ML20133A490
| ML20133A490 | |
| Person / Time | |
|---|---|
| Issue date: | 08/07/1984 |
| From: | Arlotto G NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Speis T Office of Nuclear Reactor Regulation |
| References | |
| FRN-50FR27006, FRN-51FR12502, RULE-PR-50 840807, AB76-1, AB76-2-04, AB76-2-4, NUDOCS 8508050485 | |
| Download: ML20133A490 (6) | |
Text
AW7(o-1
- " 4 UNITED ST ATES NUCLEAR REGULATORY COMMISSION 4
j WASHINGTON. D. C. 20555 j
\\..... **'
AUG 7 1984 MEMORANDUM FOR: Themis P. Speis, Director Divisicn of Safety Technology Office of Nuclear Reactor Regulation FROM:
Guy A. Arlotto, Director Division of Engineering Technology
~
Office of Nuclear Regulatory Research
SUBJECT:
INITIATION OF RULEMAKING ON GDC 4 REQUIREMENTS FOR PROTECTION AGAINST POSTULATED PIPE RUPTURES
Reference:
NRR memorandtsn from H.R. Denton to R.B. Minogue entitled, " Request for Initiation of Rulemaking Regarding Alternatives to Postulation of Pipe Breaks and Protection Against Associated Dynamic Effects," dated June 29, 1984 Enclosed for the signature and approval of R.H. Vollmer is NRC Fonn 197D for the task entitled, " Modifications to GDC 4 Requirements for Protection Against Postulated Pipe Ruptures." Additionally, the Preliminary Draft Regulatory Analysis, and the Draft NRC Regulatory Agenda Entry are included.
Timely NRR approval and return of the T sk Control form are necessary to keep to the relatively tight schedule equested by NP (5
Guy) Arlotto, Director Division of Engineering Technology Office of Nuclear Regulatory Research
Enclosures:
1.
Task Control Fonn (NRC Fonn 197D) 2.
Preliminary Draft Regulatory Analysis 3.
Draft NRC Regulatory Agenda Entry 8500050485 840007 PDR PR 50 50FR27006 PDR
l l
s'a,c..P
,orp s
va muCLt Am Celut& Tom, conswiesiON TASK CONTROL MS 402-1 f %L w 84easlatory ReneerCh office O l
l Office of Nuclear Reactor Regulation laowe sta n On c ANita tiO=
Harold R.. Denton 3 4ANCM CMi{ B
- fN J. E. Richardson DE CeleO4 uni 1 rL A%%EC ACCOut an; Mechanical / Structural Engineering Branch, DET, RES 2511
, As v ii L e,, c..,,
e e, c....
=e. e ae. =,
MODIFICATIONS TO GDC4 REQUIREMENTS FOR PROTECTION AGAINST POSTULATED PIPE RUPTURES This action will allow the use of analyses for excluding the dynamic effects i u x sCoei m = Cae- -
of pipe rupture (pipe whip and jet inpingement) fro m the design basis.
Pipe break requirements for ECC5 performance, containment sizing and environmental qualification are not affected.
All piping is covered. Relaxations will take place only when the statt Judges the analytical bases are adequate.
First use of the rule is-expected for eliminating the double-ended pipe rupture in primary loops of PWRS, leading to removal of pipe whip restraints and jet shields.
T ASK ACTION ICfwre essi y J INit ATE NEn TASK l l SCMEDutt OUT 08 MOLD l l SCMIDULE AFTim PysLIC CowutNT P!miOD REE APPROVALS lOAft TA5E LtADER D ATI TECHNICAL 60steNG SECT 10N Lt ADim (s# adreres aerwe e acAeswedi John A. O'Brien T b N XXXXXXXX n
- /9A joAT.
jo.v.
oe uf, Divis.oh o a CTOn
.uhC. C,,is,
J. E. Ric h/h L. C. Shao V
UEIR OFFICE APPROVALS (New Test imatetesa Daryl OF FICE/DtvillON APPROV A L DATE COGNIZAart lesOrvlDUAL (Chere aussistee'* F 2 maa-B. D. Liaw l ""**
IE '.
CTHER M Jul COMMENTE
Preliminary Draft Regulatory Analysis Task
Title:
Modifications to GDC 4 Requirements for Protection Against Postulated Pipe Ruptures 1.
Statement of Issue Recent investigations using both deteministic and probabilistic methodologies have demonstrated for the specific cases of the primary circuits of Westinghouse and Combustion Engineering reactors, that the double-ended guillotine rupture does not occur.
Efforts are currently underway to learn if these findings can be extended to the reactor coolant loops of Babcock and Wilcox and General Electric reactor designs.
These studies should be completed and docmented during the summer of 1985.
However, the definition of
" Loss of Coolant Accident" and the requirements of General Design Criterion 4 have been interpreted for more than a decade to mean that the double-ended guillotine rupture should be postulated in the design basis.
This interpretation has led to the placement of massive pipe whip restraints and jet shields near piping to mitigate pipe rupture accidents.
Many experts believe that these accident mitigation features actually degrade overall reliability of piping because they reduce the effectiveness of inservice inspection and because of potential difficulties in installation which could actually increase the likelihood of pipe rupture. Of course, when the General Design Criteria were written it was unclear whether certain pipes could or could not rupture, and even today it can only be convincingly demonstrated that PWR primary circuit piping will not suffer a double-ended guillotine rupture; however, it is believed that additional work could extend this conclusion to other piping.
In summary then, the issue is that the long tem interpretation of GDC 4 has led to a situation where unnecessary design features l
have been added to nuclear power plants to forestall accidents l
whico do not occur, and now indications are that these design l
features reduce reliability and increase inspector radiation exposure.
i A need exists to allow exclusion of certain pipe ruptures when supported by analyses acceptable to the staff.
2.
The Need and Urgency for Addressing the Issue The need and urgency for addressing the issue stems wholely from the widespread acceptance of the analysis results and the research findings pertaining to pipe rupture coupled with increasing confidence in its applicability.
Prior to the last few years, there was simply no sound technical basis for excluding certain pipe ruptures from the design basis.
Now it is clear that, at the very least, it is possible to defend the exclusion of PWR primary loop double-ended guillotine pipe ruptures, and that it may be possible to extend the scope to other piping.
These analytical results bye
1 2
been applied to the resolution of Unresolved Safety Issue A-2 al ready.
The new knowledge that certain piping does not rupture mandates the removal of pipe whip restraints and jet shields both from the point of safety and economics.
Rulemaking action would, in addition, promote investigations to learn dich other situations would also pemit the removal of pipe whip restraints and jet shields.
3.
Alternatives to Rulemaking Given that the NRC staff, the ACRS, the CRGR and the nuclear industry have detemined that the postulation of certain pipe ruptures has had a detrimental effect on public health and safety as well as having adversely affected construction and maintenance economics, it is imperative that steps be taken to allow renoval of design features from both plants in operation and under construction which produce these negative effects. The long tem interpretation of General Design Criterion 4 however, would require these design featu res. Thus only two potential courses of action are acceptable:
exemptions to GDC 4 and rulemaking.
The ELD has expressed the view that extensive use of exemptions to authorize the elimination of pipe whip restraints is inappropriate.
Nonetheless, now that the analytical methods have been approved for application, there will be significant motivation to seek exemptions.
It therefore appears most rational to undertake rulemaking at this time.
4.
Addressing the Issue Through Rulemaking The issue will be addressed by a modification to General Design Criterion 4.
One candidate modification is given below, where the underlined portion indicates the added text.
Criterion 4 - Enviromental and missile design bases.
Structures, systems and camponents important to safety shall be designed to accamodate the effects of and to be compatible with the environmental conditions associated with nomal operation, maintenance, testing and postulated accidents, including loss-of-coolant accidentc.
i This includes dynamic effects except when analyses acceptable to the staff show that certain types of pipe ruptures in certain l
piping systems do not occur.
These analyses may only be used
_to exclude the dynamic effects of pipe rupture. When dynamic effects must be included, these structures, systems and components shall be appropriately protected aginast dynamic effects, including the effects of missiles, pipe whipping and discharging fluids, that i
may result from equipment failures and from events and conditions outside the nuclear power unit.
.i 1
d 3
5.
Benefits and Costs This rulemaking would entail significant reductions in staff effort in evaluating plant specific exemptions to the regulations. Moreover, industry would save considerable expense in performing the necessary analyses to support the plant specific exemptions. Nuclear power plant owners will experience reduced inservice inspection costs as the need to remove and replace massive pipe whip restraints and jet shields is eliminated.
Additionally, reduced radiation exposure to plant inspectors will result. Finally, public health and safety will be enhanced as unnecessery derign features which diminish reliability are removed.
6.
NRC Resources and Scheduling Two staff years is estimated to undertake this rulemaking. The notice of proposed rulemaking should appear in the Federal Register in October 1985.
i
e.: - s Draft NRC Regulatory Agenda Entry TITLE: Modifications to GDC 4 Requirements for Protection Against t
I Postulated Pipe Ruptures CFR CITATION:
10 CFR 50, Appendix A ABSTRACT:
The proposed rule would allow less than full double-ended pipe ruptures to be postulated for design against dynamic effects such as pipe whip and jet impingement.
Other design requirements, including those relating to environmental qualification of electrical and mechanical equipment, containment design and ECCS performance are not influenced by this rule.
A benefit derived from the rule would be the avoidance of extensive exemptions to General Design Criterion 4, which would be the only acceptable alternate to the proposed rule.
The rule may only require minimum addition and/or modification of the existing text of GDC 4.
The substance of the rule would be permission to use analytical methods acceptable to the staff for determining that certain pipe ruptures need not be treated in the design basis for dynamic effects.
Implementation of the rule would facilitate the removal of unnecessary pipe whip restraints and jet shields from existing nuclear power plants. This would reduce inservice inspection costs and, in addition, would reduce inspector radiation exposure.
TIMETABLE:
Notice of Proposed Rulemaking 10/00/85 LEGAL AUTHORITY:
42 USC 2201; 42 USC 5846 EFFECTS ON SMALL BUSINESS AND OTHER ENTITIES:
Nct applicable.
AGENCY CONTACT:
John A. O'Brien Office of Nuclear Regulatory Research Washington, D.C.
20555 301 443-7860 O