B15738, Application for Amend to License DPR-65,making one-time Change to MP2 TS 3.9.1, Refueling Operations,B Concentration
| ML20112E291 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/03/1996 |
| From: | Rothen F NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES SERVICE CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20112E294 | List: |
| References | |
| B15738, NUDOCS 9606050218 | |
| Download: ML20112E291 (11) | |
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'\ . Northeast i d*" semt, seain, cm,037 Utilities System Northeut Utilities service company P.O. Box 270 liartford, CT 06141-0270 (203) 665-5000 June 3, 1996 Docket No. 50-336 B15738 Re: 10CFR50.90 U.S. Nuclear Regulatory Commission Attention: Document Control Desk j Washington, DC 20555 Millstone Nuclear Power Station, Unit No. 2 Proposed Revision to Technical Specification Refuelina Boron Concent rqt;.i.,gn Northeast Nuclear Energy Company -(NNECO) hereby proposes to amend !
Facility Operating License No. DPR-65 by incorporating changes to l the Millstone unit No. 2 (MP2) Technical Specifications as described herein. This license amendment request is submitted pursuant to the requirements of 10CFR50.90.
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NNECO proposes to make a one-time change to MP2 Technical Specification 3.9.1, " Refueling Operations, Boron Concentration".
The proposed change would remove the requirement that the boron I concentration in all' filled portions of the Reactor Coolant System i be " uniform". This change would only be applicable during the MP2 Cycle 13 mid-cycle core off-load.
In support of this proposed license amendment:
Attachment 1 provides a description of the proposed change and a safety assessment for the change.
Attachment 2 provides the determination of No Significant Hazards Consideration (SHC).
-- Attachment 3 provides the marked-up version of tho appropriate pages of the current Technical Specifications.
- Attachment 4 contains the' retyped Technical Specification pages.
On February 20, 1996, Millstone Unit No. 2 was shutdown based on the possibility that the mesh of the Emergency Containment Sump Screens was not sized to prevent the ingress of particles large enough to clog the High Pressure Safety Injection (HPSI) valves.
During the subsequent plant cooldown, boron concentration of the n
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t U.S. Nucleat Regulatory Commission B15738/Page 2 Reactor Coolant System (RCS) was increased to approximately 1320 ppm to maintain shutdown margin for Mode 5. At this time, plant management made the decision to commence the mid-cycle surveillance outage which had originally been scheduled to begin
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in April. On March 14, 1996, during surveillance testing, it was discovered that Low Pressure Safety Injection (LPSI) valve 2-SI-645_could not be closed. In order to repair valve 2-SI-645, the Shutdown Cooling System will have to be removed from service since it is not possible to isolate flow through valve 2-SI-645 with-Shutdown Cooling in operation. After reviewing possible repair options, the most appropriate option appears to be an offload of the core to the Spent Fuel Pool. This course of action will permit removal of the Shutdown Cooling System from service.
Since the core offload could not have been anticipated at the time of shutdown, the. Reactor Coolant System was not borated to refueling concentration. When the determination was made to offload the core in support of the 2-SI-645 repairs, numerous engineering solutions were evaluated for increasing boron concentration in all filled portions of the RCS to refueling boron concentration. We are continuing to evaluate these solutions. It is possible that RCS boron concentration could be made uniform during the drain and fill operations necessary to establish the conditions prerequisite to implememting this proposed amendment.
Should such uniform conditions be established, this proposed amendment will be withdrawn.
As discussed in Attachment 2, the proposed license amendment-has been determined not to involve a Significant Hazards Consideration (SHC) pursuant to 10CFR50.92. Additionally, the proposed license amendment does not significantly increase the types or amounts of effluents that may be released offsite, nor does it significantly increase individual or occupational radiation exposure. Based on the foregoing, NNECO has determined that this license amendment request meets the criteria delineated in 10CFR51.22 (c) (9) for a categorical exclusion from the requirement for an environmental impact statement.
