ML20116K737
| ML20116K737 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/13/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20116K735 | List: |
| References | |
| NUDOCS 9608150206 | |
| Download: ML20116K737 (4) | |
Text
44 g%
1 UNITED STATES s
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066-4001
.....,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
RELATED TO AMENDMENT N0. 201 TO FACILITY OPERATING LICENSE N0. DPR-65
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NORTHEAST NUCLEAR ENERGY COMPANY
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THE CONNECTICUT LIGHT AND POWER COMPANY THE WESTERN MASSACHUSETTS ELECTRIC COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT NO. 2 l
DOCKET N0. 50-336 i
1.0 INTRODUCTION
By letter dated July 3, 1996, the Northeast Nuclear Energy Company (the licensee) submitted a request for changes to the Millstone Nuclear Power Station, Unit No. 2, Technical Specifications (TSs). The requested changes would remove the requirement that the boron concentration in all filled portions of the reactor coolant system be " uniform." The requested change would only be applicable during the cycle 13 mid-cycle reactor fuel offload / reload activities.
j In February of 1996, Unit No. 2 was shut down due to operability problems.
During plant cooldown, the boron concentration of the reactor coolant system (RCS) was increased to approximately 1320 parts per million (ppm) to maintain a safe shutdown margin of at least 5 percent for Mode 5.
In mid-March of l
1 1996, it was discovered that a low pressure safety injection (LPSI) system valve could not be closed and several attempts to close the valve failed. The licensee determined that the shutdown cooling system (SCS), which shares some of its components with the LPSI system, had to be removed from service in order to isolate flow through the failed valve and allow repairs to be performed.
l The licensee also determined that the safest repair option available is to offload the reactor fuel to the spent fuel pool. Since the failure of the LPSI system valve was not known and the need for fuel offloading was not anticipated at the time of shutdown, the RCS was not borated to 1720 ppm boron concentration required in Mode 6 for offloading / reloading fuel. This led the licensee to submit a one-time TS change request for this cycle to allow for the isolation and repair of the failed LPSI valve.
9608150206 960813 PDR ADOCK 05000336 P
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' 2.0 EVALUATION
'S 3.9.1 requires that during operation-in Mode 6 with the reactor vessel head j
unbolted or removed, the boron concentration of all filled portions of.the reactor coolant system (RCS) and the fueling canal shall be maintained uniform l
and sufficient to ensure that, a) either a Keff of 0.95 (which is 5 percent suberitical) or less exists, or b) that a boron concentration greater than or i
equal to 1720-ppe exists, whichever is the more restrictive.
i As noted above, the licensee proposes to revise TS 3.9.1 to allow a one-time change during the current mid-cycle 13 shutdown, which will not require
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uniform boration and will allow the water volumes in the steam generators and i
the connecting piping to be as low as the Mode 5 requirement of 1300 ppm. The i
TS Bases will also be modified to reflect and explain the changes. This is needed because the SCS was aligned for decay heat removal and the reactor coolant pumps (RCPs) were shut off, prior to the decision in which it was determined that it would be necessary to place the unit in Mode 6 to allow the i
offloading of the reactor fuel.
With the RCPs shut off, the uniform mixing of
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the boron in the steam generators and the steam generators cold leg piping is ineffective. However, as the licensee noted, the coolant in other active regions of the RCS, the shutdown cooling loop, and the reactor vessel core i
regions are easily mixed and borated to the higher concentration required for Mode 6, which is 1720 ppm.
The change to TS 3.9.1.will require that the active regions of the RCS, the shutdown cooling loop, and the reactor vessel core region be borated to a l
boron concentration greater than 1950 ppm. To minimize the stagnant volume of 1
water in the RCS before entering into Mode 6, the licensee will drain the RCS l
level to approximately 36 inches below the reactor vessel flange, borate the i
active regions to 1950 ppe, and refill the RCS. Analysis by the licensee l
shawed that this approach ensures that the core will remain at least 5 percent j
subcritical during offloading / reloading activities.
i The licensee performed a calculation that demonstrated that a boron 1
concentration of 1950 ppm will be sufficient to ensure that, in the unlikely event that the stagnant lower concentration borated water in the cold leg regions of the steam generator and piping, mixes with the higher borated water i
while the SCS is operating, the final mixed boron concentration will be
. greater than that required for Mode 6.
The licensee analyzed the potential impact of the non-uniform boron concentration on the Final Safety Analysis Report (FSAR) Chapter 14 events.
The only accident impacted by the proposed one-time TS change is the boron dilution accident. This analyzed accident assumes a dilution rate of 88 gpm (two charging pumps) and an initial boron concentration corresponding to a Keff of at least 0.95.
It is stipulated in the FSAR that the operator has 30 minutes from the initiation of the event to take action to preclude reactor core criticality.
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3-TS 3.9.1 requirements ensure that the initial conditions assumed in the analysis of the baron dilution event are preserved. The new analysis conducted by the licensee for the proposed TS change indicates that there is at least 30 minutes for the operator to respond to a boron dilution event.
The licensee next addressed the possibility of loss of shutdown cooling flow.
With loss of shutdown cooling flow, the RCS temperature would likely increase, i
and eventually, the RCS coolant in the core would begin to boil. As the water level in the RCS decreases due to boiling, the 1300 ppm borated water in the
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cold legs and steam generators, will eventually find its way into the versel core region unmixed.
This unmixed water, at a 1300 ppm boron concentration, would still be sufficient to maintain the core greater than 5 percent subcritical (with all the rods inserted) without operator intervention. Thus, under these conditions the consequences of losing the shutdown cooling flow are acceptable with regard to maintaining subcriticality margin, j
3.0
SUMMARY
Therefore, based on the details provided above, the staff has determined that the proposed one-time changes to TS 3/4.9.1 are acceptable during the current cycle 13 mid-cycle core offload / reload activities necessary to implement repairs on the failed LPSI valve.
The staff has also determined that the modified TS Bases adequately reflect the one-time TS change.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Connecticut State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes surveillance requirements. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (61 FR 36583). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
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6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: T. Attard Date: August 13, 1996
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