ML20196B957

Application for Amends to Licenses DPR-42 & DPR-60,allowing Limited Inoperability of Bast Level Channels & Transfer Logic Channels to Provide for Required Testing & Maint of Associated Components

ML20196B957
Person / Time
Site:	Prairie Island
Issue date:	11/25/1998
From:	Sorensen J NORTHERN STATES POWER CO.
To:
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ML20196B954	List: ML20196B949 ML20196B957 ML20196B972
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NUDOCS 9812010216
Download: ML20196B957 (14)

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c UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET NO. 50-282 50-306 License Amendment Request Dated November 25,1998  !

Boric Acid Storage Tank Level Instrumentation l l

Northem States Power Company, a Minnesota corporation, with this letter is submitting information to support a requested license amendment.

This letter contains no restricted or other defense information.

NORTHERN STATES POWER COMPANY BY e

[/Joel'P. Sorensen Plant Manager Prairie Island Nuclear Generating Plant On this 2.5 day of A/oVbb E/ lM[r before me a notary public in and for said County, personally appeared Joel P. Sorensen, Plant Manager, Prairie Island Nuclear Generating Plant; and being first duly swom acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are true and that it is not interposed for delay.

! L -

l _- ________ _ _ ____ __ ______v DALE M. VINCENT l j l ,' NOTARY Pytte.plenggota ' ,

l l DAKOTACOUNTY ,

.  :: - Yf_'f; 9812010216 981125 7 PDR ADOCK 05000282r P PDR L

• , i EXHIBIT A PRAIRIE ISLAND NUCLEAR GENERATING STATION License Amendment Request dated November 25,1998 '

Evaluation of Proposed Changes to the Technical Specification Appendix A of Operation License DPR-42 and DPR-60 Pursuant to 10 CFR Part 50, Sections 50.59 and 50.90, the holders of Operating Licenses DPR-42 and DPR-60 hereby propose the following changes to the Technical Specifications contained in Appendix A of the Facility Operating Licenses:

BACKGROUND The two Prairie Island units share three boric acid storage tanks (BAST). One tank is normally aligned to each unit during power operation and the third tank acts as a  !

standby and is physically isolated. During power operation the tank acts as a source of highly concentrated boric acid to the chemical and volume control system. In addition, the boric acid tank aligned to a unit supplies the initial source of highly concentrated bonc acid solution for injection via the safety injection pumps into that unit's reactor coolant system following a safety injection signal. The injection of this highly concentrated boric acid solution is necessary, per current analyses', to mitigate the consequences of a main steam line break accident.

Each BAST is equipped with four level sensors which are divided into two channels of two sensors each (See Figure 1). The four level sensors on each BAST provide high, lo and lo-lo level alarms and associated interlocks. As described in the following paragraphs, the level channels are also interlocked to automatically open the safety injection pump RWST supply valves and close the safety injection pump boric acid supply valves on a lo-lo level in the selected BAST.

Three motor-operated valves are installed to isolate the BASTS from the suctions of the two safety injection pumps. Two of the valves2 (MV-32081 and MV-32082)(see On June 26,1997, NSP submitted a revised main steam line break methodology for NRC Staff review. If that methodology is approved by the NRC, and is then used in the analysis of the main steam line break accident, it is expected that the injection of highly concentrated boric acid will not be required for mitigation of the accident.

2 The valves noted in the following discussion are Unit i valves. There are comparable valves on Unit 2, and the following discussion is also applicable to Unit 2 1

c Figure 2) are redundant, parallel valves normally closed when the safety injection system is aligned for standby ECCS operation. The third valve (MV-32083) is located downstream of the parallel valves and per Technical Specifications is maintained open with its motor control center supply breaker physically locked in the off position. This valve is installed to allow isolation of the BASTS should one of the other two isolation valves fail to close. Each of the three valves can be controlled from the control room.

When an 'S' signal (safety injection)is generated, valves MV-32081 and MV-32082 automatically open. Valve MV-32083 also receives an 'S' signal to open but is already open with its motor control center supply breaker physically locked in the off position.

P When the level in the selected BAST falls below the 1o-10 level setpoint, an 'L' signal is generated. An "L" signal is generated by having at least one Lo-Lo level sensor in each channel activated. The 'L' signal closes valves MV-32081 and MV-32082 and i opens the safety injection pump RWST suction valves. Safety injection pump boric acid supply valve MV-32083 is not affected by the 'L' signal.

