ML20033G010
| ML20033G010 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/27/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20033G009 | List: |
| References | |
| NUDOCS 9004040271 | |
| Download: ML20033G010 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR react 0R REGULATION WAIVER OF COMPLIASCE FOR lh0PERABLE SOURCE RANGE MONITORS TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT. UNIT 1 i
DOCKET NO. 50 327
1.0 INTRODUCTION
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waiver of compliance to Limiting Condition for Operation (LCO) y requested a
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On March 25, 1990, the Tennessee Valley Authority (TVA) verball 3.0.4 of the i
Sequoyah, Unit 1. Technical Specifications (TSs).
This waiver would allow Unit 1 to move from operational Mode 5 Cold Shutdown, to Mode 6. Refuelin with less than two operable source range nuclear instrumentation channels.g, j
This is currently not allowed by LCO 3.0.4.
LCO 3.0.4 does not allow entry of i
the unit into an " operational mode" unless the conditions for all applicable LCOs l
are met without relying on provisions in the associated action statements.
1herefore..the TSs did not allow the unit to enter Mode 6 without two operable source range channels.
Because the entry into Mode 6 is on the critical path to restart Unit I from its Cycle 4 refueling outage. TVA requested the waiver i
of compliance to LC0 3.0.4.
The verbal request was followed by a written request submitted in the TVA letter dated March 26. 1990 which documented the i
justification provided by TVA to the staff en March 25, 1990, i
The source range nuclear instrumentation channels are part of the excore I
(i.e., outside the core) nuclear instrumentation to measure the leakage neutron flux from the core.
The source range channels measure the lowest levels of the neutron flux during shutdown and startup.
There is a reactor trip off the source range channels to prevent too rapid an increase in reactor
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power during startup; however, no credit is given for this trip in the accioent t
analyses in Chapter 15 of the Sequoyah Final Safety Analysis Report.
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intermediate range and power range channels are to measure the next higher levels of the neutron flux.
i 2.0 DISCUS $10N Unit I shut down for its Cycle 4 refueling outage on March 17. 1990.
On l
March 25, 1990, the unit was in Mode 5 which meant that the core was :9beriti-cal (i.e.. less than 0.99 k was not greater than 200'F,ff) and the average reactor coolant temperature j
3 For entry into Mode 6 not greater than 0.95 and coolant tempera-tures less than 140'F)(i.e.. k.theunNfmust be able to meet LCO 3.9 LCO 3.9.2 requires that at least two source range neutron flux monitors or instrument channels be operable in Mode 6.
Action statements are provided with the LCO to address operational requirements with either one or more monitors inoperable.
The bases for LCO 3.9.2 state that the redundant monitoring 1
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capability ensures the ability to detect changes in the reactivity conditivn of the core. LCO 3.0.4 states that entry into an operational mode or other i
specified condition shall not be made unless the conditions for the LC0 are met without reliance on provisions contained in the action statements.
As part of the Unit 1 Cycle 4 refueling outage activities, entry into Mode 6 (i.e., the fir n reactor vessel head closure bolt less than fully tensior.ed) was scheduled to occur on March 26, 1990.
TVA expected to comply with LCO 3.9.2 with the oportbility of Source Rangt Nuclear Instrumentation Channel N31 and the bactup control rocm source range channel (1-RM-90-210).
Source 1
Range Channel N32 is currently inoperable as the result of modifications to j
upgrade source range and intermediate range nuclear instrumentation for com pliance with Regulatory Guide 1.97 and is not expected to be operable before the scheduled entry into Mode 6.
On March 17, 1990, a work request was initi-ated to troubleshoot Source Range Channel N31 because it has indicating unusu-
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ally high and it was subsequently returried to service.
However, on March 21.
1 1990. Channel N31 failed and on March 22, 1990, TVA dettrinined that the outer shield of the detector cable was shorted to ground.
TVA stated that detailed troubleshooting has ccnfirrned that repair of the short would require the removal of the detector from its instrument well j
hhich would significtntly impact critical path activities in the area of,the reactor vessel head. TVA stated that, therefore, its efforts have been directed toward the completion of the N32 modification to return a second source range channel to service, ar.d that it previously anticipated that this could be ccepleteo before entry into Mode 6.
based on current work status, however, TVA did not expect the modifications to N32 to be completed before the scheculed entry into Mode 6, although TVA efforts are continuing to expedite its return to service. Phone conference calls on March 26, 1990 with TVA confirmed that Channel N32 will not be available before the scheduled entry into Moce 6.
TVA stated that Action Stateraent 5 of LCO 3.3.1.1 was being complied with to ensure that adequate shutdown margin is available in Mode 5.
Problems were experienced by TVA within the last week with spiking on the backup source range channel. The spiking was the result of plasma-arc cutting activities, which have been terininated.
The backup channel is considered to be fully operable and reliable at this time. However, two operable source range channels are needed to enter Mode 6.
