ML20044G246
| ML20044G246 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/24/1993 |
| From: | Hodges M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Opeka J NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| EA-92-146, NUDOCS 9306020227 | |
| Download: ML20044G246 (4) | |
See also: IR 05000336/1992022
Text
{{#Wiki_filter:o mo , j h. < 6 EY 2 41993 Docket No. 50-336 License No. DPR-65 EA No. 92-146 Mr. John F. Opeka Executive Vice President - Nuclear Northeast Nuclear Energy Company P. O. Box 270 Hartford, Connecticut 06141-0270 Dear Mr. Opeka: SUBJECT: MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2, RESPONSE TO ADDITIONAL INFORMATION CONCERNING INSPECTION REPORT 50- - 336/92-22 In the above report,' NRC Region I identified an apparent violation that was being considered for escalated enforcement action. The apparent violation concerned the action you had taken prior to and after the identification of a single failure vulnerability. The single , ' failure vulnerability had existed at Millstone 2 for over ten years and was identitied by your '
staff after a July 6,1992, event. Accordingly, we requested an enforcement conference with Northeast Nuclear Energy Company (NNECO) to discuss the issue. By telephone on February 17, 1993, NRC and NNECO agreed that NNECO would submit additional information pertaining to the apparent violation for NRC review. NhTCO provided the , ! additional information by letter dated March 11, 1993.2 The NRC staff has carefully reviewed your March 11,1993, letter and the applicable sections of our report and concluded that an enforcement conference is still necessary on this l issue. Your response focused on the probabilistic study of the identified scenario wherein i power-operated relief valves open in response to various power supply failures. However, we still need to further understand the interaction between the PRA staff with operations, , ' training and engineering during your Probabilistic Safety Study (PSS). It appears there was a failure to transfer information from the PSS to other groups for appropriate design basis and operability evaluation. >
! ' 'M. W. Hodges letter to J. F. opeka, "NRC Inspection Report No. 50-336/92-22 Millstone Unit 2," dated January 11, 1993.
- J. F. opeka letter to USNRC Document Control Desk, " Millstone Nuclear Power
Station, Unit No. 2, Reply to Request for Additional Information Inspection Report No. 50-336/92-22," dated March 11, 1993. OFFICIAL RECORD COPY A: MILL 2LN.2ND i 9306020227 930524 4 {{I O j PDR ADOCK 05000336 - G PDR v j r
1 t l i MAY 2 41993 } 1 ! i Mr. John F. Opeka 2 l For exac.ple, the design vulnerability involving emergency core cooling system response to a ' loss of two vital 120 volt AC inverters, which you identified after the July 6 event, had previously been identified by your staff in scenarios performed on the plant-specific simulator j in August 1987. These simulator exercises identified that loss of VA-10 and VA-30 would ! result in a partial loss of normal power in which a low pressure safety injection pump would trip due to generation of simultaneous safety injection and containment sump recirculation actuation signals. The failure of a single 125 volt DC bus would have similar consequences. ' These same simulator exercises also showed that loss of VA-10 and VA-20 would result in a loss of coolant accident (both power-operated relief valves open) with no safety injection. } While these scenarios may represent unlikely events from a probabilistic perspective, we l were unable to determine from your response why these vulnerabilities were not evaluated i earlier from a plant design or licensing basis perspective. j ! It appears that a strictly probabilistic approach to your evaluation persisted until your reportability/ operability evaluation in December 1990. A December 1990 presentation by your staff characterized prolonged operation of inverters on nonqualified backup power supplies as not meeting the intent of single failure design standards because a subsequent
design basis accident could result in loss of two 120 volt AC power supplies with . unacceptable results from a safety standpoint. We need to understand whether this evaluation was timely since we understand that this issue had been under evaluation since at least September 1990. We were unable to conclude from your March 11,1993, response why your staff and i management reviews of several adverse scenarios involving loss of two vital 120 volt AC inverters did not result in further followup regarding the design basis consequences of these i l scenarios. Further, we need additional assurance that similar issues would be promptly ! evaluated and corrected in the future. , 1 As discussed in a telephone call between Mr. M. Wilson of your staff and Mr. W. Ruland of my staff on May 6,1993, we will hold the enforcement conference on a date to be determined later. The purposes of this conference will be to discuss the apparent violation, ' its causes and safety significance; to provide you the opportunity to outline your proposed corrective actions; and to discuss any other information that will help us determine the appropriate enforcement action in accordance with the Enforcement Policy. In particular, we , expect you to address the questions we have raised in this letter. In addition, this is an opportunity for you to provide any information concerning your perspectives on 1) the severity of the violation,2) the application of the factors that the NRC considers when it determines the amount of a civil penalty that may be assessed in l accordance with Section VI.B.2 of the Enforcement Policy, and 3) any other application of i the Enforcement Policy to this case, including the exercise of discretion in accordance with Section VII. You will be advised by separate correspondence of the results of our deliberations on this matter. No response regarding the apparent violation is required at this time. l _
r , !!.AV 3 41993 ,
- Mr. John F. Opeka 3 In accordance with 10 CFR 2.790 of the NRC's " Rules of Practice," a copy of this letter will be placed in the NRC Public Document Room. , Your cooperation is appreciated. . Sincerely,
. , Marvin W. Hodges, Director Division of Reactor Safety , cc: W. D. Romberg, Vice President - Nuclear, Operations Services i S. E. Scace, Vice President, Millstone Station
J. S. Keenan, Nuclear Unit Director , R. M. Kacich, Director, Nuclear Licensing G. H. Bouchard, Director of Quality Services Gerald Garfield, Esquire Nicholas Reynolds, Esquire K. Abraham, PAO (2) Public Document Room (PDR) local Public Document Room (LPDR) Nuclear Safety Information Center (NSIC) NRC Resident Inspector State of Connecticut SLO ! . , i - , , t 6 l OFFICIAL RECORD COPY A: MILL 2LN.2ND ,
'- ^
IW 2 41993 , 1 I - Mr. Jahn F. Opeka 4 bec: Region 1 Docket Room (with concurrences) , bec (VIA FeMAIL): V. McCree, OEDO G. Vissing, PM, NRR J. Stolz, NRR/PD I-4 W. Ruland, DRS J. Durr, DRS L. Doerflein, DRP D. Holody, EO r M. Hodges, DRS - . & & i P l' $6 RI:EO g'g RI:DRS RI:DRS RI:DRS RI:DRP ! Rulap <[ Durr Doc in Holody Hodge U W CW tq ' 5/f/93 5/f/93 5/6/93 5/H'93 5 f)3 l ' l OFFICIAL RECORD COPY A: MILL 2LN.2ND l l 1 . }}