The Millstone Unit No. 2 Plant Operations Review Committee (PORC) and the Nuclear Safety Assessment Board (NSAB) have reviewed and concurred with the above determ'_ nations.
In accordance with 10CFR50.91 (b), a copy of this proposed amendment is being provided to the State of Connecticut State Liaison Officer.
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t U.S. Nuclear Regulatory Commission B15738/Page 3 If you have any questions, please contact Mr. Michael D. Ehredt at (860) 440-2142. 1 Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY l 1
FOR: T. C. Feigenbaum Executive Vice President and i Chief Nuclear Officer BY:
F. C. Rothen Vice President Attachments (4) cc: T. T. Martin, Region I Administrator D. G. Mcdonald, Jr., NRC Project Manager, Millstone Unit No. 2 P. D. Swetland, Senior Resident Inspector, Millstone Unit No. 2 K. T. McCarthy, Bureau of Air Management, Department of Environmental Protection Subscribed and sworn to before me this df day of [hnt o - , 1996 L L10 o krCh '
4 L Date Commission Expires: 9[h 97
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Docket No. 50-336 i B15738 l
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l Attachment 1 ,
1 Millstone Nuclear Power Station, Unit No. 2 l l
Proposed Revision to Technical Specifications i Refueling Boron Concentration i
Description of Proposed Changes I and Safety Assessment
4 U.S. Nuclear Regulatory Commission B15738/ Attachment 1/Page 1 Millstone Nuclear Power Station, Unit No. 2 Proposed Revision to Technical Specifications Refueling Boron Concentration Descriotion of Procosed Chance Refueling Operations Technical Specification 3.9.1 requires that, with the reactor vessel head unbolted or removed, the boron concentration of all filled portions of the Reactor Coolant System and the refueling canal shall be maintained uniform and sufficent to ensure that, a) either a Keff of 0.95 or less, or b) a boron concentration of greater than or equal to 1720 ppm, whichever is more restrictive.
The. proposed one-time Technical Specification change would strike the words "of all filled portions" and " uniform and" and add a footnote indicating that, for the Cycle 13 mid-cycle core off-load activities, it is acceptable for the boron concentrations of the water volumes in the steam generators and the connecting piping to be as low as 1300 ppm.
The Bases for 3.9.1 would be modified to explain that the boron concentration of the water volumes in the Pressurizer, Shutdown Cooling System, Reactor Vessel, Refueling Pool, and the associated connecting piping will be maintained at 1820 ppm boron concentration. This concentration will be high enough to ensure that, even in the unlikely event that all of the lower boron concentration water from the Steam Generators and connecting piping were to mix with the Shutdown Cooling System water, the resulting Shutdown Cooling System boron concentration will remain greater than the minimum required refueling boron concentration.
Safety Assessment Refueling Operations Technical Specification 3.9.1 requires that, with the reactor vessel head unbolted or removed, the boron concentration of all filled portions of the Reactor Coolant System (RCS) and the refueling canal shall be maintained uniform and sufficient to ensure that the more restrictive of the following conditions is met:
- a. Either a Keff of 0.95 or less, or
- b. A boron concentration of greater than or equal to 1720 ppm.
The proposed technical specification change to the limiting condition for operation would strike the words "of all filled portions" and " uniform and" and add a footnote indicating that for l
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. I U.S. Nuclear Regulatory Commission B15738/ Attachment 1/Page 2 the Cycle 13 mid-cycle core offload activities, it is acceptable for the boron concentrations of the water volumes in the steam generators and connecting piping to be as low as 1300 ppm. In i addition, a surveillance will be added to determine that the boron l l concentration is. greater than or equal to 1300 ppm in the steam i j generators prior to entry into Mode 6.
