Yankee HREM Based Generic PHR ECCS Evaluation Model to Maine Yankee", July 1978.
2.
Attachment A, Letter MN-86-141; From G. D. Whittier of MYAPCO to A. C. Thadant of NRC; Dated November 10, 1986.
3.
Attachment B, Letter MN-86-141, From G. D. Whittier of MYAPC0 to A. C. Thadant of NRC; Dated November 10, 1986.
4.
Memorandum for P. M. Sears (NRC) from D. M. Crutchfield (NRC); Safety Evaluation of Maine Yankee Large Break ECCS Evaluation Model Modification Related to Axial Power Shape Issue, Phase I; Dated December 31, 1986.
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Encits::re MN-87-15 Page 6 of 9 TABLE 1 BREAK SPECTRUM ANALYSIS MATRIX AXIAL Peak Clad Temperatures SHAPE SPECS.
BLOM)0NN HOT CHANNEL REFLOOO T000EE 10G 08G 06G 10S 08S' 06S Peak Location 681 68%
68%
68%
1927 1943 1912 1865 1858 1767 TOP SKEN Shape TOP SKEN TOP SKEN TOP SKEN TOP SKEN i
Inj. delta P NEN (68%)
PLHGR (KW/FT) 13.5 13.5 13.5 13.5 Peak Location 681 50%
681 501 1925 1998 1914 COSINE Shape TOP SKEN COSINE TOP SKEN COSINE Inj. delta P NEN (50%)
PLGHR (KW/FT) 13.5 16.0 13.5 16.0 Peak Location 521 Shape C0 SINE BREAK SPECTRUM Inj. delta P PLHGR (KW/FT)
Peak Location 65%
Shape T0P SKEH BREAK SPECTRUM Inj. delta P PLGHR (KW/FT)
Peak Location 68%
73%
73%
731 1858 1870 1874 731 Shape TOP SKEW CY-10 CY-10 CY-10 Inj. delta P NEH PLGHR (KW-FT) 13.5 13.0 13.0 13.0 L
Peak Location 68%
85%
85%
85%
1801 1828 1839 1748 85%
Shape TOP SKEH CY-10 CY-10 CY-10 Inj. delta P NEN PLGHR (KH/FT) 13.5 11.5 11.5 11.5 8449L-GDH l
MAINE YANKEE ATOMIC POWER COMPANY Enclosure MN-87-15 Page 7 of 9 TABLE 2 SENSITIVITY OF FLOOD TO AXIAL PONER DISTRIBUTION SPECS REFLOOD T000EE-2 08G 10G 10S 08S Peak Location 68%
50%
1998 1914 Shape Top Skew Cosine Inj. delta P New Peak Location 50%
50%
2003 1922 Shape Cosine Cosine Inj. delta P New Peak Location 68%
85%
1829 1874 1894 1792 Shape Top Skew CY-10 Shape Inj. delta P New Peak Location 85%
85%
1828 1801 1839 1748 Shape CY-10 Shape CY-10 Shape Inj. delta P New i
Peak Location 68%
73%
1834 1869 l
Shape Top Skew CY-10 Shape Inj. delta P New Peak Location 73%
73%
1870 1858 1874 Shape CY-10 Shape CY-10 Shape Inj. delta P New j
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MAINE YANKEE ATOMIC POWER COMPANY 1
Enclosure
- MN-87-15 Page 8 of 9 TABLE 3 BREAK SPECTRUM ANALYSIS RESULTS AXIAL PCT FOR P0HER LIMITING THE LIMITING SHAPE BREAK BREAK COMMENTS 52%
08G 1998-2003 From equivalent (50%) break spectrum analysis.
Range of PCT from Table 2.
65%
08G 1943 From equivalent (68%) break spectrum analysis.
73%
~ 10S 1874 85%
10S 1839 8449L-GDH
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Enclosure MN-87-15 Page 9 of 9 a
18
' Figure 1 Comparison of Current and Expected Shape of LOCA Limit 16
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10' Current LOCA Limit (Technical Specification 3.10) s
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Expected Shape of New LOCA Limit Curve (Revised delta P injection penalty) 8' 3
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20 40 60 80 100 0
Core Height
(% from Bottom of Core)