05000483/LER-2003-003, Incorrect Steam Generator Tube Rupture Analysis Contained in FSAR
| ML031400570 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 05/09/2003 |
| From: | Witt W AmerenUE |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ULNRC-04845 LER 03-003-00 | |
| Download: ML031400570 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v), Loss of Safety Function |
| 4832003003R00 - NRC Website | |
text
PO Box 620 Fulton, MIO 65251 May 9, 2003 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop P1-137 Washington, DC 20555-0001 ULNRC-04845 Ladies and Gentlemen:
"AmerenUE DOCKET NUMBER 50-483 Callaway PLANT UNIT 1 UNION ELECTRIC CO.
FACILITY OPERATING LICENSE NPF-30 LICENSEE EVENT REPORT 2003-003-00 Incorrect Steam Generator Tube Rupture analysis contained in FSAR The enclosed licensee event report is submitted in accordance with 1 OCFR50.73(a)(2)(v)(C) and 1 OCFR50.73(a)(2)(v)(D) to report a condition discovered in which Steam Generator tube rupture with overfill accident analysis was not explicitly addressed in the current Final Safety Analysis Report (FSAR).
Very truly yours, 6 c / a 7 4l'e Warren A. Witt Manager, Callaway Plant WAW/ewh Enclosure a subsidiary of Ameren Corporation AmerenUE Callaway Plant
ULNRC-04845 May 9, 2003 Page 2 cc:
Dr. Bruce S. Mallett Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-4005 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Mr. Jack N. Donohew (2 copies)
Licensing Project Manager, Callaway Plant Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 7E1 Washington, DC 20555-2738 Manager, Electric Department Missouri Public Service Commission PO Box 360 Jefferson City, MO 65102 Records Center Institute of Nuclear Power Operations 700 Galleria Parkway Atlanta, GA 30339
Abstract
On 3/13/03 while at 100 % power, during a review of future plant modification packages, Callaway Plant determined a problem existed in the current safety analysis for a steam generator tube rupture (SGTR) accident accompanied by an overfill condition. The current Final Safety Analysis Report (FSAR) does not explicitly address a SGTR overfill case. Investigations determined that for current plant conditions, an overfill condition could result if an auxiliary feedwater control valve supplying the ruptured steam generator (S/G) were to fail open. In this case water could be released through the SIG safety valves, resulting in a radioactive release to the environment greater than allowed by regulatory guidance. Since the SGTR overfill case was not explicitly addressed in the FSAR, credited operator action times were not maintained current.
To assure regulatory compliance, plant procedures have been changed to administratively reduce the steady state Dose Equivalent Iodine (DEI) limit to 0.3 microcurie per gram (Technical Specifications currently limits DEI to 1.0 microcurie per gram). This lower DEI limit will ensure that if a SGTR overfill condition were to occur, post accident radiological consequences would not exceed limits contained in the FSAR and Standard Review Plan.
NRC FORM 366 (7-2001)
(If more space is required, use additional copies of NRC Forn 366A) (17)
- 1.
DESCRIPTION OF THE REPORTABLE EVENT
A. REPORTABLE EVENT CLASSIFICATION This event is being reported under 10CFR50.73(a)(2)(v)(C) and 10CFR50.73(a)(2)(v)(D), an event or condition that could have prevented the fulfillment of a safety function to control the release of radioactive material or mitigate the consequences of an accident.
B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT Mode I at 100 percent power.
C. STATUS OF STRUCTURES, SYSTEMS OR COMPONENTS THAT WERE INOPERABLE AT THE START OF THE EVENT AND THAT CONTRIBUTED TO THE EVENT Not applicable.
