Agenda - 11-17-1998 - 5a - Laserfiche WebLink

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fin... i.s ~ ~ . s .~- ~ .. -.-~ ..y.. --..~. ,.... .. ~'~~ ~;- ~ Chapter Eighr • Spent fuel R~sxs storrd an the side of the spent fuel pool.` Several other incidents in,•ulyin' peal failure are described in Appendix A. After the Haddam \eck event, the I~RC required the pustulated grcns fail- ure of the refueling ca,•it~• „•ater seals to be evaluated for e,•erv nuclear po+,'er plant. The evaluation results varied due to different seal designs and refueling ca,•ir<• geometries. Some plants required modifications to reduce the gross failure risk ur provide seal leakage indication. The results from the \ortheast Utilities' e,•aluatiun of the Millstone Unity 1, 2. and 3 plants for the Haddam Neck event represent h~pical findings. Northeast Utilities determined that in the unlikely event that the seal experienced cata- strophic failure, the Millstone Unit 1 SFP level „•ould dn.~p to 20 inches above the irradiated fuel assemblies in 11 minutes „'ith the resulting radiation field esti- mated to be 2.-1x10- Rem/hr at the spent fuel pool Wiling and 65 Rem/hr on the refueling fluor. For the same postulated e,•ent on Ivlillstune Unit 2, the SFP le,•el +,•uuld dmp to 12 inches above the irradiated fuel assemblies in SO minutes „•ith the resulting radiation field estimated to be 4.0x10" P.em/hr at the pool railing and S-1 Pem /hr on the refueling floor. For the same postulated event on Millstone Unit 3, the SFP level ,vould drop to 21 inches abu,•e the irradiated fuel assemblies in 130 minutes „•ith the resulting radiation field estimated to be 1.9x10" Rem/IZr at the pool railing and 3i Rem/hr on the refueling floor." ' - Tu put these radiation fields in perspective, a worker exposed to 3i Rem/hr receives the maximum annual radiation dose permitted by federal la„• in about 4q seconds, +,•hile a +,•orker exposed to 1.9x10" Rem/hr receives a fatal radiation dose in about one second. Because the probability that the refueling cayih• „•ate- seal suffers catastrophic failure is considered to be neg igibly small (despite already happenin, once), these otential y devastahng consequences have een accepte y the l~R at Millstone an other nuc ear power plants. 'h a spent fuel pool +,•atez in,•enton• loss involves adverse consequences. too much +,~ater can also provide problems. On June 3, 1981, demineralized eater leaked into the Sorry Unit 1 spent fuel pool causing it to overflu„•. The spent fuel pool high level alarm +,•as de-enerv,,ized at the time and did nut alert operators to the problem. 1~Nater o,•ertlo„•ed into the ne,v fuel storage area, then to the foe! receipt area and out the roll-up dour to the stationstorm drains. In addition to the unmonitored radioacti,•ih• release. the demineralized v`•ater diluted the baron concentration in the spent fuel pool water and threatened subcriticality margin. These spent fuel pool near-misses share many causal factors. [n the majori- t~• of cases, the failure of a nonemergencv s~•stem or component ~•ithout the ayail- abilih• of a backup resulted in +,~ater in,•entorv loss from the spent foe] pool. [n mam• cases, the inyentun• fuss +,~as nut promptly detected due to inoperable level instrumentation. The potential consequences from these events include high radi- ation fields and uncoyenn' irradiated fuel assemblies outside pnman• rontam- ment. Gi+•en that federal regulations require the a5wrtiptiun that nonemer~~enc~' ~+•stems and compunent~ tall l~r are una,•ailahle tally+,•m~ de~l~ll ba~« r, ents• >>5