ML19262A220

Nonroutine 10-Day Repts 74-10 & 11 Re 741129 & 1202 Unplanned Releases of Radioactive Matl.Apparently Caused by Inadequate Procedural Guidance.Relief Valves Reseated. Procedure Revised,Ensuring Proper Throtting & Flow Control

ML19262A220
Person / Time
Site:	Three Mile Island
Issue date:	12/12/1974
From:	Arnold R METROPOLITAN EDISON CO.
To:
Shared Package
ML19262A215	List: ML19262A214 ML19262A220
References
74-10, 74-11, GQL-0564, GQL-564, NUDOCS 7910260560
Download: ML19262A220 (3)

Text

~

B

. ENCLOSURE Metropolitan Edison Company Three Mile Island Nuclear Station, Unit 1 (TMI-1)

Docket No. 50-289 Operating License DPR-50 Nonroutine 10-Day Reports 74-10 and 74-11 Report of Two Unplanned Releases of Radioactive Material Occurring on November 29 and December 2,1974

1. Description of Releases Between the hours of 0730 and 0830 (1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />) on November 29 and 1541 and 1637 (56 minutes) on December 2,1974, while routine sampling of the Pressurizer Steam Space was being performed, unplanned releases of radioactive material occurred when pressure was relieved through a nuclear plant sampling system relief valve. The radioactive material was released into the Nuclear Sampling Room and was subsequently discharged to the environment by way of the Plant Vent S t ack. For both releases , an alert-level alarm was received on the gaseous chanael of the Auxiliary and Fuel Handling Exhaust Monitor (EM-A8) and a high level alarm was received on the gaseous channel of the Auxiliary Euilding Exhaust Ventilation Duct Monitor (RM-A6); and for the November 29 release, there was also a high level alarm received on the Nuclear Sampling Room Area Ga=ma Monitor (RM-G3) . In the case of the November 29 release, Operations Department personnel proceeded to locate the cause of the release, and, having succeeded in this , they then proceeded to throttle the flow control valve (this valve is located upstream of the relief valve). In the case of the December 2 release, the Health Physics Technician in the Nuclear Sampling Room at the time of the release took immediate action to terminate flow into the sampling line . In both cases, these actions served to reseat the relief valve and the releases to the Nuclear Sampling Room were thereby terminated.

The Health Physics Technicians who were in the Nuclear Sampling Room and other Operating Department personnel in the vicinity of the room at the time of the releases were monitored and no contamination was fo und.

2. Apparent Cause of the Releases November 29 Release Inadequate procedural guidance was the apparent cause of the release in that existing procedures did not direct the individual performing the sampling to properly throttle the flow control valve prior initiating pressure steam space sample flow. As it happened, whem flow was initiated the flow through the control valve was greater than it should have been; consequently, the relief valve opened and thereby allowed radioactive material to escape into the sampling room.

1482 254 7910260 N

December 2 Release Inadequate procedural guidance _ was the apparent cause of the release in that existing procedures did not prohibit the individual from using valves downstream of the flow control valve to regulate flow in the sampling line . Use of these valves caused a pressure buildup in the sampling line, which in turn caused the relief valve to open, thereby allowing radioactive material to escape into the sampling room.

3. Analysis of Releases For the following reasons it is believed that neither release endangered either the health of safety or the public:

a. None of the limits or the TMI-l Technical Specifications were exceeded.

b. None of the Maximum Permissable Concentration limits for non-radiation workers listed in 10 CFR 20 were exceeded at the site boundary .

c. No individual on site at the time of the release received a radiation dose in excess of the limits for radiation workers listed in 10 CFR 20.

For an explanation of the calculations upon which these conclusions are based, please refer to Section 6 below.

4. Corrective Action Immediate corrective action was taken, as described above, to terminate each release.

As a long-term action to prevent the recurrence of such releases, the procedure goierning pressurizer steam space sampling has been revised to insure that 1) the flow control valve is properly throttled prior to initiating pressurizer steam space sample flow and 2) valves downstream of the flow control valve are not used to regulate flow during sampling.

5. Failure Data Not Applicable.

6. Release Data Note :

• • • In no case did any member of the public or plant or contractor personnel receive a radiation dose anywhere near the applicable limits given in 10 CFR 20. ***

. . November 29 Release The total release consisted of 13.752 curies of predominately Xe-133.

This value was obtained from the chart recordings of Auxiliary and Fuel Handling Building Exhaugt Monitor RM-A8. The gross gaseous release rate was 2.4 x 10 4 m /sec,3 which is below the Technical Specification limit of 1.2 x 105 m /sec. Analysis of the release data indicates that the 24-hour average concentration of radioactive material in the Nuclear Sampling Room was 1.04 x 10-4 uC1/ce, which does not constitute an incident that need be reported pursuant to 10 CFR 20.403. To calculate this averc.ge concentration it was taken into account that 13.7 curies of Xe-133 were released over a 1-hour period with a room air flow of 2886 cfm (measured) and a pressurizer steam space Xe-133 concentration of 2 x 10-1 uC1/cc.

The two Health Physics Technicians in the room at the time of the release were exposed to a maximum concentration of 4.72 x 10-3 uCi/cc for two minutes. Based on the values listed in 10 CFR 20, Appendix B, Table I, the concentration for a two-minute. period corresponding to 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> at the MFC is 1.2 x 10-2 uC1/cc. This maximum concentration was determined by co,mparing the peak-to-average concentrations from the RM-A8 chart recordings and then applying this peak-to-average ratio to the average concentration in the room (56-minute average) .

December 2 Release The total release consisted of 7.7 curies of predominantly Xe-133 (94'!) . obtained as above. The gross gaseous release rate wasThis 3.05value x 104wag m /sec, which again is below the Technical Specification limit of 1.2 x 105 m 3 /sec. Analysis of the release data indicates that the 24-hour average concentration of radioactive material in the sampling room was 6.66 x 10-5 uC1/cc, which does not constitute an incident that need be reporte i pursuant to 10 CFR 20.403.

To calculate this average concentration, it was taken into account that 7.7 curies of Xe-133 were released over a 56-cinute period with a room air flow of 2886 cfm and a pressurizer steam space Xe-133 concentration of 2 x 10-1 uCi/cc.

The Health Physics Technician in the room at the time of the release was exposed to a maximum concentration of 7.1 x 10-3 uCi/cc for two minutes. Again, the concentratign for a two-minute period corresponding to 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> at MPC a is 1.2 x 10- uC1/cc. This maximum concentration was determined as above.

p182 256

.