NRC Generic Letter 79-48, Confirmatory Requirements Relating to Condensation Oscillation Loads for the Mark I Containment Long Term Program

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GL79048

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555

October 2, 1979

ALL BOILING WATER REACTOR LICENSEES (Except: Dresden 1, Humboldt Bay, Big Rock and LaCrosse)

SUBJECT: CONFIRMATORY REQUIREMENTS RELATING TO CONDENSATION OSCILLATION LOADS FOR THE MARK I CONTAINMENT LONG TERM PROGRAM

On August 15, 1979, the staff met with representatives of the Mark I Owners Group to discuss the acceptance criteria being developed by the staff to begin implementation of the Mark I Long Term Program (LTP). One of the staff's criteria requires confirmatory condensation tests in the Full-Scale Test Facility (FSTF). The Mark I Owners Group representatives stated that they consider additional FSTF tests unnecessary.

As a result of our review of the proposed load definition procedures for the design basis accident "condensation oscillation" loads (i.e., high vent flow rate with low air content), we have concluded that there are insufficient data to establish a reasonable measure of the uncertainty in the load magnitudes for this regime. Although we believe that the condensation oscillation loads proposed in the Mark I Containment Program Load Definition Report (LDR), NEDO-21888, are sufficiently conservative with respect to the results of FSTF test run M8, we have not found sufficient applicable data to give an adequate estimate of the uncertainty in the load magnitude so defined, such that we can assure that the uncertainty is smaller than the conservatism in the load definition technique. In making this assessment, we have considered the use of the other full-scale data sources and small-scale phenomenological studies. The questions that have been raised regarding the applicability of these data to this issue have not been resolved and will not be resolved in the near future.

We believe that the LDR condensation oscillation load specifications, as modified by the staff's acceptance criteria, form a sufficient basis to proceed with implementation of the LTP, since FSTF test M8 is prototypical for Mark I and the load definition technique has conservatively assessed that test data. Consequently, we intend to issue the acceptance criteria to unit initiate the LTP plant-unique analyses. We will require in these criteria that the conservatism in the condensation oscillation loads be confirmed by performing a sufficient number of additional large break, liquid blowdown tests in FSTF to establish the uncertainty in the load magnitudes.

In addition, the staff has recently raised concerns relating to the phenomena associated with downcomer condensation oscillation loads. These concerns evolved from insufficient downcomer-vent header response data. The additional FSTF test should provide improved instrumentation for the downcomer-vent header system, particularly for the "tied" downcomers.We will require that each licensee commit, on behalf of the Mark I Owners Group as a whole, to perform these tests and provide the associated test and plan schedule by October 31, 1979.

Sincerely,

D. G. Eisenhut, Acting Director Division of Operating Reactors

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Mr. William J. Cahill, Jr. 50-3 Consolidated Edison Company of New York, Inc. 50-247

cc: White Plains Public Library 100 Martine Avenue White Plains, New York 10601

Joseph D. Block, Esquire Executive Vice President Administrative Consolidated Edison Company of New York, Inc. 4 Irving Place New York, New York 10003

Edward J. Sack, Esquire Law Department Consolidated Edison Company of New York, Inc. 4 Irving Place New York, New York 10003

Anthony Z. Roisman Natural Resources Defense Council 917 15th Street, N.W. Washington, D. C. 20005

Dr. Lawrence R. Quarles Apartment 51 Kendal at Longwood Kennett Square, Pennsylvania 19348

Theodore A. Rebelowski U. S. Nuclear Regulatory Commission P. O. Box 38 Buchanan, New York 10511