ML20128G140
| ML20128G140 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 10/03/1996 |
| From: | Hebert J Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| JRH-96-215, MN-96-142, NUDOCS 9610080345 | |
| Download: ML20128G140 (2) | |
Text
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MaineYankee RELIABLE ELECTRICITY SINCE 1972 l
329 BATH ROAD + BRUNSWICK. MAINE 04011 * (207) 798-4100 October 3,1996 MN-96-142 JRH-96-215 UNITED STATES NUCLEAR REGULATORY COMMISSION i
Attention: Document Control Desk l
Washington, DC 20555
References:
(a)
License No. DPR-36 (Docket No. 50-309)
(b)
Letter, MYAPCo to Mr. William T. Russell, USNRC, " Status Update Associated with Discrepancy in EOP Verification Analyses" dated July 1, 1996 (MN-96-84)
(c)
Letter, MYAPCo to USNRC, " Reply to Request for Additional Information Regarding SGTR", dated July 29,1996 (MN-96-105)
(d)
Letter, MYAPCo to USNRC, " Plant Root Cause Evaluation Report for Incorrect Value for Atmospheric Steam Dump Capacity", dated August 21,1996 (MN-96-116)
(e)
Letter, MYAPCo to Mr. John F. Rogge, USNRC, Region I,
" Administrative Limit on Dose Equivalent I-131, " dated June 7,1996, 1
(MN-96-77) ~
Subject:
Status Update Associated with Discrepancy m EOP Verification Analyses Gentlernen:
. letter describes the status of our progress associated with the corrective actions concerning the satified discrepancy in the EOP Verification Analyses. The following describes the progress and initiatives taken since our last summary correspondence, Reference (b), last July 1,1996.
Inadequate Core Cooling (ICC)'
In Reference (b) we discussed measures taken to increase the steam dump capacity and identified that these measures have been incorporated into the Emergency Operating Procedures (EOP). We also stated that we were investigating additional ways to vent steam and flooding steam generators with cold water to expedite cooldown of the primary system. Neither of these initiatives appears practical and have been dropped as options.
We are now engaged in the engineering of physical modifications to the Atmospheric Dump Valve (ADV) system. These modifications include installation of a parallel ADV of about 560,000 lb/hr at 900 psig main steam pressure to the existing ADV which has a capacity of about 288,000 lb/hr at 900 psig main steam pressure. Stone and Webster Engineering has been contracted to engineer and supervise the installation of this modificatiod. We expect the, design to be. completed.by March 31,1997, and to be installed during the~first cold shutdown of sufficient duration, or in any event, no later than the next scheduled refueling outage contingent on availability of material. The installation of the additional ADV capability precludes the need to reanalyze the EOP ICC event scenario.
We conducted a root cause evaluation for the ICC event issue and forwarded the report to you in August of this year as an enclosure to Reference (d).
i 9610080345 961003
,h 0
PDR ADOCK 05000309 F
4 MaineYankee 4
UNITED STATES NUCLEAR REGULATORY COMMISSION MN-96-142 Attention: Document Control Desk Page Two
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i Steam Generator Tube Ruptures (SGTR) i We have completed a new Maine Yankee EOP verification analysis evaluating the operator action times during a SGTR with a loss of off-site power. This analysis, in conjunction with the RETRAN-02 thermal-hydraulic calculations form the basis for demonstrating that following the current EOPs, E-0 and E-3, provides reasonable assurance that operators can recover from a single tube rupture event without overfilling the ruptured steam generator.
In Reference (c) we provided information detailing the operator actions required outside of the control room and the timing tests which we were evaluating. The main objective of the rest of our effort was to demonstrate that the target operator action times established in the analyses, including l
required actions by control room operators, could be met by operators during video taped simulator exercises. Ten simulator exercises, with different crews, were conducted and video taped. The action times were verified and compared to the target times documented in the analysis.
The results of our evaluations demonstrate that the target times established in the calculations were met by the operator crews, indicating that following EOP E-0 and E-3 can prevent overfill of the ruptured steam generator.
j The reaffirmation that operator action can prevent Steam Generator Overfill minimizes the i
radiological impact of the EOP scenario. Until Maine Yankee verified that overfill was not a j
probable result of the SGTR event, we voluntarily restricted Reactor Coolant System Activity to i
10% of the maximum allowable by Technical Specification 3.2 and 4.2, Table 4.2-1.1 for Dose j
i Equivalent I-131 as indicated in Reference (e). Maine Yankee plans to remove this administrative l
limit and reestablish the Technical Specification as the controlling parameter for operation pending further discussion with Region I. Actual coolant activities remain less than 10% of Tech Specs as they did throughout the period of reanalysis.
i The modification installing a parallel ADV discussed previously will increase the margin of safety by providing a redundant steam dump path. Either the existing ADV or the new parallel ADV will be capable of handling 100% of the flow required to mitigate a SGTR. In addition, Maine Yankee has included in the modification the installation of motor operated valves which will allow isolation of the ruptured steam generator from the control room. This enhancement will make it unnecessary to dispatch an operator to the Main Steam Valve House as described in Reference (c).
We will keep the Resident Inspector informed of our plans regarding the engineering and installation of the new ADV and remote operated valves.
Very truly yours, m b-ames R. Hebert, Manager Licensing and Engineering Support c:
Mr. H. Miller Mr. J. Yerokun Mr. D. Dorman Mr. P. Dostie Mr. U. Vanags Mr. F. Miraglia