ML20209B606
| ML20209B606 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 01/23/1987 |
| From: | Robert Williams PUBLIC SERVICE CO. OF COLORADO |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| P-87037, NUDOCS 8702040080 | |
| Download: ML20209B606 (4) | |
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O Public Service ~
- c h P.o. Box 840 Denver, Co 802014840 2420 W. 26th Avenue, Suite 100D, Denver, Colorado 80211 R.O. WILLIAMS, JR.
EuctER $PE DONS January 23, 1987 Fort St. Vrain Unit No. 1 P-87037 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C.
20555 Attn: Correspondence and Records Branch Docket No.
50-267
SUBJECT:
Response to the Committee to Bridge the Gap Petition for Rulemaking of July 7, 1986
REFERENCE:
- 1) Federal Register, Vol. 51 No. 170, 9/3/86, Docket No. PRM-50-44, Page 31341
- 2) NRC Letter, Heitner to Williams, dated 9/16/86 (G-86502)
- 3) PSC Letter, Brey to Berkow, dated 12/4/86 (P-86641)
- 4) NRC Letter, Denton to Lamm, dated 5/29/86 (G-86287)
- 5) Federal Register, Vol. 51 No. 208, 10/28/86, Docket No. PRM-50-44, Page 39390 Gentlemen:
Public Service Company of Colorado (PSC) consider:
that the additional grcphite reactor regulatory requirements requested by the Committee to Bridge the Gap in their July 7, 1986 petition for rulemaking (Ref. 1) are unnecessary and technically inappropriate for application to the Fort St. Vrain Nuclear Gener1 ting Station.
DOkohhhh67 PDR gO
P-87037 Paga 2 January 23, 1987 Rulemaking Petition Summary The petition requests that the NRC amend its regulations to require operators of reactors that use graphite as a moderator or reflector to:
- 1) prepare and submit for NRC approval fire response plans and evacuation plans for a graphite fire, and
- 2) measure the energy stored in their graphite and revise their safety analyses to consider the risks and consequences of a graphite fire in their facilities.
The basis for the first requested amendment is the petitioner's assertion "that the occurrence of a graphite fire at the Chernobyl plant in the Soviet Union demonstrates that graphite fires are credible events." The "NRC and reactor licensees have held that graphite fires are 'non-credible' events and as a result have failed to take measures to help mitigate or extinguish such fires, should they occur."
The basis for the second requested amendment is the petitioner's assertion "that the NRC's generic analysis for energy stored in research reactor graphite significantly underestimates the actual amount of stored energy, and thus, underestimates the associated risk of graphite fire."
Credibility of Graphite Fires The petitioner cites the Chernobyl plant accident as evidence of the credibility of a graphite core fire, yet does not take into account the causative mechanism or the significant differences in reactor design between the Chernobyl plant and the Fort St. Vrain (FSV) plant.
The Chernobyl causative mechanism, described in the Soviet report presented at the IAEA Conference in August, 1986 (Ref. 2), was a power surge due to a large positive reactivity insertion, which was exacerbated by the reactor's positive void coefficient of reactivity.
The Chernobyl reactor was being intentionally operated at that time in a regime outside its design basis limits.
PSC has addressed the possibility of various reactor accidents resulting in graphite oxidation in both the original construction permit and the operating license proceedings for FSV. These are currently described in Section 14 of the Updated FSV FSAR, where it is found that none of these postulated accidents lead to significant graphite oxidation. Both the NRC and PSC have concluded, in these
P-07037 Pag 3 January 23, 1987 licensing proceedings, that an accident involving significant graphite oxidation at FSV is not credible.
PSC recently determined that four simultanenus independent structural failures would have to occur to permit the oxygen flow into the FSV Prestressed Concrete Reactor Vessel (PCRV) necessary to initiate and sustain significant oxidation of the FSV graphite.
No credible mechanism was found which could realistically create the air ingress necessary to sustain such oxidation.
Nevertheless, PSC has identified a method that could terminate such non-credible graphite oxidation and described it in Reference 3.
In this paper, PSC also pointed out some of the important design differences between FSV and Chernobyl, which preclude the type of accident which occurred at Chernobyl. These include FSV's negative reactivity coefficients, inert helium coolant, and high PCRV design pressure capability.
The Chernobyl event was caused by specific design features of that plant for which there is no analogy in FSV.
In their initial evaluation, the NRC staff has concurred with these conclusions (Reference 4).
FSV already has an emergency plan which provides for action to protect the health and safety of the public based on projected offsite doses.
A special
" graphite fire" evacuation plan is unnecessary. Additional special plans for this specific hypothetical accident would require devotion of resources for the development and maintenance of unnecessary procedures and documents.
The requirements requested in this petition would be duplicative of regulatory actions that the NRC has already appropriately considered and handled with respect to the FSV graphite reactor.
Stored (Wigner) Energy Storage of Wigner energy is not a significant operating concern at FSV simply because it becomes negligible at temperatures higher than 500 degrees F.
The average FSV graphite temperature exceeds this value at power levels above approximately 7% of full power.
Even if FSV were to operate at 5% power for a month the accumulated stored energy would be only 1.1 cal /g.
The maximum possible adiabatic temperature rise due to the release of this Wigner energy would be only 4 degrees C, which is insignificant considering the design temperatures of the core and PCRV.
l P-87037 Page 4 January 23, 1987 RECOMMENDATION PSC recommends that the NRC deny this Petition for Rulemaking, to the extent it may apply to the Fort St. Vrain plant.
In particular, it has been shown that FSV has been designed such that neither a graphite fire nor significant graphite oxidation is credible, and that this plant operates at temperatures well above those at which Wigner energy can be stored in graphite.
PSC concludes that the requests made in this petition are without merit when applied to FSV, as the petitioner's allegations cannot validly be concluded from the evidence presented.
The stated concerns have been determined to represent no undue risk to the public health and safety based on FSV Safety Evaluations ard actual plant operating experience.
Implementation of these requests would place a burden on PSC's resources with no resulting benefit to public health and safety.
Very truly yours,
~
R. O. Williams, Jr.
Vice President, Nuclear Operations R0W/RS:jmt CC: Mr. Samuel J. Chilk Secretary of the Coninission Regional Administrator, Region IV Attention: Mr. J.E. Gagliardo, Chief Reactor Projects Branch Mr. R.E. Farrell Senior Resident Inspector Fort St. Vrain