ML20117K329

Proposed Tech Specs Revising Safety Limit MCPR from 1.06 to 1.07 for Dual Recirculation Loop Operation & from 1.07 to 1.08 for Single Recirculation Loop Operation

ML20117K329
Person / Time
Site:	Cooper
Issue date:	06/06/1996
From:	NEBRASKA PUBLIC POWER DISTRICT
To:
Shared Package
ML20117K327	List: ML20117K323 ML20117K329 ML20117K332
References
NUDOCS 9606110119
Download: ML20117K329 (2)

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• SAFETY LIMITS LIMITING SAFETY SYSTEM SETTINGS 1.1 FUEL CLADDING INTEGRITY 2.1 FUEL CLADDING INTEGRITY Anolicability Aeolicability The SAFETY LIMITS established to The LIMITING SAFETY SYSTEM SETTINGS preserve the fuel cladding integrity apply to trip settings of the in-apply to those variables which moni- struments and devices which are tor the fuel thermal behavior, provided to prevent the fuel clad-ding integrity SAFETY LIMITS from obiective being exceeded.

The objective of the SAFETY LIMITS Obiective is to establish limits below which the integrity of the fuel cladding The objective of the LIMITING SAFETY is preserved. SYSTEM SETTINGS is to define the level of the process variables at Action which automatic PROTECTIVE ACTION is If a SAFETY LIMIT is exceeded, the initiated to prevent the fuel clad-

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• reactor shall be in at least HOT SHUTDOWN within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

• 9 ** ** *

• Snecifications Soecifications A. Reactor Pressure >800 nsia '

and Core Flow >10% of Rated A. Trin Settinas The existence of a MINIMUM The LIMITING SAFETY SYSTEM CRITICAL POWER RATIO (MCPR) SETTINGS shall be as specified less than 1.07 for two recir- belows culation loop operation (1.08 for single-loop operation) 1. Neutron Flux Trio Settinas shall constitute violation of the fuel cladding integrity a. APRM Flux Scram Trin Settina SAFETY LIMIT. (Run Mode)

B. Core Thermal Power Limit (1) Flow Referenced Scram Trio (Reactor Pressure <800 nsia Settina and/or Core Flow <10%)

When the Reactor Mode Selector When the reactor pressure is Switch is in the RUN position,

<800 psia or core flow is the APRM flow referenced flux less than 10% of rated, the scram trip setting shall be core thermal power shall not S 0.58 W + 62% - .58 AW exceed 25% of RATED POWER.

C. Power Transient S = S tting in percent of To ensure that the SAFETY

• LIMIT established in Specifi-cation 1.1.A and 1.1.B is not W = Two-loop recirculation exceeded, each required scram flow rate in percent of shall be initiated by its rated (rated loop expected scram signal. The recirculation flow rate SAFETY LIMIT shall be assumed is that recirculation flow to be exceeded when scram is rate which provides 100%

accomplished by a means other core flow at 100% power).

than the expected scram sig-AW = Difference between two- i loop and single-loop ef- I fective drive flow at the .l same core flow.

1 9606110119 960606 PDR ADOCK 05000298 P PDH _

1.1 Bases

Fuel Cladding Integrity A. Fuel Claddina Intecrity Limit at Reactor Pressure >800 osia and Core Flow >10% of Rated The fuel cladding integrity safety limit is set such that no fuel damage is calculated to occur if the limit is not violated.

Since the parameters which result in fuel damage are not directly observable during reactor operation the thermal and hydraulic conditions resulting in a departure from nucleate boiling have been used to mark the beginning of the region where fuel damage could occur. Although it is recognized that a departure from nucleate boiling would not necessarily result in damage to BWR fuel rods, the critical power at which boiling transition is calculated to occur has been adopted as a convenient limit. However, the uncertainties in monitoring the core operating state and in the procedure used to calculate the critical power result in an uncertainty in the value of the critical power. Therefore, the fuel cladding integrity safety limit is defined as the critical power ratio in the limiting fuel assembly for which more than 99.9% of the fuel rods in the core are expected to avoid boiling transition considering the power distribution within the core and all uncertainties.

The Safety Limit MCPR is determined in Reference 1 for two recirculation loop operation. This safety limit MCPR is increased by 0.01 for single-loop operation as discussed in Reference 2.

B. Core Thermal Power Limit (Reactor Pressure < 800 nsia and/or Core Flow < 10% of Rated)

At pressures below 800 psia, the core elevation pressure drop (0 power, O flow) is greater than 4.56 psi. At low power and all flows this pressure differential is maintained in the bypass region of the core.

Since the pressure drop in the bypass region is essentially all elevation head, the core pressure drop at low power and all flows will always be greater than 4.56 psi. Analyses show that with a flow of 28 x 10 lbs/hr bundle flow, bundle pressure drop is nearly independent of bundle power and has a value of 3.5 psi. Thus, thegundleflowwith a 4.56 psi driving head will be greater than 28 x 10 lbs/hr irrespective of total core flow and independent of bundle power for the range of bundle powers of concern. Full scale ATLAS test data taken at pressures from 14.7 psia to 800 psia indicate that the fuel assembly critical power at this flow is approximately 3.35 MWt. With the design peaking factors this corresponds to a core thermal power of more than 50%. Thus, a core thermal power limit of 25% for reactor pressures below 800 psi or core flow less than 10% is conservative.

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