ML19340B899

Tech Specs 3.12 & 4.12 Re Requirements for Spirally Unloading & Reloading Reactor Core

ML19340B899
Person / Time
Site:	Vermont Yankee
Issue date:	11/06/1980
From:	VERMONT YANKEE NUCLEAR POWER CORP.
To:
Shared Package
ML19340B897	List: ML19340B896 ML19340B899
References
NUDOCS 8011120539
Download: ML19340B899 (7)

Text

VYNPS .

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3 12 LIMITING CONDITION FOR OPERATION 4.12 SURVEILLANCE REQUIREMENT moved and one in an adjacent quadrant. For Thereafter, the SRMs shall be checked daily an SRM to be cons t 3ered operable the for response.

following conditions-shall be satisfied:

1. The SRM shall be inserted to the normal 00 operating level. (Use of special g

' g)g  : movable, dunking type detectors during pg. intitial fuel loading and major core alterations in place of normal detectors

-is permissible as long as the detector is connected.into the proper circuitry which contain the required rod blocks).

2. The SRM-shall have a minimum of 3 cps

\lI. with all rods fully inserted in the core.

b 3 Prior to spiral unloading, the SRMs shall Prior to spiral unloading or reloading, the

'%d) be proven operable as stated in Sections - SRMs shall be functionally tested. Prior to 3 12.B.1 and 3 12.B.2 above, however, spiral reloading, the SRMs shall be checked during spiral unloading the count rate for neutron response.

may drop below 3 cps.

4. Prior to spiral reloading, two diagonally adjacent fuel assemblies, which have previously accumulated expooure in the reactor, shall be loaded into their previous core positions next to each of the 4 SRMs. to obtain the required 3 cps.

Until these-eight bundles have been loaded,.the 3 cps requirement is not necessary.

C. Fuel Storage Pool Water Level' C. Fuel Storage Pool Water Level Whenever irradiated fuel is stored in the ' Whenever irradiated fuel is stored in the fuel storage pool, the pool water level shall fuel storage pool, the pool level shall be be maintained at a . level of at least ' 36 feet. recorded daily.

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VYNPS 3.12 LIMITING CONDITION FOR OPERATION 4.12 SURVEILLANCE REQUIREMENT 1.. The reactor mode switch shall' be locked 1. This surveillance requirement ~ is the same in the " Refuel" position. The refueling as that given in Specification 4.12. A.

interlock which prevents more than one contr'l rod from being withdrawn may be bypassed.on a withdrawn control rod afte.

~the fuel: assemblies in- the cell containing (controlled by) that control rod have' been removed from the reactor core. All other refueling interlocks shall be operable.

2. SRMb shall be operable-in the core 2. This surveillance requifement is the~same quadrant.where fuel or control rods are as that given in Specification 4.12.B. <

.being moved, and in an adjacent

. quadra nt . The requirements for an SRM to be considered operable are given 'in Specification 3 12.B.

3 If the spiral unload / reload method of core alteration is to be used, the following conditions shall be met:

a. The ohutdown margin of the core shall be verified prior to spiral unloading.

-b.  : The . core - shall be spirally unloaded with the exception of 2 diagonally adjacent. fuel assemblies next to each SRM, which shall be removed last.

c. The core shall be spirally reloaded to its original configuration in

- exactly the reverse of the unloading

. spiral with the exception of the eight' fuel assemblies described in Section 3 12.B.4.

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.1 VYNPS 3 12 LIMITING CONDITION FOR OPERATION 4.12 SURVEILLANCE REQUIREMENT

d. At least 50% of the fuel, assemblies-to be reloaded into -the core shall have previously accumulated a minimum exposure of 1000 Mwd /T.

F. Fuel Movement- F. Fuel Movement

.. Fuel shall not be moved or handled in the Prior to any fuel handling or movement in'the reactor core for' 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following reactor reactor core,Lthe licensed operator.shall'

, shutdown to cold shutdown conditions. verify that the reactor has been in the cold -

. shutdown condition for a minimum of.24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Crane Operability G.- Crane Operability G.

