ML20210L917
| ML20210L917 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 08/12/1997 |
| From: | Hill W NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9708210354 | |
| Download: ML20210L917 (3) | |
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Northem States Power Company i
Monticello Nuclear Generating Plant i
2007 West Hwy 75 Monticello, Minnesota 55362 9637 I
August 12,1997 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 l
Information and Documentation of Licensino issues The purpose of this letter is to provide documentation of NSP's position on certain licensing issues.
These issues have been discussed with the Monticello Project Manager and are addressed separately below.
Torus Level A recent modification to the ECCS suction strainess which increased the strainer area resulted in an insignificant yet finite increase in the amount of additional water displaced within the torus water volume.
This increase results in an inconsistency in the basis of the volumetric limits for the suppression chamber water voNme technical specification. This inconsistency largely arises from the method by which the limit is expressed.
The applicable technical specification (3.7.A.1) defines the water volume limit in terms of cubic feet of water. Although volumes of water in the torus are usefulin establishing inputs for Mark I loading analyses, direct measurement of volume in terms of cubic feet is unsuitable for instrumentation and surveillance purposes. The actual volume is, in fact, presently monitored in terms of the corresponding height of water in the torus above and below an established instrument zero. The table below shows the relationship between the current technical specification limit, the corresponding instrumentation limits, and the submergence bases.
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' Technical Spectitcation
' Volume (tr')
Corresponding Corresponding Torus Limit Downcomer LevelInstrument Submergence (ft)
Reference (in) from instrument zero Upper Limit 72,910 3.58 2.9 Lower Limit 68.000 3.00
-4.0 3
If the additional 69 ft of water displaced by the strainer materialis considered, a hypothetical water volume addition of 72,910 f? will result in a corresponding level slightly above the maximum downcomer submergence of about 1/100th of a foot. The addition is described as hypothetical since it would be quite difficult to meter the associaled water volume increase.
It is noteworthy that the volumetric limits were used as assumptions in Mark I analyses and containment heat capacity analyses and herefore form the bases, along with the downcomer submergence, for the suppression pool limits. Consequently it is necessary to assign instrument limits that also consider the volumetric limits.
In order to address this inconsistency, Monticello has established administrative limits that more than compensate for the water displaced by the strainer material and still preserve the bases of the limits with l
increased conservatism. Water volume is now procedurally controlled to between +2.2 and -3.3 inches.
In order to address this discrepancy in the future, NSP comrus to change the suppression pool technical specification limits to correspond to instrumentation limits under the Improved Technical Specification (ITS) Program. This change will use ths guidance provided in the BWR4 Standard Technical Specifications (NUREG-M??) which expresses the suppression poollimits in terms of feet and not in terms of water volume.
SER Clanfication By letter dated July 25,1997, staff sent NSP an SER regarding its review of containment overpressure and NPSH at MNGP. In several sections of this letter, staff reiterated various analytical assumptions and values which were derived from an NSP letter of June 19.1997. It appears that certain values and assumptions in the staff's SER are slightly different than those stated in the June 19,1997 letter. These items have been discussed with the Monticello Project Manager, and it was the staffs intent to cite the assumptions and values as reported by NSP. NSP concurs with this approach. Therefore, unless otherwise negated by the staff, NSP will assume that the analytical assumptions and values as stated in the June 19,1997 sebmittal are the assumptions and values of record.
Thirty Day Report By letter dated November 1,1996, NSP provided its 180 day response to Bulletin 96-03, " Potential Plugging of Emergency Core Cooling Suction Strainers by Debris in Boiling-Water Reactors." A commitment to report the installation of new suction strainers within 30 days of project completion was contained in this letter. This modification was completed on July 29,1997. As previously indicated to the staff, NSP will address the debris plugging issues of the bulletin in separate correspondence.
Containment Design Codes A conference call between the staff and NSP was held on June 12,1997 to discuss the staffs Mark l SER for MNGP. NSP conveyed information on the MNGP Mark I program that is repeated, in part, below.
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,The staff, by its SER and NUREG-0061, uses the requirements of ASME Code Section lil,1977 Edition through the Summer 1977 Addenda as acceptance criteria for Mark i analyses. The NSP submittals for Mark l compliance included references to the Summer 1977 Addenda. These submittals, however, also included statements that the requirements of the code through the Summer 1977 Addenda were met "in general." In addition, later addenda (post Summer 1977) were includ:d as references. The statements contained in the submittals were not, of themselves, clear and consistent.
The staff was informed that the majority of design documents referenced the appropriate addenda, but NSP had identified a few design documents for the Mark l containment program that had cited later addenda up to and including Summer of 1981. In order to address this issue, NSP proposed, with the staffs concurrence, to conduct reconciliations to the Summer 1977 Addenda for the affected design documents. NSP also committed to provide a letter documenting the progress of the code reconciliations.
The code reconciliation efforts to date have not identified any material changes in the stress allowables i
between the Summer 1977 addenda and those used for the affected portions of the containment design.
Three calculations have been identified that will require reconciliation to the Summer 1977 Addenda.
- NSP has retained a consultant to conduct code reconciliations for these calculations.
This letter contains the following new NRC commitment:
NSP commits to change the suppression pool technical specification limits to correspond to the associated instrumentation limits under the MNGP Improved Technical Specification (ITS)
Program. This change will use the guidance provided in the BWR4 Standard Technical Specifications.
. Please contact Joel Beres, Licensing Engineer, at (612) 295-1436 if you require further information.
N William J. Hill Plant Manager Monticello Nuclear Generating Plant c;
Regional Administrator -lit, NRC NRR Project Manager, NRC Sr. Resident inspector, NRC State of Minnesota, Attn: Kris Sanda Jay Silberg I
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