ML18037A564
| ML18037A564 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/19/1993 |
| From: | Williams J Office of Nuclear Reactor Regulation |
| To: | Medford M Tennessee Valley Authority |
| References | |
| TAC-M74385 NUDOCS 9311300135 | |
| Download: ML18037A564 (8) | |
Text
November 19, 1993 Docket No. 50-260 Dr. Hark 0. Hedford, Vice President Technical Support Tennessee Valley Authority 3B Lookout Place 1101 Market Street Chattanooga, Tennessee 37402-2801
Dear Dr. Hedford:
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION REGARDING THE BROWNS FERRY UNIT 2 INDIVIDUALPLANT EXAMINATION (TAC NO. M74385)
By letter dated September 1,
1992, the Tennessee Valley Authority (TVA) submitted its Individual Plant Examination (IPE) for the Browns Ferry Nuclear Plant (BFN) Unit 2.
On September 21,
- 1993, TVA provided additional information requested by the NRC staff on August 4, 1993.
After consideration of this additional information and the original submittal, the staff has determined that additional information, as described in the enclosure, is required to complete its review.
In order to support our review schedule, please provide your response within 30 days of receipt of this letter.
Please contact me at (301) 504-1470 if you have any questions regarding this request.
This request affects nine or fewer respondents, and therefore is not subject to Office of Management and Budget review under P.L.56-911.
Original signed by Joseph F. Williams, Project Manager Project Directorate II-4 Division of Reactor Projects I/II Office of Nuclear Reactor Regulation
Enclosure:
As Stated cc w/enclosure:
See next page Distribution
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ENCLOSURE RE VEST FOR ADDITION L INFORMATION BROWNS FERRY UNIT 2 INDIVIDUAL AN E AMINATIO uman e 'abi it al sis uestions How were dependencies among post-initiator human errors addressed in the Br owns Ferry Nuclear Plant (BFN) Unit 2 Individual Plant Examination (IPE)?
The discussion should address the treatment of dependencies in the quantification process with reference to the two points below:
a ~
b.
How were dependencies among human actions treated when more than'ne action was modeled in a sequence?
For example, the human action "align RHR for Suppression pool cooling" would appear in sequences where successful and non-successful operator actions have already occurred.
One would expect that previous operator success or failure would affect operator reliability.
In response to the staff's request for additional information of August 4,
- 1993, page 25 of TVA's letter of September 21, 1993 states:
"...the dependencies that would normally drive a second action to guaranteed failure, given the first action failed, would be compensated for by the ability of the crew to review the situation and by the arrival of additional personnel who can bring a fresh perspective to the situation."
However, operator ability to recover from previous failures to correctly perform subsequent actions may not be complete due to factors such as time available to perform the follow-up task and psychological effects of previous failures.
Human reliability analysis usually accounts for the effects of previous operator failures by modifying the failure probability for followup actions.
Provide a discussion and examples of your treatment of human action dependencies when complete or incomplete recovery of operator ability to perform followup actions was assumed after prior failures.
For the cases where complete independence of consecutive human actions was
- assumed, discuss the basis for this assumption.
Include a discussion of experience from operator performance in the simulator, other types of training, or actual events.
How were dependencies among human actions treated when post-initiator human events are modeled in the fault trees as basic events?
The probability that the operator performs a function such as manually actuate a system is dependent on the accident progression.
When this basic event, such as failure to manually actuate the system is modeled in the fault tree and the sequences are quantified, this basic event can appear not only in different sequences, but in different combinations with different system failures.
In addition, the basic event
2.
probability can potentially be multiplied by other human event probabilities when the sequences are quantified, resulting in artificially low calculated human error contributions if dependencies are not taken into account.
Include examples in your response.
How were dependencies associated with pre-initiator human errors addressed and treated in the Browns Ferry IPE'?
These dependencies could, for example, affect all the human events simultaneously, or could affect only certain human events such that only a series of human events are determined to fail simultaneously (e.g, complete dependence may be assumed for miscalibration of all reactor water level sensors).
Discuss by way of example(s) how the dependencies associated with pre-initiator human errors were treated.
3.
The IPE identified that decay heat removal (DHR) failure accounts for 64X (with station blackout) and 38X (without station blackout) of the total core damage frequency (CDF), with operator action-only failures consisting 58X of the total CDF.