I The safety injection pump RWST supply valves (MV-32079 and MV- 32080) are '

redundant, parallel motor-operated valves used to isolate the safety injection pump suction from the RWST. The valves are normally closed when the safety injection system is aligned for standby ECCS operation. The valves can be operated from the control room. When the selected BAST level decreases to the lo-lo level setpoint, the valves are opened automatically by the 'L' signal.

The three BASTS are numbered 11,21 and 121. A selector switch in the control room is used to designate which BAST level interlocks are aligned to the suction valves of the two safety injection pumps for emergency operations. The switch also places the BAST level interlock logic in service for the selected BAST. The three switch positions are:

1. T1-T2 - This position aligns the #11 BAST to Unit 1 and the #121 BAST to Unit 2

(#21 BAST in standby). ,

2. T2-T3 - This position aligns the #121 BAST to Unit 1 and the # 21 BAST to Unit 2

(#11 BAST in standby).

3. T1-T3 - This position aligns the #11 BAST to Unit 1 and the #21 BAST to Unit 2

(#121 BAST in standby).

Manual isolation valves are installed in the boric acid / safety injection supply headers to allow isolation of the standby BAST.

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Prairie Island Technical Specification 3.2.B.5 requires the operability of the BAST interlocks described above. In addition, Technical Specification Table TS.4.1-1C, Functional Unit 7, requires the functional testing of the BAST to RWST transfer logic on a monthly basis. In order to complete the testing required by the Technical Specifications, BAST level channels (and associated sensors) and BAST to RWST transfer logic channels must be made inoperable. However, the Prairie Island Technical Specifications do not contain the allowances for the inoperability of BAST level channels or BAST to RWST transfer logic channels necessary to perform the required testing. This lack of allowance for channel inoperability also limits the performance of preventative and corrective maintenance on the system when above MODE 5.

This License Amendment Request proposes changes to the Prairie Island Technical Specifications which would allow limited inoperability of BAST level channels and BAST to RWST transfer logic channels to provide for required testing and maintenance of the associated components.

PROPOSED CHANGES AND JUSTIFICATION OF CHANGES A brief description of the proposed changes are provided below along with a discussion of the justification for each change. The specific wording changes to the Technical Specifications are provided in Exhibits B and C.

Table TS.3.5-2B, Functional Unit 9 - Boric Acid Storage Tank The BAST level instrumentation and BAST to RWST transfer logic are being incorporated into the engineered safety features actuation system instrumentation table as new Functional Unit 9. As described below, this proposed new functional unit clearly delineates the conditions for the operability of the BAST level channels and BAST to RWST transfer logic channels, and provides references to the actions to be taken in the event that a required component is inoperable.

The proposed changes will allow the limited inoperability of BAST level channels and BAST to RWST transfer logic channels necessary for testing and maintenance  !

of the associated components.

Table TS.3.5-2B, Functional Unit 9a - Lo-Lo Level Proposed Functional Unit 9a delineates the requirements for operability of the BAST lo-lo level function. The proposed functional unit specifies the total number of level sensors and channels, the number of sensors and channels required to actuate the BAST to RWST transfer and the minimum number of sensors and channels required 3

to be operable. The proposed change is consistent in format to other instrumentation in Table TS.3.5-28 with similar logic configurations.

The proposed applicable MODES are the same as those specified for the transfer interlocks in current Technical Specification 3.2.B.5. A reference to Action 34 is provided to delineate the actions to be taken when any of the required BAST level channels are inoperable. Proposed Action 34 is discussed in more detail below.

Table TS.3.5-28, Action 34 Proposed Action 34 specifies that with the number of operable channels less than the total number of channels, operation may proceed provided the inoperable channel is placed in the tripped condition within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. Placing an inoperable channel in the tripped condition ensures that if the BAST to RWST transfer becomes necessary, the inoperable channel will not prevent the transfer. The 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> allowance for completion of this action allows adequate time for personnel to complete tripping of the channel, while minimizing the risk that the transfer function could be defeated by an inoperable channei during an event. The proposed requirement to place an inoperable channel in the tripped condition within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> is consistent with the actions specified for other similar instrumentation in Table TS.3.5-2B.

As specified in proposed Functional Unit 9a, there are two level sensors associated with each of the two level channels. A level channel can be tripped by tripping either or both of the level sensors associated with that channel. Placing a channel in the trip condition will allow either sensor in the operable channel to cause transfer on Lo-Lo BAST level.

