ML20042A967

Forwards Summary of Calculations Performed to Ensure Operator Sufficient Time to Take Action During Boron Dilution Transients Initiated by Hot & Cold Shutdown,Per 810710 Commitment.Administrative Procedures Adequate

ML20042A967
Person / Time
Site:	Maine Yankee
Issue date:	03/18/1982
From:	Garrity J Maine Yankee
To:	Clark R Office of Nuclear Reactor Regulation
References
JHG-82-49, MN-82-53, NUDOCS 8203240341
Download: ML20042A967 (9)

Text

{{#Wiki_filter:* s IRAHIE lHARHEE A10mlCP0l'KRCOMPARU*puougr,jain"g$s gdif (207) 623-3521 AQ March 18, 1982 MN-82-53 JHG-82-49 United States Nuclear Regulatory Commission Washington, D. C. 20555 W ~ \\ /t Attention: Office of Nuclear Reactor Regulation s --$[ MR 2 3 igo Division of Licensing $i...,; i trj Operating Reactor Branch #3 Mr. Robert A. Clark, Chief G W MW:sm mm

References:

NE " u.rar a Ic: ,h 8 (1) License No. DPR-36 (Docket No. 50-309). (2) USNRC letter to MYAPC, dated July 10, 1981. (3) MYAPC letter to USNRC, WMY 78-2, Evaluation of Potential Boron Dilution Accidents, dated January 5,1978. (4) YAEC-1132, " Justification for 2630 MWT Operation of the Maine Yankee Atomic Power Station," July 1977, Attachment C to MYAPC letter to USNRC, WMY 77-75, dated August 1,1977.

Subject:

Baron Oilution During Hot and Cold Shutdown (Mode 5 Operation) i

Dear Sir:

l l The time available for operator action, during boron dilution transients initiated from partially drained shutdown conditions, has been the subject of l several verbal communications with the NRC staff. These discussions focused on the administrative measures employed at Maine Yankee to ensure adequate operator action time under these circumstances. The measures employed were found to be acceptable by the staff. Maine Yankee agreed during the discussion to formally document the calculational basis for these discussions. A summary of the calculations performed to ensure tie operator sufficient time to take action prior to the loss of shutdown margin is provided in Attachment A. This transmittal is in response to the coru11tment documented in Reference (2) to provide such information. In all cases analyzed, the administrative procedures ensure sufficient time will be available. 8203240341 820318 PDR ADOCK 05000309 y( P PDR

MAINE YANKEE ATOMIC POWER COMPANY United States Nuclear Regulatory Connission March 18, 1982 Attention: Mr. Robert A.- Clark, Chief Page Two We trust this submittal is satisfactory. However, if y: a require additional information, please feel free to contact us. Very truly yours, MAINE YANKEE ATOMIC POWER COMPANY O w John H. Garrity, Senior' Director Nuclear Engineering & Licensing JHG/bjp

Enclosures:

Attachment A (1 Page) Tables 1, 2, and 3 (1 Page each)

• Figure 1 Shutdown Baron Concentration vs. Burnup.
• Figure 2 Results of Boron Dilution During Startup (Letdown)
• Figure 3 Results of Boron Dilution During Refueling

ATTACHMENT A Baron Dilution Analysis for Hot and Cold Shutdown (Mode 5) Operation Required shutdown margin under hot and cold shutdown conditions is given in the " Definitions" section of the Maine Yankee Technical Specifications as 5%6K/K subcritical. Plant operating procedures (OP l-6, Reactor Shutdown and OP l-7, Plant Cooldown) direct the operator to maintain the RCS boron concentration at the level specified in Figure 1. Maintenance of the RCS boron concentration at the value specified in Figure 1, ensures that the 5%hK/K shutdown margin requirement is met. It also ensures that the time available for operator action prior to loss of shutdown margin for an inadvertent boron dilution initiated from the most adverse condition, cold shutdown with loops drained, will be in excess of 30 minutes. Calculations are performed each cycle, to determine the critical baron concentre 1on as a function of cycle exposure over the temperature range of 6 interest. These are given for Cycle 6 in Table 1. The CEA with the highest worth is assumed to be stuck out of the core, and appropriate calculational uncertainties have been applied. These values are then increased by the equivalent of 1%CiK/K to account for the worth of the CEA's kept withdrawn from the core in accordance with (operating procedures) during a plant cooldown (Table 2). The initial boron concentration required to allow 30 minutes margin to criticality, for the limiting boron dilution event from shutdown conditions, is calculated using Figure 4.3-3 of Reference (4), attached as Figure 2. This figure provides the time to criticality as a function of the ratio of the critical to initial baron concentration, assuming maximum charging flow of diluted water, maximum RCS letdown flow, and that the RCS is filled to the normal water level in the pressurizer. This was determined to be a bounding case for all filled RCS conditions in Reference (4). The initial baron concentrations required to provide 30 minutes margin are compared in Table 3 with the values of baron concentration required by Figure 1 to meet the 5%llK/K Technical Specification. Whereas all the Figure 1 values are higher than the initial concentrations required for boron dilution concerns, it is clear that more than 30 minutes will be available for operator action for any boron dilution during shutdown from initially filled RCS conditions. The dashed lined portion of Figure 1 is applicable to drained RCS conditions and is derived in a similar manner. Reference (3) determined the limiting dilution flow rate for a drained RCS (initial RCS level assumed to just fill the reactor vessel to the lower edge of the loop piping nozzles) to be 308 gpm. From Figure 3, [ Figure 2 of Reference (3)], the maximum ratio of critical to initial boron concentration that allows 30 minutes margin, is greater than 0.60. Dividing the critical boron concentrations in Table 2 by this value, yields the initial boron concentrations required to provide 30 minutes margin for the limiting boron dilution event initiated from a drained RCS configuration. These values are specified in Figure 1 as being required whenever the RCS is to be partially drained during a shutdown. Thus, a minimum of 30 minutes margin, from initiation of the boron dilution event to loss of shutdown margin, is ensured for both normal and drained RCS configurations, during operation in hot and cold shutdown modes. J

TABLE 1 Critical Baron Concentrations, PPM ( ARI,' Less Stuck, W/ Uncertainty) TEWERATURE, OF BOC E0C* 68 889 198 300 850 134 532 747 10

• 12,000 MWD /T l

9 4 I } l I e t

TABLE 2 . Critical Boron Concentrations Increased by 1% K/K TEMPERATURE, OF. BOC EOC* 68 957 258 300 926 210 532 841 104 12,000 MWD /T i l i i i

TABLE 3 Comparison of Initial Boron Concentration - Required by Limiting Baron Dilution Event With Required Concentrations from Figure 1. l Required Initial Figure 1 Baron Concentration Boron For Dilution Event Concentration BOC 0 68 F 1035 1112 30dUF 1001 1111 532 F 909 1106

• EOC 68 F 279 533 0

300 F 227 474 U 532 F 113 266 i i l 12,000 MWD /T l l i l l l-j

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