ML20209C687
| ML20209C687 | |
| Person / Time | |
|---|---|
| Issue date: | 01/09/1984 |
| From: | Rowsome F Office of Nuclear Reactor Regulation |
| To: | Novak T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML17083B484 | List:
|
| References | |
| FOIA-86-197, FOIA-86-197PA TAC-53246, NUDOCS 8401250336 | |
| Download: ML20209C687 (8) | |
Text
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E WASHINGTON. D. C. 205S5 JAN 9 1984 MEMORANDUM FOR:
or for Licensing Division of Licensing FROM:
F. Rowsome, Assistant Director for Technology Division of Safety Technology
SUBJECT:
TRANSMITTAL OF ASSESSMENT OF P.G.&E. INFORMATION REPORT ON SISIP As requested (TAC 53246), we are transmitting the results of our review and assessment of the P.G.&E. report "Information on Seismically-Induced Systems Interaction Program (SISIP)".
Any questions should be addressed to D. Lasher, extension 24024.
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IAc4M Gr y,
F. Rowsome, Assistant Director for Technology Division of Safety Technology cc:
G. Knighton B. Buckley T. Speis F. Schroeder
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ENCLOSURE Assessment of P.G.&E. "Information Report on Seismically-Induced System Interaction Program (SISIP) Completion of Containment Activities"(1)
I.
The Program In response to an ACRS concern, P.G.&E. proposed a Seismically-Induced Systems Interaction Program (SISIP) in a series of letters dated from May 7 through September 16, 1980.( ) The staff reviewed the program scope; its goals; the criteria for target selection, source failure, interaction, target damage, and interaction resolution; the implementing organization; QA auditing procedures; and the methodology to be used in conducting the program.
NRC staff members visited the site to audit the program and observe how the walkdowns were performed.
These activities and their results were reported in Supplement 11 to the Safety Evaluation Report (NUREG 0675) dated October 1980 in which the staff concluded that the proposed program was acceptable.
The SISIP is intended to establish confidence that if a seismic event of the severity of the postulated Hosgri event occurred, then structures and equipment important to safety will not be prevented from accomplishing their safety functions,because of seismically induced failure or motion of non-safety related structures or equipment.
Also, the SISIP is to establish confidence that safety-related systems will not fail to meet the single failure criterion because of seismically-induced interactions.
. Targets are defined as structures and equipment needed to take the plant to safe shutdown and maintain it at safe shutdown.
Also, P.G.&E.
included certain accident mitigating systems such as containment isolation, main steam isolation, and containment spray systems and the manual fire suppression equipment.
Sources are defined as any other equipment whose seismically-induced failure or motion could interact with a target and prevent or inhibit a target from accomplishing its safety function.
The P.G.&E Information Report ( ) is a progress report that describes the stages of completion of the SISIP activities; changes in its organization, procedures and criteria; and presents a preliminary discussion of its results and their significance.
II.
Program Results As of September 30, 1983, P.G.&E. reported that 92% of the projected Unit 1 walkdowns were completed.
Seventy-five action items remain open as of that date.
Some of these items will be closed out prior to fuel loading.
Other action items identified in a September 10, 1983, P.G.&E.
letter ( ) will be completed after fuel has been loaded but prior to initial criticality.
. P.G.&E. actually had four ways of resolving postulated interactions.
These were: (a) Resolution by field inspection in which the interaction team could by inspection or simple field analysis show that either the source would not fail, the occurrence of the interaction was not credible, or the consequences of the interaction, if it occurred, would not adversely affect target operations.
(b) Resolution by engineering analysis in which P.G.&E. could show that the interactions would not occur or, if they did, the consequences would not affect target operations.
(c) Resolution by an expedient modification in which P.G.&E. decided it was more cost effective to resolve the interaction by modifying the plant than to justify the configuration by analysis.
(d). Resolution by a necessary modification in which further analysis showed that plant modification is the only means for resolving the interaction.
Because the last two were resolved by plant modification, P.G.&E. combined (c) and (d) and only reported three of the four resolution methods.
Plant-wide, the Containment had the largest number of resolutions by modification (167) followed by the Auxiliary Building (114), and Turbine Building (52) (Table 5.8, Ref 1).
Over five hundred interactions, belonging to all three groups, were postulated inside the containment.
