ML17174A807
| ML17174A807 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 06/21/1991 |
| From: | Zwolinski J Office of Nuclear Reactor Regulation |
| To: | Miller H NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| Shared Package | |
| ML17174A806 | List: |
| References | |
| GL-89-10, TAC-80495, TAC-80496, NUDOCS 9107240157 | |
| Download: ML17174A807 (2) | |
See also: IR 05000237/1991011
Text
Docket Nos. 50-237
and 50-249
e
UNITED STATES
NUCLEAR REGULATORY COMMISSION
WASHINGTOM, D. C. 20555
June 21, 1991
MEMORANDUM FOR:
Hubert J. Miller, Director
Division of-Reactor Safety
Region III.
FROM:*
John A. Zwolinski, Assistant Director
for Region III Reactors
Division of Reactor Projects III/IV/V
Office of Nuclear Reactor Regulation
SUBJECT:.
TIA RELATED TO THE DETERMINATION If BRANCH TECHNICAL POSITION
(BTP) ASB 3~1 IS APPLICABLE FOR SIZING MOTOR-OPERATED VALVES
- FOR GENERIC LETTER 89-10 (TAC NOS. 80495 AND 80496)
Your request for technical ass1stance dated May 24, 1991, addressed a concern
identified in Inspection Reports 50-237/91011 and 50-249/91010, in which Regfon
III inspectors discussed their review of the program being developed by
Commonwealth Edison Company (CECo) in response to Generic Letter (GL) 89-10,
11 Safety-Related Motor-Operated Valve Testing and Survei 11ance,
11 and the
implementation of that program at th~ Dresden Station.
In GL 89-10, the NRC
staff requested licensees to determine the worst case differential pressure and
other conditions for ~ach motor-operated v~lve (MOV) within the scope of the
generic letter. With respect to this design-basis review, the inspectors noted
the practice of CECo t~ use the nominal reactor pressure in determining the
worst differential pressure and fl6w conditions for MOVs that must isolate a
The inspectors stated that CECo bases its use of
nominal reactor pressurt: on 11RC Crdnch Technical Position (BTP) ASB 3-1 (July
1981), Protection Against Postulated Piping Failures in Fluid Systems Outside
Containment,"
The Region Ill inspectors considered the acceptability of the
licensee's use of this BTP as an open item pending review by the Office of
Nuclear Reactor Regulation (NRR).
The Mechanical Engineering Branch (EMEB) has reviewed the licensee's reliance
on BTP ASB 3-1 in a~suming nominal reactor pressure for its design-basis
reviews.
BTP ASB 3-1 was intended to address the protection of plant equipment
from the dynamic effects of pipe breaks and harsh environments resulting from
pipe breaks.
The original staff assumptions.regarding the selection of nominal
reactor pressur~ for tonsideration of pipe breaks are not provided in the
BTP, however, this BTP was not written for developing MOV design bases.
Through GL 89-10, the NRC staff is requesting licensees to verify that MOVs
within the scope of the generic letter are capable of performing their intended
functions under worst case differential pressure and other conditions.
By
assuming nominal reactor pressure, the licensee will not demonstrate that the
MOVs in question are capable of isolating a break initiated at maximun1 reactor
pressure.
By qualifying MOVs to ope-rate under nominal rather than maximum
differential pressure and flow conditions, the licensee limits the scenarios
for which the MOVs are required to operate to only certain events a11ci rt:duces
the options ava.ilable to p*lant operators during abnormal plar.t conditions.
9107240157 910719
QPDR
ADOCK 05000237
!I
Hubert J.* Miller
- 2 -
June 21, 1991
Further, the failure of an MOV in midposition due to its inability to overcome
worst case conditions might complicate accident scenarios or introduce new
scenarios for which plant operators have not been trained. Therefore, EMEB
does not ~onsider the use of nominal reactor pressure in the licensee's
.
design-basis reviews to be consistent with its commitments regarding GL 89-10.
Region III should request the licensee to assume maximum reactor pressure in
its determination of the worst case differential pressure for an MOV in a pipe
directly connected with the reactor vessel. With the maximum reactor pressure
(i.e;, lowest relief val~e setpoint pressure) as a starting point, the licensee
could calculate the differential pressure across the valve by considering such
factors as losses in the piping.
In this manner, the. licensee might find that
the value .of the nominal reactor pressur~ bounds the worst case*diff~rential
. pressure across the valve determined from the maximum reactor pressure minus
appropriate losses along th~ pipe.
If you have any questions regarding
contact Byrcn Siegel of my staff a:t
I~
our evaluation of this open item, please
492-3019. ~ * ~~ U .
. Jo~~Zwolinski, A.ssistant O;rector
)~~r~gion III Reactors
Division of Reactor Projects 111/lV/V
Office of Nuclear Reactor Regulation*