The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation on operation with an inoperable BAST level channel is being proposed because even though premature transfer is only a concern for a main steam line break, should a premature transfer occur during a main steam line break, it would defeat a safety function required by analysis to mitigate that event.

Because of the low probability of a main steam line break, the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation limits the risk from a premature transfer from BAST to RWST while providing time for testing and the repair or replacement of failed components. The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowance for operation with an inoperable BAST level channel is comparable to the allowed out of service times specified in Prairie Island Technical Specifications 3.2.C.5 and 3.3.A.2.d for related BAST and RWST valves.

Technical Specification 3.2.C.5 allows any one redundant automatic valve, required for boric acid injection following a steam line break, to be inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (i.e., allows one of the BAST supply valves closed by the BAST to RWST transfer 4

e e l

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4 logic to be inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />). Technical Specification 3.3.A.2.d allows any redundant valve in the system, required for safety injection, to be inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> (i.e., allows one of the RWST supply valves opened by the BAST to RWST transfer logic to be inoperable for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />). The effect of continued operation with an inoperable BAST level channel is comparable to that associated with continued operation with an inoperable BAST supply valve and RWST supply valve.

If the inoperable BAST level channel cannot be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />, proposed Action 34 requires that the unit be brought to at least hot shutdown within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. These are the standard shutdown times utilized throughout the Prairie Island Technical Specifications.

Table TS.3.5-2B, Functional Unit 9b - Automatic Actuation Logic & Relays Proposed Functional Unit 9b delineates the requirements for operability of the BAST j to RWST transfer actuation logic and actuation relay channels. The proposed l functional unit specifies the total number of channels, the number of channels required to actuate the BAST to RWST transfer and the minimum number of channels required to be operable. The proposed change is consistent in format to other actuation logic channels in Table TS.3.5-2B.

The proposed applicable MODES are the same as those specified for the transfer interlocks in current Technical Specification 3.2.B.5. References to Actions 35 and 36 are provided to delineate the actions to be taken when one or both of the required BAST to RWST transfer actuation logic channels are inoperable. Proposed Actions 35 and 36 are discussed in more detail below.

Table TS.3.5-28, Action 35 Proposed Action 35, which is associated with the BAST to RWST transfer logic channels, allows continued plant operation for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with an inoperable logic channel. The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation limits the risk incurred from operating with an inoperable logic channel, while providing time for testing and the repair or replacement of failed components.

As described above, in the discussion associated with proposed Action 34, the 72 i hour allowance for operation with an inoperable BAST to RWST logic channel is comparable to the allowed out of service times specified in Prairie Island Technical Specifications 3.2.C.5 and 3.3.A.2.d for related BAST and RWST valves. Since  ;

each BAST to RWST logic channel is only associated with one set of redundant BAST and RWST supply valves, the allowance for continued operation with an I inoperable logic channel is comparable to operation with an inoperable BAST or l RWST supply valve. With one logic channelinoperable, the impact of the failure of I 5

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4 a 1 the operable logic channelis comparable to the failure of the associated redundant BAST or RWST supply valves.

l With one channel of the BAST to RWST transfer logic inoperable, the redundant channel is still available and capable of performing the intended design function.

The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation on operation with one transfer logic channel inoperable is being proposed because even though the operable channel is still available to perform the required transfer function, a failure of the redundant channel could result in a premature transfer or failure of the BAST to RWST transfer function.

Because of the low probability of an event requiring the function of the BAST to RWST transfer, the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation limits the risk associated with an inoperable BAST to RWST transfer logic channel, while providing time for testing and the repair )

or replacement of failed components. l If the inoperable logic channel cannot be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> I proposed Action 35 requires that the unit be brought to at least hot shutdown within ,

6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and to cold shutdown within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. These are the standard l

shutdown times utilized throughout the Prairie Island Technical Specifications. 1 Table TS.3.5-2B, Action 36 i

Proposed Action 36, which is also associated with the BAST to RWST transfer logic )

channels, allows continued plant operation for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> with both BAST to RWST  ;

transfer logic channels inoperable. The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> limitation limits the risk incurred from l operating with both logic channels inoperable, while providing time for testing of the i logic channels.

As described above, one of two BASTS can be aligned to a unit to provide concentrated boric acid solution to the safety injection pumps. Because of this ability to utilize either of two BASTS, each channel of the BAST to RWST transfer logic has inputs from each of the two BASTS that can be aligned to the unit.

