ML17285A465
| ML17285A465 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/12/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17285A464 | List: |
| References | |
| NUDOCS 8905190515 | |
| Download: ML17285A465 (5) | |
Text
ENCLOSURE 1.0.
INTRODUCTION SAFETY EVALUATION REPORT INPUT MNP-2:
D RGR UND R
N LYSIS D CKET N
. 50-397 TAC k 64670 y Raman Psc umani, ESGB)
Several Fire Protection Inspections were conducted by NRC Region V in 1986 prompted by allegations one of which related to 12 inch fire protection water supply mains to Reactor Building (Ref. 1).
These mains were alleged to have been installed beneath the Emergency Diesel Generator (D.G.) Building in violation of National Fire Codes (Refs.
2 and 3).
According to reference 1,.NRR also participated in several of the Region V fire protection inspections, and issued a Request for Additional Information (RAI) in 1986.
While responding to this RAI the licensee identified two additional issues (Ref. 1):
(1)
Line 12" FP (13)-1 running under the D.G. Building into the southwest corner of the Reactor Building appears unable to take differential movements during SSE.
(2)
Line 12" FP (43)-1 running under the D.G. Building from the east appears to lack adequate thrust restraint in one direction.
The NRC Inspector's discussions with the licensee personnel in 1986 indicated that a pipe coupling break occurred in the 12" pipe FP (13)-l prior to initial startup (Ref. 4).
The licensee fixed this pipe coupling by breaking through the D.G. Building floor slab and also provided a
thrust block to restrain pipe movement (Ref. 4).
After reviewing the documentation related to the repair of the line 12" FP (13)-1 the NRC Inspection Team closed the first of the two issues mentioned above (Ref. 1).
The second fire main 12" FP (43)-1 has not been provided with thrust blocking at the elbow location where it rises from its horizontal run at about 6 ft. below the floor slab.
This line has mechanical joints which are designed in such a way that they will leak if they disengage more than 1.44 inches (Ref. 5).
The licensee performed a theoretical analysis to show that there was no need for a thrust block for the line 12" FP (43)-1 (Ref. 5).
A preliminary review of this analysis by the Plant Systems Branch of NRR in April 1987 concluded that the licensee's analysis was not adequate to show that a thrust block was not required (Ref. 6).
Apparently because of the NRR reorganization in April 1987, the resolution of this issue was delayed for a year.
In June
- 1988, the Structural and Geosciences Branch (ESGB) was requested to review the licensee's analysis that had previously been reviewed (Ref. 6).
After a brief review of the licensee's analysis the licensee was informed in a teleconference call in August, 1988 that its analysis was not applicable to this problem.
Although the analysis was not acceptable, certain mistakes made in their calculations were pointed out to the licensee at the telecon.
The licensee corrected the mistakes in its original theoretical analysis and also provided the results of another analysis using a computer program, ADLPIPE.
This safety evaluation has been prepared after reviewing the licensee's analyses.
8905i905i5 8905i2 PDR, ADOCK 05000397 P
- 2. 0 EVALUATION In the original analysis (Ref. 5), the licensee had modeled the rising 6'-5" portion of the fire main 12" FP (43)-1 as a semi-infinite, straight, vertical beam on elastic foundation.
(The 6'-5" portion of this pipe is not vertical throughout; it bends at an angle at about half the height).
This model uses the concept of subgrade reaction which was first utilized in 1888 for computing the stres'ses in railroad ties.
(Ref.
7).
This theory was extended to determine stresses in flexible foundations such as continuous footings or rafts, etc.
The same theory has also been used (since about 1920) for computing the stresses in piles that are acted upon by horizontal forces above the ground surface.
In the latter case, the direction of the subgrade reaction from the surrounding soil is horizontal.
The ratio between unit pressure and displacement had been called the coefficient of horizontal subgrade reaction.
(Ref. 7)..
The licensee assumed the loading on the "beam" (i.e. the riser portion of the line FP(43)-1) to consist of a concentrated lateral force acting at the location of the elbow 6'elow the floor slab; the magnitude of this force was calculated using the formula in ANSI Code A 21.50 which considered both the internal hydraulic pressure and a surge pressure.
Using an incorrect value for the coefficient of subgrade
- reaction, k, and assuming erroneously that the "beam" was of semi-infinite length as stated earlier, the licensee determined, with the help of a theoretical formula for a semi-infinite beam given in Ref. 8, that the maximum horizontal displacement of the pipe at the elbow location of the Fire Main FP (43)-l would be 0.089 inch.
Based on this finding, the licensee contended that this amount of lateral displacement was insignificant when compared to the allowable mechanical joint disengagement of 1.44 inches, and therefore there was no need for a thrust block at the elbow location.
As stated in Section 1.0 above, the NRC staff informed the licensee in a telecon that its analysis technicque was not applicable to this problem and also pointed out that even that analysis contained several errors.
Then, the licensee revised its calculations (a) using what it considered to be a correct value of k, (b) treating the beam to be of finite length, and (c) using the appropri3te formula in Ref. 8.