1. The reactor building crane shall be 1. a. Within one month prior to spent fuel operable when the crane is used for cask handling operations, an handling of-a spent fuel cask. inspection of' crane cables, sheaves, hook, yoke and cask lifting. trunnions will be made. These inspections shall meet the requirements of ANSI

' Standard.B30.2, 1967. . A . crane rope shall be replaced if any of the replacement criteria'given in ANSI B30.2.0-1967 are met.

b. No-load mechanical and~ electrical

- tests wi.11 tur conducted ' prior to +

lifting the empty. cask from its' transport' vehicle to verify proper operation of crane controls, brakes and lifting speeds. A functional

. test of the crane brakes will be conducted each' time an empty cask is lifted clear of its transport vehicle. ,

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VYNPS 3'12-

. LIMITING CONDITIONS FOR OPERATION 4.12 SURVEILLANCE REQUIREMENT

2. Crane Travel 2. Crane Travel

Spent' fuel- casks shall be prohibited from ' Crane. travel ~ limiting' mechanical stops-travel- over irradiated fuel assemblies, shall' be installed on the crane trolley c

rails prior to _ cask handling operations to prohibit cask travel over, irradiated i

fuel assemblies.

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H. Spent Fuel Pool Water Temperature H. Spent Fuel Pool Water Temperature Whenever irradiated ' fuel is stored in the Whenever irradiated fuel is in the spent fuel spent fuel pool, the pool water temperature pool, the pool water temperature shall be recorded daily. If the pool water

.shall be maintained'below 1500F.

temperature reaches 1500F, 'all refueling -

~ operations tending to raise the pool water temperature shall cease and measures taken immediately to reduce the pool water temperature below 1500F.

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VYNPS Bases:

3 12 & 4.12 REFUELING A. During refueling operations, the reactivity potential of the core is being altered. It is necessary to require certain interlocks and restrict certain refueling procedures such that there is assurance that inadvertent criticality does not oCour.

To minimize the possibility of loading fuel into a cell containing no control rod, it is required that all control rods are fully inserted when fuel is being loaded into the reactor core. This requirement assures that during refueling the refueling -interlocks, as designed, will prevent inadvertent criticality. The core reactivity limitation of Specification 3 2 limits the core alterations to assure that the resulting core loading can be controlled with the reactivity control system and interlocks at any time during shutdown or '".e following operating cycle.

The addition of large amounts of reactivity to the core is prevented by operating procedures, which are in turn backed up by refueling interlocks on rod withdrawal and movement of the refueling platform. When the mode switch is in the

" Refuel" position, interlocks prevent the refueling platform from being moved over the core if a comtrol rod is

. withdrawn and fuel is on a hoist.

Likewise, if the refueling platform is over the core with fuel on a hoist, control rod motion is blocked by the interlocks. With the mode switch in the refuel position only one control rod can be withdrawn.

B. The SRMs are provided to monitor the core during periods of station shutdown and to guide the operator during refueling operations and station startup. Requiring two operable SRMs in or adjacent to any core quadrant where fuel or control rods are being moved assures adequate monitoring of that quadrant during such alterations. The requirement of 3 counts per second provides assurance that neutron flux is being monitored. Under the special condition of complete spiral core unloading, it is expected that the count rate of the SRMs will drop below 3 cps before all the fuel is unloaded.

Since there will be no reactivity additions, a lower number of counts will not present a hazard. When all of the fuel has been removed to the spent fuel storage pool, the SRMs will no longer be required. Requiring the SRMs to be operational prior to fuel removal assures that the SRMs are operable and can be relied on even when the count rate may go below 3 cps.

Prior to spiral reload, two diagonally adjacent fuel assemblies, which have previously accumulated exposure in the reactor, will be loaded into their previous core positions next to each of the 4 SRMs to obtain the required 3 cps.