However, these findings appear to be in contradiction with the IPE's importance analysis (Tables 3.4-3, 3.4-4, 3.4-5),
and in particular with the operator action importance analysis (Table 3.4-6),
where these actions were not identified as important to CDF.
Further, it is not clear in the IPE why these two actions constitute the 58X of the total COF.
Provide a discussion on these issues.
According to licensee s definition of vulnerability, failure of DHR is not a vulnerability.
However, it seems that the operator contribution for DHR failures is significant enough to draw the licensee's attention for further consideration.
Discuss whether enhancements were considered to address this apparent vulnerability, and describe any changes made to plant equipment or procedures as a result.
Containment Performance uestions As the result of the Containment Performance Improvement (CPI) program, recommendations were made for licensees to consider as part of the IPE process.
These recommendations were identified in Generic Letter 88-20, Supplement I for Hark I plants.
a.
Do Browns Ferry procedures and facilities implement CPI provisions for alternate water supplies for reactor vessel injection and drywell sprays?
If so, provide simple line drawings showing the arrangement from the water supply to the 'connection with residual heat removal or other injection lines.
Clearly identify the use of spool pieces,
- hoses, blind flanges, or other non-routine system components.
Identify the accident sequences which make use of these alternate water supplies, and discuss the affects on core damage frequency, conditional containment failure probability (CCFP),
and environmental releases.
J b.
Discuss your consideration of potential enhancements to the reactor pressure vessel depressurization system reliability.
This discussion should identify the sequences it could be used for, the potential benefit (reduction in CDF,
- CCFP, and releases to the environment),
and whether such improvement will be implemented at Browns Ferry Unit 2.
c.
Specify which revision of the BWROG EPGs has been incorporated into the Browns Ferry Unit 2 EOPs used for the IPE. If Revision 4 has not been incorporated, please provide a justification.
Provide a discussion of the hardened vent system.
Identify the sequences it could be used for and the vent's affect on CDF,
- CCFP, and releases to the environment.
Specify which version of the HAAP 3.0B code was used for the analysis.
Tennessee Valley Authority ATTN:
Dr. Mark 0. Medford CC:
Mr. Craven Crowell, Chairman Tennessee Valley Authority ET 12A 400 West Summit Hill Drive Knoxville, TN 37902 Mr.
W. H. Kennoy, Director Tennessee Valley Authority ET 12A 400 West Summit Hill Drive Knoxville, TN 37902 Mr. Johnny H. Hayes, Director Tennessee Valley Authority ET 12A 400 West Summit Hill Drive Knoxville, TN 37902 Mr. R.
M. Eytchison, Vice President
, Nuclear Operations Tennessee Valley Authority 3B Lookout Place 1101 Market Street Chattanooga, TN 37402-2801 Mr. Pedro Salas Site Licensing Manager Browns Ferry Nuclear Plant Tennessee Valley Authority P.O.
Box 2000
- Decatur, AL 35602 Mr. 0. J. Zeringue, Vice President Browns Ferry Nuclear Plant Tennessee Valley Authority P.O.
Box 2000
- Decatur, AL 35602 Mr. B. S..Schofield, Manager Nuclear Licensing and Regulatory Affairs Tennessee Valley Authority 4G Blue Ridge 1101 Market Street Chattanooga, TN 37402-2801 BROWNS FERRY NUCLEAR PLANT TVA Representative Tennessee Valley Authority 11921 Rockville Pike, Suite 402 Rockville, MD 20852 General Counsel Tennessee Valley Authority ET 11H 400 West Summit Hill Drive Knoxville, TN 37902 Chairman Limestone County Commission P.O.
Box 188
- Athens, AL 35611 State Heal th Officer Alabama Department of Public Health 434 Monroe Street Montgomery, AL 36130-1701 Regional Administrator U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW., Suite 2900
- Atlanta, GA 30323 Mr. Charles Patterson Senior Resident Inspector Browns Ferry Nuclear Plant U.S. Nuclear Regulatory Commission Route 12, Box 637
- Athens, AL 35611 Mr. T.
D. Shriver Site guality Manager Browns Ferry Nuclear Plant Tennessee Valley Authority P.O.
Box 2000
- Decatur, AL 35602