The licensee s revised calculation showed that the resulting maximum horizontal displacement of the pipe was still less than the allowable joint disengagement of 1.44 inches.
In response to the NRC staff's rejection of the licensee's theoretical analysis based on the theory of a beam on elastic foundation the licensee performed another analysis using a computer
- program, ADLPIPE, to show that the elbow movement was within allowable limits.
Since this analysis also used the same concept of subgrade reaction as the previous analysis the results of this analysis are not acceptable to the staff.
After reviewing the licensee's submittals and the applicable Fire Protection Code provisions, the staff finds that it cannot accept the licensee's arguments for not providing the thrust block at the elbow where the pipe 12" FP (43)-1 rises vertically from a horizontal configuration at a depth of about 6ft. below the D.G. Building floor slab.
The reasons for the staff's findings are the following: (1) As stated in Reference 7,
the theories of subgrade reaction (on which the licensee's analyses are based)
3.0 should not be used for the purpose of estimating settlement or displacements, even though they could be reasonably relied on to compute stresses and bending moments in footings or mats; (2) The "Standard for the Installation of Private Fire Service Mains and Their Appurtenances-NFPA-24" published by the National Fire Protection Association requires that adequate means to prevent movement of underground fire mains be provided whenever there is a change in direction.
Both the 1973 and 1984 editions of. NFPA-24 require that suitable restraints be provided for all tees, plugs, caps, bends and hydrants.
They also state that pipe clamps and tie-rods, thrust blocks or mechanically restrained joints are acceptable means for providing such suitable restraints.
NFPA-24 does not provide guidance regarding the use of the analysis as a means to show that soil alone can be relied upon to prevent movement of tees and bends in underground fire mains.
It is apparent from NFPA 24 that assurance against such movement is provided only by positive restraints such, as tie-rods,,concrete. thrust "
blocks or mechani'cally restrained joints.
Therefore, these methods are shown and described in detail in the body and the appendices of NFPA 24.
The 1984 edition of NFPA 24 further refers to the need for additional restraining devices even after providing thrust blocking (where thrust blocks alone may not be sufficient).
Even though the scope of the work request given to the ESGB staff is limited to the review of the adequacy of the licensee's analysis related to the need for thrust blocking for the fire main FP (43)-1, it is important to state here that a break of this fire line is likely to affect the stability of the foundations of the adjacent Category-I structures.
Therefore, the licensee should design this fire main and any other similar pipelines that go under, or adjacent to, the Category-I structures as seismic Category-?
systems or demonstrate by suitable analyses that the break and leak of these fire mains will not endanger the integrity of seismic Category-I structures, systems and components located near them.
Reference 9 states that the licensee has submitted such an analysis.
However no seismic analysis of these firelines seems to have been submitted by the licensee along with its letter dated January 15, 1987 (Ref.
- 5) as stated in Reference 9.
CONCLUSION Based on a review of the licensees's submittals (Refs 4, 5, and 6) and the National-Fire Code provisions the staff has concluded that the licensee's analysis of the fire main 12" FP (43)-1'cannot be accepted because the basic theory of subgrade reaction used in the analysis is not applicable to the problem of estimating settlement or displacements (Ref. 7).
The licensee should provide a suitable restraint at the elbow as required by either the 1973 or 1984 edition of the "Standard for the Installation of Private Fire'ervice Mains and their Appurtenances-NFPA 24", published by the National Fire Protection Association.
4.0 REFERENCES
Letter dated July 25, 1988 from D. F. Kirsh, NRC (Region V), to Washington Public Power Supply System (WPPSS), subject:
NRC Inspection at WNP-2.
2.
National Fire Protection Association, "National Fire Codes",
1986.
Vol. 1.
3.
Standard for Outside Protection, NFPA No. 24-1973 4.
Letter dated Dec. 29, 1986 from D. F. Kirsch, NRC (Region V), to MPPSS, subject:
NRC Inspection at WNP-2.
5.
6.
Letter dated Jan.
15, 1987 from G.
C. Sorensen, MPPSS, to S. Richards, NRC, subject:
MNP-2:
Nuclear Project No.
2 Transmittal of Documentation.
Memorandum dated April 19, 1987 from L. G.
Hulman to E. Adensam, subject:
WNP-2 Underground Fire Main (TAC ¹, 64670) 7.
Terzaghi, K., "Evaluation of Coefficients of Subgrade Reaction",
Geotechnique, Vol. 5, No. 4, Dec.
1955.
8.
- Roark, R. J.
and Young,.M; C., "Formulas. for Stress and Strain,"
Fifth Edition, NcGraw-Hill Book Co.,
New York 9.
Yiemo dated March 9, 1987 from R.
M. Bernero, NRC to D. F. Kirsch, NRC (Region V),
Subject:
WNP-2 Fire Protection - Safety Evaluation Report on Information related to potential Discrepancies (TIA 86-54B)(TAC ¹62784)
'0
~
tL
~