ML14183A037

Safety Evaluation Supporting Amend 97 to License DPR-23

ML14183A037
Person / Time
Site:	Robinson
Issue date:	03/07/1986
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML14183A036	List: ML14183A035 ML14183A037
References
NUDOCS 8603190080
Download: ML14183A037 (6)

Text

RE0 0 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 97 TO FACILITY OPERATING LICENSE NO. DPR-23 CAROLINA POWER AND LIGHT COMPANY H. B. ROBINSON STEAM ELECTRIC PLANT, UNIT NO. 2 DOCKET NO. 50-261 INTRODUCTION Carolina Power and Light Company (CP&L) has requested deletion of requirements regarding maintenance of a highly borated water inventory in the Boron Injection Tank (BIT) and the associated heat tracing required to maintain the high boron concentration in solution (Ref. 1).

CP&L requested approval for two options:

1. Allow the BIT and associated piping to remain in place, but do not fill with highly borated water, and,

2. Remove the BIT and associated piping.

CP&L elected to initially pursue option 1, with the intention that the request for deletion of requirements pertinent to the BIT apply to both options.

CP&L noted, as partial justification:

"Accident analysis has shown that an inventory of highly borated water in the BIT is not necessary to maintain an acceptable margin of safety to fuel failure during the postulated steamline break event. Furthermore, CP&L has evaluated the effects of this proposed change on the environmental conditions within the containment during the postulated steamline break (SLB) and determined that the equipment's environmental qualification envelope would not be exceeded. Therefore, CP&L requests removal of the TS (Technical Specification) requirement for this highly borated water supply in order to eliminate the substantial maintenance and surveillance requirements involved in maintaining the inventory.

This change will also eliminate the potential to block the Safety Injection (SI) Flow Path due to boron precipitation should the heat tracing fail or become damaged."

Reference was also made to the recommendations of Generic Letter 85-16 (Ref.

2).

Copies of the affected TS pages were provided (enclosure to Ref. 1), as was an Exxon Nuclear Company (ENC) (Ref. 3) report which provides the results of the supporting analyses. Additional information was provided as documented in References 4 and 5.

The BIT was originally incorporated into the H. B. Robinson design to mitigate the consequences of postulated steamline breaks. It is located downstream of the SI pumps, which in turn are located downstream of the Refueljng Water Storage Tank (RWST). During SLB accidents, activation of the SI pumps would force the BIT inventory into the Reactor Coolant System (RCS), followed by water from the RWST. As identified by CP&L and Generic Letter 85-16, the BIT has been a source of problems, and the staff has approved its removal in a number of nuclear power plants.

F 6.

t603190090 0500061 j'DR ADOCK pD1--

P

-2 EVALUATION Carolina Power and Light Company (CP&L) has requested deletion of requirements regarding maintenance of a highly borated water inventory in the Boron Injection Tank (BIT) and the associated heat tracing required tg maintain the high boron concentration in solution (Ref. 1).

This request was briefly reviewed by the NRC staff, and a preliminary compilation of items requiring clarification between the staff and CP&L, was prepared. This served as the basis for a telephone conference call, between the staff and CP&L, which provided the necessary clarifications. The compilation of items needing clarification and the CP&L responses are described in Reference 4. Confirma tion of the Reference 4 information and further clarifications are provided in Reference 5.

The H. B. Robinson Design.

The H. B. Robinson SG's are equipped with integral flow restrictors at the SG outlet which reduce the size of the largest SLB. Each main steamline is equipped with a fast closing swing disk isolation valve which will block flow in the normal flow direction when allowed to close. Reverse flow is prevented by a second swing disk valve located downstream of the isolation valve. All large steamline piping located outside of containment is effectively open to the environment. The buildings which house the equipment do not have walls.

The H. B. Robinson containment building is classified as a "large dry" containment in that it has a large internal volume, is designed to meet high internal pressure requirements, and does not use ice as a means of pressure reduction in response to a large break loss-of-coolant accident (LOCA).

CP&L Analyses Supporting BIT Removal.

Analyses were provided in support of the BIT removal request which purported that injection of borated water from the BIT is unnecessary with respect to maintenance of an acceptable margin of safety to fuel failure. The analyses were based upon the assumption that the BIT remains in place, but is filled with unborated water. The Minimum Departure from Nucleate Boiling Ratio (MDNBR) was found to be decreased from that obtained with the BIT as presently configured, but a significant margin of safety remained. Slightly more energy was found to be released into containment for SLB's inside containment, but the containment conditions would not result in component temperatures above the established environmental qualification limits.

Proposed TS Changes.

The proposed TS changes delete requirements and surveillances regarding boron concentration in the BIT and operability of heat tracing. BIT volume specification and tank level surveillance requirements are also removed.

Option 1 of the CP&L request allows the BIT to remain in place, but isolated from sources of concentrated boric acid and by closed and locked-valves.

The staff does not believe such action precludes inadvertent concentration of boric acid in the BIT, and therefore requires that periodic sampling of the boron concentration in the BIT be conducted (on a rate schedule to be

-3 negotiate-d with the NRC Project Manager) until such time as inadvertent boron concentration can be precluded. Boron concentration can be considered as precluded when all piping which could serve as a path for boron with a concentration areater than that of the RWST has been physically disconnected from the BIT. This additional option, requested by Reference 1,- is summarized in Reference 4. The staff concurs with the additional option.

With the exception as described in the above paragraph, we find the TS changes acceptable.