Therefore, in order to completely test each logic channel, the BAST selector switch  ;

must be re-positioned during the logic testing. l For example, if BAST #11 were aligned for safety injection on Unit 1 and BAST #121 was the standby tank (BAST selector switch position T1-T3), the portion of the transfer logic associated with #11 would be tested first. That testing would be accomplished under proposed Action 35. Following completion of the testing of the

logic channels on BAST #11, the BAST selector switch would be re-positioned to the l T2-T3 position. In this condition BAST #11 would still be physically aligned to l provide concentrated boric acid solution to the Unit 1 safety injection system.

However, the logic controlling the transfer from BAST to RWST would be fed from 6

! the level channels on BAST #121. If an event requiring a safety injection were to

! occur while in this alignment, the boric acid solution would be drawn from BAST #11, l but the transfer to RWST would not occur because the level sensors on #121 would not see a decrease in level (#121 tank is isolated). Thus, the re-alignment of the logic to BAST #121 during the logic testing makes both channels of the BAST to

! RWST logic inoperable.

! The proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT is comparable to the time allowed by the Prairie Island Technical Specifications for the loss of function of other systems. It is also l comparable to the requirements of Technical Specification 3.0.C which allows one l hour to prepare for shutdown if an Limiting Condition for operation is not met and l there is no applicable action statement. For example, if both safety injection pumps were found to be inoperable, Technical Specification 3.0.C would allow 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to prepare for shutdown of the unit. This is comparable to the inoperability of both l BAST to RWST logic channels. Both conditions could result in the loss of the safety

! injection pump flow if an accident where to occur.

l The 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> allowed by Technical Specification 3.0.C is acceptable because of the short duration of continued plant operation in combination with the low probability of l an accident occurring during the period ofinoperability. The proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> ACT for the BAST to RWST transfer logic channels is acceptable for the same reason.

The equipment associated with the transfer from the BAST to the RWST is explicitly modeled in the Prairie Island PRA. A sensitivity analysis on the Prairie Island PRA model was performed removing credit entirely for all channels of BAST level instrumentation. This effectively fails the safety injection function for all accidents,

. since it is assumed that the automatic switchover to the RWST must occur for safety l Injection success. No credit was given for operator action to open (remotely or

( locally) the RWST supply valves normally opened by the BAST to RWST transfer j logic. The total core damage frequency (CDF) under these assumed conditions was calculated to be 6E-4/rx-yr, against a total baseline CDF of 2.4E-5/rx-yr. Applying the NEl PSA Applications Guide criteria for temporary risk increases gives a risk informed allowed out of service time (AOT) of approximately 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />.

The proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT for inoperability of both transfer logic channels will have an insignificant impact on overall plant risk. Even without credit for operator action, j the nsk informed AOT of 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> is significantly longer than the proposed AOT of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Even though not assumed in the PRA evaluation described above, operator action to mitigate a failure of the BAST to RWST transfer would be likely and such i action would further reduce the risk to the plant.

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's The insignificant increase in risk associated with the proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT is more than offset by the disadvantages associated with performing the monthly logic testing by re-aligning BASTS as described below.

The proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT is only applicable for inoperability for surveillance testing.

Proposed Action 36 requires that the plant be taken to Cold Shutdown within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> if one of the logic channels is not returned to operable status by the end of the AOT. These are the standard shutdown times utilized throughout the Prairie Island Technical Specifications Discussion of Alternative Testing Methods It is possible to complete testing of the BAST level channels and BAST to RWST transfer logic without placing the BASTS in the configuration described above if the BAST physical alignment is changed during the testing. Utilizing this technique testing of the BAST level channels on the standby BAST (#121) would be completed first. Then testing of the transfer logic channels on the inservice BAST (#11) would be completed. Then prior to testing the portion of the logic channels associated with BA.ST #121, the BASTS would be physically re-aligned such that BAST #121 was aligned for safety injection on Unit 1 (#11 BAST isolated). As part of this re-alignment the BAST selector switch would be re-positioned to the T2-T3 position and testing of the logic channels associated with BAST #121 would be completed.

At least one logic channel would remain operable at all times throughout the testing.

Finally testing of the BAST level channels on BAST #11 would be completed.