Millstone 2 was shutdown on February 20, 1996 due to a problem i concerning the' operability of the high pressure safety injection valves. Plant management decided to perform the planned mid-cycle ;
- . surveillance outage at that time. On March 14, 1996 a problem was i identified with low pressure injection valve 2-SI-645, which would not close. Over the next several weeks, attempts to close this l valve were unsuccessful and it was decided to offload the reactor.
core.
When the plant was shutdown in late-February, the Reactor Coolant j System (RCS) boron concentration was increased to approximately 1320 ppm to maintain shutdown margin for Mode 5. The shutdown cooling system was aligned and the reactor coolant pumps.were shut off. With the shutdown cooling system aligned to remove decay heat, the water in steam generators, reactor vessel upper head, !
and portions of the reactor coolant piping are stagnant. The
- water in other regions of the RCS and shutdown cooling loop are active and mixing will occur. The shutdown cooling loop and
- reactor vessel core regions can be easily borated to that required for Mode 6 operation. However, as identifiad in INPO Significant Operating Experience Report 94-2, RCS boration while on shutdown i
cooling with no reactor coolant pumps operating is ineffective in borating the stagnant regions of the RCS to that required for mode 6 operation.
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The proposed one-time technical specification change would require
- 'that the active regions of the RCS and shutdown cooling loop are borated to' greater than 1820 ppm. To minimize the stagnant volume of water in the RCS prior to entry into Mode 6,-the RCS level will be drained to mid-loop conditions, the active regions of the RCS
- will be borated to greater than 1820 ppm, and the RCS will be refilled. An calculation has been performed that demonstrates that a boron concentration of 1820 ppm will be sufficient to ensure that, in the unlikely event in which the remaining water of lower boron concentration in stagnant regions of the RCS mixes uniformly with the water in the active regions of the RCS, the resulting boron concentration would remain greater than the required refueling concentration. The assumption of uniform
. mixing is reasonable since the shutdown cooling system will be in operation.
The only event presented in FSAR Chapter 14 that is potentially impacted by this technical specification change is the boron
U.S. Nuclear Regulatory Commission B15738/ Attachment 1/Page 3 i
i dilution accident. For the boron dilution accident, it must be demonstrated that the operator has 30 minutes from the initiation of the event to take action to preclude core criticality. None of the other accidents analyzed in the FSAR are affected by the potential non-uniformity of the boron concentration in the RCS.
While an analysis of the loss of shutdown cooling flow is not presented in Chapter 14 of the FSAR, the impact of the technical specification change on a loss of shutdown cooling flow has also been evaluated.
The boron requirements of Technical Specification 3.9.1 ensure that the initial conditions assumed in the boron dilution accident analysis are preserved. The limiting boron dilution analysis in Mode 6 assumes a dilution rate of 88 gpm (two charging pumps) and an initial boron concentration corresponding to a Keff of 0.95.
The result of the boron dilution analysis ensures that there is at least 30 minutes for the operator to respond to a boron dilution in Mode 6 to prevent criticality. This boron dilution analysis in Mode 6 does not credit mixing of the water in the stagnant portions of the RCS to increase the time to criticality, as this would be non-conservative. Because portions of the RCS are stagnant and do not mix with the shutdown cooling loop and reactor vessel core region, the compensatory measure of increasing the boron concentration in the shutdown cooling loop and reactor vessel core region to greater than 1820 ppm will actually increase the time to core criticality beyond 30 minutes.