Superheat The SG that is affected by an SLB will be depleted in inventory and the tube bundle will become uncovered on the secondary side. Since the tubes will effectively be at the RCS temperature, which will be higher than the SG secondary side temperature, the tendency will be to superheat steam being generated in the SG. The temperature can then be substantially above the qualification temperature of equipment exposed to steam during a SLB. The licensee's calculation of mass and energy releases following a steam line break has incorporated steam superheating effects. The worst break was determined by the licensee to be a full double-ended break at hot zero power assuming no entrainment. We have reviewed the licensee's assumptions in determining level of superheating and the worst break and find them to be conservative. The calculation methodology used by the licensee for mass and energy release (Ref. 6) is under staff review and will be discussed in a separate section. The staff concludes that the mass and energy release data used by the licensee for containment analysis are acceptable. The methodology used is being reviewed as a separate item (see Pg. 4 Calculation Methodology).

The licensee indicated in a meeting on March 6, 1986, that all the safety related equipment outside containment is not contained in a closed building and is protected by jet shields from direct exposure to the steam. More over, the licensee stated that the actuation of all the safety-related equipment is required within 70 seconds while the steam generator tubes would not uncover until after 255 seconds for the worst case steam line break. Based on the information stated above, the staff concludes that superheated steam will not adversely affect the safety-related equipment outside containment.

The licensee has described the analysis which addresses the effects of superheat conditions on the environmental qualification of-equipment in Reference 5 and Reference 1.

The equipment items involved have been identified and the most limiting environmental profile has been calculated. The licensee states that based on surface temperature calculations all equipment items are within their qualification profiles and are still considered qualified. The licensee has certified that the surface temperature calculations were performed in accordance with the guidance in NUREG-0588 and adeouate time margin, based on the most limiting condition, has been provided in accordance with Regulatory Guide 1.89, Revision 1.

-4 The-staff has reviewed the information provided by the licensee and concludes that this issue has been adequately addressed.

Calculation Methodology A portion of the analyses supporting the CP&L request involve-application of a RELAP 5 based calculation methodology (see Ref. 3).

This methodology has been submitted to the staff for review (Ref. 6), but staff review is not complete. Methodology review is a separate issue, and is independent of the CP&L BIT modification request.

We have reviewed the CP&L submitted analysis results and conclusions, and find them reasonable when compared to other similar investigations. We have progressed sufficiently far in the methodology review upon which the results are based that we are confident they will be found acceptable.

Should the methodology review results be different than expected, further investigation will be required.

The Reference 6 methodology does not address superheat. CP&L has performed scoping calculations which establish that superheat is not a problem to equipment (see prior SER section) and that there are no unusual problems associated with RCS system response (including the core). They have further stated that consideration of superheat will not result in a return to power that significantly differs from calculations of the event which do not include superheat. This is sufficient confirmation for purposes of BIT modification. Further aspects of superheat analysis methodology will be addressed in staff review of Reference 6.

SUMMARY

The staff concurs in the CP&L position that BIT boric acid concentration is a source of problems. For example, staff experience is that problems with SI system reliability have been caused by failure to maintain the boric acid in solution at critical locations. Further, staff experience is that the safety margins are greater than originally thought, as evidenced by an increase in understanding of plant behavior via improved analysis methods. Although removal of the BIT does perturb SLB severity, in general there is sufficient safety margin that the design basis accidents are adequately mitigated.

Therefore, no undue risk to the health and safety of the public results, and the benefits are considered to outweigh the deficits.

The situation may be clarified further by considering experience and risk analysis. The general picture is one in which SLB is a low probability, low risk event. Difficulties with high boron concentration have occurred many times, in some cases to the point of disabling SI systems, with obvious impact upon risk. Hence, the practical approach of elimination or modification of the equipment containing high boron concentration solutions is a logical result.

The staff has not identified any features in the H. B. Robinson plant that would negate any of these general conclusions. We, therefore, concur with the CP&L request, subject to the one requirement that BIT boric acid concentration

-5 be periodically monitored until such time as the BIT is physically dis connected from potential sources of concentrated boric acid.

ENVIRONMENTAL CONSIDERATION This amendment involves a change in the installation or use of I facility component located within the restricted area as defined in 10 CFR Part 20.

The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR Sec 51.22(c)(9).

Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.

CONCLUSION We have concluded, based on the considerations discussed above, that:

(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.

Dated:

March 7, 1986 PRINCIPAL CONTRIBUTOR:

Warren Lyon

-6 REFERENCES

1. Cutter, A. B., "H. B. Robinson Steam Electric Plant, Unit No. 2, Docket No. 50-261/License No. DPR-23, Request for License Amendment, Boron Injection Tank Dilution, Serial NLS-85-332, Letter addressid to Director of Nuclear Reactor Regulation, Carolina Power & Light Company, Nov. 13, 1985.

2. Thompson, Hugh L., "High Boron Concentrations," Letter addressed to all licensees of operating reactors and applicants for an operating license, Generic Letter 85-16, USNRC, Aug. 23, 1985.

3. "Analysis of the Steamline Break Event with Boron Injection Tank Removal or Dilution to Zero Concentration Boric Acid for H. B. Robinson Unit 2,"

XN-NF-85-17(P) (Proprietary), Exxon Nuclear Company, Inc., May 1985.

4. Requa, Glode, "Report of Conference Call with Carolina Power & Light Regarding H. B. Robinson - 2 BIT Removal," Docket No. 50-261, March 5, 1986.

5. Zimmerman, Sherwood R., "H. B. Robinson Steam Electric Plant, Unit No. 2, Docket No. 50-261/License No. DPR-23, Boron Injection Tank (TAC No. 60301), Letter from Carolina Power and Light to Director of Nuclear Reactor Regulation, NRC, Serial NLS-86-083," March 6, 1986.

6. "Steamline Break Methodology for PWR's," XN-NF-84-93(P) Exxon Nuclear Company, Inc., November 1984.