ML19312B968

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Proposed Tech Spec 3.5.2 Revising Rod Withdrawal Limits for Units 1 & 2
ML19312B968
Person / Time
Site: Oconee  Duke Energy icon.png
Issue date: 03/08/1974
From:
DUKE POWER CO.
To:
Shared Package
ML19312B967 List:
References
NUDOCS 7911270750
Download: ML19312B968 (13)
v • d • e


Text

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1000 2000 3000 4000 5000 Temperature, F SPECIFIC HEAT OF U0 3 7[d i911270: 4

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3.5.2 Control Rod Group _ and Power Distribution Limits Applicability This specification applies to power distribution and operation of control rods during power operation.

Obiective To assure an acceptable core power distribution during power operation, to set a limit on potential reactivity insertion from a hypothetical control rod ejection, and to assure core suberiticality after a reactor trip.

Specification 3.5.2.1 The available shutdown margin shall be not less than 1% Ak/k with the highest worth control rod fully withdrawn.

3.5.2.2 Operation with inoperable rods:

a.

Operation with more than one inoperable rot as defined in Specification 4.7.1 and 4.7.2.3, in the safety or regulating rod groups shall not be permitted.

b.

If a control rod in the regulating or safety rod groups is declared inoperable in the withdrawn position as defined in Specification 4.7.1.1 and 4.7.1.3, an evaluation shall be initiated immediately to verify the existance of 1% Ak/k hot shutdown margin.

Boration may be initiated either to the worth of the inoperable rod or until the regulating and transient rod groups are fully withdrawn, whichever occurs first. Simultaneously a program of exercising the remain-ing regulating and safety rods shall be initiated to verify operability.

If within one (1) hour of determination of an inoperable c.

rod as defined in Specification 4.7.1, it is not determined that a 1% Ak/k hot shutdewn margin exists combining the worth of the inoperable rod with each of the other rods, the reactor shall be brought to the hot standby condition until this margin is established.

d.

Following the determina_ica of an inoperable rod as defined in Specification 4.7.1, all rods shall be exercised within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and exercised weekly until the rod problem is sol-ved.

If a control rod in the regulating or safety rod groups e.

is declared inoperable per 4.7.1.2, power shall be reduced to 60% of the thermal power allowable for the reactor cool-ant pump combination.

3.5-6

f.

If a control rod in the regulating or axial power shaping groups l

1s declared inoperable per Specification 4.7.1.2, operation above 60% of rated power may continue provided the rods in the group are positioned such that the rod thnt was declared inoperable is main-tained within allowabic group average position limits of Specifica-tion 4.7.1.2 and the withdrawal limits of Specification 3.5.2.5.c.

3.5.2.3 The worth of a single inserted control rod shall not exceed 0.5% ak/k at rated power or 1.0% ak/k at hot zero power except for physics testing when the requirements of Specification 3.1.9 shall apply.

3.5.2.4 Quadrant tilt:

a.

Below the power level cutoff (See Figures 3.5.2-1), except for physics tests, thermal power shall be reduced 2% for each 1% tilt in excess of 4% tilt. For less than 4 pump operation, thermal power shall be reduced 2% of the thermal power allowable for the reactor coolant pump combination for each 1% tilt in excess of 4%.

b.

Within a period of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, the quadrant power tilt shall be reduced to less than 4%, except for physics tests, or the following adjust-ments in setpoints and limits shall be made:

1.

The protection system maximum allowable setpoints (Figure 2.3-2A-Unit 1; 2.3-2B-Unit 2) shall be reduced 2% in power for each 1% tilt.

2.

The control rod group withdrawal limits (Figures 3.5.2-1A1, 3.5.2-1A2, 3.5.2-2A Unit 1; 3.5.2-1B1, 3.5.2-1B2, 3.5.2-2B Unit 2) shall be reduced 2% in power for each 1% tilt in excess of 4%.

3.

The operational imbalance limits (Figure 3.5.2-3A-Unit 1; 3.5.2-3B-Unit 2) shall be reduced 2% in power for each 1% tilt in excess of 4%.

c.

If quadrant tilt is in excess of 25%, except for physics tests or diagnostic testing, the reactor will be placed in the hot shutdown condition.

Diagnostic testing during power operation with a quad-rant power tilt is permitted provided the thermal power allowable for the reactor coolant pump combination is restricted as stated in 3.5.2.4.a above.

d.

Quadrant tilt shall be monitored en a minimum frequency of once every two hours during power operation above 15% of rated power.

3.5.2.5 Control rod positions:

a.

Technical Specification 3.1.3.5 (safety rod withdrawal) does not prohibit the exercising of individual safety rods as required by Table 4.1-2 or apply to inoperable safety rod limits in Technical Specification 3.5.2.2.

b.