In the event of a loss of shutdown cooling flow, it is possible that some of the lesser borated water from the stagnant regions of the RCS could reach the core. With the loss of shutdown cooling flow, the RCS temperatures would increase, and eventually, the RCS would begin to boil. As the RCS inventory boils off, the level in the RCS would decrease, and the lesser borated water in the stagnant regions of the RCS could reach the reactor vessel core region. If we conservatively postulate that the less borated water in the stagnant regions of the RCS were to reach the reactor vessel core region unmixed, the minimum core boron concentration of 1300 ppm would still be sufficient to maintain the core greater than 5% subcritical (all control element assemblies inserted) without operator intervention,
S Docket No. 50-336 B15738 I
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Attachment 2 Millstone Nuclear Power Station, Unit No. 2 Proposed Revision to Technical Specifications Refueling Boron Concentration No Significant Hazards Consideration (SHC)
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U.S. Nuclear Regulatory Commission ;
B15738/ Attachment 2/Page 1 Millstone Nuclear Power Station, Unit No. 2 Proposed Revision to Technical Specifications Refueling Boron Concentration No Sionificant Hazards Consideration Determination In accordance with 10CFR50.92, NNECO has reviewed the proposed changes and has concluded that they do not involve a significant hazards consideration (SHC). The basis for this conclusion is that the three criteria of 10CFR50.92 (c) are not comprised. The proposed changes do not involve an SHC because the changes would not:
- 1. Involve a significant increase in the probability or consequence of an accident previously evaluated. I l
Refueling Operations Technical Specification 3.9.1 requires that, with the reactor vessel head unbolted or removed, the i boron concentration of all filled portions of the Reactor l Coolant System and the refueling canal shall be maintained j uniform and sufficient to ensure that the more restrictive of l the following conditions is met:
- a. Either a Keff of 0.95 or less, or-i
- b. A boron concentration of greater than or equal to 1720 !
ppm.
The proposed technical specification change would strike the words "of all filled portions" and " uniform and" and add a footnote indicating that for the Cycle 13 mid-cycle core offload activities, it is acceptable for the boron i concentrations of the water volumes in the steam generators and connecting piping to be as low as 1300 ppm. In addition, a surveillance will be added to determine that the boron concentration in the steam generators is greater than or equal to 1300 ppm prior to entry into Mode 6.
The impact of the change on the boron dilution accident and the loss of shutdown cooling flow has been evaluated. Based upon this evaluation, the proposed change to Technical Specification 3.9.1 does not involve a significant increase in the probability or consequences of these accidents. The probability of a boron dilution accident or a loss of shutdown cooling event is not increased by allowing the RCS boron concentration in the stagnant regions of the RCS to be less_than the previously required concentration since this is compensated by increasing the boron concentration requirement of the shutdown cooling loop in Mode 6. The consequences of
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U.S. Nuclear Regulatory Commission B15738/ Attachment 2/Page 2 a boron dilution accident would not be increased. In fact, the compensatory measure of increasing the RCS boron concentration in the shutdown cooling loops and reactor vessel core regions will result in a higher initial boron
, concentration for the boron dilution accident, which would j actually increase the time to core criticality, ensuring that the operator has at least 30 minutes to intervene. The consequences of a loss of shutdown cooling flow are not i increased as the core would continue to remain greater than 5% subcritical without operator intervention even if the less
< borated water in the stagnant regions of the RCS reached the core region without mixing.
- 2. Create the possibility of a new or different kind of accident from any previously analyzed.
i By maintaining 1820 ppm in the active region of the RCS, the i required shutdown margin is assured, even in the unlikely event that the stagnant regins of the RCS mix with the-active regions. Thus, the proposed technical specification change would not create the possibility of a new or different type of accident than previously evaluated. Further, the proposed change has no impact on the mitigation of a boron dilution accident or a loss of shutdown cooling event.
- 3. Involve a significant reduction in the margin of safety.
The proposed technical specification change will not result in a significant reduction in the margin of safety. The results of the boron dilution accident, and the loss of shutdown cooling event are.not adversely impacted by the modification to the RCS boration technical specification. In the event of a boron dilution accident, the operator wiL'.
Continue to have at least 30 minutes to prevent core criticality. Without crediting operator intervention, the potential core boron reduction associated with a loss of shutdown cooling event will not result in core criticality. l As such, there is no reduction in the margin of safety.
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Docket No. 50-336 B15738 l
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Attachment 3 i
Millstone Nuclear Power Station, Unit No. 2 Proposed Revision to Technical Specifications l Refueling Boron Concentration i l
Marked-up Pages