While this testing configuration offers the advantage of not requiring inoperability of level channels on the inservice BAST or the simultaneous inoperability of both logic channels, it is not the preferred testing method for the following reasons:

1. If for any reason the testing of the transfer logic associated with one of the three BASTS could not be completed within the required monthly testing interval, that BAST transfer logic would have to be declared inoperable. With any one of the BASTS inoperable, the option of re-aligning the BASTS to complete testing of the logic channels would no longer be available. Technical Specifications would not allow re-alignment to an inoperable BAST. The inoperable BAST would have to remain inoperable until the next time the associated unit was taken below MODE

4. In this case testing of the level and logic channels on the two remaining inservice BASTS could not be completed by end of the next one month surveillance interval and both units would have to be shutdown.

2. The physical re-alignment of the BASTS involves sampling of the boron concentration in the tanks and the manipulation of manual valves to complete.

During the re-alignment it is likely boric acid will be transferred between the 8

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tanks. Completion of the transfer logic testing utilizing physical BAST re-alignment would require as many as four re-alignments each month to complete the logic testing for both units. This would increase the wear and tear on associated equipment and would increase the burden on the operations staff.

3. The multiple re-alignments of the BASTS on a monthly basis would also increase the potential for errors in BAST alignment. j 1

Specification 3.2.8 l Specification 3.2.B is being modified to incorporate a reference to Table TS.3.5-28.

This reference is necessary since Table TS.3.5-2B, as revised by this License Amendment Request, will contain actions to be taken in case of the inoperability of the BAST to RWST transfer instrumentation which is required to be operable per Specification 3.2.B.5.

Bases for Table TS.3.5-28, Functional Unit 9

. The bases for Section 3.5 are being revised in accordance with the changes made l

in the specification es stated above. The changes to the bases are shown in Exhibit B. I I

SAFETY EVALUATION The Prairie Island Technical Specifications currently only require the BAST to RWST l " interlocks" to be operable and require the transfer logic to be tested monthly with no specified actions or AOTs to allow for the testing. The incorporation of the proposed Function Unit 9 will enhance plant safety by more clearly defining the operability requirements associated with the BAST to RWST transfer instrumentation. The incorporation of the proposed actions and allowed out of service times for the BAST level channels and logic will also enhance plant safety by allowing testing and maintenance of the associated components without excessive manipulation of the BAST instrumentation and valves and by reducing the potential for unnecessary ,

. plant shutdowns.  :

)

1 Proposed Action 34 will help ensure that the BAST level channels are properly L tested and maintained by providing the flexibility necessary to perform testing and maintenance on the instrumentation. While the enhanced ability to perform testing and maintenance requires the addition of AOTs for the level instrumentation into the  !

. . Technical Specifications, the additional risk resulting from the proposed AOTs is  !

! minimal because;

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~ _ _ _ _ _ __ _ _ __

• The inoperability of a single BAST to RWST level channel alone will not prevent a BAST to RWST transfer or result in a premature BAST to RWST transfer, i

. Propoced Action 34 requires that an inoperable level channel be placed in the tripped condition within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. This action minimizes the risk that the transfer function could be defeated by the failure of the channel, while still providing adequate time for personnel to complete tripping of the channel.

. A unit is only allowed to operate for a maximum of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with an inoperable l BAST level channel. This limits the risk associated with the potential for a failure of the redundant channel causing a premature BAST to RWST transfer.

. The proposed 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation provides a level of nrotection comparable to the  ;

current Technical Specification AOTs associated with 'he BAST and RWST '

supply valves.

Proposed Action 35 will help ensure that the BAST to RWST logic channels are properly tested and maintained by providing the flexibility necessary to perform j testing and maintenance on a single logic channel. While the enhanced ability to '

perform testing and maintenance requires the addition of an AOT for an inoperable logic channel into the Technical Specifications, the additional risk resulting from the proposed AOT is minimal because:

. The inoperability of a single BAST to RWST transfer logic channel will not prevent a BAST to RWST transfer or result in a premature transfer.

. A unit is only allowed to operate for a maximum of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with an inoperable  !

BAST to RWST transfer logic channel. While the inoperability of one of the logic l channels alone will not prevent a BAST to RWST transfer, an additional failure in j the operable channel could result in a premature transfer or failure to transfer. l The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation on operation with an inoperable logic channel limits the l risk associated with a failure in the operable channel.

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. The proposed 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limitation provides a level of protection comparable to the current Technical Specification AOTs casociated with the BAST and RWST l supply valves.