Exposed fuel continuously produces neutrons by spontaneous fission of certain plutonium isotopes, photo fission, and photo disintegration of deuterium in the moderator. This neutron production is normally great enough to meet the 3 cps minimum SRM requirement thereby providing a iaeans by which SRM response may be demonstrated before the spiral reload begins. In the event that the core is to be spirally unloaded and reloaded, requirements to verify shutdown margin 186

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' VINPS prior to unloading the core and also to reload -only to the original core configuration' assure' that no unanticipated';

flux perturbations'will. occur during the performance of core alterations and in particular those core alterations '

.'perforsned with SRM indication less than 3 cps. During the spiral reload the fuel will be loaded 'in the exact reverse-

• order that it was unloaded with the exception of the initial eight fuel assemblies which are loaded next to tha.SRMs to-Lprovide a means of SRM ' response.

C. To assure that there is adequate water .to shield and cool the irradiated fuel assemblies stored in the pool, a minimum

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pool water level is established. . This minimum water. level of 36 feet is established because it would be a significant  :

. change from the normal level, well above' a level to assure. adequate cooling (just above' active fuel).,

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. 1 VYNPS -.'

3 12 & 4.12 (Continued)

D. . During certain periods, it is desirable to perform maintenance on two control rods and/or control rod drives at the -

same time. - This specification provides assurance that inadvertent criticality does not occur during such maintenance.

The maintenance is performed with the mode switch in the " Refuel" position to provide the refueling interlocks normally available during aefueling operations as explained in Part A of these- Bases. In order to withdraw a second control' rod af ter. withdrawal of the first rod, it is necessary to bypass the refueling interlock on the first control rod which prevents more than one control rod from being withdrawn at the same time. The requirem?nt.that an adequate shutdown margin be demonstrated with the control rods remaining in service insures that inadvertent criticality cannot occur.

during this maintenance. - The shutdown margin is verified by demonstrating that the core is shut down even if the strongest control rod remaining in service is fully withdrawn. Disarming the directional control valves.does not inhibit control rod scram capability.

-E. The intent of this specification is to permit the unloading of a significant portion of:the reactor core for such purposes as inservice inspection requirements, examiniation of the core support plate, etc. This specification provides assurance that inadvertent criticality does not occur during such operation.

This operation is performed with the mode switch in the " Refuel" position to provide the refueling interlocks normally available during refueling as explained in the Bases for Specification 312. A. In order to withdraw more than one control rod, it is necessary to bypass the refueling interlock on each withdrawn control rod RYith prevents sore than one control rod from being withdrawn at a time. The requirement that the fuel assemblies in the cell controlled by the control rod be removed from the- raactor core before the interlock can be bypassed insures that withdrawal of another control rod does not result in inadvertent criticality. Each control rod essentially provides reactivity control for the fuel assemblies in the cell associated with that control rod. Thus, removal of. an entire cell (fuel assemblies plus control rod) results in a lower reactivity pottatial of the core.

One method available for unloading or reloading the core is the spiral unload / reload. A spiral unloading pattern is one by which the fuel in the outermost cells (four fuel bundles surrounding a control rod) is removed first. Unloading continues by unloading the remaining outermost fuel by cell with the exception of 2 diagonally adjacent fuel assemblies-next to each SRM. These assemblies will be removed after the removal of the center cell, which is the last cell removed from the core. Spiral reloading is reverse of unloading with the exception that.two diagonally adjacent bundles, which have previously accumulated exposure in-core, are placed next' to each of the 4 SRMs before the actual spiral reloading begins. Additionally, at least 50% of the fuel asemblies to be reloaded into the core shall have previously accumulated a minimum exposure of 1000 Mwd /T to insure the presence of a minimum neutron flux as described in Bases Section 3 12.B.

F. The intent of this specification is to assure that the reactor core has been in the cold shutdown conditon for at . least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following power operation and prior to fuel handling or movement. The safety analysis for the postulated refueling' accident assumed that the reactor had been shut down for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for fission product decay prior to any fuel handling which could result 'in dropping of a fuel assembly.

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