TVA is requesting a waiver of compliance for Unit 1 to LCO 3.0.4 as it applies to LCO 3.9.2.
This will allow entry into Mode 6 while complying with the action statements of LCO 3.9.2.
This will allow the detensioning and removal of the reactor vessel head closure bolts to froceed as scheduled in parallel with the return to service of Channel N32, tiereby avoiding an impact to the critical path schedule for the restart of Unit 1 from the Cycle 4 refueling outage. The bolt dettnsioning and removal activities are not defined as core olterations and are not capable of inducing reactivity changes in the core, so that they riet the action statements of LCO 3.9.2.
TVA committed to not remove the reactor vessel head until two source range channels are operable.
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3-3.0 EVALUATION l
A waiver of compliance to LCO 3.0.4 is only required for the very short perion l
of time required to change from Mode 5 to Mode 6.
By Table 1.1 of the Techni-cal Specifications, the transition f rom Mode 5 to Mode 6 occurs when the first closure bolt of the reactor vessel head is less than fully tensioned.
For configuration control purposes, the unit is declared by TVA to be in Mode 6 l
when the hydraulics of the bolt detensioning tool on the closure bolts are l
activated. Af ter entry into Mooe 6 the action previsions to LCO 3.9.2 for Inoperable source range channels wt 1 continue to be complied with as requirec.
TVA stated that the reactivity of the Unit 1 core is currently being main-i tained as required for Mode 6.
The Unit I reactor coolant system is borated to 2,118 parts per million (ppm), yieloing a neutron multiplication factor (k
) of 0.85, thereby ensuring sufficient shutdown margin. Dilution control is,Nhieved by the itoplenentdtion of Surveillance Instruction ($1)-214, *Uncon-trolled Boron Dilution." This procecure tegs out possibit dilution paths as required by Surveillance Requircment 4.9.1.3.
Temperature control during the transition from Mode 5 to Mode 6 and throughout Mode 6, is maintained by the residual heet removal system to less than 140 degrees Fahrenheit as required by the Technical Spcifications.
TVA explained that nuclear instrumentation monitoring of the Unit I core is f
currently being provided by the backup control room source range channel; t
This channel indicates in the backup control room, and a recorder has been added to the instrument loop to provide continut.us indication in the main l
control room. No alarms are provided by the backup source range channel in the main control room or the containment. The high flux at shutdown alarm, j
which is driven by the N31 and N32 channels, would normally alert the control room to excessively high neutron flux in the core. The lack of this alarm for entry into Pode 6 is not significant because dilution during refueling is l
prevented by the administrative controls placed on potential dilution sources r
described above. Additional monitoring capabilities are available with Inter-l neciate Range Channel N35 which has a reactor trip at high neutron flux levels.
Although the backup source range channel coes not have the alarms ciscussed above and a reactor trip which the Channels N31 and N32 have, it is considered i
equivalent to the normal source range Char.nels N31 and N32 in Mode 6 because of the acaiinistrative controls on potential dilution of the core coolant.
There-fore, Unit 1 entered Mode 6 wit,1 only one operable source range chonnel.
The waiver of compliance will allow entry of Unit 1 into Mode 6 while complying i
with the action staterents of LCO 3.9.2 by momentarily waiving the requirements of LCO 3.0.4.
The action is viewed as having no safety significance because i
the action provisions of LC0 3.9.2 will be complied with in Mode 6 as required.
Tbtre is no need to change any requiren4nts in the Technical Specifications, l
Because the waiver is rot altering any LCO or action statenent requirnents vther than the allowance of a mode change, the prob 6bility or consequences of a previously evaluated accident are not increased; the possibility of a new accident is not created; and the margin of safety is not reduced.
Therefore,
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4 the action dces rmt represent a significant hazards consideration.
Similarly, the waiver does not involve an unreviewed environmental question because it doet t.ot increase any limits cu allowed environmental impacts, change effluents or power levels, or result in unteviewed environmental satters,
4.0 CONCLUSION
Based on the above, the staff concluded that it was safe to allow Unit 1 to enter Pode 6 with only one opereble source range channel. This will allow TVA to detension and rem 3ve the reactor vessel head closure bolt while another source range channel is being made operable. Although LCO 3.9.2 allows the reactor vessel head to be removed while there are less than two operable source range channels, TVA constitted not to remove the vessel head until two source range chat.nels are operable. Any inoperability of the source range channels following the removal of the reactor vessel head will be addressed solely by the action statements of LCO 3.9.2.
On March 25,1990 at 8:30 p.m., the staff granted TVA the waiver of compliance to LCO 3.0.4 to allcw Unit I to enter Mode 6 as scheduled. The schedule to detension a vessel head closure bolt slipped from 3:00 a.m. on the 26th to 12:10 p.m. on the 26th, when a bolt was detensioned.
Principal Contributor:
J. Donohew Dated:
March 27. 1990 1