ML19319D787
| ML19319D787 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 10/18/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19319D783 | List: |
| References | |
| NUDOCS 8003250786 | |
| Download: ML19319D787 (3) | |
Text
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20 40 60 80 100 120, 140 160 180 200 ROD INDEX, % WITHD R AWN 0
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GROUPS
- 1. ROD INDEX IS THE PERCENTAGE SUM OF THE WITH0RAWAL OF CONTROL ROD GROUPS 5,6 AND 7 FIGURE 3.S.21 RANCAO SECO UNIT 1 ROD POSITION LIMITS TECHNICAL SPECIFICATIONS CHANGE _, a,
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SMUD FSAR - 672 41574 SACRAMENTO MUNICIPAL UTILITY DISTRICT Admendment 29
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RANCHO SECO UNIT 1
? f TECHNICAL SPECIFICATIONS
. Limiting condit1'ons for Operation 3.5.2.7*
Tlie conii'rol rod drive p'dtch pancis sha,ll be locked at all times with limited access to be a'uthorized by'tho' superintendent.
Bases Thepower-imbalanceenvekopedefinedinfigure3.5.2-2isbasedonLOCA 28 i analyses which have defined the maximum linear heat rate (see figure 3.5.2-3) such that the maximum clad temperaturc+9111 not exceed the Interim' Acceptance Criteria.
Operation outside of the p50er imbalance envelope alone does not 24 constitute a situation that would cause the Interim' Acceptance Criteria to be exceeded should a LOCA occur.
The power imbalance envelope represents the boundary of operation limited by the Interim Acceptance Criteria only if the 28l control rods are at the position rimits as defined by figure 3.'5.2-1 and if a
~
4 percent quadrant power tilt exists.
Additional conserv'atism is introduced by application of:
A.
Nuclear uncertainty factors.
24 B.
Therm 1 calibration uncertainty.,
C.
Fuel densification effects.
D.
Hot rod manufacturing tolerance. factors.
The 30 percent overlap between successive control rod groups is allowed since the worth of a rod is lower at the upper and lower part of the stroke.
Control rods are arranged in groups or bcnks defined as follows:
Group yunction
'.'Saf ety l
2 Safety 3.
' Safety 4
Safety 5
Regulating 6
Regulating 7
Regula' ting 8
APSR (axial power shaping bank)
Control rod groups are withdrawn in sequence beginning with group 1.
Group 5 is overlapped 25 percent with groups 6 and 7, which o.p'erate in parallel.
The normal position at power is for groups 6 and 7 to,be partially inserted.
j The minimum available rod worth provides for achieving hot' shutdown by reactor trip at'any time assuming the highest worth control rod remains in the full
^
out positiod.(1)
Inserted rod groups during pt,wer operation will not contain single rod worths greater th,an 0.65 percent a k/k. This value has been shown to be safe by the safety analysis of the hypothetical rod ejections accident.(2) A single inserted co,ntrol worth of 1.0 percent ak/k at beginning of life, hot, zero 29 power would result in a lower peak thermal power and therefore less severe environmental. consequences than a 0.65 percent a k/k ejected rod at rated power.
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. Standby Safeguards Analysis
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"As a check on the point kinetics c'alculation
,.the rod ejection accident was fication rod worth using the exactalso analyzed for a limited number of ca TWICL digital computer program. (ll) two dimensional, space-and-time dependent flux shape remains constant during a transient.The point kinetics model assumes that the This flux shape contains peaking factors which reficct unusual red patterns such as th6 flux adjacent to a position where a high worth rod has been removed.
kinetics peaking factors are much higher than any that would actually occur in Therefore, these point the core during normal operation.
The purpose of using an exact calculation is to find the flux shape during 'a transient.
space-time But to have a transient where a rod is ejected from the core,' one cust shape that start with a flux
- fact, is necessarily depressed in the region of the ejected rod.
This flux depression also causes a fuel temperature depressio In is ejected from this position, the flux quickly assumes a shape that shows g
When the rod some local peaking.
Mcwever, when this " exact" peaking is applied to a region initially at depressed fuel temperatures, as it is in the case of the regions adjacent the ejected rod, the resultant energy deposited in'these regions causes a to lower peak te=perature and peak thermal power than does applying an arbitrar maximum peaking factor to an undepressed peak power region.
y from TUICL were used to calculate the maximum cotal energy deposited in each The results region of the core following a rod ejection; the highest energy is reported in Table 14.2-10.
The result is that the hottc~st TUICL code accus11y undergoes a less severe trcnsientregion simulated in the rod assumed in the point kinetics model.
than the hottest fuel result is uniformly true for all rod worths.-As seen in table 14.2-10, this For certain cases where the ejected rod has a low worth, or where at one reactivity coefficient least is very negative, or the initial power icvel is
~
- low, there~ is considerable pressure buildup in the reactor coolant system because of the increased heat being added to the coolant with no increase in
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heat demand.
For this class of possibility, che, high pressure trip must be ' relied this is incorporated in the calculation.
, and 14;.2.2.4.4 Results of Analysis A.
Zero Power Level
~
The nominal BOL and EOL rod ejection analysis' was performed at 10-3 of rated power, and the results can be seen. in table 14.2-11.
No DNB and no fuel damage would result from the transient caused by 29, the ejection of a rod worth.657. ak/k.
The percent of fuel rods in DNB for an ejected rod worth 1% 4k/k would be less than the number of rods in DNB with an ejected rod worth.65% Ak/k at rated power.
A sensitivity analysis has been performed around these two cases in which~the Doppler and moderator coefficients, trip delay time, and rod worth were varied.
Figure 14.2-2 shows the peak neutron power as a function of 'eje'eted rod worth from 0.2 to 0.7 percent d k/h.
The 14.2-20 Amendment 29
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aby Safegunrds Analysis TABLE 14.2 :10 COMPARISON OF SPACE-DEPENDENT.'AND POINT KINETICS
~~
RESULTS ON FUEL ENTHALPY Ejected Peak-to-Average Values Fuci Enthalpy, cal /gm Rod Worth,
%dk/k TUIGL Point Kinetics
~.TWIGL Point Kinetics 6
BOL Rated Pouer 0.38
'3. 04.
3.24 125 150
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0.83 2.67 3.24 174 225 BOL Zero Pouer O.56 4,.1
, 3,24 38 60 0.83 4.4 '
3.24 -
48 71
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TABLE 14.2-11 SUK!ARY OF CONTROL ROD EJECTION ACCIDENT ANALYSIS Peak Power, % iated poter Initial Power Level, Ejected Rod Worth,
% rated power
% ok/k Neutron Thermal
~
0.1 (BOL) 0.65 94 70 0.1 (EOL) 0.65 1,160 32 0.1 (BOL) 1.0 8,417 132 16,302 102 29 0.1 (EOL) 1.0 100.0 (BOL) 0.65 700 158 0.65 1,600 138 100.0 (EOL) l
~
I' curve shows two distinct parts corresponding to worths less than and v'dlues near to and greater than 3.
Figure 14.2-3 shows the corres-l ponding results for the peak thermal power.
It is seen that for rod worth niues near prompt critical, the period is small enough to carry the t,ra'nsient through the high neutron flux trip.
For lower values the pressure trip is relied on.
No DNB occurs for any of these parameter variations.
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- 14m2-21
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