ML20153A994

Safety Evaluation Denying Request to Remove Missile Shields from Plant Design

ML20153A994
Person / Time
Site:	Three Mile Island
Issue date:	09/16/1998
From:	NRC (Affiliation Not Assigned)
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ML20153A991	List: ML20153A986 ML20153A994 ML20153B013
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NUDOCS 9809220265
Download: ML20153A994 (3)

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p ass p i UNITED STATES g j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 30866 4 001

%*****/SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATICN GPU NUCLEAR INC.. ET AL REQUEST TO REMOVE THE MISSILE SHIELD FROM THE DESIGN BASIS OF THE THREE MILE ISLAND NUCLEAR STATION. UNIT NO.1 1.0 Backaround By letter dated March 31,1997, (Ref.1), as supplemented by letters dated June 3, and July 13, 1998, GPU Nuclear, Inc., (GPUN or licensee) submitted a license amendment request to the staff.

In this letter, GPUN informed the staff that it was seeking staff approval for removal of the missile shield from the Three Mile island Unit 1 (TMI-1) plant design, as described in the TMI-1 plant-specific Final Safety Analysis Report (FSAR). The licensee's June 3,1998, letter was in response to the staff's October 3,1997, request for additionalinformation, and the licensee's July 13,1998, letter forwarded an affidavit for the proprietary treatment of the June 3,1998, letter.

2.0 Safety Evaluation 2.1 Staff Criteria for Removing Dynamic Effects from a Plant Specific Design Basis General Design Criteria (GDC) 4 of 10 CFR Part 50, Appendix A, in part, allows for the dynamic effects (including missile generation effects) arsociated with postulated pipe ruptures in nuclear power plants to be removed from the plant design bases when " analyses reviewed and approved by the Commission demonstrate that the probability of fluid system piping rupture is extremely low under conditions consistent with the design basis for the piping."

in the final modification and Statement of Considerations (SOC) for GDC 4 (Ref. 4), the NRC stated that it would consider allowing the dynamic effects to be excluded from the plant-specific design basis if it could be demonstrated that the probability for pipe rupture is extremely low under conditions consistent with the design for the pipe. In the SOC, the Commission stated that it would allow such dynamic effects to be excluded from the plant-specific design basis if the staff could determine that the application of leak before-break (LBB) technology to a particular piping system would maintain a sufficiently high margin of safety in regard to the potential for the pipe to rupture, and if application of the technology would not affect the capability of the contsinments to perform their function of isolating the outside containment from potentia! leaks, breaks, or malfunctions within the containment. The dynamic effects covered by the rule include missile generation, pipe whipping, pipe break reaction forces, jet impingement forces, decompression waves within the ruptured pipe, and dynamic or nonstatk. pressurization in cavities.

4 in the SOC, the Commission indicated that it does not intend to consider near-term changes to emergency core cooling system and containment design bases as discussed in the Final Rule section. The staff has not considered removal of dynamic effects for any structure, system, or component other than high energy piping. The rule allows removal of plant hardware which it is believed negatively affects plant performance and safety, while not affecting emergency core cooling systems, containments, and environmental qualifications.

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2 The Commission further determined in its consideration of the final rule, that a deterministic frac +ure mechanics evaluation is mandatory for permitting the use of analyses to exclude dynamic effects of pipe ruptures in all high energy piping from the design basis. Other evaluations, such as the potential for waterhammer, corrosion, creep damage, fatigue, erosion, environmental conditions, indirect failure mechanisms and other degradation sources which could lead to pipe rupture are also required. '

l 2.2 GPUN's Basis for Removing the Missile Shield from the Design Basis of the TMI 1 Nuclear i Plant i

j According to the TMI-1 plant design, the limiting missile postulated in the accident analyses (e.g.,

Chapter 15) of the TMI-1 FSAR would occur as a result of a catastrophic failure of a control rod

' drive mechanism (CRDM) penetration noule or housing assembly. GPUN's basis for removing the TMI 1 missile shield from the plant design has been provided in the Failure Mode and Effects i Analysis (FMEA) of Babcock and Wilcox Owners Group (B&WOG) Proprietary Report No. 51-3 1230140-00, " Reactor Vessel Missile Shield Removal Report (December 1995, Ref. 2)," and the l postulated flaw analysis for the CRDM penetration nonles and housing assemblies is provided in j B&WOG Non-Proprietary Topical Report BAW-10190P, Addendum 1 "Extemal Circumferential 1