D. NARRATIVE SUMMARY OF THE EVENT, INCLUDING DATES AND APPROXIMATE TIMES On March 13, 2003 while operating at 100 % power, Callaway Plant determined a problem existed in the current safety analysis for a steam generator (SIG) tube rupture accident accompanied by an overfill condition of the ruptured S/G. This problem was discovered while reviewing future plant modification packages. The Callaway Plant screening process for modification development identified that these modifications could potentially have an adverse impact on the SGTR overfill analysis. During the re-analysis of the SGTR overfill sequence, all input values were re-validated. Preliminary analysis results for the current plant configuration with the re-validated inputs indicated that post-accident doses would involve a more than minimal increase from the radiological consequences currently presented in the Callaway FSAR. The input parameters having the dominant adverse impact on the analysis results were operator action times credited in the analysis. Since the SGTR overfill case was not explicitly addressed in the FSAR, credited operator action times were not maintained valid.
Current Technical Specifications (T/S) allow a reactor coolant system Dose Equivalent Iodine (DEI) value of 1.0 microcurie per gram. To assure compliance with FSAR analysis limits, plant procedures have been changed to administratively reduce the steady state DEI limit to 0.3 microcurie per gram, a value that has not been exceeded in the last three years. Current steady state DEI concentration in the reactor coolant system is 0.00 1769 microcurie per gram. The new lower DEI limit will ensure that if an overfill condition were to occur during a SIG tube rupture, post accident radiological consequences would not exceed the limits contained in the FSAR and the Standard Review Plan.
A formal root cause evaluation team was assembled to determine why the postulated plant conditions, including operator response times explicitly modeled in the analysis, had not been maintained current. As a result of this review, it was determined that in 1986 Callaway submitted an analysis for a SGTR with a stuck-open auxiliary feedwater (AFW) flow control valve (FCV). This analysis concluded that overfill was precluded during a design bases SGTR overfill sequence. In response, the NRC requested Union Electric (present day AmerenUE) submit a S/G tube rupture analysis which included a resultant overfill condition in the ruptured S/G. In 1987, Callaway submitted via letter ULNRC 1518, the analysis for a SGTR with a failed AFW flow control valve that did include overfill. ULNRC 1518 also included information regarding the impact of plant uprating, 15 percent tube plugging and Vantage 5 fuel transition on the overfill analyses. Plant uprating, Vantage 5 fuel transition and 15 percent tube plugging were other licensing initiatives being pursued by Union Electric during the same time frame as the SGTR analysis effort. Union Electric calculations performed in 1987 provide the bases for the analyses results presented in ULNRC 1518.
(If more space is required, use additional copies of (If more space is required, use additional copies of NRC Form 366A) (17)
B. DURATION OF SAFETY SYSTEM INOPERABILITY
Not applicable for this event.
C. SAFETY CONSEQUENCES AND IMPLICATIONS OF THE EVENT.
Based on actual DEI values over the last three years, calculated doses following a SGTR overfill event would not have exceeded any regulatory limits or the accident consequences stated in the FSAR for SGTR.
An evaluation determined that the event described in this LER is of very low risk significance.
III.
CAUSE OF THE EVENT
The cause of the event is due to Callaway failing to explicitly incorporate the SGTR with overfill accident analysis approved by the NRC.
IV.
CORRECTIVE ACTIONS
There were two immediate actions taken upon discovery of this event. I) An administrative DEI limit of 0.3 micro-curies per gram Iodine was imposed. 2) All dose assessment coordinators were informed that in the event of a SGTR with water release, the software currently used for dose assessment must be performed using field monitoring data.
Procedures have been revised to reflect this guidance.
Additional actions being pursued include:
Revising and training on Emergency Operating Procedure E-3 Reanalysis of the SGTR accident using revalidated operator response times Acquiring NRC approval of new dose calculation methodology Evaluating an alternate method for RERP dose assessment for the SGTR overfill sequence.
V.
PREVIOUS SIMILAR EVENTS
No similar events were identified where NRC SER conclusions failed to be appropriately incorporated into Callaway's FSAR.
VI.
ADDITIONAL INFORMATION
The system and component codes listed below are from the IEEE Standard 805-1984 and IEEE Standard 803A-1984 respectively.
System:
Component:
Not applicable for this event Not applicable for this event.