ML20209G546
| ML20209G546 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 09/04/1986 |
| From: | MISSISSIPPI POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML20209G215 | List: |
| References | |
| TAC-61930, NUDOCS 8609120503 | |
| Download: ML20209G546 (6) | |
Text
I NLS-86/12
SUBJECT:
Additional Infonnation pertaining to Thermal-Hydraulic Stability for Cycle 2.
DISCUSSION:
The previous submittal for the proposed Core Stability (CS)
Technical Specification (TS) changes was made via AECM-86/0255 dated August 15, 1986. These proposed TS changes have been discussed with the NRC staff in conversations held the week of August 11, 1986.
JUSTIFICATION: Based on discussions with the NRC Staff regarding the August 15, 1986 submittal, changes are proposed to TS Figure 3.4.1.1-1.
The changes are justified as discussed below:
1.
Figure 3.4.1.1-1 had been revised to expand the surveillance region of " Detect and Suppress" (D&S) to a line representing a calculated Decay Ratio (DR) of 0.60.
This will provide an upper boundary on Region II in which the DR has been shown to be less than 0.6 over the 45% flow line, and no D&S surveillance is called for.
2.
The D&S region defined in the referenced submittal had its lower right hand boundary established by a DR of 0.75.
The conservatism of this lower boundary is discussed in the Justification Section of the referenced submittal. To address NRC concerns regarding this area of the operating map, the subject lower boundary has been further reduced as discussed in Paragraph 1 above. Thus, D&S surveillances would be required for operations in the region bounded on the left by 0.90 DR line and 39% flow, and on the right by 0.60 DR line and 45% flow (when operating above the 80%
Rod Line).
3.
Justification of the use of Exxon's COTRAN methodology to define the D&S region has been provided in the referenced submittal.
4.
The definitions of the various regions identified in the proposed Figure 3.4.1.1-1 are the same as those used in the version of the Figure currently in the technical specifications (Amendment No. 16), namely:
Region 4gg I
D&S surveillance required for 8gt operation in this Region as prescribed
-$g by Specification 3/4.3.10.
II,III Operations above and below, 7
respectively, the 80% rod line where
~
h no D&S surveillances are required.
N<
IV Operations are prohibited per Sg Specification 3/4.4.1.
1 som 5.
Bases 3/4.4.10 have been modified to reflect this change in the D&S region and to include definitions of the other regions.
J16ATTC86082001 - 1
SIGNIFICANT HAZARDS CONSIDERATION:
The proposed stability surveillance region has been defined using an NRC approved methodology. The results of the stability analysis were utilized in an accepted conservative manner to provide adequate margin to stability. This proposed change has been reviewed by MP&L and found to involve no significant hazards considerations, as discussed below.
1.
The change does not involve an increase in the probability or the consequences of a previously analyzed event. This change redefines a region where special surveillance is instituted to detect and suppress potential instabilities.
The change calls for a larger region of restricted operation (above the 0.90 decay ratio (DR) line), as well as extends the region of surveillance beyond the original 45% flow line.
As the detect and suppress region was defined by plant and cycle specific analyses, the region where the decay ratio is below 0.75 is considered stable.
However, as a conservative measure, the detect and suppress surveillance region is expanded in the proposed change beyond the 0.75 decay ratio boundary to a region bounded by a calculated decay ratio of 0.60.
Overall, based on the use of plant specific analyses and the establishment of a restricted operations region and of a conservative detect and suppress surveillance region, the proposed change does not involve an increase in the probability or the consequences of a previously analyzed event.
2.
The change does not create the possibility of a new or different accident from those previously evaluated. This l
change involves no new design modifications.
It redefines the area of the operating map where stability surveillances j
are to be instituted and restricts operations in certain l
power / flow conditions based on stability concerns.
[
l 3.
The change does not decrease the margin of safety intended by the Technical Specifications. This change defines the region of stability surveillance as that where the calculated decay ratio is greater than or equal to 0.60, less than 0.90, and between the 39% and 45% flow line.
While the region proposed in this submittal revises the l
region to reflect a decay ratio of 0.60, the region is i
determined based on plant and cycle specific analyses.
Further, the surveillance criteria previously established will be maintained to adequately monitor and detect potential instabilities. Such instabilities will be
-suppressed upon detection, thereby maintaining the margin of safety intended in the technical specifications.
J16ATTC86082001 - 2
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EE Percent of Roted Flow 9m FIGURE 3. 11. 1. 1 - 1 POWER / Flow OPERATING MAP
e INSTRUMENTATION BASES 3/4.3.9 TURBINE OVERSPEED PROTECTION This specification is provided to ensure that the turbine overspeed protection instrumentation and the turbine speed control valves are OPERABLE and will protect the turbine from excessive overspeed.
Protection from turbine excessive overspeed is required since excessive overspeed of the turbine could generate potentially damaging missiles which could impact and damage safety-related components, equipment or structures.
3/4.3.10 NEUTRON FLUX MONITORING INSTRUMENTATION This specification is to ensure that neutron flux limit cycle oscillations are detected and suppressed.
"t tests at operating plants were reviewed to identif
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o the operating na eillance should be perfo ccount for varia-bility, a conservative decay r en as the basis for defining the region of potential ins he res
'.., --a'on corresponds to core flow less than ed and THERMAL POWER greater than line.
_,Tha ine is illustrated in Figure 3.4.1.1-1.
Neutron flux noise limits are also established to ensure the ea'rly detec-tion of limit cycle oscillations.
Typical APRM neutron flux noise levels at up to 12% of rated power have been observed.
These levels are easily bounded by values considered in the thermal / mechanical fuel design.
Stability tests have shown that limit cycle oscillations result in peak-to peak magnitude of 5 to 10 times the typical values.
Therefore, actions taken to suppress flux oscillations exceeding three (3) times the typical value are sufficient to ensure early detection of limit cycle oscillations. The specification includes the surveil-lance requirement to establish the requisite baseline noise data and prohibits operation in the region of potential instability if the appropriate baseline data is unavailable.
l#SSR.T N'
- GRAND GULF-UNIT 1 8 3/4 3-7 Amendment No.16 l
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INSERT "A" In order to identify a region of the operating map where surveillance should be performed, analyses-were performed by Exxon Nuclear Company for the Grand Gulf reactor consistent with the USNRC approved methodology as described in XN-NF-691(P)(A) dated August,1984.
The surveillance region was established as that region for which the calculated decay ratio is greater than or equal to a value of 0.60 and less than 0.90, between the 39% and 45% flow line. The resulting region is illustrated in Figure 3.4.1.1-1 and is identified as Region I.
Region IV is restricted from operation. This is the region where either the calculated decay ratio is greater than 0.90 or flow is below the 39% flow line.
In Region III, below the 80% rod line, and Region II, where the decay ratio is below 0.60, no detect and suppress surveillance activities are required.
l l
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