Proposed Action 36 will help ensure that the BAST to RWST logic channels can be tested in a manner which minimizes the manipulation of the BACT instrumentation and valves, reduces the potential for errors and reduces the potential for unnecessary plant shutdowns. While proposed Action 36 incorporates an AOT for the inoperability of both logic channels into the Tect nical Specifications, the additional risk resulting from the proposed AOT is n>inimal because:

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. The proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT is comparable to the time allowed by the Prairie Island Technical Specifications for the loss of function of other systems. It is also comparable to the requirements of Technical Specification 3.0.C which allows one hour to prepare for shutdown if an Limiting Condition for operation is not met and there is no applicable action statement.

. Risk to the plant incurred by the inoperability of both channels of the BAST to RWST transfer logic is minimized by the short duration of continued plant operation allowed by the proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT in combination with the low probability of an accident occurring during the allowed period of inoperability.

• Even without credit for operator action, the risk informed AOT of 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> is significantly longer than the proposed AOT of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The addition of operator action, which is likely, would significantly increase the risk informed AOT.

. The insignificant increase in risk associated with the proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT is more than offset by the disadvantages associated with performing the monthly '

logic testing by re-aligning BASTS.

. The proposed 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> AOT is only applicable for inoperability for surveillance testing. Proposed Action 36 requires that the plant be taken to Cold Shutdown  ;

within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> if one of the logic channels is not returned to operable status by '

the end of the AOT.

In conclusion, Northern States Power believes there is reasonable assurance that the health and safety of the public will not be adversely affected by the proposed Technical Specification changes.

DETERMINATION OF SIGNIFICANT HAZARDS CONSIDERATIONS

1. The proposed amendment will not involve a significant increase in the probability or consequences of an accident previously evaluated.

The proposed changes do not affect any system that is a contributor to initiating et snts for previously evaluated design basis accidents. Therefore, the proposed changes do not involve a significant increase in the probability of an accident previously evaluated.

The proposed Actions 34,35 and 36 will allow limited continued plant operation with portions of the BAST to RWST transfer instrumentation inoperable.

However, because the proposed actions place time limits on inoperability comparable to those already approved for use in the Prairie Island Technical 11

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i l Specifications the proposed changes do not involve a significant increase in the consequences of an accident previously evaluated.

The remaining proposed changes to Table TS.3.5-2B and to Specification 3.2.B are administrative in nature. The changes to Table 3.5-2B incorporate design information on the BAST to RWST transfer instrumentation which clarifies the operability requirements for the instrumentation. The changes to Specification 3.2.B add a reference to Table TS.3.5-2B. Therefore, because of the administrative nature of the changes, they do not involve a significant increase in the consequences of an accident previously evaluated.

2. The proposed amendment will not create the possibility of a new or different kind of accident from any accident previously analyzed.

The proposed changes do not alter the design or function of any plant component and do not install any new or different equipment. The proposed char.ges do not alter the operation of any plant component in a manner which could lead to a new or different kind of accident. Therefore the possibility of a new or differerit kind of accident from those previously analyzed has not been created.

3. The proposed amendment will not involve a significant reduction in the margin of safety.

The proposed Actions 34,35 and 36 will allow limited continued plant operation with portions of the BAST to RWST transfer instrumentation inoperable.

However, because the proposed actions place time limits on inoperability comparable to those already approved for use in the Prairie Island Technical Specifications the proposed changes do not involve a significant reduction in the margin of safety. j The remaining proposed changes to Table TS.3.5-2B and to Specification 3.2.B  !

are administrative in nature. The changes to Table 3.5-2B incorporate design j information on the BAST to RWST transfer instrumentation which clarifies the operability requirements for the instrumentation. The changes to Specification 3.2.B add a reference to Table TS.3.5-28. Therefore, because of the administrative nature of the changes, they do not involve a significant reduction in the margins of safety.

Considering the above evaluation and pursuant to 10CFR50.91, Northem States Power Company has determined that operation of the Prairie Island Nuclear Generating Plant in accordance with the proposed license amendment request does i

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not involve a significant hazards consideration as defined by Nuclear Regulatory Commission regulations in 10CFR50.92.

ENVIRONMENTAL ASSESSMENT l

Northern States Power Company has evaluated the proposed change and determined that:

1. The changes do not involve a significant hazards consideration,

2. The changes do not involve a significant change in the types or significant increase in the amounts of any effluents that may be released offsite, and

3. The changes do not involve a significant increase in individual or cumulative occupational radiation exposure.

Accordingly, the proposed change meets the eligibility criterion for categorical  !

exclusion set forth in 10CFR51.22(c)(9). Therefore, pursuant to 10CFR51.22(b), an )

environmental assessment of the proposed changes is not required. j I

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