Of these, the target systems subject to the most postualted interactions were Main Steam (127), Reactor Coolant (110) and Pressurizer (70).
The most frequently affected types of targets were:
. Instrumentation and Control with 220, Electrical with 157, and Piping with 98 postulated interactions respectively (Table 5.3, Ref. 1).
Of the seismically-induced interactions postulated inside the containment, 31%
were resolved through inspection by the walkdown team, 33% were resolved by engineering analysis, and 32% were resolved by plant modification.
The most frequently modified systems were the Main Steam (39), Reactor Coolant (28), and Pressurizer (28).
Piping and Pipe Supports were the sources that contributed most to both postulated and " resolved by modification" interactions (Table 5.6, Ref. 1).
Piping and Pipe Supports followed by platforms were the most common types of sources.
Together, these two categories composed 44% of all postulated interactions and 79% of those resolved by plant modifications (Table 5.2, Ref. 1).
III. Lessons Learned P.G.&E. summarized some of the lessons they learned from implementing the program.
These lessons involved the scope of the targets; formulation of the target selection, source failure, interaction, and resolution criteria; the mechanics of conducting walkdowns; and improvements to data handling and recording techniques.
Some of the lessons have resulted in changes to the Unit 1 program and all of the lessons will be incorporated into the Unit 2 program.
That lessons are recognized and fed back into the program is indicative of the thoroughness with which P.G.&E. performed their programs.
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. IV.
NRC Staff Comments and Conclusions Many postulated interactions were resolved through inspection by the walkdown team, and these have little safety significance.
Other postulated interactions were resolved by engineering analysis and these also have little safety significance.
These two groups have little safety significance because the postulated interactions in these groups could be shown not to occur or, if they did occur, the consequences would not affect target operations.
The fact that these insignificant interactions were identified demonstrates that the program criteria conservatively identified interactions and gives confidence that significant interactions could be identified by the walkdown teams.
P.G.&E. disposed of the remaining postulated interactions by plant modifications, some simply because it was more cost effective to modify rather than to analyze, and others because there was no method other than modification to resolve the interaction.
Because P.G.&E. has not separated the modifications that were economically motivated from those that were potentially safety significant, it is difficult to assess the safety significance of the reported results.
Also the inclusion of important-to-safety items as targets tends to lessen the significance of the interactions.
In addition, one modification can resolve more than one postulated interaction. Finally, P.G.&E. stated that no reports were made under either Part 21 or Part 50.55(e) of 10CFR50 for any of the modifications made under the SISIP.
This leads us to conclude that none of the modifications was safety significant.
i
- The brief description of the plans and efforts to transfer the responsibility for and operation of SISIP to the operations staff of -
DCPP gives assurance that the program will be available to handle future modifications and any seismically-induced system interactions that could be introduced because of them.
We will request that P.G.&E. (a) separate the potentially safety sign'ficant interactions from those associated with thelthe economically motivated modifications and (b) study the effect of including important-to-safety items as targets on the potential significance of the results.
In our review of this program we have not had the benefit of criteria such as the Standard Review Plan, IEEE Standards, and Regulatory Guides.
Instead we have relied largely on our professional judgment in evaluating this report.
We have benefitted from the previous review of the SISIP, the onsite audit of it, extensive informal contact with the P.G.&E.
program personnel, and the Information Report.
On this basis we conclude that_the SISIP is progressing toward its stated objectives, will be concluded prior to power operation, and should contribute to an increased assurance that the plant can be operated safely.
V. References 1.
"Information Report on the Seismically-Induced Systems Interaction Program (SISIP) Completion of Containment Activities", Enclosure to Letter from J. Schuyler, P.G.&E., to D. Eisenhut, NRC, October 13, 1983.
2.
Appendix A, US NRC Report NUREG-0675, Supplement.11, October 1980, refers to these letters:
(a) May 7, 1980 Submittal concerning the Systems Interaction Program (b) May 27, 1980 Submittal concerning the Systems Interaction Program (c) July 1, 1980 Submittal concerning the Systems Interaction Program (d) July 15, 1980 Submittal concerning the Systems Interaction Program (e) August 19, 1980 Submittal concerning the Systems Interaction Program (f) September 16, 1980 Submittal concerning the Systems Interaction Program 3.
Letter: J. Schuyler, P.G.&E. to D. G. Eisenhut, NRC, dated September 10, 1983
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