ML18101A567

Informs of Improper Presentation of Jet Expansion Model in Bechtel Technical rept,BN-TOP-2,Rev 2 Design for Pipe Break Effects Issued May 1974.NRC May Need to Consider Evaluating Consequences of Potential Misapplication of Expansion Model

ML18101A567
Person / Time
Site:	Salem, Diablo Canyon
Issue date:	02/17/1995
From:	Yang D AFFILIATION NOT ASSIGNED
To:	Grimes B Office of Nuclear Reactor Regulation
References
REF-PT21-95 NUDOCS 9503010082
Download: ML18101A567 (2)

Text

U.S. Nuclear Regulatory Commission Brain K. Grimes, Director Division of Project Support Office of Nuclear Reactor Regulation February 17,1995

SUBJECT:

IMPROPER JET EXPANSION MODEL IN BECHTEL TOPICAL REPORT, BN-TOP-2, REV.2, DESIGN FOR PIPE BREAK EFFECTS, ISSUED: MAY, 1974 Dear Mr. Brain K. Grimes This letter is to inform NRC about an improper presentation of jet expansion model (i.e., jet expansion profile) in the subject Bechtel Topical Report. Since the subject Topical Report has been previously approved by NRC, NRC may need to consider evaluating the consequences of potential misapplication of the concerned jet expansion model and taking necessary corrective actions.

Improper Presentation of Jet Model Topical Report Section 2.3 and Figure 2-3 describes and illustrates the jet expansion model in the situation of steam or water-steam blowdown. Figure 2-3 shows, in Region 1 (i.e., Moody Expansion), the jet axial travel distance to the asymptotic area is approximately 5 times of the pipe I.D.

By reviewing the original Moody Expansion Model (Ref: ASME Paper 69-HT-3 l, "Prediction ofBlowdown Thrust and Jet Forces", F.J. Moody, August 6, 1969), it is found the jet axial travel distance to the asymptotic area is 4.5 times of the pipe I.D. for saturated water blowdown, or 2.0 times of the pipe I.D. foe saturated steam blowdown.

In conclusion, Figure 2-3 of Bechtel Topical Report can only be used for saturated water blowdown. To apply Figure 2-3 for saturated steam blowdown, the jet axial travel distance to the asymptotic area shall be corrected to 2.0 times of the pipe I.D.

Consequences of Potential Misapplications PG&E Diablo Canyon Project Jet Impingement Reverification Program used the jet model in Figure 2-3 of Bechtel Topical Report for identifying the jet impingement targets and calculating the jet impingement forces in the situation of both saturated steam and saturated water blowdown. During a recent jet impingement walkdown of 28" main steam lines, it was found a Solid State Protection System (SSPS) electrical junction box would become ajet target and being destroyed ifthe correct jet model for saturated steam (i.e., axial distance to asymptotic area equal to 2.0 times of pipe I.D.) is used. However, this SSPS junction box would not become ajet target, i.e., outside of "Zone of Influence" of the jet, if the jet model in Figure 2-3 of Bechtel Topical Report is used.

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\.,**.a Sincerely Yours Peak Technical Services 1020 Wickham Dr.

Moraga, CA 94556 (510) 631-1368 cc: Gregory M. Rueger (PG&E)

Mike Angus (PG&E)

Tien Lee (PG&E)