Crack Growth for B&W Design Reactor Vessel Head Control Red Drive Mechanism Nonles (December 1993, Ref. 3)." ' GPU's basis for removing the TMI-1 missile shield stems primarily from the claim that GPUN does not consider a catastrophic failure of a CRDM penetration nonie, i

housing assembly, or adapter tube to be a credible event, even though a control rod ejection event j is covered by the scope of design basis analyses described in Chapter 15 of the TMI-1 FSAR. This i basis for removing the missile shield from the TMI-1 plant design includes the following two premises:

4 ejection of a control rod drive from the TMI 1 vessel head is not likely to occur because "upon opening of postulated circumferential crack, a significant part of the crack driving

! force would be relieved so that either the crack growth rate is drastically reduced or the

crack growth is terminated."

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a gross LBB mechanism exists in that, even if a large portion of a nonle contains a through-wall circumferential crack, there is ample room for leakage to occur and be detected before i the propagating crack would approach the net section limit ligament of the penetration i j nonle.

2.3 Staff Assessment Regarding GPUN's Analysis for Removal of the TMI 1 Missile Shield from the TMI-1 Design Basis The modification to GDC 4 which allowed licensees to propose detailed quantitative LBB technology as a basis for removing the dynamic effects associated with a postulated pipe rupture from a plant-specific design basis is only applicable to high energy piping. The Commission specifically addressed comments to allow extending the use ofleak-before-break technology to selax pipe rupture for containment design, emergency core cooling systems, and environmental qualification and stated that it does not intend to consider near term changes to other than environmental qualification. GPUN's proposal to remove the missile shields from the TMI-1 design basis is also based on a qualitative LBB argument that was proposed to support GPUN's claim that 1 Topical Report No. BAW 10190P, Addendum 1 was originally issued as a Proprietary Topical Report. This

.eport was changed to Non-Proprietary s*.stus per B&W Nuclear Technologies Letter ESL-96-574.

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3 a full guillotine rupture of a CRDM penetration nozzle was an improbable event, and therefore, the dynamic effects, including missile generation eMeets, associated with a control rod drive ejection l

event were also improbable. To date, the staff has not considered evaluations other than fully i quantitative LBB fracture mechanics analyses as a basis for removing the dynamic effects associated with postulated high energy pipe ruptures from a plant specific design basis. Further, )-

since CRDM penetration nozzles and housing ass.emblies are not high energy piping, GDC 4 cannot be used as a basis for removing the effects of a postulated control rod drive missile from the design basis for TMI-1 (as described in the TMI-1 FSAR).

GPUN's proposal also does not provide any information to show that failure to remove the missile shield could adversely aMeet plant performance and safety, which was a consideration in the final rule SOC for removal of hardware associated with preventing the dynamic effects of high energy pipe breaks.

3.0 Conclusion Based on the above, the staff concludes that the proposal to remove the missile shield from the TMI-1 plant design based on the FMEA analysis presented in Proprietary Report No.

51 1230140-00, and the qualitative LBB analysis presented in Topical Report No. BAW-10190P, Addendum 1, is not acceptable.

4.0 References

1. March 31,1997- Letter from R.W. Keaton, Vice President and Direcior of Engineering, General Public Utilities, to the U.S. Nuclear Regulatory Commission Document Control Desk (untitled).

2. December 1995 - Babcock and Wilcox Owners Group Proprietary Topical Report No. 51 1240140-00, " Reactor Vessel Missile Shield Removal Report."

3. December 1993 - Babcock and Wilcox Owners Group Non-Proprietary Topical Report No. BAW 10190P, Addendum 1, "Extemal Circumferential Crack Growth Analysis for B&W Design Reactor Vessel Head Control Rod Drive Mechanism No::zies.

4. October 27,1987. Modification of General Desian Criterion 4 Reauirements for Protection Aaainst Dynamic Effects of Postulated Pioe Ruotures. FederaIRegisler, Volume 52, No. 207, pp. 41288 - 41294.

5. November 1994 - NUREG-1061, Volume 3, " Report of the Nuclear Regulatory Commission Piping Review Committee, Evaluation of Potential for Pipe Breaks."

Principle Contributors: J. Medoff T. Colbum Date: September 16, 1998 8 .