Operating rod group overlap shall be 25% 1 5% between two sequential groups, except for physics tests.

3.5-7

c.

Except for physics tests or exercising control rods, the control rod withdrawal limits are specified on Figures 3.5.2-1Al, 3.5.2-1B1, 3.5.2-1A2, and 3.5.2-1B2 for four pump operation and on Figure 3.5.2-2A and 3.5.2-2B for three or two pump operation.

If the con-trol rod position limits are exceeded, entractive measures shall be taken immediately to achieve an acceptable control rod position.

Acceptable control rod positions shall be attained within four hours.

d.

Except for physh.s r.csts, power shall not be increased above the power level cutJif (see Figures 3.5.2-1) unless the xenon reactivity is within 10% of the equilibrium value for operation at rated power and asymptotically approaching stability.

3.5.2.6 Reactor Power 1mbalance shall be monitored on a frequency not to exceed two hours during power operation above 40 percent rated power.

Except for physics tests, imbalance shall be maintained within the envelope defined by Figure 3.5.2-3A and 3.5.2-3B.

If the imbalance is not within the envelope defined by Figure 3.5.2-3A and 3.5.2-3B, corrective measures shall be taken to achieve an acceptable imbalance.

If an acceptable imbalance is not achieved within four hours, reactor power shall be reduced until imbalance limits are met.

3.5.2.7 The control rod drive patch panels shall be locked at all times with limited access to be authorized by the superintendent.

Bases The power-imbalance envelope defined in Figure 3.5.2-3A and 3.5.2-3B is based on LOCA analyses which have defined the maximum linear heat rate (see Figure 3.5.2-4) such that the maximum clad temperature will not exceed the Interim Acceptance Criteria.

Corrective measures will be taken immediately should the indicated quadrant tilt, rod position, or imbalance be outside their specified boundary.

Operation in a situa* ton that world cause the interim acceptance criteria to be approached should a LOCA occur ic highly improbable because all of the power dis-tribution parameters (quadrant tilt, rod position, and imbalance) must be at their limits while simultaneously all other engineering and uncertainty factors are also at their limits.* Conservatism is introduced by application of:

a.

Nuclear uncertainty factors b.

Thermal calibration 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 banks defined as follows:

  • Actual operating limits depend en whether or not incore or excore detectors are used and eneir respective instrument and calibration errors.

The method used to define the operating limits is defined in plant operating procedures.

3.5-8

Group Function 1

Safety 2

Safety 3

Safety 4

Safety 5

Regulating 6

Regulating 7

Xenon transient override 8

APSR (axial power shaping bank)

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 position. (1)

Inserted rod groups during power operation will not contain single rod worths greater than 0.5% ak/k. This value has been shown to be safe by the safety analysis of the hypothetical rod ejection accident.(2) A single inserted control rod worth of 1.0% ak/k at beginning of life, hot, zero power would result in the same transient peak thermal power and therefore the same environmental consequences as a 0.5% ak/k ejected rod worth at rated power.

Control rod groups are withdrawn in sequence beginning with Group 1.

Groups 5, 6, and 7 are overlapped 25 percent.

The normal position at power is for Groups 6 and 7 to be partially inserted.

The quadrant power tilt limits set forth in Specification 3.5.2.4 have been established within the thermal analysis design base using the definition of quadrant power tilt given in Technical Specifications, Section 1.6.

These limits in conjunction with the control rod position limits in Specification 3.5.2.5c ensure that design peak heat rate criteria are not exceeded during normal operation when including the effects of potential fuel densification.

The quadrant tilt and axial imbalance monitoring in Specifications 3.5.2.4 and 3.5.2.6 respectively normally will be performed in the process computer.

The two-hour frequency for monitoring these quantities will provide adequate surveillance when the computer is out of service.

Allowance is provided for rod withdrawal limits and reactor power imbalance limits to be exceeded for a period of four hours without specification violation.

Acceptance rod positions and imbalance must be achieved within the four hour time period or appropriate action such as a reduction of power taken.

REFERENCES 1Section 3.2.2.1.2 2Section 14.2.2.2.

3.5-8a

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1.

Rod index is the percentage sum of the withdrawal of the operating groups.

2.

The restrictions on withdrawal (hashed area) are mcdified after 285 full power days of operation.

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GROUP 5 CONTROL R00 GROUP IITii1RABAL LlulTS FOR 4 PUNP OPERATION UNIT 1

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1 ROD INDEX I S THE P ERCENTAGE SLN OF THE WI THDRAWAL OF THE OP ERATING GROUPS.

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