ML20052B647
| ML20052B647 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 04/27/1982 |
| From: | Wolfe S Atomic Safety and Licensing Board Panel |
| To: | LOUISIANA POWER & LIGHT CO. |
| References | |
| ISSUANCES-OL, NUDOCS 8205030411 | |
| Download: ML20052B647 (8) | |
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UNITED STATES OF AMERICA E7 P NUCLEAR REGULATORY COMMISSION ATOMIC'SAFETYANDLICENSINGB0gD W 28 FR M Before Administrative Judges:
Sheldon J. Wolfe, Chairman '
Dr. Walter H. Jordan Dr. Harry Foreman SEMED APR 281982
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In the Matter of
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Docket No. 50-382-0L LOUISIANA POWER AND LIGHT COMPANY
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(Waterford Steam Electric Station,
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April 27, 1982 s
4 Unit 3)
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C?tiqn 1\\
MEMORANDUM AND ORDER
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(Granting Applicant's Motion For Reconsideration' D rew OSA I
\\k tuff";m g. h h6 3g CM MEMORANDUM r
D On March 18, 1982, in a Memorandum and Order, this Board raised a sua sponte question concerning the reliability of the Waterford 3 emergency feedwater system (EFWS) and the need for a feed-and-bleed capability as a back-up. On March 26, Applicant filed a Motion for Reconsideration.
The motion pointed out that our question was the topic of a recent Advisory Committee on Reactor Safeguards subconsnittee meeting.
However, the main thrust of the motion was that the Board's exercise of its sua sponte authority is precluded by 10 C.F.R. 2.760a which provides that, in operating license proceed-ings, such questions can be raised only if "a serious safety, environmental or common defense and security matter exists."
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. On April 8,1982, the Joint Intervenors advised us that they took no position with respect to the Applicant's motion at the present time.
On April 12, 1982, the Staff filed an Answer (and an attached affidavit) in support of the Applicant's motion. The Staff argued that there was no need for a feed-and-bleed back-up to the EFWS and hence the Board's question did not raise a serious safety matter.
On April 16, 1982, during a conference call with all the parties, this Board announced that we were granting the Applicant's motion and withdrawing the sua sponte question.
This men:orandum explains our reasons for that action.
We do not agree with Applicant and Staff that feed-and-bleed back-up for the EFWS is not a serious safety matter.
We believe that it is and that the matter should be pursued.
Moreover, we are now convinced that the issue should and will be explored on a generic basis.
We first turn to the question of whether a serious safety matter exists.
Waterford and other similar Combustion Engineering (CE) designed nuclear plants differ from other PWRs in one important respect.
Following certain transients, such as a loss of all feedwater (LOFW), a loss of power, and a small break LOCA, the pressure in the primary coolant system will rise until the set point of the safety valves is reached. Then steam will be released through the valves and boiling will take place in the core. This will provide adequate cooling for the fuel elements as long as they remain covered wit.h water.
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. Other PWRs have the ability to inject water into the primary system even though the pressure is high; the injection of water into the system and the release of steam through the safety valves is termed feed-and-bleed. The high pressure injection system (HPIS) in CE plants is not capable of injecting water at the pressure at which the safety valves are set so that feed-and-bleed is not possible at the high pressure following some transients.
It is the Staff's position that feed-and-bleed capability is not necessary as a back-up to the Waterford Unit 3 EFWS.
(See Affidavit, answer to Q.6.) The basis for this conclusion is that the demand failure rate is less than 4x10-5/D, that the frequency of initiating transients that require EFWS operation is less than 0.12/RY and hence core-melt, resulting from failure of the EFWS, should be less than 5x10-6/RY, a figure well below the NRC safety goal.
If we were to accept the Staff's figures without question, then we would agree that th'e lack of feed-and-bleed capability would not' be a matter of serious safety concern.
However, we do question both of the figures upon which the Staff relies and we join the ACRS in urging that the issue continue to be explored. The Staff estimates for the frequency of initiating transients and the reliability of the EFWS are based upon operating experience; however, the Staff has rejected a number of instances of failure, arguing that the Waterford 3 design is not subject to those particular failure types.
Such arguments are always open to question; while systems can be designed to reduce
. certain kinds of failures, other failure modes occur which were not anticipated.1/ An analysis of Licensee Event Reports (LERs),
NUREG/CR-2497_/ demonstrates that failure rates have not decreased 2
markedly with time.
In the previous paragraph we raised a question regarding the Staff's estimates of the frequency of initiating transients; in
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particular, we question the Staff's estimates of the frequency of loss of main feedwater (LOMF).
Reference 1 (hereafter Ref.1), which was attached to the Staff's Supporting Answer, includes a Table 1 listing a total of 48 LOMF events which is the basis for the transient frequency 0.48/RY of Ref.1, p. 4.
The Staff then eliminates 36 of those events as being events "which should be recoverable in less than
--1/ Mr. Thadani, one of the three NRC Staff members signing the affidavit attached to the Staff's Answer, is a senior author of NUREG-0460, " Anticipated Transients Without Scram for Light Water Reactors." He rejected industry arguments that reactor protection systems can be made highly reliable by changing the design so that they would no longer be vulnerable to a specific common mode failure.
It would appear that Mr. Thadani is now arguing that the Waterford EFW system, which has only two redundant channels of active components including motors, pumps, valves and human operators, will be more reliable than the reactor protection system, a quadruply redundant system of passive components which require no operator action.
He has recommended that the reactor protection system be backed up by another system but has not made a similar recommendation for the EFWS.
~~2/ Precursors To Potential Severe Core Damage Accidents: 1969-1979, draft prepared by the Oak Ridge National Laboratory.
. 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />;" they do nd claim that those events were in fact recovered within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The LOMF transient event frequency is thus reduced to 0.12/RY.
Then in answer to Q.2 of the affidavit the Staff states, "Thus, assuming procedures and operating training are in place---it is
' reasonable to expect---that the frequency of irrecoverable losses could
,be reduced to the value of 0.03/RY."
(Emphasis ours).
The Staff then uses that figure in their analysis and conclusion that LOMF is a minor contributor to possible core melt accidents.
We are not convinced.
It seems unlikely that there would be no more than a single instance of a prolonged loss of main feedwater at Waterford during the life of the plant.
In addition to our reservations on the frequency of initiating transients, we have further doubts regarding the Staff's est %ates for the reliability of the EFWS. The ORNL analysis (NUREG/CR-2497) lists 8 instances,where there have been a total loss of EFW with a failure rate on de* mand of 10-3/D. The Staff rejects all eight of the EFW events as not being relevant to Waterford 3 and estimates a failure probability of 4x10-5/0, a figure 25 times lower than the GRNL estimate. We are not able to say that the Staff's figure is wrong, although the Staff admits it could be a factor of 10 too low or too high. We remain unconvinced pending a demonstration that system interactions and operator and maintenance errors have been adequately considered.
Part of the Staff's answer supporting Applicant's motion, tells us that the Staff has under consideration the need and
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. advisability of requiring a rapid depressurization system for use in event of tube f ailures in the steam generators.
(See Affidavit answer to Q.7.)
Such a system would also be available for reducing the primary system pressure following the previously discussed transients, thereby enabling the HPIS to inject water.
The rapid depressurization system would permit feed-and-bleed back-up to the EFWS.
Even though the Staff claims that feed-and-bleed back-up is not required at Waterford 3, there is no question but that the ACRS had exactly that in mind concerning System 80 plants when it wrote the December 15, 1981 letter to the Comission. The fourth paragraph of that letter reads as follows:
In recent years, the availability of reliable shutdown heat removal capability for a wide range of transients has been recognized to be of great importance to safety. The System 80 design does not include capability for rapid, direct depressurization of the primary system or for any method of heat removal imediately after shutdown which does not require use of the steam generators.
In the present design, the steam generators must be operated for heat removal after shutdown when the primary system is at high pressure and temperature. This places extra importance on the reliability of the auxiliary feedwater system used in connection with System 80 steam generators and extra requirements on the integrity of the steam generators. The ACRS believes that special attention should be given to these matters in connection with any plant employing the System 80 design.
The Comittee also believes that it may be useful to.
give consideration to the potential for adding valves of a' size to facilitate rapid depressurization of the System 80 primary coolant system to allow more direct methods of decay heat removal. The Comittee wishes to review this matter further with the cooperation of Combustion Engineering and the NRC Staff.
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. The subject of the April 5, 1982 letter of the ACRS to the Commission was " Reliability of Shutdown Heat Removal System on the System 80 Design."
In referring to its December 15 letter, it states that "These comments addressed the lack of capability for rapid, direct depressurizaton of the primary system to allow feed-and-bleed operations and the reliance placed upon the secondary system for heat removai capability." The April 5th letter concludes as follows:
The Combustion Engineering response to the Committee's comments on the System 80 design emphasizes the expected very high reliability of the feedwater systems and the integrity of the steam generators.
We believe that these are necessary goals but note that past operating experience indicates that these goals are difficult to achieve. We believe that for this reason Combustion Engineering and the NRC Staff should consider further the addition of valves of a size to facilitate rapid depressurization of the System 80 primary coolant system as stated in the Committee's December 15, 1981 letter on the System 80 design.
We believe that a plan for addressing this issue should be formulated in the near future.
We wish to be kept informed and to discuss this further with Combustion Engineering and the NRC Staff.
We believe that, while this evaluation should be conducted expeditiously, its resolution should not now be a condition for operation of System 80 plants at full power, or of plants having similar features.
The need for future hardware or procedural changes should be contingent upon results of this evaluation.
It is apparent that the ACRS does consider the lack of feed-and-bleed on System 80 plants to be a significant t safety matter. What was not clear to us was whether Waterford 3 was included in the ACRS concerns.
Although Waterford 3 is not a System 80 plant, it does have the same deficiency.
Robert Tedesco's recent undated memorandum to us (received April 17,1982) enclosed the April 5 ACRS letter and states
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. that the ACRS position on the need for rapid depressurization capa-ability includes Watertord 3.
We conclude that our concern with respect to the reliability of the Waterford 3 EFWS and the need for feed-and-bleed back-up is being addressed by CE and the Staff and will be discussed further with the ACRS.
It is for that reason that we grant the Applicant's motion for reconsideration.
ORDER Accordingly, it is this 27th day of April,1982 ORDERED That Applicant's Motion For Reconsideration of March 26, 1982, is granted, and the sua sponte issue raised in our Memorandum and Order of March 18, 1982, is withdrawn.
Judges Jordan and Foreman concur.
FOR THE ATOMIC SAFETY AND LICENSING BOARD bW U$
She' don J.CFolfe,' Chairman ADMINISTRATIVE JUDGE O
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