ML20239A658
| ML20239A658 | |
| Person / Time | |
|---|---|
| Issue date: | 09/14/1987 |
| From: | Arlotto G NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Houston R NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| References | |
| NUDOCS 8709180062 | |
| Download: ML20239A658 (2) | |
Text
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NUCLEAR REGULATORY COMMISSION x
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MEMORANDUM FOR: Wayne R. Houston, Acting Director Division of Reactor Accident Analysis
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Of fice of Nuclear Regulatory Research FROM:
Guy A. ~ Arlotto, Director Division of Engineering
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I Office of Nuclear Regulatory Research
SUBJECT:
EFFECTS OF LEAK-BEFORE-BPEAK TECHNOLOGY ON SEVERE
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ACCIDENT ANALYSES
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The CRGR at meeting number.119 on July 22,~1987, approved'a final broad. scope i
l amendment to General Design Criterion 4 to replace the already effective limited scope amendment published as a final rule on April 11, 1986.
These amendments allow the elimination of dynamic effects of postulated pipe ruptures from the design basis and the removal of associated hardware which mitigate or I
resist the ef fects of these postulated pipe ruptures. The limited scope l
amendment was restricted to PWR primary coolant loops whereas the broad scope amendment covers all high energy piping in all LWRs which satisfy rigorous acceptance criteria. The procedures used to decide whether pipe ruptures should be postulated are now commonly referred to as leak-before-break j
technology.
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As a condition of its approval, the CRGR recommended that the staff should consider the effects of these hardware changes on severe accident analyses.
l to the Minutes of CRGR Meeting No. 119 on page 2, item 5, states this condition (see the enclosure to this memorandum).
-For background, nearly every pWR in operation or under construction has primary coolant loops which have already qualificd for leak-before-break.
A large number have actually removed massive pipe whip restraints and jet impingement shields placed near the primary coolant loop; a few additional utilities have reduced the number and size of large capaci'ty snubbers.placed on steam generators and reactor coolant pumps.
Efforts to modify reactor vessel internals (for example, spacer grids for fuel rods) and to replace brittle high strength' bolts 'are a.l.so underway. One ut.ility has applied leak-before-break
.technologyJto.four piping. lines inside the containment. but not. par,of the-
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t reactor. coolant loop)1to. make hardware changes for.these situations. c Moreo'ver, th'e final broad scope GDC-4 rule' presently before the Commission allows ad hoc relaxat, ions in env.ironmental.quali.fication requirements under certain
. conditions;; Final.ly, in,an August 28,11987. Federal. Register notice,'the staff' _
' requested comment on;whether'snd ho'w containment design. baset should be:
'Motiva.' ed by. operational
- y. 3 sino.dified as a result;of, Teak-before-break technology.
t and economic fa'ctors, the nuclear indusfry continu~es 'to inc'rease the numbe'r and/
- scope 'of: a' applications. of this. new technology.;.
8709180062 870914 PDR REVGP NRCCRGR MEETINQ119 PDR l
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Wayne R.' Houston 2
From -a risk perspective, these changes will have both negative and positive impacts. Our regulatory analysis to support these rule changes. indicated an l
unquantified reduction in public health and safety. risk, due primarily to improved inservice inspection, avoidance of restricted thermal growth in I
piping, improved functional reliability of snubbers ~and more ductile fasteners. Nonetheless, no assessment of the influence of these changes on severe accidents has been made. The CRGR believes this assessment should be performed. Any such assessment should reflect the condition that piping qualifying for leak-before-break is assured of an extremely low probability of rupture under the acceptance criteria enforced by the staff.
For further information on leak-before-break technology, contact John O'Brien (X37854) of my staf f.
Jim Conran (X29855)/s the CRGR staff contact for this
. matter.
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Guy 1. Arlotto, Director Divi sion of Engineering Of five of Nuclear Regulatory Research 0
Enclosure:
As stated cc:
E. L. Jordan, CRGR J. Scinto, OGC T. E. Murley, NRR J. A. Murphy, RES L. Hulman, RES M. Silberberg, RES J. E. Richardson, NRR K. R. Wichman, NRR J. H. Conran, CRGR g;,, f&
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