ML20044B875

Suppls 920214 License Amend Request Re Revs to Reactor Protection Sys Tech Specs,Involving Elimination of Main Steam Line High Radiation Monitor Scram & Vessel Isolation Functions

ML20044B875
Person / Time
Site:	Monticello
Issue date:	03/05/1993
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-M82783, NUDOCS 9303110226
Download: ML20044B875 (3)

Text

.

v

. Northem States Power Company l

414 Nicollet Mall Minneapolis, Minnesota 55401-1927 Telephone (612) 330 5500 March 5, 1993 5

US Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Supplemental Information Concerning February 14, 1992 License Amendment Request Concerning Revisions to Reactor Protection System Technical Specifications (TAC M827BJ1 The purpose of this letter is to bring to your attention revised information f concerning a license amendment request we submitted on February 14, 1992. At that time, we proposed three changes to the reactor protection system technical specifications involving elimination of the main steam line high radiation monitor scram and vessel isolation functions, clarification of intermediate range monitor scram functional testing requirements, and  ;

clarification of the basis for average power range monitor bypasses. The proposed revisions were approved by the NRC, with minor changes, as license amendment No. 83 issued on August 18, 1992.

While preparing the plant modification package to implement the main steam line high radiation monitor change, a discrepancy was discovered in the offsite dose calculation that was prepared in support of our February 14, 1992-license amendment request. That calculation had been performed because.our review of NEDO-31400 led us to conclude that Monticello was not totally bounded by the NEDO-31400 analysis due to the relatively small size of the Monticello augmented offgas system charcoal filters.

On page A-5 of our February 14, 1992 license amendment request, we indicated ,

that we had performed a Monticello specific dose projection using the MIDAS f '

computer code and the source term from Table 2 of NEDO-31400. At the time, we considered the Table 2 source term to be more realistic based on source terms calculated by General Electric and Bechtel. However, during the modification package review, it was recognized that it would have been more conservative, j and therefore more appropriate, to have used the source term from NEDO-31400 j Table 1 for this analysis. The values in NEDO-31400 Table 1 represent the post accident activity inventories of nucleides airborne in the~ condenser which, in the worrt case, would be available for. discharge through the plant offgas stack with minimal delay.. The NEDO-31400 Table 2 activity inventories, which were used for our initial calculation, are lower because they are based )

on the assumption that the activity will be held up in the condenser before i release (1% per day leakage). i 9303110226 930305 PDR .ADOCK 05000263 P . ,k-/ D'i

~

PDR /

l

4 .

• USNRC NORTHERN STATES POWER COMPANY March 5, 1993 Page 2 In addition, we have concluded that the MIDAS computer code, which is designed to be a "best-estimate" code, was not the preferable computer code to use for this calculation. The MIDAS computer code projects, as accurately as possible, actual offsite doses based on parameters such as actual source term, real-time meteorological conditions, etc. As a "best-estimate" code, MIDAS does not incorporate the conservatisms typically associated with a licensing basis dose calculation which ensure that the analysis results are bounding for the postulated worst case.

To resolve any concerns over the acceptability of proceeding with the main steam line high radiation monitor modification in light of calculation discrepancies noted above, an independent and specific 10 CFR Part 100 dose ,

calculation for this modification was performed for Monticello by the Bechtel Corporation. This analysis used conservative computer codes and assumptions to ensure that the results would bound the worst case scenario. The resulting t dose projections, shown below, supersede those provided in Table 1, page A-6 of our February 14, 1992 submittal.

TABLE 1 (Revised)  ;

MONTICELLO SPECIFIC ANALYSIS "

NEDO-31400 SCENARIO 2 0FFSITE DOSE PROJECTIONS (Based on NEDO-31400 Table 1 source tern)

Offges Delay Integrated Whole Body Dose  % of 10CFR100 Thyroid Dose  % of 10CFR100  ;

Time t2 hour maxlean) Limit (25 Rem) Limit (300 Rem) 198 hoors <0.1 Rem <0.4 % 1.9 Rem 0.6 %

0 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> 0.4 Rem 1.6 % 5.6 Rem- 1.9 %

Note: The minirma holdup time of the offgas system is 30 minutes due to the installed of fgas delay line.

The dose values in this row reflect no (zero) deley beyond this minimum 30 minute delay.

As was expected, use of the more conservative source term values and calculation methodology to reevaluate the control rod drop scenario resulted in projected offsite doses higher than those originally calculated. However, the new dose projections are still only a small fraction of 10 CFR Part 100 limits, and satisfy Standard Review Plan Section 15.4.9 guidelines for being well within (less than 25% of) the acceptance limit for this accident scenario. Therefore, the conclusions of our February 14, 1992 License Amendment Request safety evaluation and no significant hazards determination remain unchanged.

The revised dose projections have been considered in the modification package safety evaluation, which concluded that this change does not represent an.

unreviewed safety question. However, since the original dose projections were mentioned specifically in your August 18, 1992 Safety Evaluation Report for license amendment No. 83, we felt it was appropriate to inform you of the f

c

.'6 i o

9 USNRC - NORTHERN STATES POWER COMPANY i March 5, 1993 Page 3 revised dose projections at this time rather than wait for our next 10 CFR Part 50, Section 50.59 Safety Evaluation summary report. This letter is for your information only and no specific action or response is required. We  ;

apologize for the error and any inconvenience this may have caused.

This letter contains no new NRC commitments, nor does it modify any prior commitments.

Please contact Terry Coss, Sr Licensing Engineer, at (612) 295 1449 if you require additional information.  ;

W Thomas M. Parker - i Director of Licensing  ;

Nuclear Generation cc: Regional Administrator-III, NRC ,

NRR Project Manager, NRC  !

Resident Inspector, NRC  ;

State of Minnesota, Attn: Kris Sanda ,

J Silberg i

t i