ML20135C685
| ML20135C685 | |
| Person / Time | |
|---|---|
| Issue date: | 12/04/1996 |
| From: | Thadani A NRC (Affiliation Not Assigned) |
| To: | Reedy R REEDY ASSOCIATES, INC. |
| References | |
| GL-96-06, GL-96-6, NUDOCS 9612090043 | |
| Download: ML20135C685 (10) | |
Text
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a nog g-k UNITED STATES E
NUCLEAR REGULATORY COMMISSION f
WASHINGTON, D.C. 20%H001
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December 4, 1996 Mr. Roger Reedy Reedy Engineering, Inc.
3425 S. Bascom Avenue, Suite 210 Campbell, California 95008
SUBJECT:
NRC GENERIC LETTER 96-06
Dear Mr. Reedy:
I am responding to your letter of November 8,1996, regarding U. S. Nuclear Regulatory Commission (NRC) Generic Letter (GL) 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," which was issued on September 30, 1996.
In your letter, you enumerate several specific concerns regarding the generic letter, which the staff addresses in the enclosure to this letter. Most importantly, you expressed concerns about the accuracy of the statements made by the staff in the generic letter.
The NRC staff considers your assertion that certain statements made in the generic letter are false a very serious charge.
In Item four of your letter, you further imply that these false statements were used by the NRC staff to bypass the public review and comment process and avoid a backfit analysis.
The staff issued the generic letter without public comment because it considered the issues urgent. The urgency existed because two licensees had considered the technical issues addressed in the generic letter to be significant enough safety concerns to warrant a shutdown of their facilities.
The staff followed its procedure as specified in NRr. Inspection Manual Chapter 0730 for issuing a generic letter which allows the staff to issue a Category I generic letter without Federal Reaister notification when urgent circumstances exist.
The staff issued the generic letter without a full backfit analysis because it considered the issues to be compliance backfits under the provisions of Section 50.109 of Title 10 of the Code of Federal Reaulations (10 CFR 50.109).
Under the provisions of 10 CFR 50.109(a)(4)(1), a backfit analysis by the staff is not required if a plant modification is necessary to bring a facility into conformance with its license or the rules or orders of the Commission, or into conformance with written commitments by the licensee.
Your charge that the statements in the generic letter are false is based on the assertion that the piping codes that licensees committed to in the design of their facilities I
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did not require consideration of the issues addressed by the generic letter.
These issues involve the potential for overpressure of isolated sections of piping as a result of the heating of the trapped fluid, and the potential for I
{h water hammer because of the flashing of water in the containment fan coolers during postulated accident conditions. The staff addresses your specific concerns in the enclosure.
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2 As discussed in the enclosure, the staff believes its statements in GL 96-06 are not contradicted by the piping codes. The staff continues to conclude that the issues identified in the generic letter should have been addressed in the original plant design and, therefore, have been properly designated as compliance backfit issues in accordance with the Commission's regulations.
During the past year, the staff has had extensive correspondence with you regarding interpretation of various portions of the American Society of Mechanical Engineers Boiler and Pressure Code (the ASME Code).
In your letter, you make assertions regarding the proper interpretation of certain ASME Code paragraphs that are relevant to the issues in the generic letter.
However, you have agreed in the past that the only official interpreter of the ASME Code is ASME. Therefore, your interpretations are not considered official positions of ASME.
Sincerel
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Ashok C. Thadani, Acting Deputy Director Office of Nuclear Reactor Regulation
Enclosure:
As stated cc:
G. Eisenberg, ASME D. Modeen, NEI D_istribution:
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- See previous concurrence To recalve a copy of this document, indicate in the box C* Copy w/o attachment / enclosure E= Copy with attachment / enclosure N = No copy 0FFICE EMEB:DE E
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- See previous concurrence
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To receive a copy of this document, indicate in the box C=Copf w/o attachnent/ enclosure E-Copy with attachment / enclosure N - No copy
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2 As discussed in the enclosure, the staff believes its statements in Generic l
Letter 96-06 are not contradicted by the piping codes. The staff continues to conclude that the issues identified in the generic letter should,have been addressed in the original plant design and, therefore, have been properly designated as compliance backfit issues in accordance with the' Commission's regulations.
Over the past year, the staff has had extensive correspor}dence with you regarding interpretation of various portions of the ASMJ/ Code.
In your letter, you make assertions regarding the proper interp~retation of certain ASME Code paragraphs that are relevant to the issues 'ficial interpretor of the in the generic letter.
However, you have agreed in the past that the only 01 Code is the ASME.
Therefore, your interpretations re not considered official positions of the ASME.
/
Ashok C. Thadani, Acting Deputy Director Office of Nuclear Reactor Regulation U,S. Nuclear Regulatory Commission
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Enclosure:
As stated p'
cc:
G. Eisenberg, ASME
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D. Modeen, NEI
,/
Distribution:
Central Files WTravers GHolahan EMEB RF/CHRON TMarsh JStrosnider PDR BWetzel
/
FMiraglia GHubbard RZimmerman SMagruder!
TMartin KBohrer-96-16 DOCUMENT NAME: G:\\ FAIR \\ REEDY.RSP
- Sie previous concurrence j
To rsesive a copy of this docunent, indicate'in the box CaCopy w/o attachment /#nclosure E= Copy with attachment / enclosure N = No copy 0FFICE EMEB:DE E
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EMEB:DE )E ENChk E TECH:ED NAME JFair:jb*
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2 i As discussed in the enclosure, the staff believes its statements in Generic Letter 96-06 are not contradicted by the statements you referenced from the piping codes. The staff continues to conclude that the issues identified in the generic letter should have been addressed in the original plant design and, therefore, have been properly designated as compliance backfit issues in accordance with the Commission's regulations. Over the past year, the staff has had extensive correspondence with you regarding interpretation of the ASME Code. In your letter, you mak assertions regarding the proper interpretation of certain ASME Co paragraphs that are relevant to the issues in the generic letter. However you have agreed in\\ he past that the only official interpretor of the C de is the ASME. There, your interpretations are not considered official posi ons of the ASME Code. i e i Ashok C Thadani, Acting Deputy Director Offic of Nuclear Reactor Regulation US clear Regulatory Commission l
Enclosure:
As stated i i Distribution: 4 y gn Central Files EMEB RF/CHRON FMiraglia RZimmerman TMartin 7, y A WTravers e 7 g d,,i KBohrer-96-16
- c. a S. t pa DOCUMENT NAME: G:
IR\\ REEDY.RSP To receive a copy of this docunen indicate in the box C= Copy w/o attachment / enclosure Es py with attachment / enclosure N a No copy 0FFICE EMEB:DE F EB:DE EMEB:DE EMCB:DE TEhl:ED SPLB:DSSA JFair b/KManoly RWessman KWichman k TMarsh NAME fj/g/g6/ / /96 / /96 / /96 / )g6 / /96 DATE D:DSSA[ ADD:DE AD:DE A:ADT A:DD:NRR \\ OFFICE GHolah[n JStrosnider G:Lainas BSheron AThadani NAME / !/96 / /96 / /96 / /96 / /96 DATE 0FFICIAL RECORD COPY
THE STAFF'S RESPONSE TO SPECIFIC TECHNICAL ISSUES Posed by Roger Reedy With regard to the first item in your letter of November 8,1996, you claim the following statement in the generic letter is false: " Piping design codes as far back as U.S.A. Standard (USAS) B31.1 (1967) have explicitly recognized the need to consider the effects of heating of fluid that is trapped in an isolated section of piping." You also claim the following statement made in the backfit discussion is false: " Licensees are also required either by commitment to USAS 831.1 or the American Society of Mechanical Engineers (ASME) Code for piping design or by virtue of 10 CFR 50.55a, which endorses various editions of the ASME Boiler and Pressure Vessel Code, to comply with design criteria which specify that piping systems which have the potential to experience pressurization due to trapped fluid expansion shall either be designed to withstand the increased pressure or shall have provisions for relieving excess pressure." As an enclosure to your letter, you provided a page from the 1995 Edition of Section III to the ASME Boiler and Pressure Vessel Code that deals with design criteria for Class 2 piping. Section NC-3621.2 contains the following statement regarding fluid expansion effects. "When the expansion of a fluid may increase the pressure, the piping system shall be designed to withstand the increased pressure or provision shall be made to relieve the excess pressure." The staff believes that the statements in the generic letter regarding ASME Code requirements are consistent with this quote from the ASME Code. In your letter, you provide three arguments related to nuances of tha language used in the generic letter as compared to the ASME Code language to support your claim that the statements in the generic letter are false. You have singled out the phrases " isolated section of piping" and " trapped fluid" from the generic letter to support your argument. In the context of the generic letter, these phrases are only meant to refer to sections of piping in which the fluid is not free to expand when heated. The staff has reviewed your arguments and does not agree with your conclusions, as discussed below. Your first argument is that the generic letter only addresses accident conditions and that the ASME Code requirements related to potential overpressure as a result of the fluid expansion cited above do not apply to accident conditions. Unfortunately, you have misinterpreted the generic letter. The requested action for this issue as specified in the generic letter is not limited to accident conditions. In fact, one of the example events cited in the generic letter occurred during normai plant operations (EN 30833). However, the staff does believe that the major concern involves accident scenarios such as loss-of-coolant accident (LOCA) and main steam line break (MSLB). Your argument that the ASME Code doesn't require consideration of this potential overpressure for accident conditions is based on the words contained in the USAS B31.1 Power Piping Code. In the section of USAS B31.1 that specifies design conditions, the requirements for overpressure as a result of fluid expansion effects are under the heading of " Ambient Influences." The term " ambient influences" relates to the surrounding atmosphere. The NRC staff is not aware of any definition that states that ambient influences do not apply to the surrounding atmosphere during accident Enclosure
scenarios. The ASME Code quotation cited in the previous paragraph comes under the heading " Design and Service loadinas." As you are aware, service loadings include loads resulting from accident conditions that are evaluated for compliance with ASME Code Level C and D service limits. The ASME Code paragraph quoted does not state that the concern is limited only to normal operating conditions. The staff does not find anything in the ASME Code language that supports your argument. Your second argument is that the ASME Code does not have any requirements for an isolated section of piping. You attached a copy of ASME Code Interpretation III-1-95-19 to support your claim. The question posed in the interpretation reads: "A portion of a piping system consisting of piping and isolation valves is out of service and performs no safety function. Does Section III require 'he isolated system to be protected from overpressure during these condit.ons?" The staff did not refer to "out of service" piping systems that perform no safety function in the generic letter. Piping systems that become isolated during normal or accident conditions are not considered "out of service" but merely in a standby situation. Many of these systems form containment barriers, and some systems may have to be actuated during the course of the accident. Clearly, they Eg performing a safety function. The staff does not consider this ASME Code interpretation relevant to the issue addressed by the generic letter. ) Your third argument hinges on the fact that there is no mention of " trapped fluid" in the Codes except in relation to the internal cavity of a valve. However, Section NC-3612.4(a)(3)(e) of the ASME Code contains the following statement: " Adequate consideration shall be given to the control of fluid pressure caused by heating of the fluid trapped between two valves." The statement is contained on the ASME Code page just previous to the one you enclosed with your letter. The concern addressed by the ASME Code relates to the heating of a lower temperature section of the piping by a higher temperature section. However, it appears to demonstrate that the ASME Code is concerned with the heating of " trapped fluid" between valves. It also appears to contradict your assertion that the ASME Code considers a piping section shut off between two valves out of service. In the second item in your letter, you argued that there is no real reason to be concerned with the increase in pressure of a fluid in a portion of piping between isolation valves. You argue that the piping will probably not fail because of leakage through the valves or if valve leakage does not occur, at worst, the pipe would merely crack and the fluid " dribble" out. The staff does not agree that cracking the pipe to relieve the overpressure is an acceptable consequence, and we cannot assume the valves will always leak. In addition, the requirement cited from Section NC-3612.4(a)(3)(e) does not appear to support your position. You also discuss the case of a piping run that penetrates the containment shell and has inside and outside containment isolation valves. You argue that if the valves do not leak, the piping can only crack at a point either inside I or outside the containment in the segment confined between the two isolation 1 valves, thereby maintaining containment isolation. Although this scenario is posdble, the staff believes it would be difficult to demonstrate conclusively l 2
that only one side of the pipe would crack in an overpressure event. If a crack occurs on both sides of the penetration, containment integrity would be lost. The staff does not accept your argument as an adequate basis for ignoring this issue. As you may be aware, the staff evaluated the specific issue of inside and outside containment isolation valves in Generic Safety Issue (GSI) 150, entitled "0verpressurization of Containment Penetrations." The resolution of GSI-150 was based on probability arguments. In its evaluation, the staff assumed a uniform strain in the piping segment. On the basis of the computed uniform strain, a relatively low failure probability was estimated. In your letter, you have pointed out that the pipe cannot expand at the containment penetration. Therefore, the local strains near the penetrations may be much higher than those assumed in the staff's previous assessment. The staff is currently reassessing the technical evaluation in GSI-150. In the third item of your letter, you express the concern that thermal relief valves regularly leak in operation. You also claim that because of the possibility of a stuck-open relief valve, compliance with the generic letter can have a direct adverse effect on safety. The generic letter does not require installation of thermal relief valves. The generic letter requests that licensees evaluate the potential for overpressurization of the piping and take appropriate corrective actions. It is up to licensees to determine whether thermal relief valves are necessary to prevent overpressurization of the piping. The staff does not consider the potential for leakage or the potential for a stuck-open relief valve an adequate basis for allowing the pipe to fail due to overpressure. Further, the generic letter states that consideration must be given to the effects of stuck-open relief valves. In the fourth item of your letter, you referred to the staff's actions in issuing the generic letter without public review and backfit analysis. I discussed the staff's position on this topic in my letter transmitting this enclosure to you. In the fifth item in your letter, you include a number of unrelated statements. You state that two-phase flow is not an ASME Code issue. The staff has not made any claim that two-phase flow is an ASME Code inue. Your assertion that pressure in a system higher than desian oressure is not a safety concern is ambiguous. In the ASME Code, " design pressure" is a term associated with Level A Service Limits. For Level C and D Service Limits (typically used for accident conditions such as LOCA and MSLB), the design pressure can be exceeded as long as the level C and D Service Limits are met. The staff does not agree with the assertion that an evaluation that shows that the Level C and D Service Limits may be exceeded for a postulated service load is not a safety concern. You cite ASME Code Interpretation III-1-92-45 as clarification of the issue. This interpretation contains several carefully worded questions. No claim is made in the response to the questions posed in the interpretation that loading a piping component beyond the ASME Code criteria is not a safety concern. (In your discussion of this item, you also make reference to systems "out of service." This aspect was already addressed in our response to Item one, above). 3 l l
In the sixth item of your letter, you assert that the ASME Code does not require piping to be designed for water-hammer conditions. You base this argument on the contention that water hammer is an accident condition and, therefore, the loads need not be checked for compliance with ASME Code allowable stresses. The ASME Code page attached to your letter contains the requirements for design and service loadings. For example, in Section NC-3622.1, " Impact forces caused by either external or internal loads shall be considered on the piping design." In fact, water-hammer loads resulting from two-phase flow conditions are specifically identified in Section NC-3622.5 of the 1995 Edition of the ASME Code. Also, paragraph 101.5.1 from the page from B31.1-1995 enclosed with your letter addresses this issue. It contains the following statement: "One form of internal impact force is due to propagation of pressure waves produced by sudden changes in fluid momentum." Pressure wave propagation produced by sudden changes in fluid momentum is a water hammer. The staff believes that the ASME Code does require evaluation of water-hammer events when they are expected to occur. The staff also believes that the words in the ASME Code contradict your assertion that the ASME Code does not require piping to be designed for expected water-hammer loads. In your letter, you stated that you were not aware of any event in which piping broke because of water hammer at a nuclear plant. There have been numerous water-hammer events at nuclear power plants that have resulted in damage to piping and piping supports. These events have been documented in previous staff reports such as NUREG/CR-2059 and NUREG/CR-5250. In a recent event at Oconee Unit 2, a balance-of-plant-system pipe rupture resulting from a water hammer caused several injuries to the plant staff. Also, a feedwater water-hammer event at Indian Point Unit 2 (NUREG/CR-2059) caused a 180-degree crack in the feedwater line. Water-hammer loads have caused piping damage, including actual pressure boundary failures, at nuclear power plants. The staff believes that the preferred solution to potential water-hammer problems is to eliminate the cause. However, if internal impact forces (water hammers) are expected to occur, they should be evaluated in the piping design. In Item seven of your letter, you state, " allowable stresses have no significance with regard to operation of the equipment." Your argument is based on the margins used in design. The staff disagrees with your assertion. If a load creates a high-enough stress, it will fail the component regardless of the original design margins. In addition, the staff believes that the margins you quoted for design are not applicable to higher stress limits used for ASME Code Service Level C and D loadings. The staff does not endorse the sweeping generalization that exceeding ASME Code stress limits poses no safety concern because of the design margins. In your letter, you also state that ASME Code allowable stresses are often exceeded because of settlement of supports or foundations. You further state that this condition creates an overstress that is not an ASME Code compliance issue. In Section NC-3653.2, contrary to your statement, the ASME Code has a specific stress limit for piping stresses that are caused by predicted building settlement. In the eighth and final item in your letter, you claim that the issues in the generic letter are " imagined issues." The staff considers the technical issues in the generic letter as significant safety concerns and not " imagined issues." Two licensees have shut down their facilities because of concerns 4
i i about these issues. With regard to your assertions about the cost of the implementation of the generic letter, the staff has not received any j information from licensees on this subject. t E l